JP2001168042A - Method of manufacturing semiconductor crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing semiconductor crystal by which a large-area GaN crystal can be manufactured and various problems caused by ELO growth using an ordinary mask layer can be avoided, and then, the manufacturing process of the GaN crystal can be simplified. SOLUTION: In the method of manufacturing semiconductor crystal, a substrate 1 having a recessed and projecting growing surface and carrying a mask 3 on the recessed surface 12 is used as shown in Fig. (a). When vapor phase growth is performed by using the substrate 1, crystal growth occurs only from the tops of the projecting sections 11 due to presence of the mask 3. As shown in Fig. (b), therefore, crystal units 20 occur on the tops of the projecting sections 11 when the crystal growth is started and, as the crystal growth continues, films horizontally grown from the tops of the projecting sections 11 are joined together and, finally, a semiconductor crystal 2 is grown so as to cover the recessed and projecting sections of the substrate 1 by leaving cavity sections 13 in the recessed sections as shown in Fig. (c). Thereafter, the crystal 2 is separated from the substrate 1 at the cavity sections 13 as shown in Fig. (d).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor crystal and a method for fabricating the same, and more particularly to a structure and a method which are useful when a semiconductor material in which dislocation defects easily occur is used.

[0002]

2. Description of the Related Art When a GaN-based material is crystal-grown, Ga
N-type materials have no lattice-matched substrate, so sapphire,
A substrate that does not lattice match, such as SiC, spinel, or recently Si, is used. However, during the GaN film produced due to the fact that no lattice matching are present 10 ¹⁰ / cm ² things dislocation. In recent years, high-luminance light-emitting diodes, semiconductor lasers, and the like have been realized, but a reduction in dislocation density is desired in order to improve characteristics.

[0003]

In order to prevent defects such as dislocations due to differences in lattice constants or the like from occurring, the same crystal as the material used for crystal growth may be used. For example, a GaN substrate may be used for crystal growth of a GaN-based semiconductor, but a large GaN substrate has not yet been obtained, and sapphire or the like is actually used as the substrate. In recent years, when performing vapor phase growth on a GaN underlayer grown on sapphire, a partial mask is provided on the underlayer, and selective growth is performed to allow lateral crystal growth and reduce the dislocation density. A method for obtaining a suitable crystal has been proposed (for example, JP-A-10-312971). Although a GaN crystal can be obtained by growing this film thickly and separating and removing the substrate, a problem such as cracking or cracking of the substrate due to a difference in lattice constant or a difference in coefficient of thermal expansion causes a large area substrate. Was not obtained.

In addition, the above-mentioned method requires a step of growing a buffer layer material and a GaN-based material on a sapphire base substrate, and once removing the groove from a growth furnace and performing a groove process, and then performing a crystal growth again. The process becomes complicated and new problems arise. There was a problem that the number of work steps increased and the cost increased.

[0005] In view of the above problems, the present invention provides a large area GaN.
The purpose is to obtain crystals. It is another object of the present invention to avoid various problems caused by ELO growth using a normal mask layer and to simplify a manufacturing process.

[0006]

According to the method of manufacturing a semiconductor crystal of the present invention, a crystal growth surface of a substrate is formed as an uneven surface, and the crystal is grown exclusively from a portion above the protrusion on the uneven surface by a vapor phase growth method. The uneven surface is covered with a semiconductor crystal, and a stacked body having a cavity between the semiconductor crystal layer and the concave portion on the uneven surface is formed, and the semiconductor crystal and the substrate are separated at the hollow portion. It is a feature. In this case, the semiconductor crystal is InGaAlN
It is desirable that

It is preferable that the projection on the crystal growth surface of the substrate is a projection having a parallel stripe shape. Further, the semiconductor crystal is InGaAlN, and the longitudinal direction of the stripe is (1-10) of InGaAlN.
0) More preferably, the stripe is perpendicular to the plane.

