Method for the production of semiconductor devices

A method for the production of semiconductor devices comprising introducing source gases, etching gases or source molecules into a substrate to grow crystalline layers on said substrate or to etch said substrate, resulting in a semiconductor device, wherein said method further comprises applying a given electric potential to said substrate; applying an electric potential that is different from that of said substrate to an electron-beam irradiator disposed directly above said substrate; and irradiating said irradiator with electron beams from an electron-beam emitting means, whereby said substrate is irradiated with the secondary electron beams generated from said irradiator and/or with the electron beams transmitted through said irradiator.

BACKGROUND OF THE INVENTION 
1. Field of the invention: 
This invention relates to a method for the production of semiconductor 
devices made of III-V group compounds. More particularly, it relates to a 
method for the production of semiconductor devices in which the 
heat-temperature of a substrate is reduced, resulting in high-quality 
crystalline layers; source gases are selectively decomposed thereby 
attaining composition control at the interface between the crystalline 
layers and composition control within the surface of each of the 
crystalline layers, and amount control of dopants; or the etching of the 
substrate is selectively achieved. 
2. Description of the prior art: 
A method for the production of semiconductors made of III-V group 
compounds, in which organic metal compounds are used, is disclosed in 
Japanese Patent Publication No. 49-44788. This method is disadvantageous 
in that, in the thermal decomposition of the organic metals and hydrides 
of V group compounds, when a compound semiconductor especially containing 
Pp such as InP, etc., is formed, a source gas such as PH.sub.3 is not 
decomposed, but it reacts with the organic metals to form polymer 
intermediates such as (-InMePH-)n, and moreover, in that when the 
crystalline layer formation step is carried out at high temperatures, P is 
removed from the compound semiconductor. 
In order to eliminate the above-mentioned problems, a method in which a 
substrate is irradiated with laser light has been proposed in, for 
example, Japanese Laid-Open Patent Application No. 59-87814, wherein the 
substrate is irradiated with laser light having energy that is equal to or 
higher than the decomposition energy of the organic metals and/or PH.sub.3 
so as to accelerate the decomposition of the source gases, and moreover, 
the substrate is irradiated with infrared laser light such as that from a 
carbon dioxide laser so as to reduce the growth temperature of the 
crystalline layers. However, it is extremely difficult to use such a 
method for the following reasons: The decomposition energy of the source 
gases is so high, 5-6 eV, that laser light sources having a wavelength of 
200 nm or less must be used. Moreover, the most effective decomposition of 
the source gases can be achieved when the substrate is irradiated with 
laser light having energy equal to the composition energy of the source 
gases, but in order to achieve such decomposition, laser light sources 
capable of changing the wavelength of light in a wide range must be used, 
which is difficult to carry out. Moreover, the reduction of the growth 
temperature with the use of the irradiation with a carbon dioxide gas 
laser results in a rise of the surface temperature of the substrate, which 
diminishes the reduction of the said growth temperature. 
Thus, the conventional use of irradiation with laser light has not yet 
resolved the above-mentioned problems. 
On the other hand, the irradiation of a substrate with laser light is 
carried out so as to achieve the selective growth of semiconductor layers 
on the substrate based on the selective decomposition of source gases 
within the surface of the substrate and so as to achieve the selective 
etching of the substrate by the introduction of etching gases into the 
substrate. However, these processes require large equipment for the 
deflection of laser light, which causes difficulties in a practical use. 
For the said selective growth and the said selective etching, the use of 
elelctron beams instead of laser light has been proposed by, for example, 
S. Matsui et a., Jour. Vac. Sci & Technol. B vol. 4, Jan.-Feb., (1986). 
The apparatus used therefor is shown in FIG. 3, wherein a semiconductor 
substrate 3 disposed within a reaction tube 2 is directly irradiated with 
electron beams 5 from an electron gun 1, and source gases are introduced 
into the reaction tube 2 through the gas inlet 4. However, in order to 
directly irradiate the substrate 3 with the electron beams 5, the electron 
beams 5 must be accelerated at a level of several tens of electronvolts or 
more, so that energy of the electron beams must be several tens of 
electronvolts or more that is much higher than the decomposition energy of 
the source gases, which makes the selective decomposition of the source 
gases difficult, causing difficulties in composition control of grown 
layers. In addition, the direct irradiation of the substrate with the 
electron beams having high energy as mentioned above gives a high impact 
to the crystalline layers to be grown on the substrate, so it is sometimes 
difficult to obtain high-quality crystalline layers. As mentioned above, 
the direct irradiation of semiconductor substrates with high-energy 
electron beams involves many disadvantages and deficiencies. 
