JPH0675039B2 - Surface condition measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface condition measuring apparatus, and particularly to a surface state measuring apparatus other than a circuit pattern on a substrate such as a reticle or a photomask on which a circuit pattern used in a semiconductor manufacturing apparatus 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 an IC manufacturing process, an exposure circuit pattern formed on a substrate such as a reticle or a photomask is transferred onto a resist-coated wafer surface by a semiconductor printing apparatus (stepper or mask aligner). ing.

At this time, if foreign matter such as dust is present on the surface of the substrate, the foreign matter is also simultaneously transferred at the time of transfer, which causes a decrease in yield of IC manufacturing.

In particular, when a reticle is used and a circuit pattern is repeatedly printed on the wafer surface by the step-and-repeat method, one foreign substance on the reticle surface is printed on the entire surface of the wafer, which causes a large decrease in the yield of IC manufacturing. Is coming.

Therefore, it is essential to detect the presence of foreign matter on the substrate in the IC manufacturing process, and various inspection methods have been conventionally proposed. For example, FIG. 7 shows an example of a method of utilizing the property that a foreign substance isotropically scatters light. In the figure, the light flux from the laser 10 is divided into two by the half mirror 13 via the scanning mirror 11 and the lens 12, and is made incident on the front surface and the back surface of the substrate 15 by the two mirrors 14 and 45, respectively.
The substrate 15 is scanned by rotating or vibrating the scanning mirror 11. Then, a plurality of light receiving units 16, 17, 18 are provided at positions apart from the optical paths of the reflected light and the transmitted light directly from the substrate 15, and the substrate 15 is output by using the output signals from the plurality of light receiving units 16, 17, 18. The presence of foreign matter above is detected.

That is, since the diffracted light from the circuit pattern has a strong directivity, the output value from each light receiving part is different, but when a light beam enters a foreign object, the incident light beam is isotropically scattered, so the output values from multiple light receiving parts Will be equal to each other. Therefore, the presence of foreign matter is detected by comparing the output values at this time.

Further, FIG. 8 is an example of a method of utilizing the property that a foreign substance disturbs the polarization characteristic of the incident light beam. In the figure, a light beam from the laser 10 is made into a light beam in a predetermined polarization state through a polarizer 19, a scanning mirror 11, and a lens 12, and a half mirror 13 is used to
It is divided into two, and two mirrors 14 and 45 are made to enter the front surface and the back surface of the substrate 15, respectively, and the scanning mirror 11 scans the substrate 15. Then, two light receiving portions 21 and 23 having analyzers 20 and 21 arranged in front are provided at positions apart from the optical paths of the reflected light and the transmitted light directly from the substrate 15. Then, the difference in the amount of received light caused by the difference in the polarization ratio between the diffracted light from the circuit pattern and the scattered light from the foreign matter is detected by the two light receiving units 21 and 23, and the circuit pattern on the substrate 15 and the foreign matter are detected by this. Different.

However, in the detection methods shown in FIG. 7 and FIG. 8, neither the direct reflected light nor the transmitted light of the incident light beam is incident on the light receiving portion, but the circuit pattern at some points on the scanning line is scanned from the circuit pattern while scanning the substrate. A part of the diffracted light of each order is incident. Therefore, when the output difference between the diffracted light from the circuit pattern and the scattered light from the foreign matter is taken, if the reflectance and shape of the foreign matter are different, the output difference of both will fluctuate and the foreign matter detection rate will decrease. There was a drawback to come.

(Problems to be Solved by the Invention) According to the present invention, it is possible to detect a foreign matter in any state such as dust existing on a substrate with high accuracy by separating from a circuit pattern at all points on a scanning line. An object of the present invention is to provide a surface condition measuring device having a high separation detection rate.

(Means for Solving Problems) According to the present invention, a scanning means for making a light beam incident on a substrate on which a pattern is formed and scanning the substrate with the light beam, and a light receiving means for receiving a scattered light beam generated from the substrate. In the surface state measuring apparatus having the above, the scanning means has a scanning mirror and a scanning optical system, the light receiving means has a light receiving optical system and an aperture stop, and the optical axis of the light receiving optical system is diffracted light from the pattern. Is set to a direction different from the direction in which the above-mentioned problem occurs, the scanning mirror is arranged at the front focal position of the scanning optical system, and the aperture stop is arranged at the rear focal position of the light receiving optical system. Has been resolved.

