JPH02257631A - Cleaning of semiconductor wafer - Google Patents

Abstract

PURPOSE:To obtain a semiconductor water whose gettering effect is high by a method wherein it is cleaned by using a hydrofluoric-acid-based cleaning liquid in a light-shielding state. CONSTITUTION:An SiO2 powder is sprayed on the rear of a semiconductor wafer; as a result, a mechanical strain is caused on the rear of the semiconduc tor wafer; after that, when the semiconductor wafer is cleaned by using a hydrofluoric-acid-based cleaning liquid, the semiconductor wafer is cleaned in a light-shielding state. Thereby the semiconductor wafer whose mechanical strain is large can be obtained; the semiconductor wafer whose gettering effect is high can be formed.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to semiconductor manufacturing technology and semiconductor wafer cleaning technology, and more specifically to mechanical strain (BSD; backside damage )
The present invention relates to a technique that is effective when applied to cleaning performed after forming a semiconductor wafer on the back surface of a semiconductor wafer.

[Prior Art] An important issue in device manufacturing is the prevention of contamination by impurity atoms that are harmful to device characteristics. Conventionally, various gettering techniques have been used to trap such harmful impurities in areas other than the device region.

One of these techniques is to spray SiO□ powder onto the backside of a semiconductor wafer, thereby forming backside damage on the backside of the semiconductor wafer, and capturing harmful impurity atoms by this backside damage. Such a technique is generally called sandblasting.

By the way, in this technique, after backside damage is formed on the backside of the semiconductor wafer, HF cleaning is performed to remove SiO, powder, and other impurities adhering to the backside of the semiconductor wafer.

[Problems to be Solved by the Invention] However, after performing the above-mentioned cleaning, the backside damage existing on the backside of the semiconductor wafer is altered by thermal oxidation, and after selective etching, the backside damage existing on the backside of the semiconductor wafer is When stacking faults (OSF) were counted using a microscope, the following was found.

In other words, during the above-mentioned HF cleaning, a basket is used to process semiconductor wafers in batches, but it was found that there were variations in O8F density among the semiconductor wafers set in this basket, and the variation was large. The figure shows the results of this experiment.

In this experiment, a P-type semiconductor wafer 2 cut out from one ingot manufactured by the Czochralski method (CZ method) was used.

Also, as a basket, Fig. 8 (A).

As shown in (B), the wall 1a at its longitudinal end.

Baskets 1 in which 1b is H-shaped and H-shaped are used, and when setting the semiconductor wafers 2 in each basket 1, the SB surface (sandblast surface) of each semiconductor wafer 2 is oriented toward the U Ml, 1 a side. A semiconductor wafer 2 for monitoring was set in the basket 1.

Then, after performing HF cleaning using basket 1 as described in -, thermal oxidation was performed to change the quality of the sandblasting damage. Furthermore, selective etching was performed using a dilt-etching solution, and O5F on the back surface of the semiconductor wafer 2 was counted using a microscope. This O8F count is U
Wall 1. A semiconductor wafer 2 on the a side and the H wall lb side,
The test was performed on three semiconductor wafers 2 located at the center of the three semiconductor wafers 2.

From FIG. 7, the semiconductor wafer 2 at the U position and the C position
O8F density of semiconductor wafer 2 is high and O8F density of semiconductor wafer 2 at H position is high.
It can be seen that the F density is extremely low. Furthermore, the overall O8F density varied widely. In FIG. 7, U and H respectively indicate the t, J wall 1a side and H wall lb side positions of the basket 1, and C indicates their center position.

The inventor further conducted the following experiment to investigate the cause.

In other words, we believe that the cause of the decrease in O8F density and the variation in O8F density in the semiconductor wafers 2 other than the semiconductor wafers 2 at the U and C positions is due to the process after the backside damage is formed, and HF cleaning is performed after the backside damage is formed. As a result of comparing those with and without I(F cleaning), it was confirmed that the O8F density of the semiconductor wafer 2 on the H side was extremely lower when I(F cleaning was performed. It was found that the cause of the decrease in O3F density was mainly due to HF cleaning.

