JPS5827238B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a single crystal, and more particularly to a crystal growth method for obtaining a high-quality single crystal free of crystal defects by applying current in pulses during the growth of the single crystal.

Conventionally, in order to apply single crystals such as semiconductors Si and QaAs to electrical and electronic devices, an evixaxial growth method in which crystals of the same type or different types are grown on a single crystal substrate has been used industrially.

The key to obtaining highly crystalline crystals is to suppress the occurrence of crystal defects, particularly dislocations, by these growth methods.

In the evixaxial growth method, when growing a crystal having a different crystal lattice constant from that of a substrate, there is a problem in that dislocations occur due to lattice misfit and deteriorate the crystal quality.

To deal with this, for example, there are methods to create a so-called buffer layer, in which a crystal with a composition whose lattice constant gradually changes is first grown, and then a crystal with a predetermined composition is grown, and a method in which the lattice constant changes gradually. A method of growing different crystals in layers has been reported.

In such eviaxial growth methods, it is necessary to precisely control the lattice constant in order to create a buffer layer. For example, in liquid phase growth using a slide boat method, an extra melt reservoir is provided to create a buffer layer. The disadvantage is that it requires growth.

Another problem is that it is not always easy to precisely control the thickness of the buffer layer during growth.

The present invention aims to eliminate these drawbacks, and more specifically, to provide a method for producing a good single crystal without crystal defects from a melt or the like at low cost and with good workability.

Therefore, in the method for producing a single crystal according to the present invention, when producing a single crystal using seed crystals or substrate crystals having different lattice constants, the melt or polycrystal, which is the raw material for producing the single crystal, and the seed crystal or substrate crystal are used. During this period, a current is temporarily passed from the melt or polycrystal side to the seed crystal or substrate crystal side to interrupt the propagation of crystal dislocations and crystal defects.

According to the present invention, when growing a single crystal, crystal defects such as dislocations due to lattice misfit can be prevented by flowing a reverse current, making it possible to obtain a good single crystal.

The present invention will be explained in more detail.

In the present invention, when growing a single crystal from a melt or polycrystal, a current is temporarily passed from the melt or polycrystal to the seed crystal or substrate crystal.

Typical methods for manufacturing single crystals include (1) the so-called Czochralski method, in which a melt and a seed crystal are brought into contact and a single crystal is manufactured while rotating and raising the seed crystal; (2) a substrate method; A method of gradually lowering the temperature of the melt on the crystal to a supersaturated state and growing a single crystal on the substrate (for example, slide board method); (3) heating the polycrystal grown on the seed crystal with a ring-shaped heating element; (4) A method of forming a single crystal (for example, the floating zone melting method), (4) a method of flowing a current between the substrate crystal and the melt from the crystal substrate side (anode) (hereinafter referred to as "forward polarity"), a method of growing the crystal ( For example, electromigration method), etc., and the method according to the present invention can be used in any of these methods.

When producing a single crystal using the methods (1), (2), and (3) above, the seed crystal or substrate crystal is used as a cathode,
Using the melt or polycrystal as an anode, a current is temporarily passed through it.

In the case of the electromigration method, it can be carried out by temporarily reversing the current that was flowing in the forward polarity (flowing it in the opposite polarity), or by temporarily stopping the current and causing the reverse polarity to occur momentarily. Taking advantage of this fact, a reverse current may be caused to flow.

The timing at which the current is applied can be arbitrarily determined.

Next, examples of the present invention will be described.

Example FIG. 1 shows Ga AsGa A using the method according to the present invention.
e It is a sectional view of an example of a growth apparatus used in As-based liquid phase epitaxial growth, and in the figure, 1 is a graphite boat, 2 is a graphite slider, 3 is an insulating plate of holon nitride, 4 is a graphite slider holder, 5 , 6 are stainless steel electrode terminals, which are fixed to the graphite boat 1 and graphite slider 2, respectively.

7 is a GaAeAs Qa saturated melt, 8 is a GaAs substrate, 9 is an electrode terminal on the back surface of GaAs, and 10 is a source crystal.

The method of crystal growth using this device is almost the same as the general slide boat method.

That is, first, the slider 2 is moved, and the Ga AIJ As -Ga melt 7 in the melt reservoir of the graphite boat 1 is placed on the source crystal (usually a non-doped crystal) 10 at a predetermined temperature (usually 750 to 900'C). Equilibrate with

After reaching equilibrium, the melt 7 is moved onto the GaAs substrate 8 to start crystal growth.

The general method for crystal growth is to gradually lower the temperature of the entire boat 1 to create a supersaturation state in the melt 7, but as mentioned above, the stainless steel is heated with electric current (on the slider 2 side) from the poles 5 and 6. So-called electromigration (for example, Just
zebski, Y, 1. Mamura.

and H, C, Gatos, J, Electr.
ocnem Soc.

125, (1978) i140. ) (In these conventional growth methods, a single crystal of GaAeAs is grown on the GaAs substrate 8, but
AI When the amount of AI in As becomes 0.25 or more, GaA
It is known that misfit dislocations occur when the difference in lattice constant from s is 0.1% or more).

