JPS61132844A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To detect a minute defect with a high accuracy by providing a lens means for condensing a light reflected irregularly by a defective part of the surface of an object to be inspected, and a photoelectric converting means, and condensing efficiently an absolute quantity of a scattered light. CONSTITUTION:A titled scanner is provided with a cylindrical lens 30 which has a wider size than an effective scan width on the surrace of a wafer 10 in the vicinity of the wafer 10, also does not photodetect a regularly reflected lilght by the surface of the wafer 10 but photodetects only an irregularly reflected scattered light, and also condenses the photodetected scattered light, in parallel to the optical beam scanning direction of the surface of the wafer 10. Subsequently, the cylindrical lens 30 is connected to a photomultiplier tube 40 through an optical fiber flux 31. In this state, all scattered lights 5 contained in a solid angle theta1 reflected irregularly from a defective part 4 of the wafer 10 are condensed by the cylindrical lens 30 and inputted to the photomutiplier tube 40, and a minute scattered light is detected. In this way, a defect of the wafer 10 can be detected with a high accuracy.

Description

[Detailed description of the invention] Iwao 1ul 51st order! The present invention relates to a light beam scanning device, and more particularly, the present invention relates to a light beam scanning device that scans the surface of a substrate such as a semiconductor wafer for defects by scanning the surface with a light beam and detecting scattered light from the defective portion. This invention relates to a light beam scanning device.

! l When detecting surface defects on a test object such as a wafer by scanning a light beam such as a laser, it is possible to detect scratches, dirt, etc. on the surface compared to a method that detects defects on the surface by detecting a decrease in specularly reflected light. The method of detecting the scattered light generated by the defective part is advantageous because of its high S/N ratio. When this method is adopted, the structure of the optical system is simple, the specularly reflected light can be easily processed, and the degree of freedom for extracting the scattered light can be increased, so lI21! As shown in FIG. 1, the scanning light beam (2) is often configured so that the incident surface (3) of the scanning light beam (2) is orthogonal to the surface to be inspected (1).

In such a case, the intensity of the scattered light (5) that is diffusely reflected from the defective portion (4) of the surface to be inspected (1) is usually extremely weak compared to the scanning light beam (2). In this way, scattered light (
In addition to the fact that 5) is extremely weak, there is a problem unique to light beam scanning: the slope (scanning width) of scanning M(7). In order to cover the entire scanning width, for example, when trying to detect scattered light using a one-dimensional COD camera, the imaging lens must be placed at a large distance from the scanning M(7). In this case, the scattered light is weak to begin with, and the absolute amount of the scattered light that enters the imaging lens is extremely small, so there is a limit to the detection accuracy.

On the other hand, if we consider the case where we try to directly receive scattered light with a photoelectric conversion means such as a photoelectric element array that can cover the scanning width, we need to increase the absolute amount of received scattered light even a little. Although it is desirable to arrange the conversion means as close as possible to the scanning surface, on the other hand, since the photoelectric conversion means has a certain physical size, it is necessary to place the conversion means as close as possible to the scanning surface so that it does not interfere with the scanning light beam (2). There is a restriction that the photoelectric conversion means must be installed at a certain distance, so it is difficult for such photoelectric conversion means to efficiently receive weak scattered light. ,
The relationship with the circuit section connected to the photoelectric conversion means and processing its output signal must also be considered.

On the other hand, if the surface to be inspected (1) is wide and the defect size is, for example, on the order of millimeter, this will not be a particular problem, but if the surface to be inspected (1) is small and narrow and the defect size is on the order of microns, the scattered light For example, surface defects on semiconductor wafers of 3 inches to 6 inches in diameter require detection accuracy on the micron order. As the defect size progresses to 2μ, 1μ, and submicron, the minimum defect size to be detected also becomes submicron order.

A unique technique is required to overcome the scanning width problem and directly detect the intensity of the weak scattered light to detect submicron surface defects.

The present invention overcomes the problem related to the scanning width, and also solves the problem of how much absolute amount of scattered light can be input to the photoelectric conversion means so that even the smallest defects can be detected with high precision. This is what I am trying to do.

