JP2012199310A - Fabrication method of semiconductor element - Google Patents

Abstract

A method for manufacturing a semiconductor device capable of easily processing shapes having different etching depths in the same wafer surface.
The openings are formed so that only one of a first state in which etching of the semiconductor surface proceeds and a second state in which a polymer is generated on the semiconductor surface appears in each region having a different opening width. A mask 1900 having openings 1902, 1903, and 1904 having a set width is formed on the surface of the semiconductor 1801, and a peripheral window for controlling the concentration of hydrogen plasma supplied to the mask opening is formed around the mask 1900. A first step of forming a peripheral mask having a second step and a second step of irradiating the semiconductor surface on which the mask is formed with methane plasma and hydrogen plasma are provided.
[Selection] Figure 5

Description

  The present invention relates to a method for manufacturing a semiconductor element, and more particularly to a method for manufacturing a semiconductor element that processes shapes having different etching depths in the same wafer surface.

  In the research and development of high-performance and high-function devices, it is important to integrate the structure of complex devices, and device fabrication process technology such as processing (etching) and crystal regrowth technology is required. In particular, when a plurality of structures are integrated, a plurality of etching processes are usually required.

  An example of the etching process in the case of performing etching at different depths according to the conventional method is shown in FIGS. In the case where the sample (for example, InP crystal) 1110 is etched at a different depth, a portion not etched at the time of the first etching is covered with a mask (dielectric material) 1120 (FIG. 11A) and then etched ( FIG. 11 (b)). Next, after removing the mask for the first etching (FIG. 11C), the portion that is not etched again for the second etching is covered with a mask 1130 (FIG. 11D), and further etched ( The process of removing the mask (FIG. 11 (e)) (FIG. 11 (f)) must be repeated.

  In semiconductor optical device fabrication, when etching with different depths is required, a plurality of mask formation, etching, and mask removal processes are essential, leading to waste in terms of time and cost. . In consideration of such a problem, it has been substantially difficult to form fine and complicated structures having different depths by etching.

  Therefore, in order to solve the above-mentioned problem, when performing etching at different depths, it is possible to perform etching with different depths by performing etching once by using masks having different areas corresponding to the etching depths. Has been invented (see Patent Document 1 below).

  A basic etching process is shown in FIGS. As shown in FIGS. 12A to 12C, in the case of dry etching using a plasma state gas for semiconductor etching, the semiconductor 411 reacts with the etching species (etching gas) 412 on the semiconductor surface in the etching process by the semiconductor. As a result, etching proceeds.

  FIGS. 13A to 13C show the etching process when a mask that does not react with the etching species is used. As shown in FIGS. 13A to 13C, when etching is performed, the surface of the semiconductor is covered with a mask 513 using a substance that does not react with the etching species 512 (for example, a dielectric such as silicon oxide or silicon nitride). In this case, the etching seed 512 on the mask 513 diffuses and reaches the surface of the semiconductor 511 not covered with the mask. As a result, the density of the etching species 512 increases on the surface of the semiconductor 511 near the mask 513. This increase in the etching species 512 increases the etching rate of the semiconductor.

  As described above, the etching species flying on the mask diffuses on the semiconductor surface and promotes the etching of the semiconductor, so that the etching of the semiconductor increases as the mask area increases. Therefore, according to this method, a simple groove structure whose depth changes can be easily manufactured.

  In particular, when a hydrocarbon gas such as methane or ethane is used as the gas in dry etching using a plasma gas for semiconductor etching, the gas is decomposed into hydrocarbon groups and hydrogen in the plasma state, and each ionized. Alternatively, it is chemically activated (radicalized). In the present specification, hereinafter, ionized or chemically activated (radicalized) hydrocarbon groups are referred to as hydrocarbon plasma, and similar hydrogen atoms are referred to as hydrogen plasma.

When the hydrocarbon plasma and the hydrogen plasma come into contact with the semiconductor, a process of etching the semiconductor and a process of forming and depositing a polymer on the semiconductor without etching the semiconductor occur. In general, when there is sufficient hydrogen plasma, the etching process is the main process, and when hydrogen plasma is insufficient, the process of polymer deposition is the main process. At the same time, on the surface of the dielectric (such as SiO ₂ ) mask, hydrocarbon plasma and hydrogen plasma do not react with the dielectric, and thus deposit as a polymer.

  Here, a case where the above-described dry etching is performed on a sample having a mask will be described. FIGS. 14A and 14B show a phenomenon that occurs in a region without a mask when etching using methane plasma is performed. FIGS. 15A, 15B, and 15C show methane plasma. This shows a phenomenon that occurs in a region surrounded by a mask when etching is used.

  In the region without the mask, the hydrogen plasma 622 is uniformly distributed on the surface of the sample (InP) 610 with respect to the methane plasma 621 (FIG. 14A). When the concentration of the uniformly distributed hydrogen plasma is low, hydrogen is insufficient for etching, so that the polymer 631 is generated on the sample surface and the sample surface is covered, so that etching does not proceed (FIG. 14B). This deposition of polymer due to the lack of hydrogen plasma occurs even in a region where the opening width of the mask is wide and the distance from the mask is sufficient.

