JPH0287047A - Inspecting apparatus for surface - Google Patents

Abstract

PURPOSE:To enable execution of scanning free from a variation in the direction of a reflected light flux by a construction wherein a rotary mirror element having an inclined axis of rotation is rotated by a motor element provided with a dynamic pressure type gas bearing, and a light flux from a light source element is scanned on a wafer through an Ftheta lens. CONSTITUTION:A laser light generated by a laser light generating device 21 is expanded by a beam expander 22 and sent to a polygon mirror 24 through first and second mirrors 231 and 232. The mirror 24 rotates at a prescribed speed, and in combination with an Ftheta lens 25, it can scan a condensed laser light at a prescribed speed on a wafer 10 to be measured. The axis of rotation of this mirror 24 is positioned in a state of being inclined to the wafer 10. Besides, a motor 27 for high-speed rotation is fitted to the axis of rotation of the mirror 24. A detecting optical system 3 leads an incident scattered light to a light-sensing element 4 through an optical fiber 31.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a surface inspection device that detects minute dust, etc. on the surface of an object by light scattering, and is particularly concerned with detecting dust, defects, etc. on the surface of a wafer in semiconductor manufacturing. The present invention relates to a surface inspection device that is suitable for quantitatively detecting and has high detection accuracy.

"Conventional Technology" In recent years, as semiconductor devices have become more highly integrated, the width of one circuit pattern has become smaller and smaller, and we are now entering the submicron era. In such semiconductor manufacturing processes, dust generated during the process has been a factor in reducing product fractionation. Therefore, dust on the process line has been controlled by detecting dust adhering to the wafer surface. The method for detecting dust etc. adhering to this mirrored wafer is to irradiate the dust on the wafer with light and detect the scattered light.
A method is used to quantitatively detect the size, number, location, etc. of dust. However, in recent years, as semiconductor devices have become more highly integrated, the width of circuit patterns has tended to become smaller and finer, making it necessary to scan with a strong beam with a narrowed beam spot. There are three types of scanning methods for this light beam, as shown in Fig. 6. The scanning method shown in Fig. 6 (a) is a rotational scanning method, in which the beam substrate is fixed, This method is a method in which only the wafer side is rotated and linearly moved to scan the wafer in a spiral direction of 1k.5This method has a limit to the scanning speed, and also has the problem that the scanning speed between the center and the periphery differs greatly. there were.

The scanning method shown in FIG. 6(b) is a linear scanning method in which the beam substrate itself is scanned and the wafer side is moved linearly.7 This method uses, for example, a vibrating mirror or a polygon mirror, and a The scanning method shown in Figure 6(C) is a hybrid
It is a horizontal scanning method, in which the beam substrate itself is scanned, and the wafer side is rotated and linearly moved9.
Linear scanning method and hybrid shown in Figures 6(b) and (c)...
The I-do scanning method requires a beam scanning means. A high-speed scanning means was required to scan the entire surface of the wafer in a short period of time. Scanners and polygon mirrors were used as this high-speed scanning means. In particular, polygon mirrors can shorten the scanning period by two to three orders of magnitude compared to scanners, so they are often used in surface detection devices. There were many. In the surface inspection apparatus, as shown in FIG.
It was considered desirable to irradiate at 0.00. However, since the rotation axis of the polygon mirror 200 is normally fixed in the vertical direction, the light beam output from the polygon mirror 200 is in the horizontal direction. Therefore, Habo 4
The mirror 300 was arranged so that the wafer 100 was irradiated with an incident angle of 5 degrees. The mirror 300 has a large influence on beam distortion, and requires extremely high mirror surface precision and assembly of 8 degrees.9 Furthermore, the mirror 300 has an increased number of reflective surfaces, which causes a loss of light quantity. Furthermore, the presence of this mirror 300 has a negative effect on space saving, and requires special processing, which causes problems. Therefore, in order to omit this mirror 300 and adjust the mirror surface of the polygon mirror 200 to the final incident angle of the light beam, the polygon mirror 200 is
However, the polygon mirror 200 needs to be rotated at high speed and with high precision. I couldn't find anything other than static pressure type gas bearings. Gas bearings here use the viscosity of gas,
This method increases the pressure of the gas in the gap to levitate the object. This gas bearing can be classified into a dynamic pressure type and a static pressure type based on the principle of pressure generation, as shown in Figure 7.9 In the dynamic pressure type gas bearing shown in Figure 7 (a), the two surfaces are relatively A wedge-shaped gap 400 is adopted in which the gap gradually narrows in the direction of movement, and due to the relative movement of the surfaces, the gas is dragged by its viscosity and forced into the wedge-shaped gap 400, causing pressure to rise. It is configured to produce the following. Therefore, in the case of a hydrodynamic radial gas bearing, when a load is applied, the rotating shaft becomes eccentric, and a wedge-shaped gap 400 is formed in the bearing gap. The rotation of the rotating shaft forces gas into the wedge-shaped gap 400, creating pressure and supporting the load. Next, in the static pressure type gas bearing shown in FIG. 7(b), externally pressurized gas is introduced into the gap through the throttle 500, and the static pressure causes the bearing to float. This throttle 500 adjusts the pressure within the gap when the gap changes and provides rigidity to the bearing. As mentioned above, a dynamic pressure type gas bearing cannot be used in the motor for the polygon mirror 200 whose rotation axis is tilted. This is because when the rotating shaft is stopped, no pressure is generated in the wedge-shaped gap 400, and at the beginning of one rotation, the eccentric rotating shaft comes into contact with the bearing surface and is damaged.

