JPS61213750A - Monitor apparatus - Google Patents

Abstract

PURPOSE:To enhance measuring sensitivity, by partially or entirely arranging a fluorescence observing optical system in a container in which particles in a gaseous phase being an object to be observed are present. CONSTITUTION:Fluorescence generated at the point A in plasma P is condensed by a fluorescence condensing lens 6 to be made parallel. This parallel beam is passed through a quartz window 2 by a lens 7 to be condensed onto a detector 5. The fluorescence condensing lenses 6, 7 are attached to a holder 8 which is, in turn, fixed to a bench 9. The bench 9 is minutely movable from the outside of a vacuum container 1. By this method, the fluorescence condensing lens 6 can be allowed to approach the vicinity of the fluorescence emitting point A. As a result, the condensing of fluorescence at a wide three-dimensional angle is enabled and larger signal intensity is obtained. That is, high sensitivity measurement is enabled even with respect to active particles with low concn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an observation device for particles present in a gas phase, and particularly to a monitoring device capable of detecting these particles with high sensitivity.

[Background of the invention]

With the miniaturization of semiconductor circuit elements, the required element processing precision is becoming increasingly strict. Monitoring technology for active particles in plasma is essential for improving this processing accuracy.

As this monitoring technology, emission spectroscopy, which observes light emission from plasma, has conventionally been used. However, considering that not all active particles in plasma emit light, and that there are non-emissive particles that are closely related to plasma processes, monitoring techniques using emission spectroscopy are incomplete. I have to say that this is a great monitor technology.

Laser-induced fluorescence is a particle observation technique that allows observation of both luminescent and non-luminescent particles. Furthermore, the laser-induced fluorescence method has excellent features that other measurement techniques do not have, such as high spatial resolution (~0, 1 mm) and the ability to perform "in-situ a measurement" of particles. is attracting attention as a monitoring technology.

FIG. 1 shows the basic configuration of a monitor device using the laser-induced fluorescence method disclosed in Japanese Patent Application Laid-Open No. 58-66838. Furthermore, FIG. 2 shows a principle diagram of the laser-induced fluorescence method using a diatomic molecule as an example. Assume that active particles to be measured exist in the vacuum container 1. It is assumed that the energy level of the active particle is determined as shown in FIG. In FIG. 2 or the ground state, A represents the excited state. A vibrational level v'v' exists in each state. In order to observe these particles using the laser-induced fluorescence method, for example, the following method is used. First, set the wavelength of the laser beam of laser 4 to X (
The active particles in the vacuum container 1 are irradiated with the energy adjusted to match the energy difference between v' = O) and A (v' = O). At this time, the particle is X (v' = O) → A (v'
=O). A particle that has transitioned to an excited state transitions to another state after a certain period of time (lifetime). At this time, for example, there are particles that transition to X (v'=1). Such a particle is A (v' = O) - X (v' = 1)
Since the light is emitted as fluorescence of a wavelength corresponding to the energy difference between the laser beams, this fluorescence is detected using the detector 5 from a direction perpendicular to the incident laser light. This fluorescence intensity is X (v' = O)
Since it is proportional to the concentration of active particles at X (v' = O), the change in fluorescence intensity provides information about the change in the concentration of active particles at X (v' = O). The above is an outline of particle measurement using the laser-induced fluorescence method.

As described above, the laser-induced fluorescence method is based on a clear principle and has excellent features not found in other measurement methods, so it is considered as the next generation monitoring technology. but,
There are also problems that need to be solved in the future in order to make it practical and widespread. The biggest problem is improving measurement sensitivity.

For active particle measurement in plasma processes.

The active particles in the plasma are the measurement target. In this case, it is necessary to clearly distinguish between light emission due to discharge (background light) and laser-induced fluorescence (signal).

To this end, in many observation systems, as shown in FIG. 1, an incident laser beam is emitted by an optical system 3 (often by a lens) and is incident into a vacuum vessel 1. Further, the generated fluorescence is also emitted by the optical system 3' (also by the lens) and guided to the detector 5.

