JPH0514857B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foreign matter inspection apparatus suitable for inspecting foreign matter on a surface on which a pattern is formed, such as a patterned wafer or a photomask.

[Prior Art] Wafers and the like used in the manufacture of semiconductor devices are extremely susceptible to foreign matter adhesion, so a foreign matter inspection device is used to inspect the surface of wafers for foreign matter.

Such a wafer foreign matter inspection device is designed to spirally scan the wafer surface by irradiating an S-polarized beam onto the wafer surface while rotating and moving the wafer, and then pass the reflected light from the wafer surface into a lens system. A known method is to collect light from the reflected light, extract a P-polarized light component from the reflected light using a polarizing plate, make it incident on a photoelectric conversion element, and detect foreign matter on the wafer surface based on the level of the photoelectric conversion signal.

Even if a pattern exists within the irradiation spot of the S-polarized beam, the surface of the pattern is microscopically smooth, so that the reflected light is almost exclusively the S-polarized component. On the other hand, the surface of a foreign object generally has minute irregularities, so if a foreign object is present within the irradiation spot,
The irradiated S-polarized beam is scattered and the plane of polarization is disturbed, and the reflected light contains a considerable amount of P-polarized light component. Therefore, by comparing the level of the photoelectric conversion signal of the P-polarized light component with a certain threshold value, and determining that it is a foreign object when the photoelectric conversion signal exceeds the threshold value, the foreign object can be detected by distinguishing it from the pattern.

[Problems to be Solved] However, when such a conventional foreign matter inspection device attempts to detect minute foreign matter, there are cases in which patterns are periodically erroneously detected.

[Object of the Invention] An object of the present invention is to provide a foreign matter inspection device that prevents such erroneous detection of patterns.

[Means for Solving the Problem] According to the inventor's research, patterns are erroneously detected in conventional foreign object inspection equipment because the irradiation direction of the S-polarized beam is within a certain range with respect to the normal direction of the pattern. In the case of a conventional scanning method in which the ratio inspection surface is rotated, which is often the case at a certain angle, a pattern that satisfies such conditions appears periodically at a certain angle.

When a certain pattern meets such an angular condition, the level of the P-polarized light component ratio in the reflected light from that pattern will be higher than that of the P-polarized light component included in the reflected light from a relatively minute foreign object. It will be at the same level. For this reason, when a threshold proportional to the photoelectric conversion signal of the P-polarized light component is selected to detect a foreign object with a relatively small diameter, the pattern cannot be distinguished from the foreign object, resulting in erroneous detection of the pattern.

Focusing on these points, and in order to solve the above-mentioned problems, the foreign matter inspection apparatus of the present invention adopts a foreign matter detection method using XY scanning. However, this XY scanning method has a problem in that the foreign object detection processing speed is lower than that of the rotary scanning method.

Therefore, in order to perform high-speed processing without reducing the foreign object detection processing speed even when using the XY scanning method, the foreign object inspection apparatus of the present invention includes a two-dimensional scanning mechanism that scans the inspection surface in A cut ellipse with a cross section of approximately 1/4, which is provided along either the X or Y main scanning direction of the two-dimensional scanning mechanism over the scanning range, and whose first elliptical cut surface side faces the surface to be inspected. a mirror; an S-polarized light cutting means provided over the travel range on the first elliptical cut surface side; and an S-polarized light cut means integrally formed with the elliptical mirror adjacent to the second ellipse cut surface side of the elliptical mirror, An integrating sphere with an aperture that receives light from an elliptical mirror with a width of and means.

[Function] Most wafer patterns are oriented in the orthogonal axis direction with respect to the orientation flat. Naturally, the same applies to photomasks and reticles.

Therefore, if the main and sub-scanning directions of the XY scan are selected so that the main pattern and the irradiation beam do not have an unfavorable angular relationship as described above, the erroneous detection of patterns as in the conventional method can be almost eliminated. This will no longer occur, and foreign objects can be reliably distinguished from the pattern and detected.

