JP2005306680A - Semiconductor substrate, stand-alone substrate, and method for manufacturing these, as well as method for polishing substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor substrate which has at an as-grown state a high flatness on the surface of at least the side of an epitaxial growth layer and which thereafter is easy to polish, and to provide a manufacturing method therefor. <P>SOLUTION: The semiconductor substrate 10 of a crystal growth system which causes the warpage because of forming a GaN epitaxial growth layer 12 on a sapphire substrate 11, is such one that the GaN epitaxial growth layer 12 is so formed for the purpose of canceling out previously the effect of the warpage by thinning the thickness t<SB>1</SB>on the central part of the sapphire substrate 11 thinner than a thickness t<SB>2</SB>on the edge part of the sapphire substrate 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor substrate having a small warp having an epitaxial semiconductor growth layer, a self-standing substrate, a method for manufacturing the same, and a method for polishing the substrate.

Nitride-based semiconductor materials such as gallium nitride (GaN), indium gallium nitride (InGaN), and gallium aluminum nitride (GaAlN) have a sufficiently large forbidden band width and a direct transition type between bands. Application to is actively studied. In addition, application to electronic devices is also expected due to the high saturation drift velocity of electrons and the use of two-dimensional carrier gas by heterojunction.
Silicon (Si) and gallium arsenide (GaAs), which are already widely used in the world, are homoepitaxially grown on a substrate made of the same kind of material such as a Si substrate and a GaAs substrate, respectively. Have been used. In homoepitaxial growth on the same type of substrate, there is no difference in lattice constant or linear expansion coefficient between the substrate and the epitaxial growth layer, so that the substrate after epitaxial growth does not warp and a flat epitaxial growth surface can be obtained.

  On the other hand, nitride-based semiconductor materials are difficult to grow bulk crystals, and therefore, a GaN free-standing substrate that can withstand practical use is still under development. Currently, sapphire is a substrate for GaN growth that is in widespread use. Metal organic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), hydride vapor phase epitaxy on a single crystal sapphire substrate. In general, a method of growing a nitride-based semiconductor epilayer for heteroepitaxial growth of GaN once and continuously or in another growth furnace by using a vapor phase growth method such as (HVPE) is used. Yes.

Since the sapphire substrate has a lattice constant different from that of GaN, a single crystal film cannot be grown by directly growing GaN on the sapphire substrate. For this reason, a method has been devised in which a buffer layer of AlN or GaN is once grown on a sapphire substrate at a low temperature of about 500 ° C., lattice strain is relaxed by this low temperature growth buffer layer, and then GaN is grown thereon. (For example, refer to Patent Document 1). Using this low-temperature grown nitride layer as a buffer layer, GaN single crystal epitaxial growth has become possible. However, even with this method, the difference between the lattice of the substrate and the crystal is still difficult, and since the crystal growth proceeds in the three-dimensional island growth mode at the beginning of the growth, the GaN thus obtained has 10 ⁹ to 10. ^It has as many as ¹⁰ cm ^-2 dislocations. This defect becomes an obstacle to manufacturing a GaN-based LD.

In recent years, as a method of reducing the density of defects generated due to the difference in lattice constant between sapphire and GaN, ELO (for example, see Non-Patent Document 1), FIELO (for example, see Non-Patent Document 2), pens. Growth techniques such as deoepitaxy (for example, see Non-Patent Document 3) have been reported. In these growth techniques, a mask patterned with SiO ₂ or the like is formed on GaN grown on a substrate such as sapphire, and further a GaN crystal is selectively grown from the window portion of the mask. By covering GaN with lateral growth, the propagation of dislocations from the underlying crystal is prevented. With the development of these growth techniques, the dislocation density in GaN can be drastically reduced to about 10 ⁷ cm ⁻² (see, for example, Patent Document 2).

On the other hand, a method has been proposed in which a dislocation density-reduced GaN layer is thickly grown on a dissimilar substrate such as a sapphire substrate, and the GaN layer is peeled off from the underlying layer after growth to use the GaN layer as a self-supporting GaN substrate (Patent Literature). 3). It has also been proposed to form a GaN layer on a sapphire substrate using the above-described ELO technique, and then remove the sapphire substrate by etching or the like to obtain a GaN free-standing substrate (see Patent Document 4). Furthermore, by growing GaN on a substrate such as sapphire via a TiN thin film with a network structure, a void is formed at the interface between the base substrate and the GaN layer, and the GaN substrate can be peeled off and the dislocation can be reduced at the same time. Technology (VAS (Void-Assisted Separation)) is also disclosed (see Non-Patent Document 4 and Patent Document 5).
Japanese Patent Laid-Open No. 4-297003 Japanese Patent Laid-Open No. 10-312971 JP 2000-22212 A JP-A-11-251253 JP 2003-178984 A Appl. Phys. Lett. 71 (18) 2638 (1997) Japan. J. et al. Appl. Phys. 38, L184 (1999) MRS Internet J.M. Nitride Semicond. Res. 4S1, G3.38 (1999) Y. Oshima et. al. , Jpn. J. et al. Appl. Phys. Vol. 42 (2003) p. L1-L3

However, as described above, a GaN crystal for producing a GaN free-standing substrate is once heteroepitaxially grown on a heterogeneous substrate such as sapphire having a greatly different lattice constant. The GaN crystal grown on the heterogeneous substrate causes a warp caused by a difference in lattice constant and a difference in linear expansion coefficient from the heterogeneous substrate serving as a base substrate. For example, since the linear expansion coefficient of GaN is 1.9% different from the linear expansion coefficient of the sapphire substrate, when GaN is epitaxially grown on the sapphire substrate, the epitaxial substrate is cooled to room temperature, so that the substrate is It will warp convexly. It has also been reported that when a GaN single layer is grown 2 μm on a φ4 inch sapphire substrate, the center of the substrate warps more convexly by 40 μm than the peripheral portion.
Further, it is known that warpage is remarkably observed even in a GaN free-standing substrate from which the base substrate is removed. Warping has already begun to occur during crystal growth, and it may grow in a warped shape, or it may be warped by growing under the presence of strain and removing the underlying substrate. For example, in the above-described VAS method, when a GaN free-standing substrate having a thickness of 350 μm is formed, the free-standing substrate warps downward, and if the film thickness is almost uniform, the central portion and the peripheral portion of the substrate have several hundred μm May cause warping.

