KR102341835B1 - Film thickness sensor - Google Patents

Abstract

[Problem] To provide a film thickness sensor with excellent thermal shock characteristics.
[Solutions] A film thickness sensor according to one embodiment of the present invention includes a crystal oscillator.
The crystal oscillator is composed of an AT-cut crystal oscillator having a film-forming surface having a surface roughness (Ra) of 0.4 µm or less and a load length ratio (tp) of 95% or more at a cut level of 50%. . It is preferable that the load length ratio tp at 50% of the cut level of the said film-forming surface is 97 % or more, and it is preferable that the surface roughness Ra of the said film-forming surface is 0.25 micrometer or less.

Description

Thickness sensor {FILM THICKNESS SENSOR}

The present invention relates to a film thickness sensor used in a film forming process.

BACKGROUND ART Conventionally, in a film forming apparatus such as a vacuum vapor deposition apparatus, a technique called a quartz crystal microbalance (QCM) method is used in order to measure the thickness and the film forming rate of a film formed on a substrate. This method utilizes that the resonant frequency of the crystal oscillator disposed in the chamber decreases due to an increase in mass due to deposition of the deposit. Therefore, by measuring the change in the resonant frequency of the crystal oscillator, it becomes possible to measure the film thickness and the film formation speed.

In this kind of thickness sensor, the resonance frequency of the crystal oscillator gradually decreases with the increase in the film deposition amount, and when a predetermined frequency is reached, the frequency fluctuation becomes large enough that stable thickness measurement cannot be performed. For this reason, when the resonance frequency is lowered by more than a predetermined value, it is judged that the service life has expired, and the crystal vibrator is replaced. In order to facilitate the exchange, for example, in Patent Document 1, a plurality of quartz plates having a resonance frequency of 5 MHz are held, and the quartz plates to be used can be individually switched. A configured sensor head is described.

On the other hand, this type of film thickness sensor has a problem that the measured value of the film formation rate fluctuates greatly due to thermal shock characteristics. For example, when the crystal oscillator is switched using a sensor head as described in Patent Document 1, or when the shutter that shields the evaporator is opened, the crystal oscillator receives instantaneous radiant heat from the evaporator, and the frequency characteristic of the crystal oscillator fluctuates greatly. There are cases. In order to improve such a problem, for example, Patent Document 2 discloses that the surface roughness (Ra) of the film-forming surface of the crystal resonator is set to a predetermined level or less, and accordingly, the thermal shock characteristics of the crystal resonator are reduced. is said to be improved.

[Patent Document 1] Japanese Patent Laid-Open No. 2003-139505 [Patent Document 2] Publication No. WO2015/182090

In recent years, in film forming apparatuses such as vacuum vapor deposition apparatuses, high precision of the film thickness sensor is required. In particular, the thermal shock characteristics have a large influence on the film formation rate and control of the film thickness, so the development of a film thickness sensor with excellent thermal shock characteristics is difficult. is becoming a priority. However, merely reducing the surface roughness of the crystal oscillator is still insufficient to improve the thermal shock characteristics, and further improvement is required. In addition, although the SC cut type or IT cut type crystal vibrator has the advantage that it is relatively excellent in thermal shock characteristics, it is different from a general-purpose crystal vibrator such as the AT cut type. Since it is comparatively expensive, there exists a problem which causes the cost increase of a film thickness sensor.

In view of the above circumstances, an object of the present invention is to provide a film thickness sensor that is excellent in thermal shock characteristics and can suppress cost increase.

In order to achieve the above object, the present inventor sets the surface roughness (Ra) of the film-forming surface of the crystal vibrator to a predetermined level or less, and when the load length ratio tp at the cutting level of 50% is greater than or equal to a predetermined level, It was found that the thermal shock characteristics of the vibrator were significantly improved.

That is, the thickness sensor according to one embodiment of the present invention includes a crystal vibrator.

The crystal oscillator is composed of an AT cut crystal oscillator having a film-forming surface having a surface roughness Ra of 0.4 µm or less and a load length ratio tp of 95% or more at a cut level of 50%.

It is preferable that the load length ratio tp at 50% of the cut level of the said film-forming surface is 97 % or more. Moreover, it is preferable that the surface roughness (Ra) of the said film-forming surface is 0.25 micrometer or less.

