JPS61288143A - Surface inspecting device - Google Patents

Abstract

PURPOSE:To detect a surface defect at a high speed with high precision by projecting incident light linearly on the surface of a body t be inspected such as a wafer by using a cylindrical lens, converting reflected light from the surface into an electric signal, and processing the signal. CONSTITUTION:The wafer 1 is placed on a turntable 20 and rotated. Laser light 11 emitted by a light source 9 is passed through a polarizing prism 13 and converted into circular polarized luminous flux 14 by a 1/4lambda plate 15. This light is converged by an optical system 16 and projected on the wafer 1 as linear laser light through the cylindrical lens 17. At this time, the linear laser light 4 is controlled to the radius of the wafer 1 in its radial direction and scanned over the entire surface of the rotating wafer 1. Its reflected light is photodetected and converted photoelectrically by a photoelectric converting part 7 and an arithmetic control part 8 detects a defect from the output of the projection position. Thus, not spot light, but the linear laser light is projected and scanned, so the speed of the inspection is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface inspection apparatus suitable for automatically detecting surface defects of, for example, semiconductor wafers.

[Technical background of the invention and its problems]

Conventionally, the surface inspection of silicon wafers for semiconductor devices, etc., has mostly been carried out by visual inspection by an operator.

Therefore, various wafer surface inspection devices that utilize reflected light have recently been developed and commercially available. As shown in Figure 4, the detection principle of these devices is that a white light source or a laser light source (B) irradiates the surface of the object to be inspected (A) with a light beam (C) in a spot shape, and specularly reflected light from the surface is detected. (D) and scattered light (E) are detected by a photoelectric converter (F), one or more threshold levels are set for the output voltage, and defects such as dust and scratches are detected, This is to classify the size.

However, since the conventional inspection method projects a laser beam in the form of a spot, it takes time to scan the laser beam when inspecting the entire surface of a silicon wafer, which reduces inspection efficiency.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances.

An object of the present invention is to provide a surface inspection device that can detect surface defects at high speed and with high precision.

[Summary of the invention]

Incident light is linearly projected onto the surface to be inspected using a cylindrical lens, and the presence or absence of five surface defects is determined based on the reflected light from the surface to be inspected at this time.

[Embodiments of the invention]

An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the surface inspection apparatus of this embodiment. This surface inspection device includes an inspection object holding section (3) that vacuum-chucks Waeno (1) and rotates it in the direction of arrow (2);
A light projection unit (5) that projects a linear laser beam (4) onto the wafer (1), and a wafer (1) that projects the laser beam (4) onto the wafer (1).
) and converts the reflected light (6) from the photoelectric converter (7) into an electrical signal corresponding to the amount of received light.
) A calculation control unit (8) whose main body is a microcomputer that determines the presence or absence of surface defects (e.g., scratches, stains, dust, etc.) on the Waeno (1) based on the electrical signals output from the
It is composed of. Therefore, the light projection section (5) has 1
For example, a light source (9) such as a semiconductor laser device, a He-Ne (helium-neon) laser device, and this light source (
A first optical system (12) consisting of a combination of a collimator lens and a convex lens, for example, converts the laser beam (IIJ) emitted from the laser beam (IIJ) into a parallel laser beam αυ with an enlarged diameter. A polarizing prism Oj that receives laser light (1υ) and transmits only parallel polarized light.

This polarizing prism (1/4λ2 (1-!9) converts the parallel light emitted from the first floor into a clockwise circularly polarized light flux αa,
A second optical system (10) includes a convex lens (not shown) that focuses the circularly polarized light originally transmitted through the 1/4λ plate (L'5).

This second optical system (circularly polarized light flux I focused by 1e
and a cylindrical lens αη for projecting laser light (4) linearly onto the wafer (1). The polarizing prism (1) has a dielectric thin film 08 coated on the boundary surface at the center of the prism.
8, parallel polarized incident light beams are transmitted through 100 directions without being reflected at all, whereas vertically polarized light beams are totally reflected. On the other hand, the photoelectric conversion section (7).

A one-dimensional line sensor that receives right-handed circularly polarized reflected light (6) reflected from a wafer (1), and is composed of a plurality of light-receiving elements (7a) arranged one-dimensionally ( (See Figure 3). In other words, one reflected light (6) passes through one cylindrical lens (17) and a second optical system (16), and is converted into a vertically polarized light beam when it enters the 1/4 λ plate (1). Therefore, the reflected light emitted from the 1/4λ plate 09 (
The polarizing prism 0 (6) totally reflects the laser beam (11) in the direction of the arrow (11) perpendicular to the optical path. but.

It is arranged. This reflected light (6) is a laser beam (4)
Corresponding to this, the photoelectric conversion unit (7) is linear in the plane perpendicular to the optical path, so the longitudinal direction of the linear light receiving part and the longitudinal direction of the laser beam (4) in the light receiving part match. is set to. Furthermore, the arithmetic control section (8
) l"j is connected to a display section (8a), such as a cathode ray tube, for displaying the inspection results. On the other hand, the inspection object holding section (3) has a plurality of vacuum suction holes opened on the top surface. A disc-shaped rotary table (to) on which the Tewino (1) is placed coaxially, a stepping motor C (1) that rotates the rotary table top, and a stepping motor (21) attached to the rotating shaft of the stepping motor (21). Rotating table (a)
The rotary encoder outputs a rotation angle signal Sθ indicating the rotation angle of the rotary encoder.

