JPS61215287A - Method for forming thin film and apparatus therefor - Google Patents

Abstract

PURPOSE:To enable the epitaxial growth of an element at a low temperature, by irradiating the surface of a specimen substrate with light having a wavelength effective to the rearrangement of the surface layer atoms during the vacuum-evaporation of the element. CONSTITUTION:One or more kinds of elements are evaporated by the electron gun 71 and deposited on the specimen substrate 81 placed in the vacuum chamber 32 to form a thin film consisting of monoatomic layer. One or more kinds of elements different from those used in the preceding deposition process are evaporated by the electron gun 71 and deposited on the monoatomic layer to an extent to form a monoatomic layer. A semiconductor thin film can be formed on the substrate 81 by repeating the above process several times. In the course of the above operation, the surface of the substrate 81 is irradiated with light (e.g. laser beam) effective to the rearrangement of the surface layer atoms through the window 22 from the light source 61 placed outside of the vacuum chamber 32.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for forming a semiconductor thin film on an insulator or semiconductor substrate.

[Prior art and its problems]

In recent years, there has been an increasing demand for the development of ultra-high-speed devices and low-threshold, highly reliable semiconductor lasers, and MBC (Molecular Boundary Synthesis), which can grow semiconductor crystal thin films with thickness precision in the λ unit, has become a fundamental technology for manufacturing these devices. The line epitaxial growth) method and the ALE (atomic layer epitaxial growth) method are attracting attention. In addition, superlattices, which have a multilayer structure of semiconductor crystal thin films with different compositions with periods ranging from a few to several tens of layers, are expected to enable devices based on unprecedented new operating principles. In this research, the above-mentioned growth method has also been actively introduced.

Taking the epitaxial growth of II-VI group compound semiconductors as an example, comparing both the MBE method and the ALE method, the MB
While the E method grows continuously in the thickness direction, in the ALE method, group (1) and group (2) atoms grow discontinuously by alternating one atomic layer at each growth cycle. From this, it is thought that the ALE method is more advantageous in terms of precisely controlling the growth of compound semiconductor crystals on a compound molecular layer basis, and research on this method has recently become very active.

The ALE method can be divided into two types in principle. One method uses chemical reactions and is applied to the growth of binary compound semiconductors. For example, in the case of ZnS growth, ZnCj! Gas is introduced, and only one layer of ZnCf gas is adsorbed onto the substrate surface heated to an appropriate temperature by controlling the gas pressure and adsorption time, and the remaining ZnCf gas is exhausted, and then H2
When S gas is introduced, a chemical reaction occurs and one molecular layer of ZnS is formed. The remaining H2S gas is immediately exhausted. At this time, since the surface layer becomes S atoms, if the gas pressure is appropriately selected, the excess gas pressure will not contribute to the chemical reaction, so the adsorption efficiency will be small, and if the gas pressure is appropriately selected, no adsorption will occur.

Therefore, by repeating the process after introducing ZnCjl gas, ZnS can be grown layer by layer in the same way.

Furthermore, in the ALE method that utilizes such a chemical reaction, attempts have been made to lower the epitaxial growth temperature by irradiating the substrate surface with light for the purpose of reducing defects in the crystal.

Another ALE method is a method in which when molecular beams from a deposition gun are deposited on a substrate surface using an apparatus similar to the MBE method, the timing of the molecular beams is shifted for each element. This method has been tried in the past for the growth of binary and ternary compound semiconductors. Taking CdTa as an example,
Growth is performed in a vacuum chamber by repeating a cycle in which a Cd molecular beam is first deposited on the substrate, and then a Cd molecular beam is deposited to stop the Cd deposition. At this time, the amount of Cd and To that reaches the substrate is about twice the amount required to form one atomic layer, respectively.
This method takes advantage of the fact that if one atomic layer of atoms of one element is formed on a layer of different atoms, the adsorption efficiency of the excess atoms becomes low and they are not deposited.

For this reason, this method is also called atomic layer deposition.

Of the two ALE methods described above, the latter method, which does not require introducing a reactive gas into the ultra-high vacuum system, is considered to have a simpler device configuration and higher reliability.

