JPH08236494A - Wafer cleaner and method of cleaning the same - Google Patents

Abstract

PURPOSE: To immediately sense a mixture of many metal impurities into cleaning liquid and to suppress semiconductor wafer contamination with metal impurities. CONSTITUTION: A circulating tube to a cleaning bath of a wafer cleaner is equipped with a hydrogen peroxide concentration meter 6. A controlling part 7 is provided so as to transmit a signal representing whether or not it is possible to clean a wafer to a display board 17 and a carrier transfer system driving part 15 by data analysis in which measured data by the concentration meter 6 are compared to judgement data stored beforehand. When many metal impurities are mixed with cleaning liquid (APM), the decrease of hydrogen peroxide concentration becomes great comparing to a normal state. Therefore it is judged that there has been a mixture of metal impurities based on the change of the hydrogen peroxide concentration, the wafer cleaning is inhibited, the cleaning liquid (APM) is drained, the cleaner is cleaned and new cleaning liquid (APM) is supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer cleaning apparatus.

[0002]

2. Description of the Related Art In a wet cleaning process of a semiconductor wafer (hereinafter simply referred to as a wafer), a liquid (Ammoni) mixed with ammonium hydroxide, hydrogen peroxide and pure water is used.
umHydroxide Hydrogen Pero
xide Deionized Water Mix
ure: called APM), a mixture of hydrochloric acid, hydrogen peroxide and pure water (Hydrochlorica a)
cid Hydrogen Peroxide Dei
Animated Water Mixture: HPM), a mixture of hydrofluoric acid and pure water (Dilute)
d Hydrogen Fluorid (referred to as DHF), a mixture of sulfuric acid, hydrogen peroxide and pure water (Sul
furic acid Hydrogen Perox
(ideMixture: referred to as SPM) and a mixture of hydrofluoric acid, hydrogen peroxide and pure water (Hydrogen
n Fluoride Hydrogen Perox
side Deionized Water Mixtu
re: FPM) is used as the cleaning liquid.

[0003] APM is used for the purpose of removing fine particles adhering to the wafer surface, and is used for HPM, DHF, FP.
M is SP for the purpose of removing metal impurities on the wafer surface.
M is mainly used for removing organic impurities on the wafer surface. Although APM cleaning has a high effect of removing fine particles, it has no effect of removing metal impurities, and conversely has a drawback that if the solution contains metal impurities, it is easily adsorbed on the wafer surface. In a semiconductor device manufacturing process, a metal-based material is often used in the inside of a wafer processing apparatus, a wafer transfer jig, and the like, so that it easily adheres to the wafer surface, particularly the back surface. The wafer to which the metal impurities are attached is referred to as A
When put in PM, metal impurities dissolve in the liquid,
A clean wafer to be cleaned next is contaminated with metal impurities. Figure 7 shows metallic impurities (iron) contained in APM.
FIG. 4 is a graph showing a relationship between the concentration of a metal impurity (iron) and the concentration of metal impurities (iron) adhering to the surface of a wafer cleaned with the liquid. A
It is shown that as the concentration of metal impurities in PM increases, the concentration of metal impurities adsorbed on the wafer surface also increases.

Next, the influence of metal impurities attached to the wafer surface on the semiconductor element will be described with reference to the drawings. FIG. 8 shows that, in a MOS capacitor manufacturing process, a metal impurity (iron) is added to APM by cleaning immediately before formation of a gate oxide film, a wafer adjusted to a desired wafer surface metal impurity concentration is subjected to thermal oxidation treatment, and the gate oxidation is performed. It is the result of measuring the initial withstand voltage characteristic of the film. Here, the gate oxide film thickness was 8 nm, the gate area was 20 mm ² , and the breakdown determination current was 0.1 mA / cm ² . It has been shown that when the concentration of metal impurities (iron) on the wafer surface after APM cleaning is 10 ¹¹ atoms / cm ² or more, the yield rate of the gate oxide film is reduced. Therefore, the concentration of metal impurities (iron) on the wafer surface must be suppressed to 10 ¹¹ atoms / cm ² or less, and according to FIGS. 7 and 8, the amount of metal impurities (iron) in the APM is controlled to be 1 ppb or more. I know I have to do. This means that although the allowable concentration is different, metal impurities other than iron (nickel, chromium, zinc,
The same applies to gold, platinum, tungsten, titanium, etc.).

