JPH0360800B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for phase growth of a single layer or multilayer film of a compound semiconductor such as InP. (Prior Art and Its Problems) One of the methods for growing crystals of compound semiconductor layers is vapor phase growth, in which the raw material for crystal growth is vaporized (gasified). However, in this vapor phase growth method, the distance x from the gas injection port, that is, the upstream end of the gas flow flowing onto the substrate 1 (hereinafter referred to as the substrate upstream end), is As the distance increases, the thickness D(x) of the crystal-grown semiconductor layer 2 tends to decrease. Generally, the relationship between the distance x from the upstream end of the substrate and the film thickness D(x) of the semiconductor layer 2 is called the uniformity of film thickness distribution, and the film thickness D(x) is
If the thickness differs depending on the conditions, it is expressed as "poor uniformity of film thickness distribution." Furthermore, there is a problem in that the surface morphology of the semiconductor layer 2 grown by the vapor phase growth method is deteriorated mainly due to the presence of surface defects called growth hills and hills. In this way, if the uniformity of the film thickness or the surface morphology of the semiconductor layer 2 grown by the vapor phase growth method deteriorates, the yield during device fabrication will decrease, and it will be difficult to fabricate a device with a long distance in the x direction. It becomes difficult to do so. Therefore, improving the uniformity of the film thickness or surface morphology of the semiconductor layer 2 is an important issue in manufacturing the semiconductor layer 2. Conventionally, film thickness uniformity and surface morphology were considered to be caused by completely different causes, and separate countermeasures were taken for each as described below. (1) Measures to improve film thickness uniformity: Komeno
According to [J. Electrochem Soc. 124 (1977) 1440], the film thickness D at a distance x from the upstream end of the substrate 1
If (x) is a constant, then D(x)=C1/(25.0μ/ρV) ^1/2・(K _s /D _s )・
It is shown that it is given by x ^1/2 + 1...(1). Here, μ is the viscosity coefficient of the gas (carrier gas and source gas are collectively referred to as "gas" hereafter), ρ is the gas density, V is the gas flow rate, and K _s is the rate of chemical reaction on the surface of the substrate. The constant, Ds, is the diffusion coefficient.
The rate constant K _s of the chemical reaction on the surface of this substrate
is a function of temperature only and assumes that the chemical reaction at the surface is a first-order reaction. By further transforming equation (1), the following equation regarding film thickness can be obtained. The first equation of equation (2) shows that [{D(0)/D(x)}-1] ² and x are in a proportional relationship, and the proportionality constant is F _h . Here, D(0) is the film thickness at which the distance x from the upstream end of the substrate is zero, and F _h is a film thickness parameter used as a parameter representing the uniformity of the film thickness. As is clear from the second equation (2), the film thickness parameter F _h is inversely proportional to the gas flow rate V, that is, the gas flow rate. Therefore, in order to reduce the film thickness parameter F _h and improve the uniformity of the film thickness, the gas flow velocity V
In other words, the gas flow rate may be increased. this
Komeno et al.'s proposal has wide public support. The following method is actually used to improve the uniformity of film thickness. a○ Based on the prediction that as the gas flow rate increases, the thickness of the boundary layer becomes thinner, diffusion control is suppressed, and the uniformity of the film thickness distribution improves. and grow it. This is an example of an improvement based on the idea of Mr. Komeno et al. mentioned above. b○ The substrate surface is tilted at an angle θ with respect to the gas flow, and the substrate is further rotated. The optimum value for the angle θ is found through experiments. However, for a○, the flow rate of gas is about five times higher than usual, so the flow rate of highly toxic Group V gases such as AsH ₃ and PH ₃ must also be increased, which poses safety concerns. There is a problem with this. In addition, the amount of gas consumed increases, and the processing capacity for exhaust gas must also be increased, which poses problems in terms of economic efficiency. Regarding b○, it is relatively easy to implement in a vapor phase growth apparatus that has one growth chamber and is mainly used for producing a single layer, but it is typical for semiconductor lasers that have two or more growth chambers. This is extremely difficult, if not impossible, to implement in a vapor phase growth apparatus for producing a multilayer structure. (2) Measures to improve surface morphology: For example, the InP crystal surface has growth hills with a diameter of 1 mm or less and a height of several μm, close to a cone, and an ellipse with a major axis of several hundred μm and a minor axis of several 10 μm. There are hills with a shaped bottom and a height of several μm. There are various theories as to the origin of growth mounds and hirotsuku, and they can be summarized as follows. Foreign matter adhering to the substrate acts as a nucleus for crystallization during growth, causing abnormal growth and forming surface defects there. Alternatively, precipitates on the inner wall of the reaction tube fall onto the substrate during growth, which exerts the same effect as the foreign matter adhering to the substrate. If the type of etchant, etching conditions, and etching treatment method are not optimized during substrate etching, a portion of the substrate surface will undergo deterioration such as oxidation, and this deterioration will cause surface defects to be formed. If the partial pressure of the gas supplying the group during compound semiconductor growth is greater than the partial pressure of the gas supplying the group, liquefied metal of the group tends to be formed on the substrate, where the VSL mechanism Abnormal growth occurs based on the principle explained in . Conventionally, surface morphology has been improved based on these factors. for example,
