JPH05129255A - Treatment of semiconductor substrate - Google Patents

Abstract

PURPOSE:To provide the treatment of a semiconductor substrate by removing a natural oxide film without heating a silicon wafer and ensuring the flatness of the surface by uniform etching when the surface of the silicon wafer is cleaned. CONSTITUTION:A silicon wafer is placed in the mixed gas atmosphere of chlorine fluoride gas and hydrogen chloride gas. Then, the mixed gas is irradiated with ultraviolet rays so as to simultaneously generate hydrogen fluoride radical and chlorine radical, and a natural oxide film formed on the surface of the silicon wafer is removed by the hydrogen fluoride radical and the silicon wafer is etched by the chlorine radical.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor substrate processing method,
In particular, it relates to a method for cleaning the surface of a semiconductor substrate by utilizing a photochemical reaction.

[0002]

2. Description of the Related Art Conventionally, as a method for cleaning the surface of a silicon wafer, a gas such as a halogen gas that reacts with silicon to generate a volatile silicon compound is excited by irradiation light to generate radicals. A method is known in which radicals are reacted with a silicon wafer to clean the surface of the wafer. As such a method, JP-A-64-9621
The publication describes a method using chlorine gas (Cl ₂ ) as a reaction gas. Further, JP-A-2-28322 discloses a method of removing a natural oxide film formed on the surface of a silicon wafer by using hydrogen chloride gas (HCl) as a reaction gas.

In the radical cleaning method, heavy metal impurities such as Fe, Cu and Ni remaining on the surface of the silicon wafer,
Alternatively, alkali or alkaline earth metal impurities such as Na, K and Ca are vaporized as chlorides and removed from the wafer surface. At this time, unlike a cleaning method using a solution, impurities in the processing solution do not redeposit, so that the wafer surface can be highly cleaned. Further, this radical cleaning is a process which is an alternative to the sacrificial oxidation process, and has the advantage that the processing temperature can be lowered and therefore the re-diffusion of impurities implanted in the wafer and the diffusion of impurities in the insulating film can be suppressed.

[0004]

In the above-mentioned cleaning method using chlorine gas as the reaction gas, the silicon wafer itself can be etched, but the natural oxidation of about 10 Å formed on the surface of the silicon wafer is possible. There is a drawback that the film cannot be removed. Since this natural oxide film is a non-homogeneous film, there is a problem in that the underlying silicon wafer is unevenly etched and unevenness is formed on the surface of the silicon wafer.

Further, although the natural oxide film on the surface of the silicon wafer can be removed by the cleaning method using hydrogen chloride gas as the reaction gas, the silicon wafer is removed by 50
It is necessary to heat to a high temperature such as 0 to 550 ° C. Therefore, there is a problem that re-diffusion of implanted impurities in the wafer and diffusion of impurities in the insulating film occur, deteriorating the device characteristics.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional method and to effectively remove the native oxide film formed on the surface of the semiconductor substrate without heating the semiconductor substrate to a high temperature. An object of the present invention is to provide a method for treating a semiconductor substrate, which enables etching without forming irregularities on the surface of the semiconductor substrate.

[0007]

According to the method of treating a semiconductor substrate of the present invention, a semiconductor substrate whose surface is to be cleaned is placed in a mixed gas atmosphere containing a chlorine fluoride gas and hydrogen chloride gas, and this mixture is mixed. It is necessary to remove the natural oxide film formed on the surface of the semiconductor substrate by hydrogen fluoride radicals generated by irradiating the gas with ultraviolet rays and etch the surface of the semiconductor substrate with chlorine radicals simultaneously generated by irradiating the gas with ultraviolet rays. It is a feature.

[0008]

In the method for treating a semiconductor substrate according to the present invention, hydrogen fluoride (HF) radicals and chlorine (Cl) radicals are obtained by irradiating a mixed gas of chlorine fluoride gas and hydrogen chloride gas with ultraviolet rays. As a result, HF radicals can remove the natural oxide film formed on the surface of the semiconductor substrate, and chlorine radicals also etch the surface of the semiconductor substrate to deposit various metallic impurities. Can be removed. Further, in the method of the present invention, since it is possible to remove the natural oxide film and etch the semiconductor substrate at room temperature without the need to apply heat, re-diffusion of implanted impurities and diffusion of impurities in the insulating film can be prevented. It does not occur and does not deteriorate the device characteristics.

Further, due to the action of chlorine radicals, not only etching of the semiconductor substrate but also metal impurities existing on the surface of the semiconductor substrate can be vaporized as chlorides,
Therefore, it can be easily removed from the processing system.

[0010]

EXAMPLE An example of a method for processing a semiconductor substrate according to the present invention will be described. First, an N-type silicon wafer is placed at a predetermined position in a chamber, and then ClF _{3 is} supplied from a gas supply box.
Gas and HCl gas are introduced into the chamber, respectively. The gas partial pressures at this time are 10 ^{-3 to} 10 Torr and 10 ^-1 to
Set to 100 Torr. The silicon wafer was not heated,
Keep at room temperature.

