JPS62215843A - Particle detector for wafer processor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to particle detectors, and more particularly to particle detectors for monitoring airborne particles or particles in a vacuum or fluid environment.

As wafer sizes increase and device geometries become smaller, particle object detection and control becomes even more important in semiconductor processing. Particle level monitor
It is important for processes performed in an air environment at atmospheric pressure, such as the exposure of photoresist patterns, and for processes performed in a vacuum chamber, such as the deposition of metal films. By using so-called clean rooms using air filtration methods, it is possible to reduce particle contamination for processes carried out in an air environment at atmospheric pressure. However, even with air filtration methods, processing equipment uses moving parts that generate particles, and particle level monitoring is essential for early detection of system breakdowns that generate excessive particle levels. desirable.

One conventional method of detecting airborne particles is shown in FIG. Sampled air (indicated by arrow 5 in FIG. 1) is drawn through narrow transparent tube 6 by a vacuum pump (not shown) attached to end 6+1 of cylindrical tube 6. Monochromatic light 1 from a laser (not shown) or white light from a lamp (not shown) forms a focused beam 3 that is focused by a lens 2, which is directed at a selected point along a transparent tube 6. pass through. Pass through beam 3
The light scattered by particles in the sampled air 5 drawn in through the tube 6 is detected by a detector 7. Alternatively, an aperture (not shown) in the tube 6 and an air sheath may be provided such that one focused beam passes through the aperture in the tube. The detector 7 has a photomultiplier,
Its configuration is conventionally known. Scattering intensity is approximately proportional to particle size. Such systems are 0.1 micron and 7
．． Particles with an average diameter in the range between 5 microns are typically detected, and in principle it is possible to detect smaller and larger particles using the system described above.

Prior art particle monitoring devices have several drawbacks.

(1) The conventional device basically consists of the following points: the opening of the tube;
sample the air from the ground and do not provide adequate measurements of particle contamination over a larger spatial area. As often encountered in semiconductor processing environments, moving parts of various machines can generate particles that are not detected by sampling at specific points. Therefore, prior art particle monitoring devices.

It does not adequately monitor particles from multiple or dispersed sources.

(2) Prior art monitoring systems require airflow to transport the particles and therefore operate in air, but not in a vacuum chamber.

(3) Particles may stick to the sides of the tube 6 and become airborne again at a later time, creating a retardation effect.

(4) The physical end 6b of the tube must be located physically close to the point being monitored, which may interfere with other parts of the processing system.

The present invention has been made in view of one or more points, and it is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to provide a particle detector suitable for detecting particles existing in air or in a vacuum. purpose.

In one embodiment, the detector includes a laser and a beam-forming lens that generates a beam whose height is small compared to its width. The beam is reflected back and forth between the two mirrors a selected number of times, forming a "sheet J" or "net" of light between the two mirrors.

The path of the glare is terminated by a beam stop J which monitors the intensity of the beam and thereby provides a degree of system alignment. Light scattered from particles falling through the light net generated between the two mirrors is detected by one or more photodiodes. The signal generated by the photodiode is amplified and processed by a peak detector.

Peaks above a selected threshold value are counted by a microprocessor, which calculates the particle Franks density.

In one embodiment, the beam is chopped and a lens is used to focus the beam and compensate for beam divergence. The protruding member prevents debris from falling onto the reflective surface of the mirror and prevents light scattered by imperfections in the mirror surface from reaching the photodiode.

In certain configurations, the photocell is positioned to directly observe the light sheet between the two reflective mirrors, allowing very compact sensor assemblies to be constructed. . Since the reflective mirrors are moved in close proximity together within the miniature sensor assembly, a significant improvement in response to the detected light beam is realized. In another configuration useful for monitoring particles in high temperature environments, such as high temperature or corrosive gases or liquids, the sensor assembly comprises a narrow length of pipe fitted with a glass window and a reflective mirror. It leaves a small gap in between. The glass window functions to protect the optics from corrosion and heat. The housing for the sensor assembly is water cooled to reduce thermal effects.