When the substrate is warped, various problems occur in the subsequent device manufacturing process.
For example, if the substrate is warped, when the device structure is epitaxially grown on the substrate, the back surface of the substrate and the susceptor do not adhere to each other, and thus the heat transfer to the substrate is uneven when the substrate is heated. As a result, temperature distribution occurs in the substrate surface. If there is a difference in temperature within the substrate plane, variations in the growth film thickness, composition, impurity concentration, etc. occur during epitaxial growth, and uniform growth cannot be achieved within the plane. It becomes a factor to increase the variation.

  Furthermore, if the substrate is warped, various problems occur in the photolithography process. For example, a substrate with a large warp is difficult to hold by vacuum suction, and it is difficult to accurately fix the substrate to a spinner or mask aligner. Further, in the contact-type mask aligner, it is difficult to bring the mask into close contact with the substrate. For this reason, when the mask pattern is baked, the patterning accuracy is lowered depending on the location. In order to avoid this, if the mask is pressed against the substrate, there is an increased risk that the substrate will break. Even if it is a non-contact type mask aligner, if the substrate surface is warped, the focus of the projected mask pattern will not be constant within the substrate surface, resulting in variations in line width, and particularly fine stripes with high accuracy. Fabrication of short wavelength laser devices that require patterning is a fatal problem.

  On the other hand, a method for flattening the front and back surfaces of a warped substrate by polishing has also been proposed. However, in order to polish a substrate, it is necessary to stick it to a flat polishing jig and determine a reference surface for polishing. However, it is difficult to stick a substrate with a large warp to a flat surface. When attaching a warped substrate to a polishing jig, the risk of cracking increases if the substrate is pressed and applied forcibly. Even if the substrate can be elastically deformed and stuck without cracking, the elastically deformed substrate will be warped again if it is removed from the jig after polishing. Therefore, if wax is put in the gap between the substrate and the jig in a warped shape, the parallelism between the substrate and the polishing jig tends to vary, and therefore the accuracy of the reference surface does not come out. .

  In general, in order to protect the substrate surface used in the device process, the substrate is polished by first polishing the back surface of the substrate, re-mounting the front and back of the substrate from the jig on the way, and polishing the surface of the substrate later. Therefore, the surface that is first attached to the polishing jig is the surface of the substrate, and the surface that serves as the reference for polishing is determined here. Therefore, the higher the flatness of the substrate surface in the as-grown state, the easier the polishing of the substrate. However, the conventional crystal is controlled so that the film thickness distribution is uniform, so that the substrate is warped. Then, the front and back of the substrate were warped in the same manner, and the above-described problems were generated.

  Accordingly, an object of the present invention is to provide a semiconductor substrate, a manufacturing method thereof, and a polishing method for a semiconductor substrate, in which the flatness of at least the surface of the epitaxial growth layer is high in an as-grown state and can be easily polished thereafter.

  As a result of diligent research in view of the above object, the present inventors have intentionally changed the film thickness of the layer to be epitaxially grown according to the position of the substrate, rather than suppressing the occurrence of warping, so that at least the surface in an as-grown state. If it is possible to manufacture a semiconductor substrate that has a high flatness on the side and offsets the influence of warpage, and can manufacture a substrate that has at least a high flatness on the front surface side, the surface can be used as a polishing jig even if the back surface is greatly warped. The present invention has been completed by finding that it is possible to process the substrate with high accuracy and high yield by pasting and polishing the back surface.

  That is, in order to solve the above-mentioned problems, the semiconductor substrate of the present invention is a crystal growth type semiconductor substrate in which warpage is caused by forming an epitaxial growth layer on a heterogeneous substrate, and cancels out the influence of the warp in advance. Thus, the film thickness of the epitaxial growth layer is distributed.

  Also, the semiconductor substrate of the present invention is a crystal growth type semiconductor substrate in which an epitaxial growth layer is formed on a heterogeneous substrate to cause a warp in a convex manner on the epitaxial growth surface side so as to cancel out the influence of the warp in advance. Further, the epitaxial growth layer is formed so that the film thickness is larger at the end than at the center on the heterogeneous substrate.

  Furthermore, the semiconductor substrate of the present invention is a crystal growth type semiconductor substrate in which an epitaxial growth layer is formed on a heterogeneous substrate to cause a concave warp on the epitaxial growth surface side, so that the influence of the warp is canceled in advance. Further, the epitaxial growth layer is formed so that the film thickness is smaller at the end portion than at the central portion on the heterogeneous substrate.

The heterogeneous substrate may be sapphire, and the epitaxial growth layer may be a semiconductor represented by In _x Ga _y Al _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). .

  In order to solve the above problems, the self-supporting substrate of the present invention is a material-based self-supporting substrate that warps only in the epitaxial growth layer, and is distributed in the thickness of the epitaxial growth layer so as to cancel out the influence of the warp in advance. It is characterized by having.

  Further, the self-supporting substrate of the present invention is a material-based self-supporting substrate that generates a convex warp only on the epitaxial growth layer on the epitaxial growth surface side, and the film thickness of the epitaxial growth layer is set so as to cancel the influence of the warp in advance. It is characterized by being formed so as to be larger at the end than at the center on the different substrate.

