JP2008093615A - Cleaning method of electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method which enables the effective removal of a contaminant such as metal sticking to an attracting face of an electrostatic chuck without heating it to a high temperature. <P>SOLUTION: The cleaning method of an electrostatic chuck is characterized by comprising the step of immersing the same in a cleaning liquid comprised of an aromatic hydrocarbon and/or a nonionic surfactant and the step of subjecting it to a surface treatment by dry ice (CO<SB>2</SB>) blasting and is further characterized by decreasing an alkali metal element, an alkali earth metal element or iron element present on the surface of the electrostatic chuck after cleaning measured by inductively coupled plasma mass spectrometry to 300×10<SP>10</SP>atoms/cm<SP>2</SP>or lower respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an electrostatic chuck that is incorporated in a flat panel display manufacturing apparatus such as a semiconductor manufacturing apparatus or a liquid crystal panel and used in a process of fixing a substrate such as a Si wafer or a glass substrate.

An electrostatic chuck incorporated in a semiconductor manufacturing apparatus adsorbs a wafer with electrostatic force in processes such as etching and film formation. Since such semiconductor manufacturing processes are performed by laminating various elements on the wafer by reaction and doping, if impurities other than the necessary elements are mixed, the performance of the semiconductor element is deteriorated and the yield is reduced. Invite. In particular, if an organic component or metal adheres to the surface of the electrostatic chuck that contacts the wafer, the yield of the wafer is directly reduced. Furthermore, once the contaminants are mixed in the manufacturing apparatus, the entire apparatus is contaminated. Therefore, the cleaning is very troublesome and the loss due to the manufacturing interruption is significant.

Also, in the electrostatic chuck manufacturing process, there is contamination due to adhesion of metal from the furnace in the firing and brazing processes, adhesion of grinding fluid in the grinding process, and contact with people between these processes. It is difficult to manufacture without adhesion of metal elements and organic components such as alkali metals, alkaline earth metals or iron which are main pollutants. Therefore, when using the electrostatic chuck, it is essential to remove the contaminants as described above.

A method of heating to a high temperature has been attempted as a method for removing contaminants from ceramic members such as electrostatic chucks used in semiconductor manufacturing equipment. As a heating method, there are a heating method using ordinary Joule heat and a heating method using plasma, and a method of performing a heat treatment at a temperature of 1000 ° C. or higher has been proposed (for example, see Patent Document 1).

JP-A-9-328376

Heat treatment at a high temperature is generally used for ceramic members because most of the surface contaminants can be removed. However, at a high temperature of 1000 ° C. or higher, for example, the surface of a non-oxide ceramic material such as aluminum nitride often used for electrostatic chucks is significantly oxidized, the volume resistivity of the insulating layer is changed, or the oxide layer is degranulated. Particles are generated. Further, if the metal component remains, the metal component diffuses into the member due to heating, which may affect the characteristics of the electrostatic chuck. In the heating by plasma, there is a problem that the etching of the grain boundary portion proceeds and the surface roughness changes.

Furthermore, electrostatic chucks often have their power supply terminals brazed and joined due to their structure, and the joints cannot withstand high temperatures, causing the brazing material to deteriorate and causing poor conduction, or the power supply terminals to drop off. There is a fear. Further, there is a problem that the built-in electrode is peeled off due to thermal expansion due to heating, and the flatness of the electrostatic chuck surface is deteriorated due to the influence. On the other hand, in order to avoid the above problems, when the temperature of the heat treatment is lowered to, for example, about 500 ° C., the organic component and the metal component cannot be sufficiently removed and cannot be completely cleaned. There arises a problem that the organic component is colored by heating.

 The present invention has been made in view of the above-described problems of the prior art, and provides a cleaning method capable of effectively removing contaminants such as metal adhering to the adsorption surface of the electrostatic chuck without heating to a high temperature. There is to do.

The electrostatic chuck cleaning method of the present invention includes a step of immersing in a cleaning liquid using an aromatic hydrocarbon compound and / or a nonionic surfactant, and a step of performing a surface treatment by CO ₂ blasting. It is characterized by including.

