JP2000228384A - Method for wet-cleaning semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for wet-cleaning a semiconductor substrate, which can eliminate an organic substance and a metal impurity on the surface of the semiconductor substrate and can prevent these organic substance and metal impurity from re-adhering to the surface of the semiconductor substrate. SOLUTION: The surface of a semiconductor substrate is cleaned with a chemical liquid (HCl/O3/H2O/BHF or DHF) in which DHF(diluted hydrofluoric acid) or BHF(buffered hydrofluoric acid) is added to HCl/O3 water. It is preferable that a substance be used such that O3 is annexed to a hydrochloric acid of 5% or less as the HCl/O3 water. Furthermore, it is desirable that the chemical liquid (HCl/O3/H2O/BHF or DHF) be a substance that DHF or BHF of 1% or less is added to the HCl/O3 water. It is suitable to use this cleaning method, particularly for cleaning the surface of the semiconductor substrate prior to the growth of a gate oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for wet cleaning a semiconductor substrate used in semiconductor manufacturing.

[0002]

2. Description of the Related Art A trace amount of heavy metal element represented by Fe (1e10-1) is present on the surface of a semiconductor substrate before a gate oxide film is grown.
If you 1atoms / cm ² or so) to, various residues of the resist, ULPA filter, occur several ng / cm ² level desorbed hard organic matter at elevated temperatures such as phthalates released from the carrier casing or the like of Plastic In this case, it is known that the reliability of the gate oxide film decreases. In particular, when the thickness of the gate oxide film is reduced, the influence of the contamination by the organic substances and metal impurities becomes remarkable.

[0003]

Therefore, cleaning is performed to remove organic substances and metal impurities on the surface of the semiconductor substrate before the growth of the gate oxide film and the like, and to prevent the organic substances and metal impurities from re-adhering to the surface of the semiconductor substrate. Requires a process. In this case, H is obtained by adding ozone to a hydrochloric acid aqueous solution.
It is conceivable to clean the surface of the semiconductor substrate with Cl / O ₃ water. According to the cleaning using HCl / O ₃ water, organic substances and metal impurities can be simultaneously removed by a high oxidation-reduction potential and a low pH level. is there. However, when impurities are present on the bare silicon surface and in the natural oxide film and at the interface of the natural oxide film, cleaning with only HCl / O ₃ water removes organic substances and metal impurities on the semiconductor substrate surface, and removes these organic substances, It has been difficult to prevent metal impurities from re-adhering to the surface of the semiconductor substrate.

The present invention has been made in view of the above circumstances, and removes organic substances and metal impurities on the surface of a semiconductor substrate even when impurities exist on the bare silicon surface and in the natural oxide film and at the interface with the natural oxide film. It is another object of the present invention to provide a method for wet cleaning a semiconductor substrate, which can prevent the organic substances and metal impurities from re-adhering to the semiconductor substrate surface.

[0005]

In order to achieve the above object, the present invention provides a chemical solution (H) prepared by adding DHF (dilute hydrofluoric acid) or BHF (buffered hydrofluoric acid) to HCl / O ₃ water.
(Cl / O ₃ / H ₂ O / BHF or DHF) for cleaning a semiconductor substrate surface.

The wet cleaning method of the present invention comprises the following (1)
(5), whereby organic substances and metal impurities on the surface of the semiconductor substrate can be effectively removed, and the removed organic substances and metal impurities can be satisfactorily prevented from re-adhering to the surface of the semiconductor substrate. You can do it. (1) Since DHF or BHF having an oxide film removing action is added to HCl / O ₃ water, contaminants in a natural oxide film and contaminants on bare silicon can be simultaneously removed. (2) a high oxidation-reduction potential (ORP ≧ 1000 mV);
Since HCl / O ₃ water having a low pH (pH ≦ 3) is used, metal impurities (heavy metals and metals) and organic substances can be removed at the same time. (3) Due to the effects of O ₃ and ClO _x ⁻ in HCl / O ₃ water, organic substances desorbed from the surface of the semiconductor substrate are decomposed and removed (CO ₂ + H ₂ O + C _{x Hy} ). Therefore, accumulation of organic substances in the cleaning liquid and reattachment of the organic substances to the wafer are prevented. (4) C in HCl / O ₃ water and DHF or BHF
Since l, F, NH ₄ ^+, etc. are liable to form on the metal ligand,
The metal released from the semiconductor substrate under the acidic region forms a complex ion. Therefore, reattachment of the metal to the wafer is prevented. (5) A high-quality chemical oxide film is formed by the effect of O ₃ , and reattachment of the metal to the wafer is prevented.

In this case, in the present invention, it is preferable to use HCl / O ₃ water obtained by adding O ₃ to dilute hydrochloric acid of 5% or less. The chemical (HCl / O ₃ / H ₂ O)
/ BHF or DHF) is desirably obtained by adding 1% or less of DHF or BHF to HCl / O ₃ water. Further, the present invention can be particularly suitably used for cleaning the surface of a semiconductor substrate before growing a gate oxide film.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface of a semiconductor substrate prior to the growth of a gate oxide film is treated with a chemical solution (HCl) obtained by adding a very small amount (1% or less) of dilute hydrofluoric acid (DHF) or buffered hydrofluoric acid (BHF) to HCl / O ₃ water. / O ₃ / H ₂ O / BHF or DHF).

