JP2005251914A - Method for processing semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a deposit from adhering to the rear face of a substrate by a simple method, when a chemical semiconductor thin film is grown by an MOCVD method, and to prevent the occurrence of crosshatches. <P>SOLUTION: When the chemical semiconductor thin film is grown on the surface of the chemical semiconductor substrate by the MOCVD method, a compound having Si and O is coated on the rear face of the chemical semiconductor substrate prior to the growth. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for processing a semiconductor substrate before growth when a compound semiconductor thin film is grown on a compound semiconductor substrate by chemical vapor deposition (MOCVD) using an organic metal.

  Compound semiconductor devices such as GaAs and InP are used in mobile communication devices such as mobile phones by utilizing their high driving speeds, and in optical communication devices and display devices by utilizing light emission characteristics having a wide wavelength range. in use. These compound semiconductor elements are formed by epitaxially growing a compound semiconductor thin film on a compound single crystal substrate (hereinafter simply referred to as “substrate”). As a method for forming a thin film, a chemical vapor deposition method (MOCVD method) using an organic metal is widely used. Normally, an epitaxial layer is grown only on one surface (front surface) of the substrate and no epitaxial layer is grown on the back surface. However, the organic metal that is the raw material of the thin film is contained in the gap between the substrate and the components that support the substrate. The gas is also supplied to the back of the substrate, and the raw material decomposed by thermal decomposition accumulates and adheres. Therefore, the state of the back surface of the substrate changes, the heat absorption of the substrate becomes non-uniform, and the temperature distribution of the substrate becomes non-uniform. In particular, in the growth of mixed crystals represented by the growth of an AlGaInP layer on a GaAs substrate or an InGaAsP layer on an InP substrate, the raw material composition range in which the interstitial distance between the substrate and the epitaxial layer matches is narrow. For this reason, there is a problem that due to non-uniform temperature distribution of the substrate, a defect called cross-hatch occurs in the outer peripheral portion of the substrate, which deviates from the raw material composition range in which the interstitial distance between the substrate and the epitaxial layer matches. Since the characteristics of the semiconductor element formed in the region where the cross hatching occurs are deteriorated, the yield of the semiconductor element manufacturing process is lowered. For this reason, conventionally, as disclosed in Japanese Patent No. 3127616 and Japanese Patent Laid-Open No. 2003-22975, measures for controlling the growth rate of the epitaxial layer and the temperature increase rate of the substrate are known.

Japanese Patent No. 3127616 JP 2003-22975 A

Further, cross-hatch for prevention of, by introducing small amounts of H ₂ gas containing H ₂ or the group V is a carrier gas to the back side of the substrate, penetration of the raw material gas containing an organic metal on the substrate surface side The method to prevent is adopted. In addition, a method is employed in which the source gas is prevented from entering the back surface of the substrate by bringing the back surface into close contact with the substrate support ring and eliminating the space on the back surface of the substrate. In addition, a method is employed in which a gap between the substrate support ring and the peripheral edge of the substrate is eliminated, and a raw material gas containing an organic metal is prevented from entering the back surface of the substrate. Further, a method is employed in which a film made of several tens of nm to several μm of SiN or SiO ₂ is grown on the back surface of the substrate by a sputtering method, an EB vapor deposition method, a P-CVD method, or a sol-gel method.

However, when H ₂ or the like, which is a carrier gas, is introduced on the back side of the substrate, the gas also flows into the front side of the substrate, the source gas composition changes, the growth rate of the epitaxial film decreases, The uniformity of the film thickness is deteriorated. In order to avoid this problem, there is a method in which the gas supplied to the back side is exhausted at the outer periphery of the substrate so that it does not flow into the surface. However, in a general mass production MOCVD apparatus, the epitaxial film is uniform in the plane. Since the substrate is rotated and revolved for the purpose of improving the performance and uniformity in the batch, it is difficult to provide such an exhaust line because it is necessary to incorporate a pipe in the substrate rotation mechanism itself. In addition, it is necessary to provide a mechanism for controlling the flow rate of the gas introduced to the back side for each set substrate. For this reason, the structure of the apparatus becomes very complicated, and not only the price of the apparatus increases, but also the running cost increases because the maintainability of the apparatus is poor.