Moreover, in XY scanning, the elliptical mirror (approximately 1/4 cut ellipse) and integrating sphere are integrated by providing an aperture that corresponds to the main scanning direction and receives the light from the elliptical mirror over the scanning range. , X, or Y main scanning speed, the elliptical mirror can receive the detection light from the surface to be inspected for one scanning line in a static state.

As a result, regardless of the scanning position of one line,
Scattered light at each position is received by an elliptical mirror and an integrating sphere through an aperture spanning the scanning range, and guided through these to a photoelectric conversion element where the scattered light is concentrated, so if the main scanning speed is increased, Foreign object detection becomes possible in accordance with the scanning speed, and this enables detection comparable to spiral scanning.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a simplified structure of a foreign matter inspection apparatus to which the present invention is applied, and FIG. 2 is a schematic cross-sectional view showing a part thereof in an enlarged manner.

In FIG. 1, 10 is a movable table mechanism movable at least in the Y direction, and its driving means, encoder for position detection, etc. are omitted in the figure. This moving table mechanism 10 includes a wafer 1
A chuck 14 is attached to the chuck 14 for holding the parts 2 and the like by, for example, vacuum suction.

In this foreign matter inspection device, as an S-polarized beam,
An S-polarized laser light beam is used. To generate it, S-polarized laser oscillators 16, 18
is provided. The S-polarized laser oscillator 16 is
It is a device that generates an S-polarized laser beam of a certain wavelength λ ₁ , and is, for example, a semiconductor laser oscillator with a wavelength of about 8300 angstroms. S-polarized laser oscillator 1
8 generates an S-polarized laser beam of another wavelength λ ₂ , for example, a He--Ne laser oscillator with a wavelength of 6328 angstroms. Generating S-polarized laser beams with different wavelengths in this way is
This is to increase the irradiation density of the S-polarized laser beam on the surface to be inspected, and to avoid the influence when the example pattern on the surface to be inspected acts as a diffraction grating to enable detection of foreign matter.

After passing through the beam expander 20, the S-polarized laser beam having the wavelength λ ₁ is reflected by the half mirror 22 and enters the galvanometer mirror 24 for main scanning. The S-polarized laser beam of wavelength λ ₂ passes through the beam expander 26 and the half mirror 22 and enters the galvanometer mirror 30 .

Each beam is reflected by the galvanometer mirror 24, passes through the f-theta lens 30, and hits the surface of the wafer 12 (surface to be inspected) at an irradiation angle φ of approximately 2° (see Fig. 2).
irradiated with. Here, the galvanometer mirror 30 is
Since the drive means (not shown) rotates back and forth at high speed as shown by the arrow 28, the S-polarized laser beam of each wavelength falls at a certain angle in the X direction (main scanning direction) and hits the f-theta lens 30. It is made to be incident.
Thus, the spot of the S-polarized laser beam on the wafer surface (surface to be inspected) moves linearly at high speed in the X direction as the galvanometer mirror 24 rotates. In other words, main scanning is performed.

In synchronization with this main scanning, the moving table mechanism 10
The chuck 14 is moved in the Y direction by pitch feeding. By this movement in the Y direction, sub-scanning is performed by the S-polarized laser beam. In this way, the wafer surface (surface to be inspected) is scanned in the XY direction.

An elliptical mirror (semi-cylindrical lens) 34 is provided to condense reflected light from the wafer surface (surface to be inspected) approximately in the Z direction. On the lower surface of this elliptical mirror 34, there is an elongated opening 36 extending in the X direction as a transparent window, facing the position corresponding to the main scanning line of the S-polarized laser beam on the wafer surface (surface to be inspected). is formed. This opening has
A polarizing plate 38 is provided as an S-polarization cut filter means. Therefore, only the P-polarized light component of the light reflected from the wafer surface in the Z direction is reflected by the polarizing plate 3.
8 and enters the elliptical mirror 34.

An integrating sphere 40 is provided on one side of the elliptical mirror 34. An elongated aperture 42 extending in the X direction is formed on the coupling surface of the integrating sphere 40 and the elliptical mirror 34, and the two are optically coupled via this aperture 42. The P-polarized laser beam focused on the elliptical mirror 34 enters the integrating sphere 40 through the aperture 42 and is scattered inside the sphere.

