JPH03130602A - Optical film-thickness measuring apparatus - Google Patents

Abstract

PURPOSE:To improve measuring reproducibility, to exclude dust and to reduce a providing area by supporting a measuring optical system with a supporting post, holding a wafer surface in parallel with the vertical direction, and adopting a longitudinal state. CONSTITUTION:Stage 8 and 9 are moved. A wafer 5 is moved to a position facing an objective lens. At this time, the light emitted from a light source 2 is projected on the wafer 5 through the lens 3. The incident light becomes the upper-surface reflected light and the bottom-surface reflected light. Interference occurs between the two reflected light beams. Then, the interference light is inputted into a measuring system 1 through the lens 3 again. The interference light is spliet in the measuring system 1 and projected on a line sensor. The reflectivity of the projected interference light is measured as the output voltage of each element of the line sensor in response to each wavelength. The rigidity is enhanced with a vertically supporting post 11 for supporting the measuring system 1 and the light source 2 from the lower side. Therefore, the effect of vibration is decreased, and the measurement is performed with high measuring reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical film thickness measuring means for measuring the thickness of a film on a wafer using an optical interference method.

[Prior Art] Conventionally, as shown in FIG. 2, an optical film thickness measuring device includes a chuck 6 that chucks the wafer 5, an X-Y stage 8°10 that moves the chuck 6 horizontally, and a It consists of a measurement system 1 and a light source 2 located at , and an arm 12 that supports the measurement system 1 and light source 2 .

The performance that is important in such a film thickness measuring device is the absolute accuracy of the calculated film thickness value and the reproducibility of the measurement. Vibrations of the measurement system (spectroscope) 1 and vibrations of the light source 2 are strong factors in measurement reproducibility, which is one of its important performances.

[Problems to be Solved by the Invention] However, in the conventional example described above, since the measurement system 1 and the light source 2 are cantilever-supported by the arm 12, vibrations from the outside (forced vibration) and when the wafer is moved No swing! (
It has the disadvantage that it is easily affected by self-supporting vibrations, and the transmitted vibrations deteriorate measurement reproducibility. Furthermore, as the X-Y stage 8.10 grows from 6-inch wafers to 8-inch wafers in the future, the arm length will also become longer, making it necessary to place greater emphasis on vibration countermeasures. .

In addition, since the wafer is always moved with its surface facing upward,
Dirt and dust generated from the moving parts of the equipment or floating in the air adhered to the surface of the wafer, causing a decline in the quality of the wafer. Furthermore, since the entire area of the wafer must be used as the measurement area, there is a drawback that the installation area of the entire apparatus becomes large.

In view of the problems of the prior art, an object of the present invention is to
The purpose of this invention is to improve measurement reproducibility, eliminate dust, and reduce the installation area in an optical film thickness measuring device.

[Means for Solving the Problems] In order to achieve the above object, the optical film thickness measuring device of the present invention includes a chuck means for holding a wafer with the wafer surface parallel to the vertical direction, and a chuck means for holding the wafer in a state in which the wafer surface is parallel to the vertical direction. Horizontal -
A stage means for moving in the axial direction; a measurement optical system that illuminates the wafer held by the chuck means and interferes with the reflected light to optically obtain information regarding the thickness of the film on the wafer surface; and the measurement optical system. It is equipped with a pillar that supports the vertical direction.

[Operation] In this configuration, when measuring the film thickness on the wafer surface, the wafer is transported to the measurement position and positioned, but at that time, the wafer surface is made parallel to the vertical direction by vacuum suction, that is, the wafer is While holding the wafer with its surface oriented horizontally, the wafer is held in one horizontal axis and one vertical axis (X-Z) instead of the conventional two horizontal (X-Y) directions.
) direction, the wafer surface is always parallel to the vertical direction, and measurements are performed with less dust adhering to the surface. Furthermore, since the measurement is performed with the wafer surface parallel to the vertical direction, the measurement direction is horizontal, so there is no need to cantilever the measurement optical system as in the conventional case. In other words, the measurement optical system is directly supported by a support and has a highly rigid structure, so there is little influence from external forced vibration or self-supported vibration due to wafer movement, and measurements are performed with good measurement reproducibility. . Furthermore, since the chuck means and the stage means are vertical, or the measuring optical system is supported by a column, the apparatus can be constructed with a smaller installation area.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows an optical film thickness measuring device according to an embodiment of the present invention. In the figure, 1 is a measurement system that detects interference light reflected from a wafer, 2 is a light source, 3 is an objective lens, 4 is a TV camera, 5 is a wafer as an object to be measured, and 6 is a measurement system that detects interference light reflected from a wafer. 7 is a calibration sample for calibrating the reflection characteristics of the measuring device itself; 8 is an X stage that moves the chuck 6 in the X direction; 9 is a chuck 6 that moves the chuck 6 in the Z direction; The Z stage 11 is a support for supporting the measurement optical system including the measurement system 1 to the TV camera 4.

