Cleaning solution for electronic materials and method for using the same

Abstract: A cleaning solution for electronic materials contains dissolved oxygen gas at a concentration greater than atmospheric saturation concentration, 0.1-10,000 mg/liter of ammonia, and 0.1-10,000 mg/liter of hydrogen peroxide in water. Alternatively, the cleaning solution contains dissolved reducing agents, 0.1-10,000 mg/liter of ammonia, and 0.1-10,000 mg/liter of hydrogen peroxide in water. A method for making the cleaning solution of the present invention is provided. A method for cleaning electronic materials using the cleaning solution of the present invention is also provided.

Description: BACKGROUND OF THE INVENTION The present invention relates to a cleaning solution for electronic materials. In particular, the present invention involves wet cleaning where impurities and especially particulate matter are removed from the surface of electronic materials. The cleaning solution is effective at room temperature using low concentrations of dissolved chemicals. The present invention includes a method for cleaning electronic materials. Removing particulate matter, or particles, from the surfaces of electronic materials such as semiconductor silicon substrates, liquid crystal glass substrates, and photomask quartz substrates, is extremely important in order to prevent defective products. Traditionally, an aqueous solution of a mixture of ammonia and hydrogen peroxide is used with heat to achieve this objective. This method is called APM cleaning. The standard mixing ratio of the chemicals used in APM cleaning is a solution of aqueous ammonia (29% by weight), aqueous hydrogen peroxide (30% by weight), and water in a 1:1:5 ratio. Generally, washing takes place at a temperature of around 80° C. The APM cleaning method is extremely effective in removing particles. However, the APM method has several problems. Since a high concentration of high purity chemicals is used, a great deal of ultrapure water is needed for the rinse after cleaning. Ultrapure water has a resistivity less than 16MΩ and less than 10µg/l total organic carbon. The high demand for ultrapure water results in excessive waste water processing. In addition, the APM method requires a mechanism for heating and temperature adjustment. This generates chemical contaminated steam, requiring an air pollution control system for removing contamination of the steam. The required local exhaust ventilation, air pollution control devices, and replacement of exhausted air with tempered fresh air, becomes very costly. A number of methods have been investigated to overcome these disadvantages without losing the particle removal effect. For example, one method uses several-fold dilutions of the chemicals of the prior art, while the temperature is maintained at approximately 40° C, or ambient temperature. This is used in conjunction with ultra sonic vibrations. The improvement is based on the APM method of prior art. Although this method is easily implemented, and may be adapted for use in a mass production factory, the improvement over the disadvantages indicated above is not significant. A cleaning solution for electronic materials is sought that uses low concentrations of chemicals and is effective at room temperature. EP-A-0,789,071 discloses a surface treatment composition for cleaning a substrate surface and which prevents the substrate surface from being contaminated with metal impurities from the surface treatment composition. The composition comprises a liquid medium containing a complexing agent as a metal deposition preventive, in which the complexing agent is selected from different groups of compounds having an atom as a donor which can provide electrons for a co-ordinate bond with the metal impurity. EP-A-0,560,324 discloses an acidic or basic hydrogen peroxide cleaning fluid for cleaning a semiconductor substrate, comprising a phosphonic acid chelating agent and a wetting agent, or comprising a wetting agent alone. The wetting agent is a polyhydric alcohol or its oxidised substances. JP-A-6,163,495 discloses a cleaning solution for cleaning a semiconductor wafer which comprises ammonium hydroxide, hydrogen peroxide and a hydrazone derivative or its tautomer. US-A-3,954,645 discloses a cleaning solution for cleaning metals, which comprises hydrogen peroxide, ammonia and a nitrite iron source. In light of the above, it is an object of the present invention to provide a cleaning solution for electronic materials which overcomes the limitations of the prior art. It was discovered that dissolving reducing agents into water containing low concentrations of ammonia and hydrogen peroxide results in a cleaning solution that is extremely effective in removing particles adhered to the surface of electronics