JP2005142591A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck capable of improving temperature uniformity within a small region of a surface of a sheet sample and is equipped with a sufficient sucking force and a releasing property after suspending application of electric voltage, without reducing chemical and mechanical properties of a surface such as a projected upper surface to come into contact with the sheet sample and introducing excessive gas. <P>SOLUTION: A flat base and a number of projections 5, projected in a sucking region on the flat base are provided to make the projections 5 suck the sheet sample. An upper surface of the projections 5 consists of an outer periphery surface 20 which is a smooth region and an inner periphery surface 21 which is a rough surface region. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrostatic chuck. More specifically, the present invention relates to an electrostatic chuck that adsorbs and fixes a plate-like sample such as a silicon wafer, a printed board, or a glass substrate by an electrostatic chuck method.

  As a conventional technique for fixing a plate-like sample, various suction fixing methods such as a vacuum chuck and an electrostatic chuck are known. For example, a plate-like sample is transported or exposed, film-formed, or finely formed on a plate-like sample. It is used when processing, cleaning, dicing, etc.

  In such an adsorption / fixation device, the surface of the adsorption / fixation device facing the sample is provided with a grid-like slit, a protrusion is erected, or a hole is provided to contact the surface contacting the sample. Forming a surface that does not. In this way, by providing the non-contact surface, in the case of the electrostatic chuck method, the detachability after the voltage application is stopped can be improved. Further, the presence of the non-contact surface can prevent dust from entering between the contact surface and the sample.

  In addition, when the plate-like sample is subjected to a treatment such as etching in a plasma atmosphere, it is necessary to carry out the process under reduced pressure, that is, in an atmosphere where plasma is easily generated. When an etching process or the like is performed on a plate-like sample in a plasma atmosphere, the surface of the semiconductor wafer becomes high temperature due to plasma heat. When the surface temperature increases, problems such as bursting of the resist film on the surface arise. Further, if the temperature is nonuniform in the plane of the plate-like sample, the chemical treatment becomes nonuniform. Therefore, in the electrostatic chuck type adsorption device, a cooling gas such as helium is flowed into the space between the lower surface of the plate sample and the non-contact surface, and the surface temperature of the plate sample is uniformed so that the chemical processing of the plate sample is performed uniformly. Is cooled uniformly.

In this case, a higher cooling effect can be obtained by increasing the area of the non-contact surface as much as possible. However, if the area of the non-contact surface is increased and the area of the contact surface is too small, the attractive force is insufficient. Therefore, attempts have been made to increase the smoothness of the contact surface so that sufficient adsorption force can be obtained even with a small contact area. For example, in the electrostatic chuck described in Patent Document 1, the specific resistance of the dielectric layer is set to 10 ⁹ Ωm or less, and Rmax (maximum height) of the upper surface serving as an adsorption surface for a number of protrusions provided on the upper surface of the dielectric layer. Is 2.0 μm or less, or Ra (centerline average roughness) is 0.25 μm or less, and the area ratio of the total area of the upper surface of the protrusion to the upper surface of the dielectric layer is 1% or more and less than 10%.

  On the other hand, the plate-like sample is heated by energizing and heating the heater built in the adsorption-fixing device, and the adsorption surface is simultaneously heated while adsorbing the plate-like sample to the adsorption surface of the adsorption-fixing device. An adsorption fixing device capable of heating a plate-like sample is also known. Even in such an adsorbing and fixing device, it is required to make the surface temperature of the plate-like sample uniform in order to perform chemical treatment of the plate-like sample uniformly. Therefore, a gas such as helium is caused to flow in the space between the lower surface of the plate-like sample and the non-contact surface so that the heating effect by the heater is spread over the entire surface of the plate-like sample.

  Forming a non-contact surface on the surface of the adsorption / fixing device facing the sample in this way not only improves the detachability (in the case of an electrostatic chuck), prevents the adhesion of dust, but also makes the temperature of the plate-shaped sample uniform. And plays an important role in performing uniform chemical treatment on plate-like samples.