On the other hand, in the region surrounded by the mask and in particular the region where the opening width of the mask is narrow, the hydrogen plasma 722 is first formed on the surface of the sample (InP) 710 with respect to the methane plasma 721. And uniformly distributed on the surface of the sample 710 in the mask opening 711a of the mask 711 (FIG. 15A). Since the mask material (SiO ₂ ) is not etched on the mask, the polymer 731 is generated without the methane plasma 721 contributing to the etching. The hydrogen plasma 722 on the mask diffuses on the mask without reacting with the methane plasma 721 and aggregates in the mask opening 711a. As a result, the concentration of the hydrogen plasma 722 at the mask opening 711a increases (FIG. 15B). Therefore, the etching proceeds because the concentration of the hydrogen plasma 722 reaches a concentration sufficient to cause etching in the mask opening 711a (FIG. 15C).

  Thus, in the region without the mask or in the region where the opening width of the mask is wide, the polymer is generated and the etching does not proceed, and the etching proceeds in the region where the opening width of the mask is narrow. Therefore, according to this method, shapes having different depths can be processed in one etching process.

  However, when producing a diffraction grating using this method, as shown in FIG. 16, not only the etching species 84 that has come on the mask 82 in the outer part of the diffraction grating but also the etching that has come on the mask 81 in the diffraction grating part. Since the seed 83 also affects the etching, it becomes difficult to control the etching shape of the diffraction grating.

  In order to solve this problem, a method using a mask having a different thickness has been invented (for example, see Patent Document 2 below). This method will be described below with reference to FIGS. 17 (a) and 17 (b). FIG. 17A shows the behavior of the etching species when a mask having a thin mask thickness (film thickness) is used, and FIG. 17B shows the behavior of the etching species when a mask having a thick mask thickness (film thickness) is used. Show.

  As shown in FIG. 17A, when the mask 1011 having a small mask thickness is used, the etching species 1012 can be diffused from the surface of the semiconductor 1010 to the mask 1011 beyond the edge of the mask. The density of the etching seed 1012 does not increase. Therefore, the etching rate of the semiconductor does not increase. On the other hand, as shown in FIG. 17B, when the mask 1021 having a large mask thickness is used, the etching seed 1022 becomes a barrier at the mask end and cannot be passed over the mask edge. The density of the etching species 1022 on the surface of the semiconductor 1020 is increased by being confined in the region. Thus, the thicker the mask, the higher the semiconductor etch rate.

  Alternatively, in the case of using a mask having a thin mask thickness (for example, a mask 1011 as shown in FIG. 17A), since the amount of charge-up of the mask during plasma irradiation is small, the etching species attracted to the mask It is considered that the etching rate of the semiconductor does not increase because there are few (mainly ions). On the other hand, when a mask with a large mask thickness (for example, a mask 1021 as shown in FIG. 17B) is used, the amount of charge up of the mask during plasma irradiation increases, so that the etching is attracted to the mask. It is thought that the seed (mainly ions) increases and the etching rate of the semiconductor increases.

  Therefore, if the thickness of the mask 82 (see FIG. 16) in the outer portion of the diffraction grating is made larger than the thickness of the mask 81 (see FIG. 16) in the diffraction grating portion, the outside of the diffraction grating having a larger mask thickness is changed to the opening. The contribution of the etching species diffusing in the opening width direction (Y direction) is large, and the contribution of the etching species diffusing in the diffraction grating direction (X direction) from the diffraction grating portion having a thin mask thickness to the opening can be reduced. Therefore, in a region having a wide thick mask width (mask width of a mask having a large mask thickness), a large amount of etching species that do not react on the mask diffuse into the opening, so that the etching species at the opening becomes high in concentration and the etching rate. Will increase. On the other hand, in the region where the thickness of the thick mask is narrow, the etching species which does not react on the mask and diffuses into the opening is smaller than that in the region where the mask is wide, and the etching rate is slow. Therefore, the etching depth is deep in the region where the mask width is wide and shallow in the region where the mask width is narrow.

  Alternatively, when the thickness of the thick mask is constant, an etching species that diffuses from the thick mask (thick mask) opens in a narrow region of the thick mask opening width (opening width of the mask with thick mask). Since it spreads over the entire area, the etching rate increases. On the other hand, in the region where the thick layer mask opening width is wide, the etching species diffusing from the thick layer mask does not reach the entire opening portion, so that the etching rate is reduced.

  When the above-mentioned hydrocarbon plasma and hydrogen plasma are used as the etching gas, if the hydrocarbon plasma is at a high concentration, etching occurs in the opening due to diffusion of the hydrogen plasma from the thick mask to the opening, or a polymer is generated. Or is decided. Therefore, when the thickness of the thick mask is constant, etching proceeds because the hydrogen plasma diffused from the thick mask spreads over the entire opening in a region where the opening of the thick mask is narrow. On the other hand, in the region where the thick layer mask opening width is wide, the hydrogen plasma diffused from the thick mask does not spread sufficiently over the entire opening portion, so that polymer is generated and etching does not proceed.

