JPH0333203B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a deposited film thickness monitor that corrects resonance frequency shifts due to temperature changes in a crystal resonator and enables accurate film thickness measurements.

Deposition film thickness monitors using quartz crystal resonators have been widely used to control the thickness and deposition rate of thin film coatings. This utilizes the phenomenon that when a vapor deposited film is deposited on the crystal resonator plate of the AT cut, the resonant frequency of the thickness shear vibration of the crystal resonator shifts according to the thickness of the deposited film. This is to know the thickness of the film.

Conventionally, a film thickness monitor of this type and a film thickness controller using the same were constructed as shown in FIG. That is, the evaporation material jumps out from the evaporation source 14 placed in the vacuum container 16 and is deposited on the substrate 15 and the crystal resonator 2 to form a thin film. The crystal resonator 2 is connected by a lead wire 3 to a resonator 4 placed outside the vacuum, and resonates at a frequency corresponding to the thickness of the deposited film. This resonant frequency is counted by a frequency counter 5, and this counted value is converted into a film thickness by a film thickness calculator 6, which is displayed as a film thickness moment by moment by a display 7. Also, the film thickness calculator 6
The output of is converted into a film formation rate by a differentiator 8,
An error signal with respect to the desired film formation rate is calculated by the comparator 10 and sent to the evaporation source power supply 12, and the power of the evaporation source power supply 12 is varied to keep the deposition rate, that is, the film formation rate constant. It works to control. On the other hand, the film thickness signal from the film thickness calculator 6 is sent to the comparator 9, and when it reaches a preset desired film thickness, a signal is sent to the shutter drive power supply 11, which closes the shutter 13 and removes the evaporated material from the evaporation source. The vapor deposition is terminated at the required film thickness.

The drawbacks of the conventional method are as follows. As is well known, the resonant frequency of the crystal resonator has a large temperature coefficient, so if the temperature of the crystal resonator 2 changes due to radiant heat from the evaporation source 14 or the radiant heat from the heater 17 for heating the substrate, the film thickness will increase. The resonant frequency changes regardless of the change in , which causes errors in film thickness measurements, which in turn causes serious errors in film formation rate control and film thickness end point detection. Particularly in film formation by sputtering, the radiant heat from the evaporation source is large and the film formation rate itself is low, resulting in serious errors in controlling the film formation rate. For example, in an AT-cut crystal resonator with a cut angle of 35°17', when the temperature of the crystal plate increases from 20°C to 100°C, a frequency shift of about 70 ppm occurs. This change corresponds to a film thickness change of 250° when converted to the film thickness of aluminum, for example, and is a major obstacle in precisely controlling the production rate and film thickness.

The present invention provides a film thickness monitor that provides means for correcting film thickness measurement errors due to temperature changes in the crystal resonator, and enables accurate film thickness measurement and precise film formation rate and film thickness control. . The present invention will be explained below using examples.

FIG. 2 shows an embodiment of the present invention. In this embodiment, another crystal resonator 2' is placed close to the crystal resonator 2 for film thickness measurement. The crystal oscillator 2' has a temperature measuring element 2, such as a thermocouple, for example.
0 is attached in sufficient thermal contact and its temperature is measured by a thermometer 21 placed outside the vacuum vessel. Since the crystal resonator 2' is placed in an environment thermally equivalent to that of the crystal resonator 2, its temperature almost accurately represents the temperature of the crystal resonator 2 used for film thickness measurement. A crystal oscillator 2 for film thickness measurement is made to vibrate by a resonator 4 at a resonant frequency corresponding to the deposited film thickness and the temperature of the crystal plate, and the resonant frequency is counted by a frequency counter 5 and sent to a film thickness calculator 6. sent as a signal. The film thickness calculator 6 uses the signal from the thermometer 21 and the pre-stored temperature coefficient of the crystal oscillator to calculate the frequency change with respect to the temperature change of the crystal oscillator 2, and outputs the output signal of the frequency counter 5. The component due to temperature change is removed from , and only the frequency change due to film thickness change is converted into film thickness and displayed on the display 7.

In this way, in this embodiment, with respect to changes in the resonant frequency of the crystal resonator 2, the amount due to the temperature change is corrected, and only the amount due to the change in film thickness is calculated and converted to film thickness. This eliminates the measurement error caused by the comparator 9, and allows the film thickness end point to be detected by the comparator 9, and the film formation rate to be precisely controlled by the differentiator 8, the comparator 10, and the evaporation source power supply 12.

FIG. 3 shows another embodiment of the present invention. In this embodiment, another crystal oscillator 2' is placed close to the crystal oscillator 2 for film thickness measurement, and is connected to a lead wire 3'. It is guided to a resonator 4' placed outside a vacuum, and resonates in a vibration mode, such as contour vibration, in which the resonance frequency does not change or hardly changes depending on the thickness of the deposited film. This resonant frequency is converted into a frequency signal by a frequency counter 5' and sent to a film thickness calculator 6. On the other hand, the crystal oscillator 2 for film thickness measurement resonates at a frequency corresponding to the deposited film thickness and temperature, as in the embodiment shown in FIG. The signal is sent to the arithmetic unit 6.