  However, in the conventional electrostatic chuck having the non-contact surface, the temperature uniformity is not always sufficient in consideration of the minute region of the plate-like sample. This is because heat is more easily transferred on the contact surface than on the non-contact surface. For this reason, when the plate-shaped sample is heated by the heater, the contact portion of the plate-shaped sample that comes into contact with the contact surface is likely to be hotter than the portion that is not in contact. In addition, when the plate-like sample is heated by plasma or the like, the non-contact portion where no heat escape is likely to be hot.

  In particular, when helium gas or the like cannot be introduced, the influence of temperature non-uniformity due to the above causes is large. Even when helium gas or the like can be introduced, when viewed microscopically, the temperature uniformity effect due to helium gas or the like is difficult to reach the contact portion of the plate-like sample that contacts the contact surface, and the temperature is sufficiently uniform. Conversion was difficult. Although it can be expected that the effect of homogenizing the temperature will be increased by increasing the gas pressure of helium or the like, an excessive gas pressure is not appropriate because it causes cracking of the plate-like sample.

In order to eliminate the in-plane temperature non-uniformity of the microscopic plate-shaped sample, the area of each contact surface should be as small as possible. It is effective to make the area of the area as small as possible. However, if the area of the contact surface is reduced, the chemical corrosion resistance is lowered and the protrusions are easily damaged. Further, there is a problem that the peripheral portion of the contact surface is easily worn by contact with the plate-like sample.
Japanese Patent Laid-Open No. 7-153825

  In view of the circumstances of the prior art, the present invention provides a plate-like sample without deteriorating the chemical and mechanical properties of the surface contacting the plate-like sample such as the upper surface of the protrusion, and without introducing excessive gas. It is an object of the present invention to provide an electrostatic chuck that can improve the uniformity of the in-plane temperature in a very small region and that has sufficient adsorption force and detachability after voltage application is stopped.

  As a result of intensive studies, the present inventors have found that the above-mentioned problems of the prior art can be efficiently solved by devising the shape of the top surface of the protrusion, which has been a mere flat surface, and completed the present invention. did.

  That is, the present invention includes an internal electrode for electrostatic attraction inside, a flat base made of a dielectric, and a large number of protrusions protruding from an adsorption region of the flat base, and the large number of protrusions An electrostatic chuck for adsorbing a plate-like sample on the upper surface of the projection, the upper surface of the protrusion from a smooth region having a center line average roughness of 0.5 μm or less and a rough surface region having a center line average roughness of 0.5 μm or more The electrostatic chuck is characterized in that the difference between the center line average roughness of the smooth region and the center line average roughness of the rough surface region is 0.2 μm or more.

  In the present invention, the rough surface region is preferably formed at a position surrounded by a smooth region. Moreover, it is preferable that the area ratio with respect to the total area of the upper surface of the said protrusion of the total area of the said smooth surface is 10 to 90% of range.

  The electrostatic chuck of the present invention can be used in a region where the in-plane temperature of the plate-like sample is small without deteriorating the chemical and mechanical properties of the protrusions formed in the adsorption region and without introducing excessive gas. It is possible to provide an electrostatic chuck that can improve uniformity and that has sufficient adsorption power and detachability after voltage application is stopped.

  In the following, an embodiment of the present invention will be described with reference to the accompanying drawings, taking an electrostatic chuck with no integrated heater as an example.

"Reference form"
FIG. 1 is an electrostatic chuck according to a reference embodiment, and FIG. 2 is an enlarged view of a main part in II of FIG. 1, each showing a plan view in (a) and a sectional view in (b). As shown in the figure, the electrostatic chuck 1 is formed by bonding a dielectric layer 3 as a flat base on a metal plate 2, and an internal electrode 4 is embedded or sandwiched in the dielectric layer 3.

  On the upper surface of the dielectric layer 3, a peripheral wall 3 a having a width of 1 to 5 mm and the same height as the projections 5, 5... Described later is formed so as to prevent a cooling gas such as He from leaking, and this inner side is adsorbed. A region 3b is provided, and a number of protrusions 5, 5... Are erected in the suction region 3b. The peripheral wall 3a and the protrusions 5, 5,... May be formed integrally with the dielectric layer 3 or may be formed as separate members.