The cleaning liquid used in the present invention uses an aromatic hydrocarbon compound and / or a nonionic surfactant. In general, an anionic surfactant is used as a cleaning liquid for an electrostatic chuck. However, according to studies by the present inventors, it has been found that a hydrophilic substance such as an anionic surfactant tends to remain on the surface. This is because the anionic surfactant is bonded to the hydrophilic group on the electrostatic chuck surface. Of the ceramic members used as the material of the electrostatic chuck, not only oxide ceramics but also non-oxide ceramics, the vicinity of the surface is usually oxidized, and OH groups are formed due to hydrophilicity. Therefore, the OH group and the anionic surfactant are combined to remain as an organic component residue, and this residue becomes a contaminant in the manufacturing apparatus.

On the other hand, aromatic hydrocarbon compounds and non-ionic surfactants of the present invention, since no binding with the hydrophilic groups of the electrostatic chuck surface, does not remain as a residue, moreover, by combination with CO ₂ blast Organic components and metals can be effectively removed. Details of this effect are not clear, but aromatic hydrocarbon compounds and nonionic surfactants can remove contaminants that are chemically bonded to the electrostatic chuck surface, whereas CO ₂ blasting is This is thought to be due to the difference in action that the contaminants that are bound to each other can be removed. In addition, with CO ₂ blast alone, it is conceivable that even if the deposits are physically scattered and peeled off, they re-adhere, but in the present invention, before the CO ₂ blast treatment, the aromatic hydrocarbon compound and Since the treatment with a cleaning solution using a nonionic surfactant is performed, it seems that it is difficult to cause a strong chemical bond even after reattachment. Therefore, in the present invention, since it is not necessary to heat to a high temperature as is normally performed, even a ceramic member such as an electrostatic chuck in which a power supply terminal is brazed to an internal electrode can be cleaned without causing any trouble. Can do.

The aromatic hydrocarbon compound is a monocyclic or bicyclic aromatic compound and a compound containing an alkyl substituent thereof, and examples thereof include alkylbenzene, naphthalene, alkylnaphthalene, indane, and alkylindan. Of these, alkylbenzene, naphthalene and alkylnaphthalene are preferable. These may be used alone or in combination of two or more as required.

Specific examples of nonionic surfactants include polyalkylene glycol ether type nonionic surfactants such as polyoxyalkylene alkyl ethers and polyoxyalkylene phenol ethers, polyalkylene glycol monoesters, polyalkylene glycol diesters and the like. Alkylene glycol ester type nonionic surfactants, alkylene oxide adducts of fatty acid amides, polyhydric alcohol type nonionic surfactants such as sorbitan fatty acid esters, sucrose fatty acid esters, fatty acid alkanolamides, polyoxyalkylene alkylamines, etc. Can give. You may use these individually or in mixture of 2 or more types.

As the cleaning liquid, either an aromatic hydrocarbon compound or a nonionic surfactant, or a mixture of both may be used without dilution or diluted with water or alcohol. However, since an aromatic hydrocarbon compound or a nonionic surfactant alone may remain on the surface of the electrostatic chuck, it is desirable to use it diluted. The concentration of the cleaning liquid is preferably 5 to 10% by mass for the aromatic hydrocarbon compound and 10 to 20% by mass for the nonionic surfactant. If it is at least the upper limit, there is a high possibility that the cleaning liquid will remain, and if it is at most the lower limit, the cleaning effect cannot be expected.

By performing CO ₂ blasting after cleaning, organic components and metals can be more effectively removed. CO ₂ blasting has the effect of physically peeling and removing contaminants by impact when fine dry ice is blown, and the effect of removing surface deposits by latent heat when dry ice evaporates. Therefore, the deposits can be removed without processing the surface. By performing this CO ₂ blasting, it is possible to remove the remaining cleaning liquid and contaminants that could not be removed.

