JPH04147613A - Crystal growing substrate - Google Patents

Abstract

PURPOSE:To provide a crystal growing substrate excellent in growing low dislocation density crystal by forming a groove in the opposite side surface to the crystal growing surface. CONSTITUTION:A crystal growing substrate 11 is adapted to include grooves 12 for making flexible an opposite side surface to a crystal growing surface 11a formed on the surface thereof, i.e., the back surface 11b thereof. The grooves 12 each having V-shaped cross section and having a depth not cracked upon treating the crystal growing substrate 11 are coaxially formed in an equal interval substantially over the whole surface. The grooves 12 formed as such reduce the rigidity of the crystal growing substrate 11 and ensure flexibility to the crystal growing substrate 11. Further, in the case where a crystal is grown on the crystal growing surface 11a, stress applied to the back surface 11b side of the crystal growing substrate 11 is lower substantially over the whole surface of the crystal growing substrate 11 than that to the grown crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a crystal growth substrate for growing a crystal of compound semiconductor or the like on a crystal growth substrate of silicon or the like.

<Prior art> A silicon substrate is used as a crystal growth substrate, and a compound semiconductor gallium arsenide (Ga) is grown as a crystal on this silicon substrate.
When a film is formed by epitaxial growth of As), the GaAs film is subjected to tensile stress from the silicon substrate during the cooling process after the GaAs film is formed.

In other words, due to the difference between the coefficient of thermal expansion of the GaAs film and the coefficient of thermal expansion of the silicon substrate, the contraction rate of the GaAs film during the cooling process becomes larger than that of the silicon substrate. Therefore, the GaAs film tries to pull the silicon substrate toward its center.

However, since the silicon substrate has sufficient rigidity than the GaAs film, the GaAs film is pulled outward by the silicon substrate, so that tensile stress is generated in the GaAs film.

At this time, in an attempt to relieve the tensile stress generated in the GaAs film, dislocations occur or move within the GaAs film. In particular, dislocations occur at crystal growth temperatures (approximately 700°
C) occurs more frequently during the cooling process to approximately 350'C. Therefore, even if few dislocations occur at the crystal growth temperature, many dislocations occur during the cooling process of the crystal growth substrate.

Conventionally, in order to reduce the dislocations generated in GaAs 1ll, approximately 900
The dislocation density in the GaAs film was reduced by repeatedly performing annealing at a temperature of .degree. Alternatively, a strained superlattice such as InGaAs/GaAs is formed on a silicon substrate, GaAs1llj is epitaxially grown on it, and the tensile stress generated in the grown GaAs film is relaxed by the strained superlattice. Was.

Furthermore, GaAs films have been formed by combining these methods.

<Problems to be Solved by the Invention> However, in any of the above cases, it is difficult to reduce the tensile stress in the GaAs film caused by the difference in thermal expansion between the GaAs film and the silicon substrate, and the dislocation density in 1L of GaAs is reduced to 106/1. It is very difficult to reduce the thickness to less than 1 cm.

As a result, when a semiconductor device such as a semiconductor laser device is formed using GaAs having a dislocation density of 10-cm'' or higher, carriers tend to concentrate on the dislocations in the CaAs film, and the semiconductor device lifespan becomes shorter.

The present invention is a method made to solve the above problems, and an object of the present invention is to provide a crystal growth substrate that is excellent for growing crystals with a low dislocation density.

<Means for Solving the Problems> The present invention has been accomplished in order to achieve the above objects.

In other words, it is a crystal growth substrate on which a crystal growth surface for growing crystals such as compound semiconductors is formed, and grooves are formed on the surface opposite to this crystal growth surface to make the crystal growth substrate flexible. It has the following.

<Function> The crystal growth substrate described above has grooves formed on the surface opposite to the crystal growth surface, thereby imparting flexibility to the crystal growth substrate and relieving tensile stress generated in the grown crystal.

In other words, in the process of growing a crystal on the crystal growth surface formed on the surface of this crystal growth substrate and then cooling the crystal growth substrate, the thermal expansion coefficient of the grown crystal is larger than that of the crystal growth substrate. , the grown crystal shrinks more than the crystal growth substrate.

Therefore, compressive stress acts on the crystal growth side of the crystal growth substrate, and tensile stress acts on the back side. Since this tensile stress is relieved by the grooves formed in the crystal growth substrate, the crystal growth substrate is warped toward the crystal growth surface due to the compressive stress. Further, the rigidity of the crystal growth substrate is reduced by the grooves, and the crystal growth substrate has flexibility. Therefore, the crystal growth substrate is warped by the compressive stress acting on the crystal growth substrate.

Therefore, since almost no tensile stress is applied to the grown crystal, the crystal growth substrate reduces the occurrence of dislocations in the grown crystal.

<Example> An example of the present invention is shown in the rear view in FIG. 1 and A in FIG.
-A will be explained using an enlarged sectional view.

As shown in the figure, the crystal growth substrate 11 has a surface opposite to a crystal growth surface 11a formed on its surface, that is, a back surface 11b.
Groove 12 (shown as a shaded area in Figure 1) to provide flexibility to the
was formed.

The grooves 12 have a U-shaped cross section, and are formed concentrically at equal intervals over almost the entire surface of the back surface 11b, with a depth that will not break the crystal growth substrate 11 when handled.

