CLEANING LIQUID FOR SEMICONDUCTOR SUBSTRATE

Abstract: Metallic impurities are prevented from adhering to the surface of a semiconductor substrate when the substrate is cleaned with a basic aqueous solution of hydrogen peroxide. The cleaning liquid contains a chelating agent having at least two phosponic acid groups. Even when the cleaning liquid is contaminated by the metallic impurities, since they are prevented from adhering to the surface of the substrate, the characteristic of the semiconductor device made of the substrate is stabilized.

Description: The present invention relates to a cleaning solution for a semiconductor substrate. More specifically, it relates to a cleaning solution for a semiconductor which comprises an aqueous solution containing 0.1 to 20% by weight of hydrogen peroxide and 1 ppb to 1000 ppm of a chelating agent based on the total amount of the aqueous solution. In producing semiconductor elements, cleaning has been carried out with chemicals to remove contaminants adhered on a surface of a semiconductor substrate including silicon wafer. As the chemicals, cleaning solutions containing mainly hydrogen peroxide are often used. For example, a mixed aqueous solution of hydrochloric acid and hydrogen peroxide, a mixed aqueous solution of sulfuric acid and hydrogen peroxide, a mixed aqueous solution of ammonia and hydrogen peroxide and the like are known. Particularly, a mixed aqueous solution of ammonia indicating basicity in an aqueous solution and hydrogen peroxide is most widely used since it is effective in removing fine particles adhered on a substrate surface. However, in a basic cleaning solution, there has been a problem that metal impurities including Fe and Cu come to be insoluble and adhere on a substrate to exert a bad influence on a characteristics of a semiconductor element. In order to solve the problem, high purification of ammonia and hydrogen peroxide themselves has been promoting. Presently, a concentration of metal impurities in ammonia and hydrogen peroxide leads to 1 ppb or below. However, on the contrary, there has been a problem that a high purified cleaning solution comes to be sensitive to metal contamination from the outside and metal contamination from a cleaning vessel etc., causes instability for characteristics of a semiconductor element. On the other hand, as the other methods for preventing adhesion of metal impurities to a semiconductor substrate, addition of a chelating agent has been suggested. For example, in DE-A-3822350, a method of using ethylenediaminetetraacetic acid (EDTA) as a chelating agent has been suggested. However, in fact, advantageous effects due to addition of EDTA are scarcely observed. Accordingly, a method for treatment of rendering stable advantageous effects has been desired. EP-A-0276774 discloses a storable semiconductor cleaning solution, a method for producing same and a process of cleaning a semiconductor using said cleaning solution, whereby said solution consists essentially of water, sulfuric acid and hydrogen peroxide, whereby the cleaning solution may optionally comprise a sequestrant which may be a pentavalent phosphorus compound. Further, the solution may comprise tin ions. EP-A-0496605 discloses a process for cleaning a semiconductor surface with a surface treating solution and subsequently with ultra-pure water, whereby said treating solution comprises an inorganic or organic alkali, hydrogen peroxide and water as major components. At least one of the treating solution and the ultra-pure water contains a chelating agent having one or more phosphonic acid groups or a salt thereof. The object of the present invention is to solve the foregoing problems and to provide a cleaning solution which, even if an aqueous cleaning solution of hydrogen peroxide is contaminated with metal impurities, makes it possible to prevent contaminants adhering to a substrate surface and carry out stabilized cleaning of the substrate. The present inventors have made extensive study to attain the foregoing object. As a result, it has been found that the above object can be solved by providing a cleaning solution for a semiconductor substrate which comprises an aqueous solution containing 0.1 to 20% by weight of hydrogen peroxide and 1 ppb to 1000 ppm of a chelating agent based on the total amount of the aqueous solution,characterized in that the aqueous solution is a basic aqueous solution and the chelating agent is propylenediaminetetra(methylenephosphonic acid). The present invention has been accomplished on the basis of