As a means for solving the above-mentioned problem of the substrate climbing, the present invention provides a test object transport means that holds a mounted substrate such as a wafer and moves it in one direction, and a test object transport means that moves the test object transport means in one direction. a beam scanning means for sequentially scanning the surface of the object to be inspected with a light beam deflected in a direction crossing the direction; The basic feature is that it is equipped with a condensing lens for receiving and condensing the scattered light diffusely reflected on the surface of the condenser, and photoelectric conversion means for converting the light from the condensing lens into an electrical signal. be.

Work 1 - In the above configuration, the scattered light that is diffusely reflected on the surface of the object to be inspected enters the condensing lens arranged close to and parallel to the light beam scanning direction at a large stylistic angle, and is further efficiently Since the light is well focused and input to the charge conversion means, even extremely minute defects can be detected with high accuracy.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically explained with reference to embodiments shown in the drawings.

FIG. 1 is an embodiment showing a V4 configuration of a light beam scanning device for inspecting the surface condition of a semiconductor wafer. A semiconductor wafer (10) as an object to be inspected is placed on a transfer stage (11 ) and transported at a constant speed, for example, in the five-wheel a/S″t'X direction.

The light and beam scanning means (12) includes, for example, two upper and lower surface plates (
13) and (14), for example, a He-Ne laser (15) with a wavelength of 633n- is used as the light source. , (17), the beam is deflected by 180° and enters the beam expander (18). The light beam whose beam diameter has been expanded by the beam expander (18) is deflected downward by the reflection mirror (19), passes through the hole (13m) in the surface plate (13), and is further deflected by the reflection mirror (2).
0) and enters the vibrating mirror (21). The I-shaped mirror (21) vibrates at, for example, 200 Hzt' and swings the light beam left and right in a horizontal plane. The light beam swung left and right by the moving Mihu (21) passes through the imaging lens (21).
2), the beam is converged to a predetermined beam diameter on a semiconductor wafer (1G) and a grating (2), which will be described later, while heading toward a reflecting mirror (23).

Thereafter, the light beam is deflected downward at a right angle by a reflecting mirror (23), passes through the elongated hole (14a) of the surface plate (14), and is imaged to a predetermined beam diameter on the surface of the semiconductor wafer (10). Then, the surface is scanned with a predetermined scanning width.

A half mirror (25) is provided between the imaging lens (22) and the reflection mirror (23), and a part of the light beam is directed to the grating (27) via the reflection mirror (26).
). 7 on the back of the grating (27)
A seven-point sensor array (28) is attached, and the output of this seven-point sensor array (28) is used as a reference clock for a signal processing system (not shown).

In addition, a cylindrical lens (3G
) is provided. This cylindrical lens (3
0) has a dimension wider than the effective scanning width on the surface of the wafer (10) by the light beam, and does not receive the light specularly reflected on the surface of the wafer (10), but only receives the specularly reflected scattered light. Collects the received scattered light.

Wafer (10) Defects (X, dust, etc.) on the surface cause 8
The scattered light reflected by L is cylindrical lene X (30)
The light is focused at the entrance window (31W) of Optical 7 Fipa East (31).
The light is focused on.

The optical fiber east (31) as a light guiding means is connected to the entrance window (3
1W) Opposite III? , head-on photomultiplier tube (
40), and the guided scattered light is emitted from the head window (40W) to the photomultiplier tube (40).

As is well known, the photomultiplier tube (40) has the highest detection sensitivity and excellent time response as a photoelectric conversion means. Therefore, it is optimal for detection of weak scattered light and high-speed signal processing. The optical 7-eye light guide (31) serving as a light guiding means is provided so as to use this photomultiplier tube (40). Therefore, if high detection accuracy is not required, a direct-seeding diode 7 ray may be provided at the condensing and imaging position of the cylindrical lens (30).

FIG. 3 is a partially enlarged view of FIG. 1. As shown in this figure, the scattered light (50) is distributed radially from the defective part (4o), but from the defective part (4e) to the cylindrical lens (
All of the scattered light (50) included within the stylistic angle (θ1) facing the light receiving surface of 30) is collected without being missed and sent to the photomultiplier tube (40) via the optical fiber bundle (31). I am trying to input it.