The crystal oscillator may be constituted by a crystal oscillator having a cutting orientation of 3°05'±03' with respect to the r-plane of the crystal.

The fundamental oscillation frequency of the crystal oscillator is not particularly limited, and is typically 4 MHz, 5 MHz, or 6 MHz.

The said film-forming surface may be comprised with a metal film. The metal film is typically an Ag film or an Au film.

The crystal oscillator may have a plano-convex shape in which the film-forming surface is a flat surface. Thereby, a vibrator with low equivalent resistance and easy to vibrate can be obtained.

As mentioned above, according to the film thickness sensor of this invention, it is excellent in a thermal shock characteristic, and cost increase can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which shows the film-forming apparatus provided with the film-thickness sensor which concerns on one Embodiment of this invention.
Fig. 2 is a schematic cross-sectional view showing the configuration of the thickness sensor.
3 is a block diagram showing the configuration of a measurement unit in the film forming apparatus.
4 is a front view schematically showing the film-forming surface of the crystal oscillator in the film thickness sensor, and B is a rear view thereof.
It is a figure which shows an example of the thermal shock characteristic of the said crystal diaphragm.
It is a figure which shows an example of the thermal shock characteristic of the said crystal diaphragm.
Fig. 7 is an enlarged view of a principal part showing an example of a film-forming surface of the crystal diaphragm.
It is a schematic diagram of the correction explaining the cut angle of a general AT cut board|substrate.
Fig. 9 is a diagram showing an example of the thermal shock characteristics of the crystal diaphragm.
Fig. 10 is a diagram showing an example of the thermal shock characteristics of the crystal diaphragm.
It is a figure which shows an example of the thermal shock characteristic of the said crystal diaphragm.
Fig. 12 is a diagram showing an example of thermal shock characteristics of the crystal diaphragm.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which shows the film-forming apparatus provided with the film-thickness sensor which concerns on one Embodiment of this invention. The film-forming apparatus of this embodiment is comprised as a vacuum vapor deposition apparatus.

The film forming apparatus 10 of the present embodiment includes a vacuum chamber 11 , an evaporation source 12 disposed inside the vacuum chamber 11 , and a substrate holder 13 facing the evaporation source 12 ; It has a thickness sensor 14 disposed inside the vacuum chamber 11 .

The vacuum chamber 11 is connected with the vacuum exhaust system 15, and it is comprised so that it can exhaust and maintain the inside by a predetermined reduced pressure atmosphere.

The vapor deposition source 12 is comprised so that it is possible to generate|occur|produce the vapor|steam (particles) of a vapor deposition material. In the present embodiment, the vapor deposition source 12 constitutes an evaporation source from which vapor deposition particles are emitted by heating and evaporating a metal material, a metal compound material, or an organic material. The type of the evaporation source is not particularly limited, and various methods such as resistance heating type, induction heating type, electron beam heating type are applicable.

The substrate holder 13 is configured such that it is possible to hold the substrate W as a film formation target, such as a semiconductor wafer or a glass substrate, toward the deposition source 12 .

The film thickness sensor 14 incorporates a crystal oscillator having a predetermined fundamental frequency (natural frequency), and constitutes a sensor head for measuring the film thickness and the film formation rate of the deposited film on the substrate W, as will be described later. The film thickness sensor 14 is inside the vacuum chamber 11 , and is disposed at a position facing the evaporation source 12 . The film thickness sensor 14 is typically arranged in the vicinity of the substrate holder 13 .

The output of the thickness sensor 14 is supplied to the measurement unit 17 . The measurement unit 17 measures the film thickness and the film formation rate based on the change in the resonant frequency of the crystal oscillator, and controls the deposition source 12 so that the film formation rate becomes a predetermined value. For the relationship between the frequency change and the mass load due to the adsorption of QCM, Sauerbrey's equation shown in the following equation (1) is used.

In Equation (1), ΔFs is the amount of change in frequency, Δm is the amount of change in mass, f ₀ is the fundamental frequency, ρ _Q is the density _{of the crystal, μ Q} is the shearing stress of the crystal, and A is The electrode area and N respectively represent an integer.

The film forming apparatus 10 further has a shutter 16 . The shutter 16 is disposed between the evaporation source 12 and the substrate holder 13, and opens or It is configured to be capable of shielding.

