下面，將參照隨附圖式描述本發明的實施例。然而，下面描述的各個實施例僅是本發明的實施例，且本發明不限於此。在下面的描述和圖式中，多個圖式中相同的部件用相同的參考編號指代。相同的部件將會參照多個圖式來進行描述，並且將酌情省略對由相同的參考編號指代的部件的描述。
圖1A是根據本實施例的第一示例的基板保持板1的透視圖。本實施例中的基板保持板1包括基部2和位於基部2上或上方的突起3。基板保持板1的兩個主要表面(前表面和後表面)中的一個表面(為方便起見稱為前表面)是基板保持表面，且突起3設置在基板保持表面處。至少突起3的最上表面和側表面構成基板保持表面。
圖1B是示出了在基板7被放置在圖1A中的基板保持板1上或上方時的基板保持板1的透視圖。基板7被放置在基板保持板1的保持表面上或上方。基部2和設置在基部2上或上方的突起3保持基板7。特別地，位於保持表面處的突起3支撐基板7。由於突起3支撐基板7，因此減少了基板保持板1與基板7之間的接觸面積，並且與未設置突起3的情況相比可以抑制對基板7的損壞。當基板7被放置在保持表面上或上方時，突起3的最上表面是基板保持板1與基板7之間的接觸表面。當基板7沒有放在保持表面上或上方時，突起3的最上表面與基板保持板1的氣氛(例如，空氣或惰性氣體)接觸。第一示例中放置在基板保持板1上的基板7是用於製造電子設備的基板7。基板7可以構成電子設備的一部分，或者可以在電子設備的製造過程中被移除而不構成電子設備。例如，基板7可以是用於製造有機電激發光(EL)顯示器、液晶顯示器、太陽能電池板等的玻璃基板、樹脂基板或藍寶石基板。
抽吸孔4設置在本示例的基板保持板1中。基板7透過抽吸孔4被抽真空。然而，可以省去抽吸孔4。
圖1C是根據本實施例的第二示例的基板保持板1的透視圖。圖1D是示出了在基板7被放置在圖1C中的基板保持板1上時的基板保持板1的透視圖。第二示例的基板保持板1與圖1A的基板保持板的不同之處在於其外部形狀為圓形；但是，其他構造是相同的。要放置在第二示例的基板保持板1上的基板7可以是例如，諸如Si晶圓或SiC晶圓的半導體基板、諸如玻璃晶圓或塑料晶圓的絕緣體基板、或藍寶石基板。
圖1A至1D中示出的基板保持板1可以用於製造各種電子設備的裝置。例如，在曝光裝置(其對應用在基板7上的光阻劑進行曝光)中保持基板7時可以使用基板保持板1。基板保持板1不僅可以用於曝光裝置，而且還可以用於成膜裝置、蝕刻裝置等。
如圖1E所示，多個基板保持板1可以被佈置並用作基板保持工具11。
第一實施例
接下來，將參照圖2A至2C描述第一實施例。
圖2A是圖1A或圖1C中被圓圈IIA包圍的區域的放大剖視圖。圖2B是圖2A中被圓圈IIB包圍的區域的放大圖。圖2C是圖2B中被圓圈IIC包圍的區域的放大圖。
如參照圖1A或1C描述的，本實施例的基板保持板1包括基部2和突起3。在保持表面中，至少每一個突起3的最上表面均是粗糙表面。
以下描述中的“粗糙表面”可以是具有0.4μm以上的算術平均粗糙度Ra的表面。每個突起3包括高硬度部分5，其為具有硬度高於基部2的硬度的部分。這一點不僅可以適用於本實施例，而且也可以適用於其他實施例。在本實施例中，保持表面中的突起3的最上表面將被描述為粗糙表面。此外，高硬度部分5將被描述為設置在保持表面中的突起3的最上表面處。
將描述基部2。基部2包括組成部分21、組成部分22和組成部分23。組成部分21、22和23由相同的材料製成。至少由相同材料製成的組成部分21、22和23被稱為基部構件，由與組成部分21、22和23的材料相同的材料製成的部分也被稱為基部構件。組成部分21、22和23位於同一平面上。組成部分21、22和23的下表面也位於同一平面上，並且限定與基板保持表面相反的後表面24。組成部分22位於組成部分21和23之間。
將描述突起3。突起3存在於基部2的組成部分22上或上方。突起3不存在於組成部分21和23上或上方，並且提供了空間。突起3存在於組成部分21上方的空間與組成部分23上方的空間之間。在兩個突起3之間存在空間。
突起3由低硬度部分31(其是由與基部2的材料相同的材料製成的部分)和高硬度部分5構成。低硬度部分31也是基部構件。
接下來，將描述高硬度部分5。高硬度部分5是具有硬度比基部2的硬度高的部分。高硬度部分5可以是具有硬度比低硬度部分31的硬度高的部分。
將描述圖2C。在本實施例中，在保持表面中，至少突起3的最上表面是粗糙表面，並且突起3具有高硬度部分5。高硬度部分5設置在與粗糙表面的頂部51相距距離D的範圍內。該距離D小於頂部51和與該頂部51相鄰的底部52之間的高度差H(D＜H)。
在最上表面處設置粗糙表面的至少一個頂部51。較佳地，在最上表面處設置多個頂部。更佳地，在最上表面處設置五個以上的頂部。對於五個以上的頂部51中的每一個，高硬度部分5的設置範圍可以小於相對於相鄰底部52的高度差H。此外，可以限定最上表面處的粗糙表面的最高頂部51與相鄰底部52之間的高度差Hmax。對於五個以上的頂部51中的每一個，高硬度部分5可以設置在與粗糙表面的頂部51相距距離Dmax的範圍內。在這種情況下，距離Dmax小於高度差Hmax(Dmax＜Hmax)。
高度差Hmax可以大於從頂部到低硬度部分31的距離。
在本實施例中，高硬度部分5設置在比從粗糙表面的頂部到相鄰底部的高度差H小的距離D的範圍內，因而最上表面的粗糙表面由高硬度部分5形成，並且可以抑制粗糙表面的磨損。
至少最上表面的至少一部分是高硬度部分5。在一個示例中，粗糙表面的頂部可以由高硬度部分5構成。藉由這樣的構造，由於基板7與最上表面的粗糙表面之間的接觸造成的磨損可以被高硬度部分5所抑制。在本實施例中，只有保持表面中的突起3的最上表面被粗糙化，並且突起3的最上表面的粗糙表面由高硬度部分5構成。只要至少突起3的最上表面的粗糙表面(其為與基板7的接觸表面)是由高硬度部分5構成的，就比最上表面的粗糙表面不由高硬度部分5構成的情況更適於抑制粗糙表面的磨損。
藉由使突起3的最上表面為粗糙表面，可以在執行曝光處理時降低基板保持板的前表面處的反射率。因此，減少了輻照強度的變化，並且可以抑制曝光不均勻。
此外，與突起3的最上表面不是粗糙表面的情況相比，有提高基部2和高硬度部分5之間的附著力的效果、以及藉由減少與基板的接觸面積來減少對基板的損害的效果。
在本實施例中構成基部構件(基部2和低硬度部分31)的材料是黑氧化鋁。黑氧化鋁的硬度例如為約1600Hv。基部構件(基部2和低硬度部分31)需要足夠厚以確保基板保持板1的機械強度。例如，基部構件的厚度為10至100mm，較佳為60mm以下。
基部構件(基部2和低硬度部分31)的厚度可以是30mm以下。
構成基部構件的材料不限於黑氧化鋁，可以是氧化鋁、陶瓷、氧化鋯、玻璃、塑料、金屬或類似材料。低硬度部分31的硬度可以是1000至2000Hv。
在本實施例中，突起3的低硬度部分31的上表面也是粗糙表面。低硬度部分31的上表面的粗糙表面是藉由對低硬度部分31進行噴砂而形成的。突起3的最上表面的粗糙表面的形狀可以反映低硬度部分31的上表面的粗糙表面的形狀。
隨著高硬度部分5的厚度減少，低硬度部分31的上表面的粗糙表面的形狀與突起3的最上表面的粗糙表面的形狀之間的相關性增大。
突起3的最上表面的算術平均粗糙度Ra例如在0.4至10μm的範圍內。突起3的最上表面的算術平均粗糙度Ra可以是0.6μm以上，0.8μm以上，或1.0μm以上。突起3的最上表面的算術平均粗糙度Ra可以是8.0μm以下，6.0μm以下，4.0μm以下，或2.0μm以下。為了將反映低硬度部分31上表面的粗糙表面形狀的突起3最上表面的算術平均粗糙度Ra設定為0.4μm以上，低硬度部分31的上表面的算術平均粗糙度Ra可以超過0.4μm，且可以設定為例如0.6μm以上。基部2和突起3的最上表面的算術平均粗糙度Ra可以在0.4至4.0μm的範圍內。
只要突起3可以支撐基板7，突起3的形狀和陣列間距可以是任意的。在本示例中，突起3各自具有截頭的圓錐形形狀或圓柱形形狀。突起3的間距例如是1mm以上且100mm以下，較佳是10mm以上且30mm以下。突起3的間距可以是1mm以上且10mm以下。突起3的高度例如是10μm以上且1mm以下，且較佳是0.2mm以上且0.8mm以下。突起3的高度例如可以是50μm以上且0.5mm以下，或可以是0.3mm以下。
作為高硬度部分5的材料，使用藉由電漿化學氣相沉積(plasma chemical vapor deposition；CVD)形成為膜的類金剛石碳(diamond-like carbon；DLC)，以改善磨損抑制效果。DLC可以含有氫。DLC中的氫含量越低，硬度和脆性就容易越高。DLC中的氫含量越高，硬度就容易越低，韌性就容易越高。例如，DLC的硬度可以是6至16GPa；然而，藉由調整氫含量可以是9至13GPa。例如，當DLC中的氫含量為21至26at%時，在形成具有粗糙表面的高硬度部分5時可以獲得良好的膜品質(高硬度和高韌性)。DLC中的氫含量可以是23至26at%。DLC中的氫含量可以用成膜條件(例如，源氣體的流速和基板偏壓)來控制。DLC中的氫含量可藉由彈性反衝檢測分析(elastic recoil detection analysis；ERDA)來進行分析。DLC可以含有氬。DLC中的氬含量越高，DLC的折射率就可越低，這對抑制反射是有效的。DLC中的氬含量可以低於10at%。注意，表示元素含量的“at%”代表“原子%”或“原子的百分比”。除了本說明書中描述的分析方法外，還可以藉由飛行時間二次離子質譜法(time-of-flight secondary ion mass spectrometry；TOF-SIMS)來分析元素的含量(濃度)。
高硬度部分5的材料不限於類金剛石碳(DLC)，且可以是碳化矽(SiC)、氮化鈦(TiN)、碳化鈦(TiC)、陶瓷或燒結碳化物。當基部構件的硬度為約1600Hv時，高硬度部分5的硬度可以是2000至4000Hv。
藉由用高硬度部分5構成最上表面的粗糙表面，可以抑制粗糙表面的磨損。
高硬度部分5的厚度需要是用於抑制由於與基板7接觸而導致的粗糙表面磨損的厚度。高硬度部分5的厚度例如為0.4μm以上，較佳為1μm以上。然而，當高硬度部分5的厚度為10μm以上時，很有可能在高硬度部分5中產生裂縫。因此，高硬度部分5的厚度可以小於10μm。
高硬度部分5的膜厚度可以大於突起3的最上表面的粗糙表面的高度差H。
進一步地，高硬度部分5的設置範圍可以小於與底部52相距的高度差H。
從粗糙表面的頂部51到粗糙表面的相鄰底部52的高度差H可以是0.1μm以上且1.2μm以下。
低硬度部分31可以被稱為第一部分，高硬度部分5可以被稱為第二部分。
高硬度部分5的厚度可以是小的，以將低硬度部分31的上表面的粗糙表面的形狀反映在突起3的最上表面的粗糙表面的形狀上。具體來說，高硬度部分5的厚度μm較佳為低硬度部分31的上表面的粗糙表面的算術平均粗糙度Ra的4倍以下，且更佳為2倍以下。可以近似地認為低硬度部分31的上表面的粗糙表面的算術平均粗糙度Ra等於突起3的最上表面的粗糙表面的算術平均粗糙度Ra。在這種情況下，可以說高硬度部分5的厚度較佳為突起3的最上表面的粗糙表面的算術平均粗糙度Ra的4倍以下，且更佳為2倍以下。突起3的最上表面的粗糙表面的高度差H可以近似於突起3的最上表面的粗糙表面的算術平均粗糙度Ra的約2倍。因此，可以說高硬度部分5的厚度較佳為突起3的最上表面的粗糙表面的高度差H的2倍以下，且更佳為1倍以下。此外，只要突起3的最上表面的算術平均粗糙度Ra為0.4μm以上，高度差H就可以是0.8μm以上。當高硬度部分5的厚度等於或小於突起3的最上表面的粗糙表面的算術平均粗糙度Ra的2倍時，突起3的最上表面的粗糙表面的底部52容易位於比低硬度部分31的上表面的粗糙表面的頂部(其對應於突起3的最上表面的粗糙表面的頂部51)低的位置。這有利於利用作為高硬度部分5的底層基部的低硬度部分31的上表面的粗糙表面的形狀來控制突起3的最上表面的粗糙表面的形狀。隨著低硬度部分31的上表面的粗糙表面的粗糙度越小，高硬度部分5的厚度可越小。隨著低硬度部分31的上表面的粗糙表面的粗糙度越大，高硬度部分5的厚度可越大。
接下來，將描述根據本實施例的抽吸孔4。為了吸住並保持放置在突起3上的基板7，每個抽吸孔4的下部開口與真空泵(未示出)連接，從而可以抽吸並減壓突起3周圍的空氣。藉由設置突起3，與不設置突起3的情況相比，可以吸到更多的空氣。儘管在本實施例中抽吸孔4的側表面塗有高硬度部分5，但由於該側表面不是面對基板7的表面，因此該側表面不需要塗有高硬度部分5。類似地，高硬度部分5也不需要應用於塗覆到基部2的後表面24和基部2的側表面。
第二實施例
接下來，將參照圖3A、3B和3C描述第二實施例。
圖3A是示出了根據本實施例的基板保持板1的示例的剖視圖。圖3B是圖3A中由圓圈IIIB包圍的區域的放大圖。圖3C是圖3A中由圓圈IIIC包圍的區域的放大圖。注意，圖3B中被圓圈IIC包圍的區域中的突起3的最上表面的結構可以與參照圖2C(其是圖2B中被圓圈IIC包圍的區域的放大圖)描述的結構相同，因此省去其描述。
本實施例的基板保持板1與第一實施例的不同之處在於：由高硬度部分5構成的粗糙表面不僅設置在突起3的最上表面上，而且還設置在突起3的側表面上和設置在基板保持板1的保持表面處的組成部分21和23(第一區段，其為在該區段上或上方不具有突起的區段)上。
在基板保持板1中，基部2可以表示除突起3之外的整個部分。基部2的最上表面與突起3兩側的空間接觸。與突起3包括高硬度部分5和低硬度部分31的第一實施例類似，在第二實施例中基部2可以包括高硬度部分5和低硬度部分31。在第一實施例中，基部2可以等同於組成部分21至23。然而，在第二實施例中，基部2可以包括除組成部分21至23外的高硬度部分和低硬度部分。因此，基部2的除組成部分21至23外的高硬度部分和低硬度部分被特別地稱為過渡部分9。過渡部分9是基部2的一部分。
在本實施例的基板保持板1中，基部2除組成部分21至23外還包括過渡部分9。將描述過渡部分9。過渡部分9是基部2的從組成部分22過渡到突起3的部分，或者是基部2的從組成部分21或23過渡到設置在組成部分21或23上方的空間的部分。在本實施例中，過渡部分9由與組成部分21至23相同的材料(基部構件)製成的部分(低硬度部分)和高硬度部分5構成。
過渡部分9存在於過渡部分9從組成部分22經由低硬度部分過渡到突起3的位置或從組成部分21或23經由高硬度部分5過渡到設置在組成部分21或23上方的空間的位置處。具體而言，組成部分22和突起3之間的過渡部分9包括由低硬度部分(基部構件)構成的部分以及由於低硬度部分兩側上的高硬度部分5構成的部分。
將描述圖3C。圖3C是圖3A中由圓圈IIIC包圍的區域的放大圖。在本實施例中，如圖3B所示，保持表面中的突起3的側表面是粗糙表面。作為基部構件的組成部分21和23的上表面也是粗糙表面。此外，由高硬度部分5構成的第二區段55設置在每個組成部分21和23上。由高硬度部分5構成的第二區段55在基板保持表面側的上表面是粗糙表面。其中第二區段55在基板保持表面側的上表面(其為不與基板接觸的表面)是粗糙表面的構造適合降低反射率。
此外，由於突起3的側表面以及組成部分21和23上或上方的部分是由高硬度部分5構成的，因此增大了基板保持板1與高硬度部分5之間的接觸面積，並且可以抑制基板保持板1與高硬度部分5之間的膜分離。
在本實施例中，圖3C中示出的距離D存在於小於高度差H的範圍內。然而，至少在突起3的最上表面處的距離D落在小於高度差H的範圍內便足夠。
高硬度部分5(第二區段55)的表面形狀和作為高硬度部分5的底層基部的低硬度部分(組成部分21和23)的表面形狀可以與第一實施例中的高硬度部分5和低硬度部分31的表面形狀相同。基部2的最上表面的算術平均粗糙度Ra例如在0.4至10μm的範圍內。基部2的最上表面的算術平均粗糙度Ra可以是0.6μm以上，0.8μm以上，或1.0μm以上。基部2的最上表面的算術平均粗糙度Ra可以是8.0μm以下，6.0μm以下，4.0μm以下，或2.0μm以下。為了將反映組成部分21和23上表面的粗糙表面形狀的基部2最上表面的算術平均粗糙度Ra設定為0.4μm以上，組成部分21和23的上表面的算術平均粗糙度Ra可以大於0.4μm，且可以設定為例如0.6μm以上。基部2和突起3的最上表面的算術平均粗糙度Ra可以在0.4至4.0μm的範圍內。
第三實施例
接下來，將參照圖4A和4B描述第三實施例。本實施例與第二實施例的不同之處在於：低硬度部分31的上表面與突起3的最上表面的粗糙表面相比是平的。在這種情況下，與第一實施例和第二實施例一樣，由於高硬度部分5被包括在突起3的最上表面的粗糙表面中，因此可以抑制粗糙表面的磨損。
第四實施例
接下來，將參照圖5A和5B描述第四實施例。本實施例提供了與第二實施例類似的形式；然而，不同的是突起3僅由高硬度部分5構成。
在本這種情況下，由於高硬度部分5被包括在用於降低反射率的粗糙表面中，因此可以抑制粗糙表面的磨損。在本實施例中，過渡部分9是由高硬度部分5構成的。
第五實施例
接下來，將參照圖6A和6B描述第五實施例。在本實施例中，基部2是由與高硬度部分5和低硬度部分31不同的部分50構成的，突起3的上部是由高硬度部分5構成的，而突起3的下部是由低硬度部分31構成的。在本示例中，由於最上表面的粗糙表面是由高硬度部分5構成的，因此可以抑制粗糙表面的磨損。
在本實施例中，低硬度部分31可以被稱為第一部分，而高硬度部分5可以被稱為第二部分。
第六實施例
接下來，將參照圖7A和7B描述第六實施例。
圖7A是示出了根據本實施例的基板保持板1的示例的剖視圖。圖7B是圖7A中由圓圈VIIB包圍的區域的放大圖。
本實施例的構造與第二實施例的不同之處在於：組成部分21和23上方的部分、突起3的最上表面、和突起3的側表面的至少一部分是由具有折射率比高硬度部分5的折射率低的低折射率部分6構成的。
將描述圖7B。如圖7B所示，在本實施例中，最上表面的粗糙表面的底部由低折射率部分6構成。最上表面的粗糙表面由高硬度部分5和低折射率部分6構成。
在這種構造的情況下，入射到最上表面的粗糙表面的底部上的光經由低折射率部分6入射到高硬度部分5上。因此，可以降低基板保持板1的保持表面上的反射率。
在本實施例中，由於最上表面的粗糙表面是由高硬度部分5構成的並且維持了從頂部51到底部62的高度差H，因此可以抑制由於與基板7接觸而導致的粗糙表面的磨損。
將描述低折射率部分6。低折射率部分6具有的折射率低於高硬度部分5的折射率。因此，藉由在高硬度部分5的基板保持表面側設置低折射率部分6，相對於空氣的折射率變緩並且反射率被降低。低折射率部分6具有比高硬度部分5的折射率和硬度低的折射率和硬度：
將描述基板保持板的前表面處的反射。形成精細圖案的曝光裝置使用波長為365nm(i線)、405nm(h線)和436nm(g線)的光束。基板保持板的前表面處的反射主要是菲涅耳(Fresnel)反射，可以根據下面的公式獲得：
R = {(N
0- N
1)/(N
0+ N
1)}
2+ {(N
1- N
2)/(N
1+ N
2)}
2，
其中，R是反射率，
N
0是空氣的折射率，
N
1是低折射率部分的折射率，和
N
2是高硬度部分的折射率。
藉由使用由無機氧化物製成的多孔材料作為設置在基板保持板的保持表面上的低折射率部分6，與使用非多孔材料的抗反射材料的情況相比可以提供低反射率。其原因是，由無機氧化物製成的多孔材料的表面存在細微的不規則性，並且在與空氣的界面處形成了折射率的梯度。
由於低折射率部分6構成基板保持板1的保持表面上的部分，因此空氣和高硬度部分5之間的折射率變化變緩，並且可以降低保持表面上的反射率。即使不設置高硬度部分5，也可以藉由使空氣和低硬度部分31之間的折射率變化變緩來降低保持表面上的反射率。
低折射率部分6藉由使用折射率比高硬度部分5的折射率低的材料而具有降低基板保持板1的前表面上的反射率的效果。無機氧化物可以是氧化鋁材料或二氧化矽材料，但不能是樹脂材料。
低折射率部分6由鏈狀顆粒、空心顆粒或實心顆粒構成。低折射率部分6可以形成為具有例如0.1至1.0μm的厚度，且較佳是0.1至0.4μm的厚度。
低折射率部分6以均勻形成的狀態或以分散的狀態存在。
在本實施例中，底料8用於使高硬度部分5和低折射率部分6彼此更牢固地緊密接觸。底料8存在於高硬度部分5和低折射率部分6之間的交界處。底料8以均勻形成的狀態或以分散的狀態存在。在這種情況下，使用矽烷偶聯劑作為底料8；然而，底料8不限於此。只要該材料能改善高硬度部分5和低折射率部分6之間的附著力，就可以使用任何材料。
