JPH0247541A - Surface condition measuring device - Google Patents

Abstract

PURPOSE:To increase a rate of separative detection of an extraneous substance by avoiding a diffracted light generated from a circuit pattern and by sensing selectively only a scattered light flux from the extraneous substance. CONSTITUTION:A beam from a laser 1 passed through a stop 101 and enters a beam expander 102, whereby the radius of the beam is expanded. Then, it is reflected by a polygon mirror 2 and made to fall on each position of a beam scan line on a circuit board 5, through a lens 61 whose optical axis is inclined at an angle alpha to the surface of the board and at an angle beta to the longitudinal direction. The polygon mirror 2 is rotated for scanning on the board 5, while it is moved on the board 5 for scanning the whole surface. A condenser element of a light-sensing optical system condenses a scattered light flux from an extraneous substance on the board 5, and the flux is focused on a focal point PG on the rear side of the lens 61, passed through a stop 103 and led onto the light-sensing surface of a light-sensing element 9 by a lens 8.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface condition measuring device, and particularly to a surface condition measuring device that is used in semiconductor manufacturing equipment to measure a surface condition on a substrate such as a reticle or a photomask on which a circuit pattern is formed. The present invention relates to a surface condition measuring device suitable for detecting foreign matter such as impermeable dust.

(Prior Art) Generally, in the IC manufacturing process, a semiconductor printing device (stepper or mask aligner) is used to print a circuit pattern for exposure formed on a substrate such as a reticle or a photomask.
It is manufactured by transferring it onto eight surfaces of sea urchins 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 time of transfer, causing a decrease in the yield of IC manufacturing.

In particular, when a reticle is used to repeatedly print a circuit pattern on eight surfaces using a step-and-repeat method, a single foreign object on the reticle surface is printed onto the entire wafer, which greatly reduces the yield of IC manufacturing. It becomes.

Therefore, in the IC manufacturing process, it is essential to detect the presence of foreign matter on the substrate, and various inspection methods have been proposed. For example, FIG. 7 shows an example of a method that utilizes the property of foreign matter to scatter light isotropically. In the figure, a beam from a laser 10 is divided into two by a half mirror 13 via a scanning mirror 11 and a lens 12, and is made incident on the front and back surfaces of a substrate 15 by two mirrors 14 and 45, respectively. The scanning mirror 11 is rotated or vibrated to scan the substrate 15. A plurality of light receiving sections 16, 17.18 are provided at positions away from the optical path of direct reflected light and transmitted light from the substrate 15, and output signals from these plurality of light receiving sections 16, 17.18 are used to Detecting the presence of foreign matter on the top.

In other words, since the diffracted light from the circuit pattern has strong directionality, the output value from each light receiving part will be different, but when the light beam is incident on a foreign object, the incident light flux will be isotropically scattered, so the output value from multiple light receiving parts will be different. become equal. Therefore, the presence of foreign matter is detected by comparing the output values at this time.

Further, FIG. 8 shows an example of a method that utilizes the property that foreign matter disturbs the polarization characteristics of an incident light beam. In the figure, a laser 10 is transmitted through a polarizer 19, a scanning mirror 11, and a lens 12.
Half mirror 1
3, and the scanning mirror 11 is divided into two parts by two mirrors 14.
The substrate 15 is scanned by. Two light receiving sections 21.21 each have analyzers 20.21 disposed in front of them, respectively, at positions away from the optical paths of direct reflected light and transmitted light from the substrate 15.
There are 23. Then, the difference in the amount of light received due to the difference in polarization ratio between the diffracted light from the circuit pattern and the scattered light from the foreign object is detected by the two light receiving sections 21 and 23, thereby distinguishing between the circuit pattern on the board 15 and the foreign object. Separate.