Two or more particle detectors of the present invention can be combined to detect particles falling through large areas, such as 8 inches by 8 inches.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figures 2a and 2c show a plan view and a side view, respectively (not to scale) of an embodiment of the particle monitor of the present invention. Laser 10 is preferably a semiconductor laser, such as an AlGaAs laser operating at a wavelength of 820 nm. R.C.A.
Laser number C86000E and Hitachi laser number HL 8
312 E is suitable for this purpose. Other light sources (not necessarily monochromatic) can also be used in the present invention. The beam 11 emerging from the PN junction of the semiconductor laser 10 is collimated by one cylindrical beam-forming lens 12 and 13, which are combined to shape the beam in the horizontal and vertical planes. The beam 14 emitted from the lens 13 is
Further details are shown in the figure, which shows a cross-section of the laser beam 14 along line A shown in FIG. 2a.

In one embodiment, beam 14 is modulated or chopped by the circuitry shown schematically in FIG. The beam 14 has an initial height H6 and an initial width W determined by the width of the PN junction (not shown) of the semiconductor laser 1 and the shaping lenses 12 and 13. have.

In one embodiment, the width of the PN junction is approximately 40 microns, and beam 14 has a width of 2.0 no++ and a height of 0.4 mm at the point where it exits shaping lens 13. Laser 10 and beam shaping lenses 12 and 13 are positioned relative to flat M electric mirrors M1 and M2, such that dielectric surfaces S1 and S2 of mirrors M and M2, respectively, are parallel to each other. Moreover, as shown in FIG. 2b, it is perpendicular to the plane P through the center of the beam 14. The reflective surfaces S and S2 of mirrors M1 and M2 have lengths Ll and H2, respectively, and a height h, as indicated by arrows L1 and H2 in FIG. 2a and by h in FIG. 2c. ing.

In FIG. 2a, the solid line emerging from laser 10 indicates the center of beam 14. In FIG. Light at the center of beam 14 is incident on surface S1 at Pl with an angle of incidence α of less than 90 degrees and is reflected to point P2 on surface S2 and generally from Pk to Pk+1 (where k=1.,
,,． 6), thus forming the zigzag pattern shown in FIG. 2a.

The light reflected from point P7 is received by beam stop 20, which includes a photocell (not shown).

In Figure 2a, the area between each pair of adjacent parallel lines, indicated by long dotted lines, is the area of the light beam 1 traveling towards the surface S.
The area between each pair of adjacent parallel lines representing segments of 4 and represented by short dotted lines is from surface S1 to surface S
2 represents a segment of beam 14 proceeding to 2; Surface S Yoto 8
2 and the angle of incidence α, the distance between Pl and P3 is the width W of the beam 14. is selected so that Since the surface S and 82 are parallel, the distance between Pk and Pk+1 is W for k=2.3, 4.5.

It should be noted that for this choice of parameters S and α, the zigzag path of beam 14 covers the entire area of the trapezoid defined by end points 15 and 16 of surface S1 and points 17 and 18 of S2. form a light sheet. In fact, this total area is.

It is covered both by light traveling from surface S1 to surface S2 and by light traveling from surface S2 to surface S1.

FIG. 2d shows another choice of the spacing S between the 5 surfaces S□ and 82, and another choice of the angle of incidence α, in which case:
The distance between the first and second points A1 and A1 where the center of the beam 14 is incident on the surface S1 is the width W of the beam 14. even bigger than. For this parameter selection, beam 1
The zigzag pattern (optical net) formed by the reflection of
It does not cover the entire area of the trapezoid defined by 27°28. The shaded triangles indicate these areas not covered by the beam.

A side view of reflective surfaces S0 and S2 is shown in FIG. 2c. Collector mirrors 21 and 22 collect the light scattered from the falling particles through the light net generated by the beam 14 between the surfaces S and 82. These collector mirrors are typically parabolic in shape and focus the scattered light onto photodiodes PD and PO2, respectively. The height h of mirrors M0 and M2 is relatively small with respect to the dimensions of collector mirrors 21 and 22. because.

M 21 and 22 are reflected from the surface of the light sheet generated by the laser beam 14 and mirrors M□ and M
This is because it is possible to "clear" 2 and further collect only the light that "overhangs" O□, 0□, Ol, and ○. "Overhang" 01102.0. and 0.
prevents dust from falling onto the surfaces S□ and S2, and since they are opaque, the surface S and S2
The light scattered by the defect is reflected in the collector mirror 21.
and 22.

It should be noted that the side view of the optical net formed by the reflection of beam 14 from surface S and S2 is shown schematically only as a line. Without compensation means, as the beam progresses, beam divergence would cause beam 1
The thickness of No. 4 tends to increase gradually. This will reduce the power density of the beam. For simplicity, this gradual increase in beam thickness is not shown in FIG. 2c.