在第一至第五實施例中，基板保持板1的最上表面是粗糙表面，因此可以散射入射光並且可以降低反射率。然而，在第一至第五實施例中，由於高硬度部分5和空氣之間的折射率差異大，因此容易產生散射光。在本實施例中，基板保持板1的最上表面是粗糙表面，並設置了低折射率部分6。因此，在與空氣的界面處形成了折射率的梯度。與未設置低折射率部分6的情況相比，可以進一步降低反射率。
在本實施例中，從粗糙表面的頂部到高硬度部分5的距離D小於從粗糙表面的頂部到粗糙表面的與該頂部相鄰的底部的高度差H。不需要為與某一頂部相鄰的所有底部都提供這種構造，為一個頂部提供一個這樣的底部便足夠。
高硬度部分5設置在與頂部51相距距離D的範圍內，在本實施例中，頂部51由高硬度部分5形成。然而，頂部可以由低折射率部分6形成。當頂部51由低折射率部分6形成時，低折射率部分6由於與基板接觸而在超過距離D的範圍被磨損。然而，在此之後，高硬度部分5形成頂部51，並且高硬度部分5構成突起3的最上表面的粗糙表面，從而可以抑制粗糙表面的磨損。
本實施例的基板保持板1預計不僅在具有不可透過高硬度部分5的波長的光下使用，而且還在具有可透過高硬度部分5的波長的光下使用。例如，當高硬度部分5是DLC時，紫外線不能透過DLC，但紅外線可以透過DLC。因此，高硬度部分5的折射率n
2與具有第一部分的基部構件的折射率n
1之間的差n
2-n
1小於高硬度部分5的折射率n
2與低折射率部分6的折射率n
3之間的差n
2-n
3。
藉由這種構造，可以防止透過高硬度部分5的光被基部構件反射。
n
1、n
2和n
3中的每一個是對可透過高硬度部分5的波長的光的折射率。高硬度部分5的折射率n
2高於低硬度部分31的折射率n
1。
藉由這種構造，即使在使用可透過高硬度部分5的光時，也可以抑制在高硬度部分5和基部構件之間的界面處的光反射。
將描述本實施例中的抽吸孔4。由於本實施例的抽吸孔4的側表面不是面對基板7的表面，因此抽吸孔4的側表面不需要設置低折射率部分6。
在本實施例中，低硬度部分31可以被稱為第一部分，高硬度部分5可以被稱為第二部分，低折射率部分6可以被稱為第三部分。
第七實施例
接下來，將參照圖8A、8B和8C描述第七實施例。
本實施例與第六實施例的不同之處在於：最上表面的粗糙表面僅由低折射率部分6而不是高硬度部分5構成。本實施例提供了其中從由低折射率部分6構成的粗糙表面的頂部61到由高硬度部分5構成的頂部51的距離D小於從粗糙表面的頂部61到底部62的高度差H的形式。
由於最上表面處的低折射率部分6與基板7接觸，因此在放置基板7後低折射率部分6立即被磨損。然而，隨著低折射率部分6的磨損進展，高硬度部分5變為突起3的粗糙表面的頂部，並且維持了從頂部51到底部62的距離H-D。因此，可以抑制粗糙表面的磨損。
將描述圖8C。圖8C是示出了與圖8B不同的形式的視圖，不同之處在於距離D大於高度差H。在這種情況下，低折射率部分6由於與基板7接觸而被磨損。由於低折射率部分6從頂部61被磨損到由高硬度部分5組成的頂部51，因此底部62也類似於頂部61被磨損。為此，由於突起3的最上表面是由低折射率部分6構成的，因而在保持表面處的反射率被低折射率部分6降低。然而，突起3的最上表面中的粗糙表面很可能被磨損。
第八實施例
在本實施例中，基部構件(低硬度部分31和組成部分21和23)具有含氮區。含氮區可以存在於高硬度部分5附近，例如在與高硬度部分5相距100nm以內的範圍內。含氮區的含氮量可以為1at%以上。
含氮區中的最大含氮量較佳為5at%以上，且更佳為10at%以上。含氮區具有的最大含氮量可以低於25at%。在基部構件中，在與高硬度部分5分離的位置處，例如在與高硬度部分5充分分離的位置處，例如在與高硬度部分5相距100μm的位置處，氮含量可以低於1at%。由於氮相對於其他元素具有較高的擴散抑制功能，因此藉由設置含氮區可以抑制雜質在基部構件(低硬度部分)和高硬度部分5之間的擴散。此外，在基部構件中的氧含量為25at%以上並且設置在基部構件上的無機材料膜(高硬度部分5)中的碳含量或氮含量為25at%以上的情況下，當在基部構件中設置含氮區時，基部構件和無機材料膜之間的附著力得到改善。具有氧含量為25at%以上的基部構件的典型示例包括氧化物，諸如矽的氧化物(二氧化矽)、鋁的氧化物(氧化鋁)和鋯的氧化物(氧化鋯)。
具有碳含量或氮含量為25at%以上的無機材料膜是諸如DLC的碳膜、諸如碳化矽(SiC)或碳化鈦(TiC)的碳化物膜、或諸如氮化矽(SiN)或氮化鈦(TiN)的氮化物膜。無機材料膜除了氮或碳以外還含有25 at%以上的與氮或碳形成化合物的元素(諸如鈦的金屬或諸如矽的半金屬)。碳膜、碳化物膜和氮化物膜通常對氧化物的附著力較低。特別地，DLC幾乎不會與底層基部構件發生附著或化學反應，因此對金屬或氧化物的附著力低。然而，當在氧化物中設置含氮區時，含氮區與碳膜、碳化物膜或氮化物膜之間的附著性會得到改善。在無機材料膜形成於基部構件上之前，可以藉由將氮植入基部構件的表面中來形成含氮區。因此，含氮區可以含有由於植入的氮而產生的1at%以上(進一步說，5at%以上)的氮以及在植入氮之前基部構件中就含有的25at%以上的氧。此外，含氮區含有25 at%以上的與植入氮之前基部構件中就含有的氧形成化合物的元素(諸如鋁的金屬或諸如矽的半金屬)。
代替將氮植入諸如氧化鋁的基部構件中的是，可以在基部構件上設置SiC層作為附著層，並且可以在SiC層上設置DLC膜。當在劃痕試驗中比較兩種膜的附著力時，只植入氮時DLC膜的附著力可比只設置SiC層時DLC膜的附著力高。將氮植入SiC層下方的基部構件可以增大SiC層與氧化鋁基板之間的附著力。
當在基板保持板的基部構件上形成DLC膜時，如果成膜失敗，則需要去除DLC膜。由於DLC在與氧氣反應時會蒸發，因此例如藉由在大氣中加熱膜或將膜暴露在氧氣電漿中來去除該膜。當附著層是SiC層時，由於受到DLC膜去除步驟的影響，SiC的表面被氧化而形成SiO或SiO
2。當DLC膜形成於其上時，由於SiO或SiO
2與DLC之間的附著力低，因此DLC可能很容易剝落。另一方面，當藉由對基板保持板的基部構件進行氮化處理而獲得的含氮區被用於附著層時，附著層不太可能被DLC膜去除步驟氧化。因此，即使在去除DLC膜後再次形成DLC膜，DLC也具有足夠的附著力。
這裡，作為示例描述了基部構件是氧化物的情況；然而，即使基部構件是金屬，碳化物膜或氮化物膜與金屬之間的附著力也低。因此，當在金屬基部構件的表面上設置含氮區時，金屬基部構件和碳化物膜或氮化物膜之間的附著力會得到改善。
本發明不限於上述實施例，在本發明的技術構思範圍內可以進行許多修改。
圖9是曝光裝置的示意圖。作為曝光裝置的光學裝置EQP包括光源14和構成照明光學系統的反射鏡16和17。光學裝置EQP包括支撐作為圖案形成單元的光罩18的光罩台19、投影在光罩18上形成的圖案的投影光學系統25、和支撐基板7的基板保持板1。來自光源14的曝光用光15被照明光學系統的反射鏡16和17反射並被引導至光罩18，帶有形成於光罩18上的圖案的曝光用光15被投影光學系統25聚焦並投影到基板7上。基板7和基板保持板1由基板移動單元26移動。光源14將形成在光罩18上的圖案投影到基板7上。光阻劑被應用到基板7上。光阻劑被暴露於曝光用光15。基板7可以是半導體晶圓或平板顯示器(flat panel display；FPD)的玻璃基板。曝光裝置的曝光用光通常是紫外光。曝光用光的波長對於g線光源來說是436nm，對於i線光源來說是約365nm。曝光用光的波長對於KrF準分子雷射光源來說是約248nm，對於ArF準分子雷射光源來說是約193nm，對於極紫外(extreme ultraviolet；EUV)光源來說是約10至20nm。
投影光學系統可以是縮小投影類型、等倍率投影類型、或放大投影類型。雖然這裡示出的是透射式光罩18，但也可以使用反射式光罩18。投影光學系統可以是使用透鏡的折射類型或使用反射鏡的反射類型。
示例
接下來，將參照圖7A和7B描述具體示例。
在本示例中，使用長為200mm至1500mm、寬為800mm至1500mm的基板。
本示例中的基板是玻璃基板；然而，該基板可以是SiC晶圓或液晶面板基板。本示例中的基板可以是透明基板。在這種情況下的透明基板是可以透過各種波長的光中的任一種的基板。
首先，將描述基部2。基部2可以具有任何性質，只要它不會因失焦而導致曝光失敗即可。使用具有厚度為60mm的由黑氧化鋁製成的基部2。在本示例中，藉由噴砂對表面進行粗糙化。Ra的值約為0.8μm，Rz的值約為5.0μm。使用表面粗糙度測量儀Surftest SJ-210(Mitutoyo公司)來測量表面粗糙度。評估長度為5mm，測量速度為0.5mm/s。
接下來，將描述突起3。只要突起3能夠支撐基板7，突起3的形狀和陣列間距可以是任意的。本示例中每個突起3的形狀是截頭的圓錐形或圓柱形，直徑為0.8mm，高度為0.5mm。此外，相鄰突起3的間距被設定為20 mm。由於突起3與基部2同時被噴砂，因此可以認為基部構件在突起3處的表面粗糙度與基部構件在基部2處的表面粗糙度基本相同(相差10%以內)。
接下來，將描述高硬度部分5。在本示例中，使用DLC來改善磨損抑制效果。藉由電漿CVD來形成DLC膜，且至少突起3的表面被塗有DLC。DLC膜的厚度需要是用於抑制磨損的厚度，且可以是1μm以上。然而，當DLC膜的膜厚度為10μm以上時，產生裂紋的可能性很大。因此，在本示例中，DLC膜的膜厚度被設定為2μm。本示例中的成膜條件如下：氬氣流速為50 sccm，甲苯氣體流速為2.5 sccm，壓力為5 Pa，RF功率為500 W/13.56 MHz，成膜時間為2小時。當用橢圓儀測量所形成的DLC膜時，DLC膜的折射率為2.1。當用奈米壓痕儀測量所形成的DLC膜時，DLC膜的硬度約為15GPa。在這種情況下，藉由在與上述成膜條件相同的成膜條件下在Si晶圓上形成厚度為100nm的DLC膜、用奈米壓痕儀測量DLC膜、並根據30nm深度處的應力計算DLC的硬度來獲得DLC的硬度。由於DLC膜均勻地形成在基部構件上，因此可以認為DLC膜的上表面的表面粗糙度與藉由噴砂形成的基部構件的表面粗糙度基本相同(相差10%以內)。
接下來，將描述低折射率部分6。由無機氧化物製成的多孔材料被用於低折射率部分6。在本示例中，無機氧化物是具有厚度為300nm的氧化矽材料。在本示例中，底料8被用來使高硬度部分5和低折射率部分6彼此更牢固地緊密接觸。底料8被設置在高硬度部分5與低折射率部分6之間的交界處。底料8以均勻形成的狀態或以分散的狀態提供。在本示例中，使用矽烷偶聯劑作為底料材料。然而，底料材料不限於此。只要該材料能提高高硬度部分5和低折射率部分6之間的附著力，就可以使用任何材料。
低折射率部分6和底料8是藉由使用無機顆粒分散液進行噴塗形成的。本示例中的噴塗條件如下：底料8和低折射率部分6兩者的液體供應率為7g/min，噴槍移動速度為20m/min，霧化壓力為0.1MPa。
塗層液體中的無機顆粒的濃度對於底料8是0.1wt%，對於低折射率部分 6為2wt%。當用橢圓儀測量形成的低折射率部分6時，低折射率部分的折射率為1.2。由於低折射率部分6的厚度充分小於基部構件的表面粗糙度，因此低折射率部分6的最上表面和基板保持板1的底料8的表面粗糙度可被認為與藉由噴砂形成的基板的表面粗糙度基本相同(相差10%以內)。
當用光譜色度計(Konica Minolta公司製造的CM-26d)測量本示例中的基板保持板1時，確認了藉由形成低折射率部分6使反射率降低4.5%的效果。此外，藉由使突起3的最上表面粗糙化增強了突起3和高硬度部分5之間的附著力，並且可以藉由散射大大降低正反射。
將描述設置第八實施例中所述的含氮區的示例。將基板保持板的包括氧化鋁作為主要成分的基部構件安裝在電漿處理裝置中。電漿處理裝置可以是電漿CVD裝置。更具體地，電漿處理裝置可以是電漿源離子植入(plasma source ion implantation；PSII)裝置、電離氣相沉積裝置或RF電漿CVD裝置。在電漿處理裝置被抽空到預定的壓力後，引入氮氣並且藉由電漿發生器產生電漿以產生氮離子。負電位可以藉由DC脈衝電源或DC電源施加到基板保持板的基部構件上，或者藉由對基板保持構件施加RF所產生的自偏壓來施加負電位。氮離子藉由施加在基板保持板的基部構件上的負電位而被加速並使其入射到基板保持板的基部構件上，以執行氮離子向基板保持板的基部構件的表面的植入。
作為藉由X射線光電子能譜(X-ray photoelectron spectroscopy；XPS)在深度方向上分析以這種方式處理過的基板保持板的基部構件的結果，可以確認從基部構件的最上表面到20nm的深度存在氮。特別地，從最上表面到2.5nm深度的氮含量可為高(5at%以上)。例如，在氮含量最高的最上表面處可發現15at%的氮，而在2.5nm的深度處可發現5at%的氮。氮可以基本均勻地分佈在基板保持板的基部構件的整個表面上。當在設置有上述含氮區的基板保持板上形成DLC膜時，DLC膜和氧化鋁基部構件之間的附著力得到改善。
此外，在DLC膜被去除後重新形成膜也是合適的。
根據本發明，能夠提供一種在抑制基板保持板的粗糙表面的磨損方面有利的技術。
上述實施例可以在不偏離技術構思的範圍內酌情修改。本說明書的揭露內容不僅包括本說明書中所描述的內容，而且還包括根據本說明書和本說明書所附的圖式中可以掌握的所有事項。
應當注意的是，關於所例舉的具體數值範圍，對“e至f”(e和f是數字)的描述表示e以上和/或f以下。此外，在一起描述範圍“i至j”和範圍“m至n”(i、j、m和n是數字)的情況下，關於所例舉的具體數值範圍，下限和上限組不限於i和j組或m和n組。
例如，可以考慮多種下限和上限組的組合。也就是說，在一起描述範圍“i到j”和範圍“m到n”時，只要不發生矛盾，就可以考察範圍“i到n”或範圍“m到j”。此外，等於或大於e代表等於e或大於e(超過e)，並且可以採用大於e的值而不採用e。此外，f以下代表f或小於f(小於f)。可以採用小於f的值而不採用f。
本說明書的揭露內容還包括對本說明書中描述的各個構思的補充。也就是說，當本說明書中有“A大於B”的描述時，例如，即使沒有“B不大於A”的描述，本說明書也可以說是公開了“B不大於A”。這是因為“A大於B”的描述是基於考慮了“B不大於A”的前提的。
雖然本發明已經參照示例性實施例進行了描述，但應當理解，本發明不限於所公開的示例性實施例。以下請求項的範圍應被給予最廣泛的解釋，以涵蓋所有此類的修改以及同等的結構和功能。
本申請要求享有2020年11月27日提交的No.2020-196852和2021年4月7日提交的No.2021-065237日本專利申請案的權益，這些專利藉由參考全文併入本文中。
Below, an embodiment of the present invention will be described with reference to the accompanying drawings. However, the various embodiments described below are only embodiments of the present invention, and the present invention is not limited thereto. In the following description and drawings, the same components in multiple drawings are referred to by the same reference numerals. The same components will be described with reference to multiple drawings, and the description of the components referred to by the same reference numerals will be omitted as appropriate. Figure 1A is a perspective view of a substrate retaining plate 1 according to a first example of the present embodiment. The substrate retaining plate 1 in this embodiment includes a base 2 and a protrusion 3 located on or above the base 2. One of the two main surfaces (front surface and rear surface) of the substrate retaining plate 1 (referred to as the front surface for convenience) is a substrate retaining surface, and the protrusion 3 is arranged at the substrate retaining surface. At least the uppermost surface and the side surface of the protrusion 3 constitute the substrate retaining surface. FIG. 1B is a perspective view showing the substrate holding plate 1 when the substrate 7 is placed on or above the substrate holding plate 1 in FIG. 1A . The substrate 7 is placed on or above the holding surface of the substrate holding plate 1. The base 2 and the protrusion 3 provided on or above the base 2 hold the substrate 7. In particular, the protrusion 3 located at the holding surface supports the substrate 7. Since the protrusion 3 supports the substrate 7, the contact area between the substrate holding plate 1 and the substrate 7 is reduced, and damage to the substrate 7 can be suppressed compared to the case where the protrusion 3 is not provided. When the substrate 7 is placed on or above the holding surface, the uppermost surface of the protrusion 3 is the contact surface between the substrate holding plate 1 and the substrate 7. When the substrate 7 is not placed on or above the holding surface, the uppermost surface of the protrusion 3 is in contact with the atmosphere (e.g., air or an inert gas) of the substrate holding plate 1. The substrate 7 placed on the substrate holding plate 1 in the first example is a substrate 7 for manufacturing an electronic device. The substrate 7 may constitute a part