Opening and closing of the shutter 16 is controlled by a control unit (not shown). Typically, at the start of vapor deposition, the shutter 16 is closed until emission of vapor deposition particles from the vapor deposition source 12 is stabilized. Then, when the emission of the deposited particles is stabilized, the shutter 16 is opened. Thereby, the vapor deposition particle|grains from the vapor deposition source 12 arrive at the board|substrate W on the board|substrate holder 13, and the film-forming process of the board|substrate W is started. At the same time, the vapor-deposited particles from the vapor deposition source 12 reach the film thickness sensor 14, and the film thickness of the vapor-deposited film on the substrate W and its film-forming rate are monitored.

[Behind the scenes sensor]

Then, the detail of the film thickness sensor 14 is demonstrated. 2 is a schematic cross-sectional view of the thickness sensor 14 .

As shown in FIG. 2, the film thickness sensor 14 has the crystal oscillator 20 and the case 140 which supports the crystal oscillator 20 so that vibration is possible. The crystal oscillator 20 is a plano convex (flat convex) in which the surface 21 as a film forming surface is a flat surface, and the reverse surface 22, which is the opposite surface, is a convex surface. have a shape The crystal oscillator 20 is accommodated in the case 140 so that the film-forming surface thereof faces the evaporation source 12 .

Moreover, the film thickness sensor 14 is in contact with the electrode film 32 (FIG. 4B) of the periphery of the back surface 22 of the crystal vibrator 20 inside the case 140 . A plurality of biasing members 141 and a retaining member in contact with the electrode film 31 (FIG. 4A) on the periphery of the surface 21 of the crystal vibrator 20 (142). The biasing member 141 is made of a conductive material such as a metal that is electrically insulated from the case 140 , and is electrically connected to an oscillation circuit 41 , which will be described later. The holding tank 142 constitutes the periphery of the opening of the case 140 exposing the surface 21 of the crystal vibrator 20 toward the evaporation source 12 . The case 140 and the holding tank 142 are made of a conductive material such as metal, and are electrically connected to the oscillation circuit 41 .

The thickness sensor 14 is not limited to the structure which holds the single crystal vibrator 20, You may be comprised so that holding the some crystal vibrator 20 is possible. In this case, although not shown in figure, the some crystal oscillator is rotatably hold|maintained on the same circumference in a case. The case is provided with a single opening for exposing a crystal oscillator positioned at an arbitrary rotation angle to an evaporation source, and a switching mechanism for selectively switching the crystal oscillator facing the opening is provided. .

[Measurement unit]

Next, the measurement unit 17 will be described.

3 is a schematic block diagram showing an example configuration of the measurement unit 17 . The measurement unit 17 includes an oscillation circuit 41 , a measurement circuit 42 , and a controller 43 .

The oscillation circuit 41 oscillates the crystal oscillator 20 of the film thickness sensor 14 . The measurement circuit 42 is for measuring the resonance frequency of the crystal oscillator 20 output from the oscillation circuit 41 . The controller 43 acquires the resonant frequency of the crystal oscillator 20 for each unit time through the measurement circuit 42 , the deposition rate of the vapor deposition material particles on the substrate W and the deposition film deposited on the substrate W Calculate the thickness of the Furthermore, the controller 43 controls the deposition source 12 so that the film formation rate becomes a predetermined value.

The measuring circuit 42 includes a mixer circuit 51 , a lowpass filter 52 , a low frequency counter 53 , a high frequency counter 54 , and a reference signal generating circuit 55 . The signal output from the oscillation circuit 41 is input to the high frequency counter 54, and first, an approximate value of the oscillation frequency of the oscillation circuit 41 is measured. The approximate value of the oscillation frequency of the oscillation circuit 41 measured by the high-frequency counter 54 is output to the controller 43 . The controller 43 oscillates the reference signal generating circuit 55 with a reference frequency (for example, 5 MHz) of a frequency close to the measured approximate value. The signal of the frequency oscillated at this reference frequency and the signal output from the oscillation circuit 41 are input to the mixer circuit 51 .

The mixer circuit 51 mixes two types of input signals, and outputs them to the low-frequency counter 53 through the low-pass filter 52 . Here, assuming that the signal input from the oscillation circuit 41 is cos((ω+α)t) and the signal input from the reference signal generator circuit is cos(ωt), in the mixer circuit 51, cos(ωt)· An alternating-current signal expressed by the expression cos((ω+α)t) is generated. This formula is a form obtained by multiplying cos(ωt) and cos((ω+α)t), and the AC signal represented by this formula is a signal of a high-frequency component expressed by cos((2·ω+α)t) It is the same as the sum of the signals of the low-frequency components expressed by and cos(αt).

