JPH04333846A - Foreign matter detection optical system for reticle mask - Google Patents

Abstract

PURPOSE:To provide the foreign matter detection optical system which detects only foreign matter without detecting a wiring pattern by utilizing the features of the directivity of scattered light from the foreign matter and scattered light from the wiring pattern of a reticle by a reticle foreign matter detection device. CONSTITUTION:The features of the directivity of the scattered light from the foreign matter and the scattered light from the wiring pattern of the reticle are taken into consideration, and two projection systems project laser beams opposite each other at a low angle; and both the laser beams are scattered by the foreign matter in all directions, so the scattered light beams are transmitted through the transmission part of a spatial filter and detected by a CCD element while the quantity of received light is increased. The laser beam which is projected on the wiring pattern and scattered with large directivity in projection direction is cut off by the spatial filter and not detected and the scattered light from the wiring pattern is excluded in the reticle foreign matter inspection device, so that only the foreign matter can surely be detected.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical system for detecting foreign matter attached to a reticle mask for semiconductor IC manufacturing, and more specifically, the present invention relates to an optical system for detecting foreign matter attached to a reticle mask for semiconductor IC manufacturing. The present invention relates to an optical system that reliably detects.

0002

[Background Art] In the manufacture of semiconductor ICs, a thin chromium film is first deposited on the surface of a glass plate, and then etched to form a wiring pattern in which fine width wiring is formed in a predetermined pattern in the vertical, horizontal, and diagonal directions. is formed, and a reticle mask (hereinafter simply referred to as a reticle) is created. Using the reticle as a master, the wiring pattern is transferred onto the wafer using a reduction projection method. If foreign matter such as dust adheres to the reticle, the foreign matter will be transferred to all wafers in the same way, resulting in a defect, so it is necessary to carefully inspect the reticle for foreign matter. Note that foreign matter may adhere to the reticle during handling, so to prevent this, the reticle is covered with a dustproof frame with a pellicle (transparent thin film) stretched over it to prevent dust from entering the reticle, and the inspection is performed in this condition. There is.

A reticle, a dustproof frame for the reticle, and a conventional foreign matter inspection method for the reticle will be explained with reference to FIGS. 3(a), 3(b), and 3(c). In Figure (a), on the surface of the reticle 1, the above-mentioned chrome wiring pattern 1b is formed inside the boundary line 1a indicated by a chain line. On the other hand, the dust-proof frame 2 shown in Figure (b) is made up of a rectangular frame 2a with a pellicle 2b extended on one side, which is overlapped with the reticle 1 during inspection and handling to prevent dust. Next, regarding the inspection method, initially inspection of reticles for foreign substances was carried out visually using a microscope, but in order to improve inspection efficiency, this has been automated using the optical system shown in Figure 3(c). In the figure, a laser beam L from a laser light source 3 is projected diagonally downward onto a reticle 1 to form a spot with a minute diameter on the surface, and the surface is scanned by moving the reticle 1 in the X or Y direction. . When a foreign object p adheres to the surface of the reticle 1, the laser spot is scattered, and the scattered light R is focused by the condenser lens 4 and received by the CCD element 5, and the foreign object p is detected by its output voltage. be done. Note that when a foreign substance p' is attached to the surface of the pellicle 2b, the diameter of the spot on the pellicle 2b is large due to the height of the frame 2a, and therefore the intensity is small, so the scattered light of the foreign substance p' is weak and the light is not focused. Since the focal position of the lens 4 is deviated, the foreign object p' is not detected, and there is no problem in detecting the foreign object p.

0004

[Problem to be Solved by the Invention] Now, as described above, the wiring pattern 1b is formed on the reticle 1,
In the above inspection method, the light scattered by the wiring pattern 1b is received and detected together with the foreign matter p attached to the reticle 1, and the two cannot be distinguished. Furthermore, it is necessary to detect only the foreign matter and not the wiring pattern. On the other hand, it is considered possible to prevent the wiring pattern from being detected by utilizing the directivity characteristics of the scattered light of the foreign object and the wiring pattern. That is, the scattered light from the foreign object is scattered almost equally in all directions, regardless of the projection direction. On the other hand, each wiring in the wiring pattern has side surfaces on both sides, and when a laser beam is projected at a low angle from one side, the edge of the side has strong directivity in the projection direction. Scattered light is scattered. However, when the laser beam is projected from the opposite side, it is not scattered by the edge, that is, the scattered light of the wiring pattern is different depending on the direction in which the laser beam is projected. The present invention provides a foreign object detection optical system in a reticle foreign object inspection apparatus that detects only the foreign object without detecting the wiring pattern by utilizing the directional characteristics of the scattered light of the foreign object and the scattered light of the wiring pattern of the reticle. The purpose is to