of the electronic device, or may be removed in the manufacturing process of the electronic device without constituting the electronic device. For example, the substrate 7 may be a glass substrate, a resin substrate or a sapphire substrate used to manufacture an organic electroluminescent (EL) display, a liquid crystal display, a solar cell panel, etc. A suction hole 4 is provided in the substrate holding plate 1 of the present example. The substrate 7 is vacuumed through the suction hole 4. However, the suction hole 4 may be omitted. FIG. 1C is a perspective view of a substrate holding plate 1 according to a second example of the present embodiment. FIG. 1D is a perspective view of the substrate holding plate 1 when the substrate 7 is placed on the substrate holding plate 1 in FIG. 1C. The substrate holding plate 1 of the second example differs from the substrate holding plate of FIG. 1A in that its outer shape is circular; however, the other structures are the same. The substrate 7 to be placed on the substrate holding plate 1 of the second example can be, for example, a semiconductor substrate such as a Si wafer or a SiC wafer, an insulator substrate such as a glass wafer or a plastic wafer, or a sapphire substrate. The substrate holding plate 1 shown in Figures 1A to 1D can be used in devices for manufacturing various electronic devices. For example, the substrate holding plate 1 can be used when holding the substrate 7 in an exposure device (which is exposed to a photoresist on the substrate 7). The substrate holding plate 1 can be used not only for exposure devices, but also for film forming devices, etching devices, etc. As shown in Figure 1E, a plurality of substrate holding plates 1 can be arranged and used as a substrate holding tool 11. First Embodiment Next, the first embodiment will be described with reference to Figures 2A to 2C. Figure 2A is an enlarged sectional view of the area surrounded by circle IIA in Figure 1A or Figure 1C. FIG. 2B is an enlarged view of the area surrounded by circle IIB in FIG. 2A. FIG. 2C is an enlarged view of the area surrounded by circle IIC in FIG. 2B. As described with reference to FIG. 1A or 1C, the substrate retaining plate 1 of the present embodiment includes a base 2 and a protrusion 3. In the retaining surface, at least the uppermost surface of each protrusion 3 is a rough surface. The "rough surface" in the following description may be a surface with an arithmetic mean roughness Ra of 0.4 μm or more. Each protrusion 3 includes a high hardness portion 5, which is a portion having a hardness higher than that of the base 2. This point may be applicable not only to the present embodiment, but also to other embodiments. In the present embodiment, the uppermost surface of the protrusion 3 in the retaining surface will be described as a rough surface. In addition, the high hardness portion 5 will be described as being disposed at the uppermost surface of the protrusion 3 in the retaining surface. The base 2 will be described. The base 2 includes a component 21, a component 22, and a component 23. Components 21, 22 and 23 are made of the same material. At least components 21, 22 and 23 made of the same material are called base members, and parts made of the same material as components 21, 22 and 23 are also called base members. Components 21, 22 and 23 are located on the same plane. The lower surfaces of components 21, 22 and 23 are also located on the same plane and define a rear surface 24 opposite to the substrate holding surface. Component 22 is located between components 21 and 23. Protrusion 3 will be described. Protrusion 3 exists on or above component 22 of base 2. Protrusion 3 does not exist on or above components 21 and 23, and a space is provided. Protrusion 3 exists between the space above component 21 and the space above component 23. There is a space between the two protrusions 3. The protrusion 3 is composed of a low hardness portion 31 (which is a portion made of the same material as the base 2) and a high hardness portion 5. The low hardness portion 31 is also a base member. Next, the high hardness portion 5 will be described. The high hardness portion 5 is a portion having a hardness higher than that of the base 2. The high hardness portion 5 can be a portion having a hardness higher than that of the low hardness portion 31. Figure 2C will be described. In this embodiment, in the retaining surface, at least the uppermost surface of the protrusion 3 is a rough surface, and the protrusion 3 has a high hardness portion 5. The high hardness portion 5 is arranged within a range of a distance D from a top 51 of the rough surface. The distance D is less than the height difference H (D＜H) between the top 51 and the bottom 52 adjacent to the top 51. At least one top 51 of the rough surface is arranged at the uppermost surface. Preferably, a plurality of tops are arranged at the uppermost surface. More preferably, more than five tops are provided at the uppermost surface. For each of the more than five tops 51, the setting range of the high hardness portion 5 can be smaller than the height difference H relative to the adjacent bottom 52. In addition, the height difference Hmax between the highest top 51 of the rough surface at the uppermost surface and the adjacent bottom 52 can be limited. For each of the more than five tops 51, the high hardness portion 5 can be provided within a range of a distance Dmax from the top 51 of the rough surface. In this case, the distance Dmax is smaller than the height difference Hmax (Dmax＜Hmax). The height difference Hmax can be greater than the distance from the top to the low hardness portion 31. In the present embodiment, the high hardness portion 5 is disposed within a range of a distance D that is smaller than a height difference H from the top of the rough surface to the adjacent bottom, so that the rough surface of the uppermost surface is formed by the high hardness portion 5, and the wear of the rough surface can be suppressed. At least a portion of the uppermost surface is the high hardness portion 5. In one example, the top of the rough surface can be constituted by the high hardness portion 5. With such a configuration, the wear caused by the contact between the substrate 7 and the rough surface of the uppermost surface can be suppressed by the high hardness portion 5. In the present embodiment, only the uppermost surface of the protrusion 3 in the retaining surface is roughened, and the rough surface of the uppermost surface of the protrusion 3 is constituted by the high hardness portion 5. As long as at least the rough surface of the uppermost surface of the protrusion 3 (which is the contact surface with the substrate 7) is composed of the high hardness portion 5, it is more suitable for suppressing the wear of the rough surface than the case where the rough surface of the uppermost surface is not composed of the high hardness portion 5. By making the uppermost surface of the protrusion 3 a rough surface, the reflectivity at the front surface of the substrate retaining plate can be reduced when performing the exposure process. Therefore, the variation of the radiation intensity is reduced, and the exposure unevenness can be suppressed. In addition, compared with the case where the uppermost surface of the protrusion 3 is not a rough surface, there is an effect of improving the adhesion between the base 2 and the high hardness portion 5, and an effect of reducing damage to the substrate by reducing the contact area with the substrate. In this embodiment, the material constituting the base member (base 2 and low hardness portion 31) is black aluminum oxide. The hardness of black aluminum oxide is, for example, about 1600 Hv. The base member (base 2 and low hardness portion 31) needs to be thick enough to ensure the mechanical strength of the substrate retaining plate 1. For example, the thickness of the base member is 10 to 100 mm, preferably 60 mm or less. The thickness of the base member (base 2 and low hardness portion 31) can be 30 mm or less. The material constituting the base member is not limited to black alumina, and can be alumina, ceramic, zirconia, glass, plastic, metal or similar materials. The hardness of the low hardness portion 31 can be 1000 to 2000 Hv. In this embodiment, the upper surface of the low hardness portion 31 of the protrusion 3 is also a rough surface. The rough surface of the upper surface of the low hardness portion 31 is formed by sandblasting the low hardness portion 31. The shape of the rough surface of the uppermost surface of the protrusion 3 can reflect the shape of the rough surface of the upper surface of