On the other hand, static pressure type gas bearings force pressurized gas into the gap from the outside, so they do not have the same problems as dynamic pressure type gas bearings, but they require an external pressure generator and the equipment is complicated. This increases the cost, and there are problems in that dust and vibrations are generated from the pump of the pressure generator, etc., and this affects the measurement accuracy of the surface inspection device.

"Means for Solving the Problems" The present invention has been devised in view of the above-mentioned problems, and includes a wafer receiving portion to be inspected which is arranged substantially horizontally and on which a wafer to be inspected is placed; a light source section for emitting a narrow beam of light, a rotating mirror section for scanning the light beam emitted from the light source section onto the wafer to be inspected via an Fθ lens, and a rotating mirror section for rotating the rotating mirror section at an angle. Fθ
A motor unit equipped with a hydrodynamic gas bearing made of ceramic material for scanning the wafer to be inspected through a lens, and a light beam scattered by the wafer to be inspected generated by the scanning light beam by the rotating mirror unit. It consists of a light receiving section for detection.

1. In the present invention configured as described above, the rotating mirror section scans the light flux emitted from the light source section, via the Fθ lens, onto the wafer to be inspected j) placed on the receiving section. 9 Then, a motor unit equipped with a hydrodynamic gas bearing made of ceramic material rotates a rotating mirror unit with an inclined rotation axis, and directs the light beam emitted from the light source unit onto the wafer through an Fθ lens. Further, the light receiving section is capable of receiving scattered light generated by the scanning light beam by the rotating mirror section. . Figure 1 shows
This shows the configuration of this embodiment, and the surface inspection device main body 1 includes:
This surface inspection device main body 1 consists of a laser beam generating means 21, an optical fiber 31, and a first light receiving element 4.
A wafer 10, which is an object to be inspected, is placed on a wafer receiver to be inspected. The laser beam generating means 21 corresponds to a light source, and in this embodiment, an argon ion laser is adopted.9 The optical fiber 31 forms a detection optical system 3 and detects light scattered by dust on the wafer 10. This is for guiding the light to the light receiving element 4. Since the end faces of the optical fibers 31 are arranged in the longitudinal direction of the wafer 10 to be measured,
Can guide scattered light to Prince Uko. This light receiving element 4
Although a photomultiplier tube (optional) can be used, other light-receiving elements may also be used; in other words, any device capable of receiving laser light will suffice. When the wafer 10 is irradiated with the laser light generated by the laser generating means 21, specularly reflected light is generated on the wafer 109. At this time, if dust is deposited on the wafer 10, scattered light is generated.

The optical fiber 31 guides this scattered light to the light receiving element 4.

Next, the optical system of this embodiment will be explained in detail. 9 The optical system of this embodiment is composed of an irradiation optical system 2 and a detection optical system 3. The nine-laser light generating means 21 includes an argon ion laser 21, a beam expander 22, a first mirror 231, a second mirror 232, a polygon mirror 24, and an Fθ lens 25. This is a light source for performing high-intensity irradiation, and not only an argon ion laser but also a He-Ne laser, a laser diode, or the like can be used. The laser beam generated by the laser beam generating means 21 is expanded by the beam expander 22, and then passed through the first and second mirrors 231 .
It is sent to the polygon mirror 24 via 232. The polygon mirror 24 is.

It rotates at a constant speed, and in combination with the Fθ lens 25, it is possible to scan the laser beam focused on the wafer 10 to be measured at a constant speed. This polygon mirror 2
The rotation axis of the polygon mirror 2 is positioned at an angle with respect to the wafer 10 to be measured.
On the rotation axis of 4.

In this embodiment configured in this manner, in which a motor 27 for rotating the polygon mirror 24 at high speed is installed, a beam spot of about 10 microns (μm) can be scanned.

The detection optical system 3 is composed of an optical fiber 31 and is configured to guide the incident scattered light to the light receiving element 4.

Next, the arithmetic processing system of this embodiment will be explained based on FIG. The determining means 8 is for determining dust on the wafer 1o based on the output signal from the light receiving element 4.

