JPH0992883A - Semiconductor wafer, semiconductor device, manufacture thereof, and deposition equipment to be used for manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode of a high efficiency or a laser that oscillates at a low shreshold value by distributing carbon atoms in at least one layer of a semiconductor thin film in such a profile that the concentration of carbon atoms may become lower as the thin film grows. SOLUTION: A layer structure is constituted of two or more different kinds of semiconductor thin films 41-45 which are made by the organic metal vapor phase deposition method. In other words, a semiconductor device is made by depositing two or more kinds of semiconductor thin films 41-45 on a sapphire substrate 2. In such a semiconductor device, at least one layer 41 out of these semiconductor thin films 41-45 contains carbon. In the layer 41, carbon is so distributed that the concentration of carbon atoms may become lower as it gets near the surface of the semiconductor thin film 41. The semiconductor thin films 41-45 are formed from gallium arsenide nitride and they emit blue light. By this method, a light emitting diode of a high efficiency or a laser which oscillates at a low threshold value can be manufactured with a high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor element such as a semiconductor wafer, an emitting diode, a semiconductor laser, etc., and a growth apparatus used for manufacturing the same.

[0002]

2. Description of the Related Art A large amount of carbon impurities are mixed in a semiconductor thin film obtained by metalorganic vapor phase epitaxy, forming non-radiative recombination centers, lowering the electrical activation rate of additional elements, It is considered to be a factor such as the deterioration of ohm characteristics.
For example, in a gallium nitride thin film, if the carbon concentration is high,
The major problem is that good ohmic characteristics cannot be obtained in the electrode. When the carbon concentration is low, it is a big problem that good ohmic characteristics cannot be obtained in the electrode. When the carbon concentration is low, good ohmic characteristics can be obtained at the electrode, but in the measurement based on the photoluminescence method, the light emission in the deep order mainly becomes, and the band edge light emission intensity largely decreases. Therefore, in a semiconductor issuing device manufactured using a layered structure of a gallium nitride thin film, there is no clear control guideline for carbon concentration,
It was a situation where it was not possible to improve the light emission efficiency of light emitting diodes and the oscillation threshold characteristics of semiconductor lasers.

Further, in the growth apparatus used for manufacturing the semiconductor element as described above, the temperature of the susceptor is raised by the transfer of radiant heat from the resistance heating element to the substrate, and the temperature unevenness on the substrate placed on the susceptor is increased. In order to make as small as possible, it is necessary to set the distance between the resistance heating element and the susceptor as long as possible. Therefore, the thermal efficiency is very poor, and in order to maintain the high temperature state on the surface of the substrate, it is necessary to keep the temperature of the heating body much higher than the temperature of the substrate. Further, when the reactive gas comes into contact with the resistance heating element, the life of the resistance heating element is shortened. The resistance heating body deteriorates from the surface due to the reactive gas, and the cross-sectional area of the conductive portion becomes smaller. The conductive portion having a small cross-sectional area will generate more heat even with the same supply current, and partial deterioration will be accelerated. As a result, the heat generation distribution of the resistance heating element is changed, temperature unevenness on the substrate is increased, and the film quality of the semiconductor thin film to be vapor-grown, the in-plane uniformity of the substrate, and the film thickness uniformity are impaired. In order to avoid this, the surface of the resistance heating element is covered with a thin film such as a ceramic material,
Alternatively, measures have been taken such as flowing a gas that does not react with the material of the heating body between the susceptor and the resistance heating body to prevent a reactive gas such as a raw material from coming into contact with the resistance heating body.

[0004]

The conventional semiconductor device described above has problems that the luminous efficiency is not sufficiently high or that the threshold value for laser oscillation is high. Further, in a growth apparatus used for manufacturing a light emitting device using, for example, gallium nitride as a semiconductor, high temperature (1000 ° C. or higher)
However, there is a problem that the uniform heating cannot be performed. Further, the countermeasure of covering the surface of the resistance heating element with a thin film such as a ceramic material has little effect because a crack occurs in the coating thin film due to the difference in the coefficient of thermal expansion between the material of the heating element and the coating thin film material. Even if there is a method of flowing a gas that does not react with the heating material between the susceptor and the resistance heating element,
At a high temperature (1000 ° C. or higher), the deterioration rate cannot be ignored, and there is a problem that a semiconductor thin film cannot be stably formed with good reproducibility.