the low hardness portion 31. As the thickness of the high hardness portion 5 decreases, the correlation between the shape of the rough surface of the upper surface of the low hardness portion 31 and the shape of the rough surface of the uppermost surface of the protrusion 3 increases. The arithmetic average roughness Ra of the uppermost surface of the protrusion 3 is, for example, in the range of 0.4 to 10 μm. The arithmetic average roughness Ra of the uppermost surface of the protrusion 3 may be greater than 0.6 μm, greater than 0.8 μm, or greater than 1.0 μm. The arithmetic average roughness Ra of the uppermost surface of the protrusion 3 may be less than 8.0 μm, less than 6.0 μm, less than 4.0 μm, or less than 2.0 μm. In order to set the arithmetic average roughness Ra of the uppermost surface of the protrusion 3 reflecting the shape of the rough surface of the upper surface of the low hardness portion 31 to greater than 0.4 μm, the arithmetic average roughness Ra of the upper surface of the low hardness portion 31 may exceed 0.4 μm, and may be set to, for example, greater than 0.6 μm. The arithmetic mean roughness Ra of the uppermost surface of the base 2 and the protrusion 3 can be in the range of 0.4 to 4.0 μm. As long as the protrusion 3 can support the substrate 7, the shape and array spacing of the protrusion 3 can be arbitrary. In the present example, the protrusions 3 each have a truncated conical shape or a cylindrical shape. The spacing of the protrusions 3 is, for example, greater than 1 mm and less than 100 mm, preferably greater than 10 mm and less than 30 mm. The spacing of the protrusions 3 can be greater than 1 mm and less than 10 mm. The height of the protrusion 3 is, for example, greater than 10 μm and less than 1 mm, and preferably greater than 0.2 mm and less than 0.8 mm. The height of the protrusion 3 can be, for example, greater than 50 μm and less than 0.5 mm, or can be less than 0.3 mm. As a material for the high hardness portion 5, diamond-like carbon (DLC) formed into a film by plasma chemical vapor deposition (CVD) is used to improve the wear suppression effect. DLC may contain hydrogen. The lower the hydrogen content in DLC, the higher the hardness and brittleness tend to be. The higher the hydrogen content in DLC, the lower the hardness tends to be, and the higher the toughness tends to be. For example, the hardness of DLC may be 6 to 16 GPa; however, it may be 9 to 13 GPa by adjusting the hydrogen content. For example, when the hydrogen content in DLC is 21 to 26 at%, good film quality (high hardness and high toughness) may be obtained when forming the high hardness portion 5 having a rough surface. The hydrogen content in DLC may be 23 to 26 at%. The hydrogen content in DLC may be controlled by film forming conditions (e.g., the flow rate of the source gas and the substrate bias). The hydrogen content in DLC can be analyzed by elastic recoil detection analysis (ERDA). DLC may contain argon. The higher the argon content in DLC, the lower the refractive index of DLC can be, which is effective for suppressing reflection. The argon content in DLC may be less than 10 at%. Note that "at%" indicating the element content represents "atomic %" or "atomic percentage". In addition to the analysis method described in this specification, the content (concentration) of the element can also be analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The material of the high hardness portion 5 is not limited to diamond-like carbon (DLC), and may be silicon carbide (SiC), titanium nitride (TiN), titanium carbide (TiC), ceramics, or sintered carbide. When the hardness of the base member is about 1600Hv, the hardness of the high hardness portion 5 can be 2000 to 4000Hv. By constituting the rough surface of the uppermost surface with the high hardness portion 5, the wear of the rough surface can be suppressed. The thickness of the high hardness portion 5 needs to be a thickness for suppressing the wear of the rough surface caused by contact with the substrate 7. The thickness of the high hardness portion 5 is, for example, not less than 0.4μm, preferably not less than 1μm. However, when the thickness of the high hardness portion 5 is not less than 10μm, cracks are likely to occur in the high hardness portion 5. Therefore, the thickness of the high hardness portion 5 can be less than 10μm. The film thickness of the high hardness portion 5 can be greater than the height difference H of the rough surface of the uppermost surface of the protrusion 3. Furthermore, the setting range of the high hardness portion 5 can be less than the height difference H from the bottom 52. The height difference H from the top 51 of the rough surface to the adjacent bottom 52 of the rough surface can be greater than 0.1μm and less than 1.2μm. The low hardness portion 31 can be referred to as the first portion, and the high hardness portion 5 can be referred to as the second portion. The thickness of the high hardness portion 5 can be small so as to reflect the shape of the rough surface of the upper surface of the low hardness portion 31 on the shape of the rough surface of the uppermost surface of the protrusion 3. Specifically, the thickness μm of the high hardness portion 5 is preferably less than 4 times the arithmetic average roughness Ra of the rough surface of the upper surface of the low hardness portion 31, and more preferably less than 2 times. It can be approximately considered that the arithmetic average roughness Ra of the rough surface of the upper surface of the low hardness portion 31 is equal to the arithmetic average roughness Ra of the rough surface of the uppermost surface of the protrusion 3. In this case, it can be said that the thickness of the high hardness portion 5 is preferably less than 4 times the arithmetic average roughness Ra of the rough surface of the uppermost surface of the protrusion 3, and more preferably less than 2 times. The height difference H of the rough surface of the uppermost surface of the protrusion 3 can be approximated to about 2 times the arithmetic average roughness Ra of the rough surface of the uppermost surface of the protrusion 3. Therefore, it can be said that the thickness of the high hardness portion 5 is preferably less than 2 times the height difference H of the rough surface of the uppermost surface of the protrusion 3, and more preferably less than 1 times. In addition, as long as the arithmetic average roughness Ra of the uppermost surface of the protrusion 3 is greater than 0.4μm, the height difference H can be greater than 0.8μm. When the thickness of the high hardness portion 5 is equal to or less than 2 times the arithmetic mean roughness Ra of the rough surface of the uppermost surface of the protrusion 3, the bottom 52 of the rough surface of the uppermost surface of the protrusion 3 is easily located at a position lower than the top of the rough surface of the upper surface of the low hardness portion 31 (which corresponds to the top 51 of the rough surface of the uppermost surface of the protrusion 3). This is conducive to controlling the shape of the rough surface of the uppermost surface of the protrusion 3 by utilizing the shape of the rough surface of the upper surface of the low hardness portion 31 as the bottom layer base of the high hardness portion 5. As the roughness of the rough surface of the upper surface of the low hardness portion 31 is smaller, the thickness of the high hardness portion 5 can be smaller. As the roughness of the rough surface of the upper surface of the low hardness portion 31 is larger, the thickness of the high hardness portion 5 can be larger. Next, the suction hole 4 according to the present embodiment will be described. In order to suck and hold the substrate 7 placed on the protrusion 3, the lower opening of each suction hole 4 is connected to a vacuum pump (not shown) so that the air around the protrusion 3 can be sucked and depressurized. By providing the protrusion 3, more air can be sucked compared to the case where the protrusion 3 is not provided. Although the side surface of the suction hole 4 is coated with the high hardness portion 5 in the present embodiment, since the side surface is not the surface facing the substrate 7, the side surface does not need to be coated with the high hardness portion 5. Similarly, the high hardness portion 5 does not need to be applied to the rear surface 24 of the base 2 and the side surface of the base 2. Second Embodiment Next, the second embodiment will be described with reference to Figures 3A, 3B and 3C. Figure 3A is a sectional view showing an example of a substrate retaining plate 1 according