JPH04274324A - Wafer surface washing method - Google Patents

Abstract

PURPOSE:To enable degree of surface cleanness to be improved by washing a surface of a wafer using a mixed liquid of ammonium water, hydrogen peroxide water, and pure water and then washing the wafer with a dilution hydrochloric acid which is obtained by mixing a hydrochloric acid of a specific concentration with pure water in a specific volume ratio. CONSTITUTION:An Si wafer substrate is washed by using a washing liquid which is obtained by mixing ammonium water, hydrogen peroxide water, and pure water. Then, this Si wafer substrate is rinsed by pure water and further is washed by using a washing liquid which is obtained by mixing pure water with a hydrochloric acid with a concentration of 33-38% in a volume ratio of 10-10,000. The dilution hydrochloric acid is suppressed to a particle level by reducing the number of particles which exceed 0.20mum after circulation filtering to 10 pieces. Then, after it is washed in pure water, it is subjected to drying treatment, thus enabling a degree of cleanness of a surface of the substrate to be improved from both sides of particle level and metal level.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method for semiconductor Si wafers, and more particularly to a cleaning method that can improve the surface cleanliness of the wafer.

0002

2. Description of the Related Art In recent years, as the degree of integration of semiconductor devices has increased and pattern dimensions have become smaller, it has become necessary to further improve the surface cleanliness of Si wafer substrates.

Conventionally, a method for cleaning Si wafer substrates involves removing contaminants adhering to the wafer surface by sequentially passing the wafer through a number of cleaning tanks containing various chemical solutions.
A wet cleaning method called the so-called RCA cleaning method is generally adopted.

As the final chemical cleaning step of the wet cleaning method, there is cleaning (SC-1 cleaning) for the purpose of removing organic matter and particles (mostly crushed particles of silicon) on the surface of the silicon wafer. This cleaning is performed at a concentration of 28
% ammonia water, 30% hydrogen peroxide solution, and pure water in the following volume ratio. NH4OH:H2O2:H2O=1:1:5

0005
] By the way, in the above-mentioned cleaning, ammonia water and hydrogen peroxide water contain aluminum and heavy metal impurities, although in very small amounts (several parts per billion), and these metal impurities inevitably remain on the wafer surface after cleaning. There was a dissatisfaction that

[0006] These impurities pose a problem in LSIs having submicron pattern dimensions, so in order to remove these impurities, cleaning with the ammonia-based chemical solution described above and hydrofluoric acid to remove the impurities along with the natural oxide film are performed. A hydrochloric acid-based chemical solution made by mixing hydrochloric acid, hydrogen peroxide and pure water (H2O:H2O2:HCl=5:1:
1) (SC-2 cleaning) has been performed in combination.

[0007]

[Problems to be Solved by the Invention] However, in the above method, it is known that removing the natural oxide film with hydrofluoric acid adsorbs particles. Chemical solution (H2O:H2O2:
Although cleaning using HCl=5:1:1) is effective in removing metal ions, it is not effective in removing particles.
It was a known fact that this is usually done before the SC-1 cleaning.

[0008]

[Means for solving the problem] Therefore, the present inventors
As a result of intensive research to solve the above problems, we have discovered the following knowledge.

That is, the present inventors have discovered that by performing dilute hydrochloric acid cleaning after SC-1 cleaning, the metal level on the wafer surface can be reduced and the particle level on the surface is not worsened.

Furthermore, the dilute hydrochloric acid cleaning performed after SC-1 cleaning is effective when using extremely dilute hydrochloric acid, which is prepared by mixing pure water at a volume ratio of 10 to 10,000 to hydrochloric acid with a concentration of 33 to 38%. I discovered something.

The present inventors conjecture the reason for this as follows. In other words, the metal that adheres to the wafer surface during SC-1 cleaning is mainly Al that comes in from the cleaning solution, so it can be easily removed even with a dilute solution, and the surface is covered with a hydrophilic natural oxide film, so the particle level can be reduced. Don't make it worse.

The present invention has been made based on the above-mentioned knowledge, and the wafer surface cleaning method according to claim 1 uses a mixed solution of ammonia water, hydrogen peroxide solution, and pure water. After cleaning the surface of the wafer with
The volume ratio of pure water to 3-38% hydrochloric acid is 10-100.
This method is characterized in that the wafer is cleaned with dilute hydrochloric acid mixed at a ratio of 0.00 to 0.00.