However, in the surface inspection apparatus having the above configuration.

First, the wafer (1) is attracted and fixed to the rotary table (21) so that it is almost coaxial. Next, the laser beam αQ is oscillated from the light source (9). Then, this laser beam
The first optical system (1 unit) converts the laser beam αυ into a parallel beam with an expanded diameter.
Since it is parallel polarized light, it passes through polarizing prism 0 (and is converted into circularly polarized light flux I through 1/4λ plate α9. Then, this circularly polarized light flux (14) is transmitted through polarizing prism 0 (14).
and a cylindrical lens (17), as shown in Figure 2,
The laser beam (4) is projected onto the wafer (1) in a straight line. Here, the length of the laser beam (4) is the length of the wafer (3
), and the longitudinal direction is set to be the radial direction of the wafer (3). -r, the chipping motor t21) is started, and the one-turn table (2
1 in the direction of arrow (2). Then, the wafer (
1) is scanned by the incident light (4). During this scanning period, the reflected light (6), which is specularly reflected light reflected by the wafer (1), is reflected by one cylindrical lens (
17), second optical system α→, via 1/4λ plate u9.

When light enters the polarizing prism (13), it is totally reflected in the direction of arrow α'' and is received by the photoelectric converter (7).On the other hand, the rotation angle signal Sθ is transmitted from the rotary encoder e23 to the calculation control unit (8 ).As shown in FIG. 3, the photoelectric converter (7) outputs a detection signal SA having an output voltage corresponding to the amount of received light to the arithmetic control section (8). By the way, as shown in FIG. 3, this detection signal SA is sequentially applied to each light receiving element (7a
)..., and each of these light receiving elements (7a)... indicates the projection position of the laser beam (4), that is, the radial position of the wafer (1).

Thus, if dirt (24) is present on the wafer (1) as shown in FIG.

Since the laser beam (4) projected onto the part of the dust (b) is diffusely reflected by the dust C41, the proportion of specular reflection 5 is lower than that of other parts. the result. Detection signal 8A too.

The level of the output voltage in the portion corresponding to the dirt C seepage decreases. Therefore, the threshold value vT and the detection signal sh are calculated by the calculation control unit (
By comparing in 8), it is possible to detect the presence of garbage f24). And garbage (two-core wafer (
The circumferential position in 1) is also determined by the rotation angle signal Sθ.

The radial position of the wafer (1) where the dirt Q has oozed out can be specified using a synchronization signal that drives the light receiving elements (7a). Thus, the surface defect inspection result of the wafer (1) is displayed on the 1 display section (8a).

In this way, the surface inspection device of this embodiment can be used for wafers (
A laser beam (4) is projected linearly onto the target 3).

Moreover, the linear direction is set to be the radial direction of the wafer (1), and the linear reflected light (6) is also received by a one-dimensional image sensor, so that scanning processing is performed quickly. As a result, inspection speed becomes faster.

In addition, in the above embodiment, the photoelectric converter (1) is used.

CCD (Charlie Coupled Device
e) A split photodiode may be used. Furthermore, the photoelectric converter may be connected to a binarization circuit to perform the detection process using hardware. Furthermore, as a target for defect detection.

The present invention is not limited to silicon wafers, and can also be applied to detect defects (eg, dents, etc.) in video discs, for example.

When inspecting the surface of this video disc, focusing control may be performed using one reflected light to make the focal position of the laser beam (4) appropriate. I cut it. A polarizing beam splinter or a polarizing mirror may be used instead of a polarizing prism.

Furthermore, the light source is not limited to a laser light source, and may be a white light source.

〔Effect of the invention〕

The surface inspection method of the present invention scans the object to be inspected using linear incident light, unlike spot light.
As a result of expanding the area to be inspected at the same time, there is a special effect of increasing the inspection speed.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a surface inspection apparatus according to an embodiment of the present invention, Fig. 2 is a plan view showing the projection position of a laser beam onto a wafer, and Fig. 3 is a diagram of a surface inspection apparatus according to an embodiment of the present invention. Explanatory diagram, 4th
The figure is an explanatory diagram of conventional surface inspection. (1): Waeno (tested object), (3): Tested object holding section. (4): Laser photoelectric (5) Binary projection section. (6): Reflected light, (Crab photoelectric conversion unit. (8): Arithmetic control unit. Agent: Patent attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2 Received light value! Figure 4 Figure 3

Claims (1)

[Claims] A surface inspection device characterized by having the following configuration. (a) An inspection object holder that holds an inspection object having an inspection surface on which the presence or absence of a surface defect is to be determined and moves it along the inspection surface. (b) A light projection unit comprising a light source that projects light and a cylindrical lens that receives the light projected from the light source and projects it linearly onto the surface to be inspected. (C) Receiving the specularly reflected light from the object to be inspected of the light projected from the light projection unit, and generating an electric signal indicating the presence or absence of the surface defect at the linear light incident portion on the surface to be inspected. Photoelectric conversion unit that converts. (d) An arithmetic control unit that determines the presence or absence of the surface defect based on the electrical signal output from the photoelectric conversion unit.