to the present embodiment. FIG. 3B is an enlarged view of the area surrounded by circle IIIB in FIG. 3A. FIG. 3C is an enlarged view of the area surrounded by circle IIIC in FIG. 3A. Note that the structure of the uppermost surface of the protrusion 3 in the area surrounded by circle IIC in FIG. 3B may be the same as the structure described with reference to FIG. 2C (which is an enlarged view of the area surrounded by circle IIC in FIG. 2B), and therefore its description is omitted. The substrate retaining plate 1 of this embodiment is different from the first embodiment in that the rough surface composed of the high hardness portion 5 is not only provided on the uppermost surface of the protrusion 3, but also provided on the side surface of the protrusion 3 and on the components 21 and 23 (the first section, which is a section without a protrusion on or above the section) provided at the retaining surface of the substrate retaining plate 1. In the substrate retaining plate 1, the base 2 may represent the entire portion except the protrusion 3. The uppermost surface of the base 2 contacts the spaces on both sides of the protrusion 3. Similar to the first embodiment in which the protrusion 3 includes a high hardness portion 5 and a low hardness portion 31, in the second embodiment, the base 2 may include a high hardness portion 5 and a low hardness portion 31. In the first embodiment, the base 2 may be equivalent to the components 21 to 23. However, in the second embodiment, the base 2 may include a high hardness portion and a low hardness portion other than the components 21 to 23. Therefore, the high hardness portion and the low hardness portion of the base 2 other than the components 21 to 23 are specifically referred to as a transition portion 9. The transition portion 9 is a part of the base 2. In the substrate retaining plate 1 of the present embodiment, the base 2 includes a transition portion 9 in addition to the components 21 to 23. The transition portion 9 will be described. The transition portion 9 is a portion of the base 2 that transitions from the component 22 to the protrusion 3, or a portion of the base 2 that transitions from the component 21 or 23 to a space provided above the component 21 or 23. In the present embodiment, the transition portion 9 is composed of a portion (low hardness portion) made of the same material (base member) as the components 21 to 23 and a high hardness portion 5. The transition portion 9 exists at a position where the transition portion 9 transitions from the component 22 to the protrusion 3 via the low hardness portion or from the component 21 or 23 to the space provided above the component 21 or 23 via the high hardness portion 5. Specifically, the transition portion 9 between the component 22 and the protrusion 3 includes a portion composed of a low hardness portion (base member) and a portion composed of the high hardness portions 5 on both sides of the low hardness portion. FIG. 3C will be described. Fig. 3C is an enlarged view of the area surrounded by circle IIIC in Fig. 3A. In the present embodiment, as shown in Fig. 3B, the side surface of the protrusion 3 in the holding surface is a rough surface. The upper surfaces of the components 21 and 23 as the base member are also rough surfaces. In addition, a second segment 55 composed of a high hardness portion 5 is provided on each of the components 21 and 23. The upper surface of the second segment 55 composed of the high hardness portion 5 on the substrate holding surface side is a rough surface. The structure in which the upper surface of the second segment 55 on the substrate holding surface side (which is a surface that does not contact the substrate) is a rough surface is suitable for reducing reflectivity. In addition, since the side surface of the protrusion 3 and the portion on or above the components 21 and 23 are composed of the high hardness portion 5, the contact area between the substrate holding plate 1 and the high hardness portion 5 is increased, and the film separation between the substrate holding plate 1 and the high hardness portion 5 can be suppressed. In the present embodiment, the distance D shown in FIG. 3C exists in a range less than the height difference H. However, it is sufficient that at least the distance D at the uppermost surface of the protrusion 3 falls within a range less than the height difference H. The surface shape of the high hardness portion 5 (second section 55) and the surface shape of the low hardness portion (components 21 and 23) as the bottom layer base of the high hardness portion 5 can be the same as the surface shape of the high hardness portion 5 and the low hardness portion 31 in the first embodiment. The arithmetic mean roughness Ra of the uppermost surface of the base 2 is, for example, in the range of 0.4 to 10 μm. The arithmetic average roughness Ra of the uppermost surface of the base 2 can be greater than 0.6μm, greater than 0.8μm, or greater than 1.0μm. The arithmetic average roughness Ra of the uppermost surface of the base 2 can be less than 8.0μm, less than 6.0μm, less than 4.0μm, or less than 2.0μm. In order to set the arithmetic average roughness Ra of the uppermost surface of the base 2 reflecting the rough surface shape of the upper surfaces of the components 21 and 23 to be greater than 0.4μm, the arithmetic average roughness Ra of the upper surfaces of the components 21 and 23 can be greater than 0.4μm, and can be set to, for example, greater than 0.6μm. The arithmetic average roughness Ra of the uppermost surfaces of the base 2 and the protrusion 3 can be in the range of 0.4 to 4.0μm. Third embodiment Next, the third embodiment will be described with reference to Figures 4A and 4B. This embodiment is different from the second embodiment in that the upper surface of the low hardness portion 31 is flat compared to the rough surface of the uppermost surface of the protrusion 3. In this case, as in the first and second embodiments, since the high hardness portion 5 is included in the rough surface of the uppermost surface of the protrusion 3, the wear of the rough surface can be suppressed. Fourth Embodiment Next, the fourth embodiment will be described with reference to Figures 5A and 5B. This embodiment provides a form similar to the second embodiment; however, the difference is that the protrusion 3 is composed only of the high hardness portion 5. In this case, since the high hardness portion 5 is included in the rough surface for reducing the reflectivity, the wear of the rough surface can be suppressed. In this embodiment, the transition portion 9 is composed of the high hardness portion 5. Fifth Embodiment Next, the fifth embodiment will be described with reference to Figures 6A and 6B. In the present embodiment, the base 2 is composed of a portion 50 different from the high hardness portion 5 and the low hardness portion 31, the upper portion of the protrusion 3 is composed of the high hardness portion 5, and the lower portion of the protrusion 3 is composed of the low hardness portion 31. In this example, since the rough surface of the uppermost surface is composed of the high hardness portion 5, the wear of the rough surface can be suppressed. In the present embodiment, the low hardness portion 31 can be referred to as the first portion, and the high hardness portion 5 can be referred to as the second portion. Sixth embodiment Next, the sixth embodiment will be described with reference to Figures 7A and 7B. Figure 7A is a sectional view showing an example of a substrate retaining plate 1 according to the present embodiment. Figure 7B is an enlarged view of the area surrounded by circle VIIB in Figure 7A. The structure of this embodiment is different from that of the second embodiment in that the portion above the components 21 and 23, the uppermost surface of the protrusion 3, and at least a portion of the side surface of the protrusion 3 are composed of a low refractive index portion 6 having a refractive index lower than that of the high hardness portion 5. FIG. 7B will be described. As shown in FIG. 7B, in this embodiment, the bottom of the rough surface of the uppermost surface is composed of the low refractive index portion 6. The rough surface of the uppermost surface is composed of the high hardness portion 5 and the low refractive index portion 6. In the case of this structure, light incident on the bottom of the rough surface of the uppermost surface is incident on the high hardness portion 5 via the low refractive index portion 6. Therefore, the reflectivity on the holding surface of the substrate holding plate 1 can be reduced. In the present embodiment, since