GB2162206A

GB2162206A - Process for forming monocrystalline thin film of element semiconductor

Info

Publication number: GB2162206A
Application number: GB08518833A
Authority: GB
Inventors: Junichi Nishizawa; Hitoshi Abe; Soubei Suzuki
Original assignee: Research Development Corp of Japan
Current assignee: Japan Science and Technology Agency
Priority date: 1984-07-26
Filing date: 1985-07-25
Publication date: 1986-01-29
Also published as: GB2162206B; GB8518833D0; FR2578681A1; DE3526825C2; DE3526825A1; JPH0766909B2; JPS6134928A; FR2578681B1

Abstract

In a first cycle, gaseous molecules containing those of a component element of an element semiconductor (Ge, Si) which should grow on a substrate disposed in a growth vessel are externally introduced under the conditions in which the internal pressure of the growth vessel is maintained at 1 to 10<-6> Pascal, the temperature of the heated substrate is maintained at 300 to 1,100 DEG C and the duration of gas introduction ranges from 0.5 to 200 sec, and, in a second cycle, gaseous molecules (H2) chemically reactable with the former gaseous molecules are externally introduced under the same conditions. The first and second cycles are alternately repeated, whereby growth of a monocrystalline thin film of the element semiconductor is attained with precision as precise as a single molecular layer.

Description

SPECIFICATION Process for forming monocrystalline thin film of element semiconductor This invention relates to a process for forming a monocrystalline thin film of an element semiconductor, which is suitable for formation of monocrystal growth layers of the element semiconductor with precision as precise as a single molecular layer.

A chemical vapor deposition process (referred to hereinafter as a CVD process) and a molecular beam epitaxy (referred to hereinafter as an MBE process) are well known in the art as vapor phase epitaxial techniques for forming a crystalline thin film of an element semiconductor consisting of a single element such as silicon. According to the CVD process, a silicon compound, which is a source, and gas such as hydrogen gas, which is a carrier, are simultaneously introduced into a reaction chamber two cause growth of a crystal by means of thermal decomposition. However, the thermal decomposition results in a poor quality of the crystal layer formed by growth. The CVD process is also defective in that difficulty is encountered for controlling the thickness of the layer with precision as precise as a single molecular layer.

On the other hand, the MBE process is well known as a crystal growth process making use of a ultrahigh vacuum. This process, however, includes physical adsorption as its first step. Therefore, the quality of the crystal is inferior to that provided by the CVD process which makes use of a chemical reaction. Further, due to the fact that the sources themselves are disposed in a growth chamber, it is dificult to control the amount of gases produced by heating the sources, to control the rate of vaporization of the sources and to replenish the sources, resulting in difficulty of maintaining a constant growth rate for a ong period of time. Further, the evacuating device discharging, for example, the vaporized matters becomes complex in construction.Furthermore, it is difficult to precisely control the stoichiometric composition of the compound semiconductor. Consequently, the MBE process is defective in that a crystal of high quality cannot be obtained.

In the MBE process, individual component ele ments of a compound semiconductor are simul taneously deposited by vacuum evaporation. An atomic layer epitaxial process (referred to hereinaf ter as an ALE process) is an improvement over the MBE process. This ALE process is featured by alternately depositing individual component ele ments of a compound semiconductor, as disclosed in U.S. Patent No. 4,058,430 (1977) to T. Suntola et al and also in J. Vac. Sci. Technol., A2, (1984), page 418 by M. Pessa et al. Although the ALE process is suitable forthe growth of a l-VII compound, a Il-VI compound, a Ill-V compound or an oxide of such elements, an excellent crystalline property cannot be expected inasmuch as the ALE process is an exten sion of the MBE process.Rather, the ALE process is suitable for the growth of a crystal on a substrate of glass, and it is difficult with the ALE process to achieve selective epitaxial growth of a crystal which is important in the field of production of semiconductor integrated circuits and the like. An attempt has been made to attain crystal growth by the ALE process utilizing a chemical reaction instead of resorting to the ALE process utilizing the vacuum evaporation. Although the attempt has succeeded in the formation of a polycrystalline Il-VI compound such as ZnS or an amorphous compound such as Ta2O5, it has not been successful for the growth of a single crystal. As described in U.S. Patent No.