  Furthermore, the self-supporting substrate of the present invention is a self-supporting substrate of a material system in which only the epitaxial growth layer causes a concave warp on the epitaxial growth surface side, and the film thickness of the epitaxial growth layer is such that the influence of the warp is canceled out in advance. It is characterized in that it is formed so as to be smaller at the end than at the center on the different substrate.

In addition, in order to solve the above-described problem, a method for manufacturing a semiconductor substrate according to the present invention includes a crystal growth system in which a semiconductor substrate having an epitaxial layer is warped by growing an epitaxial layer on a heterogeneous substrate. The epitaxial layer is grown with a distribution of film thickness so as to cancel out the influence of warpage in advance.

  In addition, the method for manufacturing a semiconductor substrate of the present invention includes a crystal growth system in which an epitaxial layer is grown on a heterogeneous substrate so that the semiconductor substrate having the epitaxial layer is warped convexly toward the epitaxial growth surface. The epitaxial layer is grown so that the film thickness is larger at the end portion than the central portion of the heterogeneous substrate so as to cancel out the influence of the above.

  Furthermore, the method for manufacturing a semiconductor substrate according to the present invention includes the above-described warpage in a crystal growth system in which an epitaxial layer is grown on a heterogeneous substrate so that the semiconductor substrate having the epitaxial layer warps in a concave manner on the epitaxial growth surface side. The epitaxial layer is grown so that the film thickness becomes smaller at the end portion than the central portion of the heterogeneous substrate so as to cancel out the influence of the above.

  Further, in order to solve the above-described problem, the method for manufacturing a self-supporting substrate according to the present invention causes the self-supporting substrate made of the epitaxial layer to warp when the heterogeneous substrate is peeled off after the epitaxial layer is grown on the heterogeneous substrate. In such a material system, the epitaxial layer is grown with a distribution of film thickness so as to cancel out the influence of the warp in advance.

  In the method for manufacturing a self-supporting substrate according to the present invention, when the heterogeneous substrate is peeled off after growing the epitaxial layer on the heterogeneous substrate, the self-standing substrate made of the epitaxial layer is warped convexly toward the epitaxial growth surface. In the material system, the thickness of the epitaxial growth layer is formed so as to be larger at the end portion than at the central portion on the heterogeneous substrate so as to cancel out the influence of the warp in advance.

  Furthermore, in the method for manufacturing a self-supporting substrate according to the present invention, when the heterogeneous substrate is peeled off after the epitaxial layer is grown on the heterogeneous substrate, the self-supporting substrate made of the epitaxial layer warps in a concave on the epitaxial growth surface side. In a material system that causes warpage, the thickness of the epitaxial growth layer is formed so as to be smaller at the end portion than at the central portion on the heterogeneous substrate so as to cancel out the influence of the warp in advance.

  In the substrate polishing method of the present invention, the surface of the semiconductor substrate or the free-standing substrate, which has a smaller warp, is attached to a polishing jig and the surface having the larger warp is polished flat. It is characterized by that.

  Furthermore, the surface with the smaller warp can be mirror-polished by reversing the front and back.

  Further, the semiconductor substrate of the present invention is a crystal growth type semiconductor substrate in which warpage is caused by forming an epitaxial growth layer on a heterogeneous substrate, and the warpage of the epitaxial growth layer surface is caused by warpage of the back surface of the heterogeneous substrate. Is also small.

  Furthermore, the self-supporting substrate of the present invention is a material-based self-supporting substrate in which warpage occurs only in the epitaxial growth layer, and the warpage of the substrate surface is smaller than the warpage of the back surface of the substrate.

  Further, the substrate polishing method of the present invention is characterized in that the surface of the semiconductor substrate or the freestanding substrate is attached to a polishing jig and the back surface is polished flat.

  Furthermore, in the method for polishing a substrate of the present invention, the surface of the semiconductor substrate or the freestanding substrate is attached to a polishing jig, the back surface is polished flatly, and then the polishing surface is reversely applied to reverse the surface. It is characterized by mirror polishing.

  In order to solve the above problems, a method for manufacturing a self-supporting substrate according to the present invention includes a step of depositing a metal film on at least a substrate obtained by growing a single crystal gallium nitride film on a sapphire substrate, and depositing the metal film. A step of heat-treating the substrate in an atmosphere containing hydrogen gas or hydride gas to form a void in the gallium nitride film, a step of depositing single-crystal gallium nitride on the substrate, and a step from the single-crystal gallium nitride substrate. Removing the sapphire substrate to obtain a self-supporting gallium nitride substrate, and the self-supporting system in which the self-supporting gallium nitride substrate is warped so that the central portion is concave on the single crystal gallium nitride growth surface side. In the method for manufacturing a substrate, the step of depositing the single crystal gallium nitride may be performed in advance so that the center portion of the gallium nitride substrate is offset from the end portion in advance so as to cancel the influence of warpage of the self-supported gallium nitride substrate. And wherein the depositing such a film thickness is increased.

  Further, the epitaxial growth surface of the free-standing substrate and the opposite surface can be bonded to a polishing jig and the opposite surface can be polished flat.

  Furthermore, of the epitaxial growth surface of the self-supporting substrate and the opposite surface, first, the epitaxial growth surface is attached to a polishing jig and the opposite surface is polished flat, and then the polishing surface is reversed and the epitaxial growth surface is mirror-polished. You can also.

  Here, the “warp” in the present invention refers to the maximum displacement excluding the thickness of the substrate when placed on a plane, that is, the maximum displacement between the plane of the substrate facing the plane and the plane. Say. Therefore, if there is a distribution in the thickness of the substrate, the warpage may be different between the front surface and the back surface of the substrate.