The signal generated by the mixer circuit 51 is input to the low-pass filter 52, the high-frequency component signal cos((2·ω+α)t) is removed, and only the low-frequency component signal cos(αt) is output by the low-frequency counter 53 ) is entered. That is, in the low-frequency counter 53, the absolute value |α| of the frequency of the difference between the signal cos((ω+α)t) of the oscillation circuit 41 and the signal cos(ωt) of the reference signal generator circuit 55 . A low-frequency component signal is input.

The low frequency counter 53 measures the frequency of the signal of this low frequency component, and outputs the measured value to the controller 43 . The controller 43 calculates the frequency of the signal output by the oscillation circuit 41 from the frequency measured by the low frequency counter 53 and the frequency of the output signal of the reference signal generating circuit 55 . Specifically, when the frequency of the output signal of the reference signal generating circuit 55 is smaller than the frequency of the output signal of the oscillation circuit 41, the frequency of the low-frequency component signal is added to the output signal of the oscillation circuit 41 and vice versa, it is subtracted.

For example, when the measured value of the oscillation frequency of the oscillation circuit 41 by the high frequency counter 54 exceeds 5 MHz and the reference signal generator circuit 55 oscillates at a frequency of 5 MHz, the reference signal generator circuit The oscillation frequency of (55) is lower than the actual oscillation frequency of the oscillation circuit 41 . Therefore, in order to obtain the actual oscillation frequency of the oscillation circuit 41, the frequency |α| of the low-frequency component signal obtained by the low-frequency counter 53 may be added to the set frequency of the reference signal generator circuit 55 at 5 MHz. . If the frequency |α| of the low-frequency component is 10 kHz, the correct oscillation frequency of the oscillation circuit 41 is 5.01 MHz.

Although the resolution of the low-frequency counter 53 has an upper limit, the resolution can be assigned to measure the difference frequency |α|, so the oscillation frequency of the oscillation circuit 41 with the same resolution Compared to the case of measuring , accurate frequency measurement can be performed.

In addition, since the oscillation frequency of the reference signal generating circuit 55 is controlled by the controller 43, and the oscillation frequency can be set so that the difference frequency |α| is smaller than a predetermined value, the low frequency counter ( 53) can be effectively utilized. The obtained frequency value is stored in the controller 43 . The controller 43 calculates the film thickness and the film formation rate of the vapor deposition material deposited on the substrate W by using the arithmetic expression shown in the above equation (1) from the obtained frequency value.

[Crystal Oscillator]

Then, the detail of the crystal oscillator 20 is demonstrated. 4A and 4B are a front view and a rear view of the crystal vibrator 20, respectively.

On the front surface 21 and the back surface 22 of the crystal oscillator 20, electrode films 31 and 32 having a predetermined shape are respectively formed. The electrode layer 31 contacts the holding tank 142 , and the electrode layer 32 contacts the biasing member 141 . The electrode films 31 and 32 are formed in different shapes as indicated by shaded portions in A and B of FIG. 4 , but the shapes of the electrode films 31 and 32 are not limited to the illustrated examples. The electrode films 31 and 32 are each formed of a metal film such as gold (Au) or silver (Ag).

The crystal vibrator 20 oscillates in a thickness-shear vibration mode by applying a high-frequency voltage to the electrode films 31 and 32 through the oscillation circuit 41 . For the crystal oscillator 20 of the present embodiment, a crystal oscillator having a fundamental frequency of 5 MHz or 6 MHz at 25°C is used.

In addition, the fundamental frequency of the crystal oscillator 20 is not limited to 5 MHz, and a crystal oscillator having an arbitrary frequency less than 5 MHz (eg, 4 MHz, 3.25 MHz, 2.5 MHz, etc.) as the fundamental frequency is applicable. do. Alternatively, a crystal oscillator having an arbitrary frequency exceeding 5 MHz (eg, 6 MHz, etc.) as the fundamental frequency may be used.