4,058,430 (1977), the ALE process is based on the principle of depositing a monomolecular layer of one of component elements of a compound on a monomolecular layer of another component element of the compound. Therefore, the ALE process is limited to the growth of a thin film of a compound and is not applicable to the growth of an element semiconductor such as Si or Ge. On the other hand, one of the inventors has reported, in a magazine entitled "Electronic Materials", Dec., 1981, page 19, as to the possibility of application of a developed version of the ALE process to the growth of a single crystal of Si. However, the paper does not teach any practical information of the factors including the growth temperature and gas introduction rate.

Thus, the CVD process and MBE process have both been defective in that they are difficult to form a high-quality crystal with precision as precise as a single molecular layer, while, the ALE process has also been defective in that a single crystal cannot be formed by growth, and, especially, growth of an element semiconductor such as Si or Ge is impossible in principle.

With a view to obviate the prior art defects pointed out above and to improve the quality of a crystal growth layer, it is a primary object of the present invention to provide a process for forming a monocrystalline thin film of an element semiconductor, which can form the thin film by growth with precision as precise as a single molecular layer.

In accordance with the present invention, there is provided a process for forming a monocrystalline thin film of an element semiconductor comprising the steps of introducing gaseous molecules containing those of a component element of the element semiconductor onto a substrate disposed in a growth vessel for a period of time of from 0.5 to 200 sec while maintaining the internal pressure of the growth vessel within the range of from 1 to 10-6 Pascal, evacuating the growth vessel, introducing gaseous molecules chemically reactable with the former gaseous molecules onto the substrate for a period of time of from 0.5 to 200 sec while maintaining the internal pressure of the growth vessel within the range of from 1 to 10-6 Pascal, evacuating the growth vessel, and repeating a sequence of the above steps while maintaining the temperature of the substrate at 300 to 1,1 00 C, whereby growth of a monocrystalline thin film of the element conductor having a desired thickness is attained with precision as precise as a single molecular layer.

By such a crystal growth process, growth of a high-quality monocrystalline thin film of the element semiconductor can be attained with precision as precise as a single molecular layer.

When, in the above process, gaseous molecules containing those of an impurity element of the element semiconductor are introduced simultaneously or alternately with the gaseous molecules containing those of the component element of the element semiconductor or the gaseous molecules chemically reactable with the gaseous molecules containing those of the component element of the element semiconductor, the impurity element can be distributed with a desired impurity concentration distribution in thethicknesswise direction of the film, or a molecular layer containing the impurity element and a molecular layer not containing the impurity element can be cyclically formed.Further, since the doping with the impurity can be made in one layer after another while taking into consideration the compensation of the distortion of the crystal lattices of the mother semiconductor due to the impurity doping, a very steep impurity concentration distribution can be provided while maintaining the good crystalline quality of the film, so that a semiconductor device capable of operating at a very high speed with a satisfactory operating characteristic can be produced.

Other objects and features of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

Brief description of the drawings Figures 1 and 2 are diagrammatic views showing the construction of crystal growth apparatus preferably used for practice of embodiments of the process according to the present invention, respectively.

Figure 3 illustrates the case of doping silicon (Si) with both of,germanium (Ge) and boron (B), wherein Figure 3A is a sequence chart of gases introduced in pulse forms, and Figure 3B is a schematic view of a growth layer doped with Ge and B.

Figure 4 is a diagrammatic view showing the construction of a crystal growth apparatus preferably used for the practice of another embodiment of the present invention.

Referring to Figure 1, a crystal growth vessel 1 is made of a metal such as stainless steel. The growth vessel 1 is coupled through a gate valve 2 to an evacuating unit 3 which evacuates the interior of the vessel 1 to a ultrahigh vacuum. Nozzles 4 and 5 extend into the growth vessel 1 for introducing a gaseous compound containing a component element of the IV group and a gaseous compound chemically reactable with the aforementioned gaseous compound, respectively. The nozzles 4 and 5 are provided with on-offvalves 6 and 7 controlling the introduced amounts of the gaseous compound 8 containing the component element of the IV group and the gaseous compound 9 chemically reactable with the gaseous compound 8, respectively.A heater 10 for heating a substrate 12 is disposed in the growth vessel land a thermocouple 11 is associated with the heater 10 for measuring the temperature of the substrate 12. The heater 10 includes a tungsten filament sealed in a quartz glass tube, and of the substrate 12 formed of an element semiconductor is mounted on the heater 10. A pressure gauge 13 for measuring the value of the internal vacuum is also disposed on the growth vessel 1.

