JPH02186248A - Surface condition inspecting device - Google Patents

Abstract

PURPOSE:To achieve a stable inspection of a foreign matter by making a laser beam P polarized while it is made incident on the surface of a substrate at less than 75 deg. in the angle of incidence in a surface condition inspecting device which makes a laser beam incident onto a substrate to inspect a surface condition of the substrate detecting scattered light thereof. CONSTITUTION:When a laser beam 6 is made incident P polarized at 75 deg. in the angle of incidence, in the transmission thereof through a pellicle film 2, a transmissivity varies in a range of 95-87% of the maximum transmissivity for a scattering of a film thickness. If an angle theta2 about optical axes P2P2' of a light receiving element 7b is also 75 deg., a quantity of light received with the light receiving element 7b varies with a squaring of variations in the transmissivity, namely, in a range of 90-76%. Thus, when a foreign matter is on the surface of glass, variations in the thickness of the pellicle film can be suppressed downto 18% at the worst.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface condition inspection device, and in particular, to a surface condition inspection device used in semiconductor manufacturing equipment on and to a substrate such as a reticle or photomask on which a circuit pattern is formed. The present invention relates to a surface condition inspection device that accurately detects foreign matter such as impermeable dust adhering to the surface of a protective film such as an optical thin film such as a pellicle protective film.

[Prior Art] Generally, in the IC manufacturing process, a reticle or a
A semiconductor printing device (stepper or mask aligner) is used to print circuit patterns for exposure formed on substrates such as masks.
It is manufactured by transferring onto a wafer surface coated with resist.

At this time, if foreign matter such as dust is present on the substrate surface, the foreign matter will also be transferred at the same time, causing a decrease in the yield of IC manufacturing.

Therefore, in the IC manufacturing process, it is essential to detect the presence of foreign substances on the substrate, and various inspection methods have been proposed. For example, FIG. 2 shows an example of a method that utilizes the property of a foreign object to scatter light evenly.

In the figure, the light beam from the laser 10 is divided into upper and lower parts through the scanning mirror 11 and lens 12 by inserting and removing the mirrors, and is made incident on the front and back surfaces of the substrate 18 by two mirrors 14 and 15, respectively. The substrate 18 is scanned by rotating or vibrating. and board 1
Two light receiving sections 16 and 17 focused on the front and back surfaces of the substrate 18 are provided at positions away from the optical path of the direct reflected light and transmitted light from the substrate 18, and output signals from these two light receiving sections 16 and 17 are provided. is used to detect the presence of foreign matter on the substrate 18.

That is, when a light beam is incident on a foreign object, the incident light beam is uniformly scattered. Therefore, if a foreign object is present on one surface, the output from the light receiving section focused on that surface will increase. Therefore, the presence of foreign matter is detected by comparing the output values from the two light receiving sections at this time.

Conventionally, this type of surface condition inspection apparatus uses S-polarized light, which has a high intensity of light reflected and scattered by foreign objects.

Moreover, if the substrate surface is patterned, scanning is usually performed with an oblique incident beam of 60° or more relative to the reticle normal in order to avoid the pattern diffracted light and make it easier to receive only the foreign object scattered light. It is.

However, this method requires scanning by switching the light beam from each direction of the front and back surfaces of the substrate, and when a pellicle protective film is attached to the substrate, foreign matter may also adhere to the pellicle surface. It is necessary to detect which surface the foreign matter is attached to, and it is necessary to focus the scanning light beam on each detection surface and repeatedly perform measurements.

On the other hand, Fig. 3 shows a method in which the foreign object inspection of a reticle film equipped with a Veritaru film is carried out simultaneously on four surfaces: the upper and lower pellicle surfaces, the glass surface, and the pattern surface (Japanese Patent Laid-Open No. 62
(Refer to Publication No.-188949). In this case, the laser beam 101 is incident on the reticle obliquely from above, and the laser beam 101 is incident on each inspection surface 102a.

102b 103. The number of light receiving optical systems for foreign object scattered light looking through the intersection line -t of +04 and beam 101 is provided as many as the number of surfaces to be inspected. By the way, in the same figure, 105a to 105d
is a light-receiving element that takes in the scattered light flux of the beam scanning line from each inspection surface, such as a one-dimensional imaging element such as a Selfoc lens array (Selfoc is a product name of Nippon Sheet Glass Co., Ltd.), a bar lens, or a cylindrical lens.
Reference numerals 106a to 106d are field stops for blocking light other than light beams scattered by foreign objects on the inspection surface, and 107a to 107d are optical transmission means such as optical fibers for guiding the light fluxes that have passed through the field stops to photomultiples 1088 to 108d.

