JPH0341740A - Liquid phase epitaxial growth method - Google Patents

Abstract

PURPOSE:To prevent the decrease in concentration of Cd atoms in melt under epitaxial growth and to make the composition gradient in the direction of a thickness small by arranging an epitaxial growth substrate 1 on the lower side along the depth direction of the melt, and arranging a solute supplying substrate 11 on the upper side along the depth direction of the melt so as to face the substrate. CONSTITUTION:The parts of a pair of cylindrical members of fixing jugs 6 made of quartz are linked. An epitaxial growth substrate 1 comprising a Cd0.96Zn0.04Te substrate whose lattice matches the lattice of an Hg0.8Cd0.2Te epitaxial crystal to be grown is arranged in grooves 3A at the upper parts of the fixing jigs 6. A solute supplying substrate 11 comprising a Hg0.8Cd0.2Te substrate having the same crystal composition as that of an epitaxial crystal layer to be grown is provided in grooves 3B at the lower parts of the fixing jigs 6. A forming material of solid-phase epitaxial growth melt 4 having the component composition of hg0.2Cd0.009Te0.791 is arranged at the lower part of the solute supplying substrate 11. Under this state, said device is sealed into an ampul 7. Then, the forming material is fused at the temperature of 500 deg.. Thereafter, the ampul 7 is rotated by 180 degrees. Under the state wherein the forming material is fused and the epitaxial growth substrate 1 and the solute supplying substrate are brought into contact, the epitaxial growth is started.

Description

[Detailed Description of the Invention] [Summary] Regarding a liquid phase epitaxial growth method, the object is to provide a liquid phase epitaxial growth method in which an epitaxial crystal layer formed on an epitaxial growth substrate has a uniform composition distribution along the epitaxial growth direction. In the method of growing an epitaxial crystal on the substrate by holding the substrate for epitaxial growth in a fixture housed in an epitaxial growth container and bringing the melt for epitaxial growth into contact with the substrate, the melt for epitaxial growth is applied to the substrate. When contacting
The substrate for epitaxial growth is placed on the lower side of the melt for epitaxial growth, and the substrate for solute supply is placed on the upper side of the melt for epitaxial growth, and the solute dissolved from the solute supply substrate and the The solute in the epitaxial growth melt consumed during the epitaxial growth is replenished by gravity and the specific gravity difference between the epitaxial growth melt and the solvent.

[Industrial application field]

The present invention relates to a method for liquid-phase epitaxial growth of mercury-cadmium and tellurium-based multicomponent semiconductor crystals used as materials for infrared sensors, and particularly for obtaining an epitaxial crystal layer having a uniform composition distribution in the thickness direction of the grown layer. Regarding the method.

In recent years, there has been a growing demand for infrared sensors to be more sophisticated and have more pixels, and there is a demand for the development of multi-pixel infrared sensors such as infrared charge-coupled devices that use photodiodes as light detection elements.
In particular, uniformity of characteristics between pixels is required.

For this reason, a crystal manufacturing method using a liquid phase epitaxial growth method that can obtain an epitaxial crystal layer with a uniform composition in the direction of the wafer surface used in the above-mentioned infrared sensor has been provided, but fJlIFc changes in the thickness direction of the epitaxial crystal layer. In this case, slight differences in the thickness of the epitaxial crystal layer cause variations in spectral sensitivity characteristics between pixels, so it is necessary to obtain a grown layer with a uniform composition in the thickness direction.

[Conventional technology]

As shown in FIG. 4, the apparatus used in the conventional liquid phase epitaxial growth method has a groove 3 that holds a plate-shaped substrate holder 2 that holds a substrate 1 for epitaxial growth. It consists of a fixing jig 6 made of a pair of opposing cylindrical quartz members having a space 5 for accommodating the melt 4, and an ampoule 7 enclosing the fixing jig 6.

A case in which epitaxial crystals are formed on a substrate by a conventional method using such an apparatus will be described.

4 and 5 of the cross-sectional view taken along the v-v" line in FIG.
As shown in FIG.
The fixing jig 6 on which the substrate 1 is installed is filled with a material for forming the epitaxial growth melt 4, which is obtained by melting mercury, cadmium, and tellurium and solidifying it at the opposite position facing the substrate. and seal it in ampoule 7.

Next, the ampoule 7 is placed in a furnace core tube (not shown) in a heating furnace.
The ampoule 7 is heated to melt the solidified epitaxial growth material in the ampoule 7 to form an epitaxial growth melt (solution).

Next, the ampoule 7 is rotated 180 degrees along the direction of arrow A, and as shown in FIG. After a predetermined period of time, an epitaxial crystal of 'g+-x Cdx Te is grown on the substrate.