However, even in the latter ALE method, the temperature of the vapor deposition gun is kept high at all times in order to generate atomic or molecular beams of each element, and the vapor deposition of the elements is performed using a mechanical shutter installed in front of each deposition gun. In terms of control by frequent opening and closing, sufficient reliability has not yet been achieved.

In addition, even in the method of light irradiation using the ALE method that utilizes the chemical reaction mentioned above, the energy of light is mainly used for photochemical decomposition of the supplied compound molecules, and the atoms on the substrate surface after decomposition are It has not been effectively used to selectively induce the effect of light irradiation on.

Regarding the ALE method described above, an example of using the former chemical reaction and further irradiating light to grow caAs was presented at the 16th Solid State Elements Conference (16th 1984 International Conference) by Nishizawa and Kokubu.
onference on 5olid 5tate
Devices and Materials), and a summary was published on pages 1 to 4 of the Technical Digest.

Examples of ALE growth of CdTo using the same equipment as in the case of the MBE method include Pessa, Huttrnen and Herman.
Journal of Applied Phys.
sics) magazine, 1983, Volume 54, No. 10, 604
It is described in a paper published on pages 7 to 6,050.

[Purpose of the invention]

The purpose of the present invention is to utilize the features of the conventional ALE method by performing light irradiation during vapor deposition in an ultra-high vacuum, and also to provide a method for forming a thin film with the feature that epitaxial growth is possible at low temperatures. Another object of the present invention is to provide a thin film forming apparatus for carrying out this method.

[Structure of the invention]

The present invention provides a sample substrate installed in a vacuum chamber with a
Multiple processes are performed in which more than one type of element is evaporated to form a thin film for one atomic layer, and then one or more elements different from the one deposited immediately before are evaporated to form a thin film for one atomic layer again. The atomic layer deposition method is characterized in that the surface of the sample substrate is irradiated with light of a wavelength effective for rearranging the atoms in the surface layer during the vapor deposition of the elements.

Another aspect of the present invention provides a vacuum chamber, a vacuum evacuation system for creating a high vacuum in the vacuum chamber, a mechanism for holding a sample substrate in the vacuum chamber, and a plurality of evaporation materials on the sample substrate. The thin film forming apparatus is characterized by comprising a light source for irradiating the surface of the sample substrate with light of a wavelength effective for rearranging surface layer atoms.

[Effect]

By using the present invention, good epitaxy can be achieved at a temperature lower than the normal epitaxy temperature by irradiating the sample substrate surface with light of an appropriate wavelength during the thin film growth process using the ALE method that uses molecular beam evaporation. It can be realized. In conventional methods that utilize photochemical reactions of supplied compound molecules, the energy of light is mainly consumed in the photochemical reactions. On the other hand, in the light irradiation in the present invention,
Since light energy is not consumed for the photochemical reaction of the supplied compound molecules, it is possible to effectively apply photons directly to the semiconductor itself to activate the movement of atoms on the surface. That is, by optical excitation, surface atoms can be arranged to form a clean crystal lattice at a temperature lower than the normal epitaxial growth temperature. A
In the LE method, the process of arranging atoms adsorbed on the surface of a crystal, which already has neatly arranged atoms, into chemically stable lattice positions is repeated. Therefore, in the ALE method, it is only necessary to affect the arrangement of atoms on the surface, so compared to the vapor phase epitaxial growth method or the normal MBE method, etc., in which epitaxial growth proceeds simultaneously over several atomic layers, it is particularly noticeable. The effect of light irradiation can be expected. If the epitaxial growth temperature is lowered by light irradiation, interdiffusion of atoms at the hetero interface can be prevented, which is extremely effective for creating superlattices and the like.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing an example of an apparatus used in the thin film forming method of the present invention, in order to explain an example of the thin film forming method of the present invention. In this example, in order to control vapor deposition in an ultra-high vacuum, a method of generating vapor by irradiating the vapor deposition material with laser light was used instead of using a mechanical shutter in order to improve reliability.

