JPH0882517A - Film thickness monitoring control method - Google Patents

Abstract

PURPOSE: To determine a parameter accurately while reducing time and labor in the determining of the parameter by preserving the frequency of a piezo-electric crystal at the starting point into a film monitoring device at each formation of a film. CONSTITUTION: An evaporation source 2, a substrate 3 desired to form a film, a microbalance sensor 4 comprising a piezo-electric crystal and a film thickness inspection instrument 5 are arranged in a vacuum chamber 1. The evaporation source 2 is connected to a heating power source 6. A film thickness monitoring device 7 preserves the frequency of the piezo-electric crystal of the sensor 4 at the starting point and the frequency of the piezo-electric crystal at the ending point at each formation of a film. On the other hand, an identification number is attached at each formation of a film to measure a film thickness on the substrate 3 actually with the device 5 at a plurality of time points while the frequency of the piezo-electric crystal shifts to a low position from a high position as the formation of films are repeated and actually measured values thereof are inputted into the device 7 corresponding to the film identification number. The device 7 determines an acoustic impedance ratio in the optimum shearing mode and a correction factor in the geometrical position of a quartz crystal and the substrate by the least square.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film thickness on a substrate and a film deposition rate that can be controlled by measuring the deposition of the film on a piezoelectric crystal installed in a film deposition chamber. The present invention relates to a supervisory control method.

[0002]

2. Description of the Related Art A technique called quartz microbalance is widely used to measure the film thickness and the film formation rate of a film formed by vacuum evaporation or sputtering. This utilizes the fact that when a deposit is deposited on the surface of a quartz crystal placed in a chamber during vapor deposition or sputtering, the mass of the crystal increases and, conversely, its response frequency decreases. The relationship between the film thickness tf and the response frequency fc is expressed by the following equation.

In order to display the film thickness at the substrate position on the film thickness monitoring device, the density ρf of the film to be formed, the acoustic impedance ratio z, the correction coefficient to the geometric position of the quartz crystal and the substrate to
oling and three parameters are required, and these three parameters must be determined at the stage of condition setting before starting production. Conventionally, the determination of these parameters has been performed by the following procedure. That is, 1) If the bulk density ρf of the film to be formed and the acoustic impedance ratio z are known, enter the values, and if the acoustic impedance ratio z is unknown, z =
Enter 1. 2) Next, set the tooling to 1, perform film formation several times, and measure the film thickness monitor display and the film thickness on the substrate with another film thickness inspection device, such as a stylus type film thickness meter. Calculate (= measured film thickness / display film thickness). Calculate multiple toolings and enter their average tooling values into the film thickness monitor. 3) At the time of production, the displayed film thickness is sometimes compared with the measured film thickness, and if there is a deviation, the tooling value is corrected. However, in this method, since the acoustic impedance ratio z of the film is slightly different from the bulk acoustic impedance ratio z depending on the film forming conditions, the deviation may increase as the frequency becomes lower.

Further, in order to correct the acoustic impedance ratio z of the film, when the frequency becomes low and the deviation becomes large, the value of z of the film thickness monitoring device is changed so that the displayed value and the actually measured value match. Although a method has been proposed, this method has not been practiced so much because it includes a tooling error in z to be corrected and is laborious.

[0005]

As described above, the methods conventionally proposed have problems that it takes time and labor and sufficient accuracy cannot be obtained. Therefore, an object of the present invention is to provide a film formation monitoring control apparatus capable of reducing the trouble of determining parameters and enabling accurate parameter determination.

[0005]

In order to solve the above-mentioned problems, by measuring the deposition of a film on a piezoelectric crystal installed in a film forming chamber, the film thickness on the substrate and the film forming rate can be determined. The film thickness monitoring control method according to the present invention that can be controlled stores the frequency of the piezoelectric crystal at the start and the frequency of the piezoelectric crystal at the end of each film formation in the film formation monitoring device, The film thickness of the substrate is measured at several points from the start to the end, and the measured values of the plurality of film thicknesses are input to the film formation monitoring apparatus, and the optimum acoustic impedance ratio z and shear mode in the shear mode are calculated by the least square method. It is characterized by determining the correction coefficient tooling of the geometrical positions of the quartz crystal and the substrate.

[0006]

