JPH04306847A - Vapor epitaxial growth method and device - Google Patents

Abstract

PURPOSE:To provide a vapor epitaxial growth method and a device where a CdTe and a Hg1-xCdxTe crystal grow in lamination uniform in composition oh the surface of an epitaxial growth substrate. CONSTITUTION:Material gas is fed to an epitaxial growth substrate 4 from gas feed nozzles arranged in row, and the fed material gas is thermally decomposed, whereby a first epitaxial crystal and a second epitaxial crystal different from each other in composition are formed in multilayer on the substrate 4. At this point, the distance between the substrate 4 and the tip of the material gas feed nozzle is made to vary corresponding to the growth times of the first epitaxial crystal and the second epitaxial crystal, and gas feed nozzles located confronting the center of the substrate 4 and other gas feed nozzles confronting the peripheral part of the substrate 4 are made to vary from each other in gas material concentration to effect the second epitaxial crystal growth.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor phase epitaxial growth method and a vapor phase epitaxial growth apparatus, and more particularly to a method and apparatus for epitaxially growing a compound semiconductor crystal containing mercury on a heterogeneous substrate.

0002

[Prior art] Mercury, which is a forming material for infrared sensing elements,
When epitaxially growing cadmium tellurium (Hg1-x Cdx Te), a cadmium tellurium (CdTe) crystal containing constituent atoms of Hg1-x Cdx Te crystal is used as a substrate for epitaxial growth, but this crystal has a large area. The disadvantage is that it is difficult to obtain and expensive. Therefore, as a substrate for epitaxial growth of Hg1-x Cdx Te, unlike sapphire, gallium arsenide (GaAs), or silicon (Si), it does not contain constituent atoms of Hg1-x Cdx Te crystal and is relatively easy to manufacture. A different type of substrate is used, which is large and easily available.

However, when such a heterogeneous substrate is used and a Hg1-x Cdx Te crystal is epitaxially grown on it, the constituent atoms of the heterogeneous substrate, for example, aluminum (Al) atoms in a sapphire substrate, and aluminum (Al) atoms in a gallium arsenide substrate. and gallium (Ga), arsenic (As) atoms, and in the case of a silicon substrate, Si atoms are Hg1-x Cdx T
e Diffuses into the crystal as impurity atoms. If an infrared sensing element is formed using a Hg1-x Cdx Te crystal in which such impurity atoms are diffused, the characteristics of the element may deteriorate. Therefore, before epitaxially growing the Hg1-x Cdx Te crystal, CdTe on top
A method has been adopted in which epitaxial growth is performed using a crystal as a buffer layer as an underlying layer.

By the way, the surface state of this CdTe buffer layer is similar to that of Hg1-x Cdx T formed on it.
CdTe has a large effect on the surface state of the e-crystal.
It is desirable that the buffer layer has a crystal surface that has a stable composition over the entire surface area, has no irregularities, exhibits a mirror surface when observed with a metallurgical microscope, and is free from crystal defects.

As an apparatus for epitaxially growing such a CdTe crystal, an apparatus as shown in FIG. 3 has conventionally been used. As shown in the figure, a substrate 4 for epitaxial growth such as a sapphire substrate is placed on a substrate heating table 3 made of carbon and rotated by a rotating shaft 2 installed in a reaction vessel 1, and a gas is supplied onto the substrate. Nozzles 5A, 5B, 5C, and 5D are arranged in a row, and when a CdTe crystal is epitaxially grown from these gas supply nozzles, a raw material gas of a mixed gas of dimethyl cadmium gas and diisopropyl tellurium gas is supplied.

The bottom of the reaction vessel 1 is placed on a fixed stand 7, and the fixed stand is provided with an exhaust pipe 8 through which exhaust gas that has not taken part in the epitaxial growth reaction is exhausted to the outside.

[0007] Then, by energizing the high-frequency induction heating coil 6 provided around the reaction vessel 1 and heating the substrate heating table 3, the epitaxial growth substrate 4 thereon is heated, and the gas supply nozzle 5A is heated. , 5B, 5C, and 5D are thermally decomposed to grow CdTe epitaxial crystals on the substrate.