Further, in the case of HPM cleaning for the purpose of removing metal impurities, if a large amount of metal impurities is contained in the solution, a phenomenon that metal impurities adhere to the wafer surface may occur. Also, it is necessary to reduce the metal impurities in the liquid to an allowable concentration or less. The same applies to other hydrogen peroxide mixed solutions.

In the conventional wet cleaning method for a wafer,
The following method has been used as a method for suppressing the adhesion of metal impurities to the wafer surface during cleaning. That is, as shown in the flowchart of FIG. 9, several wafers for analysis are mixed with the wafer to be cleaned, and when the wafer cleaning is completed, the wafer for analysis is extracted, and the surface of the wafer is subjected to total reflection X-ray fluorescence X-ray analysis. Analysis and qualitative evaluation by microwave-photoconductivity decay method (usually called lifetime measurement). From these measurement results, it is determined that unacceptable metal impurities are mixed in the cleaning solution. In such a case, the wet cleaning operation was interrupted, and the liquid was exchanged and the cleaning device was cleaned.

[0007]

In this conventional method for wet cleaning of a semiconductor wafer, in the evaluation of metal impurity contamination, it is necessary to rely on an analytical method as a means of evaluation, and a considerable time is required from the start to the end of the evaluation. There is a problem that it costs. For example, in the case of total reflection X-ray fluorescence analysis, a metal impurity measurement wafer is placed in an analyzer, and it takes at least 30 minutes from the start of measurement to the end of measurement result analysis. In the case of lifetime measurement, it is necessary to form an oxide film on the surface of the measurement wafer before measurement and to make the wafer surface stable,
Spent more than hours. As described above, if time is spent on the measurement of the amount of metal impurities, since the wafer is wet-cleaned even during the measurement, if a large amount of metal impurities are mixed in the cleaning solution, the metal impurities may be removed. There is a problem that all the wafers processed by the wafer cleaning apparatus until the end of the quantity measurement are contaminated with metal impurities.

An object of the present invention is to provide a wafer cleaning apparatus and a wafer cleaning method in which a wafer is not cleaned with a cleaning liquid contaminated with metal impurities.

[0009]

According to a first aspect of the present invention, there is provided a wafer cleaning apparatus for cleaning a semiconductor wafer with a cleaning solution containing hydrogen peroxide, wherein the concentration meter measures the concentration of hydrogen peroxide in the cleaning solution. And a control unit for comparing and analyzing the measurement data sent from the densitometer with the judgment data stored in advance and sending a signal indicating whether or not the wafer can be washed to a display system or a wafer transfer system. Is what you do.

According to a second aspect of the present invention, there is provided a method for cleaning a wafer using a cleaning solution containing hydrogen peroxide, wherein the concentration of hydrogen peroxide in the cleaning solution is measured and the amount of change in hydrogen peroxide before and after the wafer cleaning is determined. The method is characterized in that the mixed amount of metal impurities is determined to determine whether or not the wafer can be cleaned.

[0011]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a wafer cleaning apparatus for explaining a first embodiment of the present invention, FIG. 2 is a flowchart of a metal impurity sensing system and a cleaning method, and FIG. 3 is a metal impurity having a hydrogen peroxide concentration before and after wafer cleaning. It is the graph showing the difference by the presence or absence of mixing.

Referring to FIG. 1, a cleaning tank 1 installed in a wet apparatus is provided with a pipe 3, a pump 4 and a filter 5 for circulating a cleaning liquid. A concentration meter 6 for measuring the concentration of hydrogen peroxide in the APM 2 is attached to the pipe 3, and information obtained from the concentration meter 6 is stored in a control unit including a device such as a memory, a comparison circuit, and a CPU. 7 The control unit 7 stores data (judgment value) of the lower limit of the hydrogen peroxide concentration in advance.
The information from the densitometer 6 is compared and analyzed with the lower limit data,
The result is sent to the display panel 17 and the wafer carrier transport system drive unit 15 so that the drive unit 15 can be controlled.