In the film thickness monitoring control method according to the present invention having the above-described structure, the start frequency and the end frequency for each film formation and the RUN NO. Is displayed on the film formation monitoring device and stored internally, and some RUN NO. Measured film thickness value of the substrate corresponding to RUN NO. By inputting the values corresponding to, the optimum acoustic impedance ratio z of the shear mode and the correction coefficient tooling of the geometrical position of the quartz crystal and the substrate are calculated. You will be able to calculate. According to the film thickness monitoring control method of the present invention, it is possible to obtain the optimum tooling and z at the same time by the work that was conventionally performed to obtain the tooling. This eliminates the need to separately obtain the parameters of the acoustic impedance ratio z of the shear mode and the correction coefficient tooling of the geometrical position of the quartz crystal and the substrate, and minimizes the influence of the error of one parameter on other parameters. You will be able to hold it down.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an example of an apparatus for carrying out the film formation monitoring and controlling method of the present invention. Reference numeral 1 denotes a vacuum chamber, inside this vacuum chamber 1, an evaporation source 2, a substrate 3 on which a film is to be formed, A microbalance sensor 4 made of a piezoelectric crystal and a film thickness inspection device 5 such as a stylus film thickness meter are arranged. The evaporation source 2 is connected to a heating power source 6. Reference numeral 7 denotes a film thickness monitor, which inputs a frequency signal from the microbalance sensor 4, another input from the film thickness inspection device 5 which receives film thickness information on the substrate 3, and a control signal to the heating power source 6. It has an output to supply. That is, the film thickness monitoring device 7 stores the frequency of the piezoelectric crystal in the microbalance sensor 4 at the start of each film formation and the frequency of the piezoelectric crystal at the end of each film formation, and the identification number for each film formation. (That is, RUN NO.), The film thickness on the substrate 3 is actually measured by the film thickness inspection device 5 at a plurality of time points during which the frequency of the piezoelectric crystal changes from the high state to the low state as the film formation is repeated. The measured value is input to the film thickness monitoring device 7 in association with the film formation identification number. More specifically, in the film thickness monitoring device 7, the start and end of film formation and the RUN NO. Save and have the following table, Films are formed from a high frequency to a low frequency, and measured values of the film thickness are input at a plurality of points in the meantime, and the least squares is optimal.
Calculate tooling and z. The calculation method is f (z, t
ooli, fc), TOOLi = measured film formation / (f (z, 1, fe)-f
(z, 1, fs)), swing the value of z between 0.001 and 10, Z and TOOL are calculated. Here, fs and fe are the frequency at the start and the frequency at the end, respectively.

As an actual example, comparative examples of the conventional method and the method according to the present invention in the case of depositing aluminum by vapor deposition and the case of depositing SiO 2 by sputtering will be illustrated below. 1) When aluminum film was formed by vapor deposition: A 6 MHz type sensor was used. RUN NO. Should be from 1 to 7,
Film thickness monitor film when new crystal is used up to about 4.7MHz, density is 2.7 bulk aluminum and TOOLING is 0.587 (conventional method from several batches of deposition). The deposition was stopped at about 6 microns thick for each batch. The actually-measured film thickness is a film thickness of the film attached to the substrate at that time, which is actually measured by a stylus method.

In the conventional device shown in Table 1, although the display film thickness of the film thickness monitor shows approximately 5.8 microns, the measured film thickness is reduced from 6.2 microns to 5.5 microns, and the error is It is as large as +5.4 to -5.6%, and it can be seen that the average TOOLING is not enough to minimize the error over the entire area. On the other hand, according to the method of the present invention shown in Table 2, optimum Z-RATIO = 1.26 and TOOLING = 0.
The error is 620, which is +2.5 to -1.9%, which is less than half of the conventional case. Also, since there is almost no variation due to the crystal, there is almost no difference in this error even if the crystal is replaced with a new crystal and vapor deposition is performed next time. It was

2) When the SiO 2 film is formed by sputtering:
The sensor used was a 5 MHz type, and the experimental method was the same as in Example 1).

As can be seen from Tables 3 and 4, Z-RATIO in the conventional method has a bulk value of SiO 2 of 1.07, TOOLIN
G is 0.239 and the error is +5.8 to -9.9%, but with the method according to the invention Z-RATIO is 0.432 and TOOLING is 0.22.
7 is found to be the optimum value, and as a result, the error is +1.4 to-
It's improved by 1.8%. Actually this Z-RATIO and TO
After depositing a new crystal using the OLING value, the error was about the same. From the above specific experimental examples, when forming aluminum by vapor deposition and by sputtering SiO 2
When the bulk values z = 1.08 and z = 1.07 are used in the conventional example, the tooling values deviate as the frequency becomes lower. However, according to the method of the present invention, z = 1.258. , TOOL = 0.620, z = 0.432, TOOL = 0.
It was confirmed that 227 was the optimum value and the tooling value was almost constant.

[0012]

As described above, according to the present invention, the frequency of the piezoelectric crystal at the start and the frequency of the piezoelectric crystal at the end are stored in the film formation monitoring device for each film formation, An identification number on the substrate, measure the film thickness of the substrate at multiple times while the piezoelectric crystal frequency changes from high to low, and input the measured multiple film thickness values to the film formation monitoring device. By the least-squares method, the optimum acoustic impedance ratio z of the shear mode and the correction factor to the geometrical position of the quartz crystal and the substrate to
It's configured to determine oling, so traditional tool
The tooling and z can be obtained by the same operation as used to obtain ing, and the measurement accuracy can be improved. In addition, the same operation is performed for substances for which z is unknown.
It becomes possible to obtain oling and z.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing the configuration of an example of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 1: Vacuum chamber, 2: Evaporation source, 3: Substrate on which film is to be formed, 4: Microbalance sensor made of piezoelectric crystal, 5: Film thickness inspection device such as a stylus type film thickness meter, 6: Power supply for heating, 7: Film thickness monitor.

Claims (1)

[Claims] 1. A method for monitoring and controlling a film thickness, wherein a film thickness on a substrate and a film forming rate can be controlled by measuring a film deposition on a piezoelectric crystal installed in a film forming chamber. The frequency of the piezoelectric crystal at the start and the frequency of the piezoelectric crystal at the end of each film formation are stored in the film formation monitoring device, and an identification number is assigned to each film formation to change the state of the piezoelectric crystal from high to low. During this time, the film thickness of the substrate is measured at a plurality of time points, and the measured values of the plurality of film thicknesses are input to the film formation monitoring apparatus, and the acoustic impedance ratio z in the optimum shear mode and the quartz crystal and the substrate are measured by the least square method. A film thickness monitoring control method characterized by determining a correction coefficient tooling of the geometrical position of.