By the way, the surface state of this CdTe crystal depends on the molar ratio M of (number of moles of diisopropyl tellurium gas/number of moles of dimethyl cadmium gas). The present inventors have experimentally confirmed that when epitaxially growing a crystal, it is necessary to maintain the value of the above-mentioned molar ratio M at a predetermined appropriate value, that is, from 5 to 15.

[0009]

By the way, as shown in FIG. 4(a), gas supply nozzles 5A, 5B, 5C, 5D
When the raw material gas of the above-mentioned mixed gas of dimethyl cadmium gas and diisopropyl tellurium gas is supplied to the epitaxial growth substrate 4, after the raw material gas once hits the central part O of the substrate surface, the surface of the substrate 4 is further supplied. The liquid flows along the direction toward the peripheral portion P of the substrate as shown by the arrow.

Among these raw material gases, dimethyl cadmium gas is easier to decompose than diethyl tellurium gas;
Since Cd atoms are easily incorporated into the epitaxial growth substrate, most Cd atoms are incorporated in the central portion O of the substrate, and the amount of Cd atoms contained in the dimethyl cadmium gas flowing to the peripheral portion P of the substrate is reduced. Therefore, as shown in FIG. 4(b), as the raw material gas reaches the peripheral part P of the substrate, the raw material gas whose molar ratio M increases is supplied, and the more the raw material gas reaches the peripheral part P of the substrate, the more the raw material gas is supplied to the central part O Since the molar ratio M of the raw material gas is not maintained at a predetermined value in the peripheral region P, crystal defects and the like are formed, and there is a problem that a CdTe epitaxial crystal with a stable surface state cannot be obtained.

This also means that Hg1-x C
The same is true when growing a dx Te epitaxial crystal; as shown in FIG. 4(c), it becomes more difficult for Cd atoms to be taken in from the central part O to the peripheral part P of the epitaxial growth substrate, so the x value Small Hg1-x Cdx T
The disadvantage is that e-crystals are obtained. Therefore, the present inventors increased the flow rate of the raw material gas supplied from the gas supply nozzle, and supplied a larger amount of gas than the Cd atoms were taken into the epitaxial growth substrate, thereby increasing the molar ratio M. A method is used to maintain it at a predetermined value.

However, when the gas supply nozzle is used close to the epitaxial growth substrate and the flow rate of the raw material gas is increased, the central part of the substrate receives less gas per unit time than the peripheral part. As shown in FIGS. 5(a) and 5(b), the central portion O of the substrate becomes a low-temperature region, and the peripheral portion P of the substrate becomes a high-temperature region. Temperature distribution occurs and the entire area of the substrate is not heated at a uniform temperature. For example, if the substrate is 1.5 inches or more, CdTe crystals or Hg1-x Cdx Te crystals with a uniform composition over the entire area cannot be heated. There is a disadvantage that epitaxial growth is not possible. Curve A in FIG. 5B shows a case where the flow rate of the raw material gas is low, and curve B shows a case where the flow rate of the raw material gas is high.

[0013] Therefore, the problem can be solved by increasing the dimethyl cadmium gas flow rate in the gas supply nozzles 5A, 5D arranged at the periphery of the epitaxial growth substrate than in the gas supply nozzles 5B, 5C arranged in the center of the substrate. And so.

By the way, the raw material gas supplied from the gas supply nozzle diffuses and spreads to some extent before reaching the surface of the substrate for epitaxial growth, so if the distance between the substrate and the gas supply nozzle is too large, Even if the concentration of the gas is changed by varying the flow rate of the gas in each gas supply nozzle, it is impossible to control the molar ratio M to a predetermined value on the substrate.

[0015] Also, in this way, the gas supply nozzles 5A, 5B
, 5C, and 5D is very complicated. Therefore, when growing a CdTe crystal, the gas supply nozzle 5
A, 5B, 5C, 5D The concentration of the raw material gas supplied from the gas supply nozzles 5A, 5B, 5C, 5D is made uniform.
A method is adopted in which the gas flow rate of the source gas is increased while the distance between the 5D and the epitaxial growth substrate is increased.