In order to prevent precipitates on the inner wall of the reaction tube from falling onto the substrate, the growth surface of the substrate should be on the lower side; in order to optimize the substrate etching process and suppress deterioration of the substrate surface; It has been done to increase the partial pressure to or greater than the partial pressure of the gas supplying the group. However, although this method is easy to implement in a vapor phase growth apparatus that has one growth chamber and is used to fabricate a single layer, it has two or more growth chambers and is used to fabricate a multilayer structure such as a semiconductor laser. It is difficult to implement this method using a vapor phase growth apparatus for manufacturing. Also, regarding the method, for example,
Considering the case of etching an InP substrate, it is usually 2
Types of etchingants i.e. 1H ₂ SO ₄ : 8H ₂ O ₂ :
Using _1H2O solution and 0.6Br: _99.4CH3OH solution,
The etching conditions were 0°C for 2 minutes and 25°C for 3 minutes.
Even if the types are limited, it is by no means easy to optimize the etching process by changing the mixing ratio of each solution and further changing the temperature and processing time as etching conditions. Furthermore, although the method has the advantage of being easy to implement, for example, when growing - group compound semiconductors, extremely toxic group supply gases such as _As H ₃ and PH ₃ are used in larger quantities than usual. There is a safety issue when using it. As is clear from the explanation of the abnormality, in the past, film thickness uniformity and surface morphology deteriorated due to different causes, so separate countermeasures were taken for each cause. It has been difficult to obtain a high-quality semiconductor layer that satisfies both of the above requirements. (Object of the Invention) In view of the above-mentioned shortcomings of the prior art, the present invention improves film thickness uniformity and surface morphology at the same time by changing the partial pressure of the raw material gas without changing the gas flow rate, that is, the gas flow rate. It is an object of the present invention to provide an improved vapor phase growth method capable of growing an excellent compound semiconductor layer. (Structure and operation of the invention) In order to achieve this object, the vapor phase growth method according to the present invention provides an InP single layer film or an In _1-a film on an InP substrate.
In the hydride vapor phase growth method for compound semiconductor layers in which a multilayer film of Ga _x As _1-y P _y system (0x1, 0y1) is grown under normal pressure, the compound semiconductor to be crystal grown under conditions of a constant gas flow rate. The structure is characterized in that growth is performed so that the partial pressures of the raw material gases in each layer are equal in the range from 7/1500 to 7/2800. The present invention will be explained in detail below. From equation (2) above, it is clear that the film thickness parameter F _h is inversely proportional to the gas flow rate V, that is, the gas flow rate, and as mentioned above, the film thickness parameter F _h is determined only by the gas flow rate V. The theory that it does not depend on the partial pressure ratio of the raw material gas has been widely supported. However, the inventor of the present application found that although the phenomenon that occurs on the substrate during vapor phase growth approximately follows the growth mechanism expressed by equation (1), the rate constant K _s indicating the surface reaction of the substrate is not a simple first-order reaction. It was thought that this would be influenced by the flow rate of the raw material gas. In other words, even if the growth temperature and gas flow rate V are kept constant, the film thickness parameter F _h can be changed by changing the ratio of the source gas to the gas (= flow rate of source gas + flow rate of carrier gas), that is, the partial pressure of the source gas. I thought that would change. In order to prove this logic, the inventor of the present application fixed the growth temperature of 700 (℃) and the gas flow rate of 1500 (cc min ^-1 ) for the InP homoepitaxial layer, which is said to be particularly difficult to crystallize. Minutes of raw material gas

【table】

[Table] Experiments were conducted by changing the pressure. Table 1 shows the experimental results using hydride vapor phase growth. As is clear from Table 1, even if the growth temperature and gas flow rate of 1500 (cc min ^-1 ) are constant, 10% In-
By changing the HCl flow rate and 10% PH ₃ flow rate, that is, by changing the raw material gas flow rate (partial pressure of raw material gas), the film thickness parameter F _h also changes ^{. 1} ), the film thickness parameter F _h has the minimum value. The partial pressure of the 10% In-HCl raw material gas at this time is: Raw material gas flow rate/Gas flow rate = 70 x 10/100/1500 = 7
/1500. In addition, the growth temperature was kept constant, and the gas flow rate V (gas flow rate) was changed from 1500 (cc min ^-1 ) to 2800 (cc min -1).