  As shown in FIG. 2, each of the protrusions 5, 5... Has an upper surface 13 having an uneven shape including a sample holding surface 14 formed from the top surface of the convex portion and a concave portion 15 surrounded by the sample holding surface 14. The sample holding surfaces 14, 14... Are suction surfaces that are in direct contact with the semiconductor wafer W. Moreover, in the adsorption | suction area | region 3b, the part in which the processus | protrusion 5,5 ... is not standing is left as the groove part 16. As shown in FIG.

  1, a cooling gas introduction hole 6 is formed through the metal plate 2 and the dielectric layer 3, and the upper surface of the dielectric layer 3 and the lower surface of the semiconductor wafer W are formed through the cooling gas introduction holes 6 and 6. A cooling gas such as He is supplied to the gap between the two. Furthermore, flow paths 12 and 12 through which a coolant for cooling the electrostatic chuck flows are provided inside the metal plate.

  A DC power supply circuit 7 is connected to the internal electrode 4, and a high frequency power supply circuit 9 is connected to the conductor portion 8 on the lower surface of the dielectric layer 3. Further, the high frequency power supply circuit 9 may be connected to the internal electrode 4. In the plasma processing apparatus, a grounded counter electrode 10 is located above the electrostatic chuck 1. Thus, an electrostatic force is generated by placing the wafer W on the electrostatic chuck 1 and applying a DC voltage to the internal electrode 4, and the wafer W has the dielectric layer 3, specifically, the protrusions 5, 5. .. Are adsorbed on the upper surface of the upper sample holding surfaces 14, 14. Further, when a high frequency is applied by the high frequency power supply circuit 9, active radicals 11 are generated between the counter electrode 10 and the Si oxide film on the surface of the wafer W is etched.

  Returning to FIG. 2 again, the area ratio of the total area of the sample holding surfaces 14, 14... To the total area of the adsorption region 3 b (the area obtained by excluding the area of the peripheral wall 3 a from the area of the dielectric layer 3) is 0.5˜. The range is 30%, preferably 1 to 10%. The area ratio is set to 0.5% or more in order to secure the necessary adsorption force, and 30% or less is difficult to adhere dust existing on the adsorption surface, and the plate-like sample after voltage application is stopped. This is to ensure the detachability of the.

Further, the total area of the sample holding surfaces 14, 14... Relative to the total area of the upper surfaces 13, 13... Of the protrusions 5, 5... (Total area of the sample holding surfaces 14, 14. The ratio is preferably in the range of 10 to 90%.
That is, by setting the area ratio within the above range, sufficient adsorption force and temperature uniformity of the plate-like sample can be ensured at the same time. That is, if the area ratio is less than 10%, a necessary adsorption force cannot be ensured. On the other hand, if the area ratio exceeds 90%, a recess is substantially formed on the upper surface of the protrusion. In other words, it becomes difficult to make the temperature of the plate-like sample uniform.

Further, the width d ₁ of the holding portions 14, 14... Is preferably not more than twice the thickness of the plate sample. That is, when the holding portion 14, 14 the width _{d 1} of at least twice, and the heat transfer coefficient in the groove 16, 16 ..., the upper surface (sample-holding surface 14 and 14 ... + recesses 15, 15 ...) It becomes difficult to reduce the difference between the heat transfer coefficient at 13, 13..., And the groove portions 16, 16... And the upper surface (sample holding surfaces 14, 14... + Concave portions 15, 15...) 13, 13. Therefore, it becomes difficult to improve the uniformity of the in-plane temperature of the plate-like sample in a very small region.

It is preferable the recess 15, 15 ... processing depth _{D 1} of the formed projection 5 top is 0.1Myuemu～2.0Myuemu. Processing depth D ₁ is not to the formation of the substantially concave portion 15, 15 ...... When it is 0.1μm or less, is difficult to improve the uniformity in the small area of the surface temperature of the plate sample Become. When machining depth D ₁ is equal to or greater than 2.0 .mu.m, there is a tendency that the adsorption force is reduced.