SUMMARY OF THE INVENTION 
The method for the production of semiconductor devices of this invention, 
which overcomes the above-discussed and numerous other disadvantages and 
deficiences of the prior art, comprises introducing source gases, etching 
gases or source molecules into a substrate to grow crystalline layers on 
said substrate or to etch said substrate, resulting in a semiconductor 
device, wherein said method further comprises applying a given electric 
potential to said substrate; applying an electric potential that is 
different from that of said substrate to an intermediate body disposed 
directly above said substrate; and irradiating said body with electron 
beams from an electron-beam emitting means, whereby said substrate is 
irradiated with the secondary electron beams generated from said body 
and/or with the electron beams transmitted through said body. 
In a preferred embodiment, the body is a grounded fine mesh grid. 
In a preferred embodiment, the body is a thin plate covered with a film 
having a high secondary electron-radiation efficiency. 
Thus, the invention described herein makes possible the objects of (1) 
providing a method for the production of semiconductor devices made of, 
e.g., III-V group compounds in which the formation of highquality 
crystalline layers, the selective growth of crystalline layers within the 
surface of a substrate, and/or the selective etching of the substrate 
within the surface of the substrate can be effectively attained; and (2) 
providing a method for the production of semiconductor devices in which 
activation energy is introduced into the substrate by the electron-beam 
irradiation, causing a decrease in the heat-temperature of the substrate 
and allowing for the selective decomposition of the source gases, which 
result in high-quality crystalline layers or in a selectively etched 
substrate, and therefore by the use of the highquality crystalline layers 
and/or the selectively etched substrate, semiconductor devices having 
excellent device-characteristics can be obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention provides a method for the production of semiconductor device 
in which a semiconductor substrate is irradiated with electron beams with 
low energy when source gases, etching gases and/or source molecules are 
introduced into the substrate so as to grow semiconductor layers and/or 
etch the substrate. According to this invention, source gases, source 
molecules, etc., undergo a chemical reaction by means of electron-beam 
energy, so that the reduction of the heat-temperature of the substrate, 
the prevention of the formation of intermediates, the selective growth of 
semiconductor layers within the surface of the substrate, the selective 
etching of the substrate, etc., can be carried out under control. 
EXAMPLE 1 
FIG. 1 shows the structure of an apparatus for the production of 
semiconductor devices, which is used to carry out this invention. The 
apparatus is constructed such that a semiconductor substrate 3 is placed 
in the center of a reaction tube 2 provided with an electron gun 1 on the 
top thereof and with a gas inlet 4 on one side thereof. The substrate 3, 
which is positioned just below the electron gun 1, is irradiated with 
electron beams 5 from the electron gun 1. The inside of the reaction tube 
2 is divided by a pin hole 7 into two parts, one of which contains the 
said electron gun 1 therein and is evacuated by a differential vacuum pump 
6 and the other of which contains the said substrate 3 therein. The upper 
division containing the electron gun 1 is maintained at a high vacuum 
level due to the pin hole 7 defining the boundary between the upper and 
the lower divisions. An intermediate body 8 such as a grid or metal net 
having a fine mesh is disposed on the path through which the electron 
beams 5 from the electron gun 1 irradiates the substrate 3. An electric 
potential Vsub is applied to the semiconductor substrate 3 by a DC power 
source 9. Given that the application of electric potential to the filament 
of the electron gun 1 is Veg, the value of Vsub can be determined by the 
following equation: 