Next, the ampoule 7 is further rotated 180 degrees in the direction of arrow B, and as shown in FIG. 5(C), the epitaxial growth is stopped by a wipe-off operation in which the epitaxial growth melt adhering to the substrate falls to the bottom. .

When performing epitaxial growth using such a conventional method, Cd atoms in the epitaxial growth melt of a solution of an alloy of mercury, cadmium, and tellurium have a large segregation coefficient compared to other constituent atoms of the melt, so that the epitaxial layer is It is easily consumed as it grows, and the concentration of Cd atoms in the melt decreases.

Therefore, in the past, the amount of epitaxial growth melt was increased to prevent the concentration of Cd atoms in the melt from decreasing, thereby preventing variations in the composition gradient in the thickness direction of the epitaxial layer.

[Problem to be solved by the invention]

However, in the conventional method described above, the diffusion rate of Cd atoms in the epitaxial growth melt is low, so even if the total amount of Cd atoms in the melt is increased, the total amount of Cd atoms in the melt is increased. Utilizing Cd atoms requires time for them to diffuse into the epitaxial growth surface, and an epitaxial layer of a given thickness with a small M1 gradient can be grown only after a long period of time from the start of epitaxial growth. There are problems that arise after the time has passed.

In other words, in the conventional method, the temperature of the epitaxial growth melt is lowered and the surface of the epitaxial growth substrate is
For example, as an epitaxial crystal having a composition of Hgo, sCdo, or zTe is grown, the Cd/HgJM degree ratio in the melt is small compared to the Cd/HgtM degree ratio of the growing epitaxial crystal. The Cd concentration in the melt decreases relatively greatly, and the X value of the epitaxial crystal precipitated from the melt becomes smaller than x = 0.2, and the X value of the epitaxial crystal decreases along the epitaxial growth direction. It will have a compositional gradient.

Therefore, even if the amount of epitaxial growth melt is specified, it takes a long time to obtain a uniform epitaxial layer, and interdiffusion occurs between the epitaxial growth substrate and the epitaxial crystal layer during epitaxial growth. , a problem arises in that the composition gradient near the heterointerface between the substrate and the epitaxial crystal layer becomes large.

Furthermore, when the amount of epitaxial growth melt is increased,
Because the growth equipment is also large, it is difficult to maintain a uniform temperature in the epitaxial growth system such as an ampoule, and the main component, 11g atoms, is unevenly distributed in the low temperature part of the growth system, reducing the accuracy of composition control. be.

In addition, since the epitaxial growth melt has Hg as its main component, in order to obtain high composition control accuracy, it is necessary to use a growth system close to a closed tube, so the epitaxial growth melt I is stirred during growth. It is also difficult to add Cd metal to cough melts.

The present invention solves the above-mentioned problems, prevents a decrease in the concentration of Cd atoms in the melt during epitaxial growth without increasing the amount of melt for epitaxial growth, and allows Cd atoms in the melt to quickly reach the epitaxial growth surface. It can be supplied, and even in the thickness direction! The object of the present invention is to provide a method that can produce an epitaxial crystal with a small lJl gradient.

[Means to solve the problem]

In the liquid phase epitaxial growth method of the present invention which achieves the above object, as shown in the principle diagram of FIG. In the method of growing epitaxial crystals on the substrate by bringing the epitaxial growth melt 4 into contact with the substrate 1, when the molten epitaxial growth melt 4 is brought into contact with the substrate 1, the epitaxial growth substrate 1 is placed on the lower side of the epitaxial growth melt. At the same time, a solute supply substrate 11 is disposed above the epitaxial growth melt, and the solute supply substrate replenishes the solute in the epitaxial growth melt consumed during the epitaxial growth. Configure it as follows.

[For production]

In the method of the present invention, as shown in the principle diagram of FIG.
When performing epitaxial growth in contact with the melt, an epitaxial growth substrate 1 is placed on the lower side along the depth direction of the melt, and a solute supply substrate 1 is placed on the upper side along the depth direction of the melt, facing the substrate. Place 11. The specific gravity of Te atoms serving as the solvent for this epitaxial growth melt 4 is 6.
．． 24, whereas that of the melt? Since the specific gravity of Cd atoms, which is 8t, is 8.65, the concentration of solute in the lower part along the depth direction of the melt is larger than that in the upper part in the depth direction of the melt. become.