JP 2004-247710 A JP 2006-32573 A

Kumagai, et al., “Physics and Applications of Vacuum”, Hanafusa, 1970, p.33, 44, 89 N. Asahi and Y. Nakamura, "Nuclear magnetic resonance and molecular dynamics study of methanol up to the supercritical region", JOURNAL OF CHEMICAL PHYSICS, Vol.109, No.22, 8 DECEMBER 1998, p.9879-9887 A. S. Grove, "Physics and Technology of Semiconductor Devices", John Wiley and Sons, Inc., New York, London, Sydney, 1967, p.46

  The depth shape processed by the selective etching described above has the same plasma conditions (gas flow rate, pressure, power, etc.) within the same wafer surface, so if the mask shape is the same for each element, the depth shape is within the wafer surface. Is the same for each element. In order to perform processing at different depths for each element (for each mask) in the wafer surface, a different opening width must be set for each mask. Here, the opening width needs to be determined in consideration of the diffusion distance of hydrogen plasma from the mask to the opening.

  However, since the diffusion distance of hydrogen plasma is affected by slight fluctuations in the plasma conditions, it is not easy to change the depth to be processed in the same wafer plane by the opening width. In addition, since the shape to be processed is deviated from the design value due to slight fluctuations in the plasma conditions, there is a problem that the manufacturing margin is reduced.

  From the above, the present invention has been made to solve the above-described problems, and can easily and accurately process shapes having different etching depths for each element in the same wafer surface. An object of the present invention is to provide a method for manufacturing a semiconductor element that can be manufactured.

  In a method for manufacturing a semiconductor device according to the present invention for solving the above-described problems, a semiconductor surface on which a mask having an opening having a variable opening width is irradiated with hydrocarbon-based plasma and hydrogen plasma. A method of manufacturing a semiconductor element that etches to a plurality of different depths, wherein a polymer is generated on the semiconductor surface in a first state where etching of the semiconductor surface proceeds for each region having a different opening width. A mask having an opening with the opening width set so that only one of the second states appears is formed on the semiconductor surface, and is supplied to the opening of the mask around the mask. A first step of forming a peripheral mask having a window region for controlling a hydrogen plasma concentration, and the mask contains the hydrocarbon-based plasma and the hydrogen plasma. A second step of irradiating the formed semiconductor surface, wherein the mask is formed on the first mask portion and a first mask portion having a first pattern formed on the semiconductor surface; And a second mask portion having a second pattern that is thicker than a mask thickness of the first mask portion and defines an opening width of the first pattern.

  A method for manufacturing a semiconductor device according to the present invention that solves the above-described problem is the above-described method for manufacturing a semiconductor device, wherein the polymer deposited on the semiconductor surface in the first step is irradiated with plasma containing oxygen. It has the 3rd process to remove, It is characterized by the above-mentioned.

  In addition, a method for manufacturing a semiconductor element according to the present invention that solves the above-described problem is the above-described method for manufacturing a semiconductor element, wherein the method is expressed in at least one of the regions having different opening widths in the second step. A fourth step of changing a plasma condition so as to change the state to be either the first state or the second state, and after the fourth step, the second step The process is further performed.

  According to the method for manufacturing a semiconductor element according to the present invention, it is possible to easily and accurately process shapes having different etching depths for each element in the same wafer surface. Thereby, a high-speed semiconductor optical device can be provided.

It is a figure which shows the mask used in order to produce the diffraction grating from which the layer thickness changes within the same surface produced by the manufacturing method of the semiconductor element which concerns on the 1st Example of this invention. The concentration of hydrogen plasma supplied to the opening of a mask used to produce a diffraction grating having a layer thickness varying within the same wafer surface produced by the method for producing a semiconductor device according to the first embodiment of the present invention It is explanatory drawing of the surrounding window for control, Comprising: A state without a surrounding window is shown in FIG. 2A, an example of a state in which a surrounding window is arranged is shown in FIG. 2B, and FIG. Other examples are shown. It is a figure which shows an example of the arrangement | positioning method of a surrounding window. (A) to (d) are thicknesses in the plane used to fabricate a diffraction grating whose layer thickness varies in the same plane manufactured by the method for manufacturing a semiconductor device according to the first embodiment of the present invention. It is a figure which shows the preparation process of the mask from which a height differs. (A)-(e) is a figure which shows the manufacturing process of the diffraction grating from which the layer thickness changes within the same wafer surface produced by the manufacturing method of the semiconductor element which concerns on the 1st Example of this invention. It is explanatory drawing of the diffraction grating produced by the production method of the semiconductor element concerning the 1st example of the present invention, and shows the case where only the mask shown in Drawing 2 (a) is used for Drawing 6 (a), FIG. 6B shows a case where the mask and the peripheral window shown in FIG. 2B are used, and FIG. 6C shows a case where the mask and the peripheral window shown in FIG. 2C are used. It is a figure which shows the structure of the DBR semiconductor laser using the diffraction grating produced by the manufacturing method of the semiconductor element based on the 1st Example of this invention. (A) is a figure which shows the relationship between the distance from the end of the diffraction grating in the diffraction grating which concerns on 1st Example of this invention, and coupling coefficient (kappa), (b) is 1st Example of this invention. It is a figure which shows the reflection spectrum at the time of using the diffraction grating with the case where such a diffraction grating is used, and a coupling coefficient of 80 nm ^-1 constant. (A) is a figure which shows the relationship between the distance from the end of the diffraction grating of each element produced using the mask pattern shown to Fig.2 (a)-(c), and coupling coefficient (kappa), and a coupling coefficient and reflection It is a figure which shows the relationship of a characteristic, (b) is a figure which shows the reflective characteristic of each element. It is a figure which shows the other example of the mask used with the manufacturing method of the semiconductor element which concerns on this invention. (A)-(f) is a figure which shows the etching process in the case of performing the etching of different depth by the conventional method. (A)-(c) is a figure which shows a basic etching process. (A)-(c) is a figure which shows the etching process at the time of using the mask which does not react with an etching seed | species. (A), (b) is a figure which shows the phenomenon which arises in the area | region without a mask, when etching using methane plasma is given. (A)-(c) is a figure which shows the phenomenon which arises in the area | region enclosed by the mask, when etching using methane plasma is given. It is a figure which shows the behavior of the etching seed | species on a mask. (A) is a figure which shows the behavior of the etching seed | species when a mask with a thin mask thickness (film thickness) is used, (b) shows the behavior of the etching seed | species when a mask with a thick mask thickness (film thickness) is used. FIG.