In the wafer surface cleaning method according to claim 2,
After cleaning the wafer with diluted hydrochloric acid, the diluted hydrochloric acid after cleaning is filtered to suppress the number of particles of 0.20 μm or more contained in the diluted hydrochloric acid to 10 or less, and then the diluted hydrochloric acid is circulated and the wafer is washed again. It is characterized by being used for cleaning.

In the wafer surface cleaning method of claim 1, pure water and hydrochloric acid are mixed in the above-mentioned volume ratio because if the volume ratio of pure water is larger than the above-mentioned range, metal ion removal may be difficult. This is because the effect becomes too small, and conversely, if it is smaller than the above range, the particle level on the substrate surface becomes too bad.

In the wafer surface cleaning method of claim 2, the number of particles of 0.20 μm or more contained in dilute hydrochloric acid is suppressed to 10 or less because the number of particles of 0.20 μm or more is 10. This is because if the number of particles exceeds 1, the particles will adhere to the surface of the substrate and the particle level will deteriorate too much. Reduce particle level of dilute hydrochloric acid to 0
．． In order to suppress the number of particles of 20 μm or more to 10 or less,
Preferably, microfiltration is performed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The wafer surface cleaning method of the present invention will be explained in detail below with reference to the drawings.

(Embodiment) FIG. 1 is a process diagram showing an embodiment of the wafer surface cleaning method of the present invention. In this method, first, ■ ammonia water with a concentration of 27 to 31%, hydrogen peroxide solution with a concentration of 29 to 33%, and pure water are mixed in a volume ratio of 1.
A Si wafer substrate is cleaned at a temperature of 80° C. for 10 minutes using a cleaning solution mixed at a ratio of 1:5. (SC-1
Cleaning) (1) Next, this Si wafer substrate is rinsed with pure water, and (1) it is further cleaned using a cleaning solution prepared by mixing pure water with hydrochloric acid having a concentration of 33 to 38% in a volume ratio of 10 to 10,000. Here, the dilute hydrochloric acid is
The particles used were subjected to circulation filtration to reduce the number of particles of 0.20 μm or more to 10. ■
After washing with pure water, drying treatment (1) was performed.

In this wafer surface cleaning method, SC-
Since dilute hydrochloric acid treatment having the composition as described above is performed after the first cleaning, surface metal can be removed without reducing the particle level after the SC-1 cleaning.

(Experimental Example 1) FIG. 2 shows the metal level and particle level (0.
30 μm or more) on the HCl/H2O concentration ratio.

[0020] In the figure, the circles indicate the metal level adhering to the substrate surface after cleaning by the cleaning method of the present invention.
The triangular mark indicates the particle level on the surface of the same substrate. In addition, the black circles in the figure indicate the surface metal level when using a cleaning solution containing hydrochloric acid, pure water, and hydrogen peroxide, as in conventional SC-2 cleaning (Comparative Example 1). . Further, the black square mark indicates the metal level on the surface of the substrate subjected to only SC-1 cleaning without diluted hydrochloric acid treatment (Comparative Example 2).

According to FIG. 2, the metal level on the wafer surface cleaned with dilute hydrochloric acid within the range specified by the present invention is as follows:
Metal level on the wafer surface after only SC-1 cleaning (
It was found that the metal level was lower than that of Comparative Example 2), and that within the scope of the present invention, the metal level remained almost constant regardless of the HCl/H2O concentration ratio. Furthermore, it was found that the metal level on the wafer surface was lower when using the dilute hydrochloric acid cleaning solution specified in the present invention than when using a cleaning solution containing hydrogen peroxide like the conventional SC-2 cleaning. did.

Furthermore, in FIG. 2, it was found that the particle level on the surface of the wafer cleaned with dilute hydrochloric acid within the range specified in the present invention worsened as the HCl/H2O concentration ratio increased.