This is because dimethyl cadmium is easier to thermally decompose than diisopropyl tellurium, and if the thermal decomposition of dimethyl cadmium occurs, CdTe can be produced even if the thermal decomposition of diisopropyl tellurium is insufficient.

By the way, when growing Hg1-x Cdx Te crystals, there is a problem that if the raw material gas is supplied at a high flow rate, thermal decomposition of diisopropyl tellurium becomes insufficient, and therefore, HgTe does not grow. This generation of HgTe occurs after the diisopropyl tellurium gas is reliably thermally decomposed and then reacts with Hg to form HgTe. Therefore, if the thermal decomposition of diisopropyl tellurium is insufficient, HgTe will not be generated. Therefore, Hg1-x Cdx Te crystals do not grow. However, if this raw material gas is supplied at a low flow rate, the consumption of dimethyl cadmium increases, resulting in a phenomenon of non-uniform composition.

Therefore, when growing HgCdTe crystals, it is necessary to adjust the gas concentration for each gas supply nozzle. The present invention solves the above-mentioned problems, and even when the gas flow rate of the raw material gas is increased in order to maintain the molar ratio M at a predetermined value, uniform growth can be achieved over the entire area of the epitaxial growth substrate. The object of the present invention is to provide a vapor phase epitaxial growth method and apparatus that enable temperature distribution to be obtained.

[0019]

[Means for Solving the Problems] In the vapor phase epitaxial growth method of the present invention, a raw material gas is supplied from gas supply nozzles arranged in a row on a rotating epitaxial growth substrate in a reaction vessel. In the method of stacking a first epitaxial crystal and a second epitaxial crystal having different compositions on the substrate by thermal decomposition, the distance between the substrate and the tip of the gas supply nozzle for the raw material gas is as described above. The gas supply nozzle is configured to be variable depending on the growth of the first epitaxial crystal and the growth of the second epitaxial crystal, and a gas supply nozzle facing on the central portion O of the substrate and a peripheral portion of the substrate. The method is characterized in that the second epitaxial crystal is grown by varying the concentration in the source gas between the gas supply nozzles facing upwardly.

[0020] Also, in correspondence with the growth of the first or second epitaxial crystal to be grown on the substrate for epitaxial growth, the source gas is supplied in a direction perpendicular or horizontal to the surface of the substrate. It is characterized by

Further, the vapor phase epitaxial growth apparatus of the present invention is provided with a gas inlet pipe and a horizontal gas exhaust pipe that allow the raw material gas to pass in parallel on the substrate for epitaxial growth on the side wall of the reaction vessel, and a A gas supply nozzle is provided, and in a direction perpendicular to the epitaxial growth substrate from the gas supply nozzle or gas inlet pipe, corresponding to the growth of first or second epitaxial crystals having different compositions to be grown on the substrate, Alternatively, it is characterized in that the source gas can be supplied in a direction parallel to the substrate surface.

Furthermore, a gas inflow pipe is provided on the side wall of the reaction vessel through which the raw material gas can pass in parallel to the epitaxial growth substrate;
A horizontal gas exhaust pipe is provided, and a gas supply nozzle is provided oppositely on the substrate, so that the gas flow from the gas supply nozzle on the substrate can be shielded, and a horizontal gas exhaust pipe inserted into the gas inflow pipe and the horizontal gas exhaust pipe is provided. an insertion tube and a vertical insertion tube inserted into the reaction vessel to block the supply of raw material gas from the gas inflow tube, and to either the first or second epitaxial crystal to be grown on the substrate. Correspondingly, a horizontal insertion tube or a vertical insertion tube can be freely arranged so that the gas supply nozzle or the gas introduction tube communicating with the gas inflow tube is perpendicular to the epitaxial growth substrate or to the surface of the substrate. It is characterized by being able to supply raw material gas in parallel.