[Problems to be Solved by the Invention] However, in such an inspection device, due to variations in the thickness of the pellicle film itself, for example, the reference value is set to 0.
Even if the thickness changes by only ±0.01 μm when the thickness is 865 μm, the intensity of the laser beam that passes through the pellicle film and reaches the substrate changes.

Incidentally, if the horizontal axis is the incident angle of the beam on the pellicle film surface and the vertical axis is the transmittance when the beam passes through the pellicle film once, the result will be as shown in FIG. Therefore, in Figure 3, for example, if we consider the case where S-polarized light is incident at an incident angle of 75 degrees with respect to the normal to the beam lot, the transmittance in this case is at most 70% and at minimum 4.
It is 5%. Considering the surface of the substrate, the light flux that is finally charged and converted must pass through the pellicle film twice, once when it enters and once when it is received.If the receiving angle is also 75°, then the amount of received light will vary by the square of this. . That is, the maximum is 49% and the minimum is 20%. Therefore, even if there are exactly the same foreign matter on the substrate, the pellicle film thickness will be 0.
With a variation of only 0.02 μm, the amount of received light is 2.5 (=4
9/20) will fluctuate twice as much.

The reason for such large fluctuations is that the pellicle film is usually made of a dielectric material such as nitrocellulose, and the light beam incident on the pellicle undergoes multiple reflections within the pellicle film, resulting in a minute film thickness. Even the difference ultimately results in an optical path length change that can shift the interference condition with respect to the beam wavelength (0.6328 μm in the case of He-Ne).

This tendency becomes larger as the beam is incident at a larger angle to the normal to the pellicle film surface.

In addition to such fluctuations in the amount of received light, there is also the drawback that the amount of received light itself is reduced to about 35% on average compared to when there is no pellicle film.

A similar problem occurs not only when using a Betartal film but also when parallel plane glass is used. That is, when the parallel plane glass is thin, for example, 2 mm or less, and is within the V walking distance of the laser beam, the amount of transmitted light is attenuated for the same reason as the pellicle film described above. Furthermore, even when the thickness is large, Fresnel reflection increases when the beam enters the glass and when it exits the glass, resulting in a similar reduction in the amount of transmitted light.

In view of the problems of the prior art, an object of the present invention is to
It is an object of the present invention to enable a surface condition inspection device to perform a stable inspection with high foreign matter detection sensitivity regardless of the presence or absence of a pellicle film or the like and even if the thickness of the pellicle film varies.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a surface condition inspection apparatus that inspects the surface condition of the substrate by making a laser beam incident on the substrate and detecting its scattered light. The beam is P-polarized and is made incident on the substrate surface at an incident angle of 75° or less. Further, the angle between the detected scattered light and the normal to the substrate surface is set to be 75° or less.

A light-transmissive optical thin film or optical flat plate, such as a dustproof pellicle film, is usually mounted on the substrate surface substantially parallel to the substrate.

[Function] In this configuration, if a dustproof pellicle film is attached as an optical thin film to a substrate such as a reticle, for example, in the case of a reticle substrate, the surface condition of the glass surface or pattern surface can be scanned through the ferrite film. The laser beam used as illumination light is P(
Because it is polarized light, the change and decrease in transmittance due to changes in the thickness of the pellicle film are smaller than in the case of conventionally used S-polarized light, which is expected if the incident angle is 75° or less. Inspection is performed within a range of practically sufficient variation and decrease in transmittance with respect to thickness changes. Therefore, regardless of the presence or absence of a pellicle film or the like and variations in its film thickness, a stable inspection can be performed with high foreign object detection sensitivity.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

'fSx Figures (a) and (b) are a side view and a schematic bottom view showing how a reticle surface is inspected by a surface condition detection device according to an embodiment of the present invention.

In the figure, 1 is the reticle, 1u is the two glass surfaces of the reticle 1, 11 is the patterned surface of the lower surface of the reticle 1, 2 and 3 are pellicle films that protect the glass surface 1u and the pattern surface 11, respectively. 4 is the upper pellicle on the upper surface of pellicle l]@2, 5 is the lower pellicle surface on the lower surface of the pellicle membrane 3, 6 is the laser beam that scans each of these surfaces, and 78 to 7d are the pellicles on each of these surfaces operated by the laser beam 6. There is an object point at the scanning point P,~P4, and the point P,'~
Light-receiving elements 88 to 8d, which are lenses or mirrors that refocus images on Pa', are points P, respectively.

