JPS5857901B2 - Crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal growth method for controlling to some extent the stringiness and impurity concentration in a grown layer obtained by solution epitaxial growth.

Needless to say, manufacturing semiconductor elements with good characteristics at a high yield is the most important thing in the semiconductor industry.

Regarding the process of epitaxial growth of semiconductor crystals, one of the issues is how to make the growth layer have the desired impurity distribution profile and, in the case of mixed crystals, the desired distribution profile of the mixed crystal ratio. be.

In a typical solution epitaxial growth method, a solution containing a substance to be grown and impurities is brought into contact with a substrate at a saturation temperature, and then cooled at an appropriate rate to obtain a grown layer on the substrate.

However, in such a method, as inferred from the phase diagram, a segregation phenomenon occurs and changes in impurity concentration and mixed crystal ratio occur in the grown layer.

For example, regarding an element with a segregation coefficient greater than 1, as the growth progresses, the element is incorporated into the growth layer at a high concentration, so the concentration in the solution unilaterally decreases.

Therefore, the concentration in the growth layer also decreases unilaterally.

For elements with a segregation coefficient smaller than 1, the concentration in the growth layer increases unilaterally, contrary to the above.

It is unnecessary to explain further that these phenomena occur more strongly as the segregation coefficient becomes more distant from 1.

A solution growth length accompanied by the above-mentioned segregation phenomenon can be very difficult, especially when a thick growth layer is required.

For example, in order to maintain the mixed crystal ratio and impurity concentration above a certain value up to a certain thickness, a solution that takes into account segregation is required in advance.

In addition, the mixed crystal ratio and impurity concentration near the start or end of growth vary greatly due to this segregation phenomenon, so changes in the mixed crystal ratio also occur between the substrate and the growth layer and the growth layer itself. The resulting differences in crystal lattice constants and thermal expansion coefficients cause bending and cracking of the sample.

Even if the concentration of impurity elements changes too rapidly, the electrical resistance value may deviate from the target value or the crystallinity may deteriorate.
This makes it difficult to manufacture semiconductor devices with a high yield.

The phenomenon that the mixed crystal ratio changes is Ga(1-x)Al xAs
(xi-sithi), GaAs(,-x)PX, Ga
(1-X)AtxP.

Ib-V including In(1-X)AlxAs etc.
Commonly known as a group B mixed crystal.

The method to reduce bending and cracking of the sample as described above is as follows:
The goal is to maintain a constant minimum mixed crystal ratio for the entire growth layer.

The same can be said about impurity concentration.

In addition, by doing this, deviations from the target values of the mixed crystal ratio and impurity concentration will be eliminated, increasing the reliability of electrode alignment, diffusion, bonding, etc. in subsequent processes, leading to improved yields. is good.

The following methods are known to eliminate the above-mentioned drawbacks in normal solution growth.

This will be explained with reference to FIG. First, the solution raw material is heated to a high temperature above the saturation temperature, and all of it is dissolved to form the solution 10.Next, this is cooled down to below the saturation temperature, and the microcrystals 11 are precipitated in the solution.In this state, it is brought into contact with the substrate 12. C8 At this time, a temperature gradient is created that increases from the substrate 12 toward the liquid 10.

This temperature gradient causes a solute concentration gradient in the solution 10, and as the microcrystals 11 are redissolved, an epitaxial growth layer 13 grows on the substrate 12 (d).

Naturally, segregation occurs during this growth, but
The difference from normal solution growth is that there are 1 microcrystals in the solution 10.
1 exists.

Taking an element with a segregation coefficient larger than 1 as an example, the microcrystal 11 contains that element at a high concentration.

When the growth layer 13 starts growing on the substrate 12, the concentration of the element in the solution 10 decreases, but the element is supplied into the solution 10 by redissolving the microcrystals 11 containing the element at a high concentration.

Therefore, the decrease in the concentration of the solution taken into the growth layer 13 and the increase in the concentration supplied from the microcrystals 11 are balanced, and the concentration of the solution 10 is kept at an almost constant value, and the concentration of the solution in the growth layer 13 is kept constant. The concentration, that is, the mixed crystal ratio and the impurity concentration are also almost constant.

Contrary to the above, in the case of elements with segregation coefficients smaller than 1,
The above-mentioned inverse relationship, that is, the increase in concentration in the solution is diluted by the dissolution of the microcrystals, and is not explained here.

In any case, a grown layer with a nearly constant mixed crystal ratio and impurity concentration can be obtained.

However, the biggest drawback of the above method is that if there are microcrystals present in the immediate vicinity of the substrate, these microcrystals will not be redissolved, and on the contrary, similar to epitaxial growth on the substrate, they will grow into large crystals. It is a matter of growing up.