  According to the semiconductor substrate, the self-standing substrate and the manufacturing method thereof of the present invention, the flatness on at least the substrate surface side can be made higher than that of the conventional substrate. For this reason, when the photolithography process is applied to the surface of the as-grown substrate, the processing accuracy is improved and variations in device characteristics are reduced. As a result, the device acquisition yield can be improved.

  In addition, the substrate polishing method of the present invention enables a substrate surface that has grown substantially flat to be attached to a polishing jig, and can be used to accurately polish the back surface at a high yield with a high yield. If the surface is polished by reattaching the back side to the polishing jig, the polishing accuracy of the surface is improved. As a result, a polished substrate having high flatness on both sides and little variation in plane orientation can be obtained with high yield. For this reason, in the device manufacturing process in which the device structure is epitaxially grown on the substrate, the back surface of the substrate and the susceptor can be in close contact with each other, so that the heat transfer to the substrate becomes uniform when the substrate is heated. No temperature distribution will occur. As a result, uniform epitaxial growth can be performed, and consequently device characteristics can be stabilized.

(substrate)
The substrate of the present invention may be an epitaxial substrate obtained by epitaxially growing a semiconductor layer on a heterogeneous substrate, or a free-standing substrate made of a single material semiconductor layer.

  Examples of the former epitaxial substrate include those obtained by epitaxially growing GaAs on a Si substrate, those obtained by epitaxially growing GaN on a sapphire substrate, those obtained by epitaxially growing AlN on a sapphire substrate, and epitaxially growing AlGaN on a sapphire substrate. Various combinations such as those obtained by epitaxial growth of GaN on a GaAs substrate, or those obtained by epitaxial growth of GaN on a Si substrate can be used. In short, this corresponds to a case where a semiconductor material having a physical property such as a lattice constant or a linear expansion coefficient different from that of the base substrate is epitaxially grown on the base substrate.

  The latter free-standing substrate means a substrate having a strength that can not only maintain its own shape but also does not cause inconvenience in handling. In order to have such strength, the thickness of the self-supporting substrate is preferably 200 μm or more. In consideration of easiness of cleavage after element formation, the thickness of the self-supporting substrate is preferably 1 mm or less. When it exceeds 1 mm, cleavage becomes difficult, and irregularities occur on the cleavage surface. As a result, when applied to a semiconductor laser or the like, for example, degradation of device characteristics due to reflection loss becomes a problem.

(Substrate growth method)
As a method for growing the substrate, a known method such as the MOVPE method, the MBE method, or the HVPE method can be used. In particular, in the method of separating the epitaxially grown layer from the heterogeneous substrate after crystal growth and producing a free-standing substrate of the epitaxially grown layer, the HVPE method having a high crystal growth rate is preferable.

(Flatness of substrate surface in as-grown state)
The substantially flat surface in the present invention means that, for example, when a substrate having a diameter of 50 mm on which an epitaxial layer is grown is placed on a flat surface, the variation in the distance between the substrate surface and the flat surface is 50 μm or less, preferably 10 μm or less. It is desirable that If the above limit of variation is exceeded, the probability that the substrate will break when the mask is brought into close contact with the substrate with a contact-type mask aligner becomes very high. In addition, when the substrate is attached to the polishing jig or in the polishing process, the probability that the substrate will break increases.

(Surface polishing)
Among the above substrates, it is desirable that the surface of the self-supporting substrate is mirror-polished particularly. In general, the surface of the as-grown thick-film epitaxial growth layer has a large number of large irregularities such as hillocks and minute irregularities that appear to be caused by step bunching. These factors not only deteriorate the morphology of the epitaxial layer grown on it, but also cause the film thickness, composition, etc. to be non-uniform, and also reduce the exposure accuracy of the photolithography process in the device fabrication process. It becomes. For this reason, it is preferable that the free-standing substrate surface is a flat mirror surface.

(Flatness of substrate surface after polishing)
As the flatness of the substrate surface after the mirror polishing, the arithmetic average roughness Ra obtained by measuring a 50 μm × 50 μm range of the substrate surface is used, and the arithmetic average roughness Ra is preferably 10 nm or less. If this value is exceeded, the general flatness required when placing the substrate on the stepper will be exceeded, causing inconvenience.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to them.

FIG. 1 shows a schematic diagram of a semiconductor substrate according to an embodiment of the present invention.
The semiconductor substrate 10 has a warped shape as shown in FIG. 1 when a GaN epitaxial growth layer 12 is formed on the surface of a sapphire substrate 11. Here, the film thickness of the GaN epitaxial growth layer 12 is formed such that the thickness t ₁ on the center portion of the sapphire substrate 11 is smaller than the thickness t ₂ on the end portion of the sapphire substrate 11.

Such a semiconductor substrate 10 was manufactured as follows.
First, a GaN single crystal was epitaxially grown by 2 μm on a sapphire substrate (C surface) 11 having a diameter of 2 inches using a horizontal atmospheric pressure MOCVD furnace by MOCVD. Ammonia gas and trimethylgallium were used as raw materials, and a mixed gas of hydrogen and nitrogen was used as a carrier gas. The sapphire substrate 11 is heated to 1100 ° C. in a hydrogen atmosphere to clean the surface oxide and the like, then the substrate temperature is lowered to 550 ° C., GaN is grown to 20 nm thereon, and the substrate temperature is further raised to 1050 ° C. GaN was grown to 2 μm. The GaN epitaxial substrate obtained by cooling to room temperature had a flat and clean mirror surface. When the warpage of the epitaxial substrate was measured, the difference in height between the central portion and the peripheral portion of the substrate when the substrate was placed on a flat surface showed a relatively good flatness of 2.5 μm.