As described above, since the elongated opening 42 extending in the X direction is provided to integrate the elliptical mirror 34 of approximately 1/4 cut ellipse and the integrating sphere 44, the S-polarized laser beam in the X direction corresponding to main scanning is generated. Corresponding to the high scanning speed of the beam, the elliptical mirror 34 can receive scattered light from the surface to be inspected of the wafer 12 at all positions for one line. Therefore, regardless of the scanning position of one line, the scattered light at each position is transmitted to a photomultiplier 44 using an integrating sphere through an aperture 42 spanning the scanning range in a static state.
It leads to 46 and can be summarized here. As a result, XY
Although it is a scanning method, it is possible to detect foreign objects at a high speed corresponding to the scanning speed of the S-polarized laser beam.

Photomultipliers 44 and 46 as photoelectric elements are provided above the integrating sphere 40. Second
As shown in the figure, each photomultiplier 44,4
The light receiving end of 6 faces the inside of the integrating sphere 40, and in front of the light receiving end there is a dichroic filter 48,
50 is attached.

Of the light incident on the integrating sphere 40, only the P-polarized laser beam with the wavelength λ ₁ passes through the dichroic filter 48 and enters the photomultiplier 44, and only the P-polarized laser beam with the wavelength λ ₂ passes through the dichroic filter 48.
6 and enters the photomultiplier 46.

In this way, using the elliptical mirror 34 and the integrating sphere 40, the P-polarized component of the reflected light is transferred to the photomultiplier 4.
4 and 46, main scanning can be performed over a relatively wide range. Lens systems have problems such as defocusing, and the main scanning range has to be limited to a fairly narrow range, making them impractical and likely to be expensive.

Here, even if a pattern exists within the irradiation spot of the S-polarized laser beam, the surface of the pattern is microscopically smooth, so that the reflected light is almost only the S-polarized component. On the other hand, since the surface of a foreign object generally has minute irregularities, if a foreign object exists within the irradiation spot, the irradiated S-polarized beam will be scattered and the plane of polarization will be disturbed, and the reflected light will contain P-polarized light. It will contain a lot of ingredients. The level of the P-polarized light component is approximately proportional to the size of the foreign object. The levels of the output signals of the photomultipliers 44 and 46 are proportional to the respective amounts of incident light. Therefore, the output signal levels of the photomultipliers 44 and 46 reflect the presence or absence of foreign matter at the scanning point and the size of the foreign matter.

FIG. 3 is a block diagram of the signal processing section of this foreign matter inspection device. In this figure, the output signals of the photomultipliers 44 and 46 are transmitted to the summing amplifier 5.
4 and is added and amplified and input to the comparator circuit 56. This comparison circuit 56 compares the level of the input signal with a threshold value set by a data processing system (not shown), and outputs a logic "1" level signal when a signal with a level higher than the threshold value is input. do. This output signal is input to a data processing system. Note that the output signal of the encoder at the position of the moving table mechanism 14 is also input to the data processing system. Then, the moving table mechanism 14, the galvanometer mirror 24, and the S-polarized laser oscillator 16,1
8 is controlled by the data processing system.

The foreign matter inspection operation of the foreign matter inspection apparatus having the above configuration will be explained. First, under the control of the data processing system, XY scanning of the wafer surface (surface to be inspected) begins. Normally, both the S-polarized laser oscillators 16 and 18 are operated, and a threshold value is set in the comparator circuit 56 according to the conditions.

The P-polarized light component of the reflected laser light from the scanning point at each time is incident on the elliptical mirror 34 via the polarizing plate 38, and further incident on the integrating sphere 40. Then, a signal proportional to the wavelength λ ₁ component of the P-polarized laser light is output from the photomultiplier 44, and a signal proportional to the wavelength λ ₂ component is output from the photomultiplier 46. The summation amplification signal of each signal is obtained by the comparator circuit 56
and is compared with a threshold.

