JPH02114638A - Cleaning of semiconductor substrate - Google Patents

Abstract

PURPOSE:To conduct a cleaning of a semiconductor substrate while the dissolution of a silicon dioxide film is inhibited small by a method wherein the substrate is dipped into a cleaning fluid containing at least a nitric acid-hydrofluoric acid aqueous solution, wherein the molar ratio of a nitric acid to a hydrofluoric acid and the concentration of the hydrofluoric acid are specified, and is subjected to surface treatment at a specified amount of surface removal. CONSTITUTION:When an Si water provided with an insulating film consisting of SiO2 is cleaned, the substrate is dipped into a cleaning fluid containing at least an HNO3-HF aqueous solution, wherein the molar ratio (HNO3/HF) of HNO3 to HF is 50 or more and the concentration of the HF is 0.1wt.% or less, and is subjected to surface treatment at a range of the amount of surface removal of the wafer of less than 0.5mum. By dissolving shallowly and uniformly the insulating film at an extent that the amount of surface removal of the wafer does not reach 0.5mum, an impurity existing on the water surface, whose roughness has not been almost varied from its original state, can be removed.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for cleaning a silicon semiconductor substrate, the purpose of cleaning the substrate while minimizing dissolution of a silicon dioxide film is to clean a silicon semiconductor substrate partially provided with an insulating film made of silicon dioxide. When cleaning a semiconductor substrate, the semiconductor substrate is cleaned using at least a nitric acid-hydrofluoric acid aqueous solution having a molar ratio of nitric acid to hydrofluoric acid (HNO:l/HF) of 50 or more and a hydrofluoric acid concentration of 0.1% by weight or less. A method for cleaning a semiconductor substrate is constituted by immersing the silicon semiconductor substrate in a cleaning solution obtained by cleaning the silicon semiconductor substrate and treating the surface of the silicon semiconductor substrate within a range where the amount of surface removal is less than 0.5 μm.

[Industrial application field]

The present invention relates to a method for cleaning a silicon (St) semiconductor substrate provided with an insulating film made of silicon dioxide (Sift).

Semiconductors include elemental semiconductors such as Si and germanium (Ge), and gallium arsenide (GaAs) and indium phosphide (In).
There are compound semiconductors such as P), but LSI and VLS
The majority of integrated circuits such as L are made using Si, and are large in diameter such as 5 or 6 inches and 5 inches thick.
It is manufactured by using a thin Si semiconductor substrate (hereinafter referred to as a wafer) made of approximately 00 μm steel, and making full use of thin film formation technology, photolithography technology (photolithography or electron beam phosphorography), impurity injection technology, etc.

When manufacturing semiconductor devices, if impurities, especially heavy metal elements and alkali elements, are adsorbed onto the wafer surface, it will directly affect the characteristics of the device, so manufacturing should be carried out in a clean room and thorough wafer cleaning should be carried out. Cleaning is necessary.

The present invention relates to a method for cleaning Si wafers.

[Conventional technology]

In the manufacturing process of semiconductor devices, there are many opportunities for impurities to be adsorbed or invaded into Si wafers.

For example, mirror polishing of wafers is carried out using an alkaline solution of colloidal silica as a polishing liquid, but during this polishing process, impurity elements contained in the polishing liquid are incorporated into the wafer surface. After cleaning, Si
It is necessary to clean the surface of the wafer.

Here, for cleaning Si wafers, RCA cleaning proposed by Kern et al. (W, Kern et al., RCA Review
, 187 (1970) and its modifications have been used.

This cleaning method uses ammonium hydroxide (N) 1. Aqueous solution (SC-1 liquid) consisting of hydrogen peroxide (OH) and hydrogen peroxide (fbot),
Hydrofluoric acid (HP) aqueous solution, hydrochloric acid (ICE) and hydrogen peroxide (H
The adsorbed impurities are removed by continuous cleaning using a combination of three aqueous solutions (SC-2 liquid) consisting of 2O.

However, even with this method, it is difficult to remove heavy metals such as iron (Fe), which is one of the causes of deterioration in the characteristics of semiconductor devices.

Therefore, the inventor proposed a method for removing adsorbed impurities by using HNO3 with a molar ratio of nitric acid (HNO3)/HP of 50 or more.
A cleaning method is proposed in which a Si wafer is immersed in a NO3-)IF mixed solution so that the amount of surface removal of the Si substrate is 0.5 μm or less.

(Japanese Patent Application No. 63-093813, filed on April 15, 1986) According to this method, ultra-cleaning can be achieved without deteriorating the surface irregularities of the Si wafer.

That is, by etching the Si wafer thinly to the extent that the surface unevenness does not increase, adsorbed heavy metal elements and impurities that have invaded the very surface area of the wafer are completely removed.

However, although this method is effective for surface treatment of only Si wafers, there are problems in applying it to Si wafers on which a silicon dioxide (5ift) film is patterned.