Adsorption region 3b 16, 16 ... processing depth _{D 2} of the groove formed in is preferably 1 m to 20 m. When machining depth D ₂ is at 1μm or less, it is difficult to flow a gas such as He into the lower surface of the plate sample, also not effective against adhesion prevention of dust, cause lifting of the plate-like sample W As a result, the adsorptive power decreases, and it becomes difficult to improve the uniformity of the in-plane temperature of the plate-like sample in a very small region. Also, undesirable attraction force of the entire attraction force is reduced in the grooves 16, 16 ...... and machining depth D ₂ is 20μm or more is reduced.

  The production of the protrusion and the fine processing of the upper surface of the protrusion can be performed using, for example, mechanical processing such as grinding stone processing or laser engraving or shot blast processing. Hereinafter, with reference to FIG. 3, a case where the method for forming the protrusions and the unevenness of the upper surface in the suction region 3 b is performed using shot blasting will be described.

First, the polishing process wafers installation surface (the suction region 3b) (central line average roughness Ra ₁ is 0.5μm or less) and to the flat surface, the wafer is cleaned installation surface became smooth (adsorption region 3b). This cleaning is performed with an organic solvent such as trichlene and degreased. After this degreasing, for example, it is washed with warm water.

  Next, a mask 17 is provided on the wafer installation surface (suction region 3b) as shown in FIG. The pattern shape of the mask 17 is the same as the pattern shape of the protrusion 5 shown in FIG. As the mask 17, a photosensitive resin or a plate-like mask is used. This method follows conventional methods.

  Next, shot blasting is performed, and as shown in FIG. 3B, grooves 16, 16,... Are formed in portions not covered by the mask 17, and as a result, protrusions 5, 5,. As particles used for this shot blasting, alumina, silicon carbide, glass beads and the like are preferable, and the particle size of the particles is preferably about 300 mesh under to 1500 mesh over. Then, the mask 17 is removed. At this time, when the mask 17 is made of a photosensitive resin, a stripping solution such as methylene chloride is used.

  Next, a mask 18 is provided on the projections 5, 5... As shown in FIG. The pattern shape of the mask 18 is the same as the pattern shape of the projections and depressions on the protrusions 5, 5... Shown in FIGS. Then, shot blasting is performed again in accordance with the above-described shot blasting, and recesses 15, 15... Are formed in portions not covered by the mask 18, as shown in FIG. Then, the mask 18 is removed to obtain the electrostatic chuck shown in FIGS.

In this way, the electrostatic chuck (the ratio of the total area of the sample holding surfaces 14, 14... To the total area of the adsorption region 3b is 5%, and the protrusion 5 having the total area of the sample holding surfaces 14, 14. 5 is 8% of the total area of the upper surfaces 13, 13... And the width d ₁ is 0.5 times the thickness of the plate sample, D ₁ = 2.4 μm, D ₂ = 3.0 μm), An 8-inch Si wafer is adsorbed while flowing He gas of 1.33 × 10 ³ Pa (10 torr) through the grooves 16, 16..., And the electrostatic adsorption force, adsorption time, and desorption time of the electrostatic chuck are The determination was made at room temperature and 150 ° C. The adsorption time is a time until the electrostatic adsorption force becomes 100 gf / cm ² , that is, about 9800 Pa when a DC voltage of 500 V is applied, and the desorption time is a voltage of DC 500 V. After applying for a minute, the application is stopped, and the time from that time until the electrostatic attractive force becomes 10 gf / cm ² , that is, about 980 Pa. The measurement results are shown in Table 1.

On the other hand, this electrostatic chuck is attached to a plasma etching apparatus, and an 8-inch Si wafer is placed in a mixed gas atmosphere of 1.33 × 10 ² Pa (1.0 torr) of CF ₄ : 20 vol% and O ₂ : 80 vol%. Was subjected to 50000 wafers, and no chemical corrosion or abrasion was observed on the protrusions 5, 5,. Further, the etching amount (etching depth) of the SiO ₂ film on the Si wafer was measured, and the results are shown in Table 1.

