JP3471372B2 - Method of manufacturing semiconductor crystal - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] Field of the Invention The present invention is related to a method of manufacturing a semiconductor crystal dramatically improve the characteristics of semiconductor devices. 2. Description of the Related Art As a conventional example of a quantum well crystal growth apparatus for producing a quantum well structure for confining carriers three-dimensionally while quantum dots confine carriers three-dimensionally, an MOVPE crystal growth apparatus is known. Is shown in FIG. this is,
Reactor 31 and semiconductor single crystal substrate (GaAs, InP)
Etc.) consisting of a graphite susceptor 33 on which 32 is placed, an RF coil 34 for heating the graphite susceptor, and a gas line 35 for flowing a raw material gas into the reaction tube [Ezaki et al .: Superlattice heterostructure device, Industrial Research Institute (1988) 253] . In a conventional MOVPE crystal growth apparatus of FIG. 3, the semiconductor single crystal substrate 32 was placed in the reactor 31, intends row crystal growth by passing a raw material gas into the reactor 31 for heating the graphite susceptor 33. FIG. 4 shows a first conventional example of a crystal growth method of quantum dots. Conventional MOVPE method and MBE method
An AlGaAs layer 41 is grown on the
An As / AlGaAs ultra-thin film crystal and an AlGaAs cap layer 43 are grown (FIG. 4a). Next, a quantum box 44 is formed by etching (FIG. 4B), and a buried layer 45 is grown (FIG. 4C), or GaAs as shown in FIG.
Step 50 of AlGaAs layer 51 grown on substrate 52
Using (FIG. 5A), a GaAs quantum box 53 (FIG. 5B) is produced by alternately supplying two kinds of gases having different compositions, and a buried layer 55 is grown (FIG. 5C). Ezaki et al .: Superlattice heterostructure device, Industrial Research Committee (1988) 464]. However, in the MOVPE apparatus having the above-described structure, the thin-film quantum well structure can be grown, but the reactor tube has a large cross-sectional area and the flow rate of the source gas cannot be increased. No crystals can be obtained.
As a result, crystal growth nuclei cannot be generated uniformly, and it is impossible to grow a quantum dot structure. It will be described in detail. FIG. 6A is an enlarged view of FIG. As shown in FIG. 6A, the growth of the crystal on the substrate involves increasing the temperature of the reactor and flowing the reaction gas into the reactor 31. If the flow rate of this gas is small, the step shown in FIG. In addition, the crystal grows on the terrace 61 of the crystal. Therefore, when the gas flow rate is increased, the crystal grows flat as shown in FIG. That is, in the conventional MOVPE crystal growth apparatus, the cross-sectional area of the reactor is large, the flow rate of the reaction gas cannot be increased, and a flat crystal as shown in FIG. 6 (c) cannot be obtained. Therefore, there is a problem that quantum dots cannot be grown on a flat crystal face. SUMMARY OF THE INVENTION In view of the above problems, the present invention is directed to a semiconductor in which crystal growth nuclei are uniformly generated over the entire surface of a crystal to form quantum dots.
That provides a method of manufacturing a crystal. Further, in the above-described quantum dot crystal growth method, first, the shape of the quantum dot depends on the etching technique. At present, processing of about 0.1 μm is the limit, and processing of about 10 nm square, which is actually required as a quantum dot, is impossible. At the same time, a good regrowth interface cannot be formed due to damage caused by processing, and good device characteristics cannot be exhibited. In the method of growing the quantum dot structure using the crystal step, the crystal step is obliquely polished on the crystal surface, and then the crystal is grown. It is necessary to form regular steps in the initial state,
If the growth time of the crystal is slightly deviated, quantum dots are not formed. There is a problem that the uniformity and crystallinity of the quantum dot structure are reduced in the course of continuing the crystal growth. In view of the above problems, an object of the present invention is to provide a method of manufacturing a semiconductor crystal capable of uniformly generating crystal growth nuclei on an ultra-flat surface and manufacturing a quantum dot structure. [0010] In order to achieve this object, a method of manufacturing a semiconductor crystal according to the present invention comprises the steps of:
Consists of a reaction tube forming a passage and an outer tube containing the reaction tube
The reactor is a graphite susceptor.
The crystal growth device raises the susceptor.
