JPH03173452A - Wafer surface plate pit defects detection optical system - Google Patents

Abstract

PURPOSE:To facilitate the detection of pit defects which has been difficult, by a method wherein the fact that the direction of the reflected or scattered light from pit defects existing on a wafer plate surface changes from the normal reflection direction of the mirror surface except pits is used, and these lights are separately received to obtain the difference of the respective output signals. CONSTITUTION:When pit defects of a wafer face plate having a mirror surface are detected, scanning is performed by converging laser light passing a center hole of a first hole mirror 8-1 with a projecting and receiving lens 5 and by turning it into a spot. Normal reflection light from the mirror surface free from defects is inputted to a first light receiving apparatus 7-1 through a lens 5 and the center hole of the first mirror 8-1. When pit defects are present, the direction of the normal reflection light or irregular reflection light changes, so that the light passing the lens 5 is reflected by the first hole mirror 8-1 and a second hole mirror 8-2, and made to enter a second light receiving appara tus 7-2. At this time, the output signal level of the light receiving apparatus 7-2 increases, and the level of the light receiving apparatus 7-1 is decreased by that amount. Hence the detection sensitivity is doubled by operation with a differential operator 10.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an optical system for inspecting defects on a face plate, and more specifically, defects on a wafer face plate with a mirror surface, which have a relatively large area and a shallow depth. This is aimed at pit defects in discs.

[Prior Art] Silicon wafer faceplates, which are the raw material for semiconductor ICs, have various defects, and these defects degrade the quality of the IC, so they are inspected using a faceplate inspection device.

FIG. 2(a) shows the basic configuration of the optical system of an optical wafer face plate inspection device.
2a is focused by a projection lens 2b to form a spot on the face plate 1 to be inspected. A spot scans the entire surface of the face plate using a rotation method or an XY scanning method using a drive mechanism (not shown). During scanning, if a defect exists on the surface, the laser is scattered, and the scattered light is focused by the condensing lens 3a of the light receiving section 3, and the defect is detected by the light reception signal of the light receiver 3b. Here, as mentioned above, there are various types of defects, and the representative ones are shown in Figure 2 (
There are convex parts such as attached foreign matter or protrusions of the material itself as shown in (a) of b), and four parts with small widths or areas such as cuts shown in (b).

In these cases, since the curve on the cross section changes at a steep angle, the scattered light of the laser is relatively strong and can be detected.

[Problem to be solved] In contrast to L, the concave portion called a dish-shaped pit defect, which is relatively large in area and shallow in depth, shown in (c) of Fig. 2(b), is caused by a change in angle. Because the light is slow, the scattered light is weak, or the specularly reflected light is reflected and is not sufficiently captured by the condensing lens of the optical system, making detection difficult. A detection method for this is required, and as a prior art, the applicant of the present invention has published "No.
No. 27, “Face Plate Defect Detection Optical Device” has been applied for a patent.

FIGS. 3(a) and 3(b) show the working principle and main components of the face plate defect detection optical device according to the above patent application. In FIG. 3(a), the laser spot is shown on the pit defect When scanning from the left to the right, the reflected light at the point p where the inclination angle of the pit is falling is R1)%.If the reflected light at the point q in the flat central part is RqN, and that at the point r where the inclination angle is rising is Rr, then each The reflected light rotates counterclockwise. A pit defect is detected by receiving Rp and Rr except for Rq.

However, the concave surface of a pit defect is not necessarily smooth and may have a step or the like, which may contain scattered light.

In Figure (b), the laser beam from the laser light source 2a passes through the projection lens 2b and mirror 4, and is projected onto the face plate 1 by the projection/reception lens 5, and reflected light Rq from the surface or pit defect point q and its vicinity. After passing through the light emitting/receiving lens 5, the light is blocked by a stopper 6.

On the other hand, the reflected or scattered lights RP and Rr in the vicinity of points p or r are input to the light receiver 7 through the light projecting/receiving lens 5, and pit defects are detected.

In response to the above, the present invention is similar in principle, but the optical system is constructed using a different method from that described in 1), and the processing of the detection signal is further improved to further improve the pit defect detection performance. It is.

[Means for Solving the Problems] The present invention is a peer defect detection optical system in a defect inspection apparatus for a wafer face plate having a mirror surface.

A first hole mirror tilted at 45° with respect to the optical axis of the laser from the laser light source, a second hole mirror whose reflective surface is perpendicular to this, and a center hole of the first hole mirror that transmits light. It is equipped with a light emitting/receiving lens that focuses the laser to form a spot. The specularly reflected light from the mirror surface of the laser projected by the light projecting/receiving lens is received on an optical axis different from the optical axis of the projected laser in the light projecting/receiving lens, and the received IE reflected light is transmitted to the first hole mirror. After being reflected by the reflective surface of the wafer, it is transmitted through the center hole of the second hole mirror, and the first light receiver receives the transmitted light. A second light receiver that reflects the reflected light or diffusely reflected light by each reflecting surface of the first and second hole mirrors and receives the reflected light, and an output signal of each of the first and second light receivers. It is composed of a difference calculator that calculates the difference between the two and improves the sensitivity.