FIG. 3 shows the inside of the measuring section of the conventional device shown in FIG. 2, except that the objective lens 3 is held vertically.
The internal configuration and measurement principle of the measurement optical system of this embodiment shown in FIG. 1 are completely the same. Therefore, with reference also to FIG. 3, the measurement procedure in the apparatus of FIG. 1 will be described below.

First, when a wafer 5 is transported by a wafer transport device (not shown), the chuck 6 vacuum-chucks it. Next, the stage 8.9 is moved and a calibration sample 7 having a known reflectance characteristic is placed eight times at a position opposite the objective lens 3 for measurement, thereby calibrating the reflection characteristic of the apparatus itself. Then, the stages 8 and 9 are further moved to move the wafer 5 to a position facing the objective lens 3, and the film thickness is measured. During this measurement, the light emitted from the light source 2 is irradiated onto the wafer 5 through the objective lens 3. This incident light becomes light reflected from the top surface of the film and light reflected from the bottom surface of the film, each having a phase difference proportional to the film thickness, and interference occurs between these two reflected lights. The generated interference light passes through the objective lens 3 again and enters the measurement system (here, a spectrometer) 1. This interference light is transmitted to a wavelength of 400 to 800n by a grating 13 within the spectrometer 1.
The light is separated into wavelengths of m and projected onto the line sensor 15 via the high reflection mirror 14. The reflectance of the projected interference light is measured as the output voltage of each element of the line sensor 15 corresponding to each wavelength. In the case of calibration sample 7, the obtained voltage is used to calculate a coefficient corresponding to the voltage and reflectance based on the known reflectance, and in the case of film thickness measurement, it is used to calculate the coefficient corresponding to the above coefficient and the interference factor. The film thickness is calculated from the condition.

Here, in the conventional example, the spectrometer 1 and the light source 2 are held cantilevered by the arm 12, and the structure is such that minute vibrations are easily transmitted. Therefore, when the spectrometer 1 vibrates, the interference light from the wafer 5 is Since variations occur in the incident conditions such as the incident angle and intensity into the device 1, changes in reflectance and wavelength shift occur in the measured values. For this reason, an error occurs in the calculated value of the film thickness, resulting in poor measurement reproducibility. Further, when the light source 2 vibrates, the amount of light irradiated onto the wafer 5 changes, so the interference light from the wafer, that is, the reflectance changes, which also affects measurement reproducibility.

In contrast, in this embodiment, as shown in FIG. 1, the rigidity is increased by the support column 11 that vertically supports the spectrometer 1 and the light source 2 from below, so the effects of forced vibration and self-help vibration are reduced. This allows measurements to be performed with high measurement reproducibility.

In this embodiment, the objective lens 3 is configured to face sideways in order to chuck the wafer with the wafer surface parallel to the vertical direction. Instead, this can be easily handled by using a vertical x-Z stage 8.9. Furthermore, by making the stages 8 and 9 H-shaped, the weight of the vertical axis is reduced and the followability of the stages is improved. Furthermore, by making the stage a vertical stage in this manner, the problem of dust adhesion to the wafer is greatly improved, and the ratio of the stage to the installation area of the entire apparatus is extremely reduced.

[Effects of the Invention] As explained above, according to the present invention, the measurement optical system is supported by a support, the wafer surface is held parallel to the vertical direction, and a vertical stage is used. , the measurement reproducibility can be improved, the adhesion of dust to the surface of sea urchins can be reduced, and the installation area of the device can be reduced.

1: Measurement system, 2: Light source, 3: Objective lens, 4: TV left camera 5: Wafer, 6: Chuck, 7: Calibration sample, 8: X stage, 9: Z stage, 10:
Y stage, 11: Strut, 12: Arm.

Claims (1)

[Claims] A chuck means for holding a wafer with the wafer surface parallel to the vertical direction, and a chuck means for holding the wafer in a state in which the wafer surface is parallel to the vertical direction;
A stage means for moving in the axial direction, a measurement optical system that illuminates the wafer held by the chuck means and interferes with the reflected light to optically obtain information regarding the thickness of the film on the wafer surface; 1. An optical film thickness measuring device characterized by comprising a pillar supporting in a vertical direction.