JPH07201735A - Crystal growth method of compound semiconductor - Google Patents

Abstract

(57) [Summary] [Objective] A ternary mixed crystal or graded layer of a compound semiconductor having a different composition is formed without temperature change and growth interruption of a K cell. The temperature of the K cell is kept constant at a predetermined value, and the temperature of the substrate is changed within a temperature range in which the composition of one semiconductor does not change and the composition of the other semiconductor does not change. [Effect] A ternary mixed crystal and a graded layer of compound semiconductors having different compositions can be formed only by changing the substrate temperature without changing the K cell temperature. In addition, the interface level is not generated at the hetero interface, and the performance of the hetero device is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method for a compound semiconductor, and more particularly to a crystal growth method for a compound semiconductor suitable for growing the composition of a ternary mixed crystal continuously or stepwise.

[0002]

2. Description of the Related Art A ternary mixed crystal (eg, AlGa) used as a base in a hetero device typified by HBT (heterojunction bipolar transistor).
By growing a layer (graded layer) in which the composition of (As) is continuously changed in the film thickness direction, the band structure of the hetero interface is smoothed and a technique for improving the performance of the device is developed. It is being actively studied, for example, Applied Physics Letter. 46 (6), 15 March 1985,
Page 600 (Appl. Phys. Let. 46
(6), 15 March 1685 p600), or 1991 EEE GaAs.
IC ・ Symposium Page 117 (1991 IEEE
GaAs IC Symposium p117) and the like. In the case of AlGaAs, the composition of the ternary mixed crystal is determined by the ratio of AlAs and GaAs. For example, in the composition of x = 0.3, AlAs is 30%, G
It shows AlGaAs in which aAs is 70%.

When the above graded layer is grown by the conventional molecular beam epitaxy method (MBE method), one of the two compounds forming the ternary mixed crystal is sequentially changed to change the growth rate. The graded layer was formed by changing the ratio of the two compounds in the film thickness direction.

The growth rate in the MBE method is determined by the amount of molecules flying to the substrate. The amount of molecules flying in has a correlation with the vapor pressure of the source, and the vapor pressure is controlled by the K cell (molecular beam source) temperature. Therefore, in order to change the growth rate of the compound, a method of changing the K cell temperature is generally performed as described in, for example, Kiyoshi Takahashi, Molecular Beam Epitaxy Technology, Industrial Research Committee.

However, since the K cell is normally heated by resistance heating by a tantalum heater, there is always a time lag until the actual source temperature reaches the set value. Therefore, it is impossible to control the growth rate change in real time by changing the K cell temperature.

In order to solve this problem, the temperature control of the K cell is programmed, and the start of the temperature change of the K cell is made earlier than the start of the growth of the graded layer, so that the influence of the time lag is reduced. A method of lowering it as much as possible has been proposed.

When forming a heterostructure with a graded layer sandwiched between them, growth must be started after setting the K cell temperature in accordance with each mixed crystal ratio.
Growth had to be interrupted at each heterointerface. Therefore, there is a problem that not only the growth time becomes long, but also the interface state is generated at each hetero interface due to the interruption of the growth, and the device characteristics are deteriorated.

[0008]

As described above, according to the conventional method, in order to form a ternary mixed crystal or a graded layer having a different composition by the MBE method, the crystal is formed while changing the K cell temperature. Since it is necessary to grow the crystal, there is a time lag between the K cell temperature and the growth rate, and it is difficult to control the crystal growth in real time.

Further, when forming a heterostructure of a ternary mixed crystal having a different mixed crystal ratio or a heterostructure sandwiching a graded layer whose composition continuously changes, it is adjusted to each mixed crystal ratio. Since it was necessary to start the growth after setting the K cell temperature, it was necessary to stop the growth at each hetero interface. Therefore, not only the growth time becomes longer, but also the interface states due to the growth interruption occur at the hetero interface,
There was a problem of degrading device characteristics.

