JPH0766908B2 - Semiconductor single crystal growth method - Google Patents

Description

Description: TECHNICAL FIELD The present invention reduces defects at the interface between a semiconductor substrate and an epitaxial growth layer when a semiconductor single crystal growth layer is epitaxially grown on a semiconductor substrate in units of monomolecular layers. The present invention relates to a semiconductor single crystal growth method suitable for.

[Prior art and its problems]

Conventionally, a molecular beam epitaxy method (hereinafter referred to as MBE method) has been known to obtain an ultrathin semiconductor film. However, the MBE method requires physical adsorption as the first step,
The crystal quality is inferior to the vapor phase growth method using a chemical reaction. Ga
When growing a III-V group compound semiconductor such as As, group III and V elements are used as sources, and the source source itself is installed in the growth chamber. For this reason, it is difficult to control the emission gas and evaporation amount obtained by heating the source source, and to replenish the source, and it is difficult to keep the growth rate constant for a long time. In addition, the vacuum device becomes complicated, such as discharging evaporative substances. Furthermore, it is difficult to precisely control the stoichiometric composition (stoichiometry) of the compound semiconductor, and as a result, high quality crystals cannot be obtained.

In Japanese Patent Laid-Open No. 55-130896 and Nikkei Electronics, Nov. 9, 1981, pages 86 to 91, a raw material vapor called ALE method is alternately introduced onto a substrate to form Ta ₂ O ₅ , Al. A technique for growing amorphous such as ₂ O ₃ and polycrystal such as ZnS is shown, but the growth film thickness per cycle of steam introduction is 1 /
There was a defect that it was a small value of 3 molecular layers or less. Also this A
The LE method has a drawback that the exchange surface reaction becomes difficult unless an inert gas such as a carrier gas is used as a diffusion barrier. Furthermore, since the ALE method cannot handle gases and elements having a low vapor pressure, there is a drawback that III-V group compound semiconductors such as GaAs, which are important in the semiconductor industry, cannot grow. Further, the above-mentioned Nikkei Electronics describes that the surface is cleaned by sputtering with Ar before growth, but there is a defect that the surface is damaged by the energy due to the sputtering and a defect occurs at the interface between the substrate and the epitaxial growth layer.

In view of such a point, the inventors of the present application have developed a semiconductor single crystal growth apparatus having a controllability of a growth film thickness in a monomolecular layer unit, excluding the above-mentioned drawbacks of the prior art. This will be described with reference to FIG.

In the figure, 1 is a growth tank, the material is metal such as stainless steel, 2 is a valve such as a gate valve, 3 is an exhaust device for evacuating the growth tank 1 to an ultrahigh vacuum, and 4,5 are, for example, III-V group. A growth nozzle for introducing a raw material gas consisting of a gaseous compound of a group III or V component element of a compound semiconductor, 6 and 7 are gas introduction valves for opening and closing the growth nozzles 4,5, and 8 is a group III Raw material gas consisting of gaseous compounds containing constituent elements, 9
Is a source gas composed of a gaseous compound containing a group V component element, and 10 is a tungsten (W) wire enclosed in quartz glass by a heater for heating the substrate, which also serves as a substrate support, and electric wires and the like are not shown. There is. 11 is a thermocouple for temperature measurement, 12 is a compound semiconductor substrate, and 13 is a pressure gauge for measuring the degree of vacuum in the growth tank.

Here, the growth nozzles 4 and 5 are connected to the substrate 12 as shown in FIG.
Placed very close to the substrate and the growth nozzle tip opening is
By arranging the surface of the substrate as desired, the source gases 8 and 9 consisting of the gaseous compound emitted from the growth nozzle are transferred to the substrate 12
Reaching only the surface of, and wrapping around the substrate 12,
It will not be adsorbed on the inner wall of the growth tank 1. Therefore AL
Even if the gas phase diffusion barrier is not used unlike the E method, the exchange surface reaction can be realized simply by opening and closing the gas introduction valves 6 and 7 and evacuating by the exhaust device 3. Moreover, gas with low vapor pressure such as GaCl ₃ and TMG can be introduced into the vacuum in a rectangular pulse shape.