In another method of manufacturing a semiconductor crystal according to the present invention, the crystal growth surface of the substrate is formed as an uneven surface, and the crystal is grown exclusively from above the convex portion of the uneven surface by a vapor phase growth method. A preliminary semiconductor crystal is formed to cover the surface of the preliminary semiconductor crystal, and the surface of the preliminary semiconductor crystal is formed as an irregular surface, and the irregular surface is covered with the semiconductor crystal by performing crystal growth exclusively from above the convex portion of the preliminary semiconductor crystal irregular surface, A laminated body having a cavity between the semiconductor crystal layer and the concave portion on the uneven surface is produced, and the semiconductor crystal is separated from the laminated body in the cavity. In this case, the step of forming the preliminary semiconductor crystal may be repeated a plurality of times.

[0009]

According to the present invention, in growing a semiconductor crystal,
The first point is that an uneven surface is provided on a substrate in which even a buffer layer or the like is not formed, and a substrate for lateral growth capable of forming a substantially low dislocation density region is provided in advance from the beginning of crystal growth. It has the characteristics of When vapor-phase growth is performed using such a substrate, the raw material diffuses over the entire surface of the substrate in the initial stage of growth, but crystal growth is unlikely to occur on the concave portion, so that the growth on the convex portion becomes dominant, and thus the growth from the convex portion Semiconductor crystal layer. In the growth of the projection, so-called lateral growth occurs in the direction parallel to the C axis, and the formation of a low dislocation density region is achieved. Thus, the growth of the semiconductor crystal having the low dislocation density region can be performed only once.

In addition, as a result of suppressing the growth in the recess, a cavity is formed between the substrate and the semiconductor crystal. Therefore, the second feature is that since the contact area between the substrate and the semiconductor crystal can be reduced, distortion due to a difference in lattice constant and a difference in thermal expansion coefficient can be significantly reduced. For this reason, generation of cracks and cracks can be suppressed, and a large-area semiconductor crystal can be obtained.
In addition, since the strain is concentrated on a contact portion between the substrate and the semiconductor crystal, the strain is characterized in that the substrate and the semiconductor crystal can be efficiently separated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. 1A to 1D are cross-sectional views illustrating a method for manufacturing a semiconductor crystal according to the present invention. In the drawing, reference numeral 1 denotes a substrate, and 2 denotes a semiconductor crystal grown on the substrate 1 by vapor phase. A convex portion 11 and a concave portion 12 are formed on the crystal growth surface of the substrate 1, and the crystal growth is performed exclusively from above the convex portion 11. The recess 12 is covered with a mask 3 that cannot substantially grow from the layer.

The substrate referred to in the present invention is a substrate serving as a base for growing various semiconductor crystal layers, in which a buffer layer or the like for lattice matching has not been formed yet. Such substrates include sapphire (C plane, A plane, R plane), SiC (6H, 4H, 3C),
GaN, Si, spinel, ZnO, GaAs, NGO, and the like can be used, but other materials may be used as long as they correspond to the object of the invention. Also, the substrate may not be in a certain plane orientation, but may be off from that plane.

[0013] As the semiconductor crystal 2 is grown on the substrate 1 can use various semiconductor materials, Al _x Ga
_{In 1-xy} In _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), GaN, In _0.5 Ga _0.05 N, etc. in which the composition ratio of x and y is changed can be exemplified.

Convex part 11 formed on the crystal growth surface of substrate 1
It is effective to make the shape such that crystal growth is performed exclusively from above. The phrase “crystal growth is performed exclusively from the upper part” refers to a state in which crystal growth can be predominantly performed at the apex or top surface of the convex portion 11 and in the vicinity thereof. This means that crystal growth at the convex portion 11 becomes dominant eventually.