As mentioned above, the signal from the frequency counter 5' depends only on the temperature and not on the film thickness, so the signal from the frequency counter 5'
The temperature coefficient of the crystal oscillator 2' in the vibration mode stored in advance in the crystal oscillator 2'
The temperature of the crystal oscillator 2 is calculated, and this temperature is regarded as the temperature of the crystal oscillator 2. From the value of the temperature coefficient in the vibration mode of the crystal oscillator 2, which is also stored in advance, the change in the resonant frequency of the crystal oscillator 2 is calculated. Of this, the portion due to temperature change is calculated, removed from the overall frequency change, converted to film thickness, and displayed on display 7. In this way, also in this embodiment, the frequency change due to temperature change is corrected, allowing accurate film thickness measurement and control.

FIG. 4 shows another embodiment of the invention. In this embodiment, the temperature of the crystal resonator 2 is directly measured. The crystal resonator 2 is alternately connected by a switch 31 to two resonators 4 and 4' placed outside the vacuum by a lead wire 3. The connection switching is controlled by the film thickness calculator 6. The resonator 4 causes the crystal oscillator 2 to resonate in a thickness-shear vibration mode in which the resonant frequency changes depending on the thickness of the deposited film, while the resonator 4' has a resonant frequency that does not depend on the thickness of the deposited film or almost does not depend on the thickness of the deposited film. The crystal resonator 2 is made to resonate in another independent vibration mode. The switch 32 connects the input signal to the frequency counter 5 with the output of the resonator 4 and the resonator 4'.
Switch 3 works to alternately switch to the output of
1 and switch 32 repeatedly switch connections in synchronization with each other. In the first half of the switching period of these switches, the crystal oscillator 2 is connected to the resonator 4'
The frequency counter 5 is connected to the resonator 4'
connected to. During this half cycle, the frequency counter 5 counts the resonant frequency that depends only on the temperature, regardless of the film thickness of the crystal resonator 2, and sends a signal to the arithmetic unit 6.
The calculator 6 calculates the temperature change of the crystal oscillator 2 using the pre-stored temperature coefficient in this vibration mode of the crystal oscillator 2, and calculates the change in the resonant frequency of the thickness shear vibration with respect to that temperature. Remember.

In the latter half of the switching period of the switch, the crystal oscillator 2 is connected to the resonator 4, and the frequency counter 5 is connected to the resonator 4. At this time, the frequency counter 5 counts the resonance frequency of the thickness shear vibration of the crystal resonator 2. This resonance frequency includes a portion depending on the thickness of the deposited film of the crystal resonator 2 and a portion depending on the temperature. This signal is sent to the arithmetic unit 6, and the frequency change calculated and stored in the first half of the cycle is corrected by the frequency change due to temperature change, and the frequency change, which is only due to the film thickness, is converted into film thickness and displayed. displayed on the display 7. While repeating the above cycle, the film thickness from time to time is corrected for temperature changes and accurately measured, making it possible to accurately detect the end point and control the film formation rate.

As described above, according to the present invention, it is possible to correct the frequency change of the crystal oscillator by the frequency change due to temperature change every moment, and it is possible to accurately measure the film thickness, detect the end point, and control the film formation rate. becomes.

Therefore, the present invention greatly contributes to the manufacture of semiconductor devices and the like, and can be said to be extremely useful industrially.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a method of film thickness monitoring, film thickness end point detection, and film formation rate control using a crystal oscillator according to the prior art. FIG. 2 shows a first embodiment of the invention, FIG. 3 shows a second embodiment of the invention, and FIG. 4 is a block diagram showing a third embodiment of the invention. 1...Film thickness monitor, 2 and 2'...Crystal resonator, 3 and 3'...Lead wire, 4 and 4'...
Resonators, 5 and 5'... Frequency counter, 6...
... Arithmetic unit, 7 ... Display, 8 ... Differentiator, 9 and 10 ... Comparator, 11 ... Shutter drive power supply,
12... Evaporation source power supply, 13... Shutter, 14... Evaporation source, 15... Substrate, 16... Vacuum container, 17... Substrate heating heater, 20... Temperature probe, 31 and 32... Switch.

Claims (1)

[Claims] 1. The resonant frequency of the crystal resonator, which changes depending on both the thickness of the deposited film formed on the crystal resonator and the temperature of the crystal resonator, is measured. The temperature of the vibrator or its vicinity is also measured, and the change in the resonant frequency based on the temperature change calculated from the measured temperature is subtracted from the previously measured resonant frequency to obtain only the film thickness change. In a crystal film thickness monitor that calculates the underlying resonant frequency change and converts it into a film thickness change, it measures only the temperature "at or near the crystal oscillator" regardless of the film thickness. 1. A crystal film thickness monitor characterized in that the resonance frequency of a crystal resonator is changed in a vibration mode different from the above-mentioned resonance frequency by changing the resonance frequency. 2 The resonance frequencies of the two vibration modes mentioned above are
A quartz crystal film thickness monitor according to claim 1, wherein both are obtained from a single quartz crystal resonator. 3 The resonant frequencies of the two vibration modes mentioned above,
The quartz film according to claim 1, wherein one of the quartz films is obtained from one quartz oscillator and the other from another quartz oscillator placed in the vicinity thereof. thickness monitor.