The method for epitaxially growing GaAs molecular layers one by one on the substrate 12 is as follows. That is, the gate valve 2 is opened, and the inside of the growth tank 1 is evacuated to about 10 ^-7 to 10 ^-8 Pascal (hereinafter abbreviated as Pa) by the ultrahigh vacuum evacuation device 3. Next, heat the GaAs substrate 12 to, for example, about 300 to 800 ° C.
When heated by 10, TMG (trimethylgallium) 8 as a gas containing Ga is grown in the growth tank 1 at a pressure of 10 ^-1 to 10 ^-7 Pa (preferably in the range of 10 ^-1 to 10 ^-3 Pa). In), 0.5-1
The gas introduction valve 6 is opened for 0 seconds for introduction. afterwards,
After the gas introduction valve 6 was closed and the residual gas in the growth tank 1 was evacuated, AsH ₃ (arsine) was added as a gas containing As.
9 within the pressure range of 10 ^-1 to 10 ^-7 Pa (preferably 10 ^-1
Gas introduction valve 7 for 2 to 200 seconds in the range of ~ 10 ^-2 Pa)
Open and install. After that, the gas introduction valve 7 is closed, and the residual gas in the growth tank 1 is evacuated. By this exchange surface reaction, at least one molecular layer of GaAs can be grown on the substrate 12. On the GaAs (100) surface, a minimum of 2.83Å grows per exchange surface reaction cycle. GaAs (11
1) On the surface, a small amount grows by 3.26Å per cycle. By repeating the above operation and growing the monomolecular layers one after another, it is possible to grow the GaAs epitaxial growth layer having a desired number of molecular layers in units of the monomolecular layer. This method is called a molecular layer epitaxial growth (MLE) method.

This growth apparatus is particularly suitable for very thin crystal growth of the order of several tens of layers, but such a thin crystal growth layer is very sensitive to the crystallinity of the substrate and the surface condition of the substrate, and the surface condition is poor. In some cases, not only the crystallinity of the grown crystal deteriorates, but also the crystal does not grow in some cases.
If GaAs is used as an example of pretreatment for growth, H ₂
Wet etching with a mixed solution of SO ₄ , H ₂ O ₂ and H ₂ O is required.
There was a problem that deposits of very thin oxides called natural oxides of about 50Å were formed, resulting in defects at the substrate-epitaxial growth interface.

Fig. 5, the n-type 50 molecule layer on the GaAs substrate n ^- layer and pn who MLE grown by exchange surface reactions p ⁺ layer of the top 70 molecules layer
It shows the rising voltage (V _F ) of the junction diode.

In the figure, the alternate long and short dash line indicates the case where the above-mentioned H ₂ SO ₄ , H ₂ O ₂ , and H ₂ O mixed solution was grown only on the wet-etched surface, and there was a defect at the interface between the epitaxial growth layer and the substrate, and the leakage current Occurs and V _F is as small as 0.4 V. The mark Δ indicates that surface treatment by heat treatment in AsH ₃ (arsine) called thermal desorption was performed in the growth tank 1 in FIG. 4 to continuously grow the n ⁻ layer and the p ⁺ layer. , Substrate temperature 510
The maximum value of V _F is about 0.8 V at ℃. When the substrate temperature is lower than this, the effect of thermal desorption decreases, and it almost disappears at 420 ° C. On the other hand, even at high temperatures such as 600 ° C, ga and As escape from the GaAs substrate, and the characteristics of the pn junction diode deteriorate again.

The characteristic of the MLE method is that it enables growth of molecular layer units at 400 ℃ or less, but the temperature of thermal desorption of 510 ℃ is p ⁺ n ^- p ⁺ , n ⁺ n
^- p ⁺ n ^- a n ⁺ characteristics of the multilayer structure such as would be disturbs by thermal diffusion. For example, first, an n ⁺ n ^- p ⁺ n ^- n ⁺ layer is formed in a molecular layer unit by MLE, then a U groove is formed in the substrate, and regrowth is performed on the n ^- p ⁺ layer MLE. In the case of the process, if the heat treatment is performed at 510 ° C. before the regrowth, the steep impurity profile of the molecular layer unit is disturbed and lost.