The back surface 22 of the crystal vibrator 20 is formed of a curved surface having a predetermined radius of curvature. When the back surface 22 is configured as a curved surface, the series resistance of the crystal oscillator 20 is reduced, and the crystal oscillator 20 can be stably vibrated at a desired fundamental frequency. The radius of curvature of the back surface 22 is not particularly limited, and can be appropriately set according to the diameter of the crystal vibrator 20 or the like. In the crystal vibrator 20 of this embodiment, the diameter is 12.4 mm, and the radius of curvature of the back surface 22 is 100 mm - 200 mm.

[Thermal shock properties of crystal oscillators]

In this type of film thickness sensor, there is a problem that the measured value of the film formation rate fluctuates greatly due to thermal shock characteristics. The thermal shock characteristics referred to herein are, for example, due to the local temperature change of the crystal oscillator when the crystal oscillator is switched over or when the shutter that shields the evaporator is opened, and when the radiant heat from the evaporator is instantaneously received. It means a temporary fluctuation of the measurement frequency, and the greater the fluctuation amount of the frequency, the lower the film formation rate and the measurement accuracy of the film thickness. Experiments simulating this are shown in FIGS. 5 and 6 . The amount of change (ΔF) in frequency with the start and end of heat input is observed. The frequency fluctuation that is not caused by the temperature change of the entire vibrator but only this heat input is defined as the thermal shock characteristic.

Here, it is known that the thermal shock characteristic of a crystal vibrator is improved by making the surface roughness Ra of the film-forming surface of a crystal vibrator into a predetermined|prescribed or less. For example, in Fig. 5, the thermal shock characteristics of the crystal oscillator sample 6M-1 (fundamental frequency 6 MHz, cut angle θ = 35°15'±20') having a surface roughness (Ra) of 0.37 µm on the film-forming surface, The thermal shock characteristics of the crystal oscillator sample 6M-2 (fundamental frequency 6 MHz, cut angle θ = 35°15'±20') having a surface roughness (Ra) of 0.43 µm on the film-forming surface are compared and shown. The same figure shows the frequency change when thermal radiation is applied to the film-forming surface side of the crystal oscillator with a 30 W halogen lamp, and the lamp is turned on after 10 seconds from the start of the measurement, and the lamp is turned off after 40 seconds from the start of the measurement. ) was made. As shown in the figure, the sample 6M-1 with a small surface roughness Ra has a small frequency change and is excellent in thermal shock characteristics.

In addition, as described above, although a metal film (electrode film 31) is provided on the film-forming surface, since the thickness of the electrode film 31 is as thin as about 150 nm, the surface roughness Ra of the film-forming surface is the electrode film. It is evaluated as the surface roughness (Ra) of (31).

In recent years, high precision of the film thickness sensor has been demanded, and in particular, the thermal shock characteristics have a large influence on the film formation rate and the control of the film thickness. However, merely reducing the surface roughness of the crystal vibrator is still insufficient to improve the thermal shock characteristics, and further improvement is required.

On the other hand, in the present inventor, the thermal shock characteristics of the crystal vibrator can be significantly improved by setting the load length ratio tp at 50% of the cut level to be higher than or equal to a predetermined level while setting the surface roughness Ra of the film-forming surface of the crystal vibrator to a predetermined level or less. found to be improved. That is, the thermal shock characteristics of the crystal resonator are largely related not only to the surface roughness Ra of the film-forming surface, but also to the load length ratio tp, and even if the surface roughness Ra is suppressed to be small, the load length ratio tp ) is less than a predetermined value, the thermal shock characteristics tend to deteriorate on the contrary.

For example, Fig. 6 shows the thermal shock characteristics of a crystal oscillator sample 6M-3 (fundamental frequency 6 MHz, cut angle θ = 35°15'±20') having a surface roughness Ra of 0.34 µm on the film-forming surface. . Test conditions were the same as in the example of FIG. 5 . The load length ratio (tp) at 50% of the cut level of Sample 6M-3 is 80.2%, which is low compared to 95.2% of Sample 6M-1 and 95.5% of Sample 6M-2.

Although the surface roughness (Ra) of sample 6M-3 is smaller than that of samples 6M-1 and 6M-2, the frequency change is, as shown in FIGS. 5 and 6, samples 6M-1, 6M-2 getting worse. As described above, it is confirmed that the load length ratio at the cut level of 50% of the film-forming surface has a large correlation with the thermal shock characteristics of the crystal oscillator.