The laser beam emitted from the laser oscillator 11 is reflected by a movable mirror 14 connected to a servo motor 13 and passes through the first window 21 of the vacuum chamber 31 to the first vapor deposition material 51.
is irradiated. The inside of the vacuum chamber 31 is maintained in an ultra-high vacuum state with a pressure of 10" Torr or less by a roughing pump 41 and a main exhaust pump 42. Also, the inner wall of the vacuum chamber 31 is cooled by liquid nitrogen 32, and the adsorbed molecules are In this state, molecular beams of the first vapor deposition material 51, which is locally heated by the laser beam irradiation, are generated and vapor deposited onto the sample substrate 81.The sample substrate 81 is attached to a mount 33 with a heater, and a low-speed motor 34 is operated during deposition to ensure uniform deposition over the entire surface.
It can be rotated by Further, during a series of vapor deposition processes, the sample substrate 81 is heated to an appropriate temperature by passing current through the heater mount 33, and the second window 2
Light from a substrate irradiation light source 61 is irradiated through the substrate 2 . After the amount of vapor required to deposit one atomic layer has been generated, the laser beam irradiation is stopped to immediately stop the vapor generation and therefore the vapor deposition.

Next, the servo motor 13 is rotated by the servo motor controller 12, and an optical path is set so that the second vapor deposition material 52 is irradiated with the laser light reflected by the movable mirror 14. By irradiating the laser beam again in this state, a molecular beam of the second vapor deposition material 52 is generated, and a molecular beam of the second vapor deposition material 52 is generated on the atomic layer formed by vapor deposition from the first vapor deposition material 51 on the sample substrate 81. Two layers of vapor deposited material 52 are formed. When the second evaporation material 52 is deposited for one atomic layer,
Stop the laser beam irradiation. Thereafter, the film is grown to a desired thickness by repeating the deposition of the first vapor deposition material 51 and the second vapor deposition material 52 alternately one atomic layer at a time in the same manner as before. Further, here, it is also possible to deposit a third vapor deposition material 53 instead of the first vapor deposition material 51.

The vacuum chamber 31 was equipped with a mass spectrometer 73 for monitoring the molecular beam intensity, and an electron gun 71 and screen 72 for reflection high-speed electron diffraction (RHEHD) for evaluating the crystallinity of the grown film.

In this example, G a As / A I!
In order to form a superlattice of As, the sample substrate 81 is a GaAs crystal with a diameter of 1 inch and a thickness of 500 μm. AA was used as the vapor deposition material 53.

Further, the distance between these vapor deposition materials and the sample substrate 81 is approximately 3
It was set to 0 cm. The laser oscillator 11 has an oscillation wavelength of 3.
Using a 0.8 nm XeCn excimer laser, the energy per laser pulse is 1 mJ and the pulse width is 10 nS.
During vapor deposition, the operation was performed at IKHz. The irradiation intensity of the laser beam on the vapor deposition material was set to about 5 MW/cm2.

In addition, a Xe arc lamp is selected as the substrate irradiation light source 61,
A filter was used to irradiate only light with a wavelength of about 0.7 μm or less. In this kind of light irradiation, in addition to the effect that the ultraviolet light directly excites surface atoms, the irradiated light in all wavelength ranges is absorbed by the GaAs substrate and the thin film grown on it, and excited electrons are generated. The energy is transferred to the surface atoms, resulting in efficient surface migration.

The light of the Xe arc lamp is approximately 109 mW on the sample substrate 81.
The intensity was set to be /cm2. At this light intensity, the temperature rise on the substrate surface is 10° C. or less.

With the above configuration, A of G a A s / A I A s
In order to perform the LE method, the irradiation time of the laser beam is determined by monitoring the amount of molecular beam generated by the mass spectrometer 73.

and A1 for 5 seconds, 3 seconds, and 10 seconds, respectively.
I found that it is sufficient to set it to about seconds. Of course, ALE
In this method, there is no need to strictly control the amount of molecular beam generated based on the principle described above, so there is no need to strictly determine the laser beam irradiation time here.