  In addition, in order to bring the back surface of the substrate into close contact with the flat plate, it is necessary to increase the dimensional accuracy of both. Usually, a 2-inch substrate has a warp of 5 μm or more even at room temperature, and the dimensional accuracy of a carbon component generally used as a material for a substrate support ring is about 10 μm. Further, since the substrate is further warped during heating, the gap with the substrate support ring is further widened, so that it is difficult to maintain the state where the back surface of the substrate is in close contact with the substrate support ring. In addition, the surface temperature of the substrate is different between the portion where the substrate and the substrate support ring are in contact with each other, and the characteristics of the epitaxial layer become non-uniform.

  Similarly, when eliminating the gap between the substrate support ring and the substrate, the dimensional accuracy must be increased, and it is difficult to support the substrate without any gap. Similarly to the above, a gap is generated by the warping of the substrate during heating, and the source gas enters the back side from there.

  Furthermore, the method of protecting the back surface of the substrate with a film such as SiN can suppress the adhesion of deposits, but due to the difference in thermal expansion coefficient between the protective film and the substrate, the substrate is warped significantly during epitaxial growth, and the lattice constant of the substrate is reduced. It changes and inhibits the growth of an epitaxial film having a desired composition. Also, slippage occurs on the substrate surface due to thermal distortion that occurs when the substrate is heated or cooled. In addition, the protective film formed on the back surface of the substrate needs to be as thin as possible, preferably 10 nm or less. However, in order to uniformly form a thin film of 10 nm or less on the back surface of the substrate, it is very advanced. Film forming technology is required, and the film forming apparatus has a complicated structure, which is as expensive as or higher than MOCVD for mass production.

  Accordingly, an object of the present invention is to prevent deposits from adhering to the back surface of a substrate and to prevent occurrence of cross hatching by a simple method when growing a compound semiconductor thin film by MOCVD.

  In order to achieve this object, when a compound semiconductor thin film is grown on the surface of a compound semiconductor substrate by MOCVD, a compound containing Si and O is applied to the back surface of the compound semiconductor substrate before the growth. A method for processing a semiconductor substrate is provided.

Before the growth, when a compound having Si and O, such as an organic Si compound, is applied to the back surface of the compound semiconductor substrate in advance, when the MOCVD method is applied to the surface of the compound semiconductor substrate, A thin SiO ₂ protective film can be formed. As a result, even if the source gas penetrates into the back surface of the substrate, deposits do not adhere and the occurrence of cross hatching due to uneven temperature of the substrate can be prevented.

  In the present invention, when the compound semiconductor thin film is grown on the surface of the compound semiconductor substrate by MOCVD, before the compound semiconductor thin film is grown, the compound semiconductor substrate is formed on the back surface of the compound semiconductor substrate opposite to the surface on which the semiconductor thin film is grown. A compound containing Si and O, such as an organic Si compound, is applied in advance. Here, the compound semiconductor substrate is, for example, a group III-V compound semiconductor substrate, and specific examples thereof include GaAs, InP, GaP, GaSb, and InAs.

  Organic Si compounds such as organosiloxane or organosilazane are exemplified as the compound having Si and O applied to the back surface of the compound semiconductor substrate. These are produced industrially and are easily available as high-purity chemicals suitable for the semiconductor industry.

  Moreover, it is preferable that the number of Si atoms in the molecule | numerator of the compound which has Si and O apply | coated to the back surface of a compound semiconductor substrate in this way is the range of 3-12. When the number of atoms is less than 3, for example, organic Si compounds and other compounds having Si and O are highly volatile, and most of them evaporate from the back surface of the substrate during the MOCVD process, and in the process of growing a compound semiconductor thin film It is difficult to maintain a sufficiently thick protective film. In addition, organic Si compounds having Si atoms exceeding 12 have poor chemical stability and are easily hydrolyzed by moisture in the air, making them difficult to handle.

When applying a compound containing Si and O to the back surface of the compound semiconductor substrate, for example, an organic silicon compound may be dissolved in an organic solvent, and the solution may be applied to the back surface of the compound semiconductor substrate. In that case, it is desirable that the Si content in the solution is 0.1 mmol / liter or more. If the Si content in the solution is less than 0.1 mmol / liter, most of it evaporates from the back surface of the substrate during the temperature rising process of the MOCVD method, and the protective film has a sufficient thickness in the process of growing the compound semiconductor thin film. Difficult to maintain. If the Si concentration in the solution is too high, the SiO ₂ film formed on the back surface of the substrate becomes too thick, and slippage occurs on the substrate surface due to thermal distortion that occurs when the substrate is heated or cooled. In order to prevent such problems, the backside of the substrate is determined based on the compound semiconductor substrate used, the compound containing Si and O, the physical properties of the organic Si compound, the composition of the compound semiconductor thin film to be grown, the growth temperature, the conditions of the MOCVD apparatus, and the like. The upper limit of the Si concentration in the solution to be applied is determined as appropriate.