The object of the present invention is to solve the above-mentioned problems of the prior art and to provide a heterostructure or a gray structure of a ternary mixed crystal having a different mixed crystal ratio.
It is an object of the present invention to provide a compound semiconductor crystal growth method capable of easily forming a heterostructure sandwiching a dead layer with high accuracy.

[0011]

In order to achieve the above object, the present invention provides a method of growing a ternary mixed crystal by irradiating a laser beam on the surface of a semiconductor substrate while performing the growth.
Of the two semiconductors (compounds) that compose the original mixed crystal, the laser light output is stepwise or continuous within a temperature range in which the growth rate of one semiconductor does not decrease and the growth rate of the other semiconductor does not decrease. And the substrate temperature is changed stepwise or continuously in a state close to real time to change the growth rate of one of the two semiconductors forming the ternary mixed crystal.

[0012]

The surface temperature of the substrate on which the ternary mixed crystal is growing is irradiated with laser light while monitoring the surface temperature of the substrate with a pyrometer, and the substrate temperature is adjusted to one of two semiconductors forming the ternary mixed crystal. The mixed crystal ratio of the ternary mixed crystal is changed to an arbitrary value corresponding to the above temperature by controlling the temperature to sequentially reach a predetermined temperature within a temperature range where the growth rate decreases.

Further, by inputting the value of the pyrometer to the computer and feeding back the data to the laser output, the temperature of the substrate is adjusted so that the two semiconductors forming a ternary mixed crystal can be obtained. One of the graded layers is a substrate under growth, in which the graded layer continuously changes in a temperature region where the growth rate of one of the three decreases and near real time, and the mixed crystal ratio of the ternary mixed crystal changes continuously. It is formed only by changing the temperature.

[0014]

【Example】

<Embodiment 1> FIG. 1 shows an outline of the MBE apparatus used in this embodiment. A liquid nitrogen shroud 2 is provided in the growth chamber-1, a plurality of molecular beam sources (K cells) 3 are provided below the growth chamber-1, and a substrate heating mechanism 4 is provided above the growth chamber-1. It is maintained in an ultra-high vacuum of ⁸ pa or less.

The substrate 5 on which crystals are to be grown is
The growth surface was placed below the substrate heating mechanism 4.
A viewing port 6 is provided below the substrate 5 so that the substrate 5 can be irradiated with laser light from the laser light source 7 through the viewing port 6. In this embodiment, a YAG laser is used as the laser light source 7, and the laser output is controlled by the computer 8.

A pyrometer 9 for measuring the temperature of the substrate 5 is installed below the growth chamber-1, and the substrate temperature measured by the pyrometer 9 is controlled by the computer 8.
To control the laser output.

Using the above MBE apparatus, a graded layer of AlGaAs was grown. FIG. 2 shows the substrate temperature dependence of the growth rates of GaAs and AlAs constituting AlGaAs. As is clear from FIG. 2, the growth rate of GaAs begins to decrease from the substrate temperature of 650 ° C. when the substrate temperature is increased, but the growth rate of AlAs does not change at this temperature, and the growth rate of AlAs Is reduced by
It is approximately 800 ° C or higher. Therefore, the temperature of the substrate 5 is set to 65
The temperature is gradually raised to 0 ° C or higher, and the temperature is set to AlAs.
If the temperature is kept below 800 ° C, the growth rate of
Without changing the growth rate of lAs, only the growth rate of GaAs is changed, which causes the gray scale of AlGaAs.
A dead layer is formed.

Next, referring to FIGS. 3 and 4, Al sandwiched between AlGaAs layers having a mixed crystal ratio of 0.1 and a mixed crystal ratio of 0.3.
An example in which a GaAs graded layer (X = 0.1 to 0.3) is grown will be described. FIG. 3 shows the substrate temperature dependence of the mixed crystal ratio of AlGaAs. In FIG. 3, four curves a,
b, c, and d are AlGaAs mixed crystal ratios with an initial value of 0.0
The substrate temperature dependences when the AlK cell temperature is fixed to 1, 0.1, 0.2, and 0.3 are shown respectively.

