TWI427180B - Method of fabricating al2o3 thin film - Google Patents

Description

Preparation method of aluminum oxide film

The invention relates to a method for preparing a thin film of aluminum oxide, in particular to a deposition and fabrication of an aluminum oxide thin film layer (Al ₂ O ₃ thin film layer) in a single process under normal pressure and low temperature environment. In particular, it refers to a layer of aluminum oxide thin film having dual functions such as chemical passivation and field effect passivation.

In the past 100 years, the high growth of the global population, the progress of civilization, the progress of industry, and the requirements of quality of life have resulted in a growing demand for and dependence on energy. As a result of the large-scale use of fossil fuels, the global storage is rapidly reduced, and its prices are rising. At the same time, a large amount of pollutants are generated, causing problems such as global warming and climate anomalies, posing a threat to human living environment.

As the price of petrochemical fuels, including oil and natural gas, soars, it has attracted global attention to alternative energy sources. Generally, alternative energy sources are roughly divided into two categories, energy from the sun and energy from the sun. The energy from the sun contains wind, tides, water, biomass and solar cells. Energy from the sun is not There are geothermal and nuclear energy, but the amount of electricity generated by geothermal energy supply is very limited. Therefore, nuclear energy is one of the important alternative energy sources. However, after the nuclear accidents such as the Soviet car Nobby, the US San Francisco and the recent Japanese Fukushima, the world had to start worrying about the safety of nuclear energy.

The alternative energy system is imperative. The solar power generation system is the cleanest alternative energy source. It has no air and noise pollution to the environment, and the solar energy reserves are abundant and inexhaustible. It has become the world's key research and Alternative energy source One.

In the high-efficiency solar cells in the laboratory, the coincidence rate of the surface electron-hole pairs can be effectively suppressed by the high temperature (>900 ° C) oxidation process, and the SiO ₂ film grown on the surface of the ruthenium wafer is effectively suppressed. However, until now, the process and method have not been applied to industrial processes. The most important reason is that the minority carrier life in the block is very sensitive to high temperatures, especially polycrystalline silicon wafers, when the process temperature is higher than 900. At °C, it will cause a significant decline in the lifetime of the minority carriers in the tantalum block. Therefore, it is necessary to develop a low temperature surface passivation process.

Currently widely studied to replace the high temperature (>900 ° C) oxidation process, is SiNx film material. It is coated with a p-type substrate solar cell at a temperature of about 400 ° C by a plasma-enhanced chemical vapor deposition (PECVD) method to obtain a low surface coincidence rate. However, the SiNx thin film material has a high density of fixed positive charges and cannot be applied to the back surface of a p-type substrate solar cell.

Fortunately, the negatively charged dielectric material Al2O3 (Al ₂ O ₃ ) has been shown to provide good back surface passivation of p-type substrate solar cells, or to provide n-type substrate solar cells with good surface passivation before .

The development techniques of Al ₂ O ₃ thin film materials include Atomic Layer Deposition (ALD), plasma enhanced chemical vapor deposition, and reactive sputtering (Reactive Sputtering). The above methods and techniques must be carried out in a vacuum environment, especially the atomic layer deposition technique has a low deposition rate (<2 nm/min.), and thus is not suitable for an industrial solar cell process.

In order to make solar energy widely available, cost and efficiency are key factors. However, in view of the problems of the above-mentioned conventional techniques, the general practitioners cannot meet the needs of the user in actual use.

The main object of the present invention is to overcome the above problems encountered in the prior art and to provide a dual function of surface chemical passivation and field effect passivation in a simple and rapid single process under normal pressure and low temperature environment. The deposition and fabrication method of the aluminum oxide thin film layer.

A secondary object of the present invention is to provide a method for preparing a alumina film that can be applied to a solar cell and other photovoltaic elements to effectively reduce surface leakage current to improve or enhance the photoelectric conversion efficiency of the solar cell.

Another object of the present invention is to provide a method for preparing a film of aluminum oxide having a high deposition rate, at least greater than 10 nm/min, which can effectively reduce process time and cost.

It is still another object of the present invention to provide a thin film of aluminum oxide having a high fixed negative charge density of at least greater than 10 ¹² charges per cubic centimeter.

For the purpose of the above, the present invention is a method for preparing a film of aluminum oxide, which utilizes Atmospheric Pressure Chemical Vapor Deposition (APCVD) at a purity of 5N (99.999%) to On the surface of the p-type or n-type germanium wafer material in the range of 9N (99.9999999%), the deposition and fabrication of the aluminum oxide thin film layer is completed under the single process step, through the processes of temperature rise, temperature holding and temperature lowering.