material. The present invention is based on these findings. It is an object of the present invention to provide a cleaning solution for electronic materials that removes impurities, especially particles, from the surface of electronic materials during wet cleaning, cleans effectively at room temperature, and requires only a low concentration of dissolved chemicals. It is a further object of the present invention to provide a cleaning solution for electronic materials that conserves resources, is environmentally safe, and is easily implemented, even at mass production facilities. It is a further object of the present invention to provide a method using such a cleaning solution that is suitable for mass production facilities. According to an aspect of the present invention, there is provided a cleaning solution for electronic materials comprising: source water; from 0.00005 weight percent to 1 weight percent of at least one reducing agent selected from the group consisting of hydrogen gas, sulfite and hyposulfite; from 0.1 mg/liter to 10,000 mg/liter of ammonia in said source water; and from 0.1 mg/liter to 10,000 mg/liter of hydrogen peroxide in said source water. According to another aspect of the present invention, a method of making cleaning solution for electronic materials is provided that includes adding at least one reducing agent selected from the group consisting of hydrogen gas, sulfite and hyposulfite to a source water to a predetermined concentration from 0.00005 to 1 weight percent, adding from 0.1 mg/liter to 10,000 mg/liter of ammonia to the source water, and adding from 0.1 mg/liter to 10,000 mg/liter of hydrogen peroxide to the source water, to produce a cleaning solution. According to another aspect ofthe present invention, a method for cleaning electronic materials includes forming a cleaning solution by adding at least one reducing agent selected from the group consisting of hydrogen gas, sulfite and hyposulfite into a source water at a predetermined concentration from 0.00005 weight percent to 1 weight percent, adding ammonia to the source water at a predetermined concentration from 0.1 mg/liter to 10,000 mg/liter from an ammonia supply point, adding hydrogen peroxide to the source water at a predetermined concentration from 0.1 mg/liter to 10,000 mg/liter form a hydrogen peroxide supply point to form a cleaning solution, storing the cleaning solution in a storage container, measuring the flow rates of ammonia from the ammonia source point and of hydrogen peroxide from the hydrogen peroxide supply point, adjusting the flow rates of ammonia and hydrogen peroxide from their respective source points to maintain a constant concentration of cleaning solution in the storage container, transporting the cleaning solution to at least one use point, and cleaning electronic materials with the cleaning solution at the at least one use point. The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a system diagram of one embodiment of a device for making and supplying a cleaning solution for electronic materials of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The cleaning solution for electronic materials of the present invention is effective in removing metal contamination, organic contamination, and particulate contamination. In particular, the present invention is highly effective in removal of particulate matter contamination, or particles. It can be used for washing materials, including but not limited to, semiconductor silicon substrates, liquid crystal glass substrates, and photomask quartz substrates. There are no particular limitations on the method of manufacturing the cleaning solution of the present invention. According to the invention, the reducing agent to be used in the cleaning solution is selected from hydrogen gas; hyposulfites, such as sodium hyposulfite (Na 2 S 2 O 4 ) and ammonium hyposulfite; sulfites, such as sodium sulfite (Na 2 SO 3 ) and ammonium sulfite; hydrogen sulfites, such as sodium hydrogen sulfite (NaHSO3) and ammonium hydrogen sulfite. These reducing agents can be used alone, or in combination. Preferably, the reducing agent to be used is a high purity reagent. The concentration of the reducing agent is between 0.00005-1 weight %, and preferably between 0.05-0.5 weight %. If the concentration of reducing agent is less than 0.00005 weight %, the cleaning effectiveness may be inadequate. An adequate cleaning effect is shown with a concentration of 1 weight % or less. Normally, there is no need for the concentration of reducing agents to exceed 1 weight %. If the concentration of reducing agents is too high, an excessive amount of water for rinsing after cleaning may become necessary. If the reducing agent is hydrogen gas, the concentration is preferably 0.5-1.5 mg/liter. There