JP3576323B2 - Heat treatment method for compound semiconductor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat treatment method for a compound semiconductor substrate and an epitaxial thin film, and more particularly to a high-temperature heat treatment method such as activation annealing after ion implantation.
[0002]
[Prior art]
When an impurity is added to a Group III-V compound semiconductor substrate containing arsenic such as gallium arsenide or aluminum gallium arsenide by ion implantation and used as a conductive carrier, crystal defects generated at the time of implantation are restored or the added impurity is removed. In order to move atoms to a desired lattice position, a heat treatment called activation is required. Generally, this heat treatment temperature is higher than the arsenic evaporation temperature. As a result, arsenic molecules evaporate from the surface of the semiconductor substrate, arsenic vacancies are generated, and the activation rate of carriers is reduced, the flatness of the semiconductor substrate surface is deteriorated, and gallium remaining on the semiconductor substrate surface is a cause. There has been a problem that the characteristics of the electronic device fluctuate.
[0003]
As a method for solving the above-mentioned problem caused by arsenic evaporation, an atmosphere control annealing method and a cap annealing method have been proposed. Among them, the atmosphere control annealing method is a method of heating while applying an excessive arsenic pressure in the atmosphere of a heat treatment apparatus, and generally uses arsine as an arsenic pressure source. This arsine is very toxic and has a major safety problem. Some methods that do not use arsine have also been proposed, but have the disadvantage that the structure of the heat treatment apparatus becomes very complicated and that a sufficient arsenic pressure cannot be obtained. Further, there is a drawback that the semiconductor substrate is contaminated because the purity of the arsenic pressure source is low.
[0004]
On the other hand, the cap annealing method is a method of covering the surface of a semiconductor substrate with a thermally stable protective film and performing heat treatment, and is widely adopted as a simple method. In particular, many studies have been made on a protective film formed on a semiconductor substrate when heat treatment is performed by a lamp annealing method using an infrared lamp capable of performing rapid thermal quenching in a short time as a heating source.
[0005]
For example, if the semiconductor substrate to be heat-treated is gallium arsenide, if a silicon oxide film is formed as a protective film on the surface and heat treatment is performed, the result is that gallium diffuses into the silicon oxide film and is not suitable as a protective film. ing. Further, when a silicon nitride film is used as a protective film, the thermal expansion coefficients of silicon nitride and gallium arsenide are different, and the protective film may be peeled or cracked, and may not function as a protective film. FIG. 2 shows the surface state of the silicon nitride film after depositing a 1500 angstrom silicon nitride film directly on the gallium arsenide substrate and performing lamp annealing at 850 ° C. for 25 seconds. It is clear that cracks and peeling are seen on the surface and do not function as a protective film.
[0006]
As a protective film that solves such a defect, a method of alternately stacking a silicon oxide film and a silicon nitride film or using a composite film of these has been proposed. However, when the silicon oxide film and the silicon nitride film are formed alternately, the gas composition for forming each film is different when forming each film by the CVD method, and even if they are formed in the same reaction furnace, After the formation of one film, the reaction gas must be removed, and a step of introducing a gas for forming another film must be performed, which has a drawback that the manufacturing process is complicated. When a silicon nitride oxide film, which is a composite film of silicon oxide and silicon nitride, is formed, it is difficult to control the composition of nitrogen and oxygen, and the ability to prevent arsenic evaporation is higher than that of a silicon nitride film. There was a disadvantage of being low.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a heat treatment method for a compound semiconductor using a new protective film that can be formed by a simple manufacturing method, unlike the conventionally proposed protective film.