[0005]

[Means for Solving the Problems] This invention projects a laser spot onto the surface of a reticle of a semiconductor IC protected by a dust-proof frame to form a spot, and moves the reticle in the X and Y directions to surface the reticle. This is a foreign object detection optical system that detects foreign objects by scanning the surface of the reticle and receiving the scattered light of the foreign object attached to the surface. two sets of light projection systems that respectively project and form a spot; one condensing lens that is installed perpendicularly to the surface of the reticle and that focuses the scattered light of the laser spot at the inspection point; and a laser beam. A spatial filter that blocks scattered light in the projection direction, and a light receiving system that includes a CCD element that receives the scattered light that has passed through the transmission section of the spatial filter.

[0006]

[Operation] In the foreign object detection optical system with the above configuration,
Two sets of light projection systems project laser beams at inspection points on a reticle mask, facing each other and at low angles, to form spots. Since the scattered light from both laser spots due to the foreign matter attached to the reticle has omnidirectional directivity, it passes through the transmission part of the spatial filter, and is received and detected by the CCD element. In this case, compared to the conventional case of one laser spot, the amount of scattered light, that is, the amount of light received, is doubled by both laser spots. On the other hand, when a laser beam is projected onto the wiring pattern of the reticle, it is almost specularly reflected on the surface of each wiring, and the specularly reflected light does not enter the condenser lens installed perpendicular to the surface. . In addition, a laser spot projected from one side of the wiring will scatter light with strong directionality in the projection direction due to the edge of that side, but a laser spot projected from the opposite side will be scattered by the edge. Not done. That is, the intensity of the scattered light is relatively low since it is generated by only one laser spot. Most of the scattered light having strong directivity in the projection direction is blocked by the spatial filter, so that the amount of light received by the CCD element is small, and the wiring pattern is not detected, but foreign matter is detected as described above.

[0007]

[Embodiment] First, the directivity of the scattered light of the wiring pattern of the reticle and the scattered light of foreign objects, which are the basis of this invention, will be explained. Figure 1(a) shows the directivity and intensity of the scattered light Re, which changes depending on the direction of the wiring, when a part of the wiring pattern 1b is taken out and a laser beam LL is projected onto it from the left side and a laser beam LR is projected from the right side. In the model
The scattered light ReL is caused by the laser beam LL. (A) in the figure shows the case where the laser beam LL is projected at a low angle perpendicular to the wiring 1b, and there is strong directivity in the X direction in the XY plane due to the edge on the left side of the wiring, and the XZ
In a plane, the intensity is approximately equal in each direction. (b) is when wiring 1b is tilted at 45 degrees, and the directivity is (a)
Similar to , but less strong. In (c), the wiring 1b is connected to the laser beams LL,L
Since it is parallel to R, it is not scattered by the edge. On the other hand, in (d) and (e), the laser beam LR from the right side is not projected onto the edge of the left side surface and is therefore not scattered at all. The above is about the left side, but on the right side, the scattered light is scattered by LR. In contrast to the above, Figure (b) shows the case of a foreign object,
In this case, both laser beams LL and LR are scattered with substantially equal intensity in all directions. (a) shows the directivity in the XZ plane, and (b) shows the directivity in the XY plane.

FIGS. 2(a) and 2(b) show the block configuration, the intensity of the scattered light of the foreign object and the wiring pattern of the reticle, and the amount of light received by the CCD element in an embodiment of the reticle mask foreign object detection optical system according to the present invention. Shows changes over time. Diagram (a)
, the reticle 1 to be inspected protected by the dustproof frame 2
X from two laser light sources 3a and 3b to the surface of
and -X direction as the projection direction, approximately 30
Laser beams LL and LR are projected onto the same point (inspection point) on the surface at a low angle φ of .degree. to form respective laser spots. As in the conventional case, each spot is focused on the surface of the reticle 1 to prevent foreign matter attached to the pellicle 2b from being detected. A condenser lens 4 whose optical axis is perpendicular to the surface of the reticle 1 and a spatial filter 6 are provided behind the condenser lens 4. As shown in the figure, the spatial filter 6 includes a blocking section 6 that blocks scattered light in the projection direction of the laser beam, that is, the X direction.
a and a semicircular transmission section 6b that transmits scattered light in other directions.