Similarly, in the absence of compensation for divergence, beam 14
The width of also increases with path length, but this is not shown in FIGS. 2a and 2d for simplicity. Ho is W.

Since the width divergence of the beam 14 is typically much smaller than the height divergence of the beam.

Insulator mirrors M4 and M2 are typically formed from alternating high and low index coatings on glass or quartz substrates. A suitable mirror has a minimum reflectance of 99.3
%, such as part number /237, is a Melles Griot λ/30 mirror with a patented MAX-R coating. Therefore, the beam intensity only decreases slowly as the number of reflections of beam 14 between surfaces S1 and 82 increases. However, when using semiconductor lasers in the present invention, commercially available models thereof are currently limited in power, e.g. typically less than 20 milliwatts, and each reflection reduces the power density of the reflected beam. Therefore, to reduce the number of reflections, surfaces S4 and S2 are typically separated by a larger distance S than L and L2.

However, it should be noted with respect to both Figures 2a and 2d that typically more than 6 or 7 reflections are used between the surface S and 82; For simplicity, fewer reflections are shown in these figures.

For example, if 5=150a+Il and W=1mm, 2
Zero reflections cover an area of approximately 150 mm x 20 mm.

The beam stop 20 has a photocell (second a) inside the housing.
(not shown) which terminates the beam 14 and monitors the power of the laser beam incident on the photocell. This monitoring operation is performed by conventional circuitry (not shown) and serves to indicate when the system is misaligned. When the laser beam is misaligned.

The power of the beam incident on the photocell in beam spot 20 is reduced below a preselected level, and conventional circuitry (not shown) generates a signal from beam spot 20. This signal can operate a visual signaling device, such as a light, or can be fed to a microprocessor (not shown).

FIG. 2e shows the collector mirror 21 and the photodiode P.
FIG. 6 shows a partial diagram of an embodiment of D. The lower part of the diagram is a mirror image of the upper part, but is not shown for simplicity.

Mirror 21 has a parabolic shape. The focus of the parabola is 2 cm from the vertex V.

P whose width (vertical dimension in Figure 2e) is 0.5 cm
The center of Dl is located at the origin (0,0) of the coordinate system and is 2.6 cm from the vertex V. Mirror M4 and PD
The distance between mirror M2 and mirror M2 is 0.2 cm, and mirror ML is separated from mirror M2 by Loan. The region 21a between the parabolic mirror 21 and the flat surface 21b comprises a glass with a refractive index of 1.5, which reflects the beam of light scattered at 15 degrees as shown in FIG. 2e towards the horizon. refract. (Surface 21b is the front surface of the glass.

) By using such a glass having a refractive index greater than 1, the acceptance, that is, the permissible angle θa increases.

The acceptance angle is the maximum angle at which light can be scattered from particles in beam 14 in front of mirror M and reflected through lens 21 to photodiode PD1.

Table 1 in FIG. 20 shows the acceptance angle θa (in degrees) as a function of X, where X is the distance of the particles in beam 14 in front of mirror M4. As shown in Table 1, the minimum angle of acceptance for at least 1c11 particles in front of mirror M is 15 degrees.

Figure 3a shows the 6,328 wavelengths (He
Figure 3 shows the scattering cross-section for spherical particles as a function of angle and particle size for monochromatic light with an N e laser.

The horizontal axis in FIG. 3a is degrees and each horizontal axis O is the third
As shown in figure b, a right circular cone with an angle θ and an angle θ+5
It represents the three-dimensional area between the right circular cone and the angle. The vertical axis represents d.

Curves A, B, C, D, E, F, G, H, and T are respectively 0
．． 2 micron, 0.3 micron, 0.4 micron, 0.
5 microns, 1.0 microns, 1°5 microns, 2.0
Micron, 2.5 micron.

Figure 3 is a scattering cross section curve for a particle with a physical diameter of 3.0 microns. Because of interference effects, each particle has an apparent cross section that is different from its physical cross section. The scattering cross section shown in Figure 3a is apparently a cross section. As used in the preferred embodiment, the AlGaAs laser diode is
, generates light with a wavelength of 200 people. The intensity of the scattered light is somewhat less in this case, but the angular dependence is
This is approximately the same as curves A to I in the figure. It should be noted that the strongest scattering is in the forward direction, e.g. about 25'' into the curve.
The collector lens system shown in Figure c is used with a lens positioned approximately perpendicular to the direction of advancement of the laser beam 14 to collect the forward scatter. A system with a collector lens positioned on the side of the laser net generated by the laser beam 14 and approximately parallel to the direction of travel of the laser beam 14 is operable, but with significantly reduced efficiency.