However, in both of the detection methods shown in Figs. 7 and 8, although the direct reflected light and transmitted light of the incident light beam do not enter the light receiving section, the detection method does not allow the direct reflected light or transmitted light of the incident light beam to enter the light receiving section, but when the board is being scanned, the detection method from the circuit pattern at several points on the scanning line is detected. A part of the diffracted light of each order ends up being incident. For this reason, when taking the output difference between the diffracted light from the circuit pattern and the scattered light from a foreign object, if the reflectance or shape of the foreign object differs, the output difference between both will fluctuate and the detection rate of the foreign object will decrease. The shortcomings that come with it are gone.

(Problems to be Solved by the Invention) The present invention is capable of separating and detecting foreign matter such as dust on a board in any state from the circuit pattern at all points on the scanning line with high precision. The purpose of the present invention is to provide a surface condition measuring device that has a high separation detection rate.

(Means for Solving the Problems) The present invention provides an apparatus for measuring the surface condition of a substrate having a circuit pattern on its surface, which includes a light source means and a device for scanning a light beam from the light source means on a surface to be measured of the substrate. scanning means, and one light receiving means for receiving light from the surface to be measured scanned by the scanning means, and detecting the scattered light from the foreign matter on the surface to be measured scanned by the scanning means. A light-receiving optical system guides the light-receiving optical system to two light-receiving means, and the direction of the projected image of the optical axis of the light-receiving optical system onto the surface to be measured is a direction in which only the scattered light from the foreign matter on the surface to be measured scanned by the scanning means is emitted. The light-receiving optical system is parallel to the direction of the projected image onto the surface to be measured, and the light-receiving optical system detects scattered light in a direction in which only the scattered light from the foreign object at each point on the surface to be scanned by the scanning means is emitted. The above-mentioned problem is solved by selecting and arranging the light receiving means so as to guide the light to the two light receiving means.

Other features of the invention are described in the Examples.

(Embodiment) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention. FIG. 2 is a diagram of the optical principle of the light projection system of FIG. 1.

In the figure, 1 is a laser 1 which is a light source; 2 is a polygon mirror (polygon) which is an optical polarizer; 101 is an aperture;
02 is a beam expander 61 which is an f-theta lens, 5 is a substrate which is an object to be measured such as a reticle, and 62 is a half mirror which reflects the scattered light obtained through the f-theta lens 61 and changes its optical path. Reference numeral 9 denotes a light receiving element for receiving scattered light, which receives the scattered light reflected by the half mirror 62 and condensed at the -H position pa through the lens 8.

103 is an aperture.

In the figure, a parallel beam emitted from a laser 1 as a light source enters a beam expander 102 after its diameter is limited by a first aperture (pinhole) 101. The inside of the expander 102 includes, for example, a convex lens 1 as shown in FIG.
10 and 111, the diameter of the incident beam is expanded and the beam is emitted toward the polygon mirror 2.

The function of this expander is to establish an optical conjugate relationship between the pinhole 101 and the reflection point of the polygon (dotted line). By doing this, the reflection point of the polygon actually acts as a diaphragm for the beam projection system. As a result, the ray passing through the center of the beam on the reflecting surface at each rotational position of the polygon 2 becomes the chief ray of the projected light flux, and the f-〇 lens 6
1 to the respective positions of the beam scanning lines B and -B on the substrate 5. At this time, the optical axis of the f-theta lens 61 is inclined at an angle .alpha. with respect to the substrate surface and at an angle .beta. with respect to the vertical direction (A-A' direction) of the substrate.

In this way, the polygon mirror 2 is rotated to scan the substrate 5 from point B in the direction of point B2, and the substrate 5 is scanned by the arrow S.
1 or by moving in the direction of arrow S2.
The entire top surface is scanned.

Then, the optical axis of the condensing section (in this case, the f-theta lens 61) of the light receiving optical system is provided on the incident side with respect to the normal to the incident surface of the substrate 50, and the scattered light flux from the foreign matter on the substrate 5 is condensed. The light is focused on a point pa via a half mirror 62, and then guided to a light receiving surface of a light receiving element 9 by a lens 8. PG' corresponds to the rear focal position of the f-theta lens 61.