It is also preferable to perform acid cleaning in the cleaning step. The type of acid is not particularly limited, such as hydrofluoric acid, nitric acid, and sulfuric acid. The optimum amount of acid is 3 to 7% by mass. When acid cleaning is performed, the power supply terminal portion is protected with a covering material such as silicon rubber.

The attracting surface of the electrostatic chuck of the present invention is made of ceramics mainly composed of Al ₂ O ₃ , Si ₃ N ₄ or AlN. These ceramics have a suitable volume resistivity at the substrate processing temperature, and are suitable for use in process environments such as etching and film formation that require corrosion resistance. However, these ceramics constitute an adsorption surface formed on the surface of the insulating layer of the electrostatic chuck, and members constituting the base other than the insulating layer of the electrostatic chuck are Al ₂ O ₃ , Si Ceramics mainly composed of ₃ N ₄ or AlN may be used, or other ceramics, metals, composite materials of metals and ceramics, or the like may be used. As a method for producing the ceramic of the adsorption surface, various methods such as thermal spraying and CVD can be adopted in addition to a sintering method such as normal pressure and hot pressing.

The internal electrode and the power supply terminal of the electrostatic chuck are brazed and joined. As the brazing material to be used, a material mainly composed of gold, silver, aluminum, nickel, platinum, vanadium, or the like can be used in consideration of wetting between the internal electrode, the material of the power supply terminal, and the ceramic member. An active metal such as titanium or zircon may be added to these to improve wettability with ceramics and to provide strength. The material of the internal electrode is preferably a material having a small difference in thermal expansion from that of ceramics. Among them, refractory metal molybdenum or tungsten is preferable. Nickel is often used as the power supply terminal. Brazing is accompanied by heat treatment, but during heating, the metal component of the brazing material and the metal remaining in the furnace are scattered and adhered to the ceramic, or carbon used as the furnace wall of the heating furnace or as a firing jig is used. Cleaning after brazing is indispensable for adhesion.

As described above, in the present invention, after cleaning using an aromatic hydrocarbon compound or a nonionic surfactant as a cleaning liquid, by using CO ₂ blast, inductive coupling of the electrostatic chuck surface after cleaning is performed. Each element of alkali metal, alkaline earth metal or iron by plasma mass spectrometry can be reduced to a very small amount of 300 × 10 ¹⁰ atoms / cm ² or less, and the total molecular weight of the organic component is also 500 × Since it can be reduced to 10 ¹² molecules / cm ² or less, a clean electrostatic chuck can be obtained without performing the heat treatment that has been a cause of conventional problems.

As described above, according to the present invention, after washing with an aromatic hydrocarbon compound or nonionic surfactant as a cleaning solution, to a heat treatment by cleaning the surface using a CO ₂ blast An electrostatic chuck with less adhesion of contaminants such as organic components and metals can be provided.

Hereinafter, examples of the present invention will be specifically described together with comparative examples, and will be described in more detail.

The electrostatic chuck was produced by a known hot press method described below. A mixed powder obtained by adding a sintering aid of a rare earth oxide to a commercially available AlN powder is uniaxially pressed at 100 kg / cm ² (= 9.8 MPa) to form a disk-shaped first molded body, A bipolar molybdenum internal electrode was disposed on the first molded body, and the above-mentioned mixed powder was filled thereon to form a second molded body. Each of the first and second molded bodies has a laminated structure in which an insulating layer and a base are formed, and an internal electrode is embedded between the base and the insulating layer. A board having a diameter of 200 mm × 15 mm (insulating layer thickness: 5 mm) is obtained by performing hot press sintering on a molded body having this laminated structure under the conditions of firing temperature: 1900 ° C., firing time: 2 hours, press pressure: 100 kg / cm ^2. An electrostatic chuck member made of a ceramic was obtained. Thereafter, surface grinding such as an adsorption surface was performed to obtain a desired shape, and a hole of φ4.1 mm was formed from the base side to expose the internal electrode. A nickel feeding terminal (φ4 × 15 mm) was fitted into the hole, and joined to an internal electrode (820 ° C. under vacuum atmosphere) via a brazing material obtained by adding titanium to a silver brazing material (BAg-8).