Next, a description will be given of a method of cleaning a wafer with a cleaning apparatus and a method of coping with mixing of metal impurities in the first embodiment with reference to FIGS. In this embodiment, APM is described as a cleaning liquid, and iron is used as a metal impurity mixed in the cleaning liquid. Further, the concentration of hydrogen peroxide in APM is generally used in the range of 4 to 6% in the cleaning process of a wafer, so the description will be made on the assumption that the concentration of hydrogen peroxide is 5%.

In a normal state, that is, when a large amount of metal impurities are not mixed, the decrease in the concentration of hydrogen peroxide in the APM liquid 2 after wafer cleaning is about 0.3% by weight at the maximum as shown in FIG. (The concentration of hydrogen peroxide in APM2 before wafer cleaning is 5% by weight, that is, the concentration of hydrogen peroxide in normal APM2 is reduced to 4.7% by weight at the maximum).
This change in concentration is due to reaction with a semiconductor wafer, leaving in the atmosphere, and the like, and by replenishing fresh hydrogen peroxide at regular intervals, the change in concentration in the cleaning tank 1 is suppressed. In case of abnormality, that is, when a large amount of iron is mixed in the liquid, A
The degree of decrease in the concentration of hydrogen peroxide in PM2 increases. For example, a case will be described in which a wafer having a large amount of iron adhered to its back surface is put into APM2, and 1 ppb of iron melts into APM2. When 1 ppb of iron is mixed, the concentration of hydrogen peroxide in APM2 after wafer cleaning is reduced by 0.5% by weight to 4.5% by weight as shown in FIG. The determination value (lower limit value) of the metal impurity contamination stored in the control unit 7 is the maximum decrease amount of the hydrogen peroxide concentration at normal time, that is, 4.7% by weight. Is determined, the operation of the wafer carrier transport system drive unit 15 is stopped to prevent the wafer from entering the cleaning tank 1, and at the same time, a message indicating the abnormality is displayed on the hydrogen peroxide concentration display plate 17 together with the concentration. In the case of the embodiment, since the value clearly exceeds the determination value, the cleaning processing of the next wafer is prohibited, the waste liquid of the APM2 mixed with the metal impurities, the cleaning of the cleaning tank 1, and the supply of the new APM2 to the cleaning tank 1. I do. When the supply of the new APM2 is completed, the prohibition of the next wafer cleaning operation is released, and the new AP
The cleaning operation of the wafer is started at M2.

FIG. 4 is a block diagram of a single wafer cleaning apparatus for explaining a second embodiment of the present invention, FIG. 5 is a flow chart of a metal impurity sensing system and a cleaning method, and FIG. It is a graph showing the difference in the concentration of hydrogen peroxide in APM depending on the presence or absence of metal impurities (iron).

The cleaning chamber 10 is provided with a suction plate 14 for holding and rotating the wafer 2 and a nozzle 11 for discharging the cleaning liquid 2 onto the wafer 8. The cleaning liquid 2 is adjusted to a desired mixing ratio in the new liquid storage tank 12 and sent to the nozzle 11 by the pump 4. The cleaning liquid 2 used for the wafer cleaning is collected in the old liquid storage tank 13 and reused as the cleaning liquid. A hydrogen peroxide concentration meter 7 is attached to the new liquid storage tank 12 and the old liquid storage tank 13 to measure the concentration of hydrogen peroxide in the new liquid and the used liquid, and store the data in a memory. , A CPU and the like. And the lower limit data (judgment value) stored in advance
The result is sent to the display panel 17 and the wafer transfer system drive unit 16 so that the drive unit 16 can be controlled.

Next, a wafer cleaning method in the single-wafer cleaning apparatus according to the second embodiment and a coping method when metal impurities are mixed will be described with reference to FIGS. In the second embodiment, as in the first embodiment, APM is used as the cleaning liquid, iron is used as the metal impurity mixed into the cleaning liquid, and the concentration of hydrogen peroxide is 5%.

