JPH0364024A - Washing method of surface of semiconductor substrate - Google Patents

Abstract

PURPOSE:To prevent a polluted substance from being adhered to again by introducing a reactive gas and a non-reactive gas which does not contribute to etching into a chamber alternately for dividing a desired etching amount. CONSTITUTION:The amount of etching on the surface of a silicon wafer 22 is divided for etching. Methods for dividing etching include a method for alternately introducing chlorine (reactive gas) and a rare gas (non-reactive gas), the one for introducing the reactive gas and the non-reactive gas and then discharging these gases alternately and repeatedly, and the one for supplying the reactive gas and the non-reactive gas in pulse shape. A silicon crystal 11 and a polluted substance which are eliminated from a silicon wafer by etching reaction as shown by an arrow I are introduced intermittently as shown in a white-painted arrow II and are carried to the outside of chamber by discharged gas, thus preventing readhesion of the polluted substance.

Description

[Detailed Description of the Invention] [Summary] A semiconductor substrate surface cleaning method, particularly for cleaning inorganic contaminants such as heavy metals and alkalis adhering to the surface of a semiconductor substrate (silicon substrate) (e.g., Pe, Ni, Cr, CaSHg,
Regarding the method of dry cleaning (Na, etc.), during dry etching for cleaning the surface of a semiconductor substrate, the etching progresses without re-adhering contaminants to the substrate, thereby maintaining the cleanliness that should originally be obtained. The purpose of the present invention is to provide a dry cleaning method for the surface of a semiconductor substrate that can be realized by etching the surface of the semiconductor substrate using a halogen-based reactive gas and vaporizing and removing contaminants on the surface of the substrate. A semiconductor substrate surface cleaning method characterized in that, in dry cleaning, a reactive gas and a non-reactive gas that does not contribute to etching are introduced into a chamber alternately to divide and etch a desired amount of etching. do.

[Industrial application field]

The present invention provides a method for cleaning the surface of a semiconductor substrate, particularly cleaning inorganic contaminants such as heavy metals and alkalis (e.g., Fe, Ni, Cr, Ca,
This invention relates to a dry method for cleaning Mg, Na, etc.

[Conventional technology]

Among cleaning methods aimed at cleaning semiconductor surfaces, dry cleaning methods (dry cleaning methods) that do not use solutions are:
As ICs have become more highly integrated in recent years, there has been a need for them to be used in the cleaning process during the manufacturing process. On the surface of a semiconductor substrate (for example, a silicon wafer), there is a layer of surface contamination that ranges from a few to 500 particles, although it varies depending on the type of previous process. It is removed along with the etching process. The reactive gases used include halogen-based chlorine (CIZ), hydrogen chloride (Hel), element 77 (F2), and hydrogen 77ide (IF). Alternatively, using these reactive gases, the reactive gases are excited by irradiation with light (ultraviolet light!) to raise the energy state, etching the surface of the semiconductor substrate, and at the same time vaporizing and removing contaminants. There is also.

For example, the present applicant loaded a silicon substrate into a reaction tank, evacuated the inside of the reaction tank, and then introduced chlorine gas into the reaction tank and heated the silicon substrate at a temperature of 100°C to 50°C.
Heating to a temperature of 0°C, irradiating the silicon substrate loading part with light to generate chlorine radicals, thereby etching the silicon substrate surface, and then removing chlorine gas from the reaction tank, A method for forming a thin film on the silicon substrate by introducing a thin film forming gas into the reaction tank was developed and published (Japanese Patent Application Laid-Open No. 62-42530).

