Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
1998-11-30
2001-11-20
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S021000
Reexamination Certificate
active
06319331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for processing semiconductor substrates, and particularly to a method for processing semiconductor substrates in which contamination by impurities is prevented.
2. Description of the Background Art
Semiconductor substrates (e.g., silicon substrates) are cleaned as pretreatment prior to semiconductor device manufacturing process. The RCA cleaning process is commonly used for the cleaning. In the RCA cleaning process, semiconductor substrates are subjected to an SPM cleaning process using a mixture of sulfuric acid (H
2
SO
4
), hydrogen peroxide solution (H
2
O
2
), and pure water (H
2
O) as cleaning solution, an APM cleaning process using a mixture of ammonia (NH
4
OH), hydrogen peroxide solution (H
2
O
2
), and pure water (H
2
O) as cleaning solution, and an HPM cleaning process using a mixture of hydrochloric acid (HCl), hydrogen peroxide solution (H
2
O
2
), and pure water (H
2
O) as cleaning solution.
The SPM cleaning is suitable for removal of organic matter, the APM cleaning is suitable for removal of organic matter and heavy metals, and the HPM cleaning is suitable for removal of heavy metals. Cleaning process with pure water is performed between the individual cleaning processes described above. Only the SPM cleaning process and the APM cleaning process may be applied instead of applying all of the three kinds of cleaning processes
While the RCA cleaning process removes organic matter and heavy metals away from the surface of a semiconductor substrate, an oxide film is formed on the semiconductor substrate surface during the cleaning process. The film is formed of native oxide naturally formed by dissolved oxygen in pure water and oxidizing action of hydrogen peroxide solution. This phenomenon is described in Japanese Patent Laying-Open No. 7-86220, Japanese Patent Laying-Open No. 5-29292, and Japanese Patent Laying-Open No. 63-29516.
FIG.
7
and
FIG. 8
show results obtained by analyzing a native oxide film on a semiconductor substrate by SIMS (Secondary Ion Mass Spectrometry).
FIG. 7
shows the results obtained by analyzing boron in a native oxide film on a semiconductor substrate immediately after application of the RCA cleaning.
FIG. 8
shows the results obtained by analyzing boron in a native oxide film on a semiconductor substrate left in clean air for several hours after application of the RCA cleaning process. In either of the drawings, the abscissa shows depth (&mgr;m) and the ordinate shows concentration (Atom/cm
3
).
As shown in
FIG. 7
, immediately after the RCA cleaning process, the concentration of boron in the oxide film is not higher than the lowest limit of detection and is hidden in the background. However, as shown in the area X in
FIG. 8
, the concentration of boron becomes higher in the vicinity of the surface when it is left in clean air. This means that boron contained in air has been taken into the native oxide film on the semiconductor substrate. Needless to say, if boron acting as a semiconductor impurity moves into semiconductor layers after formation of semiconductor devices, it will exert influence on the characteristics of the semiconductor devices. Especially, when semiconductor substrates are moved into semiconductor device manufacturing process without removing the native oxide film after cleaning, it is necessary to take the utmost care to avoid inclusion of boron in the oxide film. However, as stated above, there is the problem that the native oxide film formed during the cleaning process of semiconductor substrates takes in boron when left in air. For other substances existing in air and affecting semiconductor characteristics, it is also necessary to avoid inclusion of phosphorus and sodium in the oxide film.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a method for processing a semiconductor substrate comprises the steps of: (a) applying an RCA cleaning process to the semiconductor substrate; (b) removing a native oxide film formed on a surface of the semiconductor substrate during the RCA cleaning process; and (c) exposing the semiconductor substrate from which the native oxide film has been removed to a clean atmosphere of oxygen with an oxygen percentage of 20 to 100% to form an oxide film having a thickness reaching the saturation thickness on the surface of the semiconductor substrate.
Preferably, according to a second aspect of the present invention, in the method for processing a semiconductor substrate, the step (c) comprises the steps of preparing a vacuum chamber having an evacuating device, putting the semiconductor substrate from which the native oxide film has been removed in the vacuum chamber, evacuating air from the vacuum chamber to make a vacuum, and then introducing oxygen into the vacuum chamber.
Preferably, according to a third aspect of the present invention, in the method for processing a semiconductor substrate, the step (c) comprises the steps of preparing a closed chamber, putting the semiconductor substrate from which the native oxide film has been removed in the closed chamber, removing air from the closed chamber by replacement, and then introducing oxygen into the closed chamber.
Preferably, according to a fourth aspect of the present invention, in the method for processing a semiconductor substrate, the step (c) comprises the step of supplying vapor of pure water so that the humidity in the atmosphere of oxygen is 40% or higher.
According to a fifth aspect of the present invention, a method for processing a semiconductor substrate comprises the steps of: (a) applying an RCA cleaning process to the semiconductor substrate; (b) removing a native oxide film formed on a surface of the semiconductor substrate during the RCA cleaning process; and (c) immersing the semiconductor substrate from which the native oxide film has been removed in pure water at 20 to 100° C. to form an oxide film having a thickness reaching 10 to 15 angstroms on the surface of the semiconductor substrate.
Preferably, according to a sixth aspect of the present invention, in the method for processing a semiconductor substrate, the step (c) comprises the step of immersing the semiconductor substrate in pure water for 10 to 20 hours.
According to a seventh aspect of the present invention, a method for processing a semiconductor substrate comprises the steps of: (a) applying an SPM cleaning process using a mixture of sulfuric acid, hydrogen peroxide solution and pure water as a cleaning solution to the semiconductor substrate; and (b) applying an APM ozonized-water cleaning process using a mixture of ammonia, hydrogen peroxide solution, pure water and ozonized water as a cleaning solution to the SPM-cleaned semiconductor substrate to form an oxide film on a surface of the semiconductor substrate.
Preferably, according to an eighth aspect of the present invention, in the method for processing a semiconductor substrate, the step (b) comprises the step of adding the ozonized water so that the concentration of ozone in the entire solution is 1 to 10 ppm.
According to the semiconductor substrate processing method of the first aspect of the present invention, it is possible to form an oxide film that takes in no impurities contained in air even if it is left in air on a surface of a semiconductor substrate by exposing a semiconductor substrate from which a native oxide film formed during an RCA cleaning process has been removed to an atmosphere of oxygen having at least clean room level cleanliness and having an oxygen concentration percentage of 20 to 100%. Accordingly, even if the cleaned semiconductor substrate is put in semiconductor device manufacturing process without removing the oxide film on the semiconductor substrate, characteristics of the semiconductor devices are not affected. It is then not necessary to remove the oxide film on the semiconductor substrate, thus simplifying semiconductor device manufacturing process.
According to the semiconductor substrate processing method of the second aspect
Kume Morihiko
Yamamoto Hidekazu
Gulakowski Randy
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wilkins Yolanda
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