First, in order to set the mixed crystal ratio to 0.1, A
The cell temperatures of 1, Ga and As are 1055 and
C., 1000.degree. C. and 220.degree. C. were set. Under this condition, the temperature of the substrate 41 is set to 500 ° C., and as shown in FIG. 4A, the GaAs buffer layer 42 and AlGaA are formed.
An s (X = 0.1) layer 43 was grown.

Next, the substrate 41 is irradiated with laser light L (Y
(AG laser, output: 82 W, pulse width: 10 msec), after raising the temperature to 680 ° C., monitor the substrate temperature with a pyrometer and feed back to the computer while controlling the laser output. The temperature is raised to 716 ° C., and as shown in FIG.
0.3) The graded layer 44 was grown. The temperature rising rate at this time was previously input to the computer according to the growth film thickness of the graded layer 44.

After the film thickness of the AlGaAs graded layer 44 reaches a predetermined value, the substrate temperature is kept at 716 ° C.
As shown in (c), an AlGaAs (x = 0.3) layer 45 was grown.

By the above operation, the graded layer could be grown without changing the K cell temperature. Further, the graded layer of any variation can be grown by changing the set values of the K cell temperature and the substrate temperature.

Example 2 With reference to FIGS. 5 and 6, an InGaAs layer having a mixed crystal ratio of 0.3 and InGa having a mixed crystal ratio of 0.1 are used.
InGaAs graded layer (X =
An example in which 0.3 to 0.1) is grown will be described. Figure 5
Shows the substrate temperature dependence of the InGaAs mixed crystal ratio when the InK cell temperature is fixed to X = 0.1 to 0.9, and FIG. 6 is a process chart for explaining the above growth. is there.

First, in order to set the mixed crystal ratio to 0.3, I
n, Ga and As cell temperatures of 818 ° C. and 100
The temperature was set to 0 ° C and 220 ° C, respectively. Next, FIG.
As shown in (a), the temperature of the GaAs substrate 61 is set to 50
The temperature was set to 0 ° C., and the GaAs buffer layer 62 and the InGaAs (X = 0.3) layer 63 were grown by the usual method.

Next, the substrate 61 is irradiated with laser light L (YAG laser, output 65 W, pulse width 10 msec),
After raising the substrate temperature to 540 ° C, monitor the substrate temperature with a pyrometer and feed back the value to the computer to control the laser output to bring the substrate temperature up to 597 ° C. Crystal growth was performed while gradually increasing the temperature, and an InGaAs graded layer (x = 0.1 to 0.3) 64 was grown as shown in FIG. 6B. The temperature rising rate at this time was previously input to the computer according to the growth film thickness of the graded layer 64.

After the film thickness of the InGaAs graded layer 64 reaches a predetermined value, laser light L is continuously irradiated to maintain the substrate temperature at 597 ° C., as shown in FIG.
An InGaAs (X = 0.1) layer 65 was grown.

By the above operation, the graded layer 63 could be grown without changing the K cell temperature.

<Embodiment 3> Next, a method of forming a hetero device using a graded layer will be described. The laminated structure of the graded base layer HBT formed in this example is shown in FIG. First, each K cell temperature was raised to a predetermined temperature. That is, the temperature of the Ga cell was set to the temperature (1000 ° C.) corresponding to the growth rate of 1 μm / hr, and the temperature of the Al cell was set to the temperature (946 ° C.) corresponding to the mixed crystal ratio of 0.01.