In one embodiment, the light emitted from laser diode 10 is electronically chopped (i.e., pulsed). The output signal of the photocell 31 in the beam stop 20 (shown in Figure 2a) is fed to the power source 3o of the laser diode 10 to maintain a selected constant laser power output. The purpose of chopping the beam is to generate a particle detection system that operates in the presence of light from sunlight or other unmodulated light sources. Since the detection circuit described below looks for signals at the chopping frequency rather than DC, this significantly improves the signal-to-noise ratio. In one embodiment, the frequency of the AC power source is 3 MHz and the laser beam is activated at least 10 times during the time it takes for a particle to fall under gravity vertically through the optical net generated by beam 14. It is desirable to use a frequency high enough to have an on-cycle. For example, if a particle has a speed of 1,500 cm/s and a thickness H=0.03 cm
Assuming that a beam with a force of ), 10 cycles must occur within 1150.000 seconds, which corresponds to a frequency of 500 kHz.

Since beam 14 is chopped, the scattered light received by photodiodes PD1 and PD as the particles fall through the light net generated by beam 14 is also chopped. The chopped and scattered light detected by PD 4 is amplified by amplifier 34a.

Amplifier 34a is a low noise operational amplifier, such as the LT10378 manufactured by Linear Technology Corporation.
It is C. Alternatively, amplifier 34a can be fabricated with discrete components and low noise FETs, providing an even better signal-to-noise ratio. It is preferred to mount amplifier 34a within 2 cm of photodiode PD1 to minimize noise pickup at the connections. The second stage 34b is mounted in a separate housing, shown schematically in dotted lines in FIG. A typical output signal of amplifier 34b is shown in solid line in Figure 5a (not to scale). The dotted line connecting the solid positive peaks in Figure 5a is the "positive envelope" of the signal.

The output signal of amplifier 34b is sent to a mixer 35, which is, for example, an analog multiplier manufactured by Exar, part number XR-2.
208 is possible. Mixer 35 also receives a 3 MHz signal from AC power source 20. mixer 3
The output of 5 (shown in Figure 5b) is the positive envelope of the output signal of amplifier 34b. The output signal of the mixer 35 is
For example, part number LT1055 manufactured by Linear Technology
and is then fed to a peak detector 37 whose output signal represents the magnitude of the peak of the envelope shown in FIG. 6b amplified by amplifier 36. The output of peak detector 37 is provided to an A/D converter 38 which provides a corresponding digital signal to microprocessor 39.

In this embodiment, the output signal of peak detector 37 is multiplexed with the output signal of peak detector 37a. The peak detector 37a is a peak detector that works in conjunction with the photodiode PD2.

The remaining circuitry associated with photodiode PD2 is the same as that associated with photodiode PD1 and is not shown in FIG. 4 for simplicity.

Peak detectors 37b, 37c, 37d in FIG. 4 are integrated two or more systems identical to those shown in FIG. 2a, i.e., physical 3 represents a peak detector for a photodiode (not shown) used in the embodiment, which is located in close proximity to the photodiode shown in FIG.

In a typical application, a computer calculates the particle flux density, ie, the number of particles passing through beam 14 during a selected time interval. Microprocessor 39 compares the signals it receives from peak detectors 37 and 37a. When both signals exceed a preselected threshold value, microprocessor 39 causes particles to
It is determined that the light has passed through the optical net generated by the light and has descended. The peak detector provides a signal that is held for a selected time, eg 1 millisecond, so that only the largest particles that scatter light during the selected time are counted. This is acceptable in applications since many counts are very low, for example in a clean room, typically one particle per second is counted. The microprocessor maintains this count and tracks time while calculating the particle flux density and outputting the results on a display (not shown) or via an interface bus (not shown) to an external computer. make it possible. Microprocessor is also 1
It is possible to estimate one particle size based on the gains of the circuits 34a, 34b, 35.degree. 36 and the detected signal strength provided by the A/D converter. Typically, the output of the microprocessor is also used to trigger the opening of an interlock relay (not shown) to terminate the operation of the processing device when the detected particle flux exceeds a preset critical level. It is possible to do so.