The mask 3 formed on the concave portion 12 only needs to be made so as not to substantially grow from the layer. The phrase "can not substantially grow from that layer" means a state in which crystal growth is unlikely to occur.
May grow on the mask 3, but the crystal growth of the projections 11 will eventually become dominant. That is, the low dislocation density region may be formed by lateral growth starting from the upper part. Thereby, the EL which requires the conventional mask
The same effect as O can be obtained. As such a mask 3 formed on the concave portion 12, for example, SiO ₂ , S
iN _x , TiO ₂ , ZrO _{2 and the} like can be used. It is also possible to adopt a laminated structure of these materials. Although an example in which the mask 3 is formed in the concave portion 12 is shown here, a substrate having only the uneven shape without forming the mask 3 may be used.
Hereinafter, the method for manufacturing a semiconductor crystal according to the present invention will be described step by step with reference to FIGS.

FIGS. 1 and 2 are cross-sectional views of a projection formed in a stripe shape. FIG. 1 illustrates a case where the groove depth (height of the convex portion) h is deeper than the groove width B as shown in FIG. In this case, the source gas does not sufficiently reach the concave portion 12 and its vicinity, and since the concave portion 12 is covered with the mask 3, crystal growth occurs only from above the convex portion 12. In FIG. 1B, reference numeral 20 denotes a crystal unit at the start of the crystal growth. Under such circumstances, when the crystal growth continues, the films grown in the lateral direction are connected starting from the upper part of the convex part 11, and the substrate 1 is formed while the cavity 13 is left in the concave part as shown in FIG. The semiconductor crystal 2 is formed so as to cover the uneven surface. In this case, a low dislocation density region is formed in the portion grown in the lateral direction, that is, in the upper part of the concave portion 12, thereby improving the quality of the formed film.

When a laminate comprising the substrate 1 and the semiconductor crystal 2 and having the cavity 13 therebetween is manufactured in this manner, as shown in FIG. That is, by separating the substrate 1 and the semiconductor crystal 2 at the protruding portions 11 of the substrate 1, the required low-dislocation semiconductor crystal 2 can be obtained. As a method of this separation, a method such as polishing is typically exemplified.
There is no particular limitation as long as the semiconductor crystal can be taken out.

FIG. 2 shows groove depth (groove height) with respect to groove width B.
The case where h is very shallow or the case where the groove width B is very large with respect to the width A of the projection 11 are illustrated (see FIG. 2A). In this case, since the source gas can reach the mask 3 in the concave portion 12 and its vicinity, the growth in the concave portion 12 may occur. However, the growth rate is much slower than the growth at the upper part of the protrusion. This is because the rate at which the raw material reaching the mask 3 is desorbed again into the gas is large. Thus,
Lateral growth from the upper part of the convex part 11 occurs, and FIG.
As shown in (1), crystal units 20 are generated on the upper part of the convex part 11 and on the surface of the concave part 12. Under these circumstances,
When the crystal growth continues, the films grown in the lateral direction are connected starting from the upper part of the convex portion 11, and the semiconductor crystal 2 is formed so as to cover the uneven surface of the substrate 1 as shown in FIG. become. In this case, the proportion of the low dislocation density region is large since the portion grown in the lateral direction starting from the convex portion 11 is larger than that in FIG. 1, and the quality of the manufactured semiconductor crystal 2 is higher than that in the example of FIG. Will be achieved. After the stacked body is manufactured in this manner, as shown in FIG. 2D, the substrate 1 and the semiconductor crystal 2 are separated at the portion where the cavity 13 exists, that is, at the portion of the convex portion 11 of the substrate 1. Thus, the required dislocation-reduced semiconductor crystal 2 can be obtained.

In the present invention, there is no particular limitation as long as such a convex portion 11 is used, and various shapes can be adopted. Specifically, when the groove depth (projection height) h is larger than the groove width B as described above, when the groove depth (projection height) h is smaller than the groove width B, the groove width is further increased. Various combinations can be performed, such as when the groove depth (height of the convex portion) h is very shallow with respect to B, or when the groove width B is very large with respect to the width A of the convex portion 11. In particular, it is preferable that the groove width B is very large with respect to the width A of the convex portion 11 because the portion grown in the lateral direction starting from the upper portion of the convex portion 11 increases and the ratio of the low dislocation density region is increased.