  Next, using a horizontal normal pressure HVPE furnace, the GaN epitaxial single crystal layer 12 was epitaxially grown by 300 μm on the produced substrate using the HVPE method. GaCl produced by reacting ammonia gas and metallic Ga and HCl gas at 850 ° C. was used as a raw material, and hydrogen gas was used as a carrier gas. The growth temperature is 1050 ° C. and the growth rate is 80 μm / h.

  Here, the relationship between the distance from the source gas ejection port to the sapphire substrate 11 in the horizontal atmospheric HVPE furnace and the film thickness distribution of the epitaxial growth surface of the GaN epitaxial single crystal layer 12 grown by the HVPE method was examined. As a result, when the position of the sapphire substrate 11 was brought close to the source gas ejection port, the film thickness distribution of the grown GaN epitaxial single crystal layer 12 showed a tendency that the center of the substrate became thinner. When the position of the sapphire substrate 11 is moved away from the source gas ejection port from that state, the central portion of the sapphire substrate 11 tends to be thicker. As a result, an almost uniform film thickness can be obtained. Although the distance from the source gas ejection port required to obtain the target film thickness distribution to the sapphire substrate 11 changed depending on the source gas flow velocity, the above-mentioned tendency was not changed.

  Based on the relationship between the distance from the source gas ejection port to the sapphire substrate 11 and the film thickness distribution of the GaN epitaxial single crystal layer 12 grown by the HVPE method in such a horizontal normal pressure HVPE furnace, the flow rate of the source gas is determined. As parameters, the growth conditions were intentionally set so that when the grown sapphire substrate 11 was placed on a flat surface, the substrate surface became substantially flat, that is, the center of the sapphire substrate 11 became thinner. Specifically, the distance from the source gas ejection port to the substrate was set to 80 mm, and the carrier gas flow rate was set so that the source gas flow rate was 30 mm / sec.

The semiconductor substrate 10 obtained by cooling the HVPE apparatus to room temperature exhibited a relatively clean mirror surface although a hexagonal pyramid morphology was observed on the surface. When the semiconductor substrate 10 was placed on a flat surface and the height of the surface of the semiconductor substrate was measured, the central portion of the substrate was about 40 μm higher than the peripheral portion, but the flatness of the surface was greatly improved. It was. In Figure 1, was measured using a micro-gauge thickness of the GaN epitaxial single-crystal layer 12 has been a 220μm in the t ₁ the central portion of the substrate, and thicker toward the peripheral portion of the substrate, the uppermost It was 350 μm at a point (t ₂ ) entering 5 mm from the outer periphery. When the semiconductor substrate 10 is placed on a flat surface, the surface becomes substantially flat because the amount of warpage is reduced due to the film thickness distribution of the GaN epitaxial single crystal layer 12 described above. The substrate surface is apparently flattened by the film thickness distribution of the epitaxial single crystal layer 12.
[Comparative Example 1]

  As shown in FIG. 2, a semiconductor substrate 20 was prepared by growing GaN on the sapphire substrate 11 by 2 μm by MOCVD. Next, a GaN epitaxial single crystal layer 14 was epitaxially grown about 300 μm on this substrate by HVPE. Here, epitaxial growth was performed in the same manner as in Example 1 except that the position of the sapphire substrate 11 was separated from the source gas ejection port by 110 mm so that a substantially uniform film thickness was obtained on the entire surface. I let you.

The semiconductor substrate obtained by cooling the HVPE apparatus to room temperature exhibited a relatively clean mirror surface, although a hexagonal pyramid morphology was observed on the surface. However, when this semiconductor substrate was placed on a flat surface and the height of the surface of the semiconductor substrate was measured, the central portion at the center of the substrate was about 180 μm higher than the peripheral portion. In FIG. 2, the thickness of the GaN epitaxial single crystal layer 14 measured using a micro gauge is substantially equal at t ₃ on the center and at point t ₄ entering 5 mm from the outermost periphery, and is 25 points in the plane. In the measurement, it was within the range of 300 ± 25 μm, and it was confirmed that the above-mentioned height difference of about 180 μm was caused by the warp of the substrate.

A GaN free-standing substrate was fabricated according to the steps of the VAS method shown in FIGS.
First, a φ2 inch diameter sapphire substrate (C surface) 21 is prepared (step a), and the Si-doped GaN layer 22 is formed on the sapphire substrate 21 by a MOVPE method through a 20 nm low-temperature growth GaN buffer layer. 5 μm was grown (step b). The growth pressure was normal pressure, the substrate temperature during buffer layer growth was 600 ° C., and the substrate temperature during epi layer growth was 1100 ° C. The raw materials used were TMG as a group III raw material, NH ₃ as a group V raw material, and monosilane as a dopant. The carrier gas is a mixed gas of hydrogen and nitrogen. The crystal growth rate was 4 μm / h. The carrier concentration of the epi layer was 2 × 10 ¹⁸ cm ⁻³ .

Next, a metallic Ti thin film 23 was deposited on the GaN epi substrate to a thickness of 20 nm (step c). The substrate thus obtained was placed in an electric furnace and heat-treated at 1050 ° C. for 20 minutes in an H ₂ stream containing 20% NH ₃ . As a result, a part of the Si-doped GaN layer 22 is etched to generate a void-formed GaN layer 24 having high-density voids, and the Ti layer is nitrided to form high-density submicron holes on the surface. The TiN layer 25 was changed (step d).