the rough surface of the uppermost surface is constituted by the high hardness portion 5 and the height difference H from the top 51 to the bottom 62 is maintained, the wear of the rough surface due to contact with the substrate 7 can be suppressed. The low refractive index portion 6 will be described. The low refractive index portion 6 has a refractive index lower than that of the high hardness portion 5. Therefore, by arranging the low refractive index portion 6 on the substrate holding surface side of the high hardness portion 5, the refractive index relative to the air is slowed down and the reflectivity is reduced. The low refractive index portion 6 has a refractive index and hardness lower than those of the high hardness portion 5: The reflection at the front surface of the substrate holding plate will be described. The exposure device for forming a fine pattern uses light beams with wavelengths of 365nm (i line), 405nm (h line) and 436nm (g line). The reflection at the front surface of the substrate holding plate is mainly Fresnel reflection, which can be obtained according to the following formula: R = {( N0 - N1 )/( N0 + N1 )} 2 +{( N1 - N2 )/( N1 + N2 )} 2 , wherein R is the reflectivity, N0 is the refractive index of air, N1 is the refractive index of the low refractive index portion, and N2 is the refractive index of the high hardness portion. By using a porous material made of an inorganic oxide as the low refractive index portion 6 provided on the holding surface of the substrate holding plate, a low reflectivity can be provided compared to the case of using an anti-reflection material of a non-porous material. The reason for this is that there are fine irregularities on the surface of the porous material made of an inorganic oxide, and a gradient of the refractive index is formed at the interface with the air. Since the low refractive index portion 6 constitutes a portion on the holding surface of the substrate holding plate 1, the refractive index change between the air and the high hardness portion 5 is slowed down, and the reflectivity on the holding surface can be reduced. Even if the high hardness portion 5 is not provided, the reflectivity on the holding surface can be reduced by slowing down the refractive index change between the air and the low hardness portion 31. The low refractive index portion 6 has the effect of reducing the reflectivity on the front surface of the substrate holding plate 1 by using a material having a refractive index lower than that of the high hardness portion 5. The inorganic oxide can be an alumina material or a silica material, but cannot be a resin material. The low refractive index portion 6 is composed of chain particles, hollow particles or solid particles. The low refractive index portion 6 can be formed to have a thickness of, for example, 0.1 to 1.0 μm, and preferably a thickness of 0.1 to 0.4 μm. The low refractive index portion 6 exists in a uniformly formed state or in a dispersed state. In this embodiment, the primer 8 is used to make the high hardness part 5 and the low refractive index part 6 more firmly and closely contact each other. The primer 8 exists at the junction between the high hardness part 5 and the low refractive index part 6. The primer 8 exists in a uniformly formed state or in a dispersed state. In this case, a silane coupling agent is used as the primer 8; however, the primer 8 is not limited to this. As long as the material can improve the adhesion between the high hardness part 5 and the low refractive index part 6, any material can be used. In the first to fifth embodiments, the uppermost surface of the substrate holding plate 1 is a rough surface, so that the incident light can be scattered and the reflectivity can be reduced. However, in the first to fifth embodiments, due to the large difference in refractive index between the high hardness part 5 and the air, scattered light is easily generated. In this embodiment, the uppermost surface of the substrate holding plate 1 is a rough surface, and the low refractive index part 6 is provided. Therefore, a gradient of refractive index is formed at the interface with the air. Compared with the case where the low refractive index portion 6 is not provided, the reflectivity can be further reduced. In this embodiment, the distance D from the top of the rough surface to the high hardness portion 5 is less than the height difference H from the top of the rough surface to the bottom of the rough surface adjacent to the top. It is not necessary to provide this structure for all bottoms adjacent to a certain top, and it is sufficient to provide such a bottom for one top. The high hardness portion 5 is arranged within a range of a distance D from the top 51. In this embodiment, the top 51 is formed by the high hardness portion 5. However, the top can be formed by the low refractive index portion 6. When the top 51 is formed by the low refractive index portion 6, the low refractive index portion 6 is worn in a range exceeding the distance D due to contact with the substrate. However, thereafter, the high hardness portion 5 forms the top 51, and the high hardness portion 5 constitutes the rough surface of the uppermost surface of the protrusion 3, so that the wear of the rough surface can be suppressed. The substrate retaining plate 1 of the present embodiment is expected to be used not only under light having a wavelength that cannot pass through the high hardness portion 5, but also under light having a wavelength that can pass through the high hardness portion 5. For example, when the high hardness portion 5 is DLC, ultraviolet rays cannot pass through DLC, but infrared rays can pass through DLC. Therefore, the difference n2 - n1 between the refractive index n2 of the high hardness portion 5 and the refractive index n1 of the base member having the first part is smaller than the difference n2 - n3 between the refractive index n2 of the high hardness portion 5 and the refractive index n3 of the low refractive index portion 6. By this structure, it is possible to prevent the light passing through the high hardness portion 5 from being reflected by the base member. Each of n1 , n2 and n3 is a refractive index for light of a wavelength that can pass through the high hardness portion 5. The refractive index n2 of the high hardness portion 5 is higher than the refractive index n1 of the low hardness portion 31. With this configuration, even when light that can pass through the high hardness portion 5 is used, light reflection at the interface between the high hardness portion 5 and the base member can be suppressed. The suction hole 4 in this embodiment will be described. Since the side surface of the suction hole 4 of this embodiment is not a surface facing the substrate 7, the side surface of the suction hole 4 does not need to be provided with a low refractive index portion 6. In this embodiment, the low hardness portion 31 can be referred to as a first portion, the high hardness portion 5 can be referred to as a second portion, and the low refractive index portion 6 can be referred to as a third portion. Seventh Embodiment Next, the seventh embodiment will be described with reference to Figures 8A, 8B and 8C. This embodiment is different from the sixth embodiment in that the rough surface of the uppermost surface is composed only of the low refractive index portion 6 instead of the high hardness portion 5. This embodiment provides a form in which the distance D from the top 61 of the rough surface composed of the low refractive index portion 6 to the top 51 composed of the high hardness portion 5 is smaller than the height difference H from the top 61 to the bottom 62 of the rough surface. Since the low refractive index portion 6 at the uppermost surface is in contact with the substrate 7, the low refractive index portion 6 is worn away immediately after the substrate 7 is placed. However, as the wear of the low refractive index portion 6 progresses, the high hardness portion 5 becomes the top of the rough surface of the protrusion 3, and the distance HD from the top 51 to the bottom 62 is maintained. Therefore, the wear of the rough surface can be suppressed. FIG. 8C will be described. FIG8C is a view showing a form different from FIG8B , the difference being that the distance D is greater than the height difference H. In this case, the low refractive index portion 6 is worn due to contact with the substrate 7. Since the low refractive index portion 6 is worn from the top 61 to the top 51 composed of the high hardness portion 5, the bottom 62 is also worn similarly to the top 61. For this reason, since the uppermost surface