The mode of forming such an uneven surface is as follows.
Examples include island-shaped dotted projections, stripe-shaped projections, lattice-shaped projections, and projections in which the lines forming these are curved. Among these projections, the one in which the stripe-shaped projections are provided is preferable because the manufacturing process can be simplified and a regular pattern can be easily manufactured. The longitudinal direction of the stripe may be arbitrary, but when the material to be grown on the substrate is GaN,
The <11-20> direction and the <1-100> direction of the GaN-based material are preferable. In particular, in the case of <1-100> direction,
Since the oblique facet such as the {1-101} plane is hard to be formed, the lateral growth becomes faster. As a result, it is particularly preferable that the uneven surface is quickly covered.

As shown in FIG. 1, according to the method for manufacturing a semiconductor crystal according to the present invention, the cavity 13 is provided between the substrate 1 and the semiconductor crystal 2, and the contact area between the two can be reduced. 2 can reduce the distortion caused by the lattice constant difference and the thermal expansion coefficient difference. The reduction of the distortion has an effect of significantly reducing the warpage that occurs when sapphire is used as the substrate 1 and a GaN-based material as the semiconductor crystal 2 is grown thick thereon. In particular, in the conventional method, when a GaN-based material is crystal-grown on a substrate, there is a problem that warpage and cracks are generated due to a difference in thermal expansion coefficient and high-quality crystal growth cannot be performed. This problem can be reduced by the reduction effect.

By utilizing the fact that the contact area between the substrate 1 and the semiconductor crystal 2 grown thereon can be reduced as described above,
When the film is grown to a thickness of 10 μm or more, preferably 100 μm or more, stress concentrates on this small contact portion, so that the substrate 1 and the semiconductor crystal 2 are easily separated from this portion. Thus, a substrate such as GaN can be manufactured.

The case where only one semiconductor layer 2 is grown on the substrate 1 has been described above, but a similar process may be repeated twice to reduce dislocation defects. That is, as shown in FIG. 3, a mask 3a for the projections 11a and the depressions is provided on the substrate 1 by the same method as described above, and first the crystal growth of the preliminary semiconductor layer 2a is performed so as to cover the uneven surface. The surface of the preliminary semiconductor layer 2a is processed to have an uneven surface, and the preliminary semiconductor layer 2a is formed thereon by vapor phase growth.
A necessary semiconductor crystal 2 can be formed by providing a mask 3 so that the crystal grows exclusively from the upper part of the convex portion 11 of FIG. In this case, in particular, if the convex portion 11a of the substrate 1 and the position of the convex portion 11 formed on the preliminary semiconductor layer 2a are shifted in the vertical direction, the semiconductor crystal 2 has a position above the convex portion 11a of the preliminary semiconductor layer 2a. Many dislocations will not propagate. That is, with such a configuration, the semiconductor crystal 2
The entire region can be a low dislocation density region, and a higher quality semiconductor layer can be obtained. Thereafter, the required semiconductor crystal 2 can be taken out by separating the semiconductor crystal 2 from the stacked body at the portion where the cavity 13 exists.

In the above embodiment, the spare semiconductor layer 2a
May be further formed as an uneven surface, and a second preliminary semiconductor layer similarly formed by a vapor deposition method may be formed thereon. Or, by repeating the same process,
A plurality of spare semiconductor layers may be formed in a multiplex manner. With such a configuration, it is possible to gradually reduce the number of dislocations that propagate each time a layer is stacked without intentionally adjusting the position of the upper and lower convex portions as described above. The quality of the crystal can be further improved.

The projections are formed by, for example, patterning according to the projection shape using ordinary photolithography technology,
It can be manufactured by performing an etching process using an IE technique or the like.

As a method of growing a semiconductor layer on a substrate, HVPE, MOCVD, MBE or the like may be used. When forming a thick film, the HVPE method is preferable, but when forming a thin film, the MOCVD method is preferable.