For this reason, the grown layer may adhere to the substrate, or the grown layer may become depressed in that area, making it difficult to obtain a good grown layer.

An object of the present invention is to provide a method for obtaining a grown layer in which the mixed crystal ratio and impurity concentration in the grown layer are substantially constant without causing unevenness in the grown layer, which is a drawback of the above-mentioned methods.

In order to achieve the above purpose, a solution containing microcrystals,
At least two solutions with different saturation temperatures are used, one containing little or no microcrystals.

This concept will be explained with reference to FIG.

Prepare a T1 solution 21 with a high saturation temperature and a T2 solution 22 with a low saturation temperature, and raise the temperature to the saturation temperature or higher at each different position.a
.

Next, both are cooled to the saturation temperature T2 of the solution 22.

In this case, the respective temperatures may be the same, or the solution 21 may be higher than the solution 22 by a temperature gradient that will be explained later.

In any case, since the temperature of the solution 22 is about its saturation temperature, there are almost no microcrystals present.

However, since the temperature of the solution 21 is cooled to a temperature sufficiently lower than its saturation temperature, a sufficient amount of microcrystals 24 are present.

In this state, as shown in C, the solutions 21 and 22 are brought into contact with the substrate 23 in a side inch shape.

At this time, if a temperature gradient is formed that increases from the substrate 23 toward the solutions 22 and 21, the microcrystals 24 are redissolved and a growth layer 25 is obtained on the substrate.

The reason why the mixed crystal ratio and the impurity concentration of the growth layer 25 are kept substantially uniform is the same as the principle described above, so a description thereof will be omitted here.

According to the present invention, since the solution 22 in contact with the substrate 23 does not contain microcrystals, no unevenness is created in the growth layer, and a flat growth layer can be obtained.

The following points need to be emphasized in the above.

The first point is that the number of solutions is not limited to two.

It is sufficient that only the solution in direct contact with the substrate contains almost no microcrystals, and the essence is the same even if other types of solutions containing microcrystals in contact with the substrate exist in multiple stages.

The second point is that the principles of the present invention are not changed in the relative positions of the substrate and various solutions before the start of growth, the method of moving the positions of each solution for growth, and especially the shape of the jig.

Hereinafter, an example of the apparatus used in the present invention will be explained with reference to the drawings.

The apparatus shown in FIG. 3 includes a fixing part 32 capable of holding a substrate 31, a slider part 34 for holding a solution 33,
and a slider portion 36 for holding a solution 35.

Note that the slider 36 has a hole 37 necessary for setting the solution 33 in advance.

The slider portions 34 and 36 and the fixing portion 32 overlap each other in close contact with each other as shown in the figure, and the slider portion 34 and
36 can be moved independently in the horizontal direction by operating rods (not shown).

The method for contacting the growth solution with the substrate is to first move the slider 34 horizontally to bring the solution 33 into contact with the substrate 31, and then move the slider 36 horizontally to bring the solution 35 into contact with the solution 33. good.

Alternatively, move the slider 36 to remove the solution 35 and solution 3.
The solution 33 and the substrate 31 may be brought into contact with each other by moving both the sliders 34 and 36 while keeping the solution 33 in contact with the substrate 31.

Also, the separation of the solution and the substrate after growth is done using the slider part 3.
4 and 36 may be moved to their original states or further moved.

The apparatus shown in FIG. 4 is a simplified version of the above-mentioned apparatus, and includes a fixing part 42 that holds a substrate 41, a fixing part 44 that can hold a solution 43 directly above the substrate 41, and a solution 45. It consists of a slider part 46 that can be inserted.

The slider part 46 has a hole 47 for presetting the solution 45.

The solution for growth is brought into contact with the substrate by horizontally moving the slider portion 46 using an operating rod (not shown) to bring the solution 45 into contact with the substrate 41.

At this time, since the solution 43 is located directly above the substrate 41, the solution 43 automatically comes into contact with the solution 45.

After the growth, the substrate and the solution can be separated by pulling out the slider 46 or, conversely, pushing it further.

FIG. 5 shows a cylindrical fixing part 52 for holding the board 51.
This device consists of a slider part 55 with an operating rod 54 for holding a solution 53, and a slider part 58 with an operating rod 56 for holding a solution 57.

Note that the slider portion 58 has a hole 59 for setting the solution 53 in advance.

The slider parts 55 and 58 can be slid by rotation by the operating rods 54, 56.

Contact between the solution and the substrate for growth is achieved through the slider part 55.
is rotated with the operation rod 54 to bring the solution 53 and the substrate 51 into contact with each other, and then the slider portion 58 is rotated with the operation rod 56 to bring the solution 57 and the solution 53 into contact with each other.