The present invention has been made in consideration of the above circumstances. An object of the present invention is to obtain a highly efficient light emitting diode or a laser oscillating at a low threshold value. An object of the present invention is to provide a growth apparatus capable of stably performing high temperature uniform heating in growing a semiconductor thin film.

[0006]

The gist of the present invention is to form a layer structure of at least two or more different semiconductor thin films obtained by a metal organic chemical vapor deposition method, and then manufacture a semiconductor using the layer structure. In the device, the carbon concentration in at least one layer of the semiconductor thin film is distributed so as to decrease in the growth direction of the semiconductor thin film. Further, as this means, in a vapor phase growth apparatus for forming a semiconductor thin film, an insulator is contact-inserted into a gap of a conductive portion of a resistance heater for heating a substrate installed on a susceptor. And

[0007]

The carbon in a semiconductor thin film grown by a vapor phase growth method using an organic metal as a raw material is generally considered to be incorporated into the semiconductor thin film when the organic metal is thermally decomposed and the semiconductor thin film grows. ing. For example, many gallium nitride vacancies are present in a gallium nitride thin film, and it is considered that a deep donor level is formed. The carbon described above is considered to form a shallow acceptor level, and the presence of the carbon at the same time compensates for the deep donor level, thereby effectively reducing the concentration of the deep donor level. However, in order for the electrode characteristics of the n-layer to have a good ohmic property, a sufficient donor concentration is required at least on the surface of the n-layer, so that the carbon concentration serving as an acceptor must be reduced. It is clear from the results of these experiments. However, simply controlling the carbon concentration to a specific concentration cannot solve the two independent and contradictory problems. At the same time, in order to solve this problem, the structure of the present invention in which the carbon concentration is low on the surface on which the electrode is formed and high in the portion close to the substrate is essential. The next issue is how to realize such a structure. On the other hand, the present inventors analyzed the carbon concentration in the thickness direction of gallium nitride thin films grown under various conditions. As a result, it was found that the carbon distribution in the gallium nitride thin film changes depending on the number of times the resistance heating element is specified. That is, it was estimated that the cause (carbon source) that causes the carbon concentration distribution in the thickness direction of the semiconductor thin film is closely related to the deterioration of the resistance heating body.

Therefore, a detailed study was conducted on the state of deterioration of the resistance heating element. When a gas that does not react with the material of the heating element is made to flow between the susceptor and the resistance heating element to prevent the reactive gas such as the raw material from coming into contact with the resistance heating element, the resistance heating element is mainly deteriorated. It was found that the cause was vaporization of the material of the resistance heating element itself, and the oxidation of oxygen or moisture adsorbed on the surface of the resistance heating element and the generation of its reaction product (mainly carbon monoxide). did. In addition, flowing a gas that does not react with the resistance heating material (hereinafter referred to as purge gas) between the susceptor and the resistance heating
Although there is certainly an effect that the reactive gas such as the raw material is not brought into contact with the resistance heating body, it prevents the gas of the vaporized substance or oxide of the material of the resistance heating body itself generated on the surface of the point resistance heating body from stopping on the surface. It became clear that it was working.
That is, the gas generated on the surface is blown away, and the vaporization from the resistance heating body progresses more and more, and the deterioration is accelerated. It was found that carbon is continuously mixed due to the progress of the deterioration and cannot be reduced in the growth direction of the growing semiconductor thin film. In the present invention, deterioration can be prevented by inserting the insulator into the gap of the conductive portion of the resistance heating element by contact,
Since carbon or carbon monoxide generated at the initial stage of heating start suppresses further intermittent generation of carbon or carbon monoxide, it becomes possible to reduce the growth direction of the semiconductor thin film to be grown. Furthermore, since the temperature distribution of the resistance heating element can be reduced by inserting the insulator in contact, the distance between the resistance heating element and the susceptor can be kept small while keeping the temperature unevenness on the susceptor or the substrate installed thereon. Since it can be reduced, the thermal efficiency can be increased. As a result, the amount of heat generated by the resistance heating element itself can be set low, and deterioration can be further ignored.