In addition, Hayashi Sugino, one of the inventors of the present invention, along with Yasuo Nara, Satoru Watanabe, Takashi Ito, and others, published a report entitled "Etching and cleaning of silicon using photoexcited chlorine radicals" in Electrochemistry Vol. 1.56. No. 7 (198B),
Published on p. 533-537. This report uses 99.999% high-purity chlorine as the reaction gas and a microwave-excited high-pressure mercury lamp as the ultraviolet light source.
The substrate was perpendicularly irradiated with light having a wavelength of 200 to 300 nm, which is effective for generating chlorine radicals through the selective reflection ξ multilayer film. The light intensity is 22 mW/cd (U
The reaction chamber was entirely made of quartz, and the substrate was heated by irradiating the back surface with infrared rays from outside the reaction chamber. As a sample (100
) Using a silicon wafer, the natural oxide film on the surface was removed with a dilute hydrofluoric acid solution and deionized water immediately before introducing it into the reaction chamber. The pressure inside the reaction chamber was adjusted using a dry pump and a mechanical booster pump.

It has been found that the silicon surface obtained by such photoexcitation cleaning has a higher degree of cleanliness than that obtained by solution cleaning, and that contaminants on the silicon surface that cannot be removed by solution cleaning can also be removed by photoexcitation cleaning.

To explain the reason why such a dry cleaning method was used, for example, when forming a trench in a silicon wafer, the trench has a height to width ratio (aspect ratio) for the purpose of device miniaturization. ), that is, it is necessary to form a narrow width and a large depth. At that time, in wet etching using a solution, it became difficult for the solution to enter the trench due to surface tension, and it became difficult to draw out (remove) the solution that had entered.

Additionally, residue adheres to the substrate surface after etching or cleaning with a solution. In the past, these residues did not pose much of a problem, but in the current situation of high integration and miniaturization, these residues can no longer be ignored, and wet etching has its limits. This led to the adoption of dry cleaning and dry etching methods.

[Problem to be solved by the invention]

In the above-mentioned cleaning method using a halogen-based reactive gas, contaminants are vaporized and removed during etching of the semiconductor substrate surface, so it is inevitable that the contaminants will float in the gas phase. It was also observed that the contaminant material floating in the gas phase re-attached to the surface of the etched semiconductor substrate.

FIG. 3 is a diagram for schematically explaining the problems of the conventional example. At the initial stage of etching the surface of a semiconductor substrate (silicon wafer), contaminants 12 have entered between the silicon crystals U, as shown in FIG. 2(a). As the etching progresses, as shown in Figure (B), contaminants 12 are also separated from the substrate surface together with the silicon crystals 11 on the surface, and some of these detached contaminants are indicated by arrows in the figure. so that it adheres back to the silicon wafer surface.

In this way, dry cleaning using conventional technology means that contaminants are removed and deposited repeatedly. Currently, the level of cleanliness that can be obtained is lower than that of .).

Therefore, the present invention provides a surface of a semiconductor substrate that can achieve the originally desired degree of cleaning by allowing etching to proceed without re-adhering contaminants to the substrate during dry etching for cleaning the surface of the semiconductor substrate. The purpose of this invention is to provide a method for dry cleaning.

[Means to solve the problem]

The above problem is solved by dry cleaning in which the surface of a semiconductor substrate is etched using a halogen-based reactive gas and contaminants on the surface of the substrate are vaporized and removed. This problem is solved by a semiconductor substrate surface cleaning method characterized in that a desired etching amount is divided and etched by alternately introducing etching into a chamber.

[Effect]

That is, in the present invention, etching is progressed in parts by repeating the introduction and exhaust of etching gas until the target etching amount is reached, and during the exhaust stage, the contaminants floating in the gas phase are removed from the reaction chamber. The pollutants are removed in a gaseous state without being redeposited.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to illustrated embodiments.

FIG. 2 is a diagram showing the configuration of an apparatus used to carry out the method of the present invention. In the figure, 21 is a chamber, 22 is a semiconductor Ji plate (
23 is a heater for heating the silicon wafer 22, 24 is an exhaust port, 25 is a container for a reactive gas such as chlorine gas, and 26 is a container for a non-reactive gas that does not contribute to etching (for example, Ar) Container, 2
7a and 27b are bulbs, 28 is a power source for the heater 23, 31 is a light source, and 32 is a reflector. The apparatus is the same as the known apparatus used in the past, except that the reactant gas and the noble gas are introduced alternately.

