A method for forming an oxide film in a semiconductor device comprises a pre-oxidation process, a main oxidation process and a post-oxidation process. N2O gas is used for the pre-oxidation process, a mixed gas of N2O gas and NH3 gas is used for the main oxidation process, and N2O gas is used for the post-oxidation process. The insulation characteristics of the oxide film are increased by introducing nitrogen, and amount of introduced nitrogen can be regulated by the controlling of amount of NH3 gas. Also, the problems encountered when NH3 gas and N2O gas are used separately for the oxidation process can be solved by using of the mixed gas of NH3 gas and N2O gas.
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1. A method for forming an oxide film in a semiconductor device comprising:
a) initiating oxide film formation by introducing an nitrous oxide containing gas; b) controlling the oxidation rate and influx of nitrogen by introducing ammonia into said nitrous oxide containing gas; and c) halting the introducing of ammonia gas while maintaining the flow of nitrous oxide containing gas until formation of said oxide film is complete.
0. 2. The method of
prior to said initiating oxide film formation step, loading the semiconductor device into an oxidation chamber; and introducing a nitrogen containing gas into said oxidation chamber.
0. 3. The method of
0. 4. The method of
0. 5. The method of
0. 6. The method of
supplying a nitrogen containing gas to an oxidation chamber containing said semiconductor device after said halting step; and reducing a temperature in said oxidation chamber.
0. 7. The method of
0. 8. The method of
0. 9. The method of
0. 10. The method of
0. 11. The method of
0. 12. The method of
0. 13. The method of %.
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1. Field of the Invention
The present invention relates to a method for forming an oxide film in a semiconductor device, more particularly to a method for forming an oxide film, which can obtain an oxide film of good quality by growing an oxide film under environment of mixed gas of N2O gas and NH3 gas during a main oxidation process and by using N2O gas during a pre-oxidation process and a post-oxidation process.
2. Information Disclosure Statement
In general, in order to enhance the reliability of oxide film in a semiconductor device, nitrogen is introduced in an oxide film. In the method for forming an oxide film using NH3 gas, the long-term reliability of the oxide film is deteriorated due to hydrogen ions contained in NH3 gas. There is another method for forming an oxide film using N2O gas, however, an high temperature process is required because of the high activation energy of N2O gas. Also it is impossible to control independently the oxidation rate and influx of the nitrogen. That is, N2O gas is resolved into 64.3% of N2, 31.0% of O2 gas and 4.7% of NO gas in the oxidation chamber under a temperature of 950 degree Celsius. The NO gas is needed to introduce nitrogen into the oxide film, however, NO gas exists in extremely small quantities of 4.7%. Also, most of the NO gas acts upon the O2 gas, and NO2 gas is formed according to the chemical reaction formula: (2NO+O2=2NO2). Therefore, because the influx of nitrogen depends on the degree of reaction of NO gas and O2 gas, it is impossible to control independently the oxidation rate and influx of the nitrogen.
It is an object of the present invention to provide a method for forming an oxide film using N2O gas, and mixed gas of N2O gas and NH3 gas, so that it is possible to control the oxidation rate and influx of the nitrogen and obtain an oxide film of good quality.
To achieve the above object, a method for forming an oxide film comprises the steps of:
a) initiating oxide film formation by introducing an NITROUS OXIDE containing gas;
b) controlling the oxidation rate and influx of nitrogen by introducing ammonia into the nitrous oxide containing gas; and
c) halting the introducing of ammonia gas while maintaining the flow of nitrous oxide containing gas until formation of the oxide film is complete.
The present invention will now be described with reference to the attached drawings, in which:
The FIGURE is a flow chart illustrating the method of oxidation according to the present invention.
A more complete understanding of the present invention can be obtained by considering the following detailed description.
A method for forming an oxide film according to the present invention is described in detail conjunction with the FIGURE.
A wafer is loaded in an oxidation chamber containing N2 gas at a temperature of 700 degree Celsius. Temperature in the oxidation chamber is increased to 900 degree Celsius and then stabilized. Then a pre-oxidation process, main oxidation process and post-oxidation process are executed successively in the oxidation chamber in order to form an oxide film on the surface of the wafer.
The pre-oxidation process is executed with N2O gas, the main oxidation process is performed with a mixed gas of N2O gas and NH3 gas, and the post-oxidation process is done with N2O gas.
Thereafter, the temperature of interior of the oxidation chamber is dropped to 700 degree Celsius, and N2 gas is supplied in the oxidation chamber. The oxidation process is completed, and the wafer is unloaded from the oxidation chamber.
In the above oxidation processes, temperature in the oxidation chamber, pressure and flow rate of process gases(N2O gas and NH3 gas) are varied according to the condition(thickness) of the oxide film.
As noted, prior to and after the main oxidation process using the mixed gas of N2O gas and NH3 gas, the pre-oxidation and post-oxidation processes using N2O gas are performed. The post-oxidation process is undertaken so as to prevent a nitridation of the surface of the wafer. The post-oxidation process is done to prevent penetration of any remaining NH3 to the oxide film and to prevent degeneration of the interface characteristic by hydrogen.
In the main oxidation process, NH3 gas is mixed with N2O gas, the proper ratio of NH3 gas in the mixed gas is 0.5-20%. Because of the lower activation energy of NH3 gas, the influx of nitrogen depends upon amount of NH3 gas. Therefore, enough nitrogen can be introduced in the oxide film by the mixed gas of a small quantity of NH3 gas and N2 O, and the incorporated amount of nitrogen can be controlled by a rate of NH3 gas. Also, hydrogen is acted upon oxygen which is resolved into N2O gas, and then is made OH as a wet oxidizer, OH accelerates the oxidation process.
Because nitrogen is incorporated into the oxide film simultaneously with the oxidation process, it therefore is possible to obtain .an oxide film of good quality.
According to the present invention as described above, the insulation characteristics of an oxide film is increased by an introducing nitrogen, the amount of nitrogen can be regulated by controlling of the amount of NH3 gas. Also, the present invention can solve the problems encountered when NH3 gas and N2O gas are used separately for the oxidation process, by using of the mixed gas of NH3 gas and N2O gas.
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