Furthermore, the epitaxial growth substrate is a sapphire, gallium arsenide, or silicon substrate, and the first
The epitaxial crystal is made of cadmium-tellurium or cadmium-tellurium-zinc, and the second epitaxial crystal is made of mercury-cadmium-tellurium.

[0024]

[Operation] When the distance between the epitaxial growth substrate and the tip of the gas supply nozzle is increased, the source gas spreads from the gas supply nozzle and is blown over the entire area of the epitaxial growth substrate.
It is possible to prevent the gas from concentrating in the center of the substrate and partially cooling the temperature of this area, and the temperature distribution becomes uniform over the entire area of the substrate.

Furthermore, by supplying the raw material gas in a direction parallel to the surface of the epitaxial growth substrate, it is possible to avoid a partial temperature drop in the center of the substrate, and to achieve uniform temperature over the entire area of the epitaxial growth substrate. Temperature distribution can be obtained.

[0026] Therefore, it becomes possible to supply at a high flow rate the raw material gas necessary for epitaxially growing CdTe crystals of uniform composition on a large-area substrate for epitaxial growth.

Furthermore, when forming an epitaxial crystal of Hg1-x Cdx Te, if the raw material gas is supplied at a high flow rate as in the case of forming a CdTe crystal, the rate of thermal decomposition of diisopropyl tellurium increases at the center of the substrate. In the central part of the substrate, the H content of tellurium atoms is low.
g1-x Cdx Te crystals may be formed, and if the distance between the epitaxial growth substrate and the gas supply nozzle is kept too large, the gas supply nozzle facing the center and periphery of the substrate may This is undesirable because the raw material gases with varying concentrations are mixed uniformly.
Compared to when growing a CdTe crystal, the distance between the substrate and the gas supply nozzle is shortened and the source gas is supplied vertically, and the concentration of the source gas is varied depending on the gas supply nozzle, so that , epitaxial growth is performed by supplying source gas with a high concentration of Cd.

[0028]

[Examples] Hereinafter, examples of the present invention will be explained using the drawings.
Explain in detail. As shown in FIG. 1(a), an epitaxial growth substrate 4 made of GaAs is placed on a substrate heating table 3, the temperature of the substrate is maintained at 360° C., and the substrate and gas supply nozzles 5A, 5B, 5C, When growing a CdTe crystal, the distance between the tips of 5D and Hg1-x Cd
x It is made variable depending on when the Te crystal is grown.

When growing a CdTe crystal, the epitaxial growth substrate 4 and gas supply nozzles 5A, 5B,
When the distance between the tips of 5C and 5D is kept at a value of 30 mm, the surface condition of the CdTe crystal becomes good even at the periphery of the GaAs substrate when the gas flow rate is 20 cm/sec or more. When the speed is 25 cm/sec, CdTe is formed at the center of the substrate as the temperature decreases.
The surface of the crystal becomes rough.

However, when the distance between the epitaxial growth substrate 4 and the tips of the gas supply nozzles 5A, 5B, 5C, and 5D is increased to 70 mm, the gas flow rate is reduced to 25 cm/sec.
At a high flow rate of c, there is almost no surface roughness in the center of the substrate, and a uniform surface can be formed over the entire surface of a 3-inch diameter substrate.

Therefore, when forming a CdTe crystal,
Epitaxial growth substrate 4 and gas supply nozzles 5A, 5
With the distance between the tips of B, 5C, and 5D kept at 70 mm, growth is performed using a raw material gas of a mixed gas of dimethyl cadmium and diisopropyl teter while keeping the gas flow rate at 25 cm/sec. and gas supply nozzles 5A, 5B, 5
The concentration of the raw material gas supplied from C and 5D is made uniform at all gas supply nozzles.

[0032] On top of that, Hg1-x Cdx Te
When growing crystals, if the distance between the substrate and the gas supply nozzle is 70 mm, it is impossible to make the composition uniform within the substrate, and the distance between the substrate and the gas supply nozzle is set to 30 mm.
The gas supply nozzles 5B and 5C facing the center of the substrate supply raw material gases of dimethyl cadmium, diisopropyl tellurium, and mercury, which have a high content of Cd gas, while maintaining an interval of ~50 mm. In addition, gas supply nozzles 5A and 5D facing the peripheral area of the substrate supply raw material gases of dimethyl cadmium, diisopropyl tellurium, and mercury with a small content of Cd gas, and the flow rate of this gas is set at 10 cm/
Grows as sec.