A field diaphragm, 98-9, which is placed on or near ~P,' and blocks unnecessary light beams emitted from points other than points P, ~P4.
d is a light amount transmission element such as an optical fiber, which is arranged behind the field stops 88 to 8d, and transmits the light beam condensed by the light receiving elements 7a to 7d, and 10a to 10d are light amount transmission elements 98 to 10d.
This is a photoelectric conversion element that performs photoelectric conversion on the luminous flux transmitted by 9d.

The laser beam 6 is P-polarized light as shown by the arrow in the figure.
The deflection plane is within the plane of the paper (inside the incident cross section), and as described above with reference to FIG. 2, it is scanned in a direction across the plane of the paper of FIG. 1 using a polygon mirror or a vibrating mirror. In addition, so that the entire surface of the reticle is scanned by the laser beam 6,
Reticle 1 is moved in the direction of arrow S by a stage (not shown).

The incident angle θ1 of the laser beam 6 with respect to the upper pellicle surface 4 is set to be 75° or less. In addition, the light receiving element 7
The optical axes P, P2' and Ps Ps' of the light receiving optical systems such as b and 70 are configured to make angles θ2 and θ of 75° or less with respect to the normal to the upper or lower pellicle surface 4 or 5, respectively. .

As the light-receiving elements 78 to 7d, a SELFOC lens array is particularly used in this embodiment, but other one-dimensional imaging elements such as cylindrical lenses can also be used.

Next, the foreign object detection principle of this embodiment will be explained using FIG. 1(b). FIG. 1(b) is a schematic bottom view of the surface state detection device of this embodiment, and in this figure, the pellicle 11! 3
, the light receiving element 7d, and other members are omitted for the sake of simplification. The light receiving element 7C is a Selfoc lens array consisting of a plurality of Selfoc lenses 7ca as shown in the figure (the size of the Selfoc lenses 7ca is drawn larger than it actually is). ℃ is the locus (scanning line) of the scanning laser beam at 1℃ above the bottom surface of the reticle. direction) and make an angle of 15°.

The optical axes 7C° of each SELFOC lens are all parallel to each other, and the extension lines of all the optical axes are perpendicular to the scanning line I on the lower surface lfl of the reticle. Therefore, the lower surface I of the reticle for each optical axis
The projected image onto J2 forms an angle of 15° with the vertical or horizontal direction (in this case, the Y direction) of the reticle. Further, the object-side focal positions of all SELFOC lenses 7ca are arranged so as to be on the scanning line °C. Furthermore, the light receiving NA of each SELFOC lens 7ca is limited to ±15°. Here, the scattered light from the pattern is
”, 30°, 45°, 60°, and 90°.
°, 60" is generated in the 90° direction. The projected image of the optical axis of each SELFOC lens 7ca onto the lower surface IIl of the reticle forms an angle of 15° with the Y direction, and the receiving NA is ±15°15
Therefore, the incident angle of the scattered light from the pattern above the scanning line to each SELFOC lens is always greater than the NA, and it is eclipsed and cannot pass through. On the other hand, since the scattered light from foreign objects has no directivity, a portion of it necessarily passes through each self-cleaning lens. Therefore, if the light passing through each SELFOC lens is received and detected by the light amount transmission element 9c, it is possible to detect the scattered light only from the foreign matter.

In this configuration, the laser beam 6 is incident on the upper pellicle surface 4 at an incident angle θ1 of 75° or less and each surface is scanned. When the laser beam 6 hits the foreign matter attached to the laser beam 11, the laser beam 6 is scattered by the foreign matter, and a part of the scattered light flux is collected by the light receiving elements 78 to 7d, and then passes through the light transmitting elements 98 to 9d for photoelectric conversion. The signal is transmitted to any of the elements 10a to 10d. The transmitted optical signal containing information on the foreign object is converted into an electrical signal by the photoelectric conversion element, and the presence of the foreign object is detected through predetermined signal processing.

Here, if the laser beam 6 is incident with a P polarization at an incident angle of 75', upon passing through the pellicle flI2,
As shown in Figure 4, for a film thickness variation of 002 μm,
The transmittance will vary within the range of 95% to 87% of the maximum transmittance. Furthermore, if the angle θ of the light receiving element 7b with respect to the optical axis P2P2' is also 75°, the amount of light received by the light receiving element 7b is the square of the transmittance fluctuation, that is, 90°.
It varies in the range of ~76%.

Therefore, in the conventional example, even if there was exactly the same foreign object on the glass surface, the amount of received light varied up to 245 times due to variations in the thickness of the pellicle film, whereas in the case of the present example, the amount of received light varied by a factor of 1.18 (90%) at worst. /76) times, or only 18%. In addition to such fluctuations, the amount of received light itself is 83% or more of that without the pellicle film, and can be suppressed to within 17%, whereas it was reduced to 65% in the conventional example.