A monocrystalline thin film of an element semiconductor is formed in a manner as described hereinunder by the crystal growth apparatus having the construction shown in Figure 1. Suppose, for example, the case of epitaxial growth of a single crystal of Si on the substrate 12 of Si. First, the growth vessel 1 is evacuated to a vacuum of about 10-7 to 10-8 Pascal (abbreviated hereinafter as Pa) by opening the gate valve 2 and operating the ultrahigh-vacuum evacuating unit 3.Then, the Si substrate 12 is heated upto 300 to 1,100"C by the heater 10, and gaseous SiH2C12 (dichlorosilane) 8 is introduced, as gas containing Si, into the growth vessel 1 by holding the valve 6 open for 0.5 to 10 sec and maintaining the internal pressure of the growth vessel 1 at 1 to 10-6 Pa, preferably 10- to 10-7 Pa.

After closing the valve 6 and exhausting the gas from within the growth vessel 1, H2 gas 9 is introduced, as gas chemically reacting with the SiH2C12 gas, into the growth vessel 1 by holding open the valve 7 for 2 to 200 sec and maintaining the internal pressure of the growth vessel 1 at 1 to 10-6 Pa, preferably 10 1 two 10-7 Pa. As a result, at least one molecular layer of Si grows on the substrate 12.

Thus, by repeating the above steps to cause successive growth of monomolecular layers, an epitaxial growth thin film of Si having a desired thickness can be formed with precision as precise as a single molecular layer. As the gas containing Si, SiCI4 gas, SiHC13 gas, SiH2C12 gas, SiH4 gas or a gas mixture of SiH4 and HCI may be used.

Figure 2 shows a crystal growth apparatus adapted for carrying out another embodiment of the present invention including the step of impurity doping.

in Figure 2, the same reference numerals are used to designate the same or equivalent parts appearing in Figure 1. The apparatus shown in Figure 2 differs from that shown in Figure 1 in that nozzles 14 and 15 for introducing gaseous compounds into the growth vessel 1 for impurity doping purpose are additionally provided, and that on-off valves 16 and 17 are provided on the nozzles 14 and 15 respectively so that the amount of a gaseous compound 18 containing a component element of the Ill group and that of a gaseous compound containing a component element of the V group, introduced into the growth vessel 1 can be regulated.

When growth of an n-type layer by the apparatus is desired, three gases, that is, SiH2C12 gas (dichlorosilane) 8, H2 gas (hydrogen) 9 and AsH3 gas (arsine) 18 as an impurity gas are cyclically introduced into the growth vessel 1. As another method, the SiH2C12 gas 8 and AsH3 gas 18 are introduced simultaneously but alternately with the H2 gas 9, or the H2 gas 9 and AsH3 gas 18 are introduced simultaneously but alternately with the SiH2C12 gas 8, for doping with the impurity. Further, the H2 gas 9 may not be introduced, and the SiH2C12 gas 8 and AsH3 gas 18 may be repeatedly alternately introduced.

As another method, a first cycle of alternately introducing the SiH2C12 gas 8 and H2 gas 9, and a second cycle of simultaneously introducing the SiH2C12 gas 8 and AsH3 gas 18 but alternately with the H2 gas 9, are alternately repeated, so as to cyclically alternately form a layer doped with As and a layer not doped with As. Further, a third cycle of simultaneously introducing the SiH2C12 gas 8 and PH3 gas (phosphine) but alternately with the H2 gas 9 may be added so as to cyclically form a layer doped with As whose atomic radius is larger than that of Si, a layer doped with P whose atomic radius is smaller than that of Si and a layer of Si only, thereby compensating crystal lattice distortion attributable to the difference of the atomic radii of the impurities from that of the mother semiconductor.