In order to vary the distance between the substrate and the tip of the gas supply nozzle in this way, it is preferable to cut a thread in the rotating shaft and move it up and down as appropriate using a motor and gears. As another example, as shown in FIG. 1(b), a gas inlet pipe 11 and a horizontal gas exhaust pipe 12 are provided on the side wall of the reaction vessel 1 through which source gas can pass in parallel over the epitaxial growth substrate 4.
are provided, and gas supply nozzles 5A,
5B, 5C, and 5D are provided. When growing a CdTe crystal, raw material gases of dimethyl cadmium and diisopropyl tellurium are flowed through a gas inlet pipe 11 and exhausted through a horizontal gas exhaust pipe 12. Also Hg1-x
When growing CdxTe crystal on CdTe crystal,
Gas supply nozzles 5A, 5B, 5C, and 5D feed raw material gases of dimethyl cadmium, diisopropyl tellurium, and mercury. Cd is supplied from the gas supply nozzles 5B and 5C on the center of the substrate so that the concentration of Cd is higher than that of the raw material gas, and is sprayed vertically onto the substrate, and is exhausted from the exhaust pipe 8.

[0034] In this way, even if the raw material gas for CdTe crystal formation is supplied onto the epitaxial growth substrate at a high flow rate, the gas flows parallel to the surface of the substrate, so that the central and peripheral parts of the substrate are In this case, the temperature difference is smaller than when gas is supplied perpendicularly to the substrate, and a CdTe crystal with less compositional variation can be formed between the center and peripheral portions of the substrate.

As another embodiment, as shown in FIG. 2(a), the source gas flow from the gas supply nozzles 5A, 5B, 5C, and 5D on the epitaxial growth substrate 4 can be blocked, and the gas inflow pipe 11 Then, the horizontal insertion pipe 13 inserted into the horizontal gas exhaust pipe 12 is installed in the gas inflow pipe 11 when the raw material gas is introduced into the reaction vessel from the gas inflow pipe 11. Further, as shown in FIG. 2(b), when supplying raw material gas onto the substrate from the gas supply nozzles 5A, 5B, 5C, and 5D, a vertical insertion pipe 14 that blocks the supply of raw material gas from the gas inflow pipe 11 will be established. This horizontal insertion tube 13 or vertical insertion tube 14 shall be installed freely.

When growing a CdTe crystal on the epitaxial growth substrate 4 described above, the horizontal insertion tube 13 is inserted into the gas inflow tube 11 and the horizontal gas exhaust tube 12, and dimethyl cadmium is introduced from the gas inflow tube 11. A raw material gas for CdTe crystal growth of diisopropyl tellurium is supplied.

[0037] Also, the epitaxial growth substrate 4 described above
When growing Hg1-x Cdx Te crystals, after removing the horizontal insertion tube 13 described above, the vertical insertion tube 14 is inserted into the reaction vessel 1, and the gas supply nozzles 5A, 5B,
5C and 5D feed gases of dimethyl cadmium, diisopropyl tellurium, and mercury onto the substrate. The Hg1-x Cdx Te crystal is epitaxially grown by supplying the raw material gas so that the concentration of Cd is higher than that of the raw material gas supplied from the gas supply nozzles 5B and 5C.

In this embodiment, a GaAs substrate was used as the epitaxial growth substrate, but silicon or sapphire substrates may also be used. The present invention is also applicable to the case where a CdZnTe crystal is grown instead of a CdTe crystal.

[0039]

[Effects of the Invention] As described above, according to the method and apparatus of the present invention, CdTe crystal and Hg1-x Cdx T
An e-crystal can be epitaxially grown on a large-area heterogeneous substrate such as GaAs with a uniform composition over the entire area of the substrate, and when a sensing element is formed using this crystal, a high-quality infrared sensing element can be obtained. There is.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an apparatus used in the method of the present invention.