the above finding. The chelating agent used in the present invention is desirably used in the form of the free acid. When the solubility is insufficient, it may be used also in the form of a salt including ammonium salt. The addition amount of the chelating agent in the present invention depends on the contents or degree of contamination of metal impurities, or kinds of basic compounds in an aqueous cleaning solution of hydrogen peroxide and ranges of from 1 ppb to 1,000ppm for the total amount of the cleaning solution. After a basic cleaning solution of hydrogen peroxide has been prepared, the chelating agent may be added to it. Otherwise, the chelating agent may be in advance added to ammonia, organic amine, hydrogen peroxide, water etc., and subsequently mixed with them. Ordinarily, after a basic cleaning solution of hydrogen peroxide has been prepared, the chelating agent is added to it. The basic cleaning solution of hydrogen peroxide in the present invention is typically a mixed aqueous solution of ammonia and hydrogen peroxide. The other examples include a mixed aqueous solution of organic amines including choline( hydroxyltrimethylammoniumhydroxide), tetramethylammoniumhydroxide, tetraethylammoniumhydroxide and hydrogen peroxide. In the case of a basic cleaning solution comprising a mixed aqueous solution of ammonia and hydrogen peroxide, ammonia in the range of a concentration of 0.1 to 10% by weight and hydrogen peroxide in the range of a concentration of 0.1 to 20% by weight are ordinarily used. In the case of a mixed aqueous solution of the other organic amine and hydrogen peroxide, organic amine in the range of a concentration of 0.01 to 10% by weight and hydrogen peroxide in the range of a concentration of 0.1 to 20% by weight are ordinarily used. Example In order to research the influence of metal impurities and preventing effects of a chelating agent, the basic cleaning solutions shown in table 1 were prepared and used. Preliminary cleaned silicon substrates of 3 inch were immersed to clean at 85 °C for 10 minutes in basic cleaning solutions as shown in table 1. The proportion of the high purity ammonium hydroxide (28% by weight), the high purity hydrogen peroxide (30% by weight) and ultra purity water was 1:4:20 (volume ratio). The cleaned substrates were oxidized in an oxygen gas stream to grow oxide films to a thickness of about 350Å. Thus, MOS diodes were made. As an electrical characteristic, minority carrier generation lifetime was measured. Moreover, in order to confirm that influence on electrical characteristics dues to metal impurities, an amount of metal impurities adhered on the substrates was analyzed by TREX (Total Reflection Energy dispersive X-ray fluorescence )apparatus. By adding 10ppb of iron ions, iron adhered on the surface of the substrates and minority carrier generation lifetime also remarkably decreased. However, by adding simultaneously propylenediaminetetra( methylenephosphonic acid ) (PDTMP), the adhesion of iron was prevented and a decrease of minority carrier generation lifetime also was not observed. Moreover, by adding ethylenediaminetetraacetic acid (EDTA), no preventing effect was observed. INDUSTRIAL APPLICABILITY According to the cleaning solution of the present invention, even if the basic cleaning solution is contaminated with metal impurities, contamination of a semiconductor substrate surface is effectively prevented and stabilized cleaning of the semiconductor substrate can be carried out, so that a defective proportion of elements decreases and it is possible to produce superior semiconductor elements.

Claims: A cleaning solution for a semiconductor substrate which comprises an aqueous solution containing 0.1 to 20% by weight of hydrogen peroxide and 1 ppb to 1000 ppm of a chelating agent based on the total amount of the aqueous solution,characterized in that the aqueous solution is a basic aqueous solution and the chelating agent is propylenediaminetetra(methylenephosphonic acid). A cleaning solution for a semiconductor substrate according to claim 1, wherein the basic aqueous solution contains 0.1 to 10% by weight of ammonia.

Inventors: KAWAKAMI M MITSUBISHI GAS CHEM, SUGIHARA Y MITSUBISHI GAS CHEM, TANAKA K MITSUBISHI GAS CHEM C, KAWAKAMI, M., MITSUBISHI GAS CHEM. COMP. INC., SUGIHARA, Y., MITSUBISHI GAS CHEM. COMP. INC., TANAKA, K., MITSUBISHI GAS CHEM. COMP.INC.
Applicants: MITSUBISHI GAS CHEMICAL CO, MITSUBISHI GAS CHEMICAL COMPANY, INC.
Application year: 1992
Main classification: H01L21
IPC codes: H01L21, C11D7, C23G5, C01B15