are no particular limitations on the method of making the cleaning solution ofthe present invention which includes reducing agents. It can be made by adding ammonia and hydrogen peroxide to water in which the reducing agent is already dissolved. Alternatively, it can be made by dissolving reducing agents into water already containing ammonia and hydrogen peroxide. It is also possible to make the cleaning solution by mixing aqueous solutions of reducing agents, ammonia and hydrogen peroxide. The content of ammonia is 0.1-10,00 mg/liter, and preferably 1-100 mg/liter. The cleaning solution is alkaline due to the presence of ammonia. As a result, the particles and the surface of the object to be cleaned both become negatively charged. This prevents the particles fromre-adhering to the surface ofthe object to be cleaned. Ifthe content of ammonia is less than 0.1 mg/liter, the cleaning effectiveness may be inadequate. An adequate cleaning effect is shown with an ammonia content of 10,000 mg/liter or less. Normally, an ammonia content exceeding 10,000 mg/liter is not necessary. If the ammonia content is too high, the amount of water required for rinsing after cleaning may have to be increased. The content of hydrogen peroxide is 0.1-10,000 mg/liter, and preferably 1-100 mg/liter. The presence of hydrogen peroxide in the cleaning solution results in an oxidation stability greater than when only dissolved oxygen gas is used. In addition, roughening of the surface of the object to be cleaned is prevented. If the hydrogen peroxide content is less than 0.1 mg/liter, the cleaning effectiveness may not be adequate. A hydrogen peroxide content of 10,000 mg/liter or less results in an adequate cleaning effect. Normally, a hydrogen peroxide content exceeding 10,000 mg/liter is not necessary. If the hydrogen peroxide content is too high, an excessive amount of water is required for rinsing after cleaning. There are no particular limitations for the method of contact between the cleaning solution of present invention and the electronic material, especially for an electronic material which is contaminated by particles. An appropriate method can be selected according to the type of particle, particle size, and amount of deposition. For example, an electronic material that has been contaminated by particles can be submerged in cleaning solution and batch cleaned. Alternatively, a sheet cleaning method where one sheet is processed at a time can also be used. An example of a sheet cleaning method include a spin cleaning method in which cleaning solution is poured while the electronic material contaminated with particles is rotated. When cleaning electronic material contaminated with particles using the cleaning solution of present invention, ultrasonic vibrations can be transmitted to the electronic material cleaning solution. There are no particular limitations as to the method of transmitting ultrasonic vibrations to the electronic material cleaning solution. For example, in batch cleaning, ultrasonic vibrations can be transmitted to the vat where the cleaning solution is stored. In spin cleaning, ultrasonic vibrations can be transmitted by the nozzle piece from which the cleaning solution is to be poured. The frequency of the ultrasonic vibration to be transmitted for the present invention is preferably 20 kHz or greater, and is more preferably 400 kHz or greater. If the frequency of the ultrasonic vibration is less than 20 kHz, the removal of particles from electronic materials contaminated with particles may be inadequate. In order to conduct precision cleaning without damaging the surface of the object to be cleaned, an ultrasonic vibration of particularly high frequency of 400 kHz or greater is preferably transmitted. For the present invention, a frequency of 400 kHz is more preferred, and a frequency greater than 1 MHz is most preferred. When vibrations are at several tens of kHz, as in the prior art, removal of particles from electronic materials contaminated with particles may be inadequate. Furthermore, because of the cavitation effect of ultrasonic vibrations, there may be damage to the object being cleaned. The cleaning solution of the present invention is extremely effective in particle removal at room temperature. Since the surface can be cleaned at a high particle removal rate, it is not necessary to heat to high temperatures as in the APM cleaning of the prior art. As a result, by using the cleaning solution of the present invention, energy costs can be reduced, and the working environment is improved. The cleaning solution of the present invention can be used by transporting the cleaning solution to use points from a closed cleaning solution storage tank via pipes and returning excess cleaning solution to the closed cleaning solution