After the sub-collector layer (n-GaAs) 72 and the collector layer (u-GaAs) 73 are successively grown, the AlK cell temperature is continuously raised to a temperature corresponding to a mixed crystal ratio of 0.1. , Base layer (p-AlGaAs: X = 0.01 to
0.1) 74 was grown. At this time, since the AlK cell temperature is a temperature corresponding to the mixed crystal ratio of 0.1, the growth is continued as it is, and the spacer layer (u-AlGaAs: X =
0.1) 75 was formed. Laser light (Y
The substrate temperature was raised to 716 ° C. by irradiating with AG laser, output 86 W, pulse width 10 msec). Figure 3 curve b
As is clear from the graph, when the substrate temperature is 716 ° C., the mixed crystal ratio becomes 0.3, so that the first emitter layer (n-AlGaA
s: X = 0.3) 76 has grown. Next, while controlling the laser output to lower the substrate temperature from 716 ° C. to 650 ° C., the emitter layer 2 (n-AlGaAs: X = 0.3 to
0.1) 77 was grown. Then, the cap layer (n-Ga
As) 78 was grown, and the crystal growth of the graded base layer HBT was completed.

By the above method, each semiconductor layer was continuously grown without interrupting the growth to form a hetero device.

<Embodiment 4> Next, the mixed crystal ratios are different from each other.
(X = 0.1 to 0.3) An embodiment in which a plurality of AlGaAs layers are continuously grown will be described with reference to FIGS.

First, the K cell temperatures of Al, Ga and As were preset to 1055 ° C., 1000 ° C. and 220 ° C., respectively, so that the mixed crystal ratio of AlGaAs was 0.1.

Next, the GaAs substrate temperature is set to 500 ° C., and as shown in FIG. 8A, the GaAs buffer layer 82 and AlGaAs (X = 0.
1) The layer 83 was continuously grown. Laser light L (YAG laser, output 85 W, pulse width 10 mse on GaAs substrate
c) is irradiated and the substrate temperature is calculated from AlGa derived from FIG.
It was set to 712 ° C. at which the mixed crystal ratio of As becomes 0.2, and
As shown in (b), the second AlGaAs (X = 0.
2) The layer 84 was grown. Next, the laser output was adjusted to bring the substrate temperature to 716 ° C., and a GaAs (X = 0.3) layer 85 was grown as shown in FIG. 8C.

By growing in this way, Al
The mixed crystal ratio is different (X = 0.1 to 0.3) only by changing the substrate temperature without changing the K cell temperature.
The As layer could be continuously grown.

<Embodiment 5> Next, contrary to Embodiment 4, X
An example in which an AlGaAs layer in which is changed to 0.3 to 0.1 is continuously grown will be described with reference to FIGS. 3 and 9.

First, the K cell temperatures of Al, Ga and As are
The mixed crystal ratios of AlGaAs are set to 1055 ° C., 1000 ° C. and 220 ° C., respectively, so as to be 0.1. Next, the temperature of the GaAs substrate 91 is set to 500 ° C.
Then, as shown in FIG. 9A, the GaAs substrate 91
A GaAs buffer layer 92 was grown on it.

Next, laser light L (Y
By irradiating an AG laser with an output of 85 W and a pulse width of 10 msec) L, the substrate temperature is raised to 716 ° C. which is a temperature at which the mixed crystal ratio of AlGaAs derived from FIG. 3 becomes 0.3,
As shown in FIG. 9B, AlGaAs (X = 0.3)
Layer 93 was grown.

Similarly, the laser light output is adjusted to lower the substrate temperature to 712 ° C., and as shown in FIG.
An lGaAs (X = 0.2) layer 94 was grown. Second A
When the formation of the 1GaAs (X = 0.2) layer is completed, the laser light irradiation is stopped, the substrate temperature is returned to 500 ° C., and as shown in FIG. (X =
0.1) Layer 95 was grown.

According to this embodiment, the mixed crystal ratio was changed only by changing the substrate temperature without changing the AlK cell temperature (X
= 0.3-0.1) The AlGaAs layer could be continuously grown.

Example 6 Mixed crystal ratios are different from each other (X =
0.3 to 0.1) An embodiment in which a plurality of InGaAs layers are continuously grown will be described with reference to FIGS. First, In,
The K cell temperatures of Ga and As are preset to 818 ° C., 1000 ° C. and 220 ° C., respectively, so that the InGaAs mixed crystal ratio becomes 0.3.