This substrate was put into an HVPE furnace, and a GaN layer 26 having a thickness of 600 μm was used by using a supply gas containing a source gas consisting of 8 × 10 ⁻³ atm GaCl and 4.8 × 10 ⁻² atm NH _{3 in} a carrier gas. Grow to thickness (step e). As the carrier gas, N ₂ gas containing 5% of H ₂ was used. The growth conditions for the GaN layer were atmospheric pressure and a substrate temperature of 1080 ° C. In the GaN crystal growth process, Si was doped by supplying SiH ₂ Cl ₂ as a doping source gas to the substrate region. Here, the distance from the source gas ejection port to the substrate is set to 60 mm, and the source gas flow rate is 25 mm / sec so that the film thickness distribution of the GaN layer 26 grown by the HVPE method becomes thicker toward the center of the substrate. The carrier gas flow rate was set as follows.

  After the growth is completed, in the process of cooling the HVPE apparatus, the GaN layer 26 is naturally separated from the base substrate with the void-formed GaN layer 24 as a boundary (step f), and a GaN free-standing substrate 30 is obtained (step g). .

An enlarged schematic view of the obtained GaN free-standing substrate is shown in FIG. The GaN free-standing substrate 31 had a relatively clean mirror surface although a hexagonal pyramid morphology was observed on the surface. When the height difference of the surface of the GaN free-standing substrate 31 was measured, the flatness of the surface was greatly improved although the peripheral portion of the substrate was about 30 μm higher than the central portion. In FIG. 4, the thickness of the GaN free-standing substrate 31 measured using a microgauge was 620 μm on the central portion (t ₅ ) of the substrate, but it became thinner toward the periphery of the substrate. in that enters from the outer periphery to 5mm inside _{(t 6),} was 510 .mu.m. The surface of the GaN free-standing substrate 31 becomes substantially flat because the amount of warpage is reduced due to the film thickness distribution of the GaN epitaxial growth layer, and the surface of the substrate apparently appears due to the film thickness distribution of the GaN epitaxial growth layer. It is a flattened one.

  A GaN free-standing substrate as shown in FIG. 5 was produced. The manufacturing process of the substrate is the same as in the case of Example 2 shown in FIG. A substrate having a structure in which a TiN layer 25 in which fine submicron holes are formed at a high density is laminated on the surface of a void layer forming GaN layer 24 having a high density of voids under the same conditions as in Example 2, Next, a GaN single crystal was epitaxially grown about 600 μm on the substrate by HVPE.

  Here, the difference from Example 2 is that the film thickness distribution of the GaN epilayer grown by the HVPE method is intentionally set so that the center of the substrate is thicker than in Example 2. It is in. Specifically, the thickness of the central portion of the substrate was increased by separating the position of the substrate by 10 mm from the material gas ejection port, rather than the conditions of Example 2.

An enlarged schematic view of a GaN free-standing substrate obtained by cooling the HVPE apparatus is shown in FIG. The obtained GaN free-standing substrate 33 exhibited a relatively clean mirror surface although hexagonal pyramid morphology was observed on the surface as in Example 2. When the height difference of the substrate surface was measured, the flatness of the surface was greatly improved although the center portion of the substrate was about 20 μm higher than the peripheral portion. In FIG. 5, the thickness of the GaN free-standing substrate 33, measured using a microgauge, was 640 μm on the central portion (t ₇ ) of the substrate, but it became thinner toward the periphery of the substrate. It was 540 μm at a point (t ₈ ) entering 5 mm from the outer periphery.
[Comparative Example 2]

  A GaN free-standing substrate as shown in FIG. 6 was produced. The manufacturing process of the substrate is the same as in the case of Example 2 shown in FIG. A substrate having a structure in which a TiN layer 25 in which fine submicron holes are formed at a high density is laminated on the surface of a void layer forming GaN layer 24 having a high density of voids under the same conditions as in Example 2, Next, a GaN single crystal was epitaxially grown about 600 μm on the substrate by HVPE. Here, the difference from Example 2 is that the position of the sapphire substrate 11 is separated from the source gas ejection port by 110 mm so that a substantially uniform film thickness can be obtained over the entire surface. .

An enlarged schematic view of a GaN free-standing substrate obtained after cooling to room temperature is shown in FIG. The obtained GaN free-standing substrate 41 exhibited a relatively clean mirror surface although the surface morphology equivalent to that of Example 2 was observed. When the height difference of the surface of the substrate was measured, the peripheral portion of the substrate was about 280 μm higher than the central portion. In FIG. 6, the thickness of the GaN epitaxial growth layer 41 measured using a micro gauge is 620 μm on the central portion (t ₉ ) of the substrate and 610 μm on the peripheral portion (t ₁₀ ) of the substrate. Met. That is, it was confirmed that the height difference of about 280 μm was caused by the warp of the substrate.

  The GaN free-standing substrate 31 obtained in Example 2 was planarized using the polishing process shown in FIGS.

  First, the surface side of the GaN free-standing substrate 31 obtained in Example 2 was attached to a flat ceramic polishing jig 51 using a thermoplastic wax 52. Here, if the warped substrate is forcibly pressed against a flat surface, the substrate may be broken. Therefore, the wax 52 should be inserted into the gap formed between the polishing jig 51 and the central portion of the substrate. The substrate was attached so as to float (step a).

  Next, the back surface side of the substrate was mirror-polished using diamond slurry. Since the back side of the substrate is convex as shown in FIG. 7, only the central portion of the substrate is polished at first, but when the polishing is continued until the central portion of the substrate reaches about 500 μm, the entire back surface is polished. Planarized (step b).

  Therefore, the substrate was once removed from the polishing jig 51, re-attached with the front and back reversed (step c), and the surface was mirror-polished using diamond slurry in the same manner as the back surface. Since the surface side of the substrate has a concave shape, only the outer periphery of the substrate is polished at first, but when the polishing is continued until the thickness of the substrate reaches about 450 μm, the entire surface is polished and completely flat (Step d).

  After the polished substrate was removed from the jig (step e) and washed, the flatness of the substrate surface was measured with a contact-type step meter, and the height difference obtained by scanning 1 mm was 100 nm or less. Further, Ra in the range of 50 μm × 50 μm examined using an atomic force microscope was 8 nm.

