Patent Application
20050172895
The present invention relates to MOCVD apparatus and method in which a source gas as a mixture of an MO source gas with an oxidizing gas is supplied to thereby form films.
Conventional MOCVD (metal organic chemical vapor deposition) apparatus are CVD apparatus using an organometallic compound as a source or raw material and generally use powders or other raw materials which are solid or liquid at normal pressure and temperature. In these MOCVD apparatus, such a raw material is provided in a container, is heated under reduced pressure and is thereby vaporized. The vaporized gaseous material is transmitted with a carrier gas toward a deposition chamber. A passage through which the source gas flows is thereby always heated. In addition, oxygen gas is supplied to the passage of the source gas. Then, a gaseous mixture of the source gas and oxygen gas is supplied into the deposition chamber. The material used in MOCVD remains gaseous before reaching the substrate in the deposition chamber, is thermally decomposed and undergoes a combustion reaction to on the substrate thereby form a thin film on the substrate.
In the conventional MOCVD apparatus, the deposition chamber has a large volume or capacity, the source gas supplied to the deposition chamber adiabatically expands and thereby the temperature thereof decreases. Such a source gas having a decreased temperature may not form a thin film having satisfactory properties on the substrate.
In addition, the oxygen gas to mix with the source gas is supplied at room temperature, and thereby temperature of the source gas further decreases. Thus, a thin film having satisfactory quality cannot be significantly obtained.
The present invention has been accomplished under these circumstances, and an object of the present invention is to provide an MOCVD apparatus and an MOCVD method that can form a thin film having satisfactory properties by suppressing temperature decrease of a source gas.
To solve the above problems, the present invention provides, in an aspect, an MOCVD apparatus for supplying a source gas as a mixture of an MO source gas with an oxidizing gas to a substrate to thereby form a film, the apparatus including a substrate holder for holding the substrate; a deposition chamber for housing the substrate holder; a supply mechanism for supplying the source gas to a surface of the substrate; and a heating device for heating the substrate held by the substrate holder, in which the deposition chamber includes a substrate housing unit for housing the substrate holder holding the substrate, and a passage housing unit being connected to the substrate housing unit and constituting a passage for supplying the source gas to the substrate, and the passage has a cross-sectional area smaller than the area of a deposition plane of the substrate when the passage housing unit is cut in parallel with the deposition plane of the substrate.
According to the MOCVD apparatus, the adiabatic expansion of the source gas can be suppressed to thereby effectively suppress temperature decrease of the source gas due to adiabatic expansion by reducing the inner volume of the passage housing unit of the deposition chamber. A thin film having satisfactory properties can thereby be formed.
In another aspect, the present invention provides an MOCVD apparatus for supplying a source gas as a mixture of an MO source gas with an oxidizing gas to a substrate to thereby form a film, the apparatus including a substrate holder for holding the substrate; a deposition chamber for housing the substrate holder; a gas inlet arranged in the deposition chamber; a supply mechanism for supplying the source gas to the gas inlet; and a heating device for heating the substrate held by the substrate holder, in which a gas passage in the deposition chamber has a cross-sectional area 100 times or less as large as the opening area of the gas inlet, which cross-sectional area is obtained by cutting the deposition chamber in a direction perpendicular to a flow direction of the source gas when the supply mechanism supplies the source gas to the gas inlet to thereby supply the source gas to the substrate in the deposition chamber.
According to the MOCVD apparatus just mentioned above, the adiabatic expansion of the source gas can be suppressed to thereby effectively suppress the temperature decrease of the source gas due to adiabatic expansion by reducing the volume of the gas passage in the deposition chamber. A thin film having satisfactory properties can thereby be formed.
In the MOCVD apparatus according to the present invention, it is acceptable that the supply mechanism includes an MO source container housing the MO source, a first heating mechanism for heating the MO source in the MO source container, an oxidizing gas container housing the oxidizing gas, and a second heating mechanism for heating the oxidizing gas in the oxidizing gas container, and the MO source container and the oxidizing gas container are connected to the gas inlet, respectively. By heating the oxidizing gas by the second heating mechanism and introducing the heated oxidizing gas into the gas inlet, the temperature decrease of the source gas can thereby be further suppressed.
The MOCVD apparatus according to the present invention can further include a rotating mechanism for rotating the substrate holder. By this configuration, films are sequentially formed in part of the surface of the substrate to thereby form a film on the entire surface of the substrate ultimately.
The MOCVD apparatus according to the present invention can further include an ultrasonic generator for applying ultrasonic vibration to at least one of the supply mechanism and the substrate holder.
The MOCVD apparatus according to the present invention can further include an ultraviolet irradiation device or a soft X-ray irradiation device for applying ultraviolet rays or soft X-rays to the substrate held by the substrate holder. Thus, the thin film deposited on the substrate can be crystallized at low temperatures.
The present invention further provides an MOCVD method for forming a thin film using the MOCVD apparatus of claim 2, the method including the steps of holding the substrate on the substrate holder; supplying the source gas as a mixture of the MO source gas with the oxidizing gas to a surface of the substrate by action of the supply mechanism to thereby form a thin film on the substrate; and heating the substrate by the heating device.
The MOCVD method according to the present invention can further includes supplying the source gas to the surface of the substrate while applying ultrasonic vibration to at least one of the supply means and the substrate holder in the step of forming a thin film.
The MOCVD method according to the present invention can further includes the step of applying ultraviolet rays or soft-X rays to the thin film between the step of forming the thin film and the step of heating. Thus, the thin film can be crystallized at low temperatures.
Some embodiments of the present invention will be illustrated with reference to the attached drawings.
FIGS. 1(a) and 1(b) show that the MOCVD apparatus comprises a deposition chamber which comprises a lower chamber 11 and an upper chamber 12. By connecting the lower chamber 11 with the upper chamber 12, an inner space of the chamber is formed as shown in
A deposition plane of the substrate 13 on which a film is deposited in the deposition chamber has a substantially sectional region (region A) formed between a segment of the periphery (circumference) of the substrate 13 and the vicinity of the center of the circumference, as shown in
The periphery of the substrate holder 14 in a region corresponding to the region A is arranged at a set distance 21 from the inner wall of the lower chamber 11. The periphery of the substrate holder 14 corresponding to a region other than the region A is arranged as near as possible to the inner wall of the lower chamber 11 at a distance 22. The distance 22 is smaller than the set distance 21. By thus forming the shape of the inner space of the chamber, most of the source gas brought from the gas inlet 17 can be brought into the region A on the substrate. Namely, the source gas flows from the center to the periphery of the substrate as indicated by an arrow in the region A.
The gas inlet 17 is connected via a pipe (not shown) to an MO source container (not shown). The pipe has an inner diameter substantially identical to that of the gas inlet. The MO source container houses an MO source.
The MOCVD apparatus further comprises a supply mechanism (not shown) for supplying oxygen gas as an oxidizing gas to the pipe for the MO source. The oxidizing gas is not specifically limited to oxygen gas, and any other oxidizing gas can be used. In the MOCVD apparatus, the MO source gas is supplied from the MO source container to the pipe, the oxygen gas is supplied to the pipe by action of the supply mechanism, and thus a source gas as a mixture of the MO source gas and oxygen gas is brought into the inner space of the chamber from the gas inlet 17. The brought source gas flows along the arrow above the region A in the inner space of the chamber, passes through the periphery of and under the substrate holder 14 and is exhausted by the action of the exhaust pump 16 as shown in
Specifically, the shape of the inner space of the chamber can be illustrated as follows. The deposition chamber is separated into a substrate housing unit and a passage housing unit. The substrate housing unit is the inner space of the lower chamber and serves to house the substrate holder 14 holding the substrate 13. The passage housing unit is connected to the substrate housing unit and constitutes a passage for supplying the source gas to the substrate 13. The passage housing unit is an inner space above the region A of the substrate, which is formed by the slope 12a and the substrate 13. The passage has a cross-sectional area smaller than the area of the deposition plane of the substrate when the passage housing unit is cut in parallel with the deposition plane of the substrate.
More specifically, when the source gas is brought from the gas inlet 17 into the deposition chamber to thereby supply to the substrate, a gas passage in the source gas flow has a cross-sectional area 100 times or less as large as the opening area of the gas inlet, which cross-sectional area is obtained by cutting the deposition chamber in a direction perpendicular to a flow direction of the source gas. By thus forming the gas passage, the volume of the inner space of the chamber can be reduced. Thus, the temperature decrease of the source gas due to adiabatic expansion can be effectively suppressed.
Infrared heating mechanisms (not shown) for RTA (rapid thermal annealing) serving as a substrate heating mechanism are arranged in a region C and a region D in the deposition chamber shown in
The MO source container has, in an MO source outlet, an MO source control mechanism such as a mass flow controller for controlling the amount of the MO source supplied from the MO source container to the pipe. The MO source container also has a heater (not shown) serving as a heating device for heating and vaporizing the MO source. The supply mechanism has a temperature control mechanism (not shown). More specifically, an oxygen cylinder as the supply mechanism is covered by a plane heater (not shown) which serves to increase the temperature of the oxygen gas before supply.
In the regions C and D, ultrasonic generators (not shown) for applying ultrasound to the substrate holder 14 and ultrasonic generators (not shown) for applying ultrasound to the gas inlet 17 are arranged. These ultrasonic generators serve to apply ultrasonic vibration to the substrate holder 14 and the gas inlet 17. By applying ultrasonic vibration, the thin film can be crystallized at low temperatures of about 400° C. The ultrasonic generators can be any device that can generate ultrasound.
As an modified embodiment, ultraviolet irradiation devices can be used instead of the ultrasonic generators. The ultraviolet irradiation devices are devices for applying ultraviolet rays to a thin film deposited on the substrate. The thin film can be crystallized at low temperatures of about 400° C. by applying ultraviolet rays to the thin film.
As another modified embodiment, soft X-ray irradiation devices can be used instead of the ultrasonic generators. The soft X-ray irradiation devices are devices for applying soft X-rays to a thin film deposited on the substrate. The thin film can be crystallized at low temperatures of about 400° C. by applying soft X-rays to the thin film.
The MOCVD apparatus also includes a control unit (not shown). The control unit serves to control the timing and amount of the source gas brought from the gas inlet 17, the operation of the ultrasonic generators, ultraviolet irradiation devices, or soft X-ray irradiation devices, the timing of ON and OFF of the infrared heating mechanism for RTA, and the operation of the substrate rotation unit 15 for rotating the rotary substrate holder 14. The control unit also controls the MOCVD apparatus to thereby perform a deposition method mentioned below. Other configurations not illustrated in the MOCVD apparatus are the same as those conventionally known.
A deposition method using the MOCVD apparatus shown in
Initially, the substrate 13 is placed on and held by the substrate holder 14. The temperature of the substrate 13 in this step is room temperature. Next, the exhaust pump 16 evacuates the inner space of the chamber to 0.1 to several hundred torrs, preferably to 5 to 100 torrs. Then the substrate rotation unit 15 rotates the substrate holder 14.
Next, the MO source in the MO source container is heated and thereby gasified by the heater. The gasified MO source gas is brought from the MO source container into the pipe in a controlled amount. Separately, the oxygen gas is heated by the plane heater and is brought from the oxygen cylinder into the pipe to thereby mix the MO source gas and the oxygen gas. The oxygen gas has been heated for suppressing the temperature decrease of the substrate surface. The reason is that the resulting thin film will not have satisfactory properties because if oxygen at room temperature is supplied, oxygen is hardly raised in temperature and thereby decreases the temperature of the substrate surface.
The source gas mixture is brought to the gas inlet 17 and is supplied from the gas inlet 17 to the surface of the substrate 13 in the chamber. In this procedure, the ultrasonic generator applies ultrasonic vibration to one or both of the gas inlet 17 and the substrate holder 14. Thus, a thin film is deposited on the substrate surface while rotating the substrate 13. The inside pressure of the deposition chamber during this process is from 0.1 to several hundreds of torrs, and preferably from 5 to 100 torrs.
Concurrently with the film deposition treatment, the substrate is raised in temperature to about 400° C. by action of the infrared heating mechanisms for RTA arranged in the regions C and D. Thus, the thin film deposited on the substrate is crystallized. The thin film can be crystallized at low temperatures of about 400° C., since the ultrasonic vibration is applied at least one of the gas inlet 17 and the substrate holder 14 at the time when the source gas is brought thereinto. Instead of the ultrasonic vibration, ultraviolet rays or soft X-rays can be applied to the thin film after the source gas has been brought thereinto and thus the thin film can also be crystallized at low temperatures of about 400° C.
According to the first embodiment, a gas passage is to have a cross-sectional area 100 times or less as large as the opening area of the gas inlet, which cross-sectional area is obtained by cutting the deposition chamber in a direction perpendicular to a flow direction of the source gas. Thus, the volume in the deposition chamber, particularly the volume in the chamber corresponding to the passage housing unit to be a passage for supplying the source gas to the substrate 13, is reduced. The adiabatic expansion of the source gas can be prevented and temperature decrease of the source gas due to the adiabatic expansion can be effectively prevented. As a result, a thin film having good properties can be formed.
According to the present embodiment, the oxygen gas is heated before bringing into the pipe, and thereby the temperature decrease of the source gas can be prevented. As a result, a thin film having good properties can be easily obtained.
The shapes and sizes of the lower chamber 11 and the upper chamber 12 constituting the deposition chamber are not specifically limited to those described in the embodiment. They can be any other shapes and sizes, as long as, when the source gas is brought from the gas inlet 17 into the deposition chamber to thereby supply to the substrate, a gas passage in the source gas flow has a cross-sectional area 100 times or less as large as the opening area of the gas inlet, which cross-sectional area is obtained by cutting the deposition chamber in a direction perpendicular to a flow direction of the source gas.
The apparatus according to the present embodiment has the ultrasonic generators and can thereby apply ultrasonic vibration to the gas inlet 17 when the source gas is brought from the gas inlet 17. Thus, clogging of the deposition materials in the gas inlet 17 can be prevented, and thereby the source gas can be supplied stably.
The apparatus according to the present embodiment has the ultrasonic generators and can thereby apply ultrasonic vibration to the substrate holder 14 and to the substrate 13 when the source gas is brought from the gas inlet 17. Thus, crystals can grow stably on the substrate surface and can thereby form a thin film having good properties.
The MOCVD apparatus according to the aforementioned embodiment may further comprise an inner space in the region B shown in
FIGS. 2(a) and 2(b) show that the MOCVD apparatus comprises a deposition chamber which comprises a lower chamber 31 and an upper chamber 32. By connecting the lower chamber 31 with the upper chamber 32, an inner space of the chamber is formed as shown in
A deposition plane of the substrate 13 on which a film is deposited in the deposition chamber is the entire surface of the substrate as shown in
The periphery of the substrate holder 14 is arranged at a set distance 23 from the inner wall of the lower chamber 31. By thus forming the shape of the inner space of the chamber, the source gas brought from the gas inlet 17 can be brought into the entire surface of the substrate. Namely, the source gas flows from the center to the entire periphery of the substrate substantially uniformly. The brought source gas passes through the entire periphery of and under the substrate holder 14 and is exhausted by the action of an exhaust pump 16.
Specifically, the shape of the inner space of the chamber can be illustrated as follows. The deposition chamber is separated into a substrate housing unit and a passage housing unit. The substrate housing unit is the inner space of the lower chamber and serves to house the substrate holder 14 holding the substrate 13. The passage housing unit is connected to the substrate housing unit and constitutes a passage for supplying the source gas to the substrate 13. The passage housing unit is an inner space above the entire surface of substrate, which is formed by the slope 32a and the substrate 13. The passage has a cross-sectional area smaller than the area of the deposition plane of the substrate when the passage housing unit is cut in parallel with the deposition plane of the substrate.
More specifically, in the second embodiment as in the first embodiment, when the source gas is brought from the gas inlet 17 into the deposition chamber to thereby be supplied to the substrate, a gas passage in the source gas flow has a cross-sectional area 100 times or less as large as the opening area of the gas inlet, which cross-sectional area is obtained by cutting the deposition chamber in a direction perpendicular to a flow direction of the source gas. By thus forming the gas passage, the volume of the inner space of the chamber can be reduced. Thus, temperature decrease of the source gas due to adiabatic expansion can be effectively suppressed.
A substrate heating mechanism (not shown) for heating the entire substrate 13 is arranged below the substrate holder 14. The substrate heating mechanism serves to crystallize a thin film deposited on the substrate 13, and thus a film can be continuously formed and crystallized in the same chamber. Namely, while rotating the substrate, a thin film is deposited on the substrate, and carbon in the MO source is removed by heating the substrate to about 400° C., and the thin film is crystallized. The MOCVD apparatus further comprises a cooling mechanism (not shown) for cooling the substrate holder.
The MOCVD apparatus further comprises an ultrasonic generator (not shown) for applying ultrasound to the substrate holder 14 and another ultrasonic generator (not shown) for applying ultrasound to the gas inlet 17. Instead of the ultrasonic generators, ultraviolet irradiation devices can be used as an modified embodiment. Alternatively, instead of the ultrasonic generators, soft X-ray irradiation devices can also be used as an modified embodiment.
A deposition method using the MOCVD apparatus shown in
The source gas is supplied from the gas inlet 17 to the entire surface of the substrate 13 in the chamber, passes through the entire periphery of the substrate holder 14 and is exhausted by action of the exhaust pump 16 below the substrate holder. Thus, a thin film is deposited on the substrate surface.
Concurrently with the deposition treatment, the substrate is raised in temperature to about 400° C. by action of the substrate heating mechanism. Thus, the thin film deposited on the substrate is crystallized.
The same advantages as the first embodiment can be obtained in the second embodiment. Namely, by reducing the volume in the deposition chamber, particularly the volume in the chamber corresponding to the passage housing unit to be a passage for supplying the source gas to the substrate 13, adiabatic expansion of the source gas can be prevented and temperature decrease of the source gas due to the adiabatic expansion can be effectively prevented. As a result, a thin film having good properties can be formed.
The present invention is not specifically limited to the disclosed embodiments and covers various modifications. For example, various raw materials or sources suitable for a thin film to be formed can be used as the film-forming materials.