Alternatively, the solution 53 and the solution 57 may be kept in contact with each other, and both may be rotated simultaneously to contact the substrate 51.

Alternatively, in the same way as described with the apparatus shown in FIG. 4, the solution 57 in the slider part 58 is fixed at a position directly above the substrate 51, and the slider part 55 is rotated to separate the substrate 51 and the solution 53. You may contact me.

After the growth, the solution and the substrate can be separated by rotating the slider part 55.

The above is an example of an apparatus using two types of solutions, but the principle is the same even if some of the sliders have three or more stages.

Furthermore, even if there are two or more substrates, the number of solutions held on a portion of each slider may be divided into two or more.

The present invention will be described above using Examples.

Example 1 Ga
(1-x) Al x As (x is the mixed crystal ratio.

1>x>O) was grown.

The dimensions of the device are as follows: The thickness of the fixed part 32 is 20M11L1, the length is 100 mm, and the thickness of the slider parts 34 and 36 is 1 mm each.
011L11L length is 7Qmi each.

The width of each of the three is 3Qmi. As shown in FIG. 3, the fixing part and part of the two sliders have holes 33 and 35 for inserting the substrate 31 and for inserting the solution.

The size of each is 10X10X10.

Note that the hole into which the substrate 31 is inserted has a depth of 800 μm1, and the other holes are through holes.

The substrate used was a CaAs (ioo) surface, 300 μm thick and 10×IO.

As solution 33, 20 g of Ga, 2.7 g of GaAs
g, At 501'''W and Ga as solution 35.
20 g1GaAs3.5 glAl 60mlI was used.

The device with this set was placed in a quartz reaction tube with a rectangular cross section, filled with H2 gas, and air was completely exhausted.

It was heated to 970'C in electric furnaces placed above and below the reaction tube and maintained for 1 hour.

Next, the entire device was cooled, but at this time, there was a
A temperature gradient was created that was 10°C higher than crn, and the temperature of the substrate was set at 940°C.

Note that holes for thermocouples for temperature measurement are not shown in FIG.

Next, the slider portion 36 was moved by the operating rod to bring the solutions 33 and 35 into contact, and further moved to bring them into contact with the substrate 31.

This state was maintained for 10 hours while maintaining the temperature gradient.

Next, the slider portion 34 was pulled out to separate the substrate from the solution, and the solution was cooled to room temperature.

The substrate has a mixed crystal ratio of X″F0.4 and a thickness of 500±20μ.
m of Ga1-XAIXAs were growing.

The grown layer has no irregularities due to microcrystals, and no fluctuations in the mixed crystal ratio X are observed.

In comparison, when the solution 33 having the above composition was not used, the unevenness due to microcrystals generated in the solution 35 was severe, and the thickness was 500±250 μm.

This shows that the method according to the present invention can provide an extremely good growth layer.

Example 2 GaAs was grown using the apparatus shown in FIG.

The device is made of graphite and the length of the fixed part 42.44 and the slider part 46 is 30 mm wide.

Further, the thickness of the fixed part 42, 44 is 20+++mlO, and the thickness of the slider part is 1Qmm.

The substrate is a GaAs (100) plane with a thickness of 300 μm.

The size is 10 x 20-.

Solution 43 contains Ga 20 g1GaAs4.5 glZ
n 1001'l' to solution 45 is Ga 20 g
80 intl of 1GaAs3.9 glZ n was used.

These were set as shown in FIG. 4 and inserted into the reaction tube of Example 1.

The reaction tube was filled with H2, heated to 950°C in an electric furnace, and the substrate temperature was immediately cooled to 900'C.

At this time, a temperature gradient was formed in the apparatus in which the temperature increased by 58 C per 1 cm.

Immediately move the slider 46 with the operating rod to remove the solution 45.
At the same time, the solution 45 and the substrate 41 are brought into contact with each other.
came into contact with.

This state was maintained for 30 minutes while maintaining the temperature gradient, and the slider 46 was moved again to separate the substrate from the solution, and the solution was cooled to room temperature.

As a result, GaA with a flat thickness of 300±30 μm and an impurity concentration of 1×10 cm−3 was deposited on the substrate.
s growth layer was obtained.

In comparison, in the method that does not use the solution 45, the growth layer has depressions due to the microcrystals generated in the solution 43, and 3
It had a variation of 00±100 μm.

As a result, it was found that the method of the present invention allows a growth layer with extremely good flatness to be obtained.

Example 3 Ga, -xAl-As was grown using the apparatus shown in FIG.

The outer diameter of the fixed part 52 and slider part 55°58 is 80Tn.
It is m.

The thickness of the fixed part 52 and the slider part 58 is 4Q+
It is o+.

The diameter of the hole into which solution 53.57 is placed is 12 mm.