The f-theta lens 61, the half mirror 62, and the lens 8 constitute part of an optical system that receives light scattered by foreign matter from the substrate 5. Let me explain this. In this embodiment, the lens 61 is used for both light projection and light reception. And lens 61
An aperture stop 103 is provided at or near the rear focal point PG' to limit the received light flux. Then, the chief ray of the received light beam that is scattered by foreign objects at each position of the beam scanning line on the substrate and finally reaches the light receiving element 9 is transmitted through this aperture 1.
03 is a ray of light passing through the center. The foreign object scattered light that has passed through the aperture 103 is collected onto the light receiving element 9 by the action of the condensing lens 8 .

FIG. 3 is an explanatory diagram of the incident light beam and the diffracted light generated from the circuit pattern on the substrate 5 in this embodiment. Now, it is assumed that the circuit pattern surface on the board corresponds to the equatorial plane of the schematically drawn sphere S. Most of the shapes of circuit patterns on substrates of semiconductor circuit patterns currently used are, for example, TI.
, T2, which are orthogonal to each other in the vertical and horizontal directions. Now, a point P0 on the spherical surface with an angle α obliquely upward relative to the patterns T1 and T2 on the substrate and an angle β shifted from the direction of the diffracted light generated by the main pattern.
The light flux is incident from the direction passing through.

Then, the plane formed by point A1 point μ1 point A' in the figure becomes the plane of incidence, and the direct reflected light from the substrate 5 is reflected in the direction passing through point P0' on the sphere S, as shown by arrow B.

Also, if a beam of light is incident on the center point 0 from a point P on the sphere S parallel to the direction of the pattern T2, and if the intersection of the reflected light with the sphere S is P', then each Diffraction images of each order are formed in a direction perpendicular to the patterns T r and T 2 . As mentioned above, when the circuit pattern is an isolated line, its diffraction image Q appears continuously in the direction orthogonal to the pattern T, as shown in FIG. 4(A). Further, when the circuit pattern is a repeating pattern such as a memory pattern, the diffraction image Q appears discretely as shown in FIG. 4(B). Moreover, FIG. 4(C) shows that when a light beam is incident on the substrate 5 from the direction shown by the arrow 51, the main patterns TI, T on the substrate are
2 shows that the diffracted light is generated in the directions indicated by arrows 52 and 53, that is, in a direction shifted by an angle β from the incident direction.

In either case, the intensity of the reflected light and the diffraction image from the circuit pattern becomes weaker as the distance from the points P0 and P' of the directly reflected light beam increases. That is, point P. ', a point P that passes through the normal μ in the plane of incidence and intersects the sphere on the incident side of the incident light beam. When it comes to the vicinity of , the intensity of the diffracted light becomes considerably weaker.

On the other hand, since the scattered light from foreign objects is generated in the same direction, a large amount appears on the incident side as well.

Therefore, in this embodiment, the principal ray of the received light beam is located at a position as far as possible from the optical path of the directly reflected light, that is, on the light beam incident side with respect to the normal μ of the incident surface, and the diffracted light generated from the main pattern on the substrate 5 is emitted. By positioning it at a position shifted from the direction, for example near point P0, the influence of diffracted light from the circuit pattern is minimized and only the backscattered light from the foreign matter on the substrate 5 is mainly received. There is.

That is, the principal ray of the received light beam forms an angle α with respect to the substrate 5 as shown in FIG. Here, the angle β is shifted from the direction parallel to or perpendicular to the vertical and horizontal directions of the substrate 5.

As described above, the position of the principal ray of the received light beam with respect to the substrate is specified, thereby increasing the rate of separating and detecting foreign matter from the circuit pattern. In order to increase the separation detection rate, suppose that the principal ray of the received light beam is placed on point P0. and P. The larger the angle δ with respect to the center O, the more preferably it is set in the range of, for example, 90° to δ to 180°.