Under these conditions, eight electrostatic chucks having the same structure were produced, and a cleaning test was performed. The cleaning method for each test is shown below.

[Example 1]
After ultrasonic cleaning with methanol for 10 minutes, immersion cleaning was performed with a cleaning liquid using a xylene-based aromatic hydrocarbon compound for 30 minutes. Next, immersion cleaning with methanol is performed for 30 minutes, and CO ₂ blasting is performed for 20 minutes. Nitric acid (2%) was washed for 1 minute, rinsed with ultrapure water for 5 minutes, and dried with a dryer.

[Example 2]
Cleaning was performed in the same manner as in Example 1 except that a fatty acid alkanolamide type nonionic surfactant was used and the immersion cleaning time was 40 minutes.

[Example 3]
Cleaning was performed in the same manner as in Example 1 except that a polyoxyethylene alkyl ether type nonionic surfactant was used and the immersion cleaning time was set to 20 minutes.

[Example 4]
A method similar to Example 1 except that a cleaning agent in which a xylene-based aromatic hydrocarbon compound and a fatty acid alkanolamide-type nonionic surfactant were mixed at a ratio of 2: 1 was used and the immersion cleaning time was set to 30 minutes. And washed.

[Comparative Example 1]
Cleaning was performed in the same manner as in Example 1 except that a linear alkylbenzene anionic surfactant was used and the immersion cleaning time was 30 minutes.

[Comparative Example 2]
Cleaning was performed in the same manner as in Example 1 except that the step by CO ₂ blasting was excluded.

[Comparative Example 3]
A linear alkylbenzene-based anionic surfactant was used, and cleaning was performed in the same manner as in Example 1 except that the immersion cleaning time was set to 30 minutes, followed by heat treatment at 500 ° C. in the air. .

[Comparative Example 4]
A linear alkylbenzene-based anionic surfactant was used, and after cleaning by the same method as in Example 1 except that the immersion cleaning time was 30 minutes, heat treatment was performed at 1000 ° C. in the air. .

About the adsorption | suction surface of each said electrostatic chuck, the metal component was analyzed with the inductively coupled plasma mass apparatus (ICP-MS, Shimadzu Corp. make: ICPM-8500). In addition, GC / MS was used for the analysis of the organic component, and the value obtained by subtracting the number of molecules of carrier gas Ar and moisture was evaluated as the number of molecules of the organic component.

In Examples 1 to 4 within the scope of the present invention, the amount of each element of the metal component was 300 × 10 ¹⁰ atoms / cm ² or less. On the other hand, in Comparative Examples 1 and 2, which are outside the scope of the present invention, the amount of the metal component was remarkably large as compared with the Examples. Also, the amount of the organic component was very small compared to Comparative Examples 1 and 2. In Comparative Example 3 in which the heat treatment was performed at 500 ° C., color spots were generated, and in Comparative Example 4 in which the heat treatment was performed at 1000 ° C., the power supply terminal dropped.

Claims (4)

A step of immersing in a cleaning liquid using an aromatic hydrocarbon compound and / or a nonionic surfactant;
Performing a surface treatment with CO ₂ blasting;
A method for cleaning an electrostatic chuck, comprising: A method of cleaning an electrostatic chuck in which a power supply terminal is brazed to an internal electrode, wherein the electrostatic chuck is immersed in a cleaning solution using an aromatic hydrocarbon compound and / or a nonionic surfactant;
Performing a surface treatment with CO ₂ blasting;
A method for cleaning an electrostatic chuck, comprising: ^{3. The} element of alkali metal, alkaline earth metal or iron by inductively coupled plasma mass spectrometry of the electrostatic chuck surface after cleaning is 300 × 10 ¹⁰ atoms / cm ² or less. Cleaning method for electrostatic chuck. The electrostatic chuck, the electrostatic chuck cleaning method of claim 1, wherein the suction surface is a ceramic mainly composed of _{Al 2 O 3, Si 3 N} 4 or AlN.