storage tank via pipes, using a device for circulating the cleaning solution. Because the ammonia and hydrogen peroxide is at a low concentration, and because a closed storage tank and supply pipes are used, the water quality can be maintained for extended periods. By using such a device, individual cleaning solution production devices do not have to be placed at each use point. The cleaning solution can be produced centrally, and through main pipes and branching pipes, cleaning solution having a stable water quality can be supplied to a plurality of use points. In addition, a circulating system can be used that returns excess cleaning solution that is not used at the use point to the storage tank, repeatedly sends cleaning solution to use points. Using the cleaning solution of the present invention greatly reduces the amount of chemicals used in cleaning of electronic materials contaminated by particles. Extremely effective cleaning at room temperature is achieved. In addition, the waste water processing after cleaning of the electronic material is easy. In the cleaning process of the prior art, a waste water containing high concentrations of ammonia and hydrogen peroxide is discharged. As a result, neutralization processing or breakdown processing is required. The amount of chemicals required for waste water processing is comparable to the amount of chemicals necessary for preparing the cleaning solution. The present invention produces a low concentration of ammonia and hydrogen peroxide discharge. It is of a water quality that requires only a small amount of acid for neutralization. Of course, the discharge is also of a quality that can be reused as source water. The hydrogen peroxide contained in the waste water is a trace amount. Normally, problems do not arise from these concentrations, but if necessary, the hydrogen peroxide dissolved in the waste water can be broken down as required. For example, water containing hydrogen peroxide can be brought into contact with catalysts such as platinum, palladium, manganese dioxide, or the like. In this way, the hydrogen peroxide is broken down into water and oxygen gas. The present invention will be described in more detail in the following embodiments. The invention is not limited to these embodiments. For the embodiments and the comparative examples, ultrapure water was used in preparation of cleaning solution. The ultrapure water had a resistivity of 18 MΩ and 3 µg/l of total organic carbon. Embodiment 1 outside the claimed range A 0,1524 m (6 inch) diameter silicon wafer, which has had its surface oxidized by ultrapure water containing ozone, was contaminated with alumina particles. The contaminated wafer had alumina particles adhering to its surface. The number of particles adhered onto the contaminated wafer was measured using a wafer dust detection device, [WH-3 from Topcon Corporation, Tokyo, Japan), which is based on a laser scatter light detection principle. A single wafer had 12,600 particles 0.2-0.5 µm in diameter, 31,200 particles 0.5-1.0 µm in diameter, and 200 particles 1.0 µm or greater in diameter, for a total of 44,000 particles. This contaminated wafer was rotated at 500 rpm. Cleaning solution, containing 30 mg/liter of dissolved oxygen, 10 mg/liter of ammonia, and 10 mg/liter of hydrogen peroxide, was poured at 800 ml/min. at room temperature while transmitting ultrasonic vibration using an ultrasonic shooting nozzle [Fine Jet T005J from Pre-Tech Co., Ltd., Fuchu, Tokyo, Japan] at a frequency of 1.6 MHz, and an output power of 13.5 W/cm 2 . Spin cleaning was conducted for 60 seconds. The wafer was then rinsed using ultrapure water and dried. After drying, the number of particles adhered onto the surface of the wafer was measured using the aforementioned wafer dust detection device. A single wafer had 130 particles 0.2-0.5 µm in diameter, 310 particles 0.5-1.0 µm in diameter, and 0 particles 1.0 µm or greater in diameter, for a total of 440 particles. The removal rate of particles from the wafer surface was 99%. Comparative Example 1 A silicon wafer was prepared and spin cleaned as in Embodiment 1. A cleaning solution containing oxygen gas dissolved at atmospheric saturation concentration, 10 mg/liter of ammonia, and 10 mg/liter of hydrogen peroxide, was used at room temperature. Cleaning of the wafer prepared in Comparative Example 1 was conducted in the same fashion as in Embodiment 1. After drying, the number of particles adhered on the wafer surface was measured as in Embodiment 1. A single wafer had 6,400 particles of diameter 0.2-0.5 micrometer, 16,500 particles of diameter 0.5-1.0 micrometer, and 95 particles of diameter 1.0 micrometer or greater, for a total of 22,995 particles. The removal rate of the particles from the wafer surface was 48%. Comparative