JPH01183122A - Optical window for vacuum chamber - Google Patents

Abstract

PURPOSE:To make a glass plate into a convex lens without losing pressure resistance, to expand the observation range in a vacuum chamber and to make a device compact by forming a diffraction pattern serving as a lens on at least one side of a glass plate. CONSTITUTION:A Fresnel lens 11b is directly attached or tilted against on one side of a glass plate 11a which composes an observation window 11. Therefore, among scattered lights generated in a vacuum chamber 1 due to floating impurity particles a, at least the scattered lights which strike on the glass plate 11a become parallel after transmitting the glass plate 11a and pass through the optical system to he irradiated on a counting detector 8. Since the Fresnel lens 11b is tilted against the glass plate 11a and integrated together, two light beams having different wave lengths have different paths due to the difference in diffraction directions after transmitting the Fresnel lens 11b. This expands the observation range, enables the impurity particles to be counted accurately, and makes the device compact.

Description

[Detailed Description of the Invention] [Summary] Regarding optical windows for vacuum chambers in semiconductor manufacturing equipment, etc., for the purpose of expanding the observation area and downsizing the equipment, at least one side of the observation window for internal observation attached to the wall surface of the vacuum chamber is provided. A diffraction pattern plate with a lens effect is arranged and integrated into the vacuum chamber, or a diffraction pattern plate with a lens effect is tilted on at least one side of an observation window for internal observation attached to the wall of the vacuum chamber. Arrange, integrate and configure.

[Industrial application field]

The present invention relates to an observation window for a vacuum chamber in semiconductor manufacturing equipment, etc., and more particularly to an optical window for a vacuum chamber that expands the observation area and reduces the size of the device.

[Conventional technology]

FIG. 2 is a diagram showing an example of the configuration of a conventional observation window for a vacuum chamber. Note that the figure illustrates a case where the present invention is applied to a particle counter that irradiates impurity particles floating in a vacuum chamber with a laser beam and counts the impurity particles from the scattered light.

In the figure, 1 is a vacuum chamber, 2 is a circular transparent glass plate 2
The observation window a is sealed and fixed to a metal frame 2b, and the observation window 2 is fixed to the vacuum chamber 1 with a plurality of screws 3. Note that 4 is a backing for maintaining airtightness.

In this case, inside the vacuum chamber 1, for example, impurity particles shown as a in the figure are suspended at a certain density.

Further, 5 is a light source that irradiates laser light 6, and the laser light 6 is caused by impurity particles floating in the optical path of the laser light 6.
A part of the scattered light passes through the glass plate 2a and is further irradiated to the counting detector 8 by the optical system 7.

Here, when the laser beam 6 is emitted from the light source 5, the laser beam 6 travels straight inside the vacuum chamber 1, but if there are impurity particles indicated by a in the optical path, the laser beam 6 is caused by the particles as shown in the figure 6''. The result is scattered light scattered in all directions.

Of these scattered lights, only the part directed toward the glass plate 2a passes through the glass plate 2a, and further, only the part of the scattered light that enters the optical system 7 is irradiated onto the counting detector 8 and counted.

On the other hand, the laser beam 6 traveling straight is configured to be absorbed as is inside the vacuum chamber 1.

In this case, for example, the incident angle α with respect to the optical system 7 at one point P on the optical path is determined by both the window diameter of the observation window 2 and the optical system 7, and becomes smaller, and the number of scattered lights reaching the counting detector 8 decreases. Decrease. For example, if the reflected light from impurity particles floating at point P in the figure is in the direction 6+' in the figure, the counting detector 8 will count, but if the reflected light is in the direction 62' in the figure, the counting detector 8 will not enter the optical system 7. 8 doesn't count.

Therefore, things that should be counted are not counted, resulting in the same phenomenon as when the observation area is narrowed.

On the other hand, in order to increase the incident angle α, there are methods such as increasing the window diameter of the observation window 2 and the optical system 7, or using the glass plate 2a of the observation window 2 as a convex lens.
There are restrictions on size and thickness due to pressure resistance.

[Problem that the invention seeks to solve]

Conventional observation windows for vacuum chambers have the problem that the observation area is narrow and accurate counting of impurity particles is not possible, and the optical system installed outside the observation window becomes large, which hinders miniaturization of the device. was there.

Furthermore, when emitting light in a vacuum chamber through a plasma process or the like, there is a problem in that impurity particles cannot be counted.

[Means for solving problems]

The above-mentioned problem is solved by an optical window for a vacuum chamber, which is formed by disposing a diffraction pattern plate having a lens function on at least one surface of an observation window for internal observation attached to the wall surface of the vacuum chamber.