  Embodiments for carrying out a method for manufacturing a semiconductor element according to the present invention will be specifically described in Examples.

A method for fabricating a semiconductor device according to the first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a view showing a mask used for manufacturing a diffraction grating having a layer thickness varying in the same plane manufactured by the method for manufacturing a semiconductor device according to the first embodiment of the present invention. is a diagram illustrating a SiN _x / SiO ₂ mask is formed on the sample surface in the examples.

First, as shown in FIG. 1, a mask 1900 in which the lattice width (mask opening width) 1905 of the mask opening changes is formed on the surface of the sample (InP) 1801. In the mask 1900, the thickness (mask thickness) of a diffraction grating portion mask (lattice mask) 1910 formed of SiO ₂ is 20 nm, the diffraction grating length 1907 is 500 μm, and the grating width 1905 is changed. It is 1.8 μm, 3.7 μm, and 7.5 μm from the portion toward both ends of the element. The pitch (period) 1911 is 240 nm (SiO ₂ part: 120 nm, window part: 120 nm). On the other hand, the mask (opening width adjustment mask) 1920 outside the diffraction grating formed of SiN _x has a constant thickness (mask thickness) of 1 μm and a mask width 1906 of 20 μm. In the above, the lattice mask 1910 forms the first mask portion, and the opening width adjustment mask 1920 forms the second mask portion.

  On the wafer surface, a peripheral window (opening) forming a window is arranged in a predetermined area around the mask 1900 described above. Specifically, as shown in FIGS. 2B and 2C, a peripheral mask 1701 is formed around the mask 1900 on the surface of the sample (InP) 1801, and ( A plurality of peripheral windows (openings) 1930 that form windows are arranged in a region of width 1908 of 100 μm (along the outline of the mask 1900). Each peripheral window 1930 is a square having a side of 20 μm. In FIG. 2B, the distance d2 between adjacent peripheral windows 1930 is 40 μm. In FIG. 2C, the distance d1 between adjacent peripheral windows 1930 is 5 μm. For reference, FIG. 2A shows a case where a peripheral mask 1701 is formed around the above-described mask 1900 and the above-described peripheral window 1930 is not provided on the surface of the wafer.

  When the surface of the sample (wafer) 1801 provided with the peripheral window 1930 is irradiated with hydrocarbon-based plasma and hydrogen plasma as shown in FIGS. 2B and 2C, the hydrocarbon-based plasma is mutually exchanged on the mask. The polymer is reacted to form a polymer, but the hydrogen plasma flying on the peripheral window 1930 reacts with the hydrocarbon plasma on the surface of the sample (InP) 1801 to etch the sample (InP) 1801, so that it is consumed by the etching. Hydrogen plasma decreases around the mask 1900. On the other hand, as shown in FIG. 2A, when the surface of the sample 1801 without the peripheral window 1930 is irradiated with hydrocarbon-based plasma and hydrogen plasma, the hydrogen plasma that has come to the periphery does not react and is not consumed. There are more hydrogen plasmas in the vicinity of FIG. 2 (b) and FIG. 2 (c). Comparing the case where the peripheral window 1930 shown in FIG. 2B is arranged and the case where the peripheral window 1930 shown in FIG. 2C is arranged, the density of FIG. 2C is higher than that of FIG. Since the peripheral window 1930 is arranged, the hydrogen plasma existing around the mask 1900 is small. Furthermore, if the peripheral mask 1701 formed around the mask 1900 on the surface of the sample (InP) 1801 is completely removed (not shown), it exists in the periphery of the mask 1900 compared to the case of FIG. Less hydrogen plasma to be generated. As described above, by arranging the peripheral window 1930, the amount (concentration) of hydrogen plasma existing around the mask 1900 can be controlled.

  Therefore, the amount (concentration) of hydrogen plasma contributing to selective etching can be easily changed by changing the arrangement of the peripheral window 1930 for each element (for each mask). Therefore, it is possible to process into different depth shapes for each element (for each mask) in the same wafer surface.

