JPH02232926A - Formation of oxide thin film - Google Patents

Abstract

PURPOSE:To form a single crystal thin film in high quality by a method wherein, after covering a semiconductor substrate surface with an oxide crystal film, the temperature of substrate in a vacuum vessel is raised to high degree to impress the substrate surface with high pressure for reducing the oxygen void in a deposited film. CONSTITUTION:An oxide single crystal film is deposited while sustaining the oxygen pressure by leading oxygen from an acid degree leading-in nozzle 7 in a vacuum vessel 1. At this time, the oxidation of an Si substrate 6 surface and the etching reaction are balanced with each other on the optimum Si substrate 6 surface state while sustaining the flatness of the surface. After the substrate 6 is covered with the oxide single crystal, the temperature of the substrate 6 in the vessel 1 is raised to high degrees for accelerating the growth of the deposited film. Through these procedures, the substrate 6 surface is impressed with high pressure to reduce the oxygen void caused in the oxygen contained in the deposited film as well as to make the molecules evaporated on the substrate 6 migrate for accelerating the quadratic layer deposition so that a single crystal thin film in high quality may be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming an oxide single crystal thin film on a semiconductor substrate, and in particular, a method for forming an oxide single crystal thin film on a semiconductor substrate, and in particular a method for forming an oxide single crystal thin film on a semiconductor substrate while applying an optimum oxygen pressure depending on the growth stage of the thin film. This paper relates to a method for forming oxide thin films suitable for forming single-crystal thin films of insulators such as alkaline earth metal oxides, spinel, and sapphire, and oxide high-temperature superconductors on semiconductor substrates. [Prior Art] Conventionally, a metal compound has been deposited on a semiconductor substrate in a vacuum chamber without controlling the oxygen partial pressure (D. Hoffn+ana).
ndD. Leibowitz: J. Vac. Sci.
Techno1.8 (1971) 107. ), sputtering (Y,Emonoto.T.l'lur
Akami, M. Suzuki. and K, Mo
riwaki: Jpn. J. Appl. Phys. 26
(1987) L1248. R. S. Nowicki:
J. Vac. Sci. Technol. 14 (197
7) 127) A method was proposed. [Problem to be solved by the invention] However, the conventional oxide thin film forming method
When forming high-quality single crystal thin films of metal compounds and non-metal oxides, which are dissimilar substances, on semiconductor substrates such as
It had the following shortcomings.

(1) When the surface of a semiconductor substrate is exposed to an oxygen atmosphere, oxidation reactions and ethoching reactions progress on the substrate surface, causing oxidation and roughening of the substrate surface, making it impossible to form a high-quality film thereon.

(2) In the initial growth process of metal oxides and non-metal oxides, the metal and non-metal elements constituting the oxides are Si.
and reacts with oxygen to produce compounds such as silicides and silicates, which inhibit the growth of desired metal and nonmetal oxides.

(3) High quality epitaxy. During growth at the high temperature necessary to obtain a barrel-grown film, oxygen with a high vapor pressure escapes from the oxide-grown film, making it impossible to obtain an oxide thin film that satisfies the stoichiometric composition.

Due to these drawbacks, it is considered difficult to obtain a high quality epitaxial film of crystalline oxide, for example, on a Si-based slope. Furthermore, even if a single crystal thin film is formed, high-density interface states may occur between the Si substrate and the thin film, or levels that capture carriers in the semiconductor may occur in the oxide. However, it has not been possible to apply the stacked structure of an St substrate and an oxide single crystal thin film to the formation technology of ultra-thin Sol devices, stacked LSIs, high-temperature superconducting wiring, high-temperature superconducting transistors, etc.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned drawbacks.
a first step of growing an oxide single crystal film by setting the oxygen pressure in the ultra-high vacuum chamber to a pressure value that balances the oxidation reaction and corrosion reaction occurring on the upper surface of the semiconductor substrate heated to a predetermined temperature; After the semiconductor substrate surface is covered with the oxide single crystal film in step 1, the oxygen pressure in the ultra-high vacuum layer is controlled to suppress the generation of oxygen vacancies in the oxide single crystal film, and the molecules deposited on the semiconductor substrate are a second step in which the semiconductor substrate is heated to a higher temperature than the heating temperature in the first step to grow an oxide single crystal film. are doing.

[For production]

The present invention has the following effects.

(1) An oxide single crystal film is grown by setting the oxygen pressure in the ultra-high vacuum chamber to a pressure value that balances the oxidation reaction and corrosion reaction occurring on the upper surface of the semiconductor substrate heated to a predetermined temperature.