In the embodiment of the invention shown in FIG. 2d, particles falling through the shaded triangle will of course not scatter the light to the collectors 21 and 22. However, if it is assumed that the particles falling through the mirrors S and S2 and the area delimited by the light beam are uniformly distributed, the area actually covered by the zigzag path of the light beam 14 The total count is calculated by multiplying the actual particle count generated by particles falling through the surface by the total area between surfaces S and S2 divided by the area actually covered by the zigzag path of the light beam 14. It is possible to estimate particle counts.

Since one of the principles of operation of this method is the detection of light scattered by particles falling through the beam, it is important to maintain an acceptable power density over the entire path of the beam. . The power density of a beam is defined as the beam power divided by the cross-sectional area of the beam, which falls with the distance the beam is propagated due to beam divergence.

FIG. 6 shows the vertical beam divergence for a collimated beam having an initial height Ho and an initial width W, , (shown in FIG. 2b) as a function of the distance X that the beam has propagated. As shown in FIG. 6, after propagating a distance X, the beam thickness H is given by the following equation.

)("H, + 2 d □" H6+ 2 x ta
nθ Furthermore, θ=λ/πHo, where λ is the wavelength of the monochrome or monochromatic laser beam. Therefore, H=H, + 2
xtan (λ/πH,).

Since θ is a small angle, H=H0+2xλ/7CHo=Ho(1+2xλ
/πI−r o”).

As a result of a similar analysis, the width of the beam after propagating the distance X is given by the following equation.

W ''Wo (1+2xλ/7CW,'') Therefore, the power density of the beam after it has propagated a distance of X is given by the following equation.

P (X')= P, /HW= Po/H, Wo(1+
2 X input/πHo2) (1+ 2 xλ/ x
Assuming that W a ”)■]. is significantly smaller than W., the critical interval (i.e., the point at which the power density is approximately half the original power density) is given by:

2xλ/7CHo” = 1 or x = 7CHo”
/ 2λ For example, λ = 1 micron and H8 = 3
For I Q-2 cm, the critical spacing occurs at x==15 cm.

If the beam is reflected from a total of n same surfaces S and S2, the power density is:

P(X)=P, R''/HOW, (1+2Xλ/πH,
”) (1+2xλ/x W a ”) where R is the reflectance (typically, the insulator mirror surfaces S□ and S2
It is about 99.5%. ) The power of the scattered light received by the detector PD□ is given by the following equation.

P, = ησP(x) where η is the detector collection efficiency and σ is the particle scattering cross section (ie, the particle cross section perpendicular to the beam). Noise limits the sensitivity of the detector. Noise power is expressed by the following formula.

Pn= N
5+36 bandwidth. Noise equivalent power is a standard measurement of noise power in a frequency band for a photodiode.

The minimum detectable cross section of a particle is obtained by equating the power received by the detector with the noise power and solving for σ, the particle scattering cross section, resulting in:

a -+-=N X 5QRT(B)/'7P
(X) = N X 5ORT(B)H6W, (1
+xλ/πH0”)(1+xλ/7CWo”)/ηP,
It is desirable to maximize σ, □8 as a function of RnHo. The optimal value of Ho is given by solving the following equation.

a (7MIN/a HD = 0 As a result, the following equation is obtained.

H,, optimal=sQRT(λx/π) For example, 50c at a wavelength of 820nm (AIGaAs laser)
For a propagation distance of m, Ho, optimal=0
, 036Cm. H, = 0, 936cm, W
0=O, 1cm, B=200kl(z, N=
5 x 10-13 Watts/Hz'', η=0.5,
Po=10 milliwatts, λ=820 nm, a,, N=
3,7 x 10-10 cd. This (I M
For IN, a 30 degree detector can easily detect particles of 0.3 micron diameter. A detector with a collector lens 21 and a photodiode PD is a 30 degree detector if the photodiode receives and receives rays at an angle of up to 30 degrees with respect to the plane of the optical net generated by the beam 14. FIG. 7 shows the relationship between angle (0° to 10° excluded) and integrated scattering cross section for curves B, C, and D of FIG. 3. The horizontal axis θ (degrees) in Figure 7a represents the area between the right circular cone with an angle of 10 degrees (with respect to the perpendicular) and the right circular cone with an angle O, as shown in Figure 7b. . The power of light scattered within this region, P(0), is given by P(O) = 1°σ(0), where 1° is the incident power/unit area, and σ(Ill) is The integrated scattering cross-section corresponding to O (Figure 7a).

