JP2701489B2 - Turbo molecular pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a turbo molecular pump that can be widely applied to various manufacturing fields such as a semiconductor manufacturing apparatus.

[Prior Art] A turbo molecular pump (hereinafter abbreviated as TMP) is a fifth type.
As schematically shown in the drawing, a rotor 2 is rotatably disposed in an outer cylinder 1, and a number of rotors 3 are integrally protruded around the outer periphery of the rotor 2. Outer cylinder 1
A turbine 6 is formed by alternately inserting a number of fixed blades 5 sandwiched and supported by a spacer 4 on an inner periphery thereof, and a turbine 6 is formed. It is. This type of TMP is widely used in semiconductor manufacturing equipment and other ultra-high vacuum fields, because it is superior to other vacuum pumps in exhaust capacity. Regarding the method of manufacturing the blade, the rotor 3 is formed integrally with the outer periphery of the rotor 2 made of aluminum alloy by cutting or electric discharge machining, and the fixed blade 5 is placed at a required position of a semi-annular disk made of stainless steel (or aluminum). After slitting, it is made by bending. After processing, only the degree of ultrasonic cleaning
It is assembled to the P body and put to practical use.

[Problems to be Solved by the Invention] By the way, the ultimate pressure of this type of TMP is in the order of 10 ^-10 Torr after the baking process, and even a magnetic bearing type TMP is used.
Achieving the 10 ^-11 Torr range is considered extremely difficult.

Then, as a result of various studies by the present inventor to lower the ultimate pressure, the following has been gradually clarified. In other words, in order to perform machining and the like at the time of wing processing, the crystal on the base material surface that becomes the wing is deformed and destroyed, and the lubricant,
Abrasives and the like bite into the base material, and as a result, a complex deteriorated layer using them as occlusion materials is formed. The occluded material may be hydrogen gas or the like, or a highly reactive gas releasing substance. In addition, the altered layer is covered with a porous oxidizing substance, and has a surface state in which gas molecules are easily adsorbed. Therefore, because TMP uses wings made by such processing, desorption of occluded substances, gas emission by decomposition and evaporation, and gas emission by desorption of newly adsorbed gas molecules occur in exhaust gas. This is considered to be the main factor that lowers the exhaust capacity.

The present invention has been made in view of such considerations, and an object of the present invention is to provide a TMP with improved exhaust performance as compared with the related art by taking good care of the problem of gas release.

[Means for Solving the Problems] The present invention employs the following means to achieve the above object.

That is, the TMP according to the present invention is characterized in that the surfaces of the fixed wing and the rotary wing are provided on a mirror surface having a small amount of occluded substances causing gas release and preventing the adsorption of new gas molecules. For mirror finishing, a method of performing combined polishing of electrolytic polishing and chemical polishing is employed.

[Effect] As in the present invention, when a gas-releasing substance is not occluded on the surfaces of both wings of the TMP and is a mirror surface which does not allow the adsorption of gas, the generation of gas in the exhaust gas is extremely reduced. For this reason, it is possible to effectively solve the conventional problem that causes the exhaust performance of the TMP to be reduced due to this.

In addition, when the mirror finish is performed through composite polishing, the deteriorated layer containing occlusions can be dissolved and removed by electrolytic polishing to make a glossy surface, and the electrolytic product generated by electrolytic polishing is used in combination with chemical polishing. As a result, both wing surfaces can be finished to a dense and clean mirror surface.

[Embodiment] One embodiment of the present invention will be described below with reference to FIGS. Parts common to those in FIG. 5 are denoted by the same reference numerals.

In this embodiment, the entire rotor 2 shown in FIG.
2a) and the entire fixed wing 5 shown in FIG. 2 is subjected to composite polishing after processing.

Combined polishing is realized based on a conventional electropolishing apparatus and incorporating elements of chemical polishing. That is, in general electrolytic polishing, an electrolytic solution is put in an electrolytic cell, a workpiece is immersed in the electrolytic solution to serve as an anode, and an insoluble metal is used as a cathode to dissolve the surface of the workpiece to dissolve the cathode. To deposit metal on the surface (not shown). This makes it possible to remove the invisible altered layer generated in the portion where the rotor 2 and the fixed blade 5 have been machined, and at the same time, dissolve the convex portions preferentially over the concave portions and smoothen them. Face can be obtained. However, in this state, the electrolytic product covers the surface, and a high quality mirror surface cannot be obtained. Therefore, the processing temperature and the processing liquid are set in a region close to the chemical polishing, and the way of flowing the current is devised so that the electrolytic product does not cover the surface of the workpiece in the above process. As a result, the surfaces of the rotor blades 3 and the fixed blades 5 are not destroyed by the metal crystal structure, and a dense and stable mirror-formed oxide thin film is formed thereon. Of the surface obtained in this way
The SEM observation state becomes smooth as shown in FIG. 3, and when this is compared with the figure obtained by conventional cutting or electric discharge machining (FIG. 4), it is recognized that there is a surprisingly significant difference in the surface roughness. . As a result of calculating the geometric surface area along the irregularities of the surface, it was confirmed that according to the present example, the surface could be smoothed to about 1/20 of the conventional one.

When the rotor 3 and the fixed wing 5 having such mirror surfaces are assembled to the TMP main body, and the intended use of a chamber or the like is connected to the intake port 7 for operation, the surface of the rotary wing 3 or the fixed wing 5 is exhausted during exhaust. Hydrogen gas, etc., which is unrelated to the actual exhaust gas, is hardly released, and the exhaust gas is exhausted while the gas to be exhausted or the residual gas from the previous use repeatedly adsorbs / desorbs on those surfaces. The hindrance can be effectively solved. For this reason, according to the illustrated TMP, the startup time of exhaust gas is shortened, which can reduce operating costs and is extremely effective in increasing the ultimate pressure, which is the most important factor, to below 10 ^-11 Torr. Can be

It should be noted that components other than the wings (for example, components facing the vacuum region such as the spacer 4 and the outer cylinder 1 or chambers to be used) are also subjected to the process according to the present invention, thereby realizing a TMP with less gas emission. be able to.

[Effects of the Invention] As described above, the TMP of the present invention can reduce the amount of gas harmful to the exhaust gas and make the exhaust gas effective by making the surfaces of the fixed wing and the rotary wing a dense and clean mirror surface. it can. As a result, various characteristics such as the evacuation speed and the ultimate vacuum of the turbo-molecular pump can be surely improved as compared with the related art. According to the composite polishing method, such a mirror surface can be realized relatively easily.

[Brief description of the drawings]

1 to 4 show an embodiment of the present invention, FIG. 1 is a perspective view showing a rotor in partial cross section, FIG. 2 is a perspective view of a fixed wing, and FIG. 3 is a cross section of a wing surface. FIG. FIG. 4 is a sectional view showing a conventional blade surface corresponding to FIG. 3, and FIG. 5 is a longitudinal sectional view of a general TMP. 3 ... rotor wing, 5 ... fixed wing

Claims (1)

(57) [Claims] 1. A turbo-molecular pump comprising a fixed wing and a rotary wing, wherein an occluded substance causing gas release is obtained by subjecting the surfaces of the two wings to a combined polishing of electrolytic polishing and chemical polishing. A turbo-molecular pump characterized in that it is provided on a mirror surface that can prevent the adsorption of new gas molecules.