Subsequently, in order to investigate the cause of the O3F density decrease in the H-side semiconductor wafer 2 after HF cleaning, experiments were conducted under various conditions.

First, basket 1 during HF cleaning in the HF cleaning tank.
In order to investigate the influence of the inclination of the SB plane and the influence of the direction of the SB plane, we changed the direction of the SB plane and compared the basket 1 with the U wall 1a side facing toward the front and the side toward the back. The results are shown in FIGS. 9(A) to 9(D).

From these drawings, it can be seen that the O8F density of the basket 1 with the U u 1 a side (No. side) facing toward the front is approximately equal to that of the basket 1 facing toward the back.

This indicates that the decrease in O8F density occurs in basket 1 during HF.
It can be seen that it is not affected by the slope of

Furthermore, from FIGS. 9(A) to (D), it is clear that the semiconductor wafer 2 at position C is O8 even if the orientation of the SB surface is changed.
On the other hand, there was no significant change in F density.

It can be seen that for the semiconductor wafers 2 at positions U and H, the O8F density decreases when the SB surface faces inward of the basket 1.

In order to find out the cause of this, we conducted a series of experiments and found that the cause was the irradiation of light. In other words, it has been found that when HF cleaning is performed under illumination, O8F density decreases and large variations occur.

The present invention was made based on this knowledge, and an object of the present invention is to provide a cleaning technique that can obtain a semiconductor wafer with a large amount of bag side damage and a high gettering effect.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] Representative inventions disclosed in this application will be summarized as follows.

That is, the present invention sprays Sio2 powder onto the back surface of a semiconductor wafer, thereby forming mechanical strain on the back surface of the semiconductor wafer, and then cleaning the semiconductor wafer with a hydrofluoric acid-based cleaning solution. This is done in a light-shielded state.

[Function] According to the above-described means, since cleaning is performed with a hydrofluoric acid-based cleaning liquid in a light-shielded state, a semiconductor wafer with many backside damages on the back surface of the semiconductor wafer can be obtained. As a result, it becomes possible to manufacture a semiconductor wafer with a high gettering effect.

[Example] Hereinafter, an example of the semiconductor wafer cleaning method according to the present invention will be described.

In this example, backside damage was formed by spraying SiO2 powder onto the backside of a semiconductor wafer. Next, HF cleaning was performed. In addition, during HF cleaning, the cleaning tank was made of opaque PvC resin and covered with an opaque lid having a light-blocking effect, so that no light was exposed to the semiconductor wafer during HF cleaning.

After that, the O8F density on the back surface of the semiconductor wafer was evaluated. The conditions and results at that time are shown below and in FIG. In the figure, the horizontal axis shows the position of the semiconductor wafer in the basket, and the vertical axis shows the O8F density.

1. Conditions (1) Semiconductor wafer P-type wafer of 100 mm diameter with orientation <111> and resistivity 1.10 to 1.55 Ωl cut from one ingot manufactured by the Czochralski method (CZ method). A semiconductor wafer was used.

(2) Sandblasting (Formation of Mechanical Strain) SiO powder was sprayed onto the wafer to form backside damage on the back surface of the semiconductor wafer.

(3) Setting in the basket As shown in FIG. 2, ten semiconductor wafers for monitoring were set at predetermined intervals from the U side to the H side of the basket 1. At this time, the SB surface of the semiconductor wafer was made to face the U side in the basket 1. In this way, the semiconductor wafer is set and the basket 1 is
I prepared 4 pieces.

(4) HF cleaning Two baskets 1 are actively irradiated with light, and the other two baskets 1 are subjected to HF cleaning while the light is blocked.
F cleaning was performed.