The diameter of the vacuum chamber used in plasma processes is much larger than the diameter of the chamber used in normal laser-induced fluorescence observation experiments. The ratio often reaches 10 times or more. When using a vacuum container having such a large diameter, if the optical system 3' is installed outside the container, the distance from one light emitting point to the optical system becomes long, and the fluorescence signal intensity is extremely reduced. This reduction results in a significant reduction in the signal-to-noise ratio of the measurement.

Here, the reduction in signal strength will be specifically explained using FIG. 3. In the figure, A is the focal point of the incident laser beam (fluorescent light emitting point), and B is the center of the fluorescence focusing lens. B
Let the radius of the lens installed at a point be a, and the distance between AB (that is, the focal length of the lens) be R. The fluorescence signal intensity I is proportional to the solid angle Ω at which point A is viewed from the lens.

I=toΩ (1) Here,
k: constant of proportionality The solid angle Ω is calculated using the angle θ shown in Figure 3 as Ω=2π(1
-cosθ) (2) Therefore, it holds true from equations (1) and (2). Here, if R>>3, I is approximated by the following equation from equation (3).

From equation (4), it can be seen that the signal strength is proportional to 1/R3. Installing the optical system 3' outside the vacuum vessel having a large diameter means that R in equation (4) becomes extremely large, and the processing time decreases rapidly.

For example, if R increases by a factor of 3, the workpiece decreases by approximately one order of magnitude.

As described above, increasing the size of the vacuum vessel is extremely disadvantageous for laser-induced fluorescence observation, but on the other hand, increasing the size to some extent is essential from the perspective of ensuring mass productivity in plasma processes.

In order to establish and popularize the laser-induced fluorescence method as an active particle monitoring technology in plasma processes, it is essential to secure fluorescence signal strength even in large vacuum vessels and improve measurement sensitivity.

[Purpose of the invention]

An object of the present invention is to provide a monitoring device capable of observing particles in a gas phase with high sensitivity.

[Summary of the invention]

According to equation (4), in order to perform observations with high sensitivity, that is, high signal strength, the lens diameter (a) must be increased or the distance (R) from the fluorescence emission point to the lens must be shortened. do it.

However, the former has the following problems. When the lens diameter is increased, the diameter of the fluorescence observation window (for example, the quartz window 2 in FIG. 1) must also be increased accordingly. However, depending on the plasma processing device, there are many devices in which only a small-diameter observation window can be installed. Furthermore, as the lens diameter increases, all optical systems related to the lens become larger, which causes problems such as installation space for the optical systems.

Therefore, the present invention focuses on the latter method. However, as shown in FIG. 1, if the optical system, especially the fluorescence focusing lens, is installed outside the vacuum container, R in FIG. 3 is limited by the size of the vacuum container. Therefore, in the present invention, R in equation (4) is shortened by installing part or all of the optical system for fluorescence observation inside a vacuum container. Although several problems occur when the optical system is installed in a vacuum container, these problems can be solved by taking appropriate measures (described specifically in the Examples section). Optical elements (lenses, etc.) are usually made of quartz. There was also a concern that if the optical system was installed in a vacuum container, the optical element would be damaged by the active particles and become unusable.

However, experiments have confirmed that as long as the optical element is not directly exposed to discharge (plasma) or the like, there is no major damage and the optical element can withstand use. According to experiments, by bringing the fluorescence focusing optical system closer to the laser focusing point, the signal intensity was increased by about one order of magnitude or more.

[Embodiments of the invention]

Examples of the present invention will be specifically described below.

<Example 1> The simplest example is shown in FIG. Fluorescence generated at point A in plasma P is focused by a fluorescence focusing lens 6 and converted into parallel light. This parallel light is focused onto a detector S by a lens 7 through a quartz window 2. A spectrometer (not shown) may be used in place of the detector 5, the focus may be focused on the input slit of the spectrometer, and the detector 5 may be connected to the output slit side of the spectrometer).

The fluorescence condensing lens 6 and the lens 7 are attached to a holder 8, and the holder 8 is fixed to a bench 9. By using such a system, lens adjustment and replacement becomes easy. Further, although not shown in the figure, the bench 9 can be slightly moved from outside the vacuum container 1. The material of optical elements such as lenses is quartz.