Therefore, as shown in Figure 2, water SBJUg) - kado straw um (
From the phase diagram of Cd)-tellurium (Te) system, as the molar concentration of Cd on the horizontal axis increases, that is, as the concentration of solute increases, the figure shows the liquid phase temperature of the epitaxial growth melt. As shown by the phase temperature lines 21, 22, 23, 24..., the liquid phase temperature tends to become higher, and the lower the melt, the more the solute in the melt becomes saturated. , the solute in the melt becomes less saturated as it approaches the upper part of the melt.

Therefore, epitaxial growth is selectively performed on the surface of the epitaxial growth substrate on the lower side of the epitaxial growth melt, and when the solute concentration in the melt near the growth substrate begins to decrease with epitaxial growth, the epitaxial growth in that part is performed selectively. Since the specific gravity of the melt also decreases, a melt with a high solute concentration is supplied by gravity from the upper side of the melt to the vicinity of the growth substrate surface so that the specific gravity does not exhibit an inverted distribution within the melt.

The solute concentration decreases due to this supply of solute, and the upper epitaxial growth melt, which has a large degree of unsaturation, is in contact with the solute supply substrate 11, and thus melts the solute supply substrate. Therefore, it is possible to prevent the solute concentration from decreasing in the upper part of the melt.

In this way, the solute with a low diffusion rate is also supplied to the epitaxial growth substrate from the solute supply substrate in a short time, so that it is possible to prevent the concentration of Cd atoms in the epitaxial growth melt from decreasing due to growth.

Note that Hg (specific gravity = 13.5), which is a solute other than Cd atoms in the epitaxial growth melt, has a higher specific gravity than Cd or Te atoms, but the degree of Hg'tljt in the melt is such that Hg is an easily evaporable element. Since the water root partial pressure of the melt is high, mercury is distributed so as to satisfy the condition that the partial pressure of mercury is constant within the melt, and is not excessively unevenly distributed in the lower part of the melt due to gravity.

Therefore, when the solute supply substrate is disposed above the epitaxial growth substrate at a position facing the epitaxial growth melt across the epitaxial growth substrate, the difference in the specific gravity of the solute to the solvent will cause the solute supply substrate to Since the solute with a slow diffusion rate is supplied to the growth substrate through the substrate in a short time, it is possible to grow an epitaxial crystal with a small Mi gradient in the growth direction in a short time.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

3(a) and 3(b) are explanatory diagrams of the epitaxial growth method of the present invention, with FIG. 3(a) showing the state before the start of epitaxial growth, and FIG. 3(b) showing the state before the start of epitaxial growth. shows the state after the start of Hg. 1Cd
FIG. 2 is a diagram showing a method of growing o,zTe crystals.

As shown in FIG. 3(a), in the groove 3A of the upper part of the quartz fixing jig 6, in which a pair of cylindrical members are partially connected, the Hgo, *Cdo, and zTe epitaxial crystals to be grown are lattice-matched. Cdo, +raZn6. . An epitaxial growth substrate 1 made of an aTe substrate is installed, and Hge, aCdo, and aCdo having the same crystal composition as the epitaxial crystal layer to be grown are placed in the groove 3B at the bottom of the fixing jig 6.
A solute supply substrate 11 made of a zTe substrate is installed, and llgo, zcdo, 0 are placed below the solute supply substrate 11.
A material for forming a solid-phase epitaxial growth melt 4 having a component composition of 09T'eO, ff'l+ is placed and sealed in an ampoule 7.

Next, 50% of the material for forming the epitaxial growth melt 4 was added.
After melting at a temperature of 0''C, the ampoule 7 is rotated 180 degrees to obtain a state as shown in FIG. Substrate 1 and solute supply substrate 11
Epitaxial growth is started with the two in contact with each other.

About the embodiment of epitaxial growth of the present invention Part 2-1
This will be further explained in detail with reference to FIGS. 2-2 and 2-3.

Figure 2-1 is a phase diagram of the epitaxial growth melt 4 using Te as a solvent, in which the vertical axis is the tt in the melt.
The horizontal axis shows the molar concentration of Cd in the melt. Equiliquid phase temperature lines 21 and 22 of the solid curve in the figure
, 23 and 24 indicate the temperature at which a part of the melt transitions from the liquid phase to the solid phase, or the temperature at which the melt completely becomes the liquid phase, and the isosolidus value lines 31, 32, 33, 34
．． 35.36 indicates the X value of the Hg1-xCd-Te crystal precipitated from the melt.

The epitaxial growth melt 4 has Hgo, zC(L, +1
The X value of the epitaxial crystal of Hg1-xCdTe having the component composition of 09Tea,y*+ and precipitated from the cough melt is 0.2, and its liquidus temperature is about 500°C.