Besides, the features of the present invention are described in the embodiments.

(Example) FIG. 1 is a schematic view of an optical system of an example of the present invention. FIG. 2 is an optical principle diagram of the light projecting system of FIG.

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 a diaphragm, 102 is a beam expander, 61 is an f-θ lens, 5 is a measured object such as a reticle. The substrate 62 is a half mirror that reflects scattered light obtained through the f-θ lens 61 and changes its optical path. Reference numeral 9 denotes a light receiving element for receiving scattered light, which is reflected by the half mirror 62 and once focused on the position P _G ′ to receive the scattered light via the lens 8. 103 is a diaphragm.

In the figure, a parallel beam emitted from a laser 1 which is a light source enters a beam expander 102 after its diameter is limited by a first aperture (pinhole) 101. Expander 102
The inside of is composed of, for example, convex lenses 110 and 111 as shown in FIG. 2, and the diameter of the incident beam is enlarged and emitted toward the polygon mirror 2.

The function of this expander is to connect the pinhole 101 and the reflection point of the polygon in an optically conjugate relationship (dotted line). By doing so, the reflection point of the polygon substantially acts as a diaphragm of the beam projection system. As a result, at each rotational position of the polygon 2, the ray passing through the center of the beam on the reflecting surface becomes the principal ray of the projected light beam, and the f-θ lens
It is incident on each position of the beam scanning lines B ₁ -B ₂ on the substrate 5 via 61. At this time, the optical axis of the f-θ lens 61 is inclined at an angle α with respect to the surface of the substrate and at an angle β with respect to the longitudinal direction of the substrate (direction AA ').

In this way, the polygon mirror 2 is rotated and a point is set on the substrate 5.
While scanning from B _{1 in the} direction of point B ₂ and moving the substrate 5 in the direction of arrow S ₁ or arrow S ₂ , the entire surface of the substrate 5 is scanned.

Then, the optical axis of the condensing portion (here, the f-θ lens 61) of the light receiving optical system is provided on the incident side with respect to the normal line of the incident surface of the substrate 5,
A half mirror that collects scattered light from foreign matter on the substrate 5
The light is condensed at a point P _G ′ via 62 and then guided to the light receiving surface of the light receiving element 9 by the lens 8. P _G ′ is an f-θ lens 61
It corresponds to the rear focus position.

The f-θ lens 61, the half mirror 62, and the lens 8 form a part of an optical system that receives the foreign substance scattered light from the substrate 5. This will be explained. In this embodiment, the lens 61 is used for both light projection and light reception. Then, an aperture stop 103 for limiting the received light beam is provided at or near the position of the rear focal point P _G ′ of the lens 61. Then, at each position of the beam scanning line on the substrate, it is scattered by the foreign matter, and finally the light receiving element 9
The principal ray of the received light flux reaching the is a ray passing through the center of the diaphragm 103. The scattered light of foreign matter that has passed through the diaphragm 103 is collected on the light receiving element 9 by the action of the condenser lens 8.

FIG. 3 is an explanatory diagram of incident light flux and 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 substrate coincides with the equator surface of the sphere S schematically drawn. The shape of the circuit pattern on the substrate of the semiconductor circuit pattern which is currently used is mostly T ₁ , T ₂
The patterns are orthogonal to each other in the vertical and horizontal directions. Now, the pattern T ₁ and the pattern T ₂ on the substrate
On the other hand, a light beam is made incident from a direction passing through a point P ₀ on the spherical surface at an angle β which is obliquely upward and a direction β which is deviated from the direction of the diffracted light generated by the main pattern. Then point A, point μ, point A'in the figure
The plane formed by (2) serves as the incident surface, and the light directly reflected from the substrate 5 is reflected in the direction passing through the point P ₀ ′ on the sphere S as shown by the arrow I ′.