(2) The oxygen pressure in the ultra-high vacuum layer is set to a pressure value that suppresses the generation of oxygen vacancies in the oxidized single crystal film and allows molecules deposited on the semiconductor substrate to migrate and undergo two-dimensional layered growth. At the same time, the semiconductor substrate is heated to a temperature higher than the above heating temperature to grow an oxide single crystal film.

〔Example〕

Next, embodiments of the present invention will be explained according to the drawings. FIG. 2 is a block diagram of an ultra-vacuum deposition apparatus used to carry out the method of forming an oxide thin film according to the present invention. In the figure, reference numeral 1 denotes an ultra-high vacuum chamber as a deposition chamber forming the main body of the apparatus, 2 and 3 an electron beam impact heating device as a deposition source for evaporating an oxide source, and 4 an electron beam impact device 2.3. This is a shutter that is linked to the control system 16.

This shutter 4 opens only for a certain period of time after the heating of the source begins and the vapor deposition substance begins to evaporate to a predetermined vapor pressure, and the shutter 4 opens only for a certain period of time after the heating of the source begins and the vapor deposition material begins to evaporate to a predetermined vapor pressure, and the shutter 4 opens only for a certain period of time after the heating of the source starts and the vapor deposition substance starts to evaporate and reaches a predetermined vapor pressure. enable. Reference numeral 7 denotes an oxygen gas introduction nozzle through which a certain amount of oxygen is introduced into the ultra-high vacuum chamber 1 in order to control the oxygen pressure within the ultra-high vacuum chamber 1 to an optimum value. 8 is a downward exhaust system for making the ultra-high vacuum chamber 1 ultra-high vacuum before starting vapor deposition, and 9.10 is an upper exhaust system for exhausting gas molecules flying from the evaporation source below.

11 to 13 are gate valves. Reference numeral 14 denotes an electron gun of a high-energy electron beam diffraction apparatus for in-situ observation of the structure and flatness of the substrate surface, and the diffraction pattern is observed using a fluorescent plate 15. This in-situ observation captures the growth process occurring on the Si substrate surface and controls the oxygen partial pressure to an optimal level. - The electron beam shock thermal device 2.3, the shutter 4, and the control system 16 constitute a means to alternately repeat the continuous evaporation process and exhaust process, and automatically repeat the continuous evaporation process and exhaust process until the grown film reaches the desired thickness. Continues intermittent growth. , where intermittent growth means alkaline earth metal oxide ′Jj! lJ(MgO.Cab
, SrO, BaO) on a Si substrate (see Japanese Patent Application No. 75578/1983).

Now, using this device, Sr and Ba are deposited onto the Si substrate 6.
, 40 The pretreatment for forming the single crystal thin film is performed as follows.

In FIG. 2, electron beam impact heating devices 2 and 3 in an ultra-high vacuum chamber 1 are filled with an Sr source and a BaO source, respectively. Next, the Si substrate 6 is fixed to the holder 5 after being cleaned and finally having a thin oxide film of 1 to 3 nm formed on the surface by a chemical reaction using acid. This thin oxide film is used as a protective film to prevent the surface of the Si substrate from being contaminated with carbon between cleaning and fixing in an ultra-high vacuum chamber.

Next, FIG. 1 is an explanatory diagram showing the procedure of the oxide thin film forming method according to the present invention. Here, an example of the growth procedure, substrate temperature, and optimal oxygen pressure in the ultra-high vacuum chamber 1 after the ultra-high vacuum reaches ultra-high vacuum is shown. Hereinafter, the processes (1) to (3) will be explained in order.

? First, in process (1), from time point A, the St substrate 6 is
The thin oxide film (S i O 2 ) formed in the pretreatment is removed by heating to 50 to 900° C. This process (1)
In this case, no oxygen is introduced.

Here, degassing by heating and SiO2. evaporates, the pressure inside the vacuum chamber increases. When SiQ2 is removed, a clean surface appears and the electron beam diffraction pattern on the fluorescent plate changes to a pattern caused by the surface structure unique to Si. For example, for a Si substrate with a (1 1 1) plane orientation, 7x7. In the (100) plane orientation, a pattern resulting from a 2×1 surface superlattice structure appears.

Next, process (2) in FIG.
Supplying aO molecules from a source and attaching them to the Si substrate 6,
This corresponds to the process until the entire surface of the Si substrate 6 is covered with these oxides. Here, since the molecules mentioned above do not adhere at high temperatures (850°C or higher), they are allowed to adhere at, for example, 780°C.

In this process (2), the heated surface of the Si substrate 6 is exposed to oxygen generated from the source. If the amount of oxygen that enters the substrate over a certain period of time is not controlled, the surface of the St substrate will be oxidized or corroded and become rough. Here, how to determine the optimum oxygen pressure in process (2) will be explained using FIGS. 3 and 4.