Figure 2-2 shows ltg, -XCd in equilibrium with the melt.
Mercury partial pressure of XTe crystal and )Igl- with X value of 0.20
x Cdx This is a relationship diagram showing the mercury partial pressure of the melt that precipitates the Te crystal, where the vertical axis is the mercury partial pressure (atmospheric pressure) and the horizontal axis is the temperature (°C
) is shown.

Curve 41 in the figure has an X value of 0°19 in equilibrium with the melt.
Hg, , is a curve representing the mercury partial pressure of a CdNTe crystal, and is equal to the mercury partial pressure at the liquidus temperature of the melt at which l'1g+-X Cdx Te crystals with an X value of 0.19 precipitate.

Curve 42 in the figure has an X value of 0°20 in equilibrium with the melt.
This is a curve representing the partial pressure of mercury in crystals of 11g1-, .

Curves 43, 44, and 45 in the figure have melt liquidus temperature t1.
12 and 13 are mercury partial pressure curves at a temperature higher than the liquidus temperature of a melt with a solid phase value x = 0.2. As shown in the figure, the smaller the solid phase value, the higher the mercury partial pressure in the melt, and the higher the temperature of the melt, the higher the mercury partial pressure.

Figure 2-3 shows Hg, -XCd, in equilibrium with the melt.
Water root partial pressure of Te crystal and t1g+□Cd with different X values
.

This is a diagram showing the mercury partial pressure of the melt in which Te crystals are precipitated, where the vertical axis shows the mercury partial pressure (atmospheric pressure) and the horizontal axis shows the temperature ('C). A curve 41 in the figure represents the mercury partial pressure of a HgI-x ca, Te crystal with an X value of 0.19 in equilibrium with the melt, and is equal to the mercury partial pressure at the melt's liquidus temperature.

Curve 42 shows H with an X value of 0°20 in equilibrium with the melt.
This is a curve representing the mercury partial pressure of the HgI-x Cd) (Te crystal, with an X value of 0.20.) equal.

Curves 5] and 52 in the figure show mercury partial pressure curves for melts with different solidus values, different liquidus temperatures, ts, and with the same mercury partial pressure at the liquidus temperature of 12 or higher. .

As shown in Figure 2-3, liquidus temperature 1. ．． 1. , if the mercury partial pressures match at a higher temperature, the liquidus temperature t4.
．． Similar properties exist even at other temperatures higher than ts. Therefore, if the temperature of the melt is uniform, in order for the mercury partial pressure to be uniform, the liquidus temperature will be higher in the area where the solidus value The temperature needs to be low.

Therefore, in the phase diagram shown in Figure 2-1, the average melt composition is set as point A, and in order to satisfy the conditions that the temperature inside the melt is the same and the mercury partial pressure is the same in each part, the composition of each part of the melt must be This results in separation into only a melt portion having a composition in the shaded area B and a melt portion having a composition in the shaded area C. If Cd is unevenly distributed in the lower part of the melt due to gravity, the composition in the lower part of the melt corresponds to the shaded area C, and the composition in the upper part of the melt corresponds to the shaded area B. As a result, the liquidus temperature is higher in the lower part of the melt, and the degree of saturation of the solute composed of Cd and l1g with respect to the solvent Te is higher, but Hg is excessively unevenly distributed in the lower part of the melt, and The solid phase value never becomes small. On the other hand, on the upper side of the melt, the liquid phase temperature of the melt is low and the melt is in an unsaturated state.

Since the epitaxial growth substrate 1 is located on the lower side of the epitaxial growth melt 4, epitaxial growth is selectively performed on the surface of the epitaxial growth substrate 1, and the solute, especially the CD concentration, in the epitaxial growth melt 4 near the growth substrate influences the epitaxial growth. As the specific gravity of the melt starts to decrease, the specific gravity of that part also decreases, so in order to prevent the specific gravity from showing an inverted distribution within the melt, the melt is poured from the upper side of the melt near the surface of the substrate for epitaxial growth.
'hM melt is fed by gravity.

The solute concentration decreases due to this supply of solute, and since the upper epitaxial growth melt with a large degree of unsaturation is in contact with the solute supply substrate 11, the solute supply substrate is melted and the melt is A decrease in solute concentration on the upper side is prevented. That is, in this way, since the solute of Cd atoms with a low diffusion rate is also supplied from the solute supply substrate H to the epitaxial growth substrate 1 in a short time, the Cd concentration in the melt decreases as the epitaxial growth progresses. In other words, Hg1-x cdX grows epitaxially from melt.
Changes in the X value of Te can be prevented, and the composition gradient along the growth direction of the epitaxially grown layer can be reduced.

Furthermore, an epitaxial crystal with a predetermined thickness is formed in a short time, and mutual diffusion between the substrate and the epitaxial layer can be reduced, resulting in a high-quality epitaxial crystal.