[0009]

The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 shows a schematic configuration in the vicinity of a resistance heating body in a vapor phase growth apparatus of one embodiment. Reference numeral 1 is a resistance heating element made of graphite, which has a spiral conductive portion and is connected to the electrode 2. A lower protection plate 3 made of a sintered body containing aluminum nitride as a main component is fitted on the resistance heating body 1. The lower protection plate 3 is divided into six in the circumferential direction, and similarly, the upper protection plate 4 which is also divided into six is arranged so as to be offset from the lower protection plate 3 by 30 ° so as to cover the divided portion. It has been shown from the thermal stress analysis by the finite element method that the insulator which is inserted into the gap of the conductive portion of the resistance heating body 1 in contact therewith may be damaged by thermal strain when it is not divided. Therefore, in order to operate the device stably, it is desirable to divide and form. A purge gas introduction pipe 5 is installed at the center of the resistance heating element 1, the upper protection plate 4, and the lower protection plate 3, and a susceptor 6 is provided above the introduction pipe 5.
Is provided, and the susceptor 6 can be rotated and lifted by a rotary lifting mechanism (not shown) attached to the introduction pipe 5. A substrate 7 is mounted on the susceptor 6. A hole 8 for introducing a purge gas is provided below the susceptor 6 of the introduction pipe 5.
There are four positions in the circumferential direction, and the structure is such that the purge gas can flow from the introduction pipe 5. A reflector 9 is provided below the resistance heating body 1.
Are installed by the reflector support rod 10.

With the above structure, crystal growth was performed as follows. First, a diameter of 5 washed with a mixture of methyl alcohol, sulfuric acid, hydrogen peroxide solution, and pure water.
A single crystal sapphire substrate 7 having a 0 mm (0001) plane as a main surface is mounted on the susceptor 6. Next, add 25 liters of hydrogen
/ Min, while energization of the electrode 2 was started, and while the susceptor 6 was rotated at 10 rpm, the temperature was maintained at 1200 ° C for 10 minutes. Next, the temperature of the susceptor 6 was raised to 1350 ° C., hydrogen passed through trimethylaluminum at 16 ° C. was supplied at 50 cc / min, and ammonia was supplied at 10 l / min for 3 minutes. In this growth step, the aluminum nitride layer 11 was formed to a thickness of about 25 nm as shown in FIG. Then, the supply of trimethylaluminum is stopped and the susceptor 6
After maintaining the temperature at 1200 ° C. and stopping the rotation of the susceptor 6, hydrogen passed through trimethylgallium at −15 ° C. was supplied at 100 cc / min and ammonia was supplied at 10 l / min for 1 hour to nitride the film having a thickness of about 8 μm. The gallium layer 12 was grown.
When the distribution of the film thickness in the upstream, the center and the downstream part and the direction perpendicular to the gas flow direction at these three points was measured using a scanning electron microscope, the film thickness was 8 μm ± 0.
It was found that a gallium nitride single crystal having a thickness of 5 μm and a small difference in growth rate depending on the location on the sapphire substrate 7 was obtained. The film thickness distribution using the conventional growth apparatus has a difference of 2 μm or more between the upstream and the downstream of the gas flow, and the effect of improving the film thickness distribution in the substrate surface was confirmed in this example. It was A gallium nitride layer having a similar film thickness distribution was obtained also when a 6H-type single crystal silicon carbide having a (0001) carbon plane as a main surface was used as a substrate. Secondary ion mass spectrometry was performed in the growth direction of the gallium nitride layer thus obtained to examine the carbon concentration distribution. The carbon concentration in the gallium nitride layer formed by using the conventional growth apparatus had no distribution in the growth direction of the layer and was uniform at about 1 × 10 ¹⁸ cm ⁻³ .
On the other hand, the carbon concentration in the gallium nitride layer in this example is 5 × 10 ¹⁷ cm ⁻³ on the substrate side and 2 × 1 on the surface as shown in FIG.
It was 0 ¹⁷ cm ^-3 , and it was confirmed that the carbon concentration was clearly highest on the substrate side and decreased toward the surface.
Next, this sample was measured by a photoluminescence method using a helium-cadminium laser as a light source. The results are shown in Figure 4a. A sharp peak that is considered to be band edge emission is seen near 380 nm. For comparison, when the carbon of the gallium nitride layer grown in the same manner as above was analyzed using a device in which the resistance heating element 1 was completely sealed with quartz, the carbon concentration was about 7 × 10 ¹⁶ cm ^−3. There was almost no distribution and it was uniform in the film. The photoluminescence properties of this sample are shown in Figure 4b. The peak at around 380 nm, which is considered to be band-edge emission, has very weak intensity, and a broad peak, which is not seen in FIG. 4a and is considered to be due to deep order near 550 nm, appears.