Please refer to FIG. 1 and FIG. 2 for a schematic diagram of the structure of an atmospheric pressure chemical vapor deposition apparatus and a temperature-time diagram of the Al ₂ O ₃ thin film layer process of the present invention. As shown in the figure: the present invention is a method for preparing a film of aluminum oxide, which is a single process for depositing and fabricating an Al ₂ O ₃ thin film layer, which comprises at least the following steps: A) Temperature rising step 21: Selecting a germanium wafer 2 having a purity ranging from 5N (99.999%) to 9N (99.9999999%), and placing it in an atmospheric pressure chemical vapor deposition apparatus (APCVD) 1) In the reaction chamber 10, after passing nitrogen gas, the heating power source, such as the RF coil 11, is turned on, and the temperature rise is started. After the silicon wafer 2 is heated to a heating temperature, the temperature rise is stopped, and the wafer 2 is thermally balanced throughout the wafer. Thereafter, a native Oxide layer of SiO _{2 is} deposited on the surface of the germanium wafer 2; (B) temperature holding step 22: via an air inlet The manifold 12 is provided with a first gas in the reaction chamber 10, and then through another intake manifold 13, a second gas is introduced into the reaction chamber 10 to start growing the Al ₂ O ₃ film layer. And maintaining a temperature holding time at the heating temperature, obtaining a surface between the and the surface of the silicon wafer 2 between 80 and 120 n a m-thick Al ₂ O ₃ film layer in which excess reaction gas is discharged from an outlet manifold 14; and (C) cooling step 23: cooling the Al ₂ O ₃ film layer from the heating temperature to room temperature.

The wafer of the above step (A) may be a p-type or n-type germanium wafer material, and the thickness thereof is between 160 and 240 micrometers (μm); the heating temperature of the above step (A) is between 400~500 °C, the heating time is between 8 and 12 minutes; and the holding time of the above step (B) is between 8 and 12 minutes.

When utilized, the present invention selects a p-type or n-type germanium wafer 2 material having a purity in the range of about 5N (99.999%) to 9N (99.9999999%) having a thickness of about 200 μm. After the surface cleaning process of the standard ruthenium material, the ruthenium wafer 2 is placed above the carrier 15 in the reaction chamber 10 of the atmospheric pressure chemical vapor deposition apparatus 1 to perform the Al ₂ O ₃ film layer. Production process. As shown in FIG. 2, the process can be roughly divided into three stages. In a preferred embodiment, when the germanium wafer 2 is placed in the reaction chamber 10 of the atmospheric pressure chemical vapor deposition apparatus 1, the process is performed immediately. The step of raising the temperature of the step (A), which comprises the sub-steps (a1) and (a2), wherein the sub-step (a1) means that after the nitrogen gas is supplied, the heating power source is turned on to start the temperature rise; after about 10 minutes in the normal pressure environment During the temperature rising process, the sub-step (a2) is reached, and after the temperature of the reaction chamber 10 is raised to a range of 400 to 500 ° C, the temperature is stopped, and the temperature is maintained for about 1-2 minutes, so that the entire wafer 2 is thermally balanced. An oxide layer of SiO _{2 having a} thickness of 1 to 2 nm can be grown on the surface of the germanium wafer 2.

Next, the temperature holding step of the step (B) is performed to maintain the temperature of the reaction chamber 10 in the range of 400 to 500 ° C, which includes the sub-steps (b1), (b2) and (b3), wherein the sub-step (b1) The aluminum organometallic compound (TMA) is fed into the reaction chamber 10 of the atmospheric pressure chemical vapor deposition apparatus 1 via an intake manifold 12 and nitrogen as a carrier gas. After about 1 to 2 minutes, in sub-step (b2), another gas is supplied to the reaction chamber 10 of the normal-pressure chemical vapor deposition apparatus 1 via nitrogen gas as a transport gas, and the growth begins. al ₂ O ₃ thin film layer, after a growth time of about 10 minutes, to give a 100nm thick film of al ₂ O ₃ layer on the surface of the silicon wafer 2; and when sub-step (B3), the organometallic compound of aluminum Close delivery.

When the Al ₂ O ₃ film layer is formed, after 1 to 2 minutes of the transfer of the aluminum organometallic compound is turned off, the step of cooling (C) is performed, which comprises sub-steps (c1), (c2) and (c3). Wherein sub-step (c1) is to turn off the heating power supply and start to cool down; in sub-step (c2), the process temperature is lowered from 400 to 500 ° C to about 300 ° C, and then the oxygen delivery is turned off; finally in sub-step (c3) The temperature is lowered to room temperature to complete the entire process of the Al ₂ O ₃ film layer.

It can be seen that all the processes in the above steps can complete all the processes in only about 30 minutes.

The process of the invention has the following features: (1) using an atmospheric pressure chemical vapor deposition apparatus and method (APCVD) without a vacuum system, directly depositing and obtaining an Al ₂ O ₃ thin film; ) for low temperature process, has a low impact on the life of a few carriers in the block; (3) Simplified process, compared to the traditional process of alumina film, including deposition and annealing, the invention requires only a single process The preparation of the aluminum oxide film can be completed; (4) the process has a high deposition rate, at least greater than 10 nm/min, which can effectively reduce the process time and cost; (5) the aluminum oxide thin film layer developed by the method of the invention , having a high fixed negative charge density, at least greater than 10 ¹² charge / cubic centimeter; and (6) the aluminum oxide thin film layer developed by the method of the invention, can be applied to solar cell components, has improved efficiency, simplifies the process and reduces Production costs and other effects.

