JPH0448164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring insulator film thickness.

(Prior art) Generally, as a method of measuring the film thickness of an insulator,
An optical method using an interferometer or the like and a method using parallel plate electrodes are known. Among these measurement methods, the optical method cannot be used for opaque insulator films, so the parallel plate electrode method, which can measure even opaque insulator films, is often used.

As a conventional parallel plate electrode method, for example, the second
I found something like the picture. The configuration will be explained below using figures.

In FIG. 2, reference numeral 1 denotes an insulator to be measured, and parallel plate-shaped electrodes 2 and 3 are arranged on both sides of this insulator 1. Cables 4 and 5 are connected to electrodes 2 and 3.
are connected, and a voltage V is applied between both electrodes 2 and 3 via these cables 4 and 5. In addition, insulator 1
Assume that the dielectric constant is ε, the film thickness is d, the area of the electrodes 2 and 3 is A, and the thickness is t.

Now, it is assumed that when a voltage V is applied between the electrodes 2 and 3, lines of electric force perpendicular to the gap between the electrodes are generated and an equal electric field is formed between the electrodes 2 and 3.

Then, the capacitance C becomes as shown in the following equation.

C=Q/V=εA/d...(1) However, Q: electric charge of electrodes 2 and 3.

Therefore, in the conventional measuring method, when the dielectric constant ε and the area A are known, the film thickness d of the insulator 1 is measured based on the change in the charge Q with respect to the voltage V.

As another measurement method, a method has been proposed in which the area of one of the electrodes 2 and 3 is reduced to measure the film thickness d of the insulator 1; It is difficult to obtain highly accurate measurement results due to the influence of

(Problems to be solved by the invention) However, in the conventional measurement method shown in FIG.
In order to improve measurement accuracy, the thickness t of the electrodes 2 and 3 should be made sufficiently thinner than the film thickness d of the insulator 1 so that lines of electric force that are not perpendicular to the electrode surface can be ignored. It is necessary to make the area A of the electrodes 2 and 3 sufficiently large relative to the thickness d, and to make the areas of both the electrodes 2 and 3 equal. When the film thickness d of the insulator 1 becomes thinner, there is a limit to how thin the thickness t of the electrodes 2 and 3 can be made, so the area A of the electrodes 2 and 3 is made sufficiently large to obtain an equal electric field. Therefore, if the area of the insulator 1 is small, or if the insulator 1 is not flat but has a curved shape, it becomes difficult to obtain a uniform electric field, which poses the problem of not being able to measure the film thickness with high precision. Ta.

The present invention provides an insulator film thickness measurement method that solves the problem of the prior art, which is that highly accurate film thickness measurement cannot be performed when the insulator has a small area or has a curved shape. This is what we provide.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a method for measuring the thickness of an insulator, in which the dielectric constant ε is known and the film thickness D is unknown on both sides of the insulator. a first electrode;
The first electrode and a second electrode having a width W smaller than the width of the insulator, a known length L, and a known thickness T are respectively arranged. A predetermined voltage is applied between the first and second electrodes, and a surface of the first electrode facing the second electrode, a surface of the second electrode facing the first electrode, and Electric lines of force having a fringing effect are generated between the first and second electrodes to increase the capacitance Ct per unit length of the length L between the first and second electrodes.
Measure. Then, the capacitance Cto per unit length that is uniquely determined from the dielectric constant ε, film thickness D, width W, and thickness T, and the measured capacitance Ct, width W, and thickness T. The unknown film thickness D is calculated by calculation.

(Function) According to the present invention, since the insulator film thickness measuring method is configured as described above, lines of electric force having a fringing effect are generated between the first and second electrodes, and the electric force is Measured value of capacitance Ct between both electrodes by wire,
ε of the insulator and W of the second electrode set in advance,
The unknown film thickness D can be calculated by calculating T and the capacitance Cto which is uniquely determined from ε, D, W, and T. Here, the electric lines of force generated from the side surface of the second electrode have the function of increasing the capacitance between the first and second electrodes and reducing the width W of the second electrode. Since lines of electric force with a fringing effect are used in this way, the degree of freedom in selecting the shapes of the first and second electrodes is increased, and in particular, by reducing the width W of the second electrode, the insulator can be small area,
Highly accurate film thickness measurements can be performed even on curved surfaces. Therefore, the above-mentioned problem can be eliminated.