FIG. 2 is an explanatory diagram of an apparatus used in the method of the present invention.

FIG. 3 is an explanatory diagram of an apparatus used in a conventional method.

FIG. 4 is a diagram of disadvantageous states in the conventional method.

FIG. 5 is a diagram of disadvantageous states in the conventional method.

[Explanation of symbols]

1 Reaction container 3 Substrate heating table 4 Epitaxial growth substrates 5A, 5B, 5C, 5D Gas supply nozzle 7 Fixing table 8 Exhaust pipe 11 Gas inflow pipe 12 Horizontal gas exhaust pipe 13 Horizontal insertion pipe 14 Vertical insertion pipe

Claims (1)

[Scope of Claims] [Claim 1] In a reaction vessel (1), source gas is supplied from gas supply nozzles (5A, 5B, 5C, 5D) arranged in a row on a rotating epitaxial growth substrate (4). In the method of supplying a first epitaxial crystal and a second epitaxial crystal having different compositions on the substrate (4) by thermally decomposing the raw material gas,
4) and gas supply nozzles (5A, 5B, 5C) for raw material gas
, 5D) so that the distance to the tip thereof is variable depending on the growth of the first epitaxial crystal and the growth of the second epitaxial crystal, and the distance to the tip of the Gas supply nozzle (5B, 5C)
and gas supply nozzles (5A, 5D) facing each other on the peripheral part (P) of the substrate, and a second epitaxial crystal is grown by changing the concentration in the source gas between . 2. The epitaxial growth substrate (4) according to claim 1, in a direction perpendicular to the surface of the substrate (4), or in a direction corresponding to the growth of the first or second epitaxial crystal to be grown thereon. A vapor phase epitaxial growth method characterized in that a source gas is supplied horizontally. 3. A gas inlet pipe (11) and a horizontal gas exhaust pipe (12) are provided on the side wall of the reaction vessel (1) to allow the raw material gas to pass in parallel above the epitaxial growth substrate (4), and a horizontal gas exhaust pipe (12) is provided on the epitaxial growth substrate (4). Gas supply nozzle (5
A, 5B, 5C, 5D) are provided, and the gas supply nozzle (
5A, 5B, 5C, 5D) or gas inflow pipe (11
) A vapor phase epitaxial growth apparatus characterized in that source gas can be supplied perpendicularly to the epitaxial growth substrate (4) or parallel to the surface of the substrate. 4. A gas inlet pipe (11) and a horizontal gas exhaust pipe (12) are provided on the side wall of the reaction vessel (1) so that the source gas can pass in parallel above the epitaxial growth substrate (4), and a horizontal gas exhaust pipe (12) is provided on the epitaxial growth substrate (4). Gas supply nozzle (5A
, 5B, 5C, 5D) to block the gas flow from the gas supply nozzles (5A, 5B, 5C, 5D) on the substrate (4), and a gas inlet pipe (11) and a horizontal gas exhaust pipe ( a horizontal insertion tube (13) inserted into 12);
The gas inflow pipe (11) is inserted into the reaction vessel (1).
) Vertical insertion tube (14) that shields the supply of raw material gas from
A horizontal insertion tube (1) is provided corresponding to either the first or second epitaxial crystal to be grown on the substrate.
3) Alternatively, the vertical insertion tube (14) can be freely arranged to supply the raw material in a direction perpendicular to the epitaxial growth substrate or parallel to the substrate surface from the gas supply nozzle or the gas introduction tube communicating with the gas inflow tube. A vapor phase epitaxial growth apparatus characterized by being able to supply gas. 5. The epitaxial growth substrate according to claim 1 is a sapphire, gallium arsenide, or silicon substrate, and the first epitaxial crystal is made of cadmium.
A vapor phase epitaxial growth method characterized in that tellurium or cadmium-tellurium-zinc is used, and the second epitaxial crystal is mercury-cadmium-tellurium.