Example 2 A silicon wafer was prepared and spin cleaned as in Embodiment 1 except that no ultrasonic vibration was used and the cleaning was performed at 80°C. An AMP cleaning solution containing an atmospheric concentration of oxygen gas, 4.1 weight % of ammonia and 4.3 weight % of hydrogen peroxide was used. After drying, the number of particles adhered on the wafer surface was measured, as in Embodiment 1. A single wafer had 145 particles 0.2-0.5 µm in diameter, 340 particles 0.5-1.0 µm in diameter, and 1 particle 1.0 µm or greater in diameter, for a total of 486 particles. The removal rate of the particles from the wafer surface was 99%. Comparative Example 3 A silicon wafer was prepared and spin cleaned as in Embodiment 1 except cleaning was performed at 80°C. A ten-fold dilution of APM cleaning solution containing an atmospheric saturation concentration of oxygen, 4.1 weight % of ammonia and 4.3 weight % of hydrogen peroxide was used. After drying, the number of particles adhered on the wafer surface was measured as in Embodiment 1. A single wafer had 3,440 particles 0.2-0.5 µm in diameter, 8,500 particles 0.5-1.0 µm in diameter, and 55 particles 1.0 µm or greater in diameter, for a total of 11,995 particles. The removal rate of the particles on the wafer surface was 73%. Embodiment 2 A silicon wafer was prepared and spin cleaned as in Embodiment 1. A cleaning solution, containing 0.1 weight % of sodium hyposulfite, 10 mg/liter of ammonia, and 10 mg/liter of hydrogen peroxide was used. After drying, the number of particles adhered onto the wafer surface was measured as in Embodiment 1. A single wafer had 120 particles 0.2-0.5 µm in diameter, 310 particles 0.5-1.0 µm in diameter, and 0 particles 1.0 µm or greater in diameter, for a total of 430 particles. The removal rate of the particles on the wafer surface was 99%. Referring to Table 1, the cleaning solution composition of Embodiments 1-2, Comparative Examples 1-3, cleaning conditions, and the particle removal rates are shown. Particle Removal Rates Cleaning Solution Composition Temp. Ultrasonic Vibration Particle Removal Rate (%) O 2 Gas Sodium Hyposulfite Ammonia Hydrogen Peroxide Embodiment 1 30 mg/l - 10 mg/l 10 mg/l Room Temp. Yes 99 Embodiment 2 ASC 0.1 Weight % 10 mg/l 10 mg/l Room Temp. Yes 99 Comparative Example 1 ASC - 10 mg/l 10 mg/l Room Temp. Yes 48 Comparative Example 2 ASC - 4.1 Weight % 4.3 Weight % 80°C No 99 Comparative Example 3 ASC - 0.41 Weight % 0.43 Weight % Room Temp. Yes 73 As can be seen from the results in Table 1, even though the cleaning solution as shown in Embodiments 1 and 2 have 1/4000 of the content of ammonia and hydrogen peroxide compared with the APM cleaning solution of the prior art in Comparative Example 2, and despite the cleaning being done at room temperature, the present invention has particle removal rates similar to the prior art when cleaning a wafer contaminated by particles. The particle removal rate of Comparative Example 1 was halved when the cleaning solution had the same ammonia and hydrogen peroxide content as Embodiment 1 and 2, but oxygen gas was only dissolved at atmospheric saturation concentration and no reducing agent was used. The effectiveness of the cleaning solution containing oxygen gas dissolved at a higher concentration than atmospheric saturation concentration, ammonia, and hydrogen peroxide is confirmed. The effectiveness of the cleaning solution of the present invention containing dissolved reducing agents, ammonia, and hydrogen peroxide is also confirmed. Furthermore, in the cleaning solution of Comparative Example 3, where the ammonia and hydrogen peroxide concentration was 1/10 of the concentration of APM cleaning solution of the prior art, the particle removal rate was only approximately 70%, even when ultrasonic vibrations were transmitted. In order for APM cleaning to be effective, a cleaning solution must contain a high concentration of chemicals and be used at an elevated temperature. The cleaning solution having a higher concentration of dissolved oxygen gas than atmospheric saturation concentration can have the same particle removal effect as the APM cleaning of the prior art. This is true, despite having substantially lower concentrations of ammonia and hydrogen peroxide as compared to the APM cleaning solution of the prior art. In addition, the cleaning solution of the present invention containing reducing agents can have the same particle removal effect as the APM cleaning of the prior art. This is true, despite having substantially lower concentrations of ammonia and hydrogen peroxide as compared to the APM cleaning solution of the prior art. The present invention may be used in conjunction with general devices of a mass production factory. Thus, there are no impediments to its application.