(5) Formation of thermal oxide film The semiconductor wafer was placed in a wet 02 atmosphere at 1100° C. for 60 minutes to form a thermal oxide film on the semiconductor wafer.

(5) Selective etching A semiconductor wafer was selectively etched using a dilute etching solution.

(6) Measurement of O8F density The O3F density on the back side of the semiconductor wafer was measured using a microscope.
9. Note that the measurement points in this experiment were three points: center A of the semiconductor wafer, point B 25 m from the periphery, and point C 8 meters from the periphery.

2. Experimental results The results are shown in FIG.

From FIG. 1, it can be seen that the O8F density is higher and more stable in the case where HF cleaning was performed while blocking light, compared to the case where HF cleaning was performed while irradiating light. Furthermore, when similar evaluations were performed with all the SB planes facing the semiconductor wafer facing the H side, substantially the same results as above were obtained.

Note that among those irradiated with light and subjected to HF cleaning, the reason why the O8F density of the first semiconductor wafer on the U side is high is that the SB surface of this semiconductor wafer faced outward. It seems to be.

The reason for this will be discussed later.

Furthermore, in order to confirm the effect of light blocking, we compared a structure in which light was blocked and a structure in which light was actively irradiated to the opposite surface from the SB surface. As a result, it was found that the O8F concentration in the case where the light was blocked was more than twice as high as that in the case where the light was irradiated. The measurement points are as shown in Figure 3.
There are three points: point B, which is 2511I11 from the periphery of the center A1 of the semiconductor wafer 2, and point C, which is 8 m from the periphery.

Next, we will add a theoretical consideration to the above results.

As shown in FIG. 4, for example, the P-type semiconductor wafer 2 holds holes as majority carriers.

By irradiating the semiconductor wafer 2 with light, minority carriers are excited. It is thought that the amount of minority carriers increases as the illuminance of the light increases, and that the longer the wavelength of the light, the deeper the excitation effect occurs. The minority carriers excited by the light in this way move inside the semiconductor wafer 2,
It is thought that it disappears in the defective SB strained layer (backside damage M). Due to the energy generated at that time, a stain film is generated on the front side of the semiconductor wafer 2, and a part of the backside damage is thereby altered.
As a result, Sand Plus! - O8F when evaluating effectiveness
It is thought that the density will decrease.

Furthermore, when the SB surface is irradiated with light, the excitation of minority carriers is small because the SB surface has irregularities. the result,
It seems that a stain film is difficult to form.

Note that a different trend is observed when comparing the decrease in O8F density in the normal process and the decrease in O8F density in the case of actively performing light irradiation.

In other words, in a normal process, H
While a decrease in O8F density is observed only at the side, when active light irradiation is performed, a decrease in O3F density is also observed at position C, as shown in FIG. 5(A).

The reason for this is inferred as follows.

When light hits the semiconductor wafer 2 in the normal process as shown in FIG. In the wafer 2, since the light energy is weak, the excitation effect to the extent that a stain film is generated does not occur. As a result, the semiconductor wafer 2 on the U side and the C position
In this case, no decrease in O8F density occurs. On the other hand, in the semiconductor wafer 2 on the H side, a positive voltage is applied to the SB surface due to the excitation effect from the E surface (the etched surface opposite to the SB surface), resulting in the formation of a stain film.

A decrease in O5F density occurs.

On the other hand, when the light is actively irradiated as shown in FIG. 5(B), the excitation effect from the SB side is strong on the semiconductor wafer 2 on the U side, and a reverse voltage is applied, causing the stain film to Not generated. This point is the same as in the normal process. However, in the semiconductor wafer 2 at position C,
The light energy is filled and the excitation effect from the E plane is strong <, SB
A positive voltage is applied to the surface and a stain film is generated. Also,■
(In the semiconductor wafer 2 on the side, a positive voltage is applied to the SB due to the excitation effect from the E surface (the etched surface opposite to the SB surface).
A stain film is formed on the surface. As a result, the O8F density decreases at the C position and the H side of the semiconductor wafer 2.