It has high frequency heating means for heating, susceptor and presser
The source gas is introduced into the reaction tube through the opening formed by
The vertical width of the opening is approximately one tenth of the horizontal width of the opening.
That by using the crystal growth apparatus, through the following steps: the reaction tube
The semiconductor substrate placed inside is brought to the first crystal growth temperature.
And then hold at the first crystal growth temperature
First, the total gas flow rate was set to 40 liters / min or more,
By supplying gas to the semiconductor substrate through the opening,
Ultra flat surface where the surface of the semiconductor substrate is flat at the atomic level
The first step of obtaining a plane, the temperature of the semiconductor substrate is increased to the second crystal growth
After lowering the temperature to the second crystal growth temperature,
Supply the second source gas to the semiconductor substrate through the opening.
In this way, crystal growth nuclei are generated uniformly on the ultra-flat surface.
In the second step of forming quantum dots, the temperature of the semiconductor substrate is
While maintaining the second crystal growth temperature, the third source gas is opened.
By supplying to the semiconductor substrate through the opening, the quantum
Third step of growing a crystal to bury the unit, and a semiconductor
The third crystal whose body substrate temperature is the optimal temperature for crystal growth
Do not hold at the third crystal growth temperature after heating to the growth temperature.
Meanwhile, the fourth source gas is supplied to the semiconductor substrate through the opening.
A fourth step of growing a crystal,
Is approximately 100 ° C. higher than the third crystal growth temperature
In addition, the second crystal growth temperature is about one unit lower than the third crystal growth temperature.
50 ° C lower, unlike the first source gas and the second source gas,
The second source gas and the third source gas are different . The susceptor is arranged so as to surround the crystal substrate, and the distance between the crystal growth substrate and the top plate is set to about 1 mm. The cross section perpendicular to the flow of the gas flow was 10 mm × 1 mm, the total gas flow rate was 40 L (liter) / min, and the growth pressure was 17 to.
By setting it to rr, a flow rate of 300 m / sec was obtained . Further, in order to increase the utilization efficiency of the raw materials due to the low growth pressure, the top plate is made of graphite to improve the gas decomposition efficiency. On the other hand, when contamination of impurities becomes a problem, it is possible to prevent contamination from the susceptor by laying a single crystal substrate similar to a crystal substrate under the top plate. When growing a quantum dot crystal, it is necessary to obtain an ultra-flat surface. In order to obtain this ultra-flat surface, the crystal surface is flattened at the atomic level by the aforementioned quantum dot crystal growth apparatus. This is because, by increasing the gas flow velocity, the capture rate of atoms on the crystal surface decreases with respect to the position of the kink or step, and the generation of crystal nuclei is suppressed, and the steps move one after another to the periphery of the crystal substrate. (FIG. 6
(C)), an ultra-flat surface can be obtained. However, in order to increase the migration rate of atoms on the crystal surface, the growth temperature needs to be about 100 degrees higher than the optimum conditions for crystal growth. Further, it is necessary to use a dislocation-free substrate having no screw dislocation or the like as the crystal substrate. Next, it is necessary to form quantum dots uniformly on the flat surface. To reduce the migration of material atoms of the quantum dots, and the nucleation rate of the flat surface, in order to increase than nucleation rate, the growth of the quantum dots is 1 50 degrees cold Ri by optimal conditions for crystal growth. Here, the quantum well is 1/5 of the thickness of one atomic layer.
Quantum dots can be produced uniformly by performing growth for about a time. Further, a crystal having a composition different from that of the quantum dot and having a band gap larger than that of the quantum dot is grown at a growth temperature equal to that at which the quantum dot was subsequently grown,
Quantum dots can be built into the crystal. FIG. 1 shows an example of a crystal growth apparatus used in the present invention. As shown in FIG. 1, an InP semiconductor crystal substrate 1 is held by a graphite susceptor 2, and the same crystal as the semiconductor crystal substrate 1 is used as a lid 3, and the lid 3 is placed on the susceptor 2 so as to face the substrate 1. Then, it is held by the graphite presser 4 to protect the crystal substrate 1. An opening 5 formed by the susceptor 2 and the presser 4 has a guide pipe 7 through which a raw material gas 6 flows.