[0008]
[Means for Solving the Problems]
Since the present invention is to achieve the above object, in a heat treatment method of the group III-V compound semiconductor, and nitride III-V group compound semiconductor substrate surface, after forming a nitride of an element composition of the semiconductor substrate, nitride a film made of nitrided silicon Butsujo formed successively, covering the 3-5 group compound semiconductor substrate surface, it is characterized in that the heat treatment. In particular, the nitride is at least hydrazine, by Rukoto to form a plasma of the gas is brought into contact with the group III-V compound semiconductor surface containing either dimethyl hydrazine, or ammonia, without a complicated manufacturing process, It is configured such that a protective film for realizing the heat treatment method of the present invention can be formed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the first embodiment of the present invention will be described with reference to an example in which silicon nitride is formed on a gallium arsenide substrate via gallium nitride as a protective film. First, a gallium arsenide substrate is set in a chamber used for a normal plasma CVD method. After the chamber is once evacuated, ammonia is introduced so as to have a predetermined concentration. Here, the gallium arsenide substrate is heated to about 300 to 500 ° C. When it is stabilized at a predetermined degree of vacuum, a high frequency voltage is applied to generate plasma. As the surface of the gallium arsenide substrate is heated to a higher temperature, arsenic evaporates from the surface, resulting in a gallium-rich surface. When ammonia plasma comes into contact with such a surface, gallium on the surface is nitrided and gallium nitride is generated on the surface.
[0010]
Thereafter, the temperature of the gallium arsenide substrate is set to about 300 ° C., and monosilane is introduced into the chamber at a predetermined flow rate. Ammonia and nitrogen are introduced into the chamber, and the partial pressure of monosilane in the chamber increases. When a predetermined partial pressure is reached, silicon nitride starts to be deposited on gallium nitride.
[0011]
Once the application of the high-frequency voltage is stopped, the partial pressure of each of monosilane, ammonia and nitrogen is set to a predetermined value, and silicon nitride having a predetermined thickness is deposited.
[0012]
FIG. 1 schematically shows a method of forming a protective film. When the gallium atoms 1 and 2 on the surface of the gallium arsenide (GaAs) substrate are heated to a high temperature, the arsenic atoms 2 evaporate, and the substrate surface becomes gallium-rich (FIG. 1A). When the ammonia plasma comes into contact with such a surface, it is considered that nitrogen atoms 3 combine with gallium atoms 1 and gallium nitride (GaN) is generated on the substrate surface (FIG. 1B). Furthermore, by contacting with monosilane plasma and ammonia plasma by a usual method, nitrogen atoms 3 and silicon atoms are deposited, and a silicon nitride film is formed. The gallium nitride film thus formed is continuously formed on the gallium arsenide substrate, and has a structure for relaxing the stress existing between gallium arsenide and silicon nitride.
[0013]
When used as a protective film in activation annealing after silicon ions were implanted into a gallium arsenide substrate, no peeling or cracking was generated, indicating that the film was effective as a protective film. Since silicon nitride and gallium nitride are removed when a semiconductor device is formed, gallium and arsenic are present at a stoichiometric ratio on the exposed surface, and the semiconductor device is formed on a clean surface. can do.
[0014]
Next, a second embodiment of the present invention will be described. In the first embodiment, the gallium arsenide substrate is heated to about 500 ° C. and brought into contact with the ammonia plasma, whereas in the second embodiment, the gallium arsenide substrate is heated only to about 300 ° C. At this temperature, even if the gallium arsenide substrate is brought into contact with the ammonia plasma, the amount of gallium nitride generated is small. Therefore, it is preferable to change the gas introduced into the chamber.
[0015]
First, a gallium arsenide substrate is set in a chamber. After the chamber is once evacuated, hydrazine or dimethylhydrazine is introduced together with nitrogen gas as a carrier gas so as to have a predetermined concentration. Here, heating the gallium arsenide substrate at about 300 ° C. is sufficient. When it is stabilized at a predetermined degree of vacuum, a high frequency voltage is applied to generate plasma. Since the surface of the gallium arsenide substrate is heated only at about 300 ° C., evaporation of arsenic from the surface is small, and the surface has a substantially stoichiometric composition. When hydrazine plasma or dimethylhydrazine plasma contacts such a surface, gallium nitride is generated on the surface.