Then, after drying the compound semiconductor substrate on which the compound containing Si and O is applied in advance on the back surface, the compound semiconductor substrate is set in an MOCVD apparatus and heated to a temperature at which the compound semiconductor thin film is grown. In this temperature rising process, Si contained in the compound containing Si and O applied to the back surface of the substrate exists in the compound containing Si and O or in the oxide film formed on the back surface of the substrate, in the ambient atmosphere, etc. It reacts with oxygen and forms a very thin protective film of SiO _{2 on} the back surface of the substrate.

Thereafter, a source gas is supplied to epitaxially grow a compound semiconductor thin film on the surface of the compound semiconductor substrate by MOCVD. In this case, the compound semiconductor thin film is a semiconductor thin film for example a III-V group _{compound, (Al x Ga 1-x} ) y In 1-y P (0 ≦ x ≦ 1,0 ≦ y ≦ 1), In x Ga Examples thereof include _1-x As _y P _1-y (0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

  Hereinafter, examples of the present invention will be described in comparison with conventional ones. As shown in FIG. 1, the MOCVD apparatus 1 used in the embodiment has a susceptor 12 disposed in a reaction chamber 11 formed inside a casing 10 that can be decompressed. A rotation support shaft 13 is attached to the center of the upper surface of the susceptor 12, and the susceptor 12 is driven to rotate inside the reaction chamber 11 via the rotation support shaft 13.

  The susceptor 12 is provided with a plurality of substrate support portions 15 for supporting a substantially disc-shaped compound semiconductor substrate (wafer) W. The compound semiconductor substrate W is supported on these substrate support portions 15 with the surface (the surface on which the compound semiconductor thin film is grown by the MOCVD method) facing downward. Although the description of the mechanism is omitted, these substrate support portions 15 also support the compound semiconductor substrate W so as to be freely rotatable.

  As shown in FIG. 2, the substrate support unit 15 includes a heat equalizing plate 16 and a substrate support ring 17 that are stacked one above the other, and surrounds the heat equalizing plate 16 and the substrate support ring 17 with a ring-shaped holder 18. Through the composition. In this embodiment, substrate support rings 17a and 17b having two configurations are used.

  As shown in FIG. 3, the one support ring 17a is configured to support the peripheral portion of the compound semiconductor substrate W on the three claws 20 arranged at intervals. As shown in FIG. 4, the other support ring 17 b is configured such that the peripheral portion of the compound semiconductor substrate W is placed on the ring-shaped claw 21 disposed so as to continuously contact the peripheral portion of the compound semiconductor substrate W. It is the structure which supports.

  As shown in FIG. 2, the rear surface of the compound semiconductor substrate W supported by the substrate support 15 (the surface on which the compound semiconductor thin film is not grown, the upper surface in FIG. 2) is located above the soaking plate 16. A space 22 is formed. When one support ring 17 a that supports the compound semiconductor substrate W by placing the peripheral portion on the three claws 20 as shown in FIG. 3 is used, it is between the inner edge of the support ring 17 a and the peripheral portion of the compound semiconductor substrate W. Since a gap of about 200 μm is formed, the atmosphere (raw material gas) on the surface side of the compound semiconductor substrate W (the side on which the compound semiconductor thin film is grown, the lower surface side in FIG. 2) passes through the gap to form the compound semiconductor. It is possible to easily enter the back side (space 22) of the substrate W. On the other hand, when the other support ring 17 b that supports the compound semiconductor substrate W by placing the peripheral portion on the ring-shaped claw 21 as shown in FIG. 4 is used, the ring-shaped claw 21 continues to the peripheral portion of the compound semiconductor substrate W. Therefore, the atmosphere (raw material gas) on the front surface side of the compound semiconductor substrate W can hardly enter the back surface side (space 22) of the compound semiconductor substrate W.

  As shown in FIG. 1, by arranging a partition wall 24 made of quartz around the susceptor 12, the reaction chamber 11 in the casing 10 is divided into an upper space 11a and a lower space 11b. In the upper space 11 a, a plurality of resistance heating type heaters 25 are disposed so as to face the upper surface of the susceptor 12, and the compound semiconductor substrate W supported by the substrate support portion 15 is desired by heating of the heaters 25. The temperature can be raised to

  A cooling plate 26 is disposed in the lower space 11b so as to face the lower surface of the susceptor 12, and the cooling of the cooling plate 26 causes the compound semiconductor substrate W supported by the substrate support unit 15 to have a desired temperature. Can be cooled. Note that the upper surface of the cooling plate 26 is covered with a quartz plate 27.

