JPH01189506A - Method for measuring thickness of film - Google Patents

Abstract

PURPOSE:To realize a method for simply and accurately measure a film thickness of several mum, by providing a pervious layer under a film to be measured to irradiate the surface of the film to be measured with laser beam and measuring the position of the node generated in the interference fringe pattern of reflected beam. CONSTITUTION:A film 1 to be measured is placed on a pervious layer 2 and laser beam having a definite wavelength is focused to the surface 1a of the film 1 to be measured in an oblique direction through a condensing lens 4 to irradiate the same. In this case, the laser beam is reflected from three surfaces, that is, the surface 1a, a boundary surface 1b and a reflecting surface 2a and three kinds of reflected beams are generated to interfere each other. When the interference laser beams are received by a CCD-array 3, an interference pattern is drawn and the node corresponding to the thickness of the film 1 to be measured appears in said pattern and the thickness of the film 1 to be measured can be calculated from the position of said node according to a predetermined formula.

Description

[Detailed Description of the Invention] [Summary] Regarding the improvement of an optical film thickness measurement method, we have developed a film thickness measurement method that can easily and accurately measure a film thickness of several μm without damaging the film to be measured. A transparent layer that transmits a laser beam is provided below the film to be measured, and the surface of the film to be measured, the interface between the transparent layer and the film to be measured, and the transparent layer in contact with the film to be measured are provided. The film thickness of the film to be measured is measured from the position of the node of the interference wave pattern of the three types of reflected light beams on the three non-contact surfaces.

[Industrial application field]

The present invention relates to a film thickness measurement method, and particularly to an improvement in an optical film thickness measurement method.

Film thickness measurement methods can be roughly divided into two types: an optical method and a stylus method, but each method has various drawbacks.

Optical methods require incident light of multiple wavelengths, or
It is not good at measuring film thickness of several μm.

Furthermore, the stylus method cannot measure the film thickness without damaging the film to be measured.

Under the above circumstances, there is a need for a film thickness measuring method that can easily measure a film thickness of several μm without damaging the film to be measured.

[Conventional technology]

There are two conventional methods for measuring film thickness: an optical method and a stylus method.

There are two types of optical methods: the nanospec method and the ellipsometry. Although it is suitable for measuring extremely thin films, it is not suitable for measuring film thicknesses of several μm.

In the case of the stylus method, the film thickness cannot be measured without damaging the film to be measured.

[Problem that the invention seeks to solve]

The problem with the conventional film thickness measurement methods described above is that the optical nanospec method requires incident light of multiple wavelengths, and ellipsometry is suitable for measuring extremely thin films of μm or less. Measuring a film thickness of several micrometers is inefficient, and in the case of the stylus method, the film to be measured must be damaged.

The present invention aims to provide a film thickness measuring method that can easily and accurately measure a film thickness of several μm without damaging the film to be measured.

[Means for solving problems]

The above problem is that a transparent layer that transmits the laser is provided below the film to be measured, and the surface of the film to be measured, the interface between the transparent layer and the film to be measured, and the transparent layer are not in contact with the film to be measured. This problem is solved by the film thickness measuring method according to the present invention, which measures the film thickness of the film to be measured from the position of the node of the interference wave pattern of the three types of reflected light beams on the three surfaces.

[Effect]

That is, in the present invention, the surface of the film to be measured is irradiated with a laser, a transmission layer that transmits the laser is provided below the film to be measured, and the surface of the film to be measured and the interface between the transmission layer and the film to be measured are and 3 on the three surfaces of the transmission layer that are not in contact with this film to be measured.
Since an interference wave pattern of the reflected light beam is drawn, it is possible to measure the thickness of the film to be measured from the positions of the nodes of this pattern.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 1, the film to be measured 1 is placed on the transmission layer 2,
A laser beam of a constant wavelength is focused by a condensing lens 4 and is irradiated obliquely onto the surface 1a of the film to be measured 1.

In this case, the laser beam is reflected from three surfaces, namely, the surface 1a of the film to be measured 1, the interface 1b between the film to be measured 1 and the transparent layer 2, and the reflective surface 2a of the transparent layer 2 that is not in contact with the film to be measured 1. reflected light will be generated and interfere with each other.

The interference laser beam generated by this interference is received by the CCD-array 3 installed at the position shown in FIG.
When an interference pattern as shown in the figure is drawn, knots are formed in the drawn interference pattern corresponding to the thickness of the film to be measured l.

In Figure 2, the element spacing is 14 μm and the number of elements is 2.
．． Since 048 CCD-array 3 is used, if the center point is O as shown in the figure, then both ends are 14.33
It shows that it is 6 dragons and -14,336 fl.

The position X of the node of the interference pattern shown in Fig. 2 and the film thickness m (μm
) is approximately as shown in the following equation.

Therefore, here, λ: Wavelength of incident light L: Distance from lens focus to light receiving surface n1: Refractive index of the film to be measured n: Q, 1.2.3... These constants are The values are: λ=0.78μm, L=90mm, n,=2
It is said that

To find the film thickness m from the position 2.3...
The value on the horizontal axis at the intersection with the curve is the film thickness.

For example, when X=4, the value of m is as follows for the value of n.

If n=0, m=0.70μm If n=1, m=2.10μm If n=2, m=3.49μm If n=3, m=4.89μm If n=4, m=6.29μm If n=5, m=7.68 μm If n=6, m=9.08 μm Which of the following values applies can be determined from the formation process of the film to be measured 1.

As is clear from the above example, the measurement range of the present invention is 1
~50 μm, and the measurement accuracy is considered to be about 0.1 μm.

Note that the incident laser beam used in this measurement method may be a diverging light instead of a focused light without any problem.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the film thickness of the film to be measured is measured by irradiating the film to be measured with an extremely simple laser, and by determining the position of the interference wave of the three types of reflected waves generated. It has the advantage of being able to perform the following steps, and can be expected to have significant economical and reliability-improving effects, making it extremely useful industrially.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment according to the present invention; FIG. 2 is an interference pattern diagram of an embodiment according to the present invention. Figure 3 is a theoretical correlation diagram between film thickness and node position according to the present invention; It is. In the figure, 1 is the film to be measured, 1a is the surface, lb is the boundary surface, 2 is a transparent layer, 2a is a reflective surface, 3 is a CCD-array. 4 is a condensing lens, Figure 1 is a block diagram showing an embodiment of the present invention. node position Interference pattern diagram No. 27 of one implementation of ifl+ according to the present invention

Claims (1)

[Claims] A transmission layer (2) that transmits the laser is provided under the film to be measured (1), and the surface (1a) of the film to be measured (1), the transmission layer (2), and the film to be measured (1) are From the positions of the nodes of the interference wave patterns of the three types of reflected light beams at the boundary surface (1b) and the surface (2a) of the transmission layer (2) that is not in contact with the film to be measured (1), A film thickness measuring method characterized by measuring the film thickness of a measurement film (1).