This discrimination means 8 includes a preamplifier 81, an adder 82,
It is composed of an A/D converter 94, a comparator 83, a buffer memory 84, a data processing circuit 85, a main memory 86, and a CPU 87. The preamplifier 81 converts the output signal from the photodetector 4 (photomultiple) into an electrical signal, and the signal is sent to the adder 82.
The 9 comparator 83 added is for comparing the level of the signal from the light receiving element and the signal from the CPU 87. Buffer memory 84 is for storing data.

The data processing circuit 85 is for recognizing dust on the wafer based on the signal from the light receiving element 4.
Prior to data processing, it is necessary to perform AD conversion.9 In this embodiment, beam scanning is performed while rotating the turntable, which is the wafer receiver to be inspected on which wafer lo is placed, to detect scattered light. The magnitude of the signal is compared with a preset threshold level by a comparator 83, A/'D converted, and sent to the CPU 87 together with the position data. The CPU 87 is in charge of arithmetic processing of the surface inspection apparatus main body 1. The main memory 86 is a memory necessary for storing a large amount of measurement data. The DA converter 88 has a CP for setting the threshold level in the comparator 83.
This converts the U87 signal into an analog signal. This determining means 8 includes a printer 89. FDD (Flo-Sopi disk drive) 90, CRT 91, keyboard 9
2 are connected. The printer 89 prints the test results, and it is desirable to use paper such as paper to prevent dust generation. The FDD 99 is for storing test results, but if a clean room is being centrally managed, it is desirable to send the data directly to the host computer. At this time, R3-232C, 5EC8 can be adopted as the data communication protocol. A nine-keyboard 92, which can use a plasma display, is used to input measurement mode, wafer size, edge force, etc.

Note that an argon ion laser 21 is used as the light source of the irradiation optical system 2, and this argon ion laser 21
A laser power source 211 is connected to. Further, in order to scan the laser beam spot, a motor driver 26 is provided to drive a motor 27 for rotating the polygon mirror 24. A motor 71 is provided, and is driven by a motor driver 73.9 Additionally, a motor 72 may be added to transport the wafer 10.9 These motor drivers 26 and 73 drive the sequencer 74. via CPU
87.

Here, a driving means for rotating the polygon mirror 24 at high speed will be explained based on FIG. 2.

A dynamic pressure type gas bearing 28 is employed in the polygon mirror 24 and is connected to a motor 27. This dynamic pressure type gas bearing 28 consists of a dynamic pressure radial gas bearing 281 and a dynamic pressure thrust gas bearing 282. As shown in FIG. 3(a), the dynamic pressure radial gas bearing 281 is a grooved bearing (herringbone), and when the shaft rotates, gas is forced into the groove and pressure is generated. Figure 3 (b
), the dynamic pressure thrust gas bearing 282 is also a grooved bearing, and an external suction spiral grooved bearing is adopted. Similar to dynamic pressure radial gas bearings, gas is dragged into the grooves to generate pressure. Note that both the hydrodynamic radial gas bearing 281 and the hydrodynamic thrust gas bearing 282 are made of ceramic.9 This is because the hydrodynamic gas bearing 28 does not have enough pressure at the beginning of rotation, so the rotating shaft is eccentric. However, there was a problem in that the bearing surface was damaged due to solid contact with the bearing surface.

Therefore, by constructing the hydrodynamic gas bearing 28 from extremely hard ceramic, there is an effect that no scratches or the like will occur even when it comes into contact with a solid object at the initial stage of rotation. Note that silicon carbide, for example, is used as the ceramic. Note that the hydrodynamic gas bearing 28 is not limited to a grooved hydrodynamic gas bearing, and any type of hydrodynamic gas bearing 28 such as a planar type, a multifaceted type, a flexible surface type, etc. can be adopted.

Next, 1. How to use this embodiment will be explained. 2. First, a wafer 10, which is an object to be inspected, is placed on a turntable. Then, while looking at the CRT 91, the measurement information is input from the keyboard 92. And a! The recon ion laser 21 is operated for repair.