The wafer 8 to be cleaned is adsorbed by the adsorption disk 14 and the inside of the cleaning chamber 10 is closed. When the sealing inside the cleaning champer 10 is completed, the APM stored in the new liquid storage tank 12 is sent to the nozzle 11 and discharged onto the wafer 8. At this time, the wafer 8 is rotating and the APM
2 uniformly covers the surface of the wafer 8. The APM 2 discharged onto the surface of the wafer 8 is collected in the old liquid storage tank 13 after cleaning the wafer 8. Then, the concentration of hydrogen peroxide in the APM 2 collected in the old liquid storage tank 13 is determined by the hydrogen peroxide concentration meter 6, and if the difference from the concentration of hydrogen peroxide in the new liquid is within the allowable range, the concentration of the hydrogen peroxide is determined. Liquid storage tank 1
Hydrogen peroxide is supplied to 3 and adjusted to a desired hydrogen peroxide concentration. Then, it is used again as a cleaning liquid.
The wafer 8 that has been cleaned by the APM 2 is rinsed by discharging pure water. Further, in some cases, after that, cleaning work with HPM, DHF, SPM, FPM, etc. is continuously performed.

As in the first embodiment, in a normal state, that is, when a large amount of metal impurities are not mixed, the change in the concentration of hydrogen peroxide in APM2 before and after the cleaning treatment is caused by the reaction with the wafer surface. As shown in FIG. 6, the maximum concentration is about 0.1% by weight (concentration of hydrogen peroxide in unused APM2 is 5% by weight, that is, peroxidation in APM2 at normal times). The hydrogen concentration is reduced to a maximum of 4.9% by weight). However, at the time of abnormality, that is, when a large amount of iron is mixed in the APM2 after the cleaning process is used, the difference in the concentration of hydrogen peroxide in the APM2 before and after the cleaning process is larger than in the normal case.

For example, a wafer having a large amount of iron adhered thereto is cleaned in the cleaning chamber 10 and the APM2 after the cleaning process is used.
When about 1 ppb of iron is mixed therein, the change in the concentration of APM2 before and after the use of the cleaning treatment is 0.5% by weight as shown in FIG. The determination value of the metal impurity contamination is the maximum decrease amount of the hydrogen peroxide concentration in the normal state, that is, 4.9% by weight. When the concentration becomes lower than this, it is determined that the metal impurity has been mixed, and the wafer transport system drive unit is determined. Stop the operation of 16,
The wafer 8 is prevented from entering the cleaning chamber 10, and at the same time, a message indicating the abnormality is displayed on the hydrogen peroxide display plate 17 together with the concentration. In the case of the second embodiment in which 1 ppb of iron was mixed, the determination value clearly exceeded the determination value. Therefore, the cleaning operation of the next wafer 8 was prohibited, and the iron stored in the old liquid storage tank 13 was mixed. Waste APM2,
The cleaning of the chamber 10, the old liquid recovery system piping, and the old liquid storage tank 13 are performed. And when the cleaning of the cleaning device is completed,
The prohibition of the cleaning operation of the wafer 8 is released, and the cleaning operation of the wafer 8 is performed with the new APM 2.

In the first and second embodiments, iron is taken as an example of the metal impurity mixed in the cleaning solution. In the case of iron, however, the reaction with hydrogen peroxide is particularly severe and the concentration of hydrogen peroxide decreases. Notable. However, since some metal impurities other than iron do not show a severe hydrogen peroxide decomposition reaction like iron even when mixed in a large amount, in consideration of all metal impurities that adversely affect semiconductor devices, First and second
It is desirable to judge that the metal impurities are mixed when the maximum variation amount in the normal state is exceeded, as in the embodiment.

In the above embodiment, the case where APM is used has been described, but the same effect can be obtained even when HPM or FPM is used. Although the description has been made on the assumption that the concentration of hydrogen peroxide in APM is 5%, as described in the first embodiment, the concentration of hydrogen peroxide is usually 4 to 6% in the wet processing of a semiconductor wafer. When performing a cleaning process at a concentration other than 5%, the amount of decrease in the concentration of hydrogen peroxide when no metal impurities are mixed is grasped in advance, and when the concentration exceeds the concentration, the control unit is controlled. 7 may be set so as to stop the operations of the wafer carrier transfer system drive unit 15 and the wafer transfer system drive unit 16.

Further, in the above-described embodiment, the description has been given of a method in which the control unit 7 automatically stops the cleaning operation when the metal impurities are mixed. However, the control unit 7 displays the hydrogen peroxide concentration and issues a warning sound. An abnormal method may be used, for example, by notifying an abnormality and stopping the wet processing operation by an operator.
Further, the operator may determine the concentration of hydrogen peroxide to determine whether or not to perform cleaning.

As described above, in the first and second embodiments, when a large amount of metal impurities are mixed in the cleaning solution due to cleaning of a wafer to which a large amount of metal impurities have adhered, the next wafer to be cleaned is replaced with a metal. Since impurity contamination can be prevented, a reduction in the diffusion yield in the semiconductor manufacturing process can be suppressed.

[0025]

As described above, according to the present invention, the wafer cleaning apparatus measures the concentration of hydrogen peroxide, and compares and analyzes the measured data from the concentration meter with the judgment data stored in advance. By providing a control unit that sends a signal indicating whether or not cleaning can be performed to the display system or the wafer transfer system, it is possible to detect metal impurity contamination in the cleaning solution without taking much time. Metal impurity contamination of the wafer can be prevented, and a decrease in the diffusion yield of the semiconductor manufacturing process can be suppressed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a wafer cleaning apparatus for explaining a first embodiment of the present invention.

FIG. 2 is a processing flowchart for explaining the first embodiment.

FIG. 3 is a graph showing a change over time in the concentration of hydrogen peroxide in APM for explaining the first embodiment.

FIG. 4 is a configuration diagram of a single wafer processing apparatus for explaining a second embodiment of the present invention.

FIG. 5 is a processing flowchart for explaining a second embodiment.

FIG. 6 is a graph showing a change in the concentration of hydrogen peroxide before and after using an APM cleaning process for explaining a second embodiment.

FIG. 7 is a graph showing a correlation between the concentration of iron in APM and the concentration of surface impurities of iron adhering to a wafer cleaned with the APM.

FIG. 8 is a diagram showing the relationship between the concentration of metal impurities on the wafer surface and the yield rate of the gate oxide film withstand voltage.

FIG. 9 is an evaluation flowchart of metal impurity contamination in a cleaning process using a conventional example.

[Explanation of symbols]

 1 Cleaning Tank 2 Cleaning Solution (APM) 3 Cleaning Solution Circulation Pipe 4 Pump 5 Filter 6 Hydrogen Peroxide Concentration Meter 7 Control Section 8 Wafer 9 Wafer Carrier 10 Cleaning Chamber 11 Nozzle 12 New Solution Storage Tank 13 Old Solution Storage Tank 14 Adsorption Board 15 Wafer carrier transfer system drive unit 16 Wafer transfer system drive unit 17 Hydrogen peroxide concentration display plate

Claims (6)

[Claims] In a wafer cleaning apparatus for cleaning a semiconductor wafer with a cleaning solution containing hydrogen peroxide, a concentration meter for measuring the concentration of hydrogen peroxide in the cleaning solution, and measurement data sent from the concentration meter and stored in advance. And a control unit for comparing and analyzing the judgment data and sending a signal indicating whether or not the wafer can be cleaned to a display system or a wafer transfer system. 2. A method for cleaning a wafer using a cleaning solution containing hydrogen peroxide, wherein a concentration of hydrogen peroxide in the cleaning solution is measured, and a mixed amount of metal impurities is determined from a change in hydrogen peroxide before and after the wafer cleaning. A method for cleaning a wafer, comprising determining whether or not the wafer can be cleaned. 3. The wafer cleaning apparatus according to claim 1, wherein the cleaning liquid is a mixed liquid of ammonium hydroxide, hydrogen peroxide, and water. 4. The wafer cleaning apparatus according to claim 1, wherein the cleaning liquid is a mixture of hydrochloric acid, hydrogen peroxide and water. 5. The wafer cleaning apparatus according to claim 1, wherein the cleaning liquid is a mixture of sulfuric acid, hydrogen peroxide and water. 6. The wafer cleaning apparatus according to claim 1, wherein the cleaning liquid is a mixture of hydrofluoric acid, hydrogen peroxide and water.