of the protrusion 3 is composed of the low refractive index portion 6, the reflectivity at the holding surface is reduced by the low refractive index portion 6. However, the rough surface in the uppermost surface of the protrusion 3 is likely to be worn. Eighth embodiment In this embodiment, the base component (low hardness portion 31 and components 21 and 23) has a nitrogen-containing region. The nitrogen-containing region may exist near the high hardness portion 5, for example, within a range of 100nm or less from the high hardness portion 5. The nitrogen content of the nitrogen-containing zone may be 1 at% or more. The maximum nitrogen content in the nitrogen-containing zone is preferably 5 at% or more, and more preferably 10 at% or more. The maximum nitrogen content of the nitrogen-containing zone may be less than 25 at%. In the base component, at a position separated from the high hardness portion 5, for example, at a position sufficiently separated from the high hardness portion 5, for example, at a position 100 μm away from the high hardness portion 5, the nitrogen content may be less than 1 at%. Since nitrogen has a higher diffusion suppression function than other elements, the diffusion of impurities between the base component (low hardness portion) and the high hardness portion 5 can be suppressed by providing a nitrogen-containing zone. Furthermore, in the case where the oxygen content in the base member is 25 at% or more and the carbon content or nitrogen content in the inorganic material film (high hardness portion 5) provided on the base member is 25 at% or more, when a nitrogen-containing region is provided in the base member, the adhesion between the base member and the inorganic material film is improved. Typical examples of base members having an oxygen content of 25 at% or more include oxides such as silicon oxide (silicon dioxide), aluminum oxide (aluminum oxide), and zirconium oxide (zirconia). The inorganic material film having a carbon content or a nitrogen content of 25 at% or more is a carbon film such as DLC, a carbide film such as silicon carbide (SiC) or titanium carbide (TiC), or a nitride film such as silicon nitride (SiN) or titanium nitride (TiN). The inorganic material film contains, in addition to nitrogen or carbon, more than 25 at% of an element that forms a compound with nitrogen or carbon (a metal such as titanium or a semimetal such as silicon). Carbon films, carbide films, and nitride films generally have low adhesion to oxides. In particular, DLC hardly adheres or chemically reacts with the underlying base component, and therefore has low adhesion to metals or oxides. However, when a nitrogen-containing region is provided in the oxide, the adhesion between the nitrogen-containing region and the carbon film, carbide film, or nitride film is improved. Before the inorganic material film is formed on the base component, the nitrogen-containing region can be formed by implanting nitrogen into the surface of the base component. Therefore, the nitrogen-containing region can contain more than 1 at% (more preferably, more than 5 at%) of nitrogen generated by the implanted nitrogen and more than 25 at% of oxygen contained in the base component before the nitrogen is implanted. In addition, the nitrogen-containing region contains more than 25 at% of an element (a metal such as aluminum or a semimetal such as silicon) that forms a compound with oxygen contained in the base member before the nitrogen is implanted. Instead of implanting nitrogen into a base member such as alumina, a SiC layer can be provided on the base member as an adhesion layer, and a DLC film can be provided on the SiC layer. When the adhesion of the two films is compared in a scratch test, the adhesion of the DLC film when only nitrogen is implanted can be higher than the adhesion of the DLC film when only the SiC layer is provided. Implanting nitrogen into the base member below the SiC layer can increase the adhesion between the SiC layer and the alumina substrate. When a DLC film is formed on a base member of a substrate retaining plate, if film formation fails, the DLC film needs to be removed. Since DLC evaporates when reacting with oxygen, the film is removed, for example, by heating the film in the atmosphere or exposing the film to oxygen plasma. When the adhesion layer is a SiC layer, the surface of the SiC is oxidized to form SiO or SiO 2 due to the influence of the DLC film removal step. When a DLC film is formed thereon, the DLC may be easily peeled off due to the low adhesion between SiO or SiO 2 and DLC. On the other hand, when a nitrogen-containing area obtained by nitriding the base member of the substrate holding plate is used for the adhesion layer, the adhesion layer is less likely to be oxidized by the DLC film removal step. Therefore, even if the DLC film is formed again after the DLC film is removed, the DLC has sufficient adhesion. Here, the case where the base member is an oxide is described as an example; however, even if the base member is a metal, the adhesion between the carbide film or the nitride film and the metal is low. Therefore, when a nitrogen-containing area is provided on the surface of the metal base member, the adhesion between the metal base member and the carbide film or the nitride film is improved. The present invention is not limited to the above-mentioned embodiments, and many modifications can be made within the scope of the technical concept of the present invention. Figure 9 is a schematic diagram of an exposure device. The optical device EQP as an exposure device includes a light source 14 and reflecting mirrors 16 and 17 constituting an illumination optical system. The optical device EQP includes a mask stage 19 supporting a mask 18 as a pattern forming unit, a projection optical system 25 for projecting a pattern formed on the mask 18, and a substrate holding plate 1 supporting a substrate 7. The exposure light 15 from the light source 14 is reflected by the reflection mirrors 16 and 17 of the illumination optical system and guided to the photomask 18, and the exposure light 15 with the pattern formed on the photomask 18 is focused by the projection optical system 25 and projected onto the substrate 7. The substrate 7 and the substrate holding plate 1 are moved by the substrate moving unit 26. The light source 14 projects the pattern formed on the photomask 18 onto the substrate 7. A photoresist is applied to the substrate 7. The photoresist is exposed to the exposure light 15. The substrate 7 can be a semiconductor wafer or a glass substrate of a flat panel display (FPD). The exposure light of the exposure device is generally ultraviolet light. The wavelength of the exposure light is 436 nm for a g-line light source and about 365 nm for an i-line light source. The wavelength of the exposure light is about 248 nm for a KrF excimer laser light source, about 193 nm for an ArF excimer laser light source, and about 10 to 20 nm for an extreme ultraviolet (EUV) light source. The projection optical system may be a reduced projection type, an equal magnification projection type, or an enlarged projection type. Although a transmissive light mask 18 is shown here, a reflective light mask 18 may also be used. The projection optical system may be a refractive type using a lens or a reflective type using a reflective mirror. Example Next, a specific example will be described with reference to Figures 7A and 7B. In this example, a substrate having a length of 200 mm to 1500 mm and a width of 800 mm to 1500 mm is used. The substrate in this example is a glass substrate; however, the substrate may be a SiC wafer or a liquid crystal panel substrate. The substrate in this example may be a transparent substrate. The transparent substrate in this case is a substrate that can transmit any of various wavelengths of light. First, the base 2 will be described. The base 2 can have any properties as long as it does not cause exposure failure due to defocusing. A base 2 made of black alumina with a thickness of 60 mm is used. In this example, the surface is roughened by sandblasting. The value of Ra is about 0.8μm, and the value of Rz is about 5.0μm. The surface roughness is measured using a surface roughness measuring instrument Surftest SJ-210 (Mitutoyo Corporation). The evaluation length is 5mm and the measuring speed is 0.5mm/s. Next, the protrusion 3 will be described. As long as the protrusion 3 can support the substrate 7, the shape and array spacing of the protrusion 3 can be arbitrary. The shape of each protrusion 3 in this example is a truncated cone or cylinder with a diameter of 0.8 mm and a height of 0.5 