Then, the CPU 87 drives the motor driver 26,
Rotate the polygon mirror 24. This bojgon mirror
24 and the Fθ lens 25, the beam spot can be scanned over the wafer 10. Note that the rotation axis of the polygon mirror 24 is tilted and fixed with respect to the wafer to be measured 10, and the light beam emitted from the polygon mirror 24 passes through the Fθ lens 25 and hits the wafer at an incident angle of 45 degrees. It is configured to scan the top 10. The light specularly reflected by the wafer 10 surface escapes to the outside, and the scattered light generated by the dust on the wafer 10 is
The light is sent to the light receiving means 4 by the optical fiber 31. CPU
87 drives the motor driver 73 to rotate the turntable on which the wafer 10 is placed. optical fiber 3
The scattered light collected by the light receiving element (photomultiple) 1 is converted into an electric signal by a light receiving element (photomultiple) 4. An output voltage signal corresponding to the size of the dust is generated in the light receiving element 4, and a preamplifier 81,
The signal is stored in a buffer memory 84 via an adder 82, a comparator 83, and an A, -'D converter 94. A data processing circuit then recognizes the dust and attaches an identification symbol depending on its size. Furthermore, the position of the dust is also specified and sent to the CPU 87. This process is performed in real time, and the data is stored in the main memory 86. Since the data stored in the main memory 86 is polar coordinate data, it is converted into X-Y coordinates and output to the CRT 91 or printer 89. Note that although these data processes are performed on the entire wafer 10, the number of dust particles in an area excluding one peripheral cut portion can also be classified and counted according to the size of the dust particles.

Note that this embodiment employs a calibration method using standard particles. That is, a wafer to which standard particles are uniformly adhered is prepared, and the output signal due to the scattering of two particles, which is used for calibration, has a thin pulse waveform with a height corresponding to the size of the particles. Calibration can be performed using these peak values.

In this embodiment configured as described above, the polygon mirror 24
Since the rotation axis of the wafer 1o is tilted and fixed with respect to the wafer 1o, a light beam can be supplied to the Fθ lens 25 without going through a mirror or the like.

At an incident angle of 45 degrees, the light beam can be scanned over the wafer 1o9.Furthermore, since the bearing of the polygon mirror 24 uses a hydrodynamic gas bearing made of ceramic, Even in this case, the bearing part is not damaged and high-speed rotation can be achieved even if the rotating shaft is tilted.

It goes without saying that the present invention can be applied not only to an inspection device for dust and defects on a semiconductor wafer 1o, but also to inspection devices for other purposes. a part on the wafer, a light source part, a rotating mirror part for scanning the light beam emitted from the light source part onto the wafer to be inspected; a motor section equipped with a dynamic pressure type gas bearing made of ceramic for scanning the light beam emitted from the wafer onto the wafer to be inspected via an Fθ lens; and for detecting scattered light on the wafer to be inspected. This has the effect that the light beam reflected from the polygon mirror can scan the wafer to be inspected at a desired angle of incidence without changing its direction with a mirror or the like.

Since a mirror is not required for this direction change, there is no loss of light weight, and there is an excellent effect in that it is possible to prevent a decrease in measurement accuracy due to a positioning error of the mirror surface, an assembly error, etc. Further, since a mirror for changing the direction of the light beam is not required, the optical system can be simplified and the comparison sensitivity can be improved. Furthermore, since a hydrodynamic gas bearing made of ceramic is used, the bearing part will not be damaged even in the early stages of rotation, and the tilted rotating shaft can be rotated at high speed. Furthermore, since pressure generation means such as dynamic pressure type gas bearings and static pressure type gas bearings are required, the equipment is not only complicated, but also has the outstanding effect of not generating vibrations that are harmful to surface inspection.

[Brief explanation of the drawing]

The drawings are diagrams showing an embodiment of the present invention. FIG. 1 is a diagram explaining the configuration of the present embodiment, FIG. 2 is a diagram explaining a hydrodynamic gas bearing of a polygon mirror, and FIG. ) is a diagram showing a dynamic pressure type radial gas bearing, FIG. 3(b) is a diagram showing a dynamic pressure type thrust gas bearing, FIG. 4 is a diagram showing the configuration of the discrimination means of this embodiment, and FIG. 5 is a diagram showing a conventional surface FIG. 6 is a diagram showing the configuration of the inspection device, and is a diagram explaining the scanning method of the light beam.
FIG. 7 is a diagram explaining the principle of gas bearings. 1...Surface inspection device body 21...Argon ion laser 24...Polygon mirror 25...Fθ lens 28...Dynamic pressure type gas bearing 281...Dynamic pressure type Radial gas bearing 282・Dynamic pressure type thrust gas bearing 3...Optical fiber 4...Light receiving means 8...Discrimination means 10...Wafer to be inspected Dynamic pressure type radial 5 Bone (b) Figure 3 Figure 7

Claims (1)

[Claims] (1) A wafer receiving part to be inspected which is arranged approximately horizontally and on which the wafer to be inspected is placed, a light source part to emit a thin beam of light to the wafer to be inspected, and a light beam emitted from this light source part. a rotating mirror unit for scanning the wafer to be inspected via an Fθ lens; and this rotating mirror unit is rotated about an inclined rotation axis, and the light beam emitted from the light source unit is transmitted to the inspection target wafer via the Fθ lens. a motor section equipped with a hydrodynamic gas bearing made of ceramic for scanning the wafer to be inspected; and a light receiving section for detecting scattered light from the wafer to be inspected generated by the scanning light beam by the rotating mirror section. A surface inspection device comprising: