JPS61281532A - Concentration adjustment of washing liquid for semiconductor and its device - Google Patents

Abstract

PURPOSE:To enable automatic concentration adjustment of washing liquid to be performed by a method wherein the concentration of ammonia is measured with ratio of the ultraviolet ray absorption luminous intensity of the gathered washing liquid to the ultraviolet ray absorption luminous intensity of the washing liquid whose hydrogen ion concentration is less than 4, and the concentration of the component of the washing liquid is continuously and automatically adjusted with a microcomputer. CONSTITUTION:The amount of the ultraviolet ray absorption of the probe liquid is measured at an oxygen concentration measuring section 6, 11, and the concentration of hydrogen peroxide and ammonia is calculated on the basin of the measured value so as to evaluate whether the calculated concentration is within the targeted concentration. If the concentration is too low, electromagnetic valves 19, 19' are opened so as to calculate the time to add hydrogen peroxide and ammonia t, t'. If the concentration is too high, a pump 25 is activated so as to calculate the time to add pure water t'' and perform the adding. Thus, the concentration of hydrogen peroxide and ammonia in the washing liquid is controlled so as to evaluate whether the temperature of the washing liquid is within the set range. If the measured value of the liquid temperature is within the set range in accordance with a thermometer 30, an Si wafer is washed for specified time, thereby achieving the recovery and extended lifetime of washing liquid and stabilized washing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for adjusting the component concentration of a cleaning liquid used for cleaning, for example, 8i wafers.

[Background of the invention]

In general, a cleaning solution for cleaning Si wafers using hydrogen peroxide, ammonia, and water is often heated to 80°C, so the hydrogen peroxide decomposes and the ammonia evaporates in just a few minutes due to thermal decomposition. Deterioration of the cleaning solution occurs.

Conventionally, the components of a cleaning solution in use have been confirmed as follows. In other words, either off-line and time-consuming component analysis methods such as titration are used, or a method that uses an ion electrode to measure ammonia concentration and a method that uses ultraviolet absorption to measure hydrogen peroxide concentration are used in combination. ■7 to confirm. (% Kaiwa No. 59-46052) However, off-line methods such as titration are time-consuming and impractical, and with an ion electrode for measuring ammonia concentration, the ammonia gas passing through the diaphragm and the electrode Since the chemical reaction with the internal liquid is used, the life of the electrode is short, causing problems in maintainability, and the responsiveness is also poor, making it difficult to precisely control the chemical management in the cleaning liquid.

In order to solve the above problem, the inventors focused on the following points and came to solve the problem.

The basic principle will be explained below.

When oxygen is dissolved in an aqueous solution, a very characteristic absorption band appears in the ultraviolet region. FIG. 1 is a diagram showing changes in the absorbance of oxygen and ammonia with respect to ultraviolet wavelengths due to hydrogen peroxide.

In FIG. 1, the curve α is a curve showing the absorbance of oxygen only by hydrogen peroxide, and the curved line is the curve showing the absorbance of only ammonia. As can be seen from the graph in Figure 1, both oxygen and ammonia due to hydrogen peroxide have a wavelength of 194
It has an absorption peak in the ultraviolet region around nm, and it is difficult to distinguish between the two near the peak. However, the absorption spectrum of oxygen by hydrogen peroxide is broad, and even around 500 rLrIL, where the absorption of ammonia is almost zero, it still shows considerable absorption. Therefore, by measuring the absorbance at around 50 Onm, it is possible to independently measure only the oxygen due to hydrogen peroxide in the collected sample of the cleaning liquid in which ammonia, hydrogen peroxide, and water coexist.

However, the above Ik bath solution oxygen concentration is affected by the hydrogen ion concentration of the solution.

FIG. 2 is a diagram showing the change in absorbance of ultraviolet rays when the ammonia concentration of the aqueous solution is changed and the hydrogen ion concentration of the solution is changed. According to this figure, when the hydrogen peroxide concentration is kept constant and the ammonia concentration is increased, absorption in the ultraviolet region also increases as shown by curve C. However, if an excess of acid is added to this aqueous solution and the hydrogen ion concentration of the aqueous solution is always kept below 4, the absorbance in the ultraviolet region is constant regardless of the ammonia concentration, as shown by curve d. In other words, when the hydrogen ion concentration is 4 or more, when ammonia and hydrogen peroxide coexist, a buffering effect acts in the aqueous solution, and oxygen in hydrogen peroxide dissociates in proportion to the ammonia concentration, resulting in the amount of oxygen in the aqueous solution. As a result, the absorption of ultraviolet light by oxygen also increases.

FIG. 5.4 is a diagram showing the principle of determining the concentration of hydrogen peroxide and ammonia in the actual sample collected from the cleaning liquid.

FIG. 5 is a graph showing the relationship between the absorbance in the ultraviolet region and the hydrogen peroxide concentration when an acid is added to a sample of the cleaning liquid to reduce the hydrogen iodine concentration to 4 or less. As can be seen from the graph in FIG. 3, the hydrogen peroxide concentration in the sample of the cleaning liquid to which an acid has been added to reduce the hydrogen ion concentration to 4 or less can be determined by measuring the absorbance in the ultraviolet region.

FIG. 4 is a graph showing the relationship between the absorbance ratio in the ultraviolet region and the ammonia concentration when no acid is added to the sample of the cleaning liquid and when acid is added. As can be seen from the graph in Figure 4, the ammonia concentration in the sample of the cleaning solution is the absorbance in the ultraviolet region when no acid is added (hydrogen ion concentration 4 or more) and when acid is added (hydrogen ion concentration 4 or less). It can be determined by measuring the ratio of

Based on the above principle, the hydrogen peroxide concentration in the cleaning solution can be determined by measuring the absorbance of ultraviolet rays when the hydrogen ion concentration in the cleaning solution is 4 or less, and the ammonia concentration can be determined by
This can be determined by determining the absorbance ratio of ultraviolet rays when the hydrogen ion concentration in the cleaning solution is 4 or more and 4 or less, and we have developed an actual measuring device and automatic concentration adjustment device to measure this.

[Purpose of the invention]

The present invention has been made based on the above-mentioned principle, and provides a method and apparatus for adjusting the concentration of a cleaning liquid, which enables automatic adjustment of the concentration of the cleaning liquid by detecting the component concentration of the cleaning liquid in a short time and with high precision. This is what we intend to provide.

[Summary of the invention]

That is, the method according to the present invention detects the ultraviolet absorbance of the collected cleaning liquid and the cleaning liquid with a hydrogen ion concentration of 4 or less,
The sampled cleaning liquid is introduced into a flow cell for measuring transmitted light, irradiated with an ultraviolet light source, and the absorbance of ultraviolet light is detected with an ultraviolet detector. On the other hand, a cleaning solution with a hydrogen ion concentration of 4 or less is introduced into another flow cell, irradiated with an ultraviolet light source, and the absorbance of ultraviolet rays is detected with an ultraviolet detector. The two detection values detected in this manner are input into the interface, and the hydrogen peroxide concentration and ammonia concentration in the collected cleaning liquid are calculated by a microcomputer and compared with a predetermined concentration stored in the memory. This difference is automatically supplied from the hydrogen peroxide and ammonia supply sources.

In addition, as a device for carrying out the above method, a pump is provided to guide the cleaning liquid to a transmitted light flow cell, and an oxygen pump containing an ultraviolet light source, a flow cell, and an ultraviolet detector is provided to detect the ultraviolet absorbance of the cleaning liquid collected by this pump. A concentration measuring section is provided. On the other hand, in addition to this, a hydrochloric acid supply system is installed to reduce the hydrogen ion concentration of the collected cleaning liquid to 4 or less, and an ultraviolet light source is used to detect the ultraviolet absorbance of the cleaning liquid whose hydrogen ion concentration is reduced to 4 or less. , an oxygen concentration detection section incorporating a flow cell and an ultraviolet detector is provided.

Based on the detected and output values of the two ultraviolet absorbances detected by the two oxygen concentration detectors mentioned above, the hydrogen peroxide concentration and ammonia concentration in the cleaning liquid are calculated, and these concentrations are compared with the predetermined concentration stored. A microcombination unit and a user having a function of controlling solenoid valves for supplying predetermined amounts of hydrogen peroxide and ammonia are installed, and solenoid valves controlled by this K are installed in the hydrogen peroxide and ammonia co-feeding system, respectively. It is characterized by:

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below.

In FIG. 5, 12 is a cleaning liquid stored in the cleaning tank 1. 5 is a motor for raising the temperature of the cleaning liquid 2. 4
is the Si wafer to be cleaned.

5 is a pump for collecting cleaning liquid. Reference numeral 6 denotes an oxygen concentration measuring section, which includes a built-in unit for measuring transmitted light, a flow self, an ultraviolet light source 8, and an ultraviolet detector 9. Reference numeral 10 denotes a pump for collecting cleaning liquid, and in this embodiment, it is directly connected to a flow cell for measuring transmitted light. Of course, the pump 10 may be directly connected to the cleaning tank 1. Reference numeral 11 denotes an oxygen concentration measuring section provided separately, and like 6, 1 flow cell for measuring transmitted light 12. An ultraviolet light source 15 and an ultraviolet device 14 are built-in. 15 pumps hydrochloric acid 16 to pump 1 so that the hydrogen ion concentration in the cleaning solution is 4 or less.
A pump P17 for supplying a discharge side pressure of 0 is an interface for inputting the absorbance of ultraviolet rays detected by the ultraviolet detectors 9 and 14 to the microcomputer 22.

The microcomputer 22 has the interface 1
The function calculates the concentration of hydrogen peroxide and the concentration of ammonia based on the two detected values input from 7. It has a function to compare hydrogen peroxide and ammonia) and a solenoid valve control function to supply predetermined values of hydrogen peroxide and ammonia obtained by this comparison. 1B is an electric/magnetic valve control section. 19.19
This is a solenoid valve that is controlled by an operation command from the H microcomputer 22 via the solenoid valve control section 1B. 20
21 is a hydrogen peroxide tank, and 21 is an ammonia water tank. Reference numerals 25 and 24 are discharge ports for the collected liquid, and 25 is a pump for supplying pure water 26 into the cleaning tank 1. 27 is a liquid level sensor, 50 is a thermometer, 2B is a circulation pump, and 29 is a filter.

The operation of this embodiment configured as above will be explained next.A cleaning tank 1 is filled with a cleaning liquid 2 consisting of hydrogen peroxide, ammonia, and water and heated by a heater 5.
I am cleaning the Uni No 4. A part of the cleaning liquid 2 is sampled by the sampling pump 5 and sent to the flow cell of the oxygen concentration measurement section 6, and the oxygen concentration in this flow cell is measured using a wavelength of 500nrn, which is composed of a lamp that emits ultraviolet light such as an Hf lamp, a monochromator, etc. Absorption is measured using a nearby ultraviolet light source 8 and a detector 9 for the transmitted light.

The collected sample of the cleaning liquid subjected to ultraviolet absorption measurement in the flow self is further sent to the flow cell 12 of the oxygen concentration measurement section 11 by the pump 10, and then discharged from the discharge port 24. During this discharge, hydrochloric acid 16 is added by the pump 15 to reduce the hydrogen ion concentration to 4 or less. Measurements of hydrogen oxide concentration are made. On the other hand, both this value and the value of the oxygen concentration measuring section 6 are sent to the interface 17. The ammonia concentration is calculated by the microcomputer 22 from the two sent measurement values. Due to the above, cleaning tank 1 at approximately the same time
The concentration of hydrogen peroxide and ammonia in the water is measured. Of course, in this case, the sample for measuring the hydrogen peroxide concentration may be directly collected from the cleaning tank in parallel with the sample for measuring the ammonia concentration. The measured hydrogen peroxide concentration and ammonia concentration data are compared and referenced with cleaning liquid concentration data stored in the microcomputer 22 in advance. Based on the difference between the stored data and the actual concentration, a command is given to the solenoid valve control unit 1B based on a program given in advance to the microcomputer 22, and the solenoid valves 19, 19' are opened/closed 1-, tanks 20, 2.
From 1 to 1, the required amount of hydrogen peroxide and ammonia is added to cleaning tank 1.
Due to this K, the concentration of hydrogen peroxide and ammonia in the cleaning liquid 2 is kept within a certain range, and stable cleaning of the Si wafer is performed.

Next, a method for adjusting the density using the above embodiment will be explained using FIG. 6 while referring to FIG. 5.

When starting with a step person, the pure water replenishment pump 25 is turned on (step B).

The water level in the cleaning tank 1 is measured by the liquid level sensor 27 (step C), and it is determined whether the water level in the cleaning tank 1 is at a predetermined value (step D).

When the water level reaches a predetermined level, the pure water supply pump 25 is stopped (
Step E), the heater 5 is turned on (Step F),
The pump 28 for circulating the cleaning liquid is turned on (step G),
Next, hydrogen peroxide and ammonia replenishment solenoid valve 19.19
' is t and t' is the dark time (step H). Next, the pumps 5 and 10 for liquid feeding and sampling and the pump 15 for feeding hydrochloric acid are turned on (step 2). Step J: Measure the amount of ultraviolet absorption of the sample liquid using the oxygen concentration measuring section 6.11.
).

Hydrogen peroxide and ammonia concentrations are calculated based on the measured values (step K). It is determined whether the above calculated concentration is within the target concentration range (step L).

If the calculated hydrogen peroxide and ammonia concentrations are outside the target values, and the concentrations are too low, open the solenoid valve 19.19' to separate the hydrogen peroxide and ammonia.
t' is calculated, and if the concentration is too high, the time t at which the pump 25 should be operated to sex the pure water is calculated (step M,
N), is executed (step Q). In this way, the hydrogen peroxide and ammonia concentrations in the cleaning solution are controlled, and it is determined whether the temperature of the cleaning solution is within the set range (step R). If the temperature measured by the thermometer 50 is within the set range, the Si wafer is removed. Wash for a certain period of time (step S).

