JPS6313446Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for highly accurately detecting minute irregularities on a surface that is substantially mirror-like and has extremely small irregularities.

2. Description of the Related Art Conventionally, various apparatuses for inspecting the mirror surface condition of silicon wafers used in semiconductor devices, for example, have been proposed and are commercially available. One of them is, for example, to project a narrow laser beam (several tens of microns) onto a mirror surface, to detect the position of the reflected laser beam using an image sensor, and to calculate the angle of the reflective surface based on the positional deviation. This is a method of calculating and repeating this operation horizontally one after another to find out the state of the surface. With this method, it is currently possible to detect gentle irregularities up to approximately 0.5 μm, but it is difficult to detect irregularities smaller than that, and although it is easy to detect irregularities on a straight line, it is difficult to detect irregularities that are smaller than that. Detection and detection of dirt is difficult, requires highly accurate adjustment and skill, and is also expensive and extremely difficult to operate.

Another method is to magnify a narrow laser beam and irradiate it onto a mirror surface as an enlarged parallel beam, and then project the reflected light onto the light-receiving surface overlapping the parallel beam to cause interference. This is a method of determining surface irregularities from the striped pattern. According to this method, it is possible to easily observe the entire uneven state of the surface at once, which is effective for detecting scratches, etc.;
It is very difficult to detect gentle unevenness or dirt with a width of about 0.5 μm and a width of 3 to 10 mm, and the adjustment and maintenance of the device is very difficult and expensive.

A simple method that has been proposed is to utilize a phenomenon known since ancient times as a magic mirror. In this method, as shown in FIG. 1, a light beam 12 from a point light source 11 is focused by a condenser lens 13, passes through an aperture 14, is reflected on a mirror surface 15, and is projected onto a light receiving surface 16. If there is a convex portion (convex) on the mirror surface 15, the reflected light from the convex portion becomes an expanding light beam 17 and is projected onto the light receiving surface 16. Therefore, the center of the convex part becomes a dark area D as shown in the schematic diagram above the light-receiving surface 16 that shows the brightness and darkness of the projected image, and the outer edge of the reflected light of the convex part is, for example, darker than the flat surface around the convex part. Since it overlaps with the reflected light 18, it becomes brighter than the surrounding area, as shown in B. If the concave portion is on a mirror surface, the opposite brightness and darkness will occur. This method is simple and
It has the advantage of being able to sensitively detect mild irregularities and scratches of 0.5 μm or less, dirt with different reflection coefficients, etc. However, as can be seen from Figure 1,
Since the reflected light from the mirror surface 15 is simply projected, it is difficult to separate the reflected lights 17 and 18, for example, and the resolution is very poor. In order to improve this drawback, it is necessary to use a very narrow point light source (for example, 1
mm diameter or less), and the light source 11 and mirror surface 15
Also, it is necessary to keep the distance between the mirror surface 15 and the light receiving surface 16 as far as possible (for example, 2 m each), and as the device becomes larger, it is necessary to use an impractically powerful light source, or to use a 50 to 100 W light source even in a dark room. There are drawbacks such as the need to receive the light on a highly sensitive film.

As mentioned above, both methods have many drawbacks, and there has been a desire for a simple device that can improve these drawbacks.

The present invention provides an excellent device that overcomes these drawbacks. This invention is based on the second and third
As shown in the outline of one embodiment of this method, the method using the magic mirror of FIG. 1 is adopted and has been greatly improved.

The present invention basically consists of at least the final part of the optical part that focuses the light beam expanding from a point light source, and at least one part of the optical focusing system that receives and focuses the reflected light reflected from the mirror surface. This device also has the function of projecting the image onto a light-receiving surface after being reduced in size by a condensing optical system. An embodiment of the present invention is shown in FIG. Point light source 2
The light beam 22 from 1 is focused by a condensing lens 23 (not necessarily required, but the brightness can be improved by using this), and a half mirror 2 m
The direction of the light beam 22 is changed at , and it is further focused through a convex lens 29 which is a light projecting and focusing optical system, and is projected onto a mirror surface 25 such as the surface of a silicon wafer. The reflected light is transmitted to the light projecting and condensing optical lens 2.
9 receives the light and further focuses it on the light receiving surface 2.
Project onto 6. In this device, the size is halved compared to the one in Figure 1 because the light reciprocating parts can be used in common. Furthermore, as is evident in FIG. 1, the projected image is obliquely distorted. For example, a circle is distorted into an ellipse. In contrast, in the configuration of FIG. 2, all such distortions are eliminated.

Moreover, the brightness of the image can be improved by making the entire device smaller, and by making the size of the image on the light-receiving surface 26 1/3 that of the mirror surface, even including the loss of brightness due to the 2m half mirror. It is about 9 times larger than the one in Figure 1, and can now be observed not only in a dark room but also in a room with normal brightness. If the light-receiving surface 26 is made of frosted glass, in order to prevent outside light from scattering on the glass surface, cover a portion of it as shown in Figure 2, or protect it from direct exposure to outside light. It is desirable to do so. Further, in order to increase the resolution, the point light source may be narrowed down to a very small size using a pinhole, and as mentioned above, a diameter of 1 mm or less is desirable.