The material of the holder 8 and the bench 9 is preferably aluminum or stainless steel, which has a black luster and is burnt-out, since it has little effect on degassing and plasma processes.

By using this embodiment, it is possible to bring the fluorescence condensing lens 6 close to the fluorescence emission point A. As a result, fluorescence can be collected over a wide solid angle, resulting in higher signal intensity. In other words, highly sensitive measurement is possible even for active particles with a small concentration.

This embodiment is an embodiment in which a relatively large-diameter fluorescence observation window can be installed in a direction perpendicular to the incident laser beam. If it is not possible to install a fluorescence observation window perpendicular to the incident laser beam,
The means shown in the following examples are effective.

<Embodiment 2> In the embodiment shown in FIG. 5, the fluorescence generated at point A is focused and collimated by the fluorescence focusing lens 6, and focused onto the optical fiber head 14 by the lens 10. .

The collected light passes through the optical fiber 15, heads toward the lens 11 from the other optical fiber head 13, and is focused onto the entrance slit of the spectroscope 16 by the lens 11.

Lenses and optical fiber heads are fixed to the holder 8 as in the first embodiment. The materials of the holder 8 and benches 9 and 12 are the same as in the first embodiment. In order to suppress degassing from the surface of the optical fiber 15, it is desirable to remove all unnecessary coatings and the like. Although not shown in the figure, bench 9,1
2 can be slightly moved from the outside of the vacuum container 1.

As described above, the effect of using this embodiment is that fluorescence observation can be performed from a direction perpendicular to the incident laser beam, regardless of the position of the fluorescence observation window.

Of course, it goes without saying that fluorescence observation is possible from any direction other than the orthogonal direction. Furthermore, another advantage of this embodiment is that the fluorescence observation window can be made smaller. This is due to condensing the light from the optical fiber head 13.

<Embodiment 3> FIG. 6 shows an embodiment that does not use an optical fiber.

The fluorescence generated at point A is focused and collimated by the fluorescence focusing lens 6, passes through the optical guide 17, and is focused by the lens 11 onto the entrance slit of the spectrometer 16.

The structure of the optical guide of this example is shown in FIG.
The optical guide is composed of an optical quartz rod 20 and a low refractive index material 19 surrounding it. optical fiber 1
The reason why the optical guide 17 is used instead of the optical guide 5 is to improve the fluorescence transmission efficiency. Optical fiber is the 8th
As shown in the figure, it is constructed by bundling a plurality of optical fibers 21. Since the cross section of the optical fiber 21 is approximately circular, a space 22 is created when a plurality of optical fibers are bundled. this space 2
Since 2 does not function as an optical fiber, the fluorescence transmittance decreases by the proportion of this space.

On the other hand, since the optical guide is basically a rod made of quartz (not hollow), it is easy to increase the diameter thereof, and the space 22 shown in FIG. 8 does not occur. Since the transmittance of optical quartz is close to 100% in the ultraviolet light region, the transmittance of fluorescence is improved compared to optical fiber.

Another advantage of this embodiment is that the installation of benches 9 and 12 as seen in the previous embodiment is unnecessary, and the vacuum vessel 1
The objective is to simplify the internal optical system. That is, since the optical guide 17 can have a large diameter, the fluorescence condensing lens 6 is attached to the holder 8, and this holder 8 is directly attached to the optical guide 17. Furthermore, the optical guide 17 is attached to the empty container 1 via an O-ring 18. Therefore, since the optical guide 17 can be moved back and forth while maintaining the vacuum, the focus of the fluorescence focusing lens 6 can be easily adjusted from outside the vacuum container 1.

<Fourth Embodiment> FIG. 9 shows another embodiment using an optical guide.The usage of the optical guide 17 in this embodiment is generally the same as in the third embodiment.

The feature of this embodiment is that the optical guide 17 is tapered in the middle, and one end of the tapered end is a bellows 23,
It exits to the outside of the vacuum container 1 via the ring 18. As shown in this embodiment, the optical guide can be processed to have a smaller diameter or to be bent in the middle with relative ease.

