JPS6081825A - Mask inspection method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a mask inspection method, and particularly to a simple inspection method capable of detecting the presence or absence of foreign matter.

Prior Art and Problems Exposure technology, which transfers a pattern formed on a mask onto a wafer surface, is a key technology for semiconductor manufacturing, and is especially important for forming high-precision patterns in wafer processes.

In such exposure technology, ultraviolet light exposure has been widely used, but since this light exposure method exposes a pattern provided on a mask or reticle all at once, a mask or reticle is not used. Ru.

Here, a reticle is a device that has a pattern that is projected at a scale of 5:1 or 10:1, and a mask is a substrate that has a pattern that is the same size and is transferred onto a wafer at a 1:1 ratio. Masks in a broader sense include both.

In the past, the main method for such light exposure methods was the contact type light exposure method, which used a 1:1 transfer mask, but recently, the projection method has been widely used, and the reticle The use of has been increasing. This is because when a reticle is used, a reduced pattern is printed onto a wafer, and a fine pattern is formed with high precision.

Incidentally, such masks or reticles are prone to attract foreign matter such as dust and dirt, and if foreign matter adheres to these substrates, it becomes pattern data and causes pattern defects. In particular, in the case of a reticle with an enlarged pattern of one chip or several chips, the same pattern is repeatedly printed on the wafer, so if foreign matter is attached, it will be transferred to many patterns. , all or most of the patterns on the wafer are defective. Such foreign matter is often organic or inorganic dust with a size of about 1 to 5 μm. Therefore, conventional methods have been taken to prevent pattern defects by repeatedly inspecting reticles and masks.

The conventional inspection method is as follows.

In other words, the mask to be inspected is optically scanned and compared with the pattern data (stored on the tape of the pattern generator) used when creating the mask, and if an abnormal signal is found, it is determined that there is no dust or scratches. It is determined that there is. Other inspection methods include two inspection methods within the same mask, for example, two reticles.
Compare two chip patterns using a mask comparator,
This is a method that makes it defective if there is an abnormal signal.

Figure 1 shows the principle diagram, and the pattern P1 on the right side
and pattern P2 on the left at the same time,
If foreign matter E is present in pattern P1, an abnormal signal is generated.

The former inspection method is to read out the pattern P2 on the left side as pattern data stored on the tape of the pattern generator at the same time as scanning the pattern P1 on the right side. , p2 are provided on the same reticle and scanned simultaneously in the latter inspection method.

However, although such conventional inspection methods are very detailed inspection methods that utilize electronic technology, they require expensive inspection equipment and take a long time. On the other hand, the projection exposure method eliminates scratches such as friction, and most of the abnormalities detected in mask inspections are due to adhesion of foreign matter.

tel OBJECT OF THE INVENTION In view of these problems, the present invention proposes an inspection method that can be easily checked in order to maintain quality.

(dl Structure of the Invention The purpose of the invention is to irradiate light from the back side of a mask to be inspected, project the light-shielding pattern provided on the mask to be inspected onto the surface of the exposed sample using the transmitted light, and expose the parts other than the light-shielding pattern. At the same time, by simultaneously irradiating other light from the surface of the mask to be inspected and projecting the reflected light from the surface of the light-shielding pattern onto the exposed sample surface, thus exposing the entire surface of the exposed sample, This is achieved by a mask inspection method in which unexposed areas are detected as foreign matter.

tel　Embodiments of the invention Examples will be described in detail below with reference to nine drawings.

FIG. 2 shows a schematic diagram of a projection type optical device according to the present invention. 1 and 11 are light sources (high-pressure mercury lamps).

2. 12 is a condensing lens, 3 is a mask to be inspected, 4 is a half mirror, 25 is an objective lens, 6 is an exposed sample (for example, a wafer coated with a resist film), and 7 is a sample stage (the lens barrel is not shown) Then, the light from the light source 1 is transmitted through the mask 3 to be inspected, and the light transmitted through the portion other than the light shielding pattern is projected onto the surface of the exposed sample 6 through the half mirror 4 and the objective lens 5, and is exposed. On the other hand, other light from the light source 11 passes through the condenser lens 12 and hits the half mirror 17, and the light reflected from the half mirror 17 enters the surface of the mask 3 to be inspected. Then, the reflected light from the light-shielding pattern on the mask passes through the half mirror 4, passes through the objective lens 5, and is projected onto the surface of the exposed sample 6 for exposure.

In order to use such an exposure method according to the present invention,
The light-shielding pattern formed on the surface of the exposed sample 6 must be made of a light-reflecting film with good light reflectance. However, fortunately, the chromium film used as a normal pattern has high light reflectivity and can be sufficiently exposed. Figure 3 shows a plan view of the mask, where 20 is a mask substrate made of a quartz plate that transmits light from the back surface, and 21 is a film with a thickness of approximately 600 mm that blocks light from the back surface and reflects light from the front surface. The chromium film is formed on the mask substrate 20 by a sputtering method.

Therefore, if the surface of the mask to be inspected is irradiated simultaneously from the two light sources 1.11 as described above, the pattern will disappear and the entire surface of the exposed sample 6 will be exposed. Thus, if foreign matter adheres to the front or back surface of the mask 3 to be inspected, it will be detected on the exposed sample 6 as an unexposed area. in this way,
According to the present invention, mask defects can be detected extremely easily.

Moreover, this inspection method can be easily incorporated into an exposure apparatus. That is, with the structure shown in FIG. 2, the light source 1
If it does not irradiate the light from 1 to 1, it is used as an exposure device. Therefore, there is no need to take out the mask to be inspected from the exposure device, and the exposure process and inspection can be performed without repeating the mask while it is attached to the exposure device, making the inspection even easier.

(fl) Effects of the Invention As can be seen from the above explanation, the present invention simplifies mask inspection and reduces the number of inspection steps.

Furthermore, since the inspection becomes simpler, the number of inspections can be increased and exposure quality can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of a conventional mask inspection method, FIG. 2 is a schematic diagram of a mask inspection apparatus according to the present invention, and FIG. 3 is a plan view of a mask. In the figure, 1 and 11 are light sources, and 2 and 12 are condensing lenses. 3 is a mask to be inspected, 4 is a half mirror, 15 is an objective lens, 6 is an exposure sample, 7 is a sample stage, 20 is a mask substrate, 21
indicates a mask substrate. Figure 1 Figure 3 Figure 2

Claims (1)

[Claims] Light is irradiated from the back side of the mask to be inspected, and the transmitted light projects the light-shielding pattern provided on the mask to be inspected onto the surface of the exposed sample, exposing parts other than the light-shielding pattern. By irradiating other light from the surface,
A mask characterized in that the reflected light from the surface of the light-shielding pattern is projected onto the exposed sample surface for exposure, and by exposing the entire surface of the exposed sample, unexposed areas are detected as foreign matter. Inspection method.