Next, in such a mixed gas atmosphere, the surface of the silicon substrate is irradiated with ultraviolet rays having a wavelength of 150 to 350 nm. A low-pressure mercury lamp is suitable as the ultraviolet light source, but the present invention is not limited to this, and any light source that emits ultraviolet light such as an excimer laser may be used. The gas supplied into the chamber is irradiated with ultraviolet rays to proceed the reaction as shown in the following formula, ClF ₃ + 3HCl → 3HF ^* + 4Cl ^* , and is simultaneously formed on the silicon substrate surface by the generated HF radicals and Cl radicals. The native oxide film that has formed is removed and the silicon wafer is etched.

That is, in the semiconductor substrate processing method according to the present invention, the natural oxide film formed on the surface of the silicon wafer is removed by the hydrogen fluoride radicals generated by the ultraviolet irradiation, and chlorine generated at the same time is removed. The surface of the silicon wafer can be etched by the radicals to remove the metal element attached thereto. Furthermore, since chlorine radicals can vaporize metal impurities as chlorides, they can be easily removed from the treatment system.

FIG. 1 shows the result of detecting whether or not a surface native oxide film is present by measuring the surface of a silicon wafer after treating the surface according to the above-described embodiment of the present invention by X-ray photoelectron spectroscopy. It is shown. As shown in FIG. 1, no natural oxide film (SiO ₂ ) peak was observed on the surface of the silicon wafer treated by the method of the present invention.

FIG. 2 shows the results of measurement by X-ray photoelectron spectroscopy of a silicon wafer after the surface was processed by irradiating only chlorine gas with ultraviolet rays and the peak of the natural oxide film. Indicates that a natural oxide film remains on the surface of the silicon wafer.
The thickness of the native oxide film at this time was about 6Å calculated from the peak value.

FIG. 3 shows a silicon wafer whose surface has been treated by the treatment method according to the present invention, in a dry oxygen atmosphere.
When the thermal oxidation film of 200 Å was formed by oxidation at a temperature of 900 ° C, or when the silicon wafer was treated with hydrofluoric acid solution and then oxidized to form a thermal oxidation film, chlorine gas was irradiated with ultraviolet rays. FIG. 5 shows the results of measuring the minority carrier generation lifetime when a surface-treated silicon wafer is oxidized to form a thermal oxide film. As shown in FIG. 3, the characteristics of the thermal oxide film formed after the surface treatment according to the present invention can be improved.

Although ClF ₃ gas is used as the chlorine fluoride-based gas in the above-described embodiments, other chlorine fluoride-based gas such as ClF, ClF ₂ , ClF ₅ , Cl ₂ F ₆ may be used. The same effect can be obtained. Further, in the above-mentioned embodiment, the silicon wafer was left at room temperature when the surface of the silicon wafer was cleaned by irradiating the mixed gas of the chlorine fluoride-based gas and the hydrogen chloride gas with ultraviolet rays, but 100 to 30
It is also possible to heat to a temperature of 0 ° C.

[0017]

According to the above-described semiconductor substrate processing method of the present invention, the semiconductor substrate is processed by the HF radicals and Cl radicals generated by irradiating the mixed gas of the chlorine fluoride-based gas and the hydrogen chloride gas with ultraviolet rays. Since the natural oxide film formed on the surface is removed and the semiconductor substrate is etched at the same time, it is possible to remove and etch the natural oxide film without heating the semiconductor substrate to a high temperature. It is possible to suppress the re-diffusion of impurities and the diffusion of impurities in the insulator, and since the natural oxide film does not remain on the surface after the treatment, for example, the characteristics of the thermal oxide film formed on it are improved. As a result, the device characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a peak intensity diagram showing a measurement result by an X-ray photoelectron spectroscopy method on a surface of a semiconductor substrate treated by the method of the present invention.

FIG. 2 is a peak intensity chart showing a measurement result by X-ray photoelectron spectroscopy of a surface of a semiconductor substrate treated by a conventional method.

FIG. 3 is a graph showing a comparison of minority carrier lifetimes when a thermal oxide film is formed on a semiconductor substrate processed by the method of the present invention and the conventional method.

Claims (1)

[Claims] 1. A hydrogen fluoride produced by placing a semiconductor substrate whose surface is to be cleaned in a mixed gas atmosphere containing a chlorine fluoride-based gas and hydrogen chloride gas and irradiating the mixed gas with ultraviolet rays. A method for treating a semiconductor substrate, characterized in that a natural oxide film formed on the surface of the semiconductor substrate is removed by radicals, and at the same time, the surface of the semiconductor substrate is etched and metal elements are removed by chlorine radicals simultaneously generated by irradiation of ultraviolet rays. ..