(Experimental Example 2) The relative amounts of each metal attached to the substrate surface were compared after the cleaning method of the present invention was applied and after only SC-1 cleaning was performed as a comparative example. Figure 3 (A
Figure 3(B) shows the results of comparing the relative amounts of Fe, Ni, Cu, and Zn attached to the wafer surface using TXRF (total internal reflection ) is used to compare the relative amounts of Na and Al attached to the substrate surface.

From this, it was found that the metal levels of Fe, Ni, Cu, Zn, Na, and Al were significantly reduced by applying the cleaning method of the present invention.

Furthermore, from the measurement results by SIMS, the Al level after applying the cleaning method of the comparative example was 1 to 0.7×1.
018 atoms/cm3, the Al level after applying the cleaning method of the present invention is 8 to 6 x 1016 atoms
It was found that the amount decreased significantly to /cm3.

(Experimental Example 3) FIG. 4 shows particles on the substrate surface after the cleaning method of the present invention was applied using a He-Ne laser and after the cleaning method of a comparative example without dilute hydrochloric acid treatment was applied. The results of level measurement are shown below.

This figure shows that the particle level after applying the cleaning method of the present invention is almost the same as the particle level after applying the cleaning method of the comparative example without diluted hydrochloric acid treatment. It turns out that it doesn't get worse.

(Experimental Example 4) A substrate subjected to the cleaning process of the example and a substrate subjected only to SC-1 cleaning as a comparative example were prepared, and an accelerated fog evaluation test was conducted. The test conditions were 1 cycle: heating up from room temperature to 70°C, holding at 70°C for 5 minutes, cooling down to 5°C, and holding at 5°C for 1 hour, and three cycles were performed. As a result, no difference was observed between the cleaned products of the example and the comparative example.

[0029] Also, it is formed by the CZ method and is P type with <100
Two wafers (resistance: 8.5 to 11.5 Ω) were prepared, and one of them was subjected to the cleaning process of the example, and the other was subjected to the cleaning process of the comparative example, and a pressure resistance test was conducted. As a result, the breakdown voltage of the sample treated in the example was 9.26 MV/cm, and the breakdown voltage of the sample in the comparative example was 9.12 MV/cm, and no significant difference was observed between the two.

[0030]

As explained above, in the wafer surface cleaning method of the present invention, after cleaning the wafer surface using a mixed solution of ammonia water, hydrogen peroxide solution, and pure water, Furthermore, the wafer is cleaned with diluted hydrochloric acid, which is a mixture of 33% to 38% concentrated hydrochloric acid and pure water at a volume ratio of 10% to 10,000%, thereby maintaining a good particle level on the wafer surface. Metal levels on the wafer surface can be reduced.

Therefore, according to the wafer surface cleaning method of the present invention, the cleanliness of the substrate surface can be improved from both the particle level and metal level.

After cleaning the wafer with diluted hydrochloric acid, the diluted hydrochloric acid after cleaning is filtered to suppress the number of particles of 0.20 μm or more contained in the diluted hydrochloric acid to 10 or less, and then this diluted hydrochloric acid is circulated. If the diluted hydrochloric acid is then used again to clean the wafer, the diluted hydrochloric acid can be used effectively and there is no fear of worsening the particle level on the substrate surface.

[Brief explanation of the drawing]

FIG. 1 is a process diagram for explaining the wafer surface cleaning method of the present invention.

FIG. 2 is a graph showing the relationship between particle level and surface metal level versus HCl/H2O concentration.

FIG. 3 is a graph showing the level of metal deposited on a substrate surface.

FIG. 4 is a graph showing the particle level on the substrate surface.

Claims (2)

[Claims] Claim 1: After cleaning the surface of the wafer using a mixed solution of ammonia water, hydrogen peroxide solution, and pure water, pure water is further added to hydrochloric acid with a concentration of 33 to 38% in a volume ratio. A wafer surface cleaning method comprising cleaning the wafer with dilute hydrochloric acid mixed at a ratio of 10 to 10,000. 2. After cleaning the wafer with the diluted hydrochloric acid, the diluted hydrochloric acid after cleaning is filtered to suppress the number of particles of 0.20 μm or more contained in the diluted hydrochloric acid to 10 or less, and then the diluted hydrochloric acid is 2. The method for cleaning a wafer surface according to claim 1, wherein the wafer is circulated and used again for cleaning the wafer.