  A raw material gas introduction nozzle 28 is provided through the center of the bottom surface of the casing 10 and the center of the cooling plate 26 and the quartz plate 27. An exhaust passage 29 is provided on the side of the bottom surface of the casing 10. When growing the compound semiconductor thin film, the source gas can be introduced into the lower space 11 b of the reaction chamber 11 from the introduction nozzle 28 and exhausted from the exhaust passage 29.

Using the reduced pressure MOCVD apparatus 1 described above, a compound semiconductor thin film made of an AlGaInP thin film was epitaxially grown on the surface of the compound semiconductor substrate W made of a 2-inch GaAs substrate by MOCVD. In the growth, trimethylgallium (TMG) and trimethylindium (TMI) were used as organic metals, AsH ₃ and PH ₃ were used as inorganic raw materials, and H ₂ was used as a carrier gas.

  As an example of the present invention, octamethylcyclotetrasiloxane, which is an organic Si compound (compound having Si and O), is dissolved in n-hexane, which is an organic solvent, and the solution is applied to the back surface of the compound semiconductor substrate W. Samples A, B, and C were used, respectively. The contents of Si in the solutions of these samples A, B, and C are 0.05 mmol / liter for sample A, 0.5 mmol / liter for sample B, and 5 mmol / liter for sample C.

  Also, as an example of the present invention, hexamethyldisilazane, which is an organic Si compound (compound having Si and O), is dissolved in n-hexane, which is an organic solvent, instead of octamethylcyclotetrasiloxane, and the resulting solution is compounded. The sample D was applied to the back surface of the semiconductor substrate W. The content of Si in the solution in Sample D is 0.5 mmol / liter.

  On the other hand, as a comparative example, only n-hexane not containing a compound containing Si and O was applied to the back surface of the compound semiconductor substrate W to obtain a sample E.

  As comparative examples, samples F and G in which nothing is applied to the back surface of the compound semiconductor substrate W were prepared.

  These samples A to G were respectively supported by the substrate support 15 in the MOCVD apparatus 1 described above, and a compound semiconductor thin film was grown on the surface (lower surface) of each sample A to G by the MOCVD method.

  For samples A to F, the support ring 17a described in FIG. 3 was used. In these samples A to F, since a gap of about 200 μm is formed between the inner edge of the support ring 17a and the peripheral edge of the compound semiconductor substrate W, the source gas can be easily supplied to the back surface side of the compound semiconductor substrate W. Can get in.

  On the other hand, for sample G, the support ring 17b described in FIG. 4 was used. Regarding the sample G, since the ring-shaped claw 21 is continuously in contact with the peripheral portion of the compound semiconductor substrate W, the source gas can hardly enter the back side of the compound semiconductor substrate W.

First, for each of these samples A to G, the compound semiconductor substrate W is heated to 500 ° C. under a reduced pressure of 75 Torr while flowing H ₂ gas in the MOCVD apparatus 1, and then PH ₃ and H ₂ are flown to After removing the oxide film on the surface of the semiconductor substrate W, a raw material gas is flowed to the surface of the compound semiconductor substrate W to form a GaAs layer 51 (0.5 μm), an AlGaInP layer 52 (2.0 μm), as shown in FIG. Epitaxial layers were stacked in the order of the GaAs layer 53 (1.0 m).

Next, the compound semiconductor substrate W was cooled to 100 ° C. in an H ₂ atmosphere, then taken out from the MOCVD apparatus 1, and the state of the front and back surfaces of each of the samples A to G was observed visually and with an optical microscope. Furthermore, the back surface was observed with ESCA, and the presence or absence of a peak due to Si—O bonding was observed. Table 1 shows the degree of cross-hatch on the substrate surface, the degree of adhesion of the raw material decomposition product due to the introduction of the raw material gas to the back surface of the substrate, and the peak due to the bond between Si and O in the back surface observation by ESCA. The presence or absence was compared.