Claims: A cleaning solution for electronic materials comprising: source water; from 0.00005 weight percent to 1 weight percent of at least one reducing agent selected from the group consisting of hydrogen gas, sulfite and hyposulfite; from 0.1 mg/liter to 10,000 mg/liter of ammonia in said source water; and from 0.1 mg/liter to 10,000 mg/liter of hydrogen peroxide in said source water. A cleaning solution according to Claim 1, wherein said reducing agent is hydrogen gas. A cleaning solution according to Claim 1, wherein said reducing agent is sulfite. A cleaning solution according to Claim 1, wherein said reducing agent is hyposulfite. A cleaning solution according to any one of Claims 1 to 4, wherein said ammonia is from 1mg/liter to 100 mg/liter. A cleaning solution according to any preceding claim, wherein said hydrogen peroxide is from 1mg/liter to 100 mg/liter. A cleaning solution according to any preceding claim, wherein said reducing agent is from 0.05 weight percent to 0.5 weight percent. A method for making cleaning solution for electronic materials, comprising: adding at least one reducing agent selected from the group consisting of hydrogen gas, sulfite and hyposulfite to a source water to a predetermined concentration from 0.00005 weight percent to 1 weight percent; adding from 0.1 mg/liter to 10,000 mg/liter of ammonia to said source water; and adding from 0.1 mg/liter to 10,000 mg/liter of hydrogen peroxide to said to source water, to produce a cleaning solution. The method according to Claim 8, wherein said reducing agent is from 0.05 weight percent to 0.5 weight percent. A method for cleaning electronic materials, comprising: forming a cleaning solution by adding at least one reducing agent selected from the group consisting of hydrogen gas, sulfite and hyposulfite to a source water at a predetermined concentration from 0.00005 weight percent to 1 weight percent; adding ammonia to said source water at a predetermined concentration from 0.1 mg/liter to 10,000 mg/liter from an ammonia supply point; adding hydrogen peroxide to said source water at a predetermined concentration from 0.1 mg/liter to 10,000 mg/liter from a hydrogen peroxide supply point to form a cleaning solution, storing said cleaning solution in a storage container; measuring a first flow rate of ammonia from said ammonia supply point; and a second flow rate of hydrogen peroxide from said hydrogen peroxide supply point; adjusting said first and second flow rates to maintain a constant concentration of ammonia and hydrogen peroxide in said storage container; transporting said cleaning solution to at least one use point for said cleaning solution; and cleaning said electronic materials with said cleaning solution at said at least one use point. The method according to Claim 10, wherein said cleaning step further includes transmitting ultrasonic vibrations of a frequency of at least 400 kHz to said at least one use point of said cleaning solution. The method according to Claim 10 or Claim 11, further comprising recycling excess cleaning solution from said at least one use point to said storage container. The method according to any of Claims 10 to 12, wherein the said cleaning solution is used to clean electronic materials at room temperature.

Inventors: IDA JUNICHI, MIZUNIWA TETSUO, MORITA HIROSHI, IDA, JUNICHI, MIZUNIWA, TETSUO, MORITA, HIROSHI, IDA, JUNICHI, C/O KURITA WATER IND. LTD., Mizuniwa, Tetsuo, c/o Kurita Water Ind. Ltd., Morita, Hiroshi, c/o Kurita Water Ind. Ltd.
Applicants: KURITA WATER IND LTD, KURITA WATER INDUSTRIES LTD.
Application year: 1998
Main classification: C11D3
IPC codes: C11D11, H01L21, C11D7, C11D3