As the source of impurity doping gas, AsCI3 (arsenic trichloride), PCl3 (phosphorous trichloride) or the like can also be used.

Figure 3 illustrates the case where Si is doped cyclically at a constant ratio with Ge whose atomic radius is larger than that of Si and with B whose atomic radius is smaller than that of Si. As shown in Figure 3A, BCl3 gas and SiCI4 gas are initially simultaneously introduced, and H2 gas is then introduced. As a result, a molecular layer in which Si is doped with B is formed as shown in Figure 3B.

Subsequently, a cycle of introducing SiCI4 gas, exhausting SiCI4 gas, and introducing H2 gas according to the sequence shown in Figure 3A is repeated two times to form two molecular layers of crystalline Si, as shown in Figure 3B. Thereafter, similarly, introduction of BCl3 gas and SiCI4 gas, exhausting of these gases and introduction of H2 gas forms one molecular layer of Si doped with B; introduction of SiCI4 gas, exhausting of these gases and introduction of H2 gas are repeated two times to form two molecular layers of Si; and introduction of GaCI4 gas and SiC14 gas, exhausting of these gases and introduction of H2 gas forms one molecular layer of Si doped with Ge.

On the other hand, when formation of a p-type growth layer by the apparatus is desired, B2H6 gas (diborane) 19 shown in Figure 2 is cyclically introduced as an impurity gas, together with SiH2C12 gas 8 and H2 gas 9. As another method, the SiH2C12 gas 8 and B2H6 gas 19 are introduced simultaneously but alternately with the H2 gas 9, for doping with the impurity.

The impurity gas may be BCl3 gas, BBr3 gas, TMG gas (trimethyl gallium), TMAI gas (trimethyl aluminum),TMln gas (trimethyl indium) orthe like.

In this case, the flow rate of the introduced impurity gas is preferably selected to be less by, for exaple, 10-3 to 1 of6, than those of the SiH2C12 gas 8 and H2 gas 9, and the length of time of gas introduction is preferably selected to be about 0.5 to 10 sec so as to form a molecular epitaxial growth layer having a desired impurity concentration distri bution in the thicknesswise direction.Further, it is apparent that, by suitably regulating the amount and duration of introduction ofthe impurity gases, it is possible to provide pn junctions, non-uniform im purity concentration distributions, bipolar transistor structures such as npn, npin, pnp and pnip structures, field effect transistor structures such as n+in+ and n+n-n+ structures, electrostatic induction transistor structures, pnpn thyristor structures, etc.

The aforementioned embodiments have referred to the case where the heat source for heating the substrate 12 is disposed in the growth vessel 1.

However, as, for example, shown in Figure 4, an infrared radiation emitting lamp 30 housed in a lamp housing 31 disposed outside of the growth vessel 1 may be used as the heat source, and the infrared radiation emitted from the lamp 30 may be directed toward and onto the substrate 12through a quartz glass window 32, thereby heating the substrate 12 supported on a susceptor 33. The arrangement shown in Figure 4 is advantageous in that members unnecessary for the crystal growth can be removed from the interior of the growth vessel 1, and generation of unnecessary gas components including, for example, a heavy metal due to heating by the heater 10 can be eliminated.

Further, an optical system 40 may be mounted on the growth vessel 1, and an external light source 41 such as a mercury lamp, a heavy hydrogen lamp, a xenon lamp, an excimer laser or an argon laser may be provided to direct light having a wavelength of from 180 to 600 nm toward and onto the substrate 12. When such members are provided, the temperature of the substrate 12 can be decreased to cause growth of a single crystal having a higher quality.

In the aforementioned embodiments, an ion pump or the like well known in the art can be used as the ultrahigh-vacuum evacuating unit. Further, it is needless to mention that an auxiliary vacuum vessel and a crystal transport unit for the insertion and transport of the monocrystalline substrate can be easily added to improve the mass productivity.

The aforementioned embodiments have referred principally to the introduction of gas containing Si used for the crystal growth. However, it is apparent that gas of a semiconductor such as Ge belonging to the IV group can also be used. Also, the material of the substrate is not limited to silicon and may be sapphire, spinel, or the like.