According to the semiconductor wafer cleaning method of Example 1, the following effects can be obtained.

That is, according to the semiconductor wafer cleaning method of the above embodiment, when performing HF cleaning on the semiconductor wafer after backside damage (mechanical strain) is formed on the back surface of the semiconductor wafer, the semiconductor wafer is cleaned in a light shielded state. As a result, a semiconductor wafer having a large amount of mechanical strain can be obtained. As a result, it becomes possible to manufacture a semiconductor wafer with a high gettering effect.

Further, since the variation in the occurrence of mechanical strain is small, it is possible to obtain a highly reliable semiconductor wafer.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above-mentioned Examples, and can be modified in various ways without departing from the gist thereof. Nor.

For example, in the semiconductor wafer cleaning method of the above embodiment,
Although the case of HF cleaning has been explained as an example, it can generally be used when a hydrofluoric acid-based cleaning solution is used.

Furthermore, the semiconductor wafer used above was formed by the C7 method, but the floating zone method (F
It can also be used for those formed by Z method).

It can also be used for semiconductor wafers with different orientations and N-type semiconductor wafers.

Furthermore, the semiconductor wafer cleaning method of the above-described embodiments can be applied to general cleaning of semiconductor wafers before the mechanical strain of the semiconductor wafer deteriorates due to, for example, the formation of a thermal oxide film.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below.

That is, in the present invention, SiO2 powder is sprayed onto the back surface of the semiconductor wafer, thereby creating mechanical strain on the back surface of the semiconductor wafer, and then the semiconductor wafer is cleaned with a hydrofluoric acid-based cleaning solution.

- Since the cleaning of the above 64-piece wafer is performed in a light-shielded state, semiconductor wafers with many mechanical strains can be obtained. As a result, semiconductor wafers with high gettering effects can be manufactured. By performing HF cleaning in a light-shielded state, the various stains that had previously occurred were completely eliminated.

[Brief explanation of drawings]

Figure 1 is a graph showing the results of an experiment to confirm the effects of this example. Figure 2 is a diagram showing the set state of the semiconductor wafer during the experiment shown in Figure 1. Figure 3 is a graph showing the set state of the semiconductor wafer during the experiment shown in Figure 1. FIG. 2 is a plan view of a semiconductor wafer showing O8F measurement points. Figure 4 is a diagram explaining the principle of stain film formation, Figure 5 (A) is a graph showing the decrease in O8F density when actively irradiated with light, and Figure 5 (CB) is a graph showing the decrease in O8F density when actively irradiated with light. FIG. 3 is a diagram showing the light irradiation state and the flow of electrons in this case. Fig. 6 is a diagram showing the light irradiation state and electron flow in the normal process, Fig. 7 is a graph showing the O8F density decrease in the normal process, Fig. 8 (A) is a perspective view of the basket, Fig. 8 (B ) is a rear view of the basket, and FIGS. 9(A) to (D) are graphs showing changes in O8F density depending on the inclination of the basket and the orientation of the SB surface. Figure 1 Basketball:,, 1-) Q place 1 Figure 2 Figure Roeko Figure Tayotsugu Figure 5 (A) Figure 5 (B) Kuko l E country Figure (A) Figure 1 Figure 9 CB) Figure 9 (A) Figure (C)

Claims (1)

[Claims] 1. After mechanical strain is formed on the back surface of the semiconductor wafer, the semiconductor wafer is cleaned with a hydrofluoric acid-based cleaning solution, and the semiconductor wafer is cleaned in a light-shielded state. A method for cleaning semiconductor wafers. 2. The cleaning of the semiconductor wafer according to claim 1, wherein after the mechanical strain is formed by spraying SiO_2 powder, the semiconductor wafer is cleaned with a hydrofluoric acid-based cleaning liquid in a light-shielded state. Method.