Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
1999-10-12
2002-08-13
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S001000, C134S002000, C134S003000, C134S026000, C134S028000, C134S030000, C216S099000
Reexamination Certificate
active
06431186
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
This invention concerns a method of cleaning electronic components. More specifically, this invention pertains to a method of cleaning electronic components that is capable of effectively removing contaminants, such as fine particles which adhere to the surface of a base, without making the surface of the base rough in the wet cleaning process used in industries in which such electronic components such as semiconductor silicon bases are handled.
2. Prior Art
Components such as silicon bases for semiconductors and glass bases for liquid crystals have conventionally been cleaned by RCA cleaning, a heat cleaning method that uses hydrogen peroxide-based concentrated chemical solutions (sulfuric acid+hydrogen peroxide water, hydrochloric acid+hydrogen peroxide water+water, ammonia+hydrogen peroxide water+water) However, wet cleaning processes began to receive attention in recent years for reasons pertaining to environmental protection and resource conservation.
Against this backdrop, the inventor, et al. earlier proposed a method of cleaning with an oxidizing cleaning fluid, such as ozonated water, to remove mainly metal and organic contaminants, and another cleaning method using a reducing cleaning fluid, such as hydrogenated water, principally for the removal of fine particles.
Needless to say, these two methods, used individually, achieve sufficiently high cleaning effects. However, the synergetic effects from the combination of the two have never been examined closely.
The inventors have found that the concurrent use of ultrasonic waves in the cleaning of bases by a reducing cleaning fluid resulted in extremely high levels of fine particle removal. However, this method, used on a bare silicon surface that has been stripped of an oxidation film, has a disadvantage in that the base surface roughness increases when the strength of ultrasonic waves or the cleaning time is improper, such as when cleaning is performed over a lengthy period of time with a reducing cleaning water to which large ultrasonic waves are applied. In particular, the tendency for an increase in roughness becomes pronounced when an alkaline reducing cleaning water is used.
In the actual cleaning of silicon base surface, holding down the roughness of the silicon surface or that of the silicon/silicon oxidation film interface on the order of atoms is as important as the complete removal of impurities.
Problem that the Invention Aims to Solve
This invention aims to offer a simple and easy cleaning method that can both remove metal, organic and fine particle contaminants on the surface of electronic components, in particular of silicon bases, and also control an increase in the roughness of the base surface on the order of atoms in the cleaning process.
Means of Solving the Problem
The inventors discovered that there was little likelihood of increased surface roughness caused by ultrasonic cleaning with a reducing cleaning fluid to which a chemical solution has been added, as long as the silicon base surface is oxidized prior to cleaning for the purpose of preventing an increase in the roughness of the base surface and a drop in the quality of silicon bases resulting from ultrasonic cleaning that is either too strong or too long in said ultrasonic cleaning. There is no damage to the interface between silicon and silicon oxidation film, which plays an important role in the silicon base functions. Building on these findings, this invention was completed.
Specifically, this invention consists of the inventions described in the following paragraphs.
(1) A method of cleaning electronic components characterized by cleaning of the components with an oxidizing cleaning fluid, followed by cleaning with a reducing cleaning fluid in the presence of ultrasonic vibrations.
(2) The method of cleaning electronic components according to Paragraph (1), wherein the electronic components are bare silicon bases for semiconductors.
(3) The method of cleaning electronic components according to Paragraph (1), wherein the oxidizing cleaning fluid is either ozonated water or ozonated water to which either an acidic or alkaline chemical has been added.
(4) The method of cleaning electronic components according to Paragraph (1), wherein the oxidizing cleaning fluid is either oxygenated water or oxygenated water to which either an acidic or alkaline chemical has been added.
(5) The method of cleaning electronic components according to Paragraph (1), wherein the oxidizing cleaning fluid is a fluid which contains hydrogen peroxide.
(6) The method of cleaning electronic components according to Paragraph (1), wherein the reducing cleaning fluid is either hydrogenated water or hydrogenated water to which either an acidic or alkaline chemicals been added.
(7) The method of cleaning electronic components according to Paragraph (1), wherein the ultrasonic vibrations have frequencies ranging between 400 KHz and 3 MHz.
(8) The method of cleaning electronic components according to paragraph (3), wherein the ozonated concentration in a cleaning fluid is not less than 0.1 mg/liter.
(9) The method of cleaning electronic components according to paragraph (5), wherein the hydrogen peroxide concentration in a cleaning fluid is not less than 200 mg/liter.
(10) The method of cleaning electronic components according to paragraph (6), wherein the hydrogen gas concentration in a cleaning fluid is not less than 0.7 mg/liter.
Mode of Operation of Invention
This invention is a method of cleaning electronic components with a reducing cleaning fluid in the presence of ultrasonic vibrations, following their cleaning with an oxidizing cleaning fluid, and involves a cleaning process in which components are cleaned using a reducing cleaning fluid in the presence of ultrasonic vibrations, either directly following a cleaning process that employs an oxidizing cleaning fluid or via an ultrapure water rinsing process.
The cleaning method of this invention is especially applicable to electronic components which demand strict surface roughness precision such as silicon bases for semiconductors, and glass bases for liquid crystals.
In particular, silicon bases for semiconductors used in this invention can have either a hydrophilic surface finish with an oxidized film on the surface, or a hydrophobic surface finish without an oxidized film The cleaning method of this invention is especially suitable for bare silicon bases for semiconductors and restrains the occurrence of base surface roughness.
In this invention, the initial treatment with an oxidizing cleaning fluid oxidizes the silicon base surface prior to the cleaning process in which a reducing cleaning fluid is used in the presence of ultrasonic vibrations. For this reason, the silicon/silicon oxidization film interface does not get damaged in the second cleaning process. Thus, there is no increase in electronic component (silicon base) surface roughness following the cleaning treatment.
The oxidizing cleaning fluid of this invention is an aqueous solution in which an oxidizing substance has been dissolved.
There is no special restriction on the oxidizing substance used in the oxidizing cleaning fluid. For example, oxidizing substances, such as hydrogen peroxide (H
2
O
2
), ozone (O
3
) an oxygen (O
2
); hypochlorites, such as sodium hypochlorite (NaClO) and calcium hypochlorite; chlorites, such as sodium chlorite (NaClO
2
) and potassium chlorite; and chlorates, such as sodium chlorate (NaClO
3
) and ammonium chlorate, can be used. These oxidizing substances can be used either singularly or in combination of two or more.
Among these, hydrogen peroxide and ozone are particularly suitable because they are relatively easy to handle, achieve high cleaning effects at low concentration, and place only a minor load on the rinse after cleaning. When hydrogen peroxide is used, it is desirable for the hydrogen peroxide concentration in the cleaning water to be not lower than 200 mg/liter, and more preferably not lower than 1,000 mg/liter. When
Ida Junichi
Morita Hiroshi
Armstrong Westerman & Hattori, LLP
Gulakowski Randy
Kornakov M.
Kurita Water Industries Ltd.
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