Claims

1. A process for forming a monocrystallinethin film of an element semiconductor comprising the steps of introducing gaseous molecules containing those of a component element of the element semiconductor onto a substrate disposed in a growth vessel for a period of time of from 0.5 to 200 sec while maintaining the internal pressure of the growth vessel within the range of from 1 to 10-e Pascal, evacuating said growth vessel, introducing gaseous molecules chemically reactable with the former gaseous molecules onto said substrate for a period of time of from 0.5 to 200 sec while maintaining the internal pressure of said growth vessel within the range of from 1 to 10-B Pascal, evacuating said growth vessel, and repeating a sequence of the above steps while maintaining the temperature of said substrate at 300 to 1,1 00on, whereby growth of a monocrystalline thin film of the element conductor having a desired thickness is attained with precision as precise as a single molecular layer.

2. A process as claimed in Claim 1, wherein a radiation source is provided to direct radiation toward and onto said substrate.

3. A process as claimed in Claim 1, wherein at least two radiation sources are provided to direct radiations having different wavelengths toward and onto said substrate.

4. A process as claimed in Claim 1, wherein said element semiconductor is Si.

5. A process as claimed in Claim 1, wherein said gaseous molecules containing those of the component element of said element semiconductor are selected from a group including SiH2C12,SiHC13 and SiC4, and said gaseous molecules chemically reactable said former gaseous molecules are those of hydrogen.

6. A process as claimed in Claim 1, wherein gaseous molecules containing those of an impurity element of said element semiconductor are introduced simultaneously or alternately with said gaseous molecules containing those of the component element of said element semiconductor or said gaseous molecules chemically reactable with said gaseous molecules containing those ofthe component element of said element semiconductor, whereby growth of a monocrystalline thin film of the element semiconductor having a desired impurity concentration distribution in the thicknesswise direction is attained with precision as precise as a single molecular layer.

7. A process as claimed in Claim 1,wherein, during the repetition of the sequence of said steps, gaseous molecules containing those of an impurity element of said element semiconductor are cyclically introduced simultaneously with either gas containing the component element of said element semiconductor or said gaseous molecules chemically reactable with said gaseous molecules containing those of the component element of said element semiconductor, whereby a molecular layer doped with the impurity element and a molecular layer not doped with the impurity element are cyclically formed.

8. A process as claimed in Claim 6, wherein gaseous molecules containing those of at least two impurity elements of said element semiconductor are cyclically introduced.

9. A process as claimed in Claim 7, wherein gaseous molecules containing those of at least two impurity elements of said element semiconductor are cyclically introduced.

10. A process as claimed in Claim 8, wherein said gaseous molecules containing those of the at least two impurity elements classified by the kinds are introduced in respectively different cycles or at respectively different times, whereby the impurity elements of different kinds are cyclically doped in the different molecular layers.

11. A process as claimed in Claim 8, wherein the atomic radius of one of the at least two impurity elements is larger than that of said element semiconductor, and the atomic radius of the other of the at least two impurity elements is smaller than that of said element semiconductor.

12. A process as claimed in Claim 8, wherein one of the at least two impurity elements is an element of the IV group.

13. A process as claimed in Claim 8, wherein said impurity elements are of the same conductivity type.

14. A process as claimed in Claim 9, wherein said gaseous molecules containing those of the at least two impurity elements classified by the kinds are introduced in respectively different cycles or at respectively different times, whereby the impurity elements of different kinds are doped in the different molecular layers.

15. A process as claimed in Claim 9, wherein the atomic radius of one of the at least two impurity elements is larger than that of said element semiconductor, and the atomic radius of the other of the at least two impurity elements is smaller than that of said element semiconductor.

16. A process as claimed in Claim 9, wherein one of the at least two impurity elements is an element of the IV group.

17. A process as claimed in Claim 9, wherein said impurity elements are of the same conductivity type.

18. A process according to any of claims 1 to 17 forforming a monocrystalline thin film of an element semiconductor, substantially as hereinbefore described and exemplified and with reference to the accompanying drawings.