The silicon wafer 22 is heated to 200″C by the heater 23.
It is heated to a temperature of about 500° C., and the pressure inside the chamber 21 is normally 1 to IQQ Torr, 1 to 100 Torr when introducing a reaction gas, and I
I x maintained at 10-'Torr. The flow rate of chlorine gas and rare gas (Ar gas) is 10 to 200 m each.
It is maintained at l/5hin.

In the method of the present invention, the amount of etching on the surface of the silicon wafer 22 (the desired amount within the range of several to 500 people as described above) is not etched all at once, but is etched in parts.

Methods of split etching include a method of alternately introducing chlorine (reactive gas) and rare gas (non-reactive gas) while exhausting the air for about 0.1 to 10 seconds; A method of alternately repeating the introduction of gas and exhaust of these gases, a method of repeating the cycle of reactive gas introduction → exhaust → non-reactive gas introduction → exhaust, a method of supplying reactive gas and non-reactive gas in a so-called pulse form There are methods, etc.

Furthermore, there is a method of heating the silicon wafer to 200°C to 500"C and irradiating the silicon wafer with pulsed light from the light source 31 in a chlorine atmosphere.
Using light with a wavelength of nm (the light source is a high-pressure mercury lamp), the light power is 10 to 100+W/c-, the light pulses are pulses at intervals of 0.1 seconds to 1 second, and the total irradiation time is 1t60 seconds. , the surface of a silicon wafer can be etched by 500 people.

By carrying out the above method, referring to FIG. 1, the silicon wafer is etched by the arrow I
As shown in , the separated silicon crystal 11 and the contaminant are
White arrows ■ by split etching according to the method of the present invention
As shown in , the gas that is intermittently introduced and exhausted carries the contaminants out of the chamber and prevents them from re-depositing.

The cleanliness of silicon wafers obtained by the divided dry cleaning method of the present invention was quantitatively analyzed by atomic absorption spectrometry.
The concentration of was analyzed. In the method of the present invention, a value of 2 x 10" pieces/Cl1l, which is the limit value for analysis by the above method, is obtained, which is a significant improvement compared to 4 x 10q pieces/c++1 in the conventional method. A value one order of magnitude higher than the above value was obtained by cleaning with .

Note that halogen-based gases such as fluorine, hydrogen fluoride, and hydrogen chloride are effective as the reactive gas.

〔Effect of the invention〕

As described above, according to the present invention, by performing etching in parts during dry cleaning of the surface of a semiconductor substrate using a reactive gas, redeposition of contaminants to the semiconductor substrate, which has been observed in the past, is significantly reduced. This will greatly contribute to the production of highly integrated semiconductor devices.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the present invention in detail, Fig. 2 is a block diagram of an apparatus used to carry out the method of the present invention, and Fig. 3 is a diagram for explaining the problems of the conventional method. (b) is a diagram of an initial silicon wafer surface, and (b) is a diagram of a silicon wafer surface obtained by a conventional method. In the figure, 11 is a silicon crystal, 12 is a contaminant, 21 is a chamber, 22 is a semiconductor substrate, 23 is a heater 24 is an exhaust port, 25 is a reaction gas container, 26 is a rare gas container, 27a and 27b are valves, and 28 is a A power source, 31 a light source, and 32 a reflector. +1=, shi1) Koniwadai 1- Kinomi ξ sail direction 3 arrow begging ε light group Figure 1

Claims (2)

[Claims] (1) Semiconductor substrate (2
2) In dry cleaning to vaporize and remove contaminants (12) on the surface of the substrate while etching the surface, a reactive gas and a non-reactive gas that does not contribute to etching are alternately introduced into the chamber (21). 1. A method for cleaning a surface of a semiconductor substrate, characterized in that etching is performed by dividing a desired amount of etching. 2. A method according to claim 1, characterized in that, during the introduction of the reactive gas, a light which is absorbed and excited by the reactive gas is blinked.