JPH04223202A - Method for measuring film thickness of insulation film on semiconductor wafer - Google Patents

Abstract

PURPOSE:To enable a film thickness of an insulation film on a wafer surface to be measured with an improved accuracy for the wafer surface in either a mirror surface or a recessed or projecting surface. CONSTITUTION:A detection end face of an electrostatic capacity detection sensor 1 is opposed to a surface of a wafer 3 and electrostatic capacities C2 and C1 between a detection end face of the sensor 1 and a wafer 3 is detected by the sensor 1 for two states where there is an insulation film 2 on a surface of the wafer 3 and there is no insulation film 2 on a surface of the wafer 3. A film thickness d2 of the insulation film 2 is obtained based on detected electrostatic capacities C2 and C1 and a dielectric constant epsilon2 of the above insulation film 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the thickness of an insulating film on a semiconductor wafer used as a substrate when manufacturing semiconductor devices such as semiconductor large-scale integrated circuits (LSI).

0002

[Prior Art] When manufacturing semiconductor devices such as semiconductor LSIs, the thickness of an insulating film formed on the surface of a semiconductor wafer is
This is one of the important quality control items for semiconductor devices.

[0003] Therefore, it is required that the film thickness be accurately measured.

Generally, the technique for measuring the thickness of the insulating film includes:
A thin film thickness measurement method is used. This type of thin film measurement method includes a method in which the change in the weight of the object to be measured is measured using a microbalance and the film thickness of the object to be measured is measured from the amount of increase (hereinafter referred to as the "microbalance method"), and an optical method. A method of measuring the film thickness manually or a method of mechanically measuring the film thickness (reference: "Fundamentals of Thin Film Creation" by Tatsuo Asamaki, published by Nikkan Kogyo Shimbun) are known.

[0005]

However, when the conventional thin film measuring method described above is adopted for measuring an insulating film formed on a wafer surface, the following problems occur.

That is, the microbalance method is a convenient method for measuring the average film thickness over the entire surface of a semiconductor wafer because it does not require any processing on the wafer. However, the microbalance method has a problem in that the measurement of the film thickness distribution within the plane of the wafer must be performed after the wafer is broken and processed into small pieces.

Furthermore, the optical measuring method and mechanical measuring method described above can measure the thickness of the insulating film on the wafer surface without any problem in accuracy when the wafer surface is in a mirror-like state. However, with the optical measurement method and mechanical method, it is difficult to accurately measure the thickness of an insulating film on a wafer surface with severe irregularities such as an etched wafer surface.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to produce a wafer on a wafer without destroying the wafer, regardless of whether the wafer surface is a mirror surface or an uneven surface. An object of the present invention is to provide a method for measuring the thickness of an insulating film on a semiconductor wafer, which can measure the thickness of the insulating film and its distribution.

[0009]

Means for Solving the Problems The present invention provides a method for measuring the film thickness of an insulating film formed on a semiconductor wafer surface, in which a detection end surface of a capacitance detection sensor is opposed to the wafer surface, and the wafer surface is The capacitance detection sensor detects the capacitance between the detection end surface of the sensor and the wafer surface in two states: a state with an insulating film on top and a state without the insulating film, and The above problem is solved by determining the thickness of the insulating film based on each detected capacitance and the dielectric constant of the insulating film.

0010

[Operation] The inventor has conducted various studies on techniques that can measure the thickness of an insulating film formed on a wafer, regardless of whether the wafer surface is mirror-like or uneven. .

As a result, a difference occurs in the capacitance between the detection end surface of the capacitance detection sensor and the wafer surface between the state where the insulating film is on the wafer surface and the state where the insulating film is not on the wafer surface. I focused on this. For example, if the distance between the detection end surface of the sensor and the wafer surface is constant, each detection capacitance changes according to the thickness of the insulating film and the dielectric constant of the insulating film.

Furthermore, as is well known, the capacitance C between parallel planes is determined by the area S of the planes, the dielectric constant ε between the planes, the distance d between the planes, and C
=εS/d. Furthermore, even if the detection surface has some unevenness, the capacitance can be detected with high accuracy by arranging the detection end face of the capacitance detection sensor to face each part of the unevenness.

[0013] Therefore, based on the detected capacitance, it is possible to measure the thickness of an insulating film on either a specular surface or an uneven surface.

[0014] The present invention was created based on the above-mentioned knowledge.

Therefore, the thickness of the insulating film on the surface of the semiconductor wafer can be detected with high accuracy regardless of whether the surface is a mirror surface or an uneven surface.