[0016]
Then, as in the first embodiment, a silicon nitride film is formed on gallium nitride to form a protective film. As a result of using the protective film thus formed for activation annealing, as in the first embodiment, the occurrence of peeling and cracking was suppressed, and good results were obtained.
[0017]
In addition to the above-described embodiment, gallium nitride can be formed on a gallium arsenide substrate by a thermal CVD method or a sputtering method instead of the plasma CVD method. Further, a multilayer film in which a silicon nitride film is combined with a silicon nitride oxide film or a silicon oxide film may be used.
[0018]
As still another embodiment, it is possible to form an epitaxial growth layer on a gallium arsenide substrate and use it as a protective film. As a method for epitaxially growing gallium nitride on the surface of the gallium arsenide substrate, an ordinary MBE method, MOCVD method, or the like can be employed. A silicon nitride film formed over gallium nitride can also be formed by an epitaxial growth method. Further, a method of forming a silicon nitride film by a CVD method or the like after epitaxially growing gallium nitride may be employed. Further, it is possible to form a multilayer film in which the silicon nitride film is combined with a silicon nitride oxide film or a silicon oxide film.
[0019]
Even when the film formed by the epitaxial growth method is used as a protective film for activation annealing after silicon ions are implanted into a gallium arsenide substrate, it is effective as a protective film without peeling or cracking. all right.
[0020]
Although the gallium arsenide substrate has been described as an example among the group III-V compound semiconductors, other compound semiconductors composed of elements having different evaporation temperatures, for example, aluminum gallium arsenide, indium phosphorus, gallium phosphorus, etc. It goes without saying that the present invention is effective.
[0021]
Specifically, in the case of aluminum gallium arsenide, it is possible to use almost the same method as the above gallium arsenide. In the case of indium phosphide, the surface of the indium phosphide substrate is contacted with plasma such as ammonia, or indium nitride is formed on the surface of the indium phosphide substrate by an epitaxial growth method, and a silicon nitride film is further formed thereon. Similarly, in the case of gallium phosphide, gallium nitride may be formed on a gallium phosphide substrate, and a silicon nitride film may be further formed thereon. Also in these cases, the separation and cracking of the silicon nitride film caused by the difference in the coefficient of thermal expansion between the compound semiconductor substrate and the silicon nitride film cause the nitride formed between the substrate and the protective film to act as a stress relaxation layer. By doing so, it is possible to suppress it.
[0022]
Furthermore, the heat treatment method of the present invention is not limited to the lamp annealing method of performing rapid heating and rapid cooling, and is effective even when used as a protective film in performing a process in which arsenic evaporation is a problem, such as resistance heating.
[0023]
【The invention's effect】
As described above, according to the present invention, peeling of the protective film and generation of cracks caused by a difference in the coefficient of thermal expansion between the compound semiconductor and the protective film are suppressed by interposing a nitride of an element constituting the compound semiconductor. I was able to. This protective film can be provided by a simple method. If the compound semiconductor substrate on which such a protective film is formed is heat-treated to form a semiconductor device, the surface of the compound semiconductor substrate becomes a clean surface on which constituent elements are present in a stoichiometric ratio, and a semiconductor having good characteristics. A device can be formed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an embodiment of the present invention.
FIG. 2 shows a surface state of a silicon nitride film after lamp annealing according to a conventional method.
[Explanation of symbols]
1 gallium atom 2 arsenic atom 3 nitrogen atom

Claims (2)

In group III-V compound semiconductor of the heat treatment method, nitriding the 3-5 group compound semiconductor substrate surface, after forming a nitride of an element composition of the semiconductor substrate, a film made of nitrided silicon on the nitride A heat treatment method for a compound semiconductor , comprising continuously forming, covering the surface of the Group 3-5 compound semiconductor substrate, and performing heat treatment. 2. The compound semiconductor heat treatment method according to claim 1, wherein the nitride is formed by bringing a plasma of a gas containing at least one of hydrazine, dimethylhydrazine and ammonia into contact with the surface of the group III-V compound semiconductor. Heat treatment method for a compound semiconductor.

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