(Example) FIG. 1 shows an example of the present invention, and is a schematic configuration diagram of an insulator film thickness measuring apparatus used in an insulator film thickness measuring method.

In FIG. 1, 11 is in the semiconductor element.
The insulator 11 is an insulator such as a PSG layer or a silicon oxide layer, and has a dielectric constant ε, a film thickness D, and a relatively large area. A first electrode 12 and a second electrode 13 are arranged on both sides of the insulator 11 . The first electrode 12 is made of a conductive metal layer, a semiconductor substrate, or the like, and, like the insulator 11, has a relatively large area. The second electrode 13 is made of a conductive metal layer such as Al, a semiconductor substrate, etc., and has a depth L, a left and right width W, and a thickness T, taking into consideration the fringing effect. The width W is formed to be smaller than the widths of the insulator 11 and the first electrode 12, and the thickness T is formed to be thicker than the film thickness D so as not to be ignored.

Cables 14 and 15 are connected to the first and second electrodes 12 and 13, respectively.
It is connected to the measuring device main body 16 via 4 and 15. The measuring device main body 16 has a film thickness D of the insulator 11.
This is a device for determining the , and includes a measurement section 17 , a storage section 18 , and a calculation section 19 . The measurement unit 17 includes a power source that outputs a voltage V and a capacitance measuring device. The storage unit 18 has a memory device that stores various data, and the calculation unit 19 has a memory device that stores various data.
6 and an arithmetic circuit that performs various calculations, and is composed of, for example, a CPU.

Using the above-mentioned device, a voltage V is output from the measuring section 17, and this is applied to the first and second electrodes 12, 13.
If applied between
Most of the lines of electric force from the surface of the electrode 13 facing the first electrode 12 and the side thereof terminate at the surface of the first electrode 12, and most of the lines of electric force from the first electrode 12 are It terminates at the second electrode 13.

Here, the length L of the second electrode 13 is kept constant, the width W and the thickness T are varied, and the insulator 1
1, the dielectric constant ε (=3.9) is kept constant, the film thickness D is varied, and each total capacitance Co is determined, for example, from a numerical solution of a device simulator, and the unit length of length L is 1 (cm). When the per-unit capacitance Cto is determined, a capacitance characteristic diagram as shown in FIG. 3 is obtained.

In FIG. 3, the horizontal axis represents W/D and the vertical axis represents Cto, and the capacitance curves when T/D is 10, 5.0, 2.0, 1.0, and 0.1 are indicated by X1 to X5. Note that the straight line Y indicates the capacitance characteristic of the parallel plate electrodes.

From this FIG. 3, a first-order approximation formula for the capacitance Cto as shown in the following formula can be obtained.

Cto=A(W/D)+B(T/D)+C...(1) Here, A, B, and C are constants, A is the slope, B is the correction value, and C is the vertical axis intercept. The film thickness D of the insulator 11 can be derived from equation (1) as follows.

D=AW+BT/Ct-C...(2) The data in FIG. 3 including this formula (2) is stored in advance in the storage unit 1.
8, and the film thickness D of the insulator 11 is determined as follows.

First, as the second electrode 13, the width W=4 (μm),
Using thickness T=1 (μm) and length L=1.8 (cm), the capacitance Co when the dielectric constant ε=3.9 of the insulator 11 is measured by the measurement unit 17. Next, the capacitance per 1 (cm) of the length L = 1.8 (cm) is measured by the measuring unit 17.
Calculate Ct=2.5 (PF/cm).

Here, the film thickness D to be determined is, for example, 1
(μm) to 10 (μm). Then, the calculation unit 19 calculates the horizontal axis W/D in FIG. 3 from 0.4 to
Within the range of 4.0, constant A=
0.38 (PF/cm), B=0.15 (PF/cm), C=0.8
(PF/cm), and further calculate these constants A to C,
Cto=2.5 (PF/cm), W=4 (μm), T=1 (μm)
is substituted into the above equation (2) to calculate the film thickness D as follows.

D=0.98 (μm) The actual value of film thickness D is 1 (μm), so ±2%
This means that we were able to measure the film thickness with high accuracy.