EQU Vsub=Veg-A 
wherein A is the electric potential (in general, a value ranging from 0 to 
5 V), causing electron-beam energy to irradiate the substrate 3. 
When the substrate 3 is irradiated with the electron beams 5 from the 
electron gun 1, the value of Veg must be set to be several tens of 
electronvolts or more, otherwise, a sufficient amount of electron beam 
cannot be obtained. For this reason, in a conventional method, the 
substrate 3 is irradiated with the electron beams 5 having an energy of 
Veg electronvolts that is sufficiently greater than the energy of A 
electronvolts, which caues difficulties in the selective decomposition, 
etc., of the reaction gases. On the contrary, in this example, the 
electric potential Vsub is applied to the substrate 3, so that energy of 
the electron beams 5 to irradiate the substrate 3 becomes the value of an 
electric potential difference, Veg-Vsub (i.e., A electronvolts), between 
the electric potential of the filament of the electron gun 1, Veg, and the 
electric potential of the substrate 3, Vsub. The value of Vsub can be 
changed as desired, so that the electron beams 5 having the desired energy 
can be easily applied to the substrate 3. Moreover, since the intermediate 
body 8, which is grounded, is disposed directly above the substrate 3, in 
the same manner as in a conventional method in which the substrate 3 is 
grounded, the electron beams 5 emitted from the electron gun 1 can be 
readily focused and/or deflected without any effect from the electric 
potential of the substrate 3. 
While the substrate 3, to which the electric potential Vsub has been 
applied, is irradiated with the electron beams 5 from the electron gun 1 
through the intermediate body 8, source gases, etching gases or source 
molecules are introduced into the reaction tube 2 through the gas inlet 4 
so as to grow crystalline layers on the substrate 3 or so as to etch the 
substrate 3. By the use of the resulting substrates having the crystalline 
layers thereon or having the etched portions therein, a semiconductor 
device with uniform device-characteristics can be obtained. 
EXAMPLE 2 
FIG. 2 shows another apparatus for the production of semiconductor devices, 
which is used to carry out this invention. The portions indicated by the 
same reference numerals as those in FIG. 1 are designed with the same 
structures as those in FIG. 1. The intermeidate body 80 is a thin plate 
covered with a vapor-deposition film made of materials having the 
secondary electron-radiation efficiency at a high level, e.g., GaAs 
vapor-deposition film. The electron beams 5 emitted from the electron gun 
1 are incident upon the electron beam-irradiator 80, first, through which 
some of the incident electron beams 5 are transmitted in the direction of 
the substrate 3. Thus, the electron beams transmitted through the body 80 
(i.e., elastic scattering electron beams) then irradiate the substrate 3. 
At the same time, a large amount of secondary electron beam is generated 
from the body 80 and irradiates the substrate 3. Although the elastic 
scattering electron beams have the same energy as the incident beams, the 
amount of electron beams is sufficiently smaller than that of the 
unelastic scattering electron beams within the body 80. On the other hand, 
the amount of secondary electron beams is, in general, several ten times 
that of the incident electron beams, whereas the energy of secondary 
electron beams is small, several electronvolts. The electric potential Vta 
has been applied to the intermeidate body 80 by the DC power source 10. 
The value of Vta is the difference between the energy of the incident 
electron beams to irradiate the substrate 3 and the energy of the 
secondary electron beams to be generated from the body 80. The value of 
Vta can be readily changed as desired, in the same way as that mentioned 
in Example 1, so that electron beams having the desired energy can be 
easily irradiated to the substrate 3. Moreover, since the value of Vta is 
small, generally in the range of 0 to 10 V, there is very little influence 
on the incident electron beams. 
It is understood that various other modificiations will be apparent to and 
can be readily made by those skilled in the art without departing from the 
scope and spirit of this invention. Accordingly, it is not intended that 
the scope of the claims appended hereto be limited to the description as 
set forth herein, but rather that the claims be construed as encompassing 
all the features of patentable novelty that reside in the present 
invention, including all features that would be treated as equivalents 
thereof by those skilled in the art to which this invention pertains.