In addition, in this example, the epitaxial crystal is Hg1-x
Although Cd and Te were used, Hg such as FlgZnCdTe etc.
It may also be a CdTe-based compound semiconductor. Further, although the epitaxial growth substrate is made of CdZnTe, it may be made of CdTe, CdTeSe, or the like having a similar crystal structure.

In addition, in this example, the solute supply substrate was made to have the same crystal composition as the epitaxial crystal to be grown, but since the primary purpose is to supply Cd with a large segregation coefficient, it is not necessary to use the same crystal composition as the epitaxial crystal to be grown. There is no need for it to be (, CdTe
Other crystals may be used as long as they contain as a main component.

Furthermore, in this example, in order to prevent evaporation of mercury from the epitaxial growth melt, the epitaxial growth system was a closed tube system, but instead of using an ampoule with a closed structure, it was a pseudo closed tube system using an epitaxial growth container with a lid. It's okay.

Furthermore, the temperature of the epitaxial growth melt may be maintained at a constant temperature during the growth period, or after the epitaxial growth has started, it may be cooled with a predetermined temperature gradient during the growth period in order to increase the growth rate. good.

Also, an opening is provided in the lower part of the heating furnace so that, for example, nitrogen gas for cooling can be blown onto the furnace core tube through the opening.1. During epitaxial growth, the epitaxial growth rate may be increased by making the temperature of the epitaxial growth substrate located below the epitaxial growth melt lower than the temperature of the solute supply substrate located above the melt.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a decrease in the Cd concentration in the melt near the epitaxial growth substrate accompanying epitaxial growth is prevented, an epitaxial crystal with a small composition gradient in the epitaxial growth direction can be obtained in a short time, and the substrate Interdiffusion with the substrate, which causes a composition gradient near the hetero interface between the crystal and the epitaxial layer, can also be reduced, and the use of the epitaxial crystal formed by the method of the present invention has the effect of obtaining an infrared sensor with good characteristics.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the method of the present invention, Fig. 2-1 is a state diagram of a melt for epitaxial growth of Hg-Cd-Te using Te as a solvent, and Fig. 2-2 is a diagram of the Hgt-x CdXTe crystal and melt. Figure 2-3 is a graph showing the relationship between mercury partial pressure and temperature for Hgt-, Cdx Te crystals and melts with different solid phase values.
Figure 3 from al! BL to BL are cross-sectional views showing one embodiment of the method of the present invention, FIG. 4 is a cross-sectional view of a conventional epitaxial growth apparatus, and FIG. It is a diagram. In the figure, 1 is the epitaxial growth substrate, 3A is the upper groove, and 3B is the epitaxial growth substrate.
is the bottom groove, 4 is the melt for epitaxial growth, 6 is the fixing jig, 7 is the ampoule (epitaxial growth container), 1
1 is a solute supply substrate, 21 , 22.23 , 24 isoliquid phase temperature lines of the epitaxial growth melt, 31.3
2, 33. 34, 35. 36 are iso-solidus values of epitaxial crystals precipitated from the melt for epitaxial growth, 4
1.42 is a relationship curve between mercury partial pressure and temperature of Hgt-x Cdx Te crystal and melt, 43, 44.45 is a mercury partial pressure curve when the melt liquidus temperature is different, 51
．． 52 shows mercury partial pressure curves of melts with matching mercury partial pressures. ] Figure m- and CD sorun i degree t4y-cd-Te*Tet, JXtXx and rtr? Takitsu--LAil ￥4

Claims (3)

[Claims] (1) An epitaxial growth substrate (1) is held in a fixture (6) housed in an epitaxial growth container (7), and an epitaxial growth melt (4) is placed on the substrate (1).
In the method of growing an epitaxial crystal on the substrate by contacting the substrate (1) with the epitaxial growth melt (4), the epitaxial growth substrate is positioned below the epitaxial growth melt (4). At the same time, a solute supplying substrate (11) is placed above the epitaxial growth melt, and due to the difference in specific gravity and gravity between the solute dissolved from the solute supplying substrate and the solvent of the epitaxial growth melt. . A liquid phase epitaxial growth method, characterized in that a solute in the epitaxial growth melt consumed during the epitaxial growth is replenished. (2) The solute supplying substrate (11) is formed to include an element having a large segregation coefficient among the constituent elements of the epitaxial growth melt. Liquid phase epitaxial growth method. (3) The liquid phase epitaxial growth method according to claim (1), characterized in that the temperature of the epitaxial growth substrate (1) is kept lower than the temperature of the solute supply substrate (11).