In Figure 3, the horizontal axis is the Si substrate temperature and the vertical axis is the oxygen pressure.
FIG. 3 is a characteristic diagram showing a region where oxidation occurs and a region where etoching occurs. This was determined experimentally by observing changes in the electron beam diffraction pattern. Further, the oxidized region is a region where a chemical reaction expressed as 0■+Si→S i O t occurs, while the etched region is a region where a chemical reaction expressed as 0■+2Si→SiO↑ is carried out.

Note that the symbol m indicates the boundary region between the oxidized region and the etched region.

Here, for example, when the temperature of the Si substrate 6 is 780°C, 3
It can be seen that an oxygen pressure of ˜5×10 −′ Torr is the pressure at which the oxidation and etching reactions are in equilibrium. If oxygen is introduced from the outside and the oxygen pressure is not controlled, the oxygen partial pressure during growth will be 5 x 10-'Torr, so a violent ethoching reaction will proceed on the Si substrate surface and the substrate surface will become rough. result. Therefore, compounds such as silicide and silicate that inhibit the growth of the desired oxide thin film 2 are likely to be formed on the substrate surface, and the crystallinity of the oxide film itself that grows in the upper layer is deteriorated.

On the other hand, at 780℃, 3 to 5 x 10-6 Tor
When the oxygen pressure exceeds r, the surface of the Si substrate is oxidized and it becomes impossible to grow a single crystal oxide thereon. In this case, the partial pressure of oxygen generated from the oxide source must be controlled.

In the case of this embodiment, the problem is to suppress the etching reaction. Therefore, before starting oxide growth, the oxygen pressure in the ultra-high vacuum chamber 1 is set to 3 to 5X 10-6To
If the oxygen pressure is controlled within the r r oxygen pressure range, surface roughening of the Si substrate during growth can be prevented.

Based on these results, FIG. 4 shows the results of actual growth by controlling the oxygen partial pressure.

FIG. 4 is a characteristic diagram in which the crystallinity of the film was evaluated using the backward diffusion channeling method, with the Si substrate temperature set at 780° C. and various oxygen pressures applied during the initial stage of oxide growth.

As is clear from this figure, 3 to 5 × lO-'T
It can be seen that a single crystal thin film of an oxide with the best crystallinity can be obtained by applying an oxygen partial pressure of o r r. This pressure corresponds to a value at which the oxidation and etching reactions described in FIG. 3 are in equilibrium.

In this way, once the temperature of the Si substrate 6 is determined, the oxygen pressure at which the oxidation reaction and the etching reaction, which are determined by the temperature, are in equilibrium can be obtained from the results shown in FIG. Therefore, in the process (2) shown in FIG. 1, by introducing oxygen into the vacuum chamber from the acidity introducing nozzle 7 shown in FIG. 1, growth can proceed while maintaining this oxygen pressure. This makes it possible to balance the oxidation and etching reactions on the St substrate surface, and to grow an oxide on the optimal Si substrate surface condition while maintaining surface flatness.

Next, process (3) in FIG. 1 will be explained.

By observing the electron diffraction pattern, Sr
The pattern of the XBal-xO single crystal film becomes stronger, whereas the pattern of the St substrate 6 becomes weaker and finally disappears. At this stage, the surface of the Si substrate is covered with oxide, so process (3) is entered. This process (3
), in order to promote the migration of attached SrO and BaO molecules on the substrate surface and improve the crystallinity of the grown film,
The Si substrate temperature is further increased. In this case, the high temperature creates oxygen vacancies in the growth belly, so at time C
A higher pressure is applied in advance to advance the growth. The optimum oxygen pressure for suppressing the generation of vacancies depends on the type of oxide to be grown and the growth temperature.

FIG. 5 is a characteristic diagram showing an example of the minimum oxygen pressure required to suppress the generation of oxygen vacancies when a Sr,lsat-xO film is grown at a temperature of 830°C.

The horizontal axis in this figure shows the oxygen pressure in the vacuum chamber during growth (the pressure in process (3) in Figure 1), and the vertical axis on the left shows the backscattering/channeling method, which is a guideline for crystallinity evaluation. The vertical axis on the right side shows the oxygen composition, which is normalized with the stoichiometric composition as 1.