[0016]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

This embodiment is an apparatus for measuring the film thickness d2 of the insulating film 2 on the surface of the semiconductor wafer 3, as shown in FIG.

As shown in FIG. 1, the embodiment apparatus detects the capacitance between the detection end surface of the capacitance detection sensor 1 and the three wafer surfaces, which are opposed to each other at a distance d3 on the three wafer surfaces. a capacitance detection sensor 1, a capacitance storage section 4 for storing the capacitance C1 detected in the state without the insulating film 2, and a state in which the insulating film 2 is on the surface of the wafer 3; The electrostatic capacitances C2 and C1 detected in two states, the state without the insulating film 2, and the insulating film 2, respectively.
A film thickness calculation unit 5 calculates the film thickness d2 of the insulating film 2 based on the dielectric constant ε2 of capacitance C2 transmitted and detected in the state with the insulating film
and a changeover switch 6 for transmitting the information to the film thickness calculation section 5.

Next, the operation of the embodiment will be explained.

FIG. 2 shows a state in which there is no insulating film 2 on the surface of the wafer 3 shown in FIG. 1.

When measuring the film thickness of the insulating film 2 using the film thickness measuring device of the embodiment, first, as shown in FIG. The capacitance C1 between the detection end surface and the three surfaces of the semiconductor wafer
Detect. Next, the detected capacitance C1 is stored in the capacitance storage section 4 via the switch 6.

FIG. 1 shows a state in which an insulating film 2 is present on a wafer 3 surface.

Next, as shown in FIG. 1, the capacitance detection sensor 1 is placed opposite the surface of the wafer 3 on which the insulating film 2 is located. In this case, the distance d3 between the surface of the wafer 3 and the detection end surface of the sensor 1 is made to be the same as in the case of FIG.

Next, the capacitance C2 between the detection end face of the sensor 1 and the wafer 3 is detected under the same conditions as in the case of FIG. In this case, the switch 6 is switched to the film thickness calculation section 5 side, and the detection capacitance C2 is connected via the switch 6.
is transmitted to the film thickness calculation section 5.

The detection capacitances C2 and C1 are different between the case where the insulating film 2 is present on the surface of the wafer 3 as shown in FIG. 1 and the case where the insulating film 2 is not present as shown in FIG.

Based on each of the detected capacitances C2 and C1, the thickness d2 of the insulating film 2 is determined by the following calculation formula.

First, each of the detection capacitances C1 and C2
is expressed by the following equations (1) and (2).

C1 = ε1 ・S/d3
...(1) 1/C2 = (1/S) (d1/ε1
+d2/ε2) (2) where S is the area of the sensor detection end surface, ε1 is the dielectric constant of air, and ε2 is the dielectric constant of the insulating film 2. Further, d1 is the distance between the upper surface of the insulating film 2 and the detection end surface of the sensor 1 when the insulating film 2 is present, and d1
+d2=d3 holds true.

Therefore, equations (1) and (2) can be expressed as film thickness d
If we organize 2, we get the following equation (3).

d2=S(1/C1-1/C2)/(1/ε1
-1/ε2 ) (3) That is, by substituting each of the detection capacitances C1 and C2 into the equation (3), the thickness d2 of the insulating film 2 can be calculated. this(
In the equation 3), the dielectric constant ε1 of air is known, and the dielectric constant ε2 of the insulating film 2 can be measured in advance from the material of the insulating film 2 to be produced. Further, the sensor area S can be measured in advance.

[0031]

[Effects of the Invention] As explained above, according to the present invention, the thickness of the insulating film on the wafer surface can be measured with high accuracy regardless of whether the wafer surface is a mirror surface or an uneven surface. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram including a partial cross-sectional view showing an example of a measurement state of a film thickness measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram, including a partial cross-sectional view, showing an example of a measurement state.

[Explanation of symbols]

1...Capacitance detection sensor, 2...Insulating film, 3...Semiconductor wafer, 4...Capacitance storage section, 5...Film thickness calculation section, 6...Selector switch.

Claims (1)

[Claims] 1. A method for measuring the thickness of an insulating film formed on a semiconductor wafer surface, in which a detection end surface of a capacitance detection sensor is opposed to the wafer surface, and a state in which an insulating film is present on the wafer surface is obtained. The capacitance detection sensor detects the capacitance between the detection end surface of the sensor and the wafer surface in two states, the state without the insulating film, and the capacitance detected in each state. . A method for measuring the thickness of an insulating film on a semiconductor wafer, characterized in that the thickness of the insulating film is determined based on the dielectric constant of the insulating film.