"Embodiment"
In the present embodiment, in the electrostatic chuck of FIG. 1, the shape of the protrusion 5 is not the form of FIG. 2, but the form shown in FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view. As shown in FIG. 4, the upper surfaces 19, 19... Of the protrusions 5, 5 have a center line average roughness Ra ₁ of 0.5 μm or less as a smooth region and a center line average as a rough surface region. The roughness Ra ₂ is composed of inner peripheral surfaces 21, 21... Larger than the outer peripheral surface 20 by 0.2 μm or more, and the outer peripheral surfaces 20, 20. Moreover, in the adsorption | suction area | region 3b, the part in which the processus | protrusion 5,5 ... is not standing is left as the groove part 22. FIG.

Here, the reason why the center line average roughness of the outer peripheral surfaces 20, 20... Is 0.5 μm or less is to ensure a sufficient adsorption force.
Further, the center line average roughness of the inner peripheral surfaces 21, 21... Is 0.5 μm or more. This is because the center line average roughness has a significant difference in heat transfer properties with a boundary of 0.5 μm.

The area ratio of the total area of the outer peripheral surfaces 20, 20... To the total area of the adsorption region area 3b is 0.5 to 30%, preferably 1 to 10%.
The area ratio is set to 1% or more in order to ensure the necessary suction force, and 30% or less is less likely to cause dust existing on the suction surface to adhere to the plate-like sample after voltage application is stopped. This is to ensure the detachability.

  In addition, the area ratio of the total area of the outer peripheral surfaces 20, 20... To the total area of the upper surfaces 19, 19. That is, by setting the area ratio within the above range, sufficient adsorption force and temperature uniformity of the plate-like sample can be ensured at the same time. That is, if the area ratio is less than 10%, a necessary adsorption force cannot be ensured. On the other hand, if the area ratio exceeds 90%, a substantially rough surface region is formed on the upper surface of the protrusion. It is not formed, and it becomes difficult to make the temperature of the plate-like sample uniform.

Further, the width d ₂ of the outer peripheral surfaces 20, 20... Is preferably not more than twice the thickness of the plate sample. That is, when the width d of the outer peripheral surfaces 20, 20... Is twice or more, the heat transfer coefficient and the upper surface (the outer peripheral surfaces 20, 20... + The inner peripheral surfaces 21, 21. 19, 19... Becomes difficult to reduce the difference in heat transfer coefficient, and a temperature difference occurs between the grooves 22, 22... And the upper surfaces 19, 19. It becomes difficult to improve the uniformity in the.

Adsorption region 3b grooves 22, 22 ... machining depth _{D 3} of which is formed in is preferably 1 m to 20 m. That is, when the machining depth D ₃ is at 1μm or less, it is difficult to flow a gas such as He into the lower surface of the plate sample, also not effective against adhesion prevention of dust, floating of the plate-like sample W As a result, the adsorption force decreases, and it becomes difficult to improve the uniformity of the in-plane temperature of the plate-like sample in a very small region. Also, undesirable attraction force of the entire attraction force is reduced in the grooves 22, 22 ...... and machining depth D ₃ is 20μm or more is reduced.

  The production of the protrusions and the fine processing of the upper surface can be performed using, for example, mechanical processing such as grinding wheel processing, laser engraving, or shot blast processing. Hereinafter, the case where the method of forming the protrusion and the outer peripheral surface 20 and the inner peripheral surface 21 of the upper surface in the suction region 3b is performed using shot blasting will be described with reference to FIG.

First, according to the reference embodiment, the abrasive machining a wafer mounting surface (the suction region 3b) (central line average roughness Ra ₁ is 0.5μm or less) and to the flat surface, the wafer mounting surface became smooth (adsorption region 3b) Is washed in the same manner as in the reference embodiment.

  Next, as shown in FIG. 5A, the wafer installation surface (suction area 3 b) is covered with a mask 23. Next, as shown in FIG. 5B, grooves 22, 22,..., Projections 5, 5,... Are formed in portions not covered with the mask 23 by shot blasting. The mask 17 and shot blasting conditions are the same as in the reference embodiment.