  In this embodiment, hydrogen plasma, hydrocarbon-based plasma, and InP react in the peripheral window 1930. Since the area of the peripheral window is larger than the area of the diffraction grating portion, the hydrogen plasma density does not increase. Since the etching amount is small, the device characteristics are not affected. Alternatively, when the hydrocarbon-based plasma has a sufficiently high concentration, the polymer generation rate exceeds the etching rate, so that the polymer is generated in the peripheral window and the etching does not proceed.

  FIG. 3 shows another example of the method of arranging the peripheral windows. As shown in FIG. 3, a plurality of peripheral windows 1930 can be arranged in the diffraction grating direction (X direction) only at a position adjacent to the mask 1900 in the opening width direction (Y direction) around the mask 1900. If a plurality of peripheral windows 1930 are arranged only at such positions, the effect on the etching depth change by the peripheral windows 1930 is reduced, but etching is performed in the diffraction grating direction around the diffraction grating (the optical waveguide direction in the device operation). Since there is no peripheral window, there is no influence on the element characteristics.

4A to 4D show a process for manufacturing masks having different thicknesses in a plane used for forming a diffraction grating in this embodiment.
First, a 30 nm thick silicon oxide (SiO ₂ ) film is formed on the surface of the InP clad layer 1310 on the InP substrate. After applying a resist on the SiO ₂ film, a resist pattern for forming a diffraction grating mask and a peripheral window is prepared by an electron beam exposure method. By processing the SiO ₂ film by reactive ion etching (RIE) using a fluorocarbon system (CF ₄ , C ₂ F _8, etc.) using the resist pattern as a mask, the resist pattern is converted into an SiO ₂ film. Transcript. By removing the resist pattern, a SiO ₂ mask 1311 for forming a diffraction grating part in which the diffraction grating part 1311a is formed on InP is formed.

Next, the peripheral window pattern shown in FIGS. 2B and 2C is obtained by a normal photoresist process and reactive ion etching (RIE) using a fluorocarbon system ((CF ₄ , C ₂ F _8, etc.)). 1311b is formed (see FIG. 4A), or a pattern having no peripheral window (FIG. 2A) is formed.

Next, a 1 μm-thick silicon nitride (SiN _x ) film 1321 is formed on the InP surface having the above-described diffraction grating portion SiO ₂ mask (see FIG. 4B). After applying a resist on the SiN _x film, a resist pattern 1331 for a mask outside the diffraction grating is produced (see FIG. 4C). This resist pattern can be formed not only by electron beam exposure but also by normal photolithography resist exposure. The resist pattern is transferred to the SiN _x film 1341 by processing the SiN _x film by RIE using a sulfur fluoride-based gas (SF ₆ or the like) using the resist pattern 1331 as a mask. At this time, the SiO ₂ mask in the diffraction grating portion remains resistant to the sulfur fluoride gas (SF ₆ or the like) and is therefore not etched. As a result, by removing the resist pattern 1331, masks having different thicknesses are formed on the InP on the diffraction grating portion (grating-like portion) and outside the diffraction grating (opening width adjustment portion) (FIG. 4D). reference). In the above description, the SiO ₂ mask 1311 forms the first mask portion, and the SiN _x film 1341 forms the second mask portion.

FIGS. 5A to 5E are diagrams showing a manufacturing process of a diffraction grating manufactured by the method for manufacturing a semiconductor device according to this example, and a process of etching the diffraction grating in the SiO ₂ / SiN _x mask portion. It is a figure which shows a part of diffraction grating for demonstrating these.
As shown in FIG. 5A, the above-described mask 1900 is formed on the surface of the sample (InP) 1801. Here, although not shown in the drawing, a peripheral window 1930 as shown in FIG. 2B, FIG. 2C, or FIG. 3 is arranged for each element (for each mask) around the mask 1900. . The mask 1900 has a mask (grating mask) 1910 (see FIG. 1) of a diffraction grating portion in which a mask thickness (film thickness) is thin and a plurality of mask openings are formed in a lattice shape, and on the mask of the diffraction grating portion. A mask (opening adjustment mask) 1920 outside the diffraction grating that defines the opening width of the mask opening of the mask of the diffraction grating portion, and has a mask thickness (film thickness) thicker than that of the mask of the diffraction grating portion. 1). Here, the mask 1900 has a mask opening. The mask opening includes a first opening 1902, a second opening 1903 wider than this, and a third opening 1904 wider than this. The opening width of the first opening 1902 is 1.8 μm, the opening width of the second opening 1903 is 3.7 μm, and the opening width of the third opening 1904 is 7.5 μm. In a series of etching processes described below, the contribution of methane / hydrogen plasma from the outside of the diffraction grating having a large mask thickness is large, and the contribution of methane / hydrogen plasma from the diffraction grating portion having a thin mask thickness is small.

  When this sample is first subjected to RIE using a mixed gas of methane and hydrogen on the mask 1900 at a methane flow rate of 40 sccm, a hydrogen flow rate of 2 sccm, a discharge power of 100 W, and a gas pressure of 40 Pa, it is shown in FIG. As described above, in the first opening 1902 having an opening width of 1.8 μm, since hydrogen is sufficiently supplied from above the mask 1900, etching proceeds without polymer deposition. On the other hand, in the second opening 1903 (opening width: 3.7 μm) and the third opening 3904 (opening width: 7.5 μm) whose opening width is wider than 1.8 μm, the distance from the top of the mask 1900 is increased. Since the supply of hydrogen is insufficient, the polymer 1811 is deposited and the etching does not proceed. Subsequently, when the oxygen plasma is irradiated at an oxygen flow rate of 10 sccm, a gas pressure of 10 Pa, and a discharge power of 400 W for 1 minute, the deposited polymer is removed as shown in FIG.