Another embodiment of the present invention is shown in FIG. 3, for example. In FIG. 3, 31 is a point light source, 32 is a light beam, 33 is a condenser lens, 34 is an aperture, 35 is a mirror surface, and 36 is a light receiving surface. This third
In the figure, since a concave mirror 39 is used in the light emitting and condensing optical system, the optical path is further halved, that is, the length is further shortened to 1/2, and since there is no half mirror, the brightness is quadrupled. A bright image can be obtained. If a camera or television camera is placed on the light-receiving surface 36 instead of the above-mentioned ground glass, the power output will be 0.1W.
Even when using a very dim point light source, the surface condition of the mirror surface 35 could be clearly observed. Note that the light receiving surface 36
If you look directly at the mirror surface 35 without using the ground glass, you will only see the image of the point light source 31. As the light receiving surface 36, the entire image can be seen for the first time on the light receiving surface of ground glass, film, or a television camera.

Next, the function of improving the ability to detect brightness and darkness due to unevenness, achieved by the device of the present invention, will be briefly explained with reference to the principle diagram of FIG. For the sake of simplicity, if we assume that perfectly parallel rays are reflected from the mirror surface 45, these parallel rays naturally converge at a single focal point 50 of the lens. However, if there are irregularities on the mirror surface 45 and the light 47 is generated out of parallel, it will not pass through the focal point 50. The light receiving surface 46 is located at a point A slightly away from the focal point.
, the point on the light receiving surface 46 of the slightly shifted light 47 will be expanded to the outside of the projected image of the mirror surface 45. In reality, we do not do something extreme like this and place the light receiving surface 46 at point B, so extremely large magnification does not occur as described above, but there is a tendency for large magnification within a short focal length to occur. Let's nod. In Fig. 4, a single convex lens is used, but the same thing holds true for a plurality of lens systems or a concave lens, and also holds true even for non-parallel rays.

Next, an example of a comparative experiment between the present invention and a conventional example will be shown.

[Specific example of the present invention]

Using a device as shown in Fig. 2 with a 0.1W point light source, a 3-inch silicon single crystal wafer 6
The surface of 0 was observed. The surface of this wafer is mirror-like, and when viewed with a laser interference device, the entire surface is 5μm.
Although some large "warps" were observed, no surface defects or irregularities were observed at all. However, when this wafer is observed using an apparatus using the present invention, as shown in FIG. Approximately 2 concave diameters of 0.3 to 0.5 μm
mm) appears as a white spot. The black straight line 63 is
It shows a 20mm long wound. Note that the black "lump" seen at the bottom of the surface of the wafer 60 is the sample number. FIG. 5 shows a photograph of the surface of the wafer 60. When taking a photograph, remove the ground glass from the light-receiving surface, place the camera directly on the light-receiving surface, set the focus 30 cm in front of the light, and set the exposure time to 10 cm. Seconds.

[Example using conventional method]

The same wafer 60 described above was observed by the method shown in FIG. In other words, although the subject was illuminated with a 0.1W point light source, no image was visible on the screen even though the room was completely dark. After replacing the film with a screen and exposing it to light for 10 minutes, I managed to get an image, but it was not strong enough to be resolved.

As described above, with the device using the present invention, it is possible to observe unevenness of 0.2 to 0.3 μm, which could not be detected conventionally, in stripes or concentric circles every few mm, and to improve the appearance of mirror surfaces such as semiconductor substrate surfaces. It can be highly effective in observing conditions, determining pass/fail, etc. In the above explanation, the optical system is represented by a single lens or a concave mirror for the sake of simplicity, but of course, using multiple lenses and mirrors will further increase the size of the device, especially in order to eliminate aberrations. Needless to say, this is effective for reducing the size.

As described above, the present invention is a device that is less than half the size of the conventional method using a magic mirror, and
Mirror surface condition (width 3-10mm height difference 0.2-0.3μm
It is possible to obtain a device with improved visibility that allows for easy observation in a bright room, which was not possible with conventional methods. In addition, the processing accuracy and the adjustment accuracy of the device mechanism are low, but it is an unprecedented device that can display the surface condition with very high accuracy.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle of the magic mirror that has been passed down from the past.
2 and 3 are schematic diagrams showing an observation device according to an embodiment of the present invention, FIG. 4 is a diagram illustrating the function of magnifying and detecting irregularities by the device of the present invention, and FIG. 5 is a diagram showing the apparatus of the present invention. FIG. 3 is a surface state diagram of the wafer obtained in FIG. 21, 31... point light source, 22, 32... luminous flux,
23, 33... Condensing lens, 2 m... Half mirror, 25, 35... Mirror surface, 26... Light receiving surface, 2
9, 39... Light projecting and focusing optical system (29... Convex lens, 39... Concave mirror), 6... Silicon wafer.

Claims (1)

[Claims for Utility Model Registration] (1) A point light source, and a light projection that focuses the expanding light beam from the point light source and projects it onto the surface of the sample to be observed, and also focuses the reflected light from the surface of the sample to be observed. a light-receiving surface installed at a position shifted from the focal point of the optical system, the reflected light from the sample surface being reduced and projected by the optical system; A surface observation device characterized in that the surface observation device detects this as the brightness and darkness of a projected image on the light receiving surface. (2) The surface observation device according to claim 1, wherein the sample to be observed is made of a semiconductor substrate.