The slider part 55 was prepared in five types with thicknesses of 1 mm, 2 mm, 5 mm, 10 mm, and 151 mm.

Here, as the solution 57, 20 g of Ga, 3.5 g of GaAs
25 g of Qa as solution 53 using 1A 155 mV
1GaAs3g.

Al50m? was used.

Since the amount of the solution 53 is larger than necessary, the solution 53 reaches the hole 59.

Thus, when slider portions 58 or 55 are rotated, the holes in slider portion 55 are filled to the brim with solution 53, while the volume that was in hole 59 is not available for growth.

The substrate used was a GaAs (100) plane with a thickness of 300 pm and a size of 15 x 15 mm.

The apparatus thus constructed was placed in a cylindrical quartz reaction tube and filled with H2 gas.

The reaction tube was surrounded and heated to 9700C in an electric furnace with two upper and lower duns.

Next, the temperature of the substrate is cooled to 940°C, and the slider 58
was rotated with the operating rod 56 so that the solution 57 was placed directly above the substrate 51.

Next, the slider 55 is rotated with the operation rod 54, and the solution 53 is
and the substrate 51 are brought into contact with each other.

At this time, the temperature inside the device in the electric furnace is 15°C per 1Cr above.
A temperature gradient was formed in which the temperature increased.

After maintaining this state for 15 hours, the slider portion 55 was rotated again to separate the substrate from the solution, and the solution was cooled to room temperature.

It has been found that the shape of the grown layer thus obtained is related to the thickness of the slider portion 55.

That is, when the thickness was 1 mm, unevenness due to the microcrystals in the solution 57 was generated in the growth layer, and the unevenness was 600±300 μm, which was the same as when the solution 53 was not used.

On the contrary, when a slider having a thickness of 2 mm or more was used, flat growth of about 600±40 μm was obtained.

This means that in order to obtain a good growth layer, slider 55
It can be seen that a thickness of at least 2 mm or more is required.

It is also obvious that the same thing can be said about the devices shown in FIGS. 3 and 4.

Example 4 Growth was carried out using the same apparatus and under almost the same conditions as in Example 1.

In this case, the difference from Example 1 is that after the solution came into contact with the substrate, it was cooled to 800° C. while maintaining the temperature gradient.

As a result, when the cooling rate was 10° C./hr or less, the same results as in the case of growing only with a temperature gradient without cooling (Example 1) were obtained.

However, if the cooling rate is greater than 10°C/hour,
The grown layer becomes uneven and its average thickness decreases.

This is because if the rate at which microcrystals are redissolved due to the temperature gradient is faster than the rate at which microcrystals are precipitated in the solution by cooling, unevenness will not occur in the growth layer, and the critical value is 10°C/
It is considered to be hr.

The significance of being able to perform growth while cooling is that thermal alteration of the substrate, growth layer, or solution can be reduced, and the movement of impurities due to thermal diffusion in the growth layer or substrate can be reduced.

From the above, it can be seen that the method according to the present invention may be performed by cooling.

As explained above, by using the present invention, it is possible to grow a material with a substantially uniform mixed crystal ratio and impurity concentration, and at the same time obtain a flat growth layer, thereby improving the manufacturing yield of semiconductor devices.

As described in the Examples, the method according to the present invention is based on GaA
In addition to the growth of s, Ga1-xAlxAs, GaP.

2) It goes without saying that it can be applied to various solution growths such as n1-xGaP and GaAs1-xPx.

Additionally, the shape of the device can be modified in various ways other than those shown in Figures 3, 4, and 5, but as long as the principle is not changed, the results will be exactly the same. That is clear.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of crystal growth by the conventional method, FIG. 2 is a diagram explaining the principle of the crystal growth method according to the present invention, and FIGS. 3, 4, and 5 are diagrams used in the present invention. 1 is a cross-sectional view of an example of a crystal growth apparatus. 3L4L51: Board, 32, 42, 52: Fixed part, 33
, 45, 53: Solution containing no microcrystals, 34, 46, 5
5 Part of varnish slider, 36: Part of upper slider, 44, 5
8: Upper fixed part, 35° 43.57: Solution containing microcrystals, 37, 47. 59: Hole for setting solution in advance, 54, 56: Operation rod.

Claims (1)

[Claims] 1. A crystal growth method including the following steps. (1) A step of heating two or more solutions with different string strengths to a temperature higher than the growth temperature. (2) A step of lowering the temperature of the solution to the growth temperature to form a solution containing microcrystals and a solution not containing microcrystals. (3) The solution containing the microcrystals and the solution not containing the microcrystals are stacked on the substrate so that the solution not containing the microcrystals is in contact with the substrate surface, and the temperature is adjusted in the direction from the substrate to the solution. A step of epitaxially growing on the substrate using a temperature gradient.