Next, the temperature of the GaAs substrate 101 is set to 500 ° C.
Then, as shown in FIG.
01, GaAs buffer layer 102, InGaAs (X
= 0.3) layer 103 was continuously grown.

Laser light L (YAG laser, output 7
1 W, pulse width 10 msec), and the InGaAs mixed crystal ratio obtained from the substrate temperature shown in FIG. 3 becomes 0.2 59.
At 0 ° C., as shown in FIG.
After growing the GaAs (X = 0.2) layer 104, the laser output was adjusted to bring the substrate temperature to 597 ° C., and FIG.
As shown in, the third InGaAs (X = 0.1) layer 1
05 was grown.

According to this embodiment, the mixed crystal ratio was changed by changing the substrate temperature without changing the InK cell temperature (X
= 0.3 to 0.1) A plurality of InGaAs layers could be continuously grown.

<Embodiment 7> Contrary to Embodiment 6, an embodiment in which a plurality of InGaAs layers having a mixed crystal ratio X of 0.1 to 0.3 are continuously grown is shown in FIGS. It demonstrates using. The K cell temperatures of In, Ga, and As were adjusted so that the InGaAs mixed crystal ratio was 0.18 ° C. and 10 ° C., respectively.
It is preset at 00 ° C and 220 ° C. Then G
The temperature of the aAs substrate was set to 500 ° C., and the GaAs buffer layer 112 was grown on the GaAs substrate 111 as shown in FIG.

Next, laser light L (YAG
Laser, an output of 72 W, and a pulse width of 10 msec) were applied, and the substrate temperature was set to 597 ° C., which is a temperature at which the mixed crystal ratio of InGaAs derived from FIG. 3 becomes 0.1.
As shown in (b), InGaAs (X = 0.1) layer 1
13 was grown.

The substrate temperature is adjusted to 590 by adjusting the laser light output.
Then, as shown in FIG. 11C, the second InGaAs (X = 0.2) layer 114 was grown. Second
When the formation of the InGaAs (X = 0.2) layer is completed, the laser irradiation is stopped and the substrate temperature is returned to 500 ° C.
As shown in FIG. 11C, the third InGaAs (X
= 0.3) layer 115 was grown.

According to the present embodiment, the mixed crystal ratio was changed by changing the substrate temperature without changing the cell temperature (X =
(0.1-0.3) AlGaAs layer could be continuously grown.

[0048]

According to the present invention, it is possible to form a ternary mixed crystal and a graded layer having different compositions by changing the substrate temperature without changing the K cell temperature, so that it is possible to grow in real time without a time lag. become. Further, since it is not necessary to interrupt the growth before and after the heterojunction or the graded layer of the same material having different mixed crystal ratios, not only the growth time can be shortened but also the hetero interface without the interface state can be formed. You can

[Brief description of drawings]

FIG. 1 is a schematic view of a molecular beam epitaxy apparatus used in the present invention,

FIG. 2 is a diagram showing the substrate temperature dependence of the growth rate of a compound semiconductor,

FIG. 3 is a diagram showing the substrate temperature dependence of the AlGaAs mixed crystal ratio,

FIG. 4 is a diagram showing a growth method of an AlGaAs graded layer;

FIG. 5 is a diagram showing the substrate temperature dependence of the InGaAs mixed crystal ratio,

FIG. 6 is a diagram showing a growth method of an InGaAs graded layer;

FIG. 7 is a diagram showing a laminated structure of HBT using a graded base layer;

FIG. 8 is a diagram showing a continuous growth method of AlGaAs layers having different mixed crystal ratios,

FIG. 9 is a diagram showing a continuous growth method of AlGaAs layers having different mixed crystal ratios,

FIG. 10 is a view showing a continuous growth method of InGaAs layers having different mixed crystal ratios,

FIG. 11 is a diagram showing a continuous growth method of InGaAs layers having different mixed crystal ratios.