The grooves 12 formed in this manner reduce the rigidity of the crystal growth substrate 11 and give the crystal growth substrate 1 flexibility. Furthermore, when a crystal is grown on the crystal growth surface 11a,
The stress that is applied to the back surface 11b of the crystal growth substrate 11 from the grown crystal is relieved over almost the entire surface of the crystal growth substrate 11.

In other words, the direction of stress applied to the crystal growth substrate 11 by the grown crystal is mainly in the radial direction of the crystal growth substrate 11, so in order to relieve this stress, it is necessary to apply stress in the direction perpendicular to the direction in which the stress acts. Forming the groove 12 in the groove 12 is effective in relieving stress.

Therefore, by forming the grooves 12 concentrically, the stress generated on the back surface 11b side of the crystal growth substrate 11 is alleviated. As a result, the flexible crystal growth substrate II warps due to the stress acting on the crystal growth surface la side.

Furthermore, the grooves 12 are not limited to concentric grooves. For example, as shown in FIG. 3, the grooves 12 (hatched portions in FIG. 3) formed on the back surface 11b of the crystal growth substrate 11 may be formed in a lattice shape.

In this case, the stress in the circumferential direction as well as the stress in the radial direction acting on the crystal growth surface 11a side can be relaxed. Therefore, the crystal growth substrate 11 becomes more likely to warp.

Further, the grooves 12 may be formed as spiral grooves, or may be formed as a combination of concentric grooves and radial grooves.

On the other hand, the cross-sectional shape of the groove is not limited to the above-mentioned U-shaped cross-section, and may also be formed, for example, in a ■-shaped cross-section or a square cross-section. In the case of these cross-sectional shapes, the corners of the grooves are formed rounded in order to prevent stress from being concentrated at the corners of the grooves when the crystal growth substrate 11 is warped.

Next, by epitaxial growth method as a crystal growth method,
C of a compound semiconductor as a crystal on the above-mentioned crystalline substrate 11
The operation of the crystal growth substrate 11 when a yaAs film is formed will be explained with reference to FIGS. 4 and 5.

As shown in FIG. 4, a crystal growth substrate 11 is grown using a molecular beam epitaxial apparatus to perform the epitaxial growth method.
GaAs is grown as a crystal on the crystal growth surface 11a. Then, a GaAs film 13 film type 3 is deposited on the crystal growth substrate 11.
Thereafter, the crystal growth substrate 11 is cooled from the GaAs film 13 film type 3 growth temperature (approximately 700° C.) to room temperature.

In this cooling process, as shown in FIG.
Since the thermal expansion coefficient of the three-film type 3 is larger than that of the crystal growth substrate 11, the crystal growth substrate 11 is pulled toward its center.

Therefore, the crystal growth substrate 11 has a GaAs film 13 film type 3.
Due to the force, compressive stress acts on the crystal growth surface 11a side. In particular, since concentric grooves 12 are formed over almost the entire surface of the back surface 11b of the crystal growth substrate 11, the tensile stress acting on the back surface 11b due to the grooves 12 is applied to almost the entire surface of the back surface 11b. will be relaxed over the following period. Therefore, the flexible crystal growth substrate 11 warps almost uniformly due to the compressive stress acting on the crystal growth surface 11a side.

At this time, the restoring force that tries to return to the original state becomes small due to the rigidity of the crystal growth substrate 11, so this restoring force causes Ga
G produced by pulling A s Ill 3
The tensile stress in the aAs film 13 becomes small over almost the entire surface. As a result, the generation of dislocations in the GaAs film 13 is suppressed, and the dislocation density becomes less than 106 pieces/cm''.

As described above, since the dislocation density is low over the entire surface of the GaAs film 13 film type 3, when a semiconductor laser device is manufactured using the crystal growth substrate 11 made of the GaAs film 13 film type 3, for example, the crystal growth A semiconductor laser device with excellent quality can be manufactured over almost the entire surface of the substrate 11, and therefore the yield can be improved.

<Effects of the Invention> As described above, according to the present invention, grooves are formed on the surface of the crystal growth substrate opposite to the crystal growth surface, so that the crystal growth substrate has flexibility. It becomes easier to warp, and the tensile stress generated in the grown crystal during cooling from the crystal growth temperature to room temperature becomes smaller. As a result, the number of dislocations generated in the crystal is reduced.

Therefore, when a semiconductor device is formed using a crystal grown using the crystal growth substrate of the present invention, a high-quality product with few dislocation defects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a rear view of the embodiment, FIG. 2 is an enlarged sectional view taken along line AA in FIG. 1, FIG. 3 is a rear view of another embodiment, and FIGS. 4 and 5 are It is an explanatory diagram of operation of an example. 11...Crystal growth substrate. 11a...Crystal growth surface, 11"b...Back surface. 12...Groove, 13...GaAs film. Patent applicant Oki Electric Industry Co., Ltd. agent
Patent Attorney Norizane Funahashi Death Day of Death Figure 1 L7FAfA-Mf, Person UraS Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] A crystal growth substrate having a crystal growth surface formed on its surface for growing crystals by a crystal growth method, characterized in that a groove is formed on a surface opposite to the crystal growth surface.