As the Ueno analysis shows, the power density decreases with the propagation distance of the beam 14 due to divergence.

Instead of collimating the beam using lenses 12 and 13 as described above, the divergence angle θ shown in FIG.
It is possible to compensate for beam divergence by bringing the beam to a focal point that accurately compensates for . This is a conventionally known technique.

For example, Melasgriot optical system guidebook 3 (Mell
es Griot Optics Guide 3),
349, 1985. Figure 8 shows
One embodiment for ensuring this divergence is shown in more detail. Laser diode 10 is typically packaged so that light emerging from the PN junction of laser 10 passes through glass 10a. The thickness T, of the glass 10a affects the dimensions of the beam emerging from the glass 10a (due to refraction) and can vary from manufacturer to manufacturer. lens 4
The focusing characteristics of 1 and 42 are as follows.

The selected thickness T of the glass is selected based on the beam width, which is greater than the varying thickness for plate 10a typically used by different manufacturers. Therefore, by inserting a glass plate 40 with a thickness T2 selected such that T + T2 = T, the optical The rest of the system remains unchanged.

The beam emerging from the glass plate 40 passes through a cylindrical lens 41
, the cylindrical lens focuses the beam in the vertical dimension indicated by arrow H6 in Figure 2b. The radius of curvature of lens 40 is selected to accurately compensate for the zero vertical beam divergence angle shown in FIG. The beam emerging from the cylindrical lens 41 then passes through a cylindrical lens 42 with a radius of curvature chosen to accurately ensure horizontal beam divergence (widthwise divergence of the beam).

The beam 14 emerging from lens 42 therefore maintains a constant thickness and constant width as it propagates between mirrors M4 and M2.

Alternatively, the divergence in the thickness TI of the beam 14 can be corrected by somewhat curving the mirror surfaces S1 and S7. The cylindrical lens 41 described above
and 42 is desirable for this second method. This is because curved mirrors are expensive and difficult to implement.

A third method of collimation and divergence correction is to use gradient index lenses. Gradient index lenses are manufactured by Mels Griot (M
It is available from Elles Griot. A gradient index lens is a glass rod whose refractive index varies with diameter. A focusing effect occurs as light propagates through the rod. The focal length of the gradient index lens is:

Determined by the length of the glass rod. FIG. 9 shows one embodiment of the optical means used to compensate for beam divergence using a gradient index lens. Elements in FIG. 9 that are the same as in FIG. 8 have the same reference numerals. In FIG. 9, the beam emerging from the flat glass plate 40 is received by a selected cylindrical lens 5o such that the beam emerging from the lens 50 has the desired height to width ratio. The beam from lens 50 is received by gradient index lens 51, which collimates the beam along the horizontal (width) axis and adjusts the beam divergence angle θ (FIG. 6) along the vertical thickness axis. , so that the optical net generated by beam 14 has a constant thickness.

Referring to FIGS. 10, 11, 12a and 12b, miniature direct observation sensors are shown. The direct observation sensor assembly includes a collimated laser beam 62.
It has a lens that supplies

It has a light source 60 such as a laser cartridge.

The beam is directed to the first reflective mirror 64 at an angle of approximately 15 degrees relative to the flat surface of the mirror 64. The beam is reflected onto a second mirror 66 with a surface substantially parallel to that of the first mirror 64, so that a light sheet or net is generated within the narrow gap between the mirrors. The reflected beam passes on the first mirror 64 and enters the photodiode 68-E.

The photodiode reflects the intensity of the received light beam and ensures proper operation of the laser beam and the optics of the sensor assembly. The beam is reflected from the photodiode into a beam stop cavity 70, which prevents stray light from returning to the optical system and provides a safety feature.

As shown in FIG. 11, the photoself 2 and 74 are equipped with a mirror 6 for detecting the passage of particles through the light sheet.
4 and 66. The photocell generates a signal representing the incidence of particles passing within the gap between the mirrors. the signal is amplified, peaks detected,
and processed by a microprocessor to calculate particle flux density as described above. A viewing display is provided by a display monitor connected to the microprocessor. Glass filters 74 and 76
is included in the photocell to block incidental light of different wavelengths other than the laser beam. The mirror has front parts 80 and 82, which are about 780n
It consists of an insulating laminate formed from a substrate with a MAX-R (trademark of Melles-Griot) coating that passes wavelengths of m. The front part is attached to cover glasses 84 and 86 seated on the face of the respective mirror 1.