Further, when a light flux is made incident on the center point O from a point P on the sphere S parallel to the direction of the pattern T ₂ , and P'is an intersection of the reflected light and the sphere S, the points P'are centered respectively. Diffraction patterns of respective orders are formed in the direction orthogonal to the patterns T ₁ and T ₂ .
As described above, when the circuit pattern is an isolated line, the diffraction image Q thereof continuously appears in the direction orthogonal to the pattern T, as shown in FIG. When the circuit pattern is a repeating pattern such as a memory, the diffraction image Q appears discretely as shown in FIG. 4 (B). Also, FIG. 4 (C)
When a light beam is incident on the substrate 5 in the direction indicated by the arrow 51, the diffracted light is reflected by the main patterns T ₁ and T ₂ on the substrate.
In the figure, the state occurs in the direction indicated by, that is, in the direction deviated from the incident direction by an angle β.

In either case, the intensity of the diffracted image from the reflected light and the circuit pattern becomes weaker as the distance from the point P ₀ and the point P ′ of the directly reflected light flux increases. That is, the intensity of the diffracted light becomes considerably weaker from the point P ₀ ′ to the vicinity of the point P ₀ which intersects the sphere on the incident side of the incident light flux after passing through the normal line μ in the incident plane.

On the other hand, the scattered light of the foreign matter is isotropically generated, and therefore a lot of it appears on the incident side.

In view of this, in this embodiment, the principal ray of the received luminous flux is emitted as far as possible from the optical path of the direct reflected light, that is, on the luminous flux incident side with respect to the normal line μ of the incident surface, and the diffracted light generated from the main pattern on the substrate 5 is emitted. By arranging it so as to be displaced from the direction, for example, near the point P ₀ , the influence of the diffracted light from the circuit pattern is reduced as much as possible, and only the backscattered light from the foreign matter on the substrate 5 is mainly received. ing.

That is, the principal ray of the received light beam is at an angle α with respect to the substrate 5 as shown in FIG. 3, and the projected image of the principal ray of the received light beam on the substrate 5 is the direction in which the diffracted light by the principal pattern of the substrate 5 is generated. In this case, the angle formed with the horizontal and vertical directions of the substrate 5 is parallel or orthogonal to the angle β.

As described above, the position of the principal ray of the received light flux with respect to the substrate is specified, and thereby the detection rate of foreign matter separation with respect to the circuit pattern is increased. Incidentally, as the principal ray of the received light flux to temporarily to increase the separation detection rate is greater angle δ spanned with respect to the center O of P ₀ When arranged to come onto the point P ₀ and the point P ₀ 'example
It is preferable to set in the range of 90 ° <δ <180 °. The circuit pattern on the actual board is 30 in the horizontal and vertical directions of the board.
There may also be patterns in degrees, 45 degrees and 60 degrees. In order to sufficiently exert the effects of the present invention even on such a substrate, the angle formed by the projected image of the principal ray of the received light beam on the surface of the substrate 5 and the vertical and horizontal directions of the substrate 5 is not parallel or orthogonal. It is better to set within the range of 15 degrees ± 5 degrees.

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

5 and 6 show the principal ray (solid line in the figure) of the incident beam and the received and scattered light flux at each scanning position (L, O, R) on the substrate 5 when the optical arrangement of FIG. 1 is taken. Chief ray (in the figure,
The projected image of the dotted line on the substrate 5 is shown. L
The points R and R represent arbitrary points on the left and right sides of the center O, respectively.