Using the apparatus shown in FIG. 1, the same crystal growth was carried out. This time, when the gallium nitride layer 12 was grown, 100 ppm silane having a hydrogen dilute content was additionally supplied at a rate of 2 cc / min. Created layers. When a gold / titanium electrode was formed on this sample and the voltage-current characteristics were measured, a very good ohmic property was shown.

Next, a light emitting diode having the structure shown in FIG. 5 was prepared using the apparatus shown in FIG. First, a single crystal sapphire substrate 7 having a (0001) plane having a diameter of 50 mm as a main surface washed with a mixture of methyl alcohol, sulfuric acid, hydrogen peroxide solution, and pure water is mounted on a susceptor 6.
Next, while energizing the electrode 2 while flowing hydrogen at 25 l / min and rotating the susceptor 6 at 10 rpm,
The temperature was kept at 1200 ° C for 10 minutes. Next, the temperature of the susceptor 6 was lowered to 550 ° C., and hydrogen passed through trimethylgallium at −15 ° C. was 25 cc / min, and ammonia was 10 l / l.
For 6 minutes to grow a gallium nitride layer 41. Then, raise the temperature of the susceptor 6 to 1150 ° C., and
Hydrogen passed through trimethylgallium at ℃ 50cc /
Min, ammonia at 10 l / min, hydrogen dilute 100
ppm silane was supplied at 2 cc / min for 60 minutes to grow the silicon-added gallium nitride layer 42. Then, the temperature of the susceptor 6 was lowered to 900 ° C., the nitrogen passed through trimethylgallium at −15 ° C. was 1 cc / min, the nitrogen passed through trimethylindium at 17 ° C. was 100 cc / min, and the anmore was 10
l / min, dimethyl zinc at 10 cc / min for 30 min,
A zinc-added gallium nitride layer 43 was grown. Next, the temperature of the susceptor 6 was raised to 1300 ° C., and hydrogen passed through trimethylgallium at −15 ° C. was 50 cc / min at 16 ° C.
25cc of hydrogen passed through trimethylaluminum of
/, Ammonia was supplied at 10 l / min, hydrogen passed through biscyclopentadienylmagnesium at 250 cc / min, and ammonia was supplied at 10 l / min for 30 minutes to grow the magnesium-added aluminum gallium nitride layer 44. Finally, the temperature of the susceptor 6 was lowered to 1150 ° C., the hydrogen passed through trimethylgallium at −15 ° C. was 50 cc / min, and the hydrogen passed through biscyclopentadienylmagnesium was 2 cc.
A magnesium-added gallium nitride layer 45 was grown by supplying 50 cc / min and 10 l / min of ammonia for 15 minutes. After that, the power supply to the susceptor 6 was stopped and the susceptor 6 was cooled.
After depositing a silicon dioxide film on the layer structure thus crystal-grown by a plasma CVD method, the film is grown in a nitrogen atmosphere at 750.
Heat treatment was performed at 30 ° C. for 30 minutes. Then, a patterned resist film was applied on the magnesium-added gallium nitride layer 45 by a photoetching process, and the silicon-added gallium nitride layer 42 was exposed by dry etching as shown in FIG. At this time, a sample was separately prepared by dry etching without patterning on the magnesium-added gallium nitride layer 45 by an optical etching process, and secondary ion mass spectrometry was performed.
It was confirmed that the inside carbon concentration was low on the surface and high on the substrate side. An electrode of gold / titanium was formed on the silicon-doped gallium nitride layer 42 of the sample prepared as shown in FIG. 6 by vacuum evaporation, and then the magnesium-doped gallium nitride layer 4 was formed.
After removing the silicon dioxide film from above by acid treatment, gold / nickel electrodes were formed on the magnesium-doped gallium nitride layer 45 by vacuum evaporation. When the thus-produced light-emitting diode was inspected in a pellet state, it emitted a blue light having an emission wavelength of 500 nm, and 2.
A high light output of 5 mW was obtained.