An actual circuit pattern on a board may include patterns extending at 30 degrees, 45 degrees, and 60 degrees with respect to the vertical and horizontal directions of the board. In order to fully exhibit the effects of the present invention on such a substrate, it is necessary to make the angle between the projected image of the chief ray of the received light beam onto the surface of the substrate 5 and the longitudinal and lateral directions of the substrate 5 from parallel or orthogonal directions. It is best to set it within the range of 15 degrees ± 5 degrees.

In other words, in relation to the direction of the main diffraction pattern, one of the two main diffraction pattern directions generated by the circuit pattern on the substrate 5 in directions substantially orthogonal to each other (when projected onto the substrate 5), This means that the angle formed by the principal ray of the received light beam and the projected image onto the substrate 5 is set within the range of 15 degrees ± 5 degrees.

5 and 6 show the principal ray of the incident beam (solid line in the figure) and the received scattered light flux at each scanning position fi (L, O, R) on the substrate 5 when the optical arrangement shown in FIG. 1 is taken. The chief ray of (
In the figure, the projected image of the line (dotted line) onto the substrate 5 is parallel to the projected image 00' of the optical axis of the projection system onto the substrate 5, and has an angle of β with respect to the longitudinal and lateral directions of the substrate 5. For this reason, each scanning point is always illuminated from the same direction, and in order to create this condition where the illumination state is equal in the entire scanning area, the reflection point of the polygon mirror is set to the front focal point of the f-theta lens 61 in FIG. (The floodlight system is telecentric). Also, at this time, the projected image of each principal ray of the received light beam on the substrate 5 is at the rear focal point P of the square lens.

This is achieved by providing an aperture stop 103 near '. In other words, the aperture stop 103 is such that the projected image of each chief ray of the received light beam from each point on the scanning line is within an angle range of 15°±5°. ′ in the vicinity. As a result, from each scanning point, the direction is always substantially the same (here, the direction in which only the scattered light from the foreign matter on the substrate 5 is mainly received by minimizing the influence of the diffracted light from the circuit pattern, that is, the angle β direction) This means that only the light that is scattered is received, and the light reception state can be made equal in the entire scanning area. To explain in detail using FIG. 3, each point of the beam scanning line on the reticle corresponds to the current point O. Applying the configuration of FIG. 1 to FIG. 3, since in FIG. 1 the returning scattered light toward the input lens 61 side is received, the light receiving aperture is essentially always in the direction of P0 on the sphere in FIG. 3. This means that it has been set up. As previously explained with reference to FIG. 3, since the diffracted light of the main circuit pattern on the board jumps in the direction of the black circle, p.

Light is not received near . If the equatorial plane of the sphere corresponds to the surface of the substrate 5, and the projected image of the chief ray (OPO) of the received light beam on this equatorial plane roughly coincides with the angle β direction, pattern diffraction can be performed according to the gist of the present invention. It is possible to exclude light and selectively receive only light scattered by foreign objects. The value of β at this time is set to 15°±5° in order to avoid scattered light from the circuit pattern.

At each point on the beam scanning line, the deviation angle of the projected image on the reticle surface between the principal ray of the incident beam and the principal ray of the received light beam (β-β or β-βR in Fig. 5) is determined.
is preferably within ±10@.

In contrast to FIG. 5, FIG. 6 shows that, in particular, the projected image of each principal ray of the received light beam is the projected image 00' of the optical axis of the light receiving system on the reticle.
The configuration is parallel to . To do this, it is desirable to scan the principal ray projection image of the incident beam even when the focal point is on the rear side of the light-receiving lens 61 in FIG. Generally, it is desirable that the light emitting system and light receiving system be completely telecentric, but
In order to obtain the effect of the present invention (creating conditions for reducing the pattern output equally over the entire area on the reticle), at each point on the beam scanning line on the reticle, the projected image of each principal ray of the received light beam on the reticle must be It suffices if it approximately coincides with the β direction (15°±5° direction with respect to the vertical or horizontal direction of the substrate 5). Preferably, the angle formed by the projected images of the incident beam and the received light beam is within ±10°.