When subsequently cleaning the Si wafer, the composition and temperature of the cleaning solution are measured once again, and then the 8i wafer is cleaned (steps J to S). If the Si wafer is not to be cleaned continuously, drain the liquid and end the cycle (Steps U and V).
.

〔Effect of the invention〕

As detailed above, according to the present invention, the collected cleaning liquid,
The ultraviolet absorbance of the cleaning water with a hydrogen ion concentration of 4 or less was measured, and the concentration of hydrogen peroxide was measured by the ultraviolet absorbance of the cleaning water with a hydrogen ion concentration of 4 or less. The ammonia concentration is measured by the ratio of ultraviolet absorbance of the washing water to 4 or less, and the component concentration of the washing water is continuously and automatically adjusted using a microcomputer.

This enables highly accurate and highly responsive in-line monitoring of hydrogen peroxide and ammonia components in cleaning solutions consisting of hydrogen peroxide, ammonia, and water, which are extremely widely used in the semiconductor industry. It has excellent effects such as preventing rapid etching of the Si wafer due to the reduction of hydrogen oxide, regenerating and extending the life of the cleaning solution by supplying appropriate amounts of hydrogen peroxide and ammonia, and stabilizing cleaning.

[Brief explanation of the drawing]

Figure 1 is a graph showing the change in absorbance of oxygen and ammonia with respect to ultraviolet wavelength due to hydrogen peroxide to explain the principle of measuring oxygen concentration in an aqueous solution, and Figure 2 is a graph to explain the principle of measuring hydrogen peroxide concentration. Figure 3 is a graph showing the change in ultraviolet absorbance due to changes in hydrogen ion concentration with respect to ammonia concentration in the cleaning solution. It is a graph showing the relationship between hydrogen oxide concentration. Figure 4 is a graph showing the relationship between the ratio of absorbance in the ultraviolet region and the ammonia concentration when no acid is added to the sample of cleaning liquid and when acid is added. Figures 5 and 6 are examples of the present invention. FIG. 5 is a block diagram of a cleaning liquid concentration adjustment device, and FIG. 6 is a block diagram showing a cleaning liquid concentration adjustment method. DESCRIPTION OF SYMBOLS 1... Cleaning tank, 2... Cleaning liquid, 5, 10... Collection pump, 6.11... Oxygen concentration measuring section, 8, 15...
... Ultraviolet light source, 7, 12 ... Flow cell for measuring transmitted light (flow cell), 9, 14 ... Ultraviolet light detector, 17
...Interface, 22...Microcomputer, 18...Solenoid valve control section, 19, 19''...
Solenoid valve, 20... hydrogen peroxide tank, 21... ammonia water tank.

Claims (1)

[Claims] 1. In a method for adjusting the concentration of hydrogen peroxide and ammonia in a cleaning solution consisting of hydrogen peroxide, ammonia and water, the sampled cleaning solution is introduced into a flow cell for measuring transmitted light and irradiated with an ultraviolet light source. The absorbance of ultraviolet rays is detected by an ultraviolet detector, while a cleaning solution with a hydrogen ion concentration of 4 or less is introduced into another flow cell, and it is irradiated with an ultraviolet light source and the absorbance of ultraviolet rays is detected by an ultraviolet detector. The ultraviolet absorbance and hydrogen ion concentration of the cleaning solution collected above were determined by 4.
Input the following two detected values of ultraviolet absorbance of the cleaning liquid into the interface, and calculate the hydrogen peroxide concentration and ammonia concentration in the collected cleaning liquid using the two detected values input into this interface using a microcomputer. A method for adjusting the concentration of a semiconductor cleaning liquid in which hydrogen peroxide and ammonia are automatically supplied from a supply source by comparing the concentration with a predetermined concentration. 2. A device for adjusting the concentration of hydrogen peroxide and ammonia in a cleaning solution consisting of hydrogen peroxide, ammonia, and water, including a collection pump for guiding the cleaning solution to a transmitted light flow cell and detecting the ultraviolet absorbance of the collected cleaning solution. an oxygen concentration measurement unit equipped with an ultraviolet light source, a flow cell, and an ultraviolet detector; a hydrochloric acid supply system to reduce the hydrogen ion concentration of the collected cleaning solution to 4 or less; and a hydrochloric acid supply system to reduce the hydrogen ion concentration to 4 or less. To detect ultraviolet absorbance, an oxygen concentration measurement unit equipped with an ultraviolet light source, a flow cell, and an ultraviolet detector detects the concentration of hydrogen peroxide based on the two ultraviolet absorbance detection values of the collected cleaning liquid and the cleaning liquid whose hydrogen ion concentration has been reduced to 4 or less. A microcomputer is installed in each of the hydrogen peroxide and ammonia supply systems. A semiconductor cleaning liquid concentration adjustment device consisting of a solenoid valve and a solenoid valve.