If a foreign object larger than a certain size is present at the scanning point, the level of the addition amplified signal becomes equal to or higher than the threshold value, and a logic "1" signal is output from the comparator circuit 56. When the data processing system receives the "1" signal, it determines that a foreign object has been detected at that scanning point, and the scanning position information at that time (known from the encoder output of the moving table mechanism and the angle of the galvano mirror 24), Stored in foreign object table on internal memory.

Here, the wafer 30 is oriented so that the direction of the main pattern on the wafer surface matches the X and Y directions.
If this is set, there will be very few patterns that have the above-mentioned angular relationship with the irradiation direction of the S-polarized laser beam, and therefore the erroneous detection of patterns as in the conventional case will hardly occur.

Normally, both S-polarized laser beams are irradiated as described above to increase the irradiation density, but on wafer surfaces and photomasks, minute patterns are arranged at minute intervals, so only one wavelength is used. The pattern row may act as a diffraction grating, making normal foreign matter inspection impossible.

For example, the inspection is mainly performed using the wavelength λ ₁ and the wavelength λ ₂ is used for determining the diffraction pattern. That is, when diffraction is not occurring, the detection output ratio of λ ₁ and λ ₂ maintains a constant relationship, and when diffraction is occurring, the ratio between the two changes greatly.

Note that instead of selectively operating the S-polarized laser oscillator, a switch circuit is inserted between the photomultipliers 44, 46 and the summing amplifier 54, and only one of the photomultipliers corresponding to the wavelength to be used is used as the summing amplifier. 56, foreign matter inspection may be performed using only one wavelength.

Although one embodiment of the present invention has been described above in detail, the present invention can be implemented with various modifications.

For example, the output signal of the photomultiplier may be digitized and input to a data processing system, and level comparison may be performed through software processing.

The photomultiplier can also be replaced by other photoelectric conversion elements.

Further, the present invention is also applicable to a similar foreign matter inspection device that uses a light beam other than a laser beam.

Furthermore, the present invention can be applied to objects to be inspected other than wafers,
For example, it can be applied to devices that inspect foreign substances on the surfaces of masks, reticles, pellicle membranes, and the like.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to receive the detection light from the surface to be inspected for one line in a static state by the elliptical mirror in accordance with the scanning speed of the main scan. Regardless of the scanning position of one line, the scattered light at each position is guided to the photoelectric conversion element by an integrating sphere through an aperture spanning the scanning range and concentrated, so even though it is an XY scan, the main Foreign object detection corresponding to the scanning speed becomes possible. Moreover, since XY scanning is performed, S
The angular relationship between the irradiation direction of the polarized beam and the pattern prevents false detection and enables reliable foreign object inspection.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a part of the foreign object inspection device according to the present invention, with a part cut away, FIG. It is a block diagram. 10...Moving table, 14...Chick, 1
2... Wafer, 16, 18... S-polarized laser oscillator, 22... Half mirror, 24... Galvano mirror, 30... f-theta lens, 34... Elliptical mirror, 36... Aperture (transparent window) , 38...Polarizing plate (S polarization cut filter means), 40... Integrating sphere,
42...Aperture, 44, 46...Photomultiplier, 48, 50...Dichroic filter, 5
4...Summing amplifier, 56...Comparison circuit.

Claims (1)

[Claims] 1. A two-dimensional scanning mechanism that scans a surface to be inspected in XY with an S-polarized beam; an elliptical mirror provided with a cut ellipse having a cross section of approximately 1/4, with a first elliptical cut surface facing the surface to be inspected; and an S-polarized light cut provided over the scanning range on the first elliptical cut surface side. an integrating sphere that is integrally formed with the elliptical mirror adjacent to the second elliptical cut surface side of the elliptical mirror and has an aperture that receives light from the elliptical mirror with a width that spans the scanning range; A photoelectric conversion element provided on the integrating sphere and receiving light from the integrating sphere, and means for determining the presence or absence of foreign matter on the surface to be inspected based on the output signal of the photoelectric conversion element. Foreign matter inspection equipment. 2. The two-dimensional scanning mechanism comprises means for linearly moving the inspected surface in the sub-scanning direction and means for linearly swinging the S-polarized beam in the main-scanning direction. A foreign matter inspection device according to scope 1.