Therefore, the process of the present invention is carried out in a normal pressure and a low temperature environment, and a surface chemical passivation of a p-type or n-type germanium wafer material can be obtained in a simple and rapid single process. the dual function trioxide (Chemical passivation) and the field effect passivation (field effect passivation) like aluminum (Al ₂ O ₃₎ thin film layer; thereby, may be applied to solar cells and other photovoltaic element, to effectively reduce the surface leakage current, To improve or enhance the photoelectric conversion efficiency of solar cells.

In summary, the present invention is a method for preparing a film of aluminum oxide, which can effectively improve various disadvantages of the conventional use, and is carried out and completed under normal pressure and low temperature environment, and can be performed in a simple and rapid single process. Obtaining a layer of Al ₂ O ₃ film with dual functions of chemical passivation and field effect passivation, which can be applied to solar cells and other optoelectronic components to achieve effective Reducing the surface leakage current to improve or enhance the photoelectric conversion efficiency of the solar cell, thereby making the invention more progressive, more practical, and more suitable for the user, and indeed meets the requirements of the invention patent application, and patents according to law Application.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

1‧‧‧Normal Pressure Chemical Vapor Deposition

10‧‧‧Reaction room

11‧‧‧RF coil

12, 13‧‧‧ intake manifold

14‧‧‧Exhaust fistula

15‧‧‧bearer

2‧‧‧矽 wafer

21‧‧‧(A) Warming step

22‧‧‧(B) Temperature holding step

23‧‧‧(C) Cooling step

Fig. 1 is a schematic view showing the structure of an atmospheric pressure chemical vapor deposition apparatus.

Fig. ₂ is a schematic view showing temperature-time in the process of the Al ₂ O ₃ film layer of the present invention.

1‧‧‧Normal Pressure Chemical Vapor Deposition

10‧‧‧Reaction room

11‧‧‧RF coil

12, 13‧‧‧ intake manifold

14‧‧‧Exhaust fistula

15‧‧‧bearer

2‧‧‧矽 wafer

Claims (11)

A method for preparing an aluminum oxide thin film is a deposition and fabrication of an Al ₂ O ₃ thin film layer in a single process, which comprises at least the following steps: (A) a heating step: selecting a purity The silicon wafer in the range of 5N (99.999%) to 9N (99.9999999%) is placed in an atmospheric pressure chemical vapor deposition apparatus (APCVD) reaction chamber without a vacuum system. After the nitrogen gas is introduced, the heating power source is turned on, the temperature is raised, and the temperature of the germanium wafer is raised to a heating temperature, and then the temperature rise is stopped. After the wafer is thermally balanced throughout the wafer, the surface of the germanium wafer is grown by one to two nanometers. Native Oxide of m (nm) thick cerium oxide (SiO ₂ ); (B) temperature holding step: through a gas inlet pipe, a first gas is introduced into the reaction chamber, and then A second gas is introduced into the reaction chamber through another inlet manifold to start growing the Al ₂ O ₃ film layer, and after maintaining the heating temperature for a holding time, a surface is obtained on the surface of the silicon wafer. to a thickness of 80 ~ 120nm film of Al ₂ O ₃ layer; and (C) cooling step The Al ₂ O ₃ thin film layer is cooled to room temperature by this heating. The method for preparing a thin film of aluminum oxide according to claim 1 , wherein the wafer of the step (A) is a p-type or n-type germanium wafer material. The method for preparing a thin film of aluminum oxide according to claim 1 is characterized in that the thickness of the wafer after the step (A) is between 160 and 240 micrometers (μm). According to the preparation method of the aluminum oxide film according to the first aspect of the patent application, the wafer of the step (A) is placed in the reaction chamber after the surface cleaning process of the standard tantalum material. The method for preparing a thin film of aluminum oxide according to the first aspect of the patent application, wherein the heating temperature of the step (A) is between 400 and 500 °C. According to the preparation method of the aluminum oxide film according to the first aspect of the patent application, wherein the heating time of the step (A) is between 8 and 12 minutes. According to the preparation method of the aluminum oxide thin film according to the first aspect of the patent application, the first gas composition of the step (B) is a nitrogen gas and an aluminum organometallic compound (TMA). The method for preparing a film of aluminum oxide according to claim 1 , wherein the second gas component of the step (B) is a nitrogen gas and an oxygen gas. According to the preparation method of the aluminum oxide film according to the first aspect of the patent application, wherein the temperature holding time of the step (B) is between 8 and 12 minutes. The method for preparing an aluminum oxide thin film according to claim 1, wherein the Al ₂ O ₃ thin film layer has a fixed negative charge density of at least greater than 10 ¹² charges/cm 3 . The method for preparing a film of aluminum oxide according to item 1 of the patent application has a deposition rate of at least greater than 10 nm/min.