[Function] In the bit defect detection optical system with the above configuration, the laser beam that passes through the center hole of the first hole mirror is focused by the light projecting/receiving lens to form a spot, and is projected onto the face plate to be inspected for scanning. The specularly reflected light on the mirror surface with no defects is reflected by the light emitting/receiving lens, the reflecting surface of the first hole mirror, and the second mirror.
The light is input to the first light receiver through the center hole of the hole mirror. On the other hand, if a pit defect exists, the direction of the specularly reflected light or the diffusely reflected light changes, so that the light transmitted through the light emitting/receiving lens is reflected by the reflecting surfaces of the first and second hole mirrors, respectively. The light is then received by the second light receiver. In this case, the level of the output signal of the second photoreceiver increases due to the focus defect, but the level of the output signal of the first photoreceiver decreases by this increase. The difference between the output signals of the receiver is calculated and
The detection sensitivity for pit defects is doubled.

Embodiment FIGS. 1(a) and 1(b) are explanatory diagrams of the structure and operation of an embodiment of a pit defect detection optical system for a wafer face plate according to the present invention. The laser T from the laser light source 2a is collimated by the projection lens 2b, passes through the center hole of the first hole mirror 8-1 provided at an angle of 45 degrees with respect to its tip axis, and is reflected by the plane mirror 4 as shown in the figure. reflected downward. This laser T is projected to a position where the optical axis is biased to the left side in the drawing with respect to the center of the light emitting/receiving lens 5, and as the optical axis is refracted, a focused spot is projected onto the wafer face plate 1. When the surface of the face plate l is a mirror surface or at a flat part of a pit defect, the laser T is specularly reflected, and the specularly reflected light Rq takes the path shown by the solid line in the figure to the first hole mirror 8-
It is reflected by reflective surfaces other than the center hole of No. 1. The second hole mirror 8-2 is perpendicular to the first hole mirror 8-1, and the position of the center hole is set so as to transmit the specularly reflected light Rq. The reflected light Rq passes through the center hole and is received by the first light receiver 7-1. In addition, the reflected light Rp or Rr whose angular direction has changed due to specular reflection or diffuse reflection due to the slope or step of the pit defect.
takes the path indicated by the dashed-dotted line or the dashed-double-dotted line, and is reflected by the reflective surfaces of the first and second aperture mirrors, and this reflected light is condensed by the condensing lens 9 and sent to the second light receiver 7.
-2 is received.

Output signal 1111 of each of the first and second receivers
2 is input to the difference calculator 10, and the difference (I2-Il) is output. FIG. 1(b) shows an example of the waveforms of the output signals 11112 and (I2-If). If indicates a signal Rq at a certain level for the portion of the mirror surface with no focus defects, and its level decreases for reflected light Rp and Rr from pit defects, and correspondingly, the level of I2 increases. As for the difference between the two (I2-It), the portions of Rp and Rr are doubled, and the sensitivity is improved. Note that when the laser spot is larger than the diameter of the pit defect, the laser is reflected on an average basis, resulting in an output signal R' having an average value curve as shown by the dotted line in the figure.

The above description deals with pit defects, but in this embodiment, the condenser lens 3a shown in FIG.
A light-receiving section 3 consisting of a light receiver 3b and a light-receiving section 3b are installed together to detect convex parts such as foreign objects shown in (a) of FIG.

As is clear from the explanation in ``Effects of the Invention'' 2, in the pit defect detection optical system according to the present invention, the pit defect detection optical system according to the present invention has a relatively large area and a shallow depth on the wafer face plate.

Taking advantage of the fact that the direction of reflected or scattered light from a pit defect changes with respect to the direction of specular reflection on a mirror surface, the specularly reflected light from the mirror surface and the reflected or scattered light from the pits are received separately. , the difference between the respective output signals is taken, and the detection sensitivity is doubled, which has a great effect in efficiently detecting pit defects, which was previously difficult.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are a block diagram of an embodiment of the pit defect detection optical system for a wafer face plate according to the present invention, waveform diagrams of the output signal of light reception and a difference signal, and FIGS. 2(a) and (b). 3(a) and (b) are diagrams illustrating the characteristics of reflected or scattered light due to pit defects, and FIGS. FIG. 1 is a configuration diagram of a main part of a face plate defect detection optical device according to a patent application. 1... Wafer face plate, 2... Light projecting section, 2a...
- Laser light source, 2b... Light emitting lens, 3... Light receiving section, 3a... Condensing lens, 3b... Light receiver, 4... Plane mirror 5... Light emitting/receiving lens, 6. ...Stopper, 7...Receiver, 7-1
...first light receiver, 7-2...second light receiver, 8
-1...First hole mirror 8-2...Second hole mirror, 9...Condenser lens, 10...Difference calculator.

Claims (1)

[Claims] (1) In a defect inspection device for a wafer face plate having a mirror surface, a first hole mirror is inclined at 45 degrees with respect to the optical axis of the laser from a laser light source, and a reflective surface is formed with respect to the first hole mirror. A second hole mirror forming a right angle, and a light projecting/receiving lens that focuses the laser beam transmitted through the center hole of the first hole mirror to form a spot, and the light projecting/receiving lens projects the laser beam onto the wafer face plate. The specularly reflected light of the emitted spot by the mirror surface is received on an optical axis different from the optical axis of the projected laser in the transmitting/receiving lens, and the received specularly reflected light is sent to the first hole. After the light is reflected by the reflective surface of the mirror, it is transmitted through the center hole of the second hole mirror, and the reflection angle is changed by a first light receiver that receives the transmitted light and a pit defect existing in the wafer face plate. a second light receiver that reflects the changed specularly reflected light or diffusely reflected light of the laser by each reflecting surface of the first hole mirror and the second hole mirror, and receives the reflected light resulting from the reflection; A pit defect detection optical system for a wafer face plate, comprising a difference calculator that calculates the difference between output signals of the first light receiver and the second light receiver to improve sensitivity.