Samples B and C coated with octamethyltetracyclosiloxane and sample D coated with hexamethyldisilazane have no deposit on the backside of the substrate, and cross-hatching of the substrate surface caused by the deposit on the backside of the substrate. There was no outbreak. Moreover, in the observation result of ESCA, the peak resulting from the coupling | bonding of Si-O was observed from sample B, C, D. This indicates that a very thin protective film of SiO ₂ is formed on the back surfaces of the samples B, C, and D. Since no peak due to Si—O was observed in sample E, it can be seen that the origin of SiO ₂ is octamethyltetracyclosiloxane and hexamethyldisilazane. Further, from the comparison of sample A with samples B and C, if the concentration of the organic Si compound (compound having Si and O) is too low, it will be almost volatilized during the temperature rise in the MOCVD apparatus 1 and sufficient for the back surface of the substrate. It can be seen that no protective film is formed. Similar results are easily expected for organosilazanes, which have characteristics close to those of organosiloxanes. Further, as shown in the result of the sample G, even if the source gas does not enter the back side of the compound semiconductor substrate W using the support ring 17b, the compound semiconductor substrate W is deformed by the deformation of the compound semiconductor substrate W during heating. A gap is formed between the support ring 17b and deposits adhere to the back surface of the substrate due to the raw material gas entering from there.

裏面付着物：＋＋（全面に付着），＋（部分的に付着），−（ほとんど付着無し）
クロスハッチ：＋＋（全周に渡って発生），＋（部分的に発生），−（ほとんど発生無し）
ＥＳＣＡ測定におけるＳｉ−Ｏピーク：＋＋（ピーク大），＋（ピーク小），−（ピーク無し）

Back side deposits: ++ (attached to the entire surface), + (partially attached),-(almost no adhesion)
Cross hatch: ++ (occurs over the entire circumference), + (partially occurs),-(almost no occurrence)
Si-O peak in ESCA measurement: ++ (peak large), + (small peak),-(no peak)

  According to the present invention, it is possible to prevent deposits from adhering to the back surface of the substrate generated by the source gas. Therefore, the substrate temperature becomes uniform and no cross hatch occurs on the substrate surface. In principle, the present invention is also applicable to other mixed crystal epitaxial growth represented by an InGaAsP layer on an InP substrate.

It is explanatory drawing of a MOCVD apparatus. It is explanatory drawing of a board | substrate support part. It is a bottom view of the support ring which mounts and supports the peripheral part of a board | substrate on three nail | claws. It is a bottom view of the support ring which mounts and supports the peripheral part of a board | substrate on a ring-shaped nail | claw. It is explanatory drawing of each epitaxial layer laminated | stacked on a substrate surface.

Explanation of symbols

W Compound semiconductor substrate 1 MOCVD apparatus 10 Casing 11 Reaction chamber 12 Susceptor 13 Rotation support shaft 15 Substrate support portion 16 Heat equalizing plate 17 Substrate support ring 18 Holder 20, 21 Claw 22 Space 24 Partition 25 Heater 26 Cooling plate 27 Quartz plate 28 Introduction Nozzle 29 exhaust passage

Claims (9)

  A method of processing a semiconductor substrate, comprising: applying a compound containing Si and O to the back surface of the compound semiconductor substrate before the growth when growing the compound semiconductor thin film on the surface of the compound semiconductor substrate by MOCVD.   2. The semiconductor substrate processing method according to claim 1, wherein the compound semiconductor substrate is a III-V group compound semiconductor substrate.   The III-V group compound semiconductor substrate is made of any one of GaAs, InP, GaP, GaSb, and InAs. The method for processing a semiconductor substrate according to claim 2.   4. The method for processing a semiconductor substrate according to claim 1, wherein the compound semiconductor thin film is a III-V group compound semiconductor thin film. The group III-V compound semiconductor thin _{film, (Al x Ga 1-x} ) y In 1-y P (0 ≦ x ≦ 1,0 ≦ y ≦ 1) or _{In x Ga 1-x As y} P 1-y 5. The method of processing a semiconductor substrate according to claim 4, wherein the processing method is (0 ≦ x ≦ 1, 0 ≦ y ≦ 1).   6. The method for treating a semiconductor substrate according to claim 1, wherein the compound containing Si and O is organosiloxane or organosilazane.   The number of Si atoms in the molecule | numerator of the compound which has the said Si and O is the range of 3-12, The processing of the semiconductor substrate of Claim 1, 2, 3, 4, 5 or 6 characterized by the above-mentioned. Method.   8. The method for processing a semiconductor substrate according to claim 1, wherein the compound containing Si and O is dissolved and applied in an organic solvent.   9. The method of processing a semiconductor substrate according to claim 8, wherein the content of Si in the solution obtained by dissolving the compound containing Si and O in an organic solvent is 0.1 mmol / liter or more.

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