The reason for this is that the HNO, -1(F mixed solution also dissolves the 5iOz film.

Now, in the semiconductor device forming process, it is more important to pattern a 5i02 film than to use only a Si wafer.
Wafers are often cleaned.

For these reasons, it was necessary to put into practical use a cleaning method with a high etching ratio of Si/SiO□.

In this case, it is necessary that the etching ratio of Si/5i02 is sufficiently large.

However, the problem with the method proposed by the inventor is that the etching ratio is not large, and the problem is how to solve this problem.

[Means to solve the problem]

The above problem arises when cleaning a Si wafer with an insulating film made of SiO□, when the molar ratio of HNO and IIF (HNO:l/HF) is 50 or more, and the HF concentration is 0. This problem can be solved by a method of cleaning a Si wafer in which the Si wafer is immersed in a cleaning solution containing at least 1% by weight or less of an aqueous solution of HNO, -)IF, and the surface of the Si wafer is treated to the extent that the surface removal amount is less than 0.5 μm.

[Problem to be solved by the invention]

As mentioned above, when forming semiconductor devices on a Si wafer, the wafer on which a 5i02 film has been patterned is often cleaned to remove impurity elements adsorbed on the wafer surface. [Function] In the present invention, the molar ratio of HNO,/)IF is set to 50 as in the conventional case.
This is to suppress the dissolution of SiO□ by maintaining the concentration in the liver at 0.1% or less.

In other words, the cleaning method previously proposed by the inventor utilizes the fact that HNO, oxidizes the Si wafer, and HF dissolves the oxide, and the molar ratio of HNO,/IF is slightly increased to 50 or more. The impurities existing on the wafer surface are removed by maintaining the level of dissolving action and by dissolving the Si wafer shallowly and uniformly to the extent that the amount removed from the surface of the Si wafer does not reach 0.5 μm, leaving the surface unevenness almost unchanged from the initial state. It is something to do.

However, under the condition that the molar ratio of HNO3/HP is maintained at 50 or more, the HFfi degree is sometimes high and sometimes low, and S
Is the etching rate for iO□ film mainly due to HF? It is determined by the a degree.

FIG. 1 shows this state, where the horizontal axis shows I (No.).

HF under conditions where the molar ratio of and IIF is kept at 50 or more?
4 degree, and the etching ratio of Si to SiO□ (Si/SiO□) is plotted on the vertical axis, but when the concentration of HF is 0.
At 1% or less, the etching ratio rapidly increases to 10 or more.

Further, the unevenness on the wafer surface will naturally not increase if the surface removal amount is 0.5 μm or less.

〔Example〕

After forming an interelement isolation film made of SiO□ on the surface of the St wafer to isolate the elements, the cleaning method according to the present invention was applied to gate oxidation pretreatment.

Here, the thickness of the isolation film between elements is approximately 6000, and the concentrations of HNO and HP used are 60% of the former and 0% of the latter.
It was set to 0.05%.

In this case, the molar ratio of I(No,/HP) is about 450.

Further, the amount of surface etching of the Si wafer was set to 0.05 μm.

On the other hand, the amount of etching of the SiO2 film was only about 30 people, and it sufficiently performed its function as an interelement isolation film.

Next, a Si wafer that had been subjected to a cleaning process and a conventional R
Si gate MO using CA-cleaned Si wafer
Make an S diode and calculate the charge retention time (C
− is the retention time) was measured.

Figure 2 shows this result. According to the present invention, since heavy metal elements such as Fe are sufficiently removed, the retention time for C- can be increased to 600 seconds, approximately twice as long as in the conventional method. Ta.

〔Effect of the invention〕

As described above, by carrying out the present invention, it is possible to suppress the dissolution of SiO□ and to clean the surface of Si without increasing surface irregularities, thereby making it possible to improve the characteristics of semiconductor devices. .

[Brief explanation of drawings]

Figure 1 shows llN0. /HF concentration in IIF solution and Si/
Fig. 2 is a diagram showing the relationship between the SiO□ etching ratio and a comparison diagram of the charge retention time of St age-MOS diodes. Si-gate MOS Taioh F's electric lake I1 side B rf
Irdo board 2nd exit

Claims (1)

[Claims] When cleaning a silicon semiconductor substrate partially provided with an insulating film made of silicon dioxide, the semiconductor substrate is cleaned with a nitric acid to hydrofluoric acid molar ratio (HNO_3/HF) of 50 or more and a hydrofluoric acid concentration of 0.1. 1. A method for cleaning a semiconductor substrate, which comprises immersing the substrate in a cleaning solution containing at least a nitric acid-hydrofluoric acid aqueous solution of % weight or less, and treating the surface of the silicon semiconductor substrate to the extent that the surface removal amount is less than 0.5 μm.