Furthermore, based on such effects, the following system advantages arise.

- Since the amount of scattered light from foreign objects that jumps into the light-receiving element is almost the same between a reticle with a pellicle film and a reticle without a pellicle film, both reticles can be inspected with the same sensitivity setting.

■ Stable detection sensitivity can always be maintained regardless of variations in pellicle film thickness.

FIG. 5 shows how a reticle surface is inspected by a surface condition detection device according to another embodiment of the present invention. Components with the same symbols as in FIG. 1 are the same.

The difference from the case of FIG. 1 is that the laser beam is incident on the reticle separately into a beam 6u from above and a beam 6fl from below. To achieve this,
For example, in FIG. 2, the switching mirror 13 is replaced with a half mirror.
Just change it to

The advantages of this embodiment are as follows.

In an actual reticle, the circuit pattern A is printed on the lower surface of the substrate using opaque chromium or chromium oxide. Therefore, for example, when the laser beam is incident only from above the reticle as shown in FIG.
Since the beam reaches L and P, the surface condition of these surfaces can be inspected. However, if there is a chrome pattern on the bottom surface of the reticle, the beam will be blocked by this pattern. Therefore, the dust adhering to this chromium and the dust on the lower pellicle surface 5 (above point P4) located on the extension line of the beam are not illuminated, making it impossible to inspect the surface condition on these surfaces.

On the other hand, when the beam is incident from above and below as shown in FIG. 5, the upper beam 6u always illuminates the upper pellicle surface 4 and the glass surface 1u, and the lower beam Since 6JZ illuminates the lower pellicle surface 5 and pattern surface IIl, it is impossible to inspect the surface condition of these four surfaces at the same time.

In this embodiment as well, the incident angles θ1 and θI of the upper and lower beams 6u and 61 with respect to the pellicle surfaces 4 and 5 are preferably 75'' or less, and the optical axis P2 P2' of each light receiving system on the glass surface 1u and pattern surface iIL is , Ps P3'
It is desirable that the number is 756 or less.

Furthermore, instead of using a polygon mirror or a single-axis mirror for scanning the laser beam, a one-dimensional imaging element such as a cylindrical lens may be used to form a sheet-shaped beam on each inspection surface. .

In the above-mentioned embodiment, the light receiving system receives back scattered light or upward scattered light from a foreign object, but it may be configured to receive side scattered light or forward scattered light.

[Effects of the Invention] As explained above, according to the present invention, a laser beam for illumination is P-polarized and is incident on a protective film such as an optical thin film or an optical flat plate at an incident angle of 75° or less for scanning. Furthermore, since the detected scattered light is at an angle of 75° or less with respect to the normal line of the protective film, foreign matter on the substrate surface can be detected stably with high sensitivity even through the protective film that has optical interference. Can be done.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are schematic diagrams showing how a reticle surface is inspected by a surface state detection device according to an embodiment of the present invention, and FIG. 2 is a surface state detection device according to a conventional example. FIG. 3 is a schematic diagram showing how the reticle surface is inspected using another conventional surface state detection device. FIG. 4 is a schematic diagram showing how the reticle surface is inspected using another conventional surface state detection device. A graph showing the characteristics of transmittance with respect to film thickness, and the fifth
The figure is a schematic diagram showing how a reticle surface is inspected by a surface condition detection device according to another embodiment of the present invention. 1. Reticle, 1u glass surface, 1λ: pattern surface, 2, 3: velicle film, 4: upper pellicle surface, 5: lower pellicle surface, 6.8u, 842: laser beam, 78-7cm photodetector, 88-8d : Field stop, 98-9d: Optical fiber, 10: Laser, 10a-10d: Photoelectric conversion element, 11: Scanning mirror 12: Lens, 13.14, 15: Mirror

Claims (3)

[Claims] (1) In a surface condition inspection device that injects a laser beam onto a substrate and detects its scattered light to inspect the surface condition of the substrate, the laser beam is P-polarized light and is 75° with respect to the normal to the substrate surface. A surface condition inspection device characterized in that the incident angle is as follows. (2) The surface condition inspection device according to claim 1, wherein the angle between the detected scattered light and the normal to the substrate surface is 75° or less. (3) The laser beam is incident on the substrate via a pellicle attached to the substrate, and is incident at an incident angle of 75° or less with respect to a normal to the pellicle surface. 1. The surface condition inspection device according to 1.