[Object of the Invention]

According to the present invention, a substrate surface is etched in a vacuum, and immediately after that, epitaxial growth can be performed to grow a good-quality single crystal film having a self-stable growth rate characteristic with dimensional accuracy of a single molecular layer unit on the substrate. Another object of the present invention is to provide a semiconductor single crystal growth method capable of extremely reducing defects at the interface of the epitaxial growth layer.

Also, another object of the present invention is the failure of the ALE method to grow.
Achieved growth of II-V group compound semiconductors in a single molecular layer,
Moreover, the surface defects at the interface between the substrate and the epitaxial growth layer should be extremely reduced.

Still another object of the present invention is to provide a method of realizing surface cleaning by low-temperature etching which is damage-free and immediately followed by crystal growth.

[Outline of Invention]

The present invention relates to a substrate supporting base for holding a III-V group compound semiconductor single crystal substrate thereon, a growth tank having the substrate supporting base arranged therein, a valve connected to the growth tank, and the valve. An exhaust device connected to the growth chamber, an etching nozzle which is introduced from the outside of the growth tank into the inside and is formed with its tip facing toward the surface of the III-V compound semiconductor single crystal substrate, and at least two growth nozzles. Nozzle, a gas introduction valve provided outside the growth tank in each of the growth nozzles, a heating source for heating only the III-V group compound semiconductor single crystal substrate, and the III-V group compound a semiconductor method of a single crystal substrate to grow a semiconductor crystal by growing apparatus having a mechanism for light irradiation, the method, the after evacuating the growth chamber to about 10 ^-7 Pa II
The IV compound semiconductor single crystal substrate is heated to 350 ° C. or lower,
Introducing an etching gas consisting of a gas containing an element such as C1, F, Br from the etching nozzle, evacuated by the evacuation device after performing photoetching, then the substrate temperature is 300 ~ 600 ° C., The exchange surface reaction of at least two kinds of source gases on the surface of the group III-V compound semiconductor single crystal substrate with at least two kinds of source gases is performed only by opening / closing the gas introducing valve and evacuating by the evacuation device.
^-1 to 10 ^-7 Pa, which is one of the exchange surface reactions.
It is characterized in that a single crystal epitaxial growth layer having a desired number of molecular layers is formed in a unit of a single molecular layer by repeating the formation of the group III-V compound semiconductor single crystal thin film in a unit of one molecular layer for each cycle. .

Example of Invention

FIG. 1 is a block diagram of a semiconductor crystal growth apparatus according to an embodiment of the present invention, which is equipped with a mechanism capable of vapor phase etching as a means for substrate surface treatment. 20 is an etching nozzle for introducing a gaseous compound used for vapor phase etching, 21 is a gas introducing valve for opening and closing it,
22 is a gaseous compound used for vapor phase etching. Since the parts other than the introduction of the etching gas are the same as those in the explanatory view of FIG. 4, the description thereof will be omitted.

With this configuration, vapor phase etching is performed as follows. The case where a GaAs substrate is used as the compound semiconductor substrate and GaCl ₃ is used as the gaseous compound for etching will be described as an example. The GaAs substrate is subjected to normal wet etching, then washed and dried, and placed on the substrate support 10. After the growth tank was evacuated to about 10 ^-7 Pa with an exhaust device, a gas introduction valve
Open 21 and introduce GaCl ₃ to about 10 ^-6 to 10 ^-5 Pa and change the substrate temperature to 1 Å / min to 1000 Å / min GaAs.
The substrate can be etched.

FIG. 2 (a) shows the relationship between the substrate temperature and the etching rate when the supply amount of GaCl ₃ is used as a parameter, and the curve A shows that the supply amount of GaCl ₃ is 1/3 that of the curve B. This is the case. On the other hand, FIG. 2B shows the relationship between the CaCl ₃ supply amount and the etching rate when the substrate temperature is used as a parameter. The straight line C has a substrate temperature of 350 ° C. and the straight line D has a substrate temperature of 250. This is the case of ° C.

As can be seen from these figures, the etching rate is determined by the GaCl ₃ supply amount while the substrate temperature is high, and becomes independent of the GaCl ₃ supply amount when the substrate temperature is low, and depends only on the substrate temperature. Therefore, the etching rate is
From these relationships, the substrate temperature and the GaCl ₃ supply amount can be selected and set to the optimum values.

FIG. 3 shows another embodiment of the present invention, which is provided with a mechanism capable of irradiating the substrate with light during vapor phase etching as a means for treating the substrate surface. 30 is a light source for light irradiation, which is a 500 W high-pressure mercury lamp. , 31 are ports with windows for guiding the light emitted from the light source to the semiconductor substrate 12 installed in the vacuum chamber. Since the parts other than the light irradiation are the same as those in FIG. 1, the description thereof will be omitted.

By irradiating with light, the etching temperature can be lowered by 100 degrees or more. Light irradiation may be performed continuously during vapor phase etching or intermittently. In this case, the light may be applied not only on the substrate 12 but also on the etching gas itself by forming the nozzle transparent. By doing so, the etching gas is activated and the etching process is promoted. The light source is not limited to a lamp such as a high-pressure mercury lamp or a xenon lamp, and may be an excimer laser or an argon laser light doubled.

By the way, the activation of the etching gas is not limited to the above-mentioned light irradiation, but it can be activated by providing a high frequency coil or an electrode around the nozzle and applying a voltage.

The circles in FIG. 5 indicate the case where the n-type GaAs substrate was vapor-phase-etched according to the present invention, and immediately thereafter, a pn junction diode having an n ⁻ layer (50 molecular layers) and ap ⁺ layer (70 molecular layers) was formed. Although the rising voltage V _F is shown, a very good result of V _F = 0.85 V was obtained even in low temperature vapor phase etching at 400 ° C. or lower.

In the above-described embodiments, the substrate used for crystal growth has been described mainly for the GaAs (100) plane, but other plane orientations may be used and it does not depend on the impurity density of the substrate.
Further, it is needless to say that it can be applied to other III-V group compound semiconductors such as InP, AlP, and GaP. Also, Ga _1-x Al _x As, Ga _1-x A
A mixed crystal such as l _x As _1-y P _y may be used. Furthermore, the gaseous compound used for etching is not limited to GaCl ₃ and other gaseous compounds HC
1, HBr, PCl ₃ , AsCl ₃ , Cl ₂ , SF ₆ , CCl ₂ F ₂ , CF ₄ , C ₃ F ₈ ,
CH ₃ Br etc. are also acceptable. A substrate pretreatment chamber equipped with an etching nozzle is provided next to the growth chamber, a vacuum sample moving mechanism is provided between the substrate pretreatment chamber and the growth chamber, and the substrate is etched in the pretreatment chamber in a vacuum in the growth chamber. When the sample is moved and the crystal is grown, the residual gas and reaction products after etching are ML.
Of course, the better thing is that it doesn't hinder growth.

[Effects of the Invention] As described above, according to the present invention, the etching process, which is a pretreatment process for epitaxial growth, can be performed in a vacuum chamber and is not exposed to the atmosphere after etching. Can be prepared for the state. According to the present invention, since an inert gas such as a carrier gas is not used with respect to the substrate surface, the number of carrier gas nozzles and gas introduction valves used for this can be reduced, which simplifies the structure of the apparatus and makes maintenance easier. And easy to operate. As a result, it becomes possible to surely and easily grow a high-quality single crystal satisfying the stoichiometric composition of the III-V group compound semiconductor. As a result, it is possible to obtain a semiconductor single crystal growth apparatus which is extremely effective for manufacturing very high speed transistors, integrated circuits, diodes, light emitting / receiving elements and the like.
In particular, a U-groove is formed by ECR or plasma etching on a substrate on which multi-layer MLE growth such as a cut gate type SIT is performed, and the U groove is formed.
In the step of performing the second MLE growth on the inner wall of the groove, according to the present invention, the damage of ECR or plasma etching and the natural oxide film on the surface of the U groove wall can be efficiently removed, so that the interface defects are extremely small. The second MLE growth will be possible.

Further, according to the present invention, since a single crystal of one molecular layer grows by a self-stopping mechanism per gas introduction cycle, the controllability of the film thickness is good, and a desired film thickness can be obtained in a shorter time than the ALE method. be able to. According to the present invention, the surface treatment of the substrate before the MLE growth can be performed at a low temperature of 350 ° C. or less, so that the characteristics of the MLE growth as the low temperature epitaxial growth can be sufficiently exhibited.

Further, according to the present invention, since the surface is cleaned by vapor phase etching, there is no fear of damage unlike the surface cleaning by sputtering.

[Brief description of drawings]

FIG. 1 is a block diagram of a semiconductor crystal growth apparatus according to an embodiment of the present invention, FIG. 2 (a) is a graph showing the relationship between the etching rate of a GaAs substrate by CaCl ₃ and the substrate temperature, and FIG. 2 (b). ) Is a graph showing the relationship between the etching rate and the supply amount of GaCl _3, FIG. 3 is a block diagram of a semiconductor crystal growth apparatus according to another embodiment of the present invention, and FIG. 4 was previously developed by the present inventor. It is a block diagram of a semiconductor crystal growth apparatus. FIG. 5 is a comparison diagram of rising voltage characteristics of the pn junction diode formed by the device of the present invention and the conventional device. 1 ... Growth tank, 2 ... Gate valve, 3 ... Exhaust device,
4,5 …… Growth nozzle, 20 …… Etching nozzle, 6,
7,21 ...... Gas introduction valve, 8,9,22 ...... Gaseous compound raw material gas, 10 ...... Substrate support that doubles as a substrate heating heater, 11 ...... Temperature measuring thermocouple, 12 …… Substrate, 13 ……
Pressure gauge, 30 …… light source, 31 …… port.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Abe 1-2-22-11 Midorigaoka, Sendai City, Miyagi Prefecture (56) Reference JP-A-55-113329 (JP, A) JP-A-55-130896 (JP, A) ) JP-A-58-98917 (JP, A) Nikkei Electronics, November 9, 1981, pages 86-91

Claims (4)

[Claims] 1. A substrate support for holding a III-V group compound semiconductor single crystal substrate thereon, a growth tank in which the substrate support is arranged, and a valve connected to the growth tank.
An exhaust device connected to the valve, an etching nozzle that is introduced from the outside of the growth tank into the inside and has its tip facing toward the surface of the III-V compound semiconductor single crystal substrate, and at least two nozzles. Growth nozzle, a gas introduction valve provided in each of the growth nozzles outside the growth tank, a heating source for heating only the III-V compound semiconductor single crystal substrate, and the III- A method for growing a semiconductor crystal using a growth apparatus equipped with a mechanism for irradiating a group V compound semiconductor single crystal substrate with light, the method comprising: evacuating the growth tank to about 10 ^-7 Pa;
Heating the III-V group compound semiconductor crystal substrate to 350 ° C. or lower,
Introducing an etching gas consisting of a gas containing an element such as C1, F, Br from the etching nozzle, evacuated by the evacuation device after performing photoetching, then the substrate temperature is 300 ~ 600 ° C., The exchange surface reaction of at least two kinds of source gases on the surface of the group III-V compound semiconductor single crystal substrate with at least two kinds of source gases is performed only by opening / closing the gas introducing valve and evacuating by the evacuation device.
^-1 to 10 ^-7 Pa, which is one of the exchange surface reactions.
A single crystal epitaxial growth layer having a desired number of molecular layers is formed in a unit of a single molecular layer by repeating the formation of the group III-V compound semiconductor single crystal thin film in a unit of one molecular layer for each cycle. Semiconductor single crystal growth method. 2. The method for growing a semiconductor single crystal according to claim 1, wherein at least a part of the etching nozzle is irradiated with light. 3. The method for growing a semiconductor single crystal according to claim 2, wherein at least a part of the etching nozzle is optically transparent. 4. The method for growing a semiconductor single crystal according to claim 1, wherein a high frequency coil or an electrode is provided on at least a part of the periphery of the etching nozzle to activate an etching gas.