mm. In addition, the spacing between adjacent protrusions 3 is set to 20 mm. Since the protrusion 3 and the base 2 are sandblasted at the same time, it can be considered that the surface roughness of the base component at the protrusion 3 is basically the same as the surface roughness of the base component at the base 2 (within 10% difference). Next, the high hardness portion 5 will be described. In this example, DLC is used to improve the wear suppression effect. The DLC film is formed by plasma CVD, and at least the surface of the protrusion 3 is coated with DLC. The thickness of the DLC film needs to be a thickness for suppressing wear, and can be more than 1μm. However, when the film thickness of the DLC film is more than 10μm, the possibility of cracks is very high. Therefore, in this example, the film thickness of the DLC film is set to 2μm. The film forming conditions in this example are as follows: argon gas flow rate of 50 sccm, toluene gas flow rate of 2.5 sccm, pressure of 5 Pa, RF power of 500 W/13.56 MHz, and film forming time of 2 hours. When the formed DLC film is measured with an ellipsometer, the refractive index of the DLC film is 2.1. When the formed DLC film is measured with a nanoindenter, the hardness of the DLC film is about 15 GPa. In this case, the hardness of DLC is obtained by forming a DLC film with a thickness of 100 nm on a Si wafer under the same film forming conditions as the above film forming conditions, measuring the DLC film with a nanoindenter, and calculating the hardness of DLC based on the stress at a depth of 30 nm. Since the DLC film is uniformly formed on the base member, it can be considered that the surface roughness of the upper surface of the DLC film is substantially the same as the surface roughness of the base member formed by sandblasting (within 10% difference). Next, the low refractive index portion 6 will be described. A porous material made of an inorganic oxide is used for the low refractive index portion 6. In this example, the inorganic oxide is a silicon oxide material with a thickness of 300nm. In this example, a primer 8 is used to make the high hardness portion 5 and the low refractive index portion 6 more firmly in close contact with each other. The primer 8 is arranged at the junction between the high hardness portion 5 and the low refractive index portion 6. The primer 8 is provided in a uniformly formed state or in a dispersed state. In this example, a silane coupling agent is used as the primer material. However, the primer material is not limited to this. Any material can be used as long as it can improve the adhesion between the high hardness part 5 and the low refractive index part 6. The low refractive index part 6 and the base material 8 are formed by spraying using an inorganic particle dispersion. The spraying conditions in this example are as follows: the liquid supply rate of both the base material 8 and the low refractive index part 6 is 7g/min, the spray gun moving speed is 20m/min, and the atomization pressure is 0.1MPa. The concentration of inorganic particles in the coating liquid is 0.1wt% for the base material 8 and 2wt% for the low refractive index part 6. When the formed low refractive index part 6 is measured with an elliptical meter, the refractive index of the low refractive index part is 1.2. Since the thickness of the low refractive index portion 6 is sufficiently smaller than the surface roughness of the base member, the surface roughness of the uppermost surface of the low refractive index portion 6 and the bottom material 8 of the substrate retaining plate 1 can be considered to be substantially the same as the surface roughness of the substrate formed by sandblasting (within 10% difference). When the substrate retaining plate 1 in this example was measured with a spectroscopic colorimeter (CM-26d manufactured by Konica Minolta), the effect of reducing the reflectivity by 4.5% by forming the low refractive index portion 6 was confirmed. In addition, the adhesion between the protrusion 3 and the high hardness portion 5 is enhanced by roughening the uppermost surface of the protrusion 3, and the regular reflection can be greatly reduced by scattering. An example of setting the nitrogen-containing zone described in the eighth embodiment will be described. The base member of the substrate retaining plate including aluminum oxide as the main component is installed in a plasma processing device. The plasma processing device can be a plasma CVD device. More specifically, the plasma treatment device can be a plasma source ion implantation (PSII) device, an ion vapor deposition device, or an RF plasma CVD device. After the plasma treatment device is evacuated to a predetermined pressure, nitrogen gas is introduced and plasma is generated by a plasma generator to generate nitrogen ions. A negative potential can be applied to the base member of the substrate holding plate by a DC pulse power supply or a DC power supply, or by applying a self-bias generated by applying RF to the substrate holding member. The nitrogen ions are accelerated by the negative potential applied to the base member of the substrate holding plate and made incident on the base member of the substrate holding plate to perform the implantation of the nitrogen ions into the surface of the base member of the substrate holding plate. As a result of analyzing the base member of the substrate retaining plate treated in this manner in the depth direction by X-ray photoelectron spectroscopy (XPS), it can be confirmed that nitrogen exists from the uppermost surface of the base member to a depth of 20 nm. In particular, the nitrogen content from the uppermost surface to a depth of 2.5 nm can be high (5 at %). For example, 15 at % nitrogen can be found at the uppermost surface where the nitrogen content is the highest, and 5 at % nitrogen can be found at a depth of 2.5 nm. Nitrogen can be distributed basically uniformly over the entire surface of the base member of the substrate retaining plate. When a DLC film is formed on the substrate retaining plate provided with the above-mentioned nitrogen-containing area, the adhesion between the DLC film and the alumina base member is improved. In addition, it is also appropriate to reform the film after the DLC film is removed. According to the present invention, a technology that is advantageous in suppressing the wear of the rough surface of a substrate retaining plate can be provided. The above-mentioned embodiments can be modified as appropriate without departing from the scope of the technical concept. The disclosure of this specification includes not only the contents described in this specification, but also all matters that can be grasped according to this specification and the drawings attached to this specification. It should be noted that, with respect to the specific numerical ranges cited, the description of "e to f" (e and f are numbers) means above e and/or below f. In addition, in the case of describing the range "i to j" and the range "m to n" (i, j, m and n are numbers) together, with respect to the specific numerical ranges cited, the lower limit and upper limit groups are not limited to the i and j groups or the m and n groups. For example, a variety of combinations of lower limit and upper limit groups can be considered. That is, when describing the range "i to j" and the range "m to n" together, the range "i to n" or the range "m to j" can be considered as long as there is no contradiction. In addition, equal to or greater than e represents equal to e or greater than e (exceeding e), and a value greater than e can be adopted instead of e. In addition, less than f represents f or less than f (less than f). A value less than f can be adopted instead of f. The disclosure of this specification also includes supplements to the various concepts described in this specification. That is, when there is a description of "A is greater than B" in this specification, for example, even if there is no description of "B is not greater than A", this specification can be said to disclose "B is not greater than A". This is because the description of "A is greater than B" is based on the premise of considering "B is not greater than A". Although the present invention has been described with reference to exemplary embodiments, it should be understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the following claims should be given the broadest interpretation to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2020-196852 filed on November 27, 2020 and No. 2021-065237 filed on April 7, 2021, which are incorporated herein by reference in their entirety.