min ^-1 ), the film thickness parameter F _h changes from 0.11 (mm ^-1 ) to 0.02 (mm ^-1 ) as described in the conventional improvement example.
However, the gas flow rate is 2800 (cc・
min ^-1 ), the film thickness parameter F _h is also changed by changing the flow rate of the source gas. In this way, the growth temperature and gas flow rate V (gas flow rate)
Even if F h is kept constant, the film thickness parameter F _h can be changed by changing the partial pressure of the raw material gas, and there is an optimum value of the partial pressure of the raw material gas at which the film thickness parameter F _h is minimized. It is considered that the optimum value of the partial pressure of the raw material gas (raw material gas flow rate) has a value specific to the raw material used for crystal growth. For example, in the case of ternary mixed crystal InGaAs that is lattice-matched to the InP substrate, the gas flow rate is 1000 c.c.・min ^-1 , and 10% In-HCl and 10% Ga
-The flow rates of Cl and 10% AsH ₃ were 58 c.c.・min ^-1 , respectively.
When the film thickness was 8 c.c., min ^-1 and 65 c.c.min ^-1 , F _h =0.05 was obtained as the optimum film thickness parameter. In addition, in the case of quaternary mixed crystal InGaAsP, which is lattice-matched to the InP substrate and has a wavelength-converted forbidden band width of 1.5 μm, the gas flow rate is 1100 μm.
cc・min ^-1 and 10% In-HCl, 10%-GaCl, 10
The flow rate of %PH ₃ and 10% AsH ₃ is 60c.c.・
min ^-1 , 5c.c.・min ^-1 , 20c.c.・min ^-1 , 46c.c.・
When min ^-1, the optimal film thickness parameter is F _h = 0.04
was gotten. In addition, in order to confirm whether the above-mentioned theory can be applied to heteroepitaxial growth, the following experiment was repeated. In _1-x Ga _x As _1-y P _y system (0x
InP/1,0y1) multilayer film
When growing three layers of InGaAsP/InGaAs heteroepitaxially, the InP layer as the cap layer is grown as shown in Table 1.
It was grown under the same growth conditions as wafer F62 inside.
At this time, the film thickness parameter F _h of the InP cap layer is
The value was 0.10 to 0.20 (mm ^-1 ), which was almost equal to the value during homoepitaxial growth (0.11 mm ^-1 ). That is, even in heteroepitaxial growth, the optimal value of the partial pressure of the source gas at which the film thickness parameter F _h is minimized is approximately constant. Figure 2 shows InP homoepitaxial growth on an InP substrate using hydride vapor phase epitaxy under the partial pressure conditions of the source gas for each of the samples F62, F89, F95, F97, F99, and F105 listed in Table 1. This is a diagram illustrating the thickness distribution of the layers. The horizontal axis is the distance x/mm from the upstream end of the substrate, and the vertical axis is the film thickness D(x)/D(0), which is the film thickness D(x) normalized by the film thickness D(0) at the upstream end of the substrate x=0. ). Figure 3 shows the experimental results in Table 1 based on equation (2) described above, with [D(0)/D(x)-1] ² plotted on the vertical axis and distance x/mm on the horizontal axis. It is plotted on a plane, and each sample F62, F89, F95, F97,
The measurement results for F99 and F105 are almost on a straight line. As is clear from the first equation (2), F _h can be determined from the slope of this straight line. In Figure 4, the film thickness parameter F _h is determined from the gradient of the straight line in Figure 3 on the vertical axis, and is plotted on the horizontal axis as a function of the partial pressure P _IoCl of InCl gas, which is the raw material gas of the group. Partial pressure of raw material gas and film thickness parameters from
This allows the relationship with F _h to be clearly understood. Here, the white circles are for a flow rate of 1500 c.c.・min ^-1 , and the black circles are for a flow rate of 2800 c.c.・min ^-1 . As you can see from this figure, by changing the partial pressure under the condition of constant flow rate, the optimal film thickness parameter can be determined.