Is inserted. The susceptor 2 and the guide tube 7 are shielded from the outside air by an outer tube 8 in order to prevent leakage of the source gas 6. The opening 5 has a height of 1 mm and a width of 10 mm, and the semiconductor crystal substrate 1 of 10 mm × 20 mm can be loaded. [0018] Next, a dynamic <br/> operation of the quantum dot crystal growth apparatus. First, the temperature of the graphite susceptor 2 is increased by high-frequency heating. The gas flow area was set to 10 mm ^{2 in} order to increase the gas flow rate and grow a crystal whose surface was extremely flat at the atomic level. In order to suppress a decrease in the yield of the source gas 6 due to an increase in the flow rate, the substrate 1 was placed in the susceptor 2 and the source gas 6 was supplied. That is, the gas flow area was surrounded by the susceptor 2, all the gases contributed to the growth, and the raw material gas 6 was heated from all sides to improve the gas thermal decomposition efficiency and further improve the yield of the raw material gas 6. In this apparatus, the sectional area through which the source gas passes can be considerably reduced as compared with the conventional crystal growth apparatus. In this apparatus, the gas flow path should be as short as possible in order to prevent an increase in growth pressure due to a small cross-sectional area of the gas flow path. In this case, the distance from the gas mixing section to the crystal substrate was about 50 cm. In order to prevent a rapid decrease in the growth pressure on the crystal, a susceptor is provided so as to extend from the crystal growth part to the gas downstream. The guide tube covers the susceptor to prevent the source gas from leaking from the opening. In order to control the growth pressure, a pressure sensor is installed in the gas supply pipe, and the suction force of the pump is adjusted with a butterfly valve to perform the reduced pressure growth. The susceptor temperature can be raised up to 1000 degrees. FIG . 2 illustrates a method of manufacturing a semiconductor device according to the present invention. Here, a method for manufacturing a semiconductor laser using quantum dots as a semiconductor device will be described. As shown in FIG. 2, the (001) InP substrate 21 was set in the quantum dot crystal growth apparatus described in Embodiment 1, and 50 L / 50 of hydrogen gas 6 containing 200 ccm of PH ₃ (40%) was added. min (FIG. 2a). The growth pressure is 17 torr. After raising the temperature of the susceptor 2 and holding it at 740 ° C. for 10 minutes, 200 ccm of PH3 was
I (trimethylindium 1%) is supplied at 20 ccm and the InP crystal 22 is grown to about 10 nm for 5 minutes (FIG. 2).
b). Here, by increasing the gas flow rate, as shown in FIG. 6 (c), the trapping rate of atoms on the crystal surface is reduced with respect to the position of the kink or step, thereby generating crystal nuclei. Is suppressed, and the steps move one after another to the periphery of the crystal substrate to obtain an ultra-flat surface. Next, stop only the supply of TMI lowering the susceptor temperature to 4 90 °. InGaAsP (λg =
(1.4 μm) Prepare quantum dots. In this case, the TMI
5.0 ccm, TEG (1.8%) 2.2 ccm,
The PH ₃ 20ccm, AsH3 the (10%) 3.0sc
The mixed gas added in cm is added to the hydrogen gas at intervals of 0.5 seconds for 0.8 seconds. Total gas flow is 5
0 L / min. Then, InGa with a side of 3 nm
AsP quantum dots 23 are formed at a pitch of approximately 20 nm (FIG. 2c). Here, the InP crystal 22 is made of InGaAs.
The P quantum dot 23 grows on the flat InP crystal 2
This is because the optimum condition for nucleation of the quantum dot 23 was selected on the second. The optimum conditions for generating the quantum dots 23 are as follows :
Rather about 1 50 degrees lower than the optimum conditions for crystal growth, at that temperature, the raw material atoms of the quantum dots migration is small and because the nucleation rate greater than nucleation rate, In
Quantum dots 23 can be formed on the P crystal 22. Furthermore, the susceptor 4 90 ° 200ccm and TMI a PH ₃ as a material gas while holding 20
The ccm is added, and the InP crystal 24 is grown to about 10 nm for 5 minutes, and the quantum dots are embedded (FIG. 2D). The quantum dot manufacturing process and the quantum dot embedding process are repeated 10 times. Finally, the temperature of the susceptor 2 was raised to 640 ° C., and PH ₃ was 200 ccm and TMI was 200
ccm and a growth pressure of 100 torr for 5 minutes.