FIG. 4 shows another embodiment of the apparatus according to the present invention, in which a plurality of cylindrical lenses are used. As shown in FIG. 2-inch lens (30b)
), the ratio of (effective width of the lens system)/(focal length) can be made larger than when one lens system is used, and the light receiving angle of view (θ8) of the lens system can be made larger accordingly. Temporarily, the 31st! Cylindrical rene r(3
0), the received light is -
The angle (θ2) is almost twice that of (θ1), and the angle that can receive light is
The absolute amount of L light will more than double. In addition, the distance from the light beam scanning position to the entrance window (31W) of Optical 7 Fipa East (31) is half that of the embodiment shown in Figures # & 3, so the device itself can also be made smaller. I can do it.

In addition, as shown consciously in Figures 3 and 4, the required curvature is applied to the position facing the pickup optical system consisting of the cylindrical lens (30), optical 7-Iva Higashi (31), photomultiplier tube (40), etc. It goes without saying that a concave mirror may be provided to increase the absolute amount of scattered light that can be received, and furthermore, a pick-up optical system may be separately disposed facing the four-sided mirror instead of the four-sided mirror.

In the above embodiments, the test object is a semiconductor wafer, but it is not limited to this, and may be a dry plate for a hard mask, etc.
Furthermore, the device according to the present invention is applicable to general devices that directly detect the intensity of scattered light by scanning a light beam (for example, documents, etc.).
Needless to say, it can be applied to photoelectric scanning devices for drawings, photographs, etc.).Although the above embodiments are related to reflective test objects, as an application example, it can also be applied to transmissive test objects. The present invention can also be applied in the same way to detect defects on the surface or inside of objects using diffracted light or scattered light.

Further, in the embodiment shown in FIG. 1, the optical system is arranged separately on the surface plates (13) and (14), but it goes without saying that they may be arranged all together on a single surface plate.

In addition, the apparatus of the present invention can handle not only flat objects but also cylindrical objects or sheet-like objects that are fed along a flat or suitably curved conveyance path that intersects with a linear scanning line. It goes without saying that you can also check 7.

As is clear from the above explanation, the present invention solves the problem of how to collect as much absolute amount of scattered light as possible. Compared to the method of detecting scattered light such as the amount of light, this method has the effect of greatly improving the detection accuracy.

By the way, according to the image reading device based on FIG.
It is possible to detect up to 0.5 μm.

*7r) Compared to the method of arranging a photoelectric conversion element array such as a diode 7-ray in close proximity to the scanning surface, its response is much better, and a pair of elliptical mirrors are also used to direct the scanning light on the scanning surface. Even when compared with a method in which the scattered light from the scanning surface is collected by placing it close to the scanning light beam, and the collected scattered light is photoelectrically converted by a photoelectric conversion element provided close to the scanning light beam, It has an interest that makes it easy to manufacture and adjust.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a diagram for explaining the invention in detail, and FIGS. 3 and 14 are side views of essential parts of the embodiment. DESCRIPTION OF SYMBOLS 11... Conveyance stator, 15... He-Ne laser, 21... Vibration Mi 2-124... Scanning line, 30
．． 30a. 30b...Cylindrical lens, 40...Photomultiplier tube, s, so-...Scattered light, 'Patent applicant Dainippon Screen Mfg. Co., Ltd. Agent Patent attorney Former
Kawa Iku Tomari-2 [

Claims (4)

[Claims] (1) a test object transport means for moving the test object in one direction; a light beam scanning means for scanning the surface of the test object with a light beam in a direction intersecting the moving direction of the test object transport means; lens means arranged parallel to the light beam scanning direction on the surface of the test object to receive and condense the light diffusely reflected by the defective portion of the surface of the test object; and a photoelectric converter that converts the light from the lens means into an electrical signal. A light beam scanning device comprising: means. (2) The light beam according to claim (1), further comprising a light guiding means between the lens means and the photoelectric conversion means for guiding the scattered light collected by the lens means to the photoelectric conversion means. scanning device. (3) The light beam scanning device according to claim (2), wherein the light guide means is an optical fiber bundle. (4) The light beam scanning device according to any one of claims (1) to (3), wherein the photoelectric conversion means is a photomultiplier tube.