Further, silicon carbide crystal growth required high growth temperature was performed. First, 50 mm diameter washed with a mixture of methyl alcohol, hydrofluoric acid and nitric acid
The 6H-type single crystal silicon carbide substrate 7 whose main surface is the (0001) carbon surface is attached to the susceptor 6. Next, add 5 l / hydrogen
The current is started to flow to the electrode 2 while flowing, and the susceptor 6
While rotating at 10 rpm,
Hold for 0 minutes. Next, after the rotation of the susceptor 6 was stopped, silane gas 30 cc / min, propane gas 20 cc / min, trimethylaluminum 10 cc / min, and hydrogen were supplied at 5 l / min for 1 hour. The film thickness distributions in the upstream, central, and downstream portions and in the direction perpendicular to the gas flow direction at these three points were measured using a scanning electron microscope, and the contrast between the substrate and the grown thin film was good. The film thickness was 4 μm ± 0.5 μm at all measurement points, and it was found that a p-type silicon carbide single crystal having a small difference in the growth rate depending on the location on the silicon carbide substrate was obtained.

Crystal growth was carried out 30 times while maintaining the temperature for more than 1200 ° C. for about 1 hour. However, the resistance value obtained from the voltage and current values when energizing the heating body did not rise and deteriorated. It was confirmed that there was no sign of. After that, when the device was disassembled for cleaning, no visual deterioration of the heating body was found in the visual inspection.
Further, the aluminum nitride sintered body inserted into contact with the heating body was neither damaged nor cracked. It was confirmed that the growth device was sufficiently stable.

In this embodiment, an aluminum nitride sintered body has been described as an example of the material of the insulator to be inserted in contact with the heating body. However, a material exhibiting the same insulating property, chemically stable, and high thermal conductivity. Therefore, the same effect can be expected with other materials.

Next, as another embodiment, manufacturing of a high electron mobility transistor will be described. The same metal-organic vapor phase epitaxy apparatus as that used in the above-mentioned embodiment was used. Diameter 5 for substrate
A semi-insulating gallium arsenide single crystal having a 0 mm (001) plane as a main surface was used, and arsine gas diluted with hydrogen to 3% was used as a raw material of arsenic. The growth temperature is set to 600 ° C., trimethylgallium and arsine gas are first supplied to form an undoped gallium arsenide layer of 1 μm, and then an undoped aluminum gallium arsenide layer having an aluminum composition of 30% is formed to a thickness of 20 nm. By further supplying silane gas, an aluminum gallium arsenide layer having an aluminum composition of 30% was grown to a thickness of 500 nm by adding arsenic. Source, drain and gate electrodes are attached to such a structure,
A high electron mobility transistor was created. As a result of analyzing the carbon concentration in the undoped gallium arsenide layer by secondary ion mass spectrometry, it was found to be 7 × 10 ¹⁶ cm ⁻³ at the interface with the substrate and 4 × at the interface with the undoped aluminum gallium arsenide layer having an aluminum composition of 30%. It was 10 ¹⁶ cm ^-3 . The carbon concentration in the undoped gallium arsenide layer of the high electron mobility transistor produced by the conventional method was constant at about 9 × 10 ¹⁶ cm ⁻³ , and there was no distribution in the growth direction. When the two-dimensional electron mobility of the high electron mobility transistor thus created was measured at room temperature, it was about 6 × 10 ³ cm ² / V · s in the conventional one, but in this example, Created by 5x1
It was about 0 ³ cm ² / V · s. It is considered that the reason why such high-speed operation is possible is that the impurity scattering in the undoped gallium arsenide layer (pontential inversion layer) near the undoped aluminum gallium arsenide layer having an aluminum composition of 30% is reduced. .