[Explanation of symbols]

1 ... Growth chamber-2. Liquid nitrogen shroud
3 ... Molecular beam source, 4 ... Substrate heating mechanism, 5 ... Semiconductor substrate, 6 ... Viewing port, 7 ... Laser light source, 8 ... ..Laser output control computer, 9 ... Pyrometer, 10 ... Reflector, 41 ... GaAs substrate, 42 ... GaAs buffer layer, 43 ...・ AlGa
As layer, 44 ... AlGaAs graded layer, 45
.... AlGaAs layer, 61 ... GaAs substrate, 62 ...
.... GaAs buffer layer, 63 ... InGaAs layer, 6
4 ... InGaAs graded layer, 65 ... InGa
As (X = 0.1) layer, 71 ... GaAs substrate, 72 ...
.... Sub-collector layer 73 ... Collector layer (UGaA
s), 74 ... Graded base layer, 75 ... Spacer layer, 76 ... First emitter layer, 77 ... Second emitter layer, 78 ... .... Cap layers, 81 ... GaAs
Substrate, 82 ... GaAs buffer layer, 83 ... AlG
aAs layer, 84 ... AlGaAs layer, 85 ... AlG
aAs layer, 91 ... GaAs substrate, 92 ... GaAs
Buffer layer, 93 ... AlGaAs layer, 94 ... Al
GaAs (X = 0.2) layer, 95 ... AlGaAs (X =
0.1) layer, 101 ... GaAs substrate, 102 ... Ga
As buffer layer, 103 ... InGaAs layer, 104
.... InGaAs (X = 0.2) layer, 105 ... InG
aAs layer, 111 ... GaAs substrate, 102 ... Ga
As buffer layer, 103 ... InGaAs layer, 104
.... InGaAs layer, 105 ... InGaAs layer.

Claims (9)

[Claims] 1. A method of epitaxially growing a compound semiconductor film on a substrate by irradiating a substrate with a plurality of molecular beams obtained from a plurality of molecular beam sources, wherein the temperature of the substrate is set to the compound semiconductor film. The growth rate of the first compound is reduced, and the growth rate of the second compound other than the first compound forming the compound semiconductor film is changed within a temperature range in which the growth rate of the second compound 2. A method for crystal growth of a compound semiconductor, which comprises epitaxially growing a compound semiconductor film having a desired composition distribution on the substrate. 2. A ternary mixed crystal graded layer having a continuously changing composition in the thickness direction is formed by continuously changing the temperature of the substrate within the temperature range. The method of growing a crystal of a compound semiconductor according to claim 1. 3. The compound semiconductor according to claim 1, wherein the compound semiconductor and the first compound are AlGaAs and GaAs, respectively, and the temperature range is 600 ° C. to 700 ° C. Crystal growth method. 4. The compound semiconductor according to claim 1, wherein the compound semiconductor and the first compound are InGaAs and InAs, respectively, and the temperature range is 500 ° C. to 600 ° C. Crystal growth method. 5. The crystal growth of the compound semiconductor according to claim 1, wherein the epitaxial growth is performed by controlling the temperature of the substrate to a predetermined temperature by irradiation of laser light. Method. 6. The output of the laser beam is controlled by monitoring the temperature of the substrate with a pyrometer and feeding back the data to a computer. 5. The crystal growth method of the compound semiconductor according to 5. 7. The method for growing a crystal of a compound semiconductor according to claim 1, wherein the epitaxial growth is performed while keeping the temperature of the molecular beam source substantially constant. 8. The crystal growth method of a compound semiconductor according to claim 5, 6 or 7, wherein the laser light is a YAG laser. 9. The crystal growth method of a compound semiconductor according to claim 1, wherein the epitaxial growth is performed by controlling the temperature of the substrate to a predetermined temperature by irradiation of a halogen lamp. .