  The GaN free-standing substrate 33 obtained in Example 3 was planarized using the polishing process shown in FIGS.

  First, the surface side of the GaN free-standing substrate 33 obtained in Example 3 was attached to a flat ceramic polishing jig 51 using a thermoplastic wax 52. Here, if the warped substrate is forcibly pressed against a flat surface, the substrate may be cracked, so that wax may enter the gap formed between the polishing jig 51 and the outer periphery of the substrate, The substrate was attached so as to float (step a). Since the center of the substrate surface has a slightly convex shape, the substrate is inclined with respect to the surface of the jig so that the wax is evenly placed in the gap formed between the polishing jig and the outer periphery of the substrate. The pasting work was done with care so that there was not.

  After the substrate was attached to the polishing jig, the back surface side of the substrate was mirror-polished using diamond slurry (step b). Since the substrate has a convex shape on the back side as shown in FIG. 8, only the central portion of the substrate is polished at first, but when the polishing is continued until the central portion of the substrate reaches about 550 μm, the entire back surface is polished. And flattened.

  Therefore, the substrate was once removed from the polishing jig, re-attached with the front and back reversed (step c), and then the surface was mirror-polished using diamond slurry in the same manner as the back surface. Since the surface side of the substrate has a slightly convex shape, only the center of the substrate is polished at first, but when the polishing is continued until the thickness of the substrate reaches about 500 μm, the entire surface is completely polished. (Step d).

After the polished substrate was removed from the jig (step e) and washed, the flatness of the substrate surface was measured with a contact-type step meter, and the height difference obtained by scanning 1 mm was 100 nm or less. Further, Ra in the range of 50 μm × 50 μm examined using an atomic force microscope was 7 nm.
[Comparative Example 3]

  Using the same polishing process as in Example 4, an attempt was made to planarize the GaN free-standing substrate 41 obtained in Comparative Example 2. The surface side of the GaN free-standing substrate obtained in Comparative Example 2 was attached to a flat ceramic polishing jig using a thermoplastic wax. Forcing the warped substrate against a flat surface may cause the substrate to break, so the wax should be placed in the gap between the polishing jig and the center of the substrate to float the substrate. At this time, an attempt was made to mirror-polish the back side of the substrate using diamond slurry, but immediately after the polishing was started, a crack occurred on the substrate.

  As shown in FIG. 6, the back side is largely warped in a convex shape, and the amount of wax entering the gap between the polishing jig and the substrate surface is large. Therefore, when the polishing jig is pressed against the polishing platen, the wax is elastically deformed. Thus, it was considered that stress was applied to the substrate and cracks occurred without resisting it.

  As described above, the present invention has been described in detail based on the embodiments. However, these are exemplifications, and various modifications can be made to combinations of these processes, and such modifications are also within the scope of the present invention. This will be understood by those skilled in the art. For example, in this embodiment, the growth is performed such that the crystal surface after growth is substantially flat. However, it is easily conceivable as a modified example that the back surface of the substrate is made flat. In addition, in the polishing process, all or part of the portion of the crystal that is assumed to be scraped off by polishing is polished in a material that is different from the substrate material and that facilitates flattening of the growth interface, or in a later process. Variations such as crystal growth by replacing with an easy material can be easily considered. Further, in the embodiments, the growth of a GaN single layer is taken as an example, but it is also possible to apply to other materials such as GaAs and AlGaN, or a multilayer film combining them.

1 is a schematic diagram illustrating a cross-sectional shape of a semiconductor substrate according to Example 1. FIG. 6 is a schematic diagram showing a cross-sectional shape of a semiconductor substrate according to Comparative Example 1. FIG. It is a process flow figure showing a manufacturing process of a GaN self-supporting substrate. 6 is a schematic diagram showing a cross-sectional shape of a self-supporting substrate according to Example 2. FIG. 6 is a schematic diagram showing a cross-sectional shape of a self-supporting substrate according to Example 3. FIG. 6 is a schematic diagram showing a cross-sectional shape of a self-supporting substrate according to Comparative Example 2. FIG. 6 is a process flow diagram showing a polishing process performed on a GaN free-standing substrate obtained in Example 2. FIG. 10 is a process flow diagram showing a polishing process performed on a GaN free-standing substrate obtained in Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 11 Sapphire substrate 12 GaN epitaxial growth layer 20 Semiconductor substrate 21 Sapphire substrate 22 Si doped GaN layer 23 Ti thin film 24 Void formation GaN layer 25 Hole formation TiN layer 26 GaN layers 30, 31, 33, 41 GaN freestanding substrate 51 Jig 52 Wax

Claims (22)