In the above chemical solution (HCl / O ₃ / H ₂ O / BHF or DHF), HCl / O ₃ water contains 5% or less of dilute hydrochloric acid (ordinary hydrochloric acid hydrogen peroxide: HPM is about 5% or more). It is preferable to use This HCl / O ₃ water
For example, it can be obtained by preparing diluted hydrochloric acid of 5% or less and then adding O ₃ thereto by a bubbling method. Finally, BHF or DHF is added by 1% or less to obtain the chemical solution (HCl / O ₃ / H ₂ O / BHF).
Or DHF) can be obtained. Note that BHF and DH
You may use together with F. In the present invention, the surface of the semiconductor substrate is cleaned with this chemical. The treatment is suitably performed at room temperature.

FIG. 1 shows a schematic view of the cleaning method of the present invention.
A semiconductor substrate contaminated with metal impurities (Fe, Ti, Cu, Pt, etc.) and an organic substance will be described as an example. First,
The semiconductor substrate is washed with a chemical solution (HCl / O ₃ / H ₂ O / BHF or D
When immersed in HF), the natural oxide film formed on the surface of the semiconductor substrate is removed.

At this time, organic substances taken into the natural oxide film and organic substances on the natural oxide film are removed. O ₃ and chloric acid (Cl 2) generated from HCl / O ₃ water
O _x ⁻ ) decomposes organic substances on the wafer surface and organic substances desorbed from the wafer surface into the cleaning solution. Therefore, accumulation of organic substances in the cleaning liquid and reattachment of organic substances to the wafer are prevented.

The particulate metal adhering to the natural oxide film is chloric acid (ClO _x ⁻ ) having a high oxidation-reduction potential (ORP ≧ 1000 mV) generated from HCl / O _3.
Is oxidatively decomposed and removed.

Metals such as Fe and Ti taken into the native oxide film as oxides are BHF or DHF.
Natural oxide film removing action by, ClO _x ^- in by pH effects of oxidative decomposition and HCl metals desorbed dissolved as metal ions (including complex ions) in the washing liquid.

Noble metal Cu and Pt have the property of adsorbing on the silicon interface as a single metal. That is,
Cu and Pt are unlikely to become metal oxides and have a high diffusion rate into the bulk. On the other hand, in the present invention, metal impurities such as Cu and Pt adsorbed on the silicon interface from which the natural oxide film on the surface of the semiconductor substrate has been removed by BHF or DHF can be used to remove ClO _x ^{− with} a high oxidation-reduction potential (ORP ≧ 1000 mV). , And desorbed and removed as an ionized product or oxide.

Next, a high-quality chemical oxide film is formed on the surface of the semiconductor substrate by the action of O ₃ , whereby Cu, P
Reattachment of metals such as t to the surface of the semiconductor substrate is prevented.

According to the present invention, a combination of the above-described series of the action of removing the natural oxide film, the action of oxidative decomposition and removal of organic substances and metal impurities, and the formation of a high-quality chemical oxide film, provide a clean product from which organic substances and various metal impurities have been removed. A semiconductor substrate surface can be obtained.

[0017]

As described above, according to the method for wet cleaning a semiconductor substrate according to the present invention, even if impurities are present on the bare silicon surface and in the natural oxide film and at the interface with the natural oxide film, the surface of the semiconductor substrate can be cleaned. Organic substances and metal impurities can be removed, and reattachment of these organic substances and metal impurities to the surface of the semiconductor substrate can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cleaning method of the present invention.

[Procedure amendment]

[Submission date] May 15, 2000 (2000.5.1)
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

According to the present invention, in order to achieve the above object, a semiconductor substrate is added to a chemical solution obtained by adding DHF (dilute hydrofluoric acid) or BHF (buffered hydrofluoric acid) to HCl / O ₃ water. By immersing the semiconductor substrate in the chemical solution at room temperature, a natural oxide film is removed from the surface of the semiconductor substrate, an organic substance and metal impurities on the surface of the semiconductor substrate are oxidized and decomposed, and a chemical oxide film is formed on the surface of the semiconductor substrate. And a wet cleaning method for a semiconductor substrate, wherein the method includes preventing organic substances and metal impurities from re-adhering to the surface of the semiconductor substrate.

Claims (4)

[Claims] 1. A wet cleaning method for a semiconductor substrate, comprising cleaning a semiconductor substrate surface with a chemical solution obtained by adding DHF (dilute hydrofluoric acid) or BHF (buffered hydrofluoric acid) to HCl / O ₃ water. 2. The wet cleaning method for a semiconductor substrate according to claim 1, wherein the HCl / O ₃ water is obtained by adding O ₃ to dilute hydrochloric acid of 5% or less. 3. The method for wet cleaning a semiconductor substrate according to claim 1, wherein said chemical solution is prepared by adding 1% or less of DHF or BHF to HCl / O ₃ water. 4. The wet cleaning method for a semiconductor substrate according to claim 1, wherein the surface of the semiconductor substrate before the gate oxide film is grown is cleaned with the chemical.