The sensor assembly is located within a frame 88 and support brackets 90, one of which is shown in FIG. 12, surround the ends of the frame to form a housing or enclosure for the sensor assembly. are doing.

Another embodiment of the sensor assembly is shown in FIGS. 13 and 14. The sensor assembly is useful for detecting particles in hot or corrosive gases or fluids and consists of a pipe section 89 disposed substantially transversely between two reflective mirrors 91 and 92. The pipe section 8
9 has a narrow center portion 94 and a wide flange portion 9;
6a, 96b, which make it possible to connect the pipe section to a standard diameter pipe through which the gas or fluid under detection is passed.

Glass windows 98 and 100 are provided between the mirror and the central cavity of the pipe section.

The glass window protects the optics from corrosion and heat. Sincerity is constructed from a heat resistant, low temperature coefficient glass, such as fused silica. The glass is polished flat on the front and back sides. The mirrors are assembled in good faith and they are attached to the pipe using fluorocarbon O-rings that can withstand temperatures of up to 200°C. The mirror has two sets of three bolts 102 and 10 that clamp the cord to the pipe.
4, while the O-ring provides the desired play.

When operating in a high temperature environment, the housing for the beam stop arrangement 108 containing the laser 106 and photodiode 109 is cooled by a cooling fluid or water circulating through channels or pipes located within the housing. . As mentioned above, the preamplifier 110 is provided to amplify the intensity of the laser beam.

The small gap between the mirrors, as implemented in the alternative embodiment of FIGS. 10-14, allows for a compact configuration that provides improved signal resolution. This compact configuration is made possible by reducing the number of parts and manufacturing costs.

Although specific embodiments of the present invention have been described in detail above, the present invention should not be limited only to these specific examples, and various modifications may be made without departing from the technical scope of the present invention. Of course, it is possible. For example, more than two mirrors can be used to generate the light net, and the optical system can be modified to provide the desired path for the light beam. Also, the pipe sections described with respect to FIGS. 13 and 14 can be in the form of cylindrical, rectangular channels, or any shape that provides small narrow gaps between reflective mirrors.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing a conventional airborne particle detector, Figure 2a is a schematic plan view of a particle detector of the present invention, and Figure 2b is the shape of the beam emerging from the beam expander shown in Figure 2a. FIG. 2c is a partial side view of the particle detector shown in FIG. 2a, FIG. 2d is a schematic diagram showing another path for light used in the particle detector, and FIG. The figure is a schematic diagram showing the path of the light scattered along the 156 rays reflected by the parabolic mirror 21 and focused onto the photodiode PD shown in Figures 2a and 2C; Figure 3a is θ 3b is an explanatory diagram showing the angles O and θ+5° used in FIG. 3a, and FIG. 1 is a block diagram of a circuit used to process the signals taken; FIG. FIG. 5a shows the amplifier 34 shown in FIG. FIG. 5b is an illustration showing the positive envelope of the signal shown in FIG. 5a; FIG. 6 is an illustration showing the beam divergence as a function of path length. Explanatory diagram, No. 7
Figure a is an explanatory diagram showing the relationship between the angular area and the integrated scattering cross section, Figure 7b is an explanatory diagram showing the angular area between the cone waiting for an angle of 10° and the cone having an angle φ. Figure 8 is a schematic diagram showing a lens arrangement that ensures beam divergence, Figure 9 is a schematic diagram showing another arrangement that ensures beam divergence, and Figure 10 is a compact direct lens arrangement that is another embodiment of the present invention. 11 is a side view of the sensor assembly of FIG. 10; FIG. 12 is an end view of the sensor assembly shown in FIG. 11; and FIG. 13 includes a pipe arrangement. FIG. 14 is a side view of the sensor assembly of FIG. 13. 10: Laser 12. 13: Shaping Lens 20: Beam stop 21, 22: Collector mirror 30; Power supply 34a: Amplifier 38: A/D converter 37: Beak detector 39: Microprocessor 40 Glass plate 41: Cylindrical lens 51: Gradient index lens Patent applicant
High Yield Technology: Moo Expansion Agent Kobashi - Male, '1': 1 L FIG, 3α FIG, 5a FIG, 4 10° 枦-, amm imφ mouth ""' FI
G, 7a Procedure Kokeguchi Ordinary (Method) April 6, 1988 Commissioner of the Patent Office Kuro 1) Akio Tono 1, Indication of Case 1986 Patent Application No. 29
1665 No. 2, Title of the invention: Particle detector for wafer processing equipment 3, Relationship with the person making the amendment: Patent applicant name: High Yield Technology 4, Agent: 5, Date of amendment order: February 4, 1985 ( (Shipped on February 24, 1962) 6. Number of inventions increased by amendment None τ\ t t, 2