The problem can also be solved by an optical window for a vacuum chamber, which is formed by installing a diffraction pattern plate having a lens function in an inclined state on at least one surface of an observation window for internal observation mounted on the wall surface of the vacuum chamber.

[For production]

By forming a diffraction pattern having a lens effect on at least one surface of the glass plate, the glass plate can be made into a convex lens without impairing pressure resistance.

In the optical window for a vacuum device according to the present invention, a Fresnel lens is attached directly or at an angle to one surface of a glass plate constituting a conventional observation window.

Therefore, among the scattered light generated inside the vacuum chamber by floating impurity particles, at least the scattered light incident on the glass plate becomes parallel light after passing through the glass plate, passes through the optical system, and is irradiated to the counting detector. This enables highly accurate counting of impurity particles.

Furthermore, by integrating the Fresnel lens at an angle with respect to the glass plate, two light beams with different wavelengths have different diffraction directions, resulting in a difference in the optical path after passing through the Fresnel lens.

Therefore, even when light is emitted during a plasma process or the like in a vacuum chamber, the required number of impurity particles can be counted with high accuracy.

〔Example〕

FIG. 1 is a diagram showing an embodiment of an optical window for a vacuum chamber according to the present invention.

In the figure, 11 is the observation window and 4 forms a convex lens.
A circular transparent glass plate 11a to which a Fresnel lens 1.1b is attached, as shown in the perspective view (■), which is made of a transparent acrylic resin plate or the like on which a concentric diffraction pattern is formed on one side, is sealed and fixed to a metal frame 11c. It is configured as follows. Note that, as in the case of FIG. 2, the observation window 11 is screwed and fixed to the vacuum chamber 1 via a banking 4 with a plurality of screws 3. Further, impurity particles a are suspended inside the vacuum chamber 1 as in FIG.

5 is a light source, 6 is a laser beam 6, 12 is a condensing lens,
8 is a counting detector.

Here, when the laser beam 6 is irradiated from the light source 5 in the same manner as in FIG.
The configuration is such that the parallel light passes through the condenser lens 12 and irradiates the counting detector 8.

Note that the laser beam 6 traveling straight is absorbed and disappears within the vacuum chamber 1, as in FIG. 2.

In this case, for example, the angle of incidence α1 with respect to the condenser lens 12 with respect to one point PI in the optical path corresponds directly to the window diameter of the observation window 11, so when compared with α in FIG. 2, it is always α1 > α holds true.

On the other hand, when a plasma process is performed in a vacuum chamber, plasma ions emit light and cover the scattered light of floating impurity particles, which may reduce the accuracy of counting impurity particles.

Figure (B) shows an example applied to this case, in which floating impurity particles a and plasma ions b indicated by x are mixed and floating inside the vacuum chamber 1.

In the figure, 13 shows the observation window in this case.
The Fresnel lens Ilb in the observation window 11 is replaced with a Fresnel lens 13b as shown in the circular perspective view (2), which is obtained by cutting a cylinder made of transparent acrylic resin or the like diagonally and forming a concentric elliptical diffraction pattern on the elliptical exposed cut surface. It is something that

Furthermore, the condensing lens 12 and the counting detector 8 similar to those shown in FIG.

In a Fresnel lens having such a configuration, the optical path after passing through the light varies depending on the wavelength of the light.

For example, after the reflected light from the impurity particle a at 12 points shown in the figure passes through the Fresnel lens 13b, it becomes P2'' shown by the chain line, and the light from the luminescent plasma ion b at the same 22 points passes through the Fresnel lens 13b at two points. p211 is indicated by a chain line.

Therefore, the inclination angle β in the in-circle perspective view (2) is set to a preset value to realize separation of both waves.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an optical window for a vacuum chamber that allows for highly accurate observation by expanding the observation area within the vacuum chamber, and also achieves miniaturization of the device by making the optical system more compact.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the optical window for a vacuum chamber according to the present invention, and FIG. 2 is a diagram showing an example of the configuration of a conventional observation window for a vacuum chamber. In the figure, 1 is a vacuum chamber, 3 is a screw, 4 is a backing, 5 is a light source, 6 is a laser beam, 8 is a counting detector, 11.
13 is the observation window, lla, 13a is the glass plate, 11
b, 13b are Fresnel lenses, 11c, 13c are metal frames, and 12 is a condenser lens, respectively.

Claims (2)

[Claims] (1) An optical window for a vacuum chamber, characterized in that a diffraction pattern plate having a lens function is disposed on at least one surface of an observation window for internal observation attached to a wall surface of the vacuum chamber, and is integrated with the observation window. (2) An optical window for a vacuum chamber, characterized in that a diffraction pattern plate having a lens function is arranged in an inclined state on at least one surface of an observation window for internal observation attached to the wall surface of the vacuum chamber, and is integrated with the observation window. .