JPS60122360A - Optical inspecting device - Google Patents

Abstract

PURPOSE:To inspect foreign matter on a semiconductor wafer, etc., automatically by irradiating a plate body with laser light and detecting its reflected light. CONSTITUTION:When the plate body such as a semiconductor wafer is irradiated with laser light, laser light in a fixed direction which is reflected by an etched part A on a fixed angle slanting surface of the semiconductor wafer becomes nearly a horizontal wave, which is polarized in a fixed direction. Reflected light from foreign matter B having numbers of fine slanting surfaces at various angles, on the other hand, contains a vertical wave and is not polarized. Therefore, those reflected light beams are processed by a polarizing plate to detect only the reflected light from the foreign matter, thereby inspecting the foreign matter of the plate body such as a semiconductor wafer automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical inspection device for detecting foreign matter present on the surface of an object, etc., and is mainly directed to a foreign matter inspection device for visually inspecting the surface of a semiconductor wafer. It is. For example, Japanese Patent Laid-Open No. 85793/1983 discloses an appearance inspection technique in which defects in the mask are detected by irradiating light onto a mask or the like and using the reflected light.

Foreign matter often adheres to the surface of a semiconductor wafer during the manufacturing process of semiconductor devices. The foreign matter becomes an important factor in determining the yield of semiconductor devices, and it is necessary for process control to know the size, number, etc. of the foreign matter. Therefore, inspection for foreign substances on semiconductor wafers is performed between actual semiconductor device manufacturing processes.

Conventional foreign matter inspection is generally performed using a metallurgical microscope (magnification: 100).
This was done by visual inspection using a magnification of ~200 times. By the way, this method has the problem that the inspector's subjectivity tends to be involved in determining whether or not there is a foreign object, and the inspection results vary depending on the inspector.
3 hours), and there was a problem in that the inspection results between processes could not be quickly reflected in process control, and a decrease in yield could not be effectively prevented.

For this reason, automatic foreign object inspection was considered, but the surface of semiconductor wafers has unevenness due to the etching required to construct semiconductor devices, and it is difficult to automatically distinguish between these and foreign objects. Since this is extremely difficult, foreign matter inspection has had to be carried out by visual inspection.

The present invention was created based on the idea that when a light beam is irradiated parallel to the surface of a semiconductor wafer, the etched surface of the wafer and foreign matter reflect differently, and its purpose is to automatically inspect foreign matter. The goal is to

One embodiment of the present invention to achieve the above object attempts to accurately detect the presence of foreign objects, patterns, edges, etc. on the surface of the wafer by irradiating the wafer with a coherent laser beam before being examined. It is something.

The present invention will be explained below with reference to examples.

FIG. 1 is a configuration diagram showing a foreign matter inspection device according to an embodiment of the present invention.

1 is a car for storing 7% of semiconductor wafers) Cartridge feed drive unit that moves the IJ joint in the vertical direction, 2 is a cartridge that stores semiconductor wafers to be tested, and 3 is a transfer of semiconductor wafers between the cartridge and wafer mounting table. 4 is a mounting table on which the semiconductor wafer to be inspected is placed; 5 and 6 are feed drive units that move the mounting table 4 in the horizontal direction; 7 is a light source for generating parallel light; and 8 has a slope. 2
This polarizing plate is constructed by attaching two transparent glass plates with their slopes attached to each other, and has the function of blocking a certain amplitude direction. 9 is an objective lens, 10 is a relay lens, 11 is a mirror for projecting illumination light for visual inspection, 12 is a casting for visual inspection, 13 is a lens, 14 is an aperture, and 15 is for converting light into an electrical signal. photoelectric converter,
16 is an electronic circuit device for processing the output information of the photoelectric converter and obtaining inspection results; 17 is a visual observation mirror for reflecting reflected light toward the eyepiece; 18 is an eyepiece;
9 is a lamp that generates illumination light for visual observation, 20 is a lens, and 21 is a semiconductor wafer to be inspected. Casting 1'l, 12
, 17, lens 18, 20, and lamp 19 are provided to enable visual inspection and are not essential.