Of these, FIG. 5 particularly shows that the projected image of each chief ray of the incident beam is parallel to the projected image 00 ′ of the projection system optical axis on the substrate 5.
Has an angle of β with respect to the vertical and horizontal directions. Therefore, each scanning point is always illuminated from the same direction, and in order to create this condition in which the illumination state is the same in the entire scanning area, the reflection point of the polygon mirror in FIG. Put it in the position (the projected light is telecentric). At this time, the projected image of each principal ray of the received light flux on the substrate 5 substantially coincides with the angle β. That is, β _L at point _L and β _{1 at} point O (β ₁ =
β), β _R at point _R. This is achieved by providing the aperture stop 103 near the rear focal position P _G ′ of the f-θ lens. In other words, the aperture stop 103 is provided in the vicinity of P _G ′ such that the projected image of each principal ray of the received light beam from each point on the scanning line is in the range of 15 ° ± 5 °. As a result, the direction is always substantially the same from each scanning point (here, the influence of the diffracted light from the circuit pattern is reduced as much as possible, and only the scattered light from the foreign matter on the substrate 5 is mainly received, that is, the angle β direction). Only the light scattered by the light is received, and the light receiving state can be made equal in the entire scanning area. Explaining in detail with reference to FIG. 3, each point on the beam scanning line on the reticle now corresponds to point 0. When the configuration of FIG. 1 is applied to FIG. 3, since the returning scattered light to the incident lens 61 side is received in FIG. ₁ , the light receiving aperture is substantially always in the direction of P ₀ on the sphere of FIG. Will be provided. As described above with reference to FIG. 3, since the diffracted light of the main circuit pattern on the substrate jumps in the direction of the black circle, it is not received near P ₀ . If the equatorial plane of the sphere corresponds to the surface of the substrate 5 and the projected image of the principal ray (OP ₀ ) of the received light flux substantially coincides with the angle β direction on this equatorial plane, the pattern will be obtained according to the gist of the present invention. Excluding diffracted light,
Only the scattered light of foreign matter can be selectively received. The value of β at this time is 15 ° ± to avoid scattered light from the circuit pattern.
Set at 5 °.

Then, at each point on the beam scanning line, the deviation angle (β-β _L or β-β _{R in} FIG. 5) of the projected image on the reticle surface between the principal ray of the incident beam and the principal ray of the received light flux is as described above.
Is preferably within ± 10 °.

In contrast to FIG. 5, FIG. 6 particularly takes a configuration in which the projected image of each principal ray of the received light beam is parallel to the projected image 00 ′ on the reticle of the optical axis of the light receiving system. To do so, an aperture stop 103 is provided at the rear focal position P _G ′ of the light receiving lens 61 in FIG. 1 (the light receiving system is a telecentric system). At this time, the angle of 00 'with respect to the vertical and horizontal directions (which is equal to the angle β'of the projected image of each principal ray of the received light beam) is set to 15 ° ± 5 ° to avoid scattered light of the circuit pattern. Even in this case, the chief ray projection image of the incident beam is at each position (L, O, R) on the scanning line B ₁ B ₂ ,
Are largely consistent with the projected image of the received light flux principal ray (first in FIG. 6 β'-β _{L 'or} β'-β _R' is within ± 10 °) is desirable. In general, it is desirable that the light projecting system and the light receiving system are completely telecentric systems. However, in order to obtain the effect of the present invention (creating a condition that reduces the pattern output equally over the entire reticle), the beam on the reticle At each point on the scanning line, it is sufficient that the projected image on the reticle of each principal ray of the received light beam approximately coincides with the angle 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 both 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 the other for receiving light.

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

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG. 2 is an optical principle diagram of a light projecting system according to the embodiment of FIG. 1, and FIG. 3 is an incident light flux in the embodiment of FIG. Explanatory drawing of diffracted light by circuit pattern, FIG. 4 (A), (B) and (C) are explanatory views showing the relationship between the circuit pattern and the diffraction image, and FIG. 5 is the incident beam in the embodiment of FIG. And FIG. 6 is a schematic view of the relationship between the incident beam and the received light flux of another embodiment of the present invention, and FIGS. 7 and 8 are examples of conventional surface condition measuring devices. Is. In the figure, 1 is a light source, 2 is a polygon mirror, 4 is a light projecting unit, 5 is a substrate, 6 is a light collecting unit, 7 is a mirror,
Reference numeral 8 is a lens, 9 is a light receiving surface, 10 is an optical system, and 11 is a half mirror.

Claims (2)

[Claims] 1. A surface condition measuring apparatus comprising: a scanning means for making a light beam incident on a substrate on which a pattern is formed, and scanning the substrate with the light beam; and a light receiving means for receiving a scattered light beam generated from the substrate. The scanning means has a scanning mirror and a scanning optical system, the light receiving means has a light receiving optical system and an aperture stop, and the optical axis of the light receiving optical system is set in a direction different from the direction in which the diffracted light from the pattern is generated. Then, the surface state measuring device is characterized in that the scanning mirror is arranged at a front focal position of the scanning optical system and the aperture stop is arranged at a rear focal position of the light receiving optical system. 2. The surface state measuring device according to claim 1, wherein the scanning optical system and the light receiving optical system share a single optical system.