  Next, when RIE is performed under the conditions in which the hydrogen flow rate is increased (methane flow rate: 40 sccm, hydrogen flow rate: 5 sccm, gas pressure: 10 Pa, discharge power: 100 W), as shown in FIG. In the first opening 1902 and the second opening 1903 having a thickness of 3.7 μm or less, since the supply of hydrogen increases, the etching proceeds without polymer deposition. On the other hand, in the third opening 1904 having an opening width of 7.5 μm, since the supply of hydrogen from the mask 1900 is insufficient, the polymer 1812 is deposited and the etching does not proceed. Therefore, in the first opening 1902 having an opening width of 1.8 μm, the second RIE etching further proceeds after the first RIE etching, so that the depth is larger than the depth of the second opening 1903. Also deepen.

  Subsequently, after removing the polymer by oxygen plasma irradiation, by alternately repeating RIE and oxygen plasma irradiation under the condition of changing the hydrogen flow rate, as shown in FIG. 5E, diffraction gratings having different depths are obtained. Can be formed. Thereafter, the mask is removed, mesa structure processing is performed, and then, the diffraction grating portion of the element structure as shown in FIG. 7 is formed by stacking on this diffraction grating by metal organic vapor phase epitaxy (MOVPE). Is produced.

  In the above-described etching process, the peripheral window shown in FIG. 2A is not arranged, and the etching depth in the element provided with the peripheral mask 1701 is the deepest, and then the peripheral window 1930 shown in FIG. 2B is formed. The etching depth in the device provided with the peripheral mask 1701 is deep, and the etching depth in the device provided with the peripheral mask 1701 provided with the peripheral window 1930 shown in FIG. Thus, by providing the peripheral mask 1701, it is possible to process into different etching depth shapes for each element in the same wafer surface. In the above-described mask 1900, the opening width of the mask opening is set to five types, the opening width is narrowed from the center in the direction of the diffraction grating, and FIGS. 2A and 2B are arranged around the mask having such a shape. When the peripheral masks 1701 as shown in FIGS. 6A and 7C are arranged, diffraction gratings 1820, 1822, and 1821 as shown in FIGS. 6A, 6B, and 6C are obtained, respectively. Thereafter, after removing the mask and processing the mesa structure, an element structure is fabricated by stacking on this diffraction grating by metal organic vapor phase epitaxy (MOVPE).

FIG. 7 shows the structure of a DBR semiconductor laser using the diffraction grating according to the first embodiment of the present invention. After removing the SiO ₂ mask on the sample surface having the diffraction gratings having different depths manufactured by the method for manufacturing the semiconductor element according to this example, the layers are stacked on the diffraction gratings by metal organic chemical vapor deposition (MOVPE). As a result, the DBR semiconductor laser structure using the diffraction grating whose depth changes as shown in FIG. 7 is manufactured.

  As shown in FIG. 7, the DBR semiconductor laser using the diffraction grating according to the present embodiment has an n-type InP substrate 150, an n-type InP buffer layer 151, a diffraction grating 152, and an InGaAsP (composition wavelength: 1.1 μm) guide layer. An active layer (light emission wavelength: 1.55 μm) composed of 153 and 8 InGaAsP strain quantum well (strain amount: 1.0%) layers and five InGaAsP (composition wavelength: 1.3 μm) barrier layers. , Active layer length: 400 μm) 154, DBR diffraction grating region InGaAsP (composition wavelength: 1.4 μm) guide layer (diffraction grating length is 400 μm before and after the active layer, respectively) 155, InGaAsP (composition wavelength: 1.3 μm) guide layer 156 , P-type InP cladding layer 157, p-type InGaAs (composition wavelength: 1.85 μm) contact layer 158, n-type ohmic electrode 1591, p-type An ohmic electrode 1592 is provided.

  The oscillation wavelength of the element is 1.55 μm. The length of the element is 1500 μm. The pitch (period) of the diffraction grating 152 is 240 nm (convex part: 120 nm, concave part: 120 nm), and the depth is shallow at both end faces of the element, 30 nm, and deep at the central part of the element, and 65 nm.

FIGS. 8A and 8B show reflection characteristics obtained by the diffraction grating in the DBR semiconductor laser shown in FIG. FIG. 8A shows the relationship between the distance from one end of the diffraction grating and the coupling coefficient κ. By changing the depth of the diffraction grating to be 30 nm at both ends of the element and 65 nm at the center, the coupling coefficient κ is 50 cm ⁻¹ at both ends of the element and at the center as shown in FIG. It changes to 100 cm- ¹ .