Therefore, in the measurement method of this embodiment, the insulator 11
Capacitance characteristic data for the capacitance Cto per unit length when the film thickness D, the width W, and the thickness T of the second electrode 13 are varied while keeping the dielectric constant ε constant. , Equation (2) based on the data is determined in advance. Then, the capacitance Ct per unit length of the insulator 11 to be actually measured is measured.
Next, find the constants A, B, and C in equation (2), and calculate the constants A, B, and C, the measured capacitance Ct, and the second electrode 1.
By substituting the width W and thickness T of 3 into equation (2), the unknown film thickness D can be obtained.

According to such a measurement method, lines of electric force are generated between the first and second electrodes 12 and 13 due to the fringing effect, and the capacitance Ct is measured. Since these electric lines of force are also generated from the side surface of the second electrode 13, the parasitic capacitance between the two electrodes 12 and 13 increases.
Film thickness can be measured. Therefore, not only can the insulator film thickness in a small area be easily and highly accurately measured using the small second electrode 13, but even if the insulator 11 has a curved shape, the curved surface can be regarded as substantially flat. film thickness can be measured with relatively high accuracy.

Further, in the measuring device of this embodiment, the capacitance characteristic data and equation (2) based on the data are stored in the storage unit 18. Then, the capacitance Ct of the insulator 11 to be actually measured is measured by the measurement unit 17, and the unknown film thickness D is calculated by the calculation unit 19 using the measured capacitance Ct and the data in the storage unit 18. ,
Once calculated, the film thickness can be easily measured. This device not only has the advantages of the above method, but the first and second electrodes 12 and 13 may be electrodes specially made for the measuring device, or may be made of existing conductive members, semiconductor members, etc. It may also be used as an electrode. For example, when measuring the coating film thickness on a metal plate in a large device, the metal plate is connected to the first electrode 1.
2, it is possible to bring the small second electrode 13 into contact with the paint film and measure the thickness of the paint film.

Note that the method of the present invention is not limited to the illustrated embodiment, and various modifications are possible. For example, in the above embodiment, a first-order approximation formula is used as shown in equation (1), but if the first-order approximation formula is used, the range in which an accurate film thickness D can be obtained is narrow, so a multi-order approximation formula is used. If used, measurement accuracy will be further improved.

(Effects of the Invention) As explained in detail above, according to the measuring method of the present invention, a voltage is applied to generate electric lines of force between the first and second electrodes due to the fringing effect, thereby increasing the capacitance. Measure Ct. Since these electric lines of force are also generated from the side surface of the second electrode, the capacitance between the two electrodes increases, and the film thickness can be measured without using a large second electrode as in the conventional method. In this way, the fringing effect is actively used to measure the capacitance Ct using a small second electrode, and then the film thickness is determined through calculation processing, so it is possible to measure the capacitance Ct using a small second electrode. Film thickness can also be measured easily and with high precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an insulating film thickness measuring device used in the method of the embodiment of the present invention, FIG. 2 is a diagram showing a conventional insulating film thickness measuring method, and FIG. 3 is a diagram similar to that shown in FIG. FIG. 3 is a capacitance characteristic diagram for explaining the method. 11... Insulator, 12... First electrode, 13...
...Second electrode, 14, 15...Cable, 16...
... Measuring device main body, 17... Measuring section, 18... Storage section, 19... Calculating section.

Claims (1)

[Scope of Claims] 1. A first electrode and a width W smaller than the width of the first electrode and the insulator are provided on both sides of an insulator having a known dielectric constant ε and an unknown film thickness D, and a second electrode having a known length L and a known thickness T, respectively, and applying a predetermined voltage between the first and second electrodes, generating electric lines of force having a fringing effect between the surface of the second electrode facing the first electrode and the surface of the second electrode facing the first electrode and the side surfaces thereof;
The capacitance Ct per unit length of the length L between the electrode and the second electrode is measured, and the capacitance Ct per unit length is determined uniquely from the dielectric constant ε, film thickness D, width W, and thickness T. A method for measuring an insulator film thickness, characterized in that the unknown film thickness D is calculated by calculating the capacitance Cto, the measured capacitance Ct, the width W, and the thickness T.