JPH071766B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION [Overview] In chlorine gas treatment of a Si substrate surface, a thin oxide is removed before chlorine gas treatment in order to remove and getter heavy metals in the Si substrate at a low temperature without etching the Si surface layer. A layer is provided on the Si substrate surface.

[Industrial application field]

The present invention relates to a method for manufacturing a semiconductor device,
More specifically, the present invention relates to an improvement of a cleaning process, particularly a process of cleaning heavy metals with chlorine gas, in a process of manufacturing a semiconductor device using a Si semiconductor substrate.

[Conventional technology]

Conventionally, the cleaning of the Si semiconductor substrate has been performed by wet cleaning, but there is a problem in complexity because it requires several steps of processing. In order to solve this problem, a method of cleaning using Cl ₂ gas has been proposed. In this cleaning method, contaminants are removed by heating the Si semiconductor substrate that has undergone the thin oxide film growth or deposition process to 100 to 500 ° C. in a Cl ₂ gas atmosphere.

[Problems that the invention tries to explain]

The conventional problems of decontaminating Si with chlorine gas have the following problems.

(I) Si is etched by chlorine gas, so Si
The chlorine gas cleaning method is not always suitable as a pretreatment method for the Si substrate when deep etching is performed. In particular, when a chlorine gas cleaning treatment method is performed as a pretreatment method for MOS gate oxidation, the characteristics of the gate insulating film, which are extremely sensitive to surface conditions, cause the surface of the Si substrate to be etched by the cleaning treatment, resulting in unevenness. The result is unsatisfactory.

(Ii) When the surface of the Si substrate to be etched by chlorine gas is observed, a thin blackened layer is observed. This blackened layer is a residue consisting of a Si layer having an extremely low density remaining on the surface to be etched, and is considered to be composed of ultrafine Si particles. Especially n
When treating the low-resistivity die substrate, a noticeable residue is observed. Therefore, some sort of cleaning process is required subsequently.

(Iii) Applicable etching processing conditions, particularly the range of the substrate temperature is narrow, and therefore the expected effect is also limited.

(Iv) Since the etching rate is significantly different depending on the specific resistance of the Si substrate, if regions with different specific resistance are provided on the same substrate, the etching effect will be different on the same substrate and the expected effect will be limited. To be done.

[Means for solving problems]

The feature of the present invention is that Si is irradiated with ultraviolet rays.
It is a combination of treating the surface of the substrate and forming a very thin oxide layer as a pretreatment. The Si substrate is preferably placed in a chlorine atmosphere having a pressure of 10 to 100 Torr, the substrate temperature is set to a low temperature of 100 to 500 ° C., and irradiation of ultraviolet rays causes Si etching. However, the reaction between Si and chlorine has the following problems. That is, a part of the heavy metal in the bulk under the surface of the Si to be etched is removed as a gas and a part is locally collected. By the way, when performing substrate processing through such Si etching, there are various restrictions associated with the Si substrate such as the Si film thickness that allows etching,
Since the phenomenon of etching is used, the diffusion of Cl into the substrate does not occur sufficiently and the substrate is processed (heavy metal removal).
The effect of is limited.

According to the present invention, a thin SiO ₂ layer is provided on the surface of the Si substrate prior to the chlorine gas treatment. SiO ₂ is not etched by the chlorine radicals, ultraviolet (wavelength shorter than 400 nm) SiO ₂ layer /
When the Si substrate is irradiated, conduction electrons are excited in Si. Therefore, if the SiO ₂ layer / Si substrate is placed in a chlorine atmosphere while irradiating with ultraviolet rays, Cl ₂ gas is directly dissociated by the irradiation of ultraviolet rays and C
l Radicals are adsorbed on the SiO ₂ surface by conduction electrons that have penetrated through SiO ₂ due to the tunneling phenomenon, and are further diffused into Si.
Reaching the surface of the substrate, Cl radicals react with Si or heavy metals. By such a reaction, Cl radicals bond with heavy metals in the bulk, some of the heavy metals are removed as a gas, and some of them are gettered. This reaction is 100-500 by UV irradiation.
It can be induced at a low temperature of ° C.

As mentioned above, the desired result can be achieved by UV irradiation and formation of an oxide layer. Where the thickness of the oxide layer is 20
The reason for setting to ~ 200Å is that the effect of the present invention cannot be achieved outside this range, and the reason for setting the wavelength of ultraviolet rays to 180 to 400 nm is that chlorine gas dissociation and Si conduction electron excitation are effectively performed. is there. The oxide layer may be formed by any method such as CVD or thermal oxidation.

[Action]

By previously providing the SiO ₂ layer as described above, since the etching of Si is suppressed, (i) the gettering and the bonding with the heavy metal are preferentially advanced as compared with the etching, and the chlorine gas treatment becomes possible for a long time, (Ii) The generation of residue is eliminated, and (iii) chlorine gas treatment can be applied even when the Si substrate has different resistivity regions.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is an Hg lamp, 2 is an ultraviolet selective reflection mirror, 3 is a bell jar, 4 is a synthetic quartz window, 5 is a heater, 6 is an exhaust port connected to a vacuum pump, 7 is chlorine gas as a carrier gas (inert gas). ), Or a supply port for supplying only chlorine gas.

The treatment was performed under the following conditions.

Cl ₂ pressure −50 Torr (100% Cl ₂ gas) Cl ₂ flow rate −15 sccm UV wavelength −290 to 370 nm UV intensity −800 mW / cm ² Substrate-window distance −5 cm SiO ₂ layer −30 Å (1000 ℃ dry oxidation) Treatment time −60 minutes Substrate temperature −300 ° C. After the above treatment, dry oxidation is performed to make the oxide film thickness 100 Å.
The electrode was formed. The generation life of minority carriers by Ct measurement was improved to about 200 μsec from that of about 100 μsec on an untreated substrate.

〔The invention's effect〕

By depositing or growing a thin oxide film on the Si substrate before photoexcited chlorine treatment, Si etching can be suppressed and a heavy metal removal effect can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of an apparatus for carrying out the surface treatment method of the present invention. 1 …… Hg lamp, 2 …… UV selective reflection mirror, 3 ……
Perger, 4 ... Synthetic quartz window, 5 ... Resistance heater,
6 ... vacuum exhaust port, 7 ... gas supply port.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device, which comprises a surface treatment of a Si substrate using chlorine gas, wherein 20 to 20 is provided before the treatment.
A method for manufacturing a semiconductor device, which comprises growing or depositing a 0 Å oxide layer on the surface of a Si substrate and irradiating ultraviolet rays of 180 to 400 nm during processing.