The advantages of this embodiment are that the optical guide can be introduced into the vacuum vessel 1 even if the fluorescence observation window has a small diameter, and
Regardless of the position of the fluorescence observation porthole, fluorescence observation is always possible from the direction perpendicular to the incident laser beam. Further, since the optical guide 17 is attached to the vacuum container 1 via the bellows 23, the optical guide 17 can be moved back and forth, left and right, and up and down. As a result, not only fine adjustment of the fluorescence condensing lens 6 but also the spatial distribution of fluorescence can be easily performed.

<Example 5> As described above, optical elements such as lenses can be used satisfactorily as long as they are not directly exposed to plasma.

This embodiment is an embodiment in which the life of optical elements such as lenses can be further extended. The specific configuration of this embodiment is shown in FIG.

The features of this embodiment are that a fluorescence focusing lens 6 is installed in a vacuum chamber 25, a plate 24 having a differential pumping aperture is provided between the vacuum container 1 and the vacuum chamber 25, and the vacuum chamber 25 is evacuated. The purpose is to exhaust the air independently of the container 1. By using this method, the number of active particles flowing into the vacuum chamber 25 is reduced, and the life of optical elements such as the fluorescence focusing lens 6 can be extended.

The method of this embodiment can be applied to all of Examples 1 to 4, and all such application examples are included in the present invention.

There is also a method of flowing a small amount of inert gas into the vacuum chamber 25 in order to protect the surfaces of optical elements, etc., and this method is also included in the present invention.

If a small gate valve or the like is attached to the differential pumping aperture and the gate valve is opened only during fluorescence observation, the life of the optical element can be further extended. This method is also included in the present invention.

Finally, although not included in the embodiments of the present invention, a method based on the same concept as the present invention will be described. The method is shown in FIG. In the example shown in the figure, a pipe 28 is extended into the vacuum vessel 1, and a perforated flange 27 is attached to the end of the pipe 28. With this method as well, it is possible to bring the fluorescence condensing lens 6 close to the light emitting point A. However, in this method, the vacuum container 1
The structure itself becomes complicated, and when considering the thickness of the perforated flange 27, the quartz plate 26, etc., there is a limit to the distance that the fluorescence condensing lens 6 can be brought close to the light emitting point A.

Examples 1-5 do not have these drawbacks.

〔Effect of the invention〕

According to the present invention, particles in the gas phase can be detected with high sensitivity! Therefore, the present invention has great industrial effects as a highly sensitive monitoring device for these particles.

[Brief explanation of drawings]

Figure 1 is a plan view showing the basic configuration of a monitoring device using the laser-induced fluorescence method, Figure 2 is an energy level diagram of active particles, and Figure 3 is the focal point of the incident laser beam and the fluorescence focusing lens. Explanatory diagrams showing the relationships between Figures 4 to 6 and Figures 9 to 1
Figure 0 is a longitudinal cross-sectional view of a monitor device that is an embodiment of the present invention, Figure 7 is a cross-sectional view of an optical guide, Figure 8 is a cross-sectional view of a fiber bundle, and Figure 11 is a monitor device that is a reference example. FIG. 1... Vacuum container, 2... Quartz window 1.3.3'...
·Optical system. 4...Laser, 5...Detector, 6...Fluorescence focusing lens, 7...Lens, 8...Holder, 9...Bench, 10...Lens, 11...・Lens, 12...
・Bench, 13.14...Optical fiber head, 15・
... Optical fiber, 16 ... Spectrometer, 17 ... Optical guide, 18 ... 0 ring, 19 ... Low refractive index material, 20 ... Optical quartz rod, 21 ... Light Fiber fiber, 22... Space, 23... Bellows, 24
...Plate, 25...Vacuum chamber, 26...Quartz'fI+
Mouth 3rd eye 4th eye I Kaya 5 mouth 2nd eye %7r;a 1g day two yfJ'l mouth! Part ll b

Claims (1)

[Claims] 1. In an observation device for particles in the gas phase that uses a laser-induced fluorescence method, part or all of the optical system for fluorescence observation is installed in or in a container in which particles to be observed are present. A monitor device characterized in that it is installed inside another connected container. 2. The monitor device according to claim 1, wherein the particles to be observed are semiconductor plasma process gas particles or particles generated by discharge of these gases.