Claims (1)

[Claims] 1. A light beam generating means, a first means for reflecting the light beam, and a second means for reflecting the light beam,
The generating means, the first means, and the second means are arranged such that the light beam generated by the generating means is transmitted collectively from the first means to the second means and from the second means to the second means. positioned relative to each other to be reflected N times (N being a preselected positive integer greater than or equal to 2), and the beam is initially directed to the first means for reflection at an angle not equal to 90 degrees; A particle detector, characterized in that it comprises means for detecting light scattered by particles incident on and passing through said light beam. 2. A particle detector according to claim 1, further comprising a beam stop for terminating the beam after the beam has been reflected the N times. 3. A particle detector according to claim 2, wherein the beam stop comprises means for detecting the intensity of light incident on the beam stop. 4. Particle according to claim 3, characterized in that the beam stop further comprises means for generating a signal when the intensity of light incident on the beam stop falls below a preselected value. Detector. 5. The particle detector according to claim 1, wherein the light beam generating means includes a laser. 6. Claim 1, wherein the first means for reflecting the light beam and the second means for reflecting the light beam
Particle detector, characterized in that each of the means comprises a mirror with a flat surface. 7. In claim 1, the first means for reflecting the light beam and the second means for reflecting the light beam
A particle detector characterized in that each of the means comprises a curved mirror to reduce divergence of the light beam. 8. Claim 1, wherein the means for generating a light beam is located between the light beam source and the first reflecting means and has a focal length selected to compensate for beam divergence. A particle detector characterized in that it is equipped with a lens. 9. Claim 6, further comprising at least one member extending outwardly from one of the mirrors to prevent dust from adhering to the surface of one of the mirrors. Characteristic particle detector. 10. In claim 6, one of the mirrors
particles characterized in that they have at least one opaque member extending outwardly from said one of said mirrors to prevent light scattered from defects in one of said surfaces from being detected by said detection means; Detector. 11. Particle detector according to claim 1, characterized in that the light beam generating means comprises one or more lenses for generating a light beam whose height is smaller than its width. 12. A particle detector according to claim 5, comprising means for chopping the light beam. 13. According to claim 1, the detection means is an optical element that collects the light scattered by the particles and reflects the light scattered by the particles to the means for detecting the light scattered by the particles. A particle detector comprising: 14. According to claim 13, a substance having a refractive index greater than 1 is located between the optical element and the detection means in order to increase the permissible angle of the detection means. A particle detector featuring 15. In claim 1, the means for detecting the scattered light comprises a focusing mirror and a photodiode, the focusing mirror focusing the scattered light onto the photodiode. A particle detector characterized by: 16. The particle detector according to claim 15, wherein the detection means further comprises means for detecting a representative value of the peak amplitude of the optical signal received by the photodiode. 17. In claim 16, the detection means further includes an analog-to-digital converter and a microprocessor, and the analog-to-digital converter transmits the optical signal received by the photodiode to the microprocessor. A particle detector characterized in that it provides a digital representation of said representative value of said peak amplitude of. 18. A particle detector according to claim 1, wherein the light beam generating means comprises a gradient index lens. 19, generating a light beam and directing the light beam from the first reflecting means to the second reflecting means and from the second reflecting means to the first reflecting means;
the light beam is reflected to a reflecting means a total of N times (N being a preselected positive integer greater than or equal to 2), and the beam is initially incident on the first reflecting means at an angle other than 90 degrees and passes through the light beam. A particle detection method, comprising detecting light scattered by the particles. 20. The particle detection method according to claim 19, wherein the beam is terminated after the beam is reflected the N times. 21. Particle detector according to claim 1, comprising a pipe section having a narrow cavity extending substantially transversely to the light beam. 22. A particle detector according to claim 21, further comprising window means disposed adjacent to the pipe section and between the first reflecting means and the second reflecting means. 23. A particle detector according to claim 21, wherein said light detection means is positioned closely adjacent said reflection means. 24. According to claim 21, the pipe section comprises a flanged portion for connection to an external pipe such that fluid or substrate can pass through the narrow cavity. A particle detector featuring