In this example, to suppress vacancies during growth, IXIO
An oxygen pressure of −'Torr is required, and this pressure (I
If an oxygen pressure higher than X 1 0-'Torr) is applied, the surface migration of SrO and BaO molecules that have reached the Si substrate will be inhibited, causing essential problems such as deterioration of crystallinity. . Further, problems such as a burden on the device arise. Therefore, it is sufficient to apply oxygen at at least the lowest pressure necessary to suppress oxygen vacancies during growth. This minimum oxygen pressure depends on the growth temperature, and as the growth temperature increases, it becomes necessary to apply even higher oxygen pressure.

In addition, at the end of process (3), after the substrate pressure is lowered to room temperature at time D when the oxide single crystal of the desired thickness is obtained,
Exhaust the introduced oxygen.

Next, FIG. 6 shows 5QnmSr, (Bat-x) grown on the Si-based slope using the oxide thin film growth method explained above.
FIG. 2 is a characteristic diagram showing the growth temperature dependence of the surface channeling yield evaluated by the backscattering/channeling method of a single crystal film having a composition of 0.0 (composition X=0.32). Here, characteristic X indicates a conventionally grown film (without oxygen pressure control), and characteristic Y indicates a film grown under optimal oxygen pressure control.

Moreover, the surface channeling yield is a standard for crystallinity evaluation, and the smaller the surface channeling yield, the less lattice disorder and the better the crystallinity. Further, the growth temperature is the substrate temperature in process (3) in FIG.

In the conventional growth method (characteristic

On the other hand, in the growth method of this embodiment (characteristic Y) in which the oxygen partial pressure is optimally controlled from the beginning to the end of the growth, the crystallinity is improved in the high temperature region.

Furthermore, at a temperature of 850° C., the surface channeling yield is improved to 7% even though the film is as thin as 60 nm. To date, there has been no report of an excellent surface channeling yield of 7% in such a thin oxide single crystal thin film.

Note that the above embodiments are based on high-quality S formed on a Si-based slope.
r X B a I-K O (composition ,
For example, it is also effective for forming high-quality single crystal thin films of insulators such as spinel, sapphire, YSZ (stabilized zirconia), and oxide high-temperature superconductors.

〔Effect of the invention〕

As explained above, the present invention uses the oxide thin film growth method to solve the following problems: It is possible to suppress surface roughness caused by corrosion.

(2) Formation of silicides and silicates due to reactions between metal and nonmetallic elements constituting the oxide and Si and oxygen can be suppressed.

(3) Furthermore, the generation of oxygen vacancies during high-temperature growth can be suppressed, and an extremely thin and high-quality oxide single crystal thin film can be formed.

This makes it possible to form single-crystal thin films of insulators such as alkaline earth oxides, Subinel, and sapphire, and oxide high-temperature superconductors on Si-based slopes, making it possible to form ultrathin SOI devices and stacked layers. It is extremely effective for realizing LSI, etc., and for combining high-temperature superconductivity phenomena with conventional microelectronics using Si as a base material on the same board.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the procedure of the method for forming an oxide thin film according to the present invention, FIG. The figure is a characteristic diagram showing the regions where oxidation occurs and the region where etching occurs, Figure 4 is a characteristic diagram where crystallinity was evaluated using the back diffusion channeling method, and Figure 5 is a characteristic diagram showing the regions where oxidation occurs and the region where etching occurs. FIG. 6 is a characteristic diagram showing an example of the minimum oxygen pressure, and FIG. 6 is a characteristic diagram showing the growth temperature dependence of the surface channeling yield. 1... Ultra-high vacuum chamber, 2.3... Electron beam impact heating device, 4... Shutter, 5... Substrate holder, 6
...Si substrate, 7...Oxygen gas introduction nozzle, 8...
・Lower exhaust system, 9.10...Upper exhaust system, 11~l3
...gate valve, 14...electron gun, 15...fluorescent plate, 16...control system. Figure 1 Patent Applicant: Nippon Telegraph and Telephone Corporation Agent Masaki Yamakawa Torr

Claims (1)

[Claims] In a method for forming an oxide thin film in which a single crystal oxide film is heteroepitaxially grown on a semiconductor substrate by vapor deposition in an ultra-high vacuum chamber, the oxygen pressure in the ultra-high vacuum chamber is heated to a predetermined temperature. a first step of growing an oxide single crystal film by setting a pressure value at which an oxidation reaction and a corrosion reaction occurring on the upper surface of the semiconductor substrate are in equilibrium;
After the surface of the semiconductor substrate is covered with the oxide single crystal film in the first step, the oxygen pressure in the ultra-high vacuum layer is controlled to suppress the generation of oxygen vacancies in the oxide single crystal film. The semiconductor substrate is heated to a temperature higher than the heating temperature in the first step to form an oxide. A method for forming an oxide thin film, comprising: a second step of growing a single crystal film.