In addition, the surface roughness (Ra, Ry, Ra) of each of the above-mentioned samples 6M-1, 6M-2, and 6M-3 and the load length ratio (tp) at a cutting level of 50% are shown collectively in Table 1.

Here, Ra is the arithmetic mean illuminance, Ry is the maximum height, and Rz is the 10-point average illuminance (JIS B 0601-1994).

In surface roughness, the reference plane of height data is calculated|required by the least square method, and the difference between the reference plane and the height data of each point is computed as roughness.

Surface roughness (Ra) can be calculated|required by summing up and averaging the absolute values of the deviation from a reference plane to a measurement curved surface.

The surface roughness Ry can be calculated|required by the sum of the height Yp from a reference plane to the highest mountaintop, and the depth Yv to the lowest trough.

The surface roughness (Rz) is "average of the absolute values of the elevations of the 5th to the 5th peak from the highest mountain" and "the average of the absolute values of the elevations of the 5th to the 5th valley bottoms" It can be obtained by the sum of '.

The load length ratio (tp) at the cutting level 50% is the ratio of the ratio to the reference plane of the sum of the cutting areas obtained when the roughness curved surface is cut at the cutting level parallel to the peak surface (50% of Ry) as a percentage can be saved

In this specification, each said value was measured using the surface roughness summation (KEYENCE CORPORATION controller VK-9500/measuring instrument 9510). The same applies to the description below.

The crystal vibrator 20 of the present embodiment has a surface roughness (arithmetic mean roughness: Ra) of 0.4 µm or less, and a film-forming surface (surface 21) having a load length ratio tp of 95% or more at a cutting level of 50%. )) has

When the surface roughness (Ra) of the film-forming surface exceeds 0.4 µm, even when the load length ratio (tp) is 95% or more, compared to that when the surface roughness (Ra) is 0.4 µm or less, the frequency change at the time of thermal shock is increased (see samples 6M-1 and 6M-2). In addition, when the load length ratio tp of the film-forming surface is less than 95%, even when the surface roughness Ra is 0.4 µm or less, compared with that of 95% or more, the load length ratio tp is 95% or more. The frequency change is large (see samples 6M-1 and 6M-3).

In addition, when sample 6M-1 and sample 6M-3, which have almost the same surface roughness (Ra), are compared, from the ratio of ΔF of both (390/580: 67%), sample 6M-1 is that of sample 6M-3. An improvement in ΔF of about 33% is recognized. This is because the load length ratio tp of the sample 6M-1 is higher than that of the sample 6M-3, and from this, a remarkable effect on the ΔF reduction of the load length ratio tp is recognized.

The effect of this load length ratio (tp) is similarly recognized for sample 6M-2 having a higher surface roughness (Ra) than sample 6M-3, and from the ratio of ΔF between them (480/580: 83%), sample 6M- 2, ΔF is improved by about 17% for sample 6M-3.

The lower limit of the surface roughness (Ra) is not particularly limited, but the smaller the value of the surface roughness (Ra), the smaller the frequency change during thermal shock can be suppressed, while the processing of the film-forming surface becomes difficult and processing The cost tends to increase. For this reason, the lower limit of the surface roughness Ra can be made into 0.19 micrometer, for example. Thereby, a crystal vibrator excellent in thermal shock resistance can be obtained, suppressing an increase in processing cost.

The method of obtaining the said film-forming surface is not specifically limited, Typically, after rough-polishing to the thickness in which the desired fundamental frequency is obtained with the double-sided lapping machine using free abrasive grain, medium grinding|polishing Process the quartz plate in the order of (中硏磨) and final polishing.

Although it is preferable that the said film-forming surface is a mirror surface, as mentioned above, mirror finishing normally requires a large processing cost. For this reason, rather than uniformly finishing the entire film-forming surface to a mirror surface, a part of the film-forming surface is polished to a mirror surface or near-mirror surface.

Specifically, as the finish polishing, for example, abrasive grains having a particle size of about #1000 to #2000 are used, and only the protruding portion (mountain portion) of the surface is polished off. . If necessary, chemical polishing may be used in combination. In addition, the processing direction or the processing pressure may be adjusted in stages. By such a processing method, the film-forming surface which has the said surface roughness Ra and the load length ratio tp can be obtained.