Next, a mask 24 is provided on the projections 5, 5... According to a conventional method as shown in FIG. The pattern shape of the mask 24 is the same as the pattern shape of the outer peripheral surfaces 20, 20... And the inner peripheral surfaces 21, 21. Then, shot blasting is performed again in accordance with the above-described shot blasting, and an inner peripheral surface having a center line average roughness Ra ₂ of 0.5 μm or more in a portion not covered by the mask 24 as shown in FIG. 21, 21... Are formed. At this time, the difference between Ra ₂ and Ra ₁ is set to 0.2 μm or more. Then, the mask 24 is removed, and the electrostatic chuck shown in FIGS. 1 and 4 is obtained.

The electrostatic chuck of the embodiment (the area ratio of the total area of the outer peripheral surfaces 20, 20... To the total area of the attracting region 3 b is 5%, and the protrusion top surfaces 19, 19. The ratio of the total area to the total area is 50%, the width d ₂ is 0.5 times the thickness of the plate sample, and D ₃ = 3 μm). Tested according to The results are shown in Table 1.

On the other hand, this electrostatic chuck is attached to a plasma etching apparatus, and an 8-inch Si wafer is placed in a mixed gas atmosphere of 1.33 × 10 ² Pa (1.0 torr) of CF ₄ : 20 vol% and O ₂ : 80 vol%. Was subjected to 50000 wafers, and no chemical corrosion or abrasion was observed on the protrusions 5, 5,. Further, the etching amount (etching depth) of the SiO ₂ film on the Si wafer was measured, and the results are shown in Table 1.

"Comparative example"
The same as in the reference embodiment except that the upper surfaces 13, 13... Of the projections 5, 5... Located in the adsorption region 3b of the dielectric layer 3 are not uneven (the ratio of the total area of the apexes of the projections to the adsorption region 3b) Is the same as in Embodiment 1). The electrostatic chucking force, adsorption time, desorption time, and etching characteristics of this electrostatic chuck were tested according to the test of the reference form. The results are shown in Table 1.

  As shown in Table 1, the variation in the etching amount between the reference embodiment and the embodiment is smaller than that in the comparative example. This indicates that the electrostatic chucks of the reference embodiment and the embodiment are excellent in heat uniformity in a minute region of the wafer.

1 shows an electrostatic chuck according to a reference embodiment of the present invention, in which (a) is a plan view and (b) is a cross-sectional view. The principal part of the electrostatic chuck which concerns on the reference form of this invention is shown, (a) is a top view, (b) is sectional drawing. It is a figure which shows the manufacturing method of the electrostatic chuck which concerns on the reference form of this invention. The principal part of the electrostatic chuck which concerns on embodiment of this invention is shown, (a) is a top view, (b) is sectional drawing. It is a figure which shows the manufacturing method of the electrostatic chuck which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrostatic chuck 2 Metal plate 3 Dielectric layer 3a Peripheral wall 3b Adsorption region 4 Internal electrode 5 Protrusion 6 Cooling gas introduction hole 7 DC power supply circuit 8 Conductor part 9 High frequency power supply circuit 10 Counter electrode 13 Upper surface 14 Sample holding surface 15 Recess 16 Groove 19 Upper surface 20 Outer peripheral surface 21 Inner peripheral surface

Claims (3)

  An internal electrode for electrostatic attraction is provided inside, a flat base made of a dielectric, and a large number of protrusions projecting from the adsorption region of the flat base, and a plate-like sample is placed on the many protrusions The upper surface of the protrusion is composed of a smooth region having a center line average roughness of 0.5 μm or less and a rough surface region having a center line average roughness of 0.5 μm or more. A difference between a center line average roughness and a center line average roughness of the rough surface area is 0.2 μm or more.   The electrostatic chuck according to claim 1, wherein the rough surface region is formed at a position surrounded by a smooth region. The electrostatic chuck according to claim 1, wherein an area ratio of a total area of the smooth surface to a total area of the upper surface of the protrusion is in a range of 10 to 90%.

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