  A crystal growth system semiconductor substrate that generates warpage by forming an epitaxial growth layer on a different substrate, and that the thickness of the epitaxial growth layer has a distribution so as to cancel out the influence of the warpage in advance. A characteristic semiconductor substrate.   A crystal growth system semiconductor substrate in which an epitaxial growth layer is formed on a different substrate to cause a convex warpage on the epitaxial growth surface side, and the thickness of the epitaxial growth layer is set so as to cancel out the influence of the warp in advance. A semiconductor substrate, wherein the semiconductor substrate is formed to be larger at an end portion than at a central portion on a different substrate.   A semiconductor substrate of a crystal growth system in which an epitaxial growth layer is formed on a heterogeneous substrate to cause a concave warpage on the epitaxial growth surface side, and the thickness of the epitaxial growth layer is set so as to cancel the influence of the warp in advance. A semiconductor substrate, wherein the semiconductor substrate is formed so as to be smaller at an end portion than at a central portion on a different substrate. The heterogeneous substrate is sapphire, and the epitaxial growth layer is a semiconductor represented by In _x Ga _y Al _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A semiconductor substrate according to any one of claims 1 to 3.   A self-supporting substrate of a material system that warps only in an epitaxial growth layer, wherein the thickness of the epitaxial growth layer is distributed so as to cancel out the influence of the warp in advance.   A material-based self-supporting substrate that generates a convex warp on the epitaxial growth surface side only by the epitaxial growth layer, and the thickness of the epitaxial growth layer is larger than the center portion on the heterogeneous substrate so as to cancel out the influence of the warp in advance. A self-supporting substrate that is formed so as to be large.   A self-supporting substrate of a material system in which only the epitaxial growth layer causes a concave warp on the epitaxial growth surface side, and the thickness of the epitaxial growth layer is larger than the center portion on the heterogeneous substrate so as to cancel out the influence of the warp in advance. A self-supporting substrate that is formed to be small in size.   In a crystal growth system in which a semiconductor substrate having an epitaxial layer is warped by growing an epitaxial layer on a heterogeneous substrate, the epitaxial layer is distributed with a thickness distribution so as to cancel out the influence of the warp in advance. A method of manufacturing a semiconductor substrate, comprising growing a layer.   In a crystal growth system in which an epitaxial layer is grown on a heterogeneous substrate so that a semiconductor substrate having an epitaxial layer warps convexly toward the epitaxial growth surface, the epitaxial layer is formed so as to cancel out the influence of the warp in advance. A method of manufacturing a semiconductor substrate, wherein the growth is performed so that the film thickness is larger at the end than at the center of the different substrate.   In a crystal growth system in which a semiconductor substrate having an epitaxial layer is warped concavely on the epitaxial growth surface side by growing an epitaxial layer on a heterogeneous substrate, the epitaxial layer is formed so as to cancel out the influence of the warp in advance. A method of manufacturing a semiconductor substrate, wherein the growth is performed such that the film thickness is smaller at the end than at the center of the different substrate.   In a material system in which a free-standing substrate made of the epitaxial layer is warped when the heterogeneous substrate is peeled off after the epitaxial layer is grown on the heterogeneous substrate, the film thickness is distributed so as to cancel out the influence of the warp in advance. A method of manufacturing a self-supporting substrate, wherein the epitaxial layer is grown while having a thickness.   After the epitaxial layer is grown on the heterogeneous substrate, when the heterogeneous substrate is peeled off, the influence of the warp is canceled in advance in a material system in which the self-standing substrate made of the epitaxial layer warps convexly toward the epitaxial growth surface. As described above, the method of manufacturing a self-supporting substrate is characterized in that the epitaxial growth layer is formed so that the film thickness of the epitaxial growth layer is larger at the end than at the center on the heterogeneous substrate.   In a material system in which, after growing an epitaxial layer on a heterogeneous substrate, when the heterogeneous substrate is peeled off, a self-supporting substrate made of the epitaxial layer causes a warp that causes a warp in a recess on the epitaxial growth surface side. A method for manufacturing a self-supporting substrate, wherein the epitaxial growth layer is formed so that the film thickness of the epitaxial growth layer is smaller at the end than at the center on the heterogeneous substrate so as to cancel out the influence in advance.   The surface of the semiconductor substrate according to any one of claims 1 to 4 or the self-standing substrate according to any one of claims 5 to 7 is bonded to a polishing jig by attaching the surface with the smaller warpage to the polishing jig. A method for polishing a substrate, comprising polishing a larger surface flatly.   15. The method for polishing a substrate according to claim 14, further comprising reversely reversing the front and back surfaces and mirror-polishing the surface having the smaller warpage.   A semiconductor substrate of a crystal growth system in which warpage is generated by forming an epitaxial growth layer on a different substrate, wherein the warpage of the surface of the epitaxial growth layer is smaller than the warpage of the rear surface of the different substrate. .   A self-supporting substrate made of a material system that warps only by an epitaxial growth layer, wherein the warpage of the substrate surface is smaller than the warpage of the back surface of the substrate.   A method for polishing a substrate, comprising: attaching the surface of a semiconductor substrate according to claim 16 or a self-standing substrate according to claim 17 to a polishing jig, and polishing the back surface flatly.   The surface of the semiconductor substrate according to claim 16 or the self-standing substrate according to claim 17 is attached to a polishing jig, and the back surface is polished flat, and then the polishing surface is reversely applied to mirror-polish the surface. A method for polishing a substrate, comprising:   At least a step of depositing a metal film on a substrate on which a single crystal gallium nitride film is grown on a sapphire substrate, and heat-treating the substrate on which the metal film is deposited in an atmosphere containing hydrogen gas or hydride gas, Forming a void in the gallium film; depositing single crystal gallium nitride thereon; and removing the sapphire substrate from the single crystal gallium nitride substrate to obtain a self-supporting gallium nitride substrate; In the method of manufacturing a self-supporting substrate of the system in which the self-supporting gallium nitride substrate is warped so that the central portion is concave on the single crystal gallium nitride growth surface side, the step of depositing the single crystal gallium nitride includes the self-supporting step. In order to cancel the influence of the warped of the gallium nitride substrate, it is deposited in advance so that the film thickness is larger at the center than at the edge. Production method.   21. The method of manufacturing a self-supporting substrate according to claim 20, further comprising: affixing the epitaxial growth surface to a polishing jig among the epitaxial growth surface and the opposite surface of the self-supporting substrate and polishing the opposite surface flatly.   Furthermore, of the epitaxial growth surface of the self-supporting substrate and the opposite surface, first, the epitaxial growth surface is attached to a polishing jig and the opposite surface is polished flat, and then the polishing surface is reversed and the epitaxial growth surface is mirror-polished. The method for manufacturing a self-supporting substrate according to claim 20.

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