The growth conditions (such as gas type, growth pressure, growth temperature, etc.) for growing a semiconductor layer on a substrate may be properly selected depending on the purpose as long as the effects of the present invention can be obtained.

[0028]

[Example 1] Patterning of a photoresist on a c-plane sapphire substrate (width: 2 μm, period: 6 μm,
Stripe orientation: The stripe stretching direction is <11-20> direction of the sapphire substrate, and RIE (Reactive Ion
Etching was performed in a rectangular cross section to a depth of 2 μm using an etching device. Subsequently, a 0.1 μm SiO ₂ film was deposited on the entire surface of the substrate, and then the photoresist and the SiO ₂ film deposited thereon were removed by a lift-off process. Thus, the mask layer was applied to the concave portions of the substrate. Thereafter, the substrate was mounted on a MOVPE apparatus, and the temperature was raised to 1100 ° C. in a hydrogen atmosphere to perform thermal etching. Then raise the temperature to 500
The temperature was lowered to 0 ° C., and trimethylgallium (hereinafter referred to as TMG) was used as a Group 3 raw material, and ammonia was flown as an N raw material to grow a GaN low temperature buffer layer. Then the temperature is set to 1000 ℃
Then, TMG / ammonia was flowed as a raw material and silane was flowed as a dopant for 10 h, and an n-type GaN layer was grown to 30 μm.

Observation of the obtained GaN crystal showed that although it was slightly warped, it had no crack or crack and had a mirror surface. Next, when the cross section after the growth is observed, although traces of growth are seen on the substrate concave mask, the concave and convex surface of the substrate 1 is covered with the cavity 13 left in the concave as shown in FIG. 2C. And a flat GaN crystal.

[Comparative Examples 1 and 2] For comparison, an ordinary c
A GaN layer formed on a planar sapphire substrate under the same growth conditions (Comparative Example 1) and a GaN film (Comparative Example 2) grown by ELO using the same pattern of SiO ₂ mask were prepared. When the sample was taken out of the apparatus after the growth, the sample grown without any treatment was broken into small pieces and had many cracks. In addition, it was confirmed that the ELO-grown one did not have any cracks, but had large warpage and many cracks.

An operation of separating the GaN crystal obtained in Example 1 and the GaN crystal obtained by ELO growth in Comparative Example 2 from the substrate was performed. First, the GaN crystal face was turned down and fixed with wax. Thereafter, the sapphire substrate was removed by polishing. The GaN crystal grown by ELO in Comparative Example 2 could not be uniformly polished with sapphire due to large warpage. After polishing, the GaN crystal was peeled off from the wax.
Although the GaN crystal was taken out from the sample manufactured in step 2, the sample grown by ELO in Comparative Example 2 had the GaN crystal broken into small pieces.

[Example 2] In Example 1, a GaN crystal in which a sapphire substrate was not separated was used as a preliminary crystal, and a main crystal was grown thereon. First, photoresist patterning on the GaN preliminary crystal (width: 2 μm, period: 6 μm)
m, stripe orientation: <1-100> of a GaN substrate), and etched by a RIE apparatus in a square cross section to a depth of 2 μm. At this time, the patterning was performed such that a portion of the preliminary crystal having many dislocations became a concave portion. Subsequently, a 0.1 μm SiO ₂ film is deposited on the entire surface of the substrate, and thereafter, a photoresist and a Si film
The O ₂ film was removed. After such processing, the substrate is mounted on a MOVPE device and the substrate is placed in a mixed atmosphere of nitrogen, hydrogen and ammonia for 10 minutes.
The temperature was raised to 00 ° C. Thereafter, TMG / ammonia was flowed as a raw material and silane was flowed as a dopant to grow an n-type GaN layer. The growth time at that time was set to a time corresponding to the growth of 4 μm in the GaN growth in the case where normal unevenness was not applied. Thereafter, the sample was transferred to an HVPE apparatus and grown to obtain a GaN crystal having a total film thickness of 200 μm.