It can be seen that F _h can be obtained. In the above explanation, only the relationship between the uniformity of the film thickness and the partial pressure of the raw material gas has been described. Next, the relationship between the partial pressure of the raw material gas or the uniformity of the film thickness and the surface morphology will be explained. Table 2 shows the growth temperature 700 (℃) and the gas flow rate 1500 (cc・
Wafers F62 and F89 grown with constant min ^-1 )
It shows the results of measuring the areal density of growth mounds, the diameter of growth mounds, and the areal density of hirotsuku in F95 and F95.

[Table] Wafer F62, which has the smallest film thickness parameter F _h , suppresses both growth hills and hills and obtains good surface morphology, whereas wafer F89, which has the largest film thickness parameter F _h , has a large growth hill diameter and areal density. However, as the distance x increased from the center of the wafer, countless small hills were present, and a surface morphology different from that of a normal wafer was observed. Furthermore, wafer F95, which has a relatively large film thickness parameter F _h , has many growth hills and hills, and its surface morphology is deteriorated. As mentioned above, both wafers F89 and F95 cannot be used due to poor surface morphology. Therefore, among the wafers listed in Table 1, wafers F62, F97, F99, and F105 can be used, and the maximum value of the film thickness parameter F _h at that time is 0.18 (mm ^-1 ). Here, if F105 is excluded because the partial pressure of the InCl raw material gas is small, the growth rate is slow and the growth takes time, and if this is excluded, F99, F97, and F62 are preferred examples. In these examples, InCl
The partial pressure of the raw material gas and the partial pressure of the PH ₃ raw material gas are the same for each example, and the partial pressures are each 10/280 from Table 1.
0.7/2800, 7/1500. 7/1500 is almost 13/2800
Therefore, the preferable range of the partial pressure ratio is from 7/1500 to 7/2800. Figure 5 shows the film thickness parameter F _h shown in Figure 4.
The diameter of the growth hill, the areal density of the growth hill, and the surface density of the growth hill are plotted on the same drawing so that you can see the relationship between The size of the areal density of Hirotsuku is 0.5 mm, 10 pieces cm ^-2 , 10 pieces, respectively on the right side.
It is shown as the length of the diagonal line in cm ^-2 . As is clear from the figure, when the film thickness parameter F _h is minimized, the length of each diagonal line shown in the figure becomes short, the surface morphology becomes good, and an excellent semiconductor layer can be provided. Also, similar to the experimental results for the film thickness parameter F _h ,
Even if a multilayer film such as InP/InGaAsP/InGaAs is grown by heteroepitaxial growth, Table 2
Almost the same experimental results were obtained. (Effects of the Invention) As described above, the present invention makes it possible to improve film thickness uniformity and surface morphology, which have conventionally been taken from separate viewpoints, with a single method of changing the partial pressure of the raw material gas. Since high-quality wafers can be easily obtained, it is possible to not only improve the manufacturing efficiency but also improve the yield during device manufacturing, and it is also possible to manufacture devices with long element lengths.
The effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the general characteristics of vapor phase growth, and FIGS. 2, 3, 4, and 5 are characteristic diagrams for explaining the principle of the present invention.

Claims (1)

[Claims] 1 InP single layer film or In _1-a Ga _x on InP substrate
In the bydride vapor phase epitaxy of a compound semiconductor layer in which a multilayer film of the As _1-y P _y system (0x1,0y1) is grown under normal pressure, the crystal growth of the compound semiconductor layer is performed under conditions of a constant gas flow rate. A vapor phase growth method characterized by growing the partial pressure of each source gas at the same level in the range of 7/1500 to 7/2800.