Note that the spatial filter 6 may be inserted at a position in front of the condenser lens 4. The scattered light from the foreign matter is collected by the condensing lens 4, most of it is transmitted through the transmission section 6b, the direction is changed by the mirror 7, and the light is received by the CCD element 5. The received scattered light is accumulated in the CCD element 5, sent to an A/D converter 8 at an appropriate timing to be digitized, and taken into a microprocessor (MPU) 9 for predetermined processing.

On the other hand, the scattered light due to the wiring pattern of the reticle 1 is focused by the condensing lens 4, but since its directivity is strong in the projection direction of the laser beams LL and LR, most of it is blocked by the blocking portion 6a, resulting in a small amount of light. A portion of the light passes through the transmission section 6b, passes through the mirror 7, and is received by the CCD element 5. In Figure (b), (a) shows the intensity of the scattered light Rp of the foreign object and the amount of light received by the CCD element, RPL corresponds to the laser beam LL, and RPR corresponds to LR. Since the light scattered by the foreign object is omnidirectional, RpL and RpR are equivalent, and a portion of these is blocked by the spatial filter 6 and becomes small, but the amount of received light (the sum of both times the transmission coefficient of the spatial filter 6) RpL+RpR)' is stored in the CCD element 5. On the other hand, (b) is the case of a wiring pattern, where the intensity of the scattered light ReL is quite large, but ReR is very small (or ReL<ReR), and these are almost all blocked by the spatial filter 6 and the CCD element 5 The amount of light received (ReL+ReR)' is close to zero. From the above, it is understood that foreign objects are detected well, but wiring patterns are hardly detected.

[0011]

Effects of the Invention As is clear from the above description, the foreign object detection optical system for a reticle mask according to the present invention focuses on the directivity characteristics of the scattered light of the foreign object and the scattered light of the wiring pattern of the reticle, and uses two The laser beams are projected by the light projection system facing each other at a low angle, and since the light scattered by the foreign object has omnidirectional directivity, it is transmitted through the transmission part of the spatial filter to the CCD element. The amount of light received is doubled and detected, and in contrast, the amount of light received by one of the two laser beams projected onto the wiring pattern is
Scattered light with strong directivity in the projection direction is not detected due to the blocking of the spatial filter, and the reticle foreign matter inspection device has a great effect in eliminating the scattered light from the wiring pattern and reliably detecting only the foreign matter.

[Brief explanation of drawings]

FIGS. 1A and 1B are explanatory diagrams of the directivity of the scattered light of the wiring pattern of the reticle and the scattered light of a foreign object, which are the basis of this invention.

[Fig. 2] Figs. 2(a) and 2(b) are block diagrams of an embodiment of the reticle mask foreign object detection optical system according to the present invention, and the relationship between the intensity of scattered light from foreign objects and wiring patterns and the amount of light received by the CCD element. It is a curve diagram showing a change over time.

[Figure 3] Figures 3 (a), (b) and (c) are
FIG. 2 is a configuration diagram of a reticle mask, a dustproof frame, and a conventional reticle foreign object detection optical system.

[Explanation of symbols]

1...Reticle mask (reticle), 1a...Border line, 1
b... Wiring pattern, 2... Dustproof frame, 2a... Frame,
2b...pellicle, 3, 3a, 3b...laser light source, 4
...Condensing lens, 5...CCD element, 6...Spatial filter, 6
a...blocking part, 6b...transmission part, 7...mirror, 8...A/
D converter, 9...microprocessor) MPU), L, L
L, LR...Laser beam, R...Scattered light, Rp, RpL
, RpR...Scattered light of foreign matter, Re, ReL, ReR...
Scattered light from wiring patterns.

Claims (1)

[Claims] 1. A laser beam is projected onto the surface of a reticle mask of a semiconductor IC protected by a pellicle to form a spot, and the reticle mask is moved in the X and Y directions to scan the surface. In a foreign matter inspection device that detects foreign matter by receiving scattered light of foreign matter attached to a surface,
two sets of projection systems that respectively project laser beams at inspection points on the surface of the reticle mask in opposite directions and at low angles to form spots; and a projection system that is perpendicular to the surface of the reticle mask. one condensing lens provided in the direction and condensing the scattered light of the laser spot at the inspection point, a spatial filter blocking the scattered light in the projection direction of the laser beam, and a transmitting part of the spatial filter. and a light receiving system comprising a CCD element that receives the transmitted scattered light,
Foreign object detection optical system for reticle masks.