A reflection spectrum when this diffraction grating is used is shown in L2 of FIG. For comparison, L3 in FIG. 8B shows a reflection spectrum when the coupling coefficient is constant at 100 nm ⁻¹ . It can be seen that the side mode of the reflection spectrum is suppressed by changing the depth of the diffraction grating, that is, the coupling coefficient. This suggests that side modes in the oscillation spectrum when a DBR semiconductor laser using this diffraction grating is operated are suppressed.

  Thus, according to the method for manufacturing a semiconductor element according to this example, it is possible to easily manufacture a diffraction grating whose depth (coupling coefficient) changes.

FIG. 9A shows the coupling coefficients and reflection characteristics obtained by the diffraction gratings a, b, and c in each element manufactured using the peripheral masks shown in FIGS. 2A, 2B, and 2C. The curves are indicated by curves a, b and c, respectively. When the peripheral mask 1701 shown in FIG. 2A is used, by changing the depth of the diffraction grating to 45 nm at both ends of the element and 90 nm at the center, as shown in FIG. the coupling coefficient κ is 70cm ^-1 at element end portions, changes 150 cm ^-1 in the central portion. When the peripheral mask 1701 shown in FIG. 2B is used, by changing the depth of the diffraction grating to be 30 nm at both ends of the element and 65 nm at the center, as shown in FIG. 40 cm ^-1 in the coupling coefficient κ is the element end portions, changes 100 cm ^-1 in the central portion. When the peripheral mask 1701 shown in FIG. 2C is used, the depth of the diffraction grating is changed so as to be 20 nm at both ends of the element and 35 nm at the center, so that as shown in FIG. the coupling coefficient κ is 30 cm ^-1 in the element end portions, changes 50 cm ^-1 at the central portion.

  FIG. 9B shows the reflection spectra of the diffraction gratings a, b, and c used in FIG. As shown in FIG. 9B, the diffraction grating a (curve a) has a high reflectance (reflectance: 1) and a wide stop band. The diffraction grating b (curve b) has a high reflectance (reflectance: 1), but the stop band is narrower than that of the diffraction grating a. In the diffraction grating c (curve c), the reflectance is lowered and the stop band becomes narrower than that of the diffraction gratings a and b. This suggests that according to the method for manufacturing a semiconductor device according to this example, a DBR semiconductor laser having a variable wavelength range in the oscillation spectrum for each device can be manufactured by a single process.

  In addition, the above result suggests that a manufacturing margin is increased by arranging a plurality of patterns of masks. In the etching method according to the present invention, “etched or polymer is produced” is sensitive to the amount of hydrogen supplied, so if the conditions such as the amount of hydrogen supplied become unstable, the yield and reproducibility deteriorate. It becomes a problem. For example, when the peripheral window is not arranged regardless of the present invention (in the case of the pattern a), even if the etching is performed so as to be processed into the originally designed shape, the etching condition is deviated (changed). Cannot be obtained. On the other hand, if a plurality of peripheral windows are arranged as described above, for example, when the conditions deviate in the direction in which the hydrogen supply amount decreases, the hydrogen supply amount is compensated for in the pattern a or b, so that the designed diffraction grating can get.

  Further, if the shape designed using the peripheral mask of the pattern b is processed, if the etching condition is deviated, for example, if the condition is deviated in the direction of decreasing the hydrogen supply amount, the hydrogen supply amount is compensated in the pattern a. Therefore, a designed diffraction grating can be obtained. On the other hand, when the conditions are shifted in the direction of increasing the hydrogen supply amount, the designed diffraction grating is obtained because the hydrogen supply amount is decreased in the pattern c. Thus, according to the present invention, the manufacturing margin can be improved by arranging the peripheral windows of a plurality of patterns.

  In this embodiment, three types of peripheral window patterns are arranged around the mask. However, if more types of patterns of masks are arranged, more different variable wavelength ranges can be obtained and the manufacturing margin is increased.

  In this embodiment, a square is used for the peripheral window, but other shapes may be used, and other sizes and intervals may be used.

  In this embodiment, hydrogen (plasma) that did not contribute to the reaction on the mask flows into both ends of the opening of the diffraction grating. Etching proceeds with the reaction of methane by this amount of hydrogen plasma. Therefore, even in the opening where the polymer is deposited, the etching proceeds only at a part of both ends. Thus, there may be a problem that the depth is not uniform over the entire opening. However, since a mesa structure is adopted in an actual device, both ends of the opening are cut off when the mesa is formed, and this does not cause a problem in actual device fabrication.

  In this embodiment, the mask width outside the opening in the mask is constant, but the mask width is constant as long as the distance that the hydrogen plasma diffusing into the opening diffuses on the mask is negligible. Need not be. For example, a mask 2900 having a shape as shown in FIG. 10 may be used. In the mask 2900, the opening width 2905 of the mask opening 2901 changes with respect to the waveguide length 2907, the first opening 2902, the second opening 2903 wider than the opening 2902, and the opening And a third opening 2904 wider than 2903. The mask width 2906 outside the mask opening in the mask 2900 changes with respect to the waveguide length 2907.