Thereafter, the sapphire substrate was polished and removed in the same manner as in Example 1 to obtain a GaN crystal. Evaluation of the pits on the surface after the growth revealed that the pits were reduced to 8 × 10 ⁵ cm ⁻³ . Thus, it was confirmed that a high-quality GaN crystal having a low dislocation density can be obtained by repeating this example.

[0034]

According to the method for manufacturing a semiconductor crystal of the present invention as described above, a convex portion is provided on a substrate, and the concave portion is covered with a mask which cannot substantially grow from the layer. Lateral growth capable of forming a substantially low dislocation density region can be preferentially performed from the beginning of crystal growth. In addition, since the contact area between the substrate and the crystal growth layer is small, a large-area semiconductor crystal layer can be manufactured by the effect of suppressing residual strain.

Therefore, the normal growth and E for forming the mask layer are performed.
The problem of large area growth that could not be sufficiently achieved by the thick film growth of LO, the generation of new defects in the united portion of the lateral growth portion due to the micro tilting of the axis, and the problem of autodoping can be solved. In addition, by simply performing the above-described processing on the substrate, the growth of the buffer layer and the growth of the semiconductor crystal layer such as the light-emitting portion can be continuously performed in a single growth. In particular, since the growth in the concave portion can be suppressed, there is an advantage that the efficiency of lateral growth is improved. As described above, the present invention has extremely useful effects in terms of increasing the area of the semiconductor crystal, improving the characteristics, and reducing the cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a method for manufacturing a semiconductor crystal according to the present invention.

FIG. 2 is a cross-sectional view for explaining another embodiment of the method of manufacturing a semiconductor crystal according to the present invention.

FIG. 3 is a cross-sectional view for explaining another embodiment of the method for manufacturing a semiconductor crystal according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 11 Convex part 12 Concavity 13 Cavity part 2 Semiconductor crystal 2a Spare semiconductor crystal 3 Mask

Continued on the front page (72) Inventor Masahiro Koto 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Itami Works F-term (reference) 5F041 AA40 CA23 CA34 CA40 CA46 CA65 CA74 CA75 5F045 AA04 AB14 AB17 AB18 AB32 AC01 AC08 AC12 AD09 AD14 AF02 AF03 AF04 AF09 AF11 AF13 BB08 BB12 DA53 DB02 EB15 HA03 5F073 CA07 CB05 DA05 DA25 DA35

Claims (6)

[Claims] An uneven surface is formed on a crystal growth surface of a substrate, and crystal growth is performed exclusively from a portion above a convex portion of the uneven surface by a vapor phase growth method, so that the uneven surface is covered with a semiconductor crystal. A method of manufacturing a semiconductor crystal, comprising: preparing a laminate having a cavity between a layer and a concave portion on the uneven surface, and separating a semiconductor crystal and a substrate in the cavity. 2. The method according to claim 1, wherein said semiconductor crystal is InGaAlN. 3. The method according to claim 1, wherein the projections on the crystal growth surface of the substrate are projections having a parallel stripe shape. 4. The semiconductor device according to claim 1, wherein the semiconductor crystal is InGaAlN, and a longitudinal direction of the stripe is perpendicular to a (1-100) plane of the InGaAlN.
3. The method for producing a semiconductor crystal according to 3. 5. A preliminary semiconductor crystal that covers the irregular surface by forming a crystal growth surface of the substrate as an irregular surface and performing crystal growth exclusively from a portion above the convex portion in the irregular surface by a vapor phase growth method. The surface of the semiconductor crystal is an uneven surface, and the uneven surface is covered with the semiconductor crystal by performing crystal growth exclusively from the upper part of the convex portion in the preliminary semiconductor crystal uneven surface, and the semiconductor crystal layer and the concave portion in the uneven surface are formed. A method of manufacturing a semiconductor crystal, comprising: forming a stacked body having a cavity between them, and separating the semiconductor crystal from the stacked body in the hollow part. 6. The method of manufacturing a semiconductor crystal according to claim 5, wherein the step of forming a spare semiconductor crystal is repeated a plurality of times.