In this embodiment, the lens 61 may be divided into two lenses, one for projecting light and one for receiving light.

(Effects of the Invention) According to the present invention, the diffracted light generated from the circuit pattern on the board is spatially avoided at all points on the scanning line, and only the scattered light flux from the foreign matter existing on the board is selectively received. Therefore, it is possible to achieve a surface condition measuring device with a high rate of separating and detecting foreign matter from a circuit pattern.

[Brief explanation of the drawing]

1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG. 2 is a diagram of the optical principle of the light projection system according to the embodiment of FIG. 1, and FIG. 3 is a diagram showing the incident light flux in the embodiment of FIG. An explanatory diagram of diffracted light due to a circuit pattern, Figure 4 (A). (B) and (C) are explanatory diagrams showing the relationship between the circuit pattern and the diffraction image, FIG. 5 is a schematic diagram of the relationship between the incident beam and the received light flux in the embodiment of FIG. 1, and FIG. The schematic diagrams of the relationship between the incident beam and the received light beam in another embodiment, FIGS. 7 and 8, are each an example of a conventional surface condition measuring device. In the figure, 1 is a light source, 2 is a polygon mirror, 4 is a light emitter, 5 is a substrate, 6 is a condenser, 7 is a mirror, 8 is a lens, 9 is a light receiving surface,
10 is an optical system, and 11 is a half mirror.

Claims (4)

[Claims] (1) An apparatus for measuring the surface condition of a substrate having a circuit pattern on its surface, comprising: a light source means; a scanning means for scanning a light beam from the light source means on the surface to be measured of the substrate; and scanning by the scanning means. a light-receiving optical system, the light-receiving optical system having one light-receiving means for receiving light from a surface to be measured that has been scanned by the scanning means, and guiding scattered light from a foreign object on the surface to be measured scanned by the scanning means to the one light-receiving means; The direction of the projected image of the optical axis of the light receiving optical system on the surface to be measured is such that the projected image on the surface to be measured is in a direction in which only the scattered light from the foreign matter on the surface to be measured scanned by the scanning means is emitted. parallel to the direction,
The light-receiving optical system is arranged so as to select the scattered light in a direction in which only the scattered light from the foreign object at each scanned point on the surface to be measured scanned by the scanning means is emitted, and guide the selected light to the one light-receiving means. A surface condition measuring device characterized by: (2) The light-receiving optical system is configured such that a projection image of a chief ray onto the surface to be measured is a projected image of the principal ray on the surface to be measured among the scattered lights emitted from each point optically scanned by the scanning means on the surface to be measured. 2. The surface condition measuring device according to claim 1, wherein the surface condition measuring device is arranged so as to guide only the light beam forming an angle of 15°±5° with respect to the longitudinal and lateral directions of the surface to the light receiving means. (3) The light-receiving optical system includes an objective optical system that receives scattered light from above the surface to be measured, and the objective optical system has an optical axis that projects an image onto the surface to be measured in the vertical and horizontal directions of the surface to be measured. 2. The surface condition measuring device according to claim 1, further comprising an aperture diaphragm forming an angle of 15°±5° with respect to the rear focal point position. (4) The light-receiving optical system is configured such that a projection image of a chief ray onto the surface to be measured, out of the scattered light emitted from each point optically scanned by the scanning means on the surface to be measured, is configured to be Claim 1, characterized in that the light receiving means is arranged so as to guide only the light beam forming an angle of ±10° to the projected image of the chief ray of the scanning light beam scanned to each point by the light receiving means. The surface condition measuring device described.