In this example, the temperature of the GaAs substrate 81 is set to 380° C., and after first repeating the alternate deposition of Ga and AS 200 times on the (100) plane of the substrate, the alternate deposition of AA and As is repeated 200 times.
The process consisted of eight steps, two times and two alternating depositions of Ga and As, was repeated 100 times. RHII during film growth! II! It was confirmed by monitoring using D that the grown film had good crystallinity. moreover,
When the sample after growth was evaluated by Raman scattering, it was found that the scattered light had a sharp peak at a position with a frequency shift of 200 cm' from the input light, and from the correspondence with the theoretical model, it was found that GaAs and AlAs were designed. It was found that two molecular layers were formed.

In addition, when similar growth was attempted at the same substrate temperature without irradiation with Xe arc lamp light, RHEED,
Evaluation by Raman scattering revealed that good crystal growth did not occur. In the absence of Xe arc lamp light irradiation, it was found that a film with good crystallinity grows when the temperature of the GaAs substrate is between 470°C and 500°C, but Raman scattering measurements show that the frequency width of the scattered light is very large. wide<GaA
It was observed that the layer structure of S and AffiAs was disordered.

In the above embodiments, GaAs and Aj! Although a superlattice with two layers of As was fabricated, the number of layers of GaAs and AIA.S can of course be arbitrarily selected.

Furthermore, in order to perform impurity doping during growth, only the dopant may be separately prepared as a vapor deposition material, and the other vapor deposition materials may be simultaneously irradiated with laser light at an appropriate intensity during vapor deposition.

In addition, in the above example, a superlattice of GaAS and AlAs was fabricated, but instead of independently making one atomic layer of Ga or AA, which is a group II group, the laser beam irradiation was appropriately switched to create a superlattice of Ga and AlAs. It is also possible to grow only one atomic layer by mixing Al. The present invention can be applied not only to the combination of Ga, Al and As, but also to the case where In is used as the group ① and P is used as the group V. Furthermore, it is also possible to grow not only semiconductors of the ■-■ group but also semiconductors of the ■-■ group such as pbTe and 5nTe, and II-Vl group semiconductors such as CdTe and HgTe.

In the above embodiment, a Xe arc lamp was used as a light source for irradiating the substrate during growth, but this can of course be replaced with other arc lamps or glow discharge lamps. Furthermore, instead of these lamps, a laser light source having a wavelength effective for lowering the temperature of epitaxy may be used.

Further, in the above embodiment, a pulsed laser beam was used to generate the molecular beam, but this method has the advantage that the amount of generated molecular beam can be easily controlled by the energy and number of laser pulses. However, for molecular beam generation, it is of course possible to use a Knudsen cell, an electron beam scatterer, etc. used in the ordinary MBE method.

〔Effect of the invention〕

As described above, according to the present invention, during ALE growth using molecular beam evaporation in an ultra-high vacuum, by irradiating the surface of a sample substrate with light, epitaxial growth can be achieved at a lower temperature than in conventional epitaxial growth methods. It becomes possible to do this.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a thin film forming apparatus used in an embodiment of the i-film forming method of the present invention. 11... Laser oscillator 12... Servo motor controller 13... Servo motor 14... Movable mirror 21... First window 22... Second window 31... ... Vacuum chamber 32 ... Liquid nitrogen 33 ... Mount with heater 34 ... Low speed motor 41 ... Roughing pump 42 ... Main exhaust pump 51 ... First Vapor deposition material 52...Second vapor deposition material 53...Third vapor deposition material 61...Substrate irradiation light source 71...Electron gun 72...Screen 73...Mass spectrometry Total 81...sample substrates

Claims (2)

[Claims] (1) One or more elements are deposited on a sample substrate placed in a vacuum chamber to form a thin film of one atomic layer,
In the atomic layer deposition method, in which the process of depositing one or more elements different from those deposited immediately before and forming a thin film again by one atomic layer is repeated multiple times, the surface of the sample substrate is A thin film forming method characterized by irradiating light with a wavelength effective for rearranging atoms in the surface layer. (2) A vacuum chamber, a vacuum evacuation system for creating a high vacuum in the vacuum chamber, a mechanism for holding a sample substrate in the vacuum chamber, and means for vapor depositing a plurality of vapor deposition materials onto the sample substrate. A thin film forming apparatus comprising: a light source for irradiating the surface of the sample substrate with light having a wavelength effective for rearranging atoms in the surface layer.