A P crystal 25 is grown to about 100 nm (FIG. 2e). PH ₃
The susceptor is cooled while adding 200 ccm to complete the growth. The results of the photoluminescence of the obtained crystals was measured, Enel Gishifuto amount is about 120 meV, the quantum dots effect was confirmed. Although the crystal substrate is placed on the susceptor, even if the crystal is used as a lid, quantum dots are formed. Further, the crystal to be grown is made of InP, but may be made of GaAs or ZnSe. Further, the guide tube may be structured to cover the susceptor in order to prevent the gas from leaking from the joint between the guide tube and the susceptor. As described above, the production of the semiconductor crystal of the present invention
In the method, since the cross-sectional area of the portion where the raw material gas flows can be reduced, the gas flow rate supplied to the crystal can be made ten times that of the conventional method, thereby producing an extremely flat crystal surface without kink or the like. it can. Subsequently, by supplying a small amount of a quantum dot component gas, a quantum dot crystal that dramatically improves the characteristics of a semiconductor device can be grown.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural view of a quantum dot crystal growth apparatus according to a first embodiment of the present invention. FIG. 2 is a view showing a manufacturing process of a quantum dot structure according to a second embodiment of the present invention. FIG. 3 is a view showing a structure of a MOVPE apparatus. FIG. 4 is a manufacturing process sectional view showing a manufacturing process of a quantum dot structure by etching. FIG. 5 is a manufacturing process cross section showing a manufacturing process of a quantum dot structure using a crystal step. FIG. 6 is a diagram for explaining a difference in a state of crystal growth in steps of a substrate depending on a flow rate of a source gas. [Description of References] 1 semiconductor crystal substrate 2 susceptor 3 lid 4 presser 5 opening 6 source gas 7 guide Tube 8 outer tube 21 InP substrate 22 InP crystal 23 InGaAsP quantum dot 24 InP crystal 25 InP crystal

Continuation of front page       (56) References JP-A-63-134600 (JP, A)                 JP-A-3-159287 (JP, A)                 JP-A-2-7419 (JP, A)                 JP-A-5-62896 (JP, A)                 JP-A-5-251352 (JP, A)

Claims (1)

(57) [Claims] [Claim 1] A reaction tube forming a flow path of a source gas,
A crystal growth apparatus consisting of an outer tube including the reaction tube
The reaction tube is composed of a graphite susceptor and a presser.
And the crystal growth apparatus raises the temperature of the susceptor
High frequency heating means, the susceptor and the presser
Reacts with the source gas through the opening formed by
Introduced into the tube, the vertical width of the opening is the horizontal width of the opening
The following steps were performed using a crystal growth apparatus
For producing a semiconductor crystal via the following: a semiconductor substrate placed inside the reaction tube is first crystallized.
After raising the temperature to the growth temperature, the first crystal growth temperature
While maintaining the total gas flow rate at least 40 liters / min
The first source gas is supplied to the semiconductor substrate through the opening.
By supplying the semiconductor substrate, the surface of the semiconductor substrate becomes atomic.
A first step of obtaining an ultra-flat surface that is flat at the level, and lowering the temperature of the semiconductor substrate to a second crystal growth temperature.
While maintaining the second crystal growth temperature later, the second raw material
Supplying gas to the semiconductor substrate through the opening;
With this, crystal growth nuclei are uniformly generated on the ultra-flat surface.
A second step of forming quantum dots by heating, maintaining the temperature of the semiconductor substrate at the second crystal growth temperature
While the third source gas is being introduced into the semiconductor through the opening,
The quantum dots are embedded by supplying the quantum dots to the
A third step of growing a crystal, and setting the temperature of the semiconductor substrate to a temperature optimum for crystal growth.
After raising the temperature to the third crystal growth temperature, the third crystal growth temperature
While holding the fourth raw material gas through the opening.
Crystal is grown by supplying to the semiconductor substrate
A fourth step, wherein the first crystal growth temperature is higher than the third crystal growth temperature.
About 100 ° C. higher, wherein the second crystal growth temperature is higher than the third crystal growth temperature.
Approximately 150 ° C. lower, the first source gas and the second source gas are different, and the second source gas and the third source gas are different.
A method for producing body crystals .