An example of the surface state when the film-forming surface of the crystal oscillator 20 of this embodiment is enlarged 150 times in FIG. 7 is shown. In the drawings, reference numeral S corresponds to a mirror surface or a region in a state close to the mirror surface (hereinafter referred to as a mirror surface portion). As shown in the figure, it can be seen that the mirror-surface portions S are discretely present in a part of the film-forming surface.

As the crystal oscillator 20, typically, an AT cut-type crystal oscillator (cut angle θ = 35°15'±20') having relatively excellent temperature characteristics is used. In addition, as the crystal oscillator 20, an SC-cut crystal oscillator (cut angle θ = 33°30'±11', φ = 20°25'±6°) that has superior temperature characteristics than the AT cut may be used, but usually , SC-cut substrates are expensive compared to AT-cut substrates, thus resulting in high cost of the film thickness sensor. For this reason, it is preferable to use the AT cut board|substrate for the crystal oscillator 20. As shown in FIG.

A typical AT cut substrate has an angle of 35°15' with respect to the Z-axis (growth axis) around the X-axis (electrical axis) of the crystal, as shown in Fig. 8B. It is formed by cutting out. On the other hand, the r-plane (plane index (01-11)) and the R-plane (plane index (10-11)) forming a predetermined angle with respect to the Z-axis of the crystal are, as shown in FIG. 8A , They are alternately positioned as if drawing a regular hexagon around the Z axis. The angles of the r-plane and the R-plane with respect to the Z-axis are 38°13' in both cases, as shown in FIG. 8B .

In order to obtain an actual crystal oscillator, it is necessary to cut a crystal piece from the crystal to obtain a blank. In this case, since the quartz blank becomes thin, the Z-axis becomes unclear. However, since the r-plane of the crystal can be confirmed, a quartz blank can be cut out using this r-plane as a reference. The cut angle of the AT cut substrate with respect to this r-plane is (38°13')-(35°15') = 2°58'.

Among the AT cut substrates, the crystal vibrator having a cut angle θ of 35°08'±03' (the cutting direction with respect to the r-plane is 3°05'±03') has a temperature drift of the resonance frequency from room temperature (25°C). Since it can suppress to 20 ppm or less in the range of 80 degreeC vicinity, it is excellent in thermal shock resistance. Thereby, frequency measurement can be stabilized, and high-precision film thickness monitoring and film-forming rate control can be implement|achieved.

[Experimental example]

Subsequently, an experimental example using a crystal oscillator having a fundamental frequency of 5 MHz will be described.

The present inventors prepared crystal oscillators with a fundamental frequency of 5 MHz having film-forming surfaces of various surface roughnesses shown in Table 2, and evaluated such thermal shock characteristics. In this experimental example, the allowable value of the frequency fluctuation due to thermal shock is 300 Hz, and the sample with ΔF value of 300 Hz or more is “×”, and the sample with ΔF value of 200 Hz or more and less than 300 Hz is “Δ” and ΔF. The sample whose value is less than 200 Hz was evaluated as "(circle)". In order to realize high-precision film thickness monitoring and control of the film formation rate, the value of ?F is preferably less than 300 Hz, and more preferably less than 200 Hz.

(Experimental Example 1)

A surface roughness (Ra) of 0.23 µm and a load length ratio (tp) of 98.4% at a cut level of 50%, an Au film of about 150 nm in thickness was deposited as an electrode film, 12.4 mm in diameter, and a curvature of 200 mm A plano convex crystal oscillator sample (cut angle θ = 35°08'±03' (cutting orientation with respect to the r-plane 3°05'±03')) 5M-1 was prepared. And as a result of measuring the frequency change when thermal radiation was applied to the film-forming surface side of sample 5M-1 with a 30 W halogen lamp, the frequency change amount (DELTA)F was about 140 Hz. The thermal shock properties of sample 5M-1 are shown in FIG. 9 .

(Experimental Example 2)

A crystal oscillator sample 5M-2 having the same configuration as in Experimental Example 1 was prepared, except that the surface roughness (Ra) of the film-forming surface was 0.19 µm and the load length ratio (tp) at 50% of the cutting level was 97.0%, Experimental Example 1 The frequency change during thermal shock was measured under the same conditions as As a result of the measurement, the frequency change amount (ΔF) was about 140 Hz.

(Experimental Example 3)

A crystal oscillator sample 5M-3 having the same configuration as in Experimental Example 1 was prepared except that the surface roughness (Ra) of the