Inspection by this foreign substance inspection device is performed as follows.

Transfer the semiconductor wafer in the cartridge 2 to the mounting table 4,
The semiconductor wafer 21 is fixed to the center of the mounting table 4.
A laser beam is irradiated parallel to the wafer surface from the side of the 2.
The reflected light is detected through the photoelectric converter 15 while rotating the mounting table 4, and based on the reflected light with the polarizing plate 8 installed at a rotation angle such that polarized light is cut by the polarizing plate 8 and only non-polarized light can be detected. to detect the size and number of foreign objects.

Note that the wafer surface is magnified (
For example, since the field of view is narrow because the reflected light is detected by magnifying the lens 9 and IO, etc. The detection unit is moved by moving the feed drive unit (feed drive unit) to thoroughly inspect the entire surface of the semiconductor wafer. When the inspection of one semiconductor wafer is completed, the semiconductor wafer is returned to the cartridge 2Vc, and the next semiconductor wafer is inspected.

The principle of the present invention will be explained below.

Strictly speaking, the amplitude of light has a property that should be expressed not as a scalar quantity but as a vector quantity, and has not only magnitude but also directionality. Light is a type of electromagnetic wave, and as Maxwell's theory revealed, waves of electric and magnetic fields travel while oscillating in a plane perpendicular to the direction in which the light travels, and the directions of their vectors are mutual. It has the property of being perpendicular to. Therefore, at least, completely unbiased light emitted from a light source, that is, natural light, has vertical waves (indicated by a thick solid line in Fig. 2) and horizontal waves (indicated by a thin solid line in Fig. 2). (Although it cannot be shown in this figure because it has an amplitude in a direction perpendicular to the vertical wave, it is shown in the same way as a vertical wave for convenience.)

In natural light irradiated onto the boundary surface of media with different refractive indexes, since the incident angle to the boundary surface is different for vertical waves and horizontal waves, most of the vertical waves are refracted, as shown in Figure 2.
A polarized reflection phenomenon may occur in which most of the horizontal waves are reflected. This phenomenon is also a manifestation of Brewster's law, which states that the amount of polarization of light reflected by an object varies depending on the angle of incidence, and the amount of polarization is maximum when the angle of incidence is the polarization angle of the object.

As shown in FIG. 3, the parallel light beam (for example, laser beam) directed toward the semiconductor wafer 21 is approximately
It is reflected by the etched surface A having an inclination angle of 0° and the foreign object B, and the incident angle in this case is about 30 (θ) on the etched surface.
, ), whereas on the surface of a foreign object, the angle is not constant and varies from 0 to 90 degrees.

In contrast, the polarization angle on the etched surface is effectively about 55 (
Similarly, the polarization angle on the surface of the foreign object is approximately 55 (.theta.), assuming that the foreign object has the same properties as the etched portion.

Therefore, the incident angle of the light reflected on the etched surface is relatively close to the polarization angle, so 80% of it becomes polarized light, whereas the light reflected on the foreign object surface has an incident angle of 55 (θ). Only 80% of the light is polarized; the majority of all other light is unpolarized. In other words, most of the light reflected from the etched surface (80% in the above example) is polarized and has a certain directionality, whereas only a small portion of the light reflected from the surface of a foreign object is polarized. Most of the light is not polarized and does not have a fixed directionality.

Therefore, when observing the semiconductor wafer surface through the polarizing plate 8, polarized light is canted and a state can be created in which only non-polarized light is visible. In other words, a state is obtained in which only the unpolarized light reflected from the foreign object is detected, and the rest is not visible at all, or even if it is seen, the light is extremely weak and can be ignored. In this state, all the detected light comes from the foreign object. Therefore, by processing the electric signal obtained by photoelectrically converting the detected light in an electronic circuit device, foreign matter inspection can be performed automatically.

The principle of the present invention can also be explained as follows.