[0017]

As described above, according to the present invention, the vapor phase growth apparatus has an advantage that the structure is extremely simple, uniform heating at high temperature can be stably performed, and the life of the resistance heating body is remarkably extended. Therefore, it is easy to grow a single crystal of a material that requires high temperature, and has a remarkable effect of economical efficiency, reproducibility, and reliability, which is industrially extremely advantageous. Further, by using such a growth apparatus, it becomes possible to distribute the carbon concentration in the semiconductor thin film so as to be lowered in the growth direction, and as a result, a highly efficient light emitting diode or a laser that oscillates at a low threshold value can be obtained. Manufacturing is possible with high yield.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment according to the present invention.

FIG. 2 is a cross-sectional view showing the structure of a thin film grown on a sapphire substrate according to an embodiment of the present invention.

FIG. 3 is a diagram showing a result of quantifying carbon concentration in a gallium nitride thin film of one example according to the present invention by secondary ion mass spectrometry.

FIG. 4 is a diagram showing a comparison of photoluminescence characteristics of gallium nitride thin films of one example according to the present invention.

FIG. 5 is a cross-sectional view of a layer structure formed using the gallium nitride thin film of one example according to the present invention.

FIG. 6 is a structural cross-sectional view of a light emitting diode manufactured using a gallium nitride thin film according to an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Graphite manufacturing resistance heating body 2 ... Electrode 3 ... Aluminum nitride sintered compact lower protective plate 4 ... Aluminum nitride sintered compact upper protective plate 5 ... Purge gas introduction pipe 6 ... Susceptor 7 ... Sapphire substrate 8 ... Purge gas introduction Hole 9 ... Reflector 10 ... Reflector support rod 11 ... Aluminum nitride layer 12, 41 ... Gallium nitride layer 42 ... Silicon-added gallium nitride layer 43 ... Zinc-added gallium indium nitride layer 44 ... Magnesium-added aluminum gallium nitride layer 45 ... Magnesium Addition gallium nitride layer

Claims (5)

[Claims] 1. A semiconductor wafer characterized in that a semiconductor thin film formed on a substrate contains carbon, and that carbon is less on the substrate side and more on the thin film surface side. 2. A semiconductor device comprising two or more kinds of semiconductor thin films laminated on a substrate, wherein carbon is contained in at least one layer of the semiconductor thin films, and the carbon concentration varies according to the surface direction of the semiconductor thin film. A semiconductor device characterized by being distributed so as to be low. 3. The semiconductor device according to claim 2, wherein the substrate is made of aluminum oxide and the semiconductor thin film is made of gallium nitride, and emits blue light. 4. The semiconductor device according to claim 2, wherein when the semiconductor thin film is formed by a vapor phase growth method, the substrate is heated by a resistance heating body and the vapor phase growth method uses an organic metal. Production method. 5. An apparatus for forming a semiconductor thin film according to claim 2 by a vapor phase growth method using an organic metal comprises a resistance heating body for heating the substrate, and the resistance heating body is an insulator in a gap between conductive parts. A vapor phase growth apparatus characterized by being inserted into contact.