  In this embodiment, the compound semiconductor InP crystal is used as the element semiconductor crystal. However, it is also possible to use a compound semiconductor crystal such as GaAs or SiGe or a mixed crystal such as InGaAsP, AlGaInAs, InGaN, GaInNAs, or AlGaSb. . Further, although 1.55 μm is used as the wavelength of the laser beam to which the apparatus according to the present invention is applicable, the wavelength is changed from 1.0 μm to 1.7 μm by changing the structure such as the composition of the InGaAsP crystal and the pitch (period) of the diffraction grating. Up to a long wavelength band up to 1, and by using other materials (InGaAlN, AlGaInP, AlGaSb, etc.) for the active layer, it also supports a short wavelength band of less than 1.0 μm and a long wavelength band of 1.7 μm or more. it can. The multi-quantum well structure in the active layer includes an 8 layer, 5 nm thick InGaAsP strained quantum well layer (strain amount: 1.0%), a 5 layer, 10 nm thick InGaAsP barrier layer (composition wavelength: 1.1 μm). However, structural factors such as the amount of strain, the number of layers, the layer thickness, and the crystal composition may be changed.

  In this embodiment, methane is used as an etching gas in dry etching for processing a semiconductor such as a diffraction grating, but other hydrocarbon gases such as ethane may be used. In addition, as a dilution gas when using a mixed gas as an etching gas, hydrogen, nitrogen, or argon may be used together with oxygen gas as well as oxygen gas.

  Further, although oxygen plasma is irradiated to remove the polymer, plasma containing oxygen may be used. For example, a mixed gas of oxygen and an inert gas such as nitrogen or argon, a mixed gas of oxygen and hydrogen, or the like may be used.

Further, although RIBE and RIE methods are used for the dry etching method, processing can also be performed using ion beam assist etching or the like. In addition to the electron beam exposure method, an interference exposure method can be used for producing the resist pattern. Although silicon oxide (SiO ₂ ) is used as a mask formed on the semiconductor surface during etching, a dielectric such as silicon nitride or titanium oxide, or a metal such as gold or titanium can also be used.

  The method for manufacturing a semiconductor device according to the present invention can easily process shapes having different etching depths within the same wafer surface while suppressing surface irregularities, thereby providing a high-speed semiconductor optical device. Therefore, it can be used extremely beneficially in various industries including the communication industry.

81, 82 Mask 83, 84 Etching species 150 n-type InP substrate 151 n-type InP buffer layer 152 Diffraction grating 153 InGaAsP (composition wavelength: 1.1 μm) guide layer 154 Active layer (emission wavelength: 1.55 μm, active layer length: 400μm)
155 DBR diffraction grating region InGaAsP (composition wavelength: 1.4 μm) guide layer 156 InGaAsP (composition wavelength: 1.3 μm) guide layer 157 p-type InP cladding layer 158 p-type InGaAs (composition wavelength: 1.85 μm) contact layer 411 Semiconductor 412 Etching species 511 Semiconductor 512 Etching species 513 Mask 710 InP
711 Mask 721 Methane plasma 722 Hydrogen plasma 731 Polymer 610 InP
621 Methane plasma 622 Hydrogen plasma 631 Polymer 1010, 1020 Semiconductor 1011, 1021 Mask 1012, 1022 Etching species 1110 Semiconductor 1120, 1130 Mask 1310 InP substrate 1311 InP clad layer 1321, 1341 Silicon nitride (SiN _x ) film 1331 Resist pattern 1591 n-type Ohmic electrode 1592 p-type ohmic electrode 1701 Peripheral mask 1801 Sample (InP)
1811, 1812 Polymer 1820, 1821, 1822 Diffraction grating 1900 Mask 1902 First opening 1903 Second opening 1904 Third opening 1905 Lattice width of mask opening (mask opening width)
1906 Mask width 1907 Diffraction grating length 1908 Region 1910 Diffraction grating mask (grating mask)
1920 Mask outside diffraction grating (opening width adjustment mask)
1930 Perimeter window (opening)

Claims (3)

A method for manufacturing a semiconductor device, comprising irradiating a hydrocarbon surface and a hydrogen plasma on a semiconductor surface on which a mask having an opening having a variable opening width is formed, and etching the semiconductor surface to a plurality of different depths,
In each of the regions having different opening widths, the opening is formed so that only one of the first state in which etching of the semiconductor surface proceeds and the second state in which a polymer is generated on the semiconductor surface appears. A mask having an opening having a set width is formed on the semiconductor surface, and a peripheral mask having a window region for controlling the concentration of hydrogen plasma supplied to the opening of the mask is formed around the mask. A first step;
A second step of irradiating the surface of the semiconductor on which the mask is formed with the hydrocarbon-based plasma and the hydrogen plasma;
A first mask portion having a first pattern formed on the semiconductor surface; and a first mask portion formed on the first mask portion, the mask being thicker than a mask thickness of the first mask portion, A method of manufacturing a semiconductor element, comprising: a second mask portion having a second pattern that defines an opening width of one pattern. The method of manufacturing a semiconductor device according to claim 1, further comprising a third step of removing the polymer deposited on the semiconductor surface in the first step by plasma irradiation having oxygen. Manufacturing method. 3. The method for manufacturing a semiconductor device according to claim 2, wherein in the second step, the states that are manifested in at least one of the regions having different opening widths are the first state and the second state. The method further includes a fourth step of changing the plasma condition so as to change to any of the following:
The method for manufacturing a semiconductor element, wherein the second step is further performed after the fourth step.

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