Using such an apparatus, single crystals of GaO, 6A6o, and 4As were produced by the electromicresion method.

When a current of 10 A/H was passed with forward polarity at 800° C. (melt e1 substrate ■), the growth rate was 03 μm/7iπ.

Prior to the start of growth, the surface of the substrate 8 is melted by applying a current of opposite polarity, that is, the melt (2) and the substrate (e), and the Ga A
6 After improving the wettability between the As--Ga melt 7 and the substrate 8, the growth is started with forward polarity and allowed to grow for about 10 minutes.

This initial growth is caused by impurities contained in the substrate 8 in the melt 7.
This has the effect of preventing the particles from diffusing into the melt and contaminating the melt 7, but misfit dislocations occur.

Next, turn off the current and leave it in a non-energized state for about 1 second, then turn on again.
When a current was applied at OA/7, a single crystal layer with few misfit dislocations could be grown.

Although the reason why this phenomenon occurs is not necessarily clear, it can be considered as follows.

When GaAe As begins to elongate on the GaAs substrate 8,
Misfit dislocations are generated, and among these dislocations, those generated at angles perpendicular or close to perpendicular to the 8 surfaces of the substrate are considered to propagate without disappearing midway through the progress of crystal growth.

However, if the current is cut off during the growth, not only will the growth stop instantaneously, but it is thought that, as a general property of electrical switching, a portion A of opposite polarity as shown in Figure 2 will appear, and at this moment, It is assumed that remelting occurs at the crystal growth end face.

Therefore, the dislocations that have propagated up to that point will be cut off by this remelting, and even if they grow again, they will no longer be able to reach the substrate 8.
It is presumed that a dislocation-free crystal layer can be obtained since there are no dislocations propagated from the crystal.

FIG. 3 shows a 2000x micrograph (1.1 crrL corresponds to 10 μm) of a cross section of the crystal obtained in this example.

In Fig. 3, it can be seen that there are many etch pits (black dots) that are thought to be misfit dislocations in the central band, and above the fingers there are good Gao, 6Alo, 4A
It can be seen that the s single crystal is growing (by the way, the lower part of the finger is a GaAs substrate).

It can be seen that the place where the current is temporarily stopped is the boundary between the band and a good single crystal, and that a good single crystal without misfit dislocations is grown by the temporary stop of the current.

Similarly to the above embodiment, GaO, 6 A60.4 As
FIG. 5 shows a 2000x microscopic photograph of a crystal cross section obtained in this example in which a single crystal was grown.

In this Figure 5, the black line visible in the lower 1/3 of the photo is the time when growth started (therefore, below it is the GaAs substrate), and the upper end of the white part immediately above it is where the reverse polarity pulse current was applied. (that is, the area surrounded by the black line and the upper end of the white part is the band-shaped part).

As is clearer from FIG. 5, it can be seen that a good single crystal grows after the reverse polarity pulse current is applied.

As explained above, if an electric pulse that instantaneously melts the growing surface of the crystal is applied during crystal growth, the dislocations that have been propagating in the crystal up to that point will be cut off. By applying a plurality of pulses, a dislocation-free or defect-free single crystal can be grown thereafter.

This effect can be applied to the fabrication of double heterostructure laser diodes.

Up until now, Ga As substrates have been used with Ga
Since the In As-based layer has a too large lattice constant and many defects, it was necessary to use InP, which has a larger lattice constant than GaAs.

However, InP is expensive and cannot be obtained with good quality.

Therefore, even if GaInAsP is grown with high defects on a GaAs substrate, the method of the present invention can eliminate dislocations or crystal defects similar to dislocations by applying a pulsed current to the epitaxial growth diameter, so there is no need to use an InP substrate. There is no.

Furthermore, by applying the present invention to the peripheral boundary region between the substrate and the active layer in an FET, a defect-free active layer can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of an apparatus for carrying out the method of the present invention, FIG. 2 is a graph schematically showing changes in electric polarity in Examples, and FIG. 3 is a microscopic photograph of a crystal cross section of Examples. 4
The figure shows a current application program in another example, and FIG. 5 is a cross-sectional micrograph of a crystal grown in the above example. DESCRIPTION OF SYMBOLS 1... Graphite board, 2... Graphite slider, 3... Boron nitride insulating board, 4... Graphite slider holder, 5, 6... Stainless steel electrode terminal, 7- Ga Ae As -Ga fusion Liquid, 8”・Ga
As substrate, 9...electrode terminal, 10...source crystal.

Claims (1)

[Claims] 1. When producing a single crystal using seed crystals or substrate crystals with different lattice constants, the melt or polycrystal is temporarily placed between the melt or polycrystal, which is the raw material for the single crystal, and the seed crystal or substrate crystal. A method for producing a single crystal, comprising the step of passing a pulsed current from the crystal side to cut off the propagation of crystal dislocations and crystal defects.