In other words, the angle of the slope A of the etched portion of the semiconductor wafer is 60 degrees, and the vertical waves of parallel light rays irradiated from the side face mostly undergo a refraction phenomenon and are absorbed into the semiconductor wafer, whereas the horizontal waves are reflected. do. Since the etched surface A can be said to be a mirror surface (flat surface), this reflection is cast surface (flat surface) reflection, and the directions of the reflected light are approximately the same.

On the other hand, since the surface of the foreign object is, of course, a non-cast surface (curved surface), the incident angle of the light irradiated on the foreign object varies.
Therefore, not only horizontal waves are reflected, but both horizontal and vertical waves are reflected (of course, some horizontal and vertical waves cause refraction and are absorbed internally).

That is, all the light reflected from the etched surface has a certain directionality, whereas the light reflected from the foreign object is diffusely reflected in different directions and does not have a certain directionality.

Therefore, the light reflected by the etched surface can be cut by the polarizing plate 8, so that only the diffusely reflected light from the foreign object can be detected.

The reason why the polarizing plate 8 is rotated during inspection is to match the angle of the light canted by the polarizing plate 8 to the direction of the light actually reflected by the etched surface.

If the inspection method according to the present invention as explained above is applied to the actual foreign matter inspection of semiconductor wafers, it would be difficult to conduct foreign matter inspection because even the light reflected from the etched surface would be detected when the present invention was not applied. On the other hand, in the method of the present invention, the light reflected on the etched surface is not detected, but only the light diffusely reflected by the foreign object is detected, so the foreign object can be easily inspected based on the detection result. I can do it.

Note that the principle of the present invention can also be explained as follows.

In other words, the laser light used for this inspection is originally light in a certain direction, and is reflected directly from slopes at a certain angle, so as shown in Figure 2, only horizontal waves are obtained. Since a foreign object has countless small slopes at various angles, vertical wave reflected light can also be obtained from the surface of the foreign object, so even if a polarizing plate is used, the light from the foreign object can be detected. The presence of foreign matter can be confirmed by light.

As described above, according to the present invention, only the light reflected by a foreign object can be detected, so even if unevenness due to etching exists on the surface of a semiconductor wafer, only the foreign object can be detected separately from it, so that automatic inspection is possible. becomes possible. Therefore, foreign object inspection can be performed objectively without human subjectivity, and it is also possible to meet the demand for labor saving. Furthermore, the automatic inspection method was able to significantly shorten the inspection time (to about one-tenth) compared to the conventional visual inspection method.

[Inspection time for one wafer reduced from conventional 2 to 3 hours to 1
It was shortened to 5 minutes. ]), necessary measures can be taken promptly based on the inspection results, and as a result, a decrease in yield can be effectively prevented.

The present invention can be applied not only to foreign matter inspection of semiconductor wafers but also to inspection of photomasks.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of a foreign matter inspection device according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing that the vertical component of light irradiated onto an object at a certain range of incident angles is refracted, and the horizontal component is reflected. FIG. 3 is an explanatory diagram showing the difference between the light reflected on the etched surface A of the semiconductor wafer surface and the light reflected on the surface of a foreign object. DESCRIPTION OF SYMBOLS 1... Cartridge feed drive part, 2... Cartridge, 3... Wafer feed part, 4... Mounting table, 5...
X-direction feed drive unit, 6...Y-direction feed drive unit, 8...
- Polarizing plate, 9... Objective lens, 10... Relay lens, 11... Mirror for illumination, 12... Mirror for visual inspection, 13... Lens, 14... Aperture, 15.
...Photoelectric converter, 16...Electronic circuit device, 17...
Visual observation mirror, 18...eyepiece, 19...run/', 20...lens, 21...semiconductor ueno to be tested.

Claims (1)

[Claims] 1. An optical inspection device that irradiates a plate-shaped object with light and detects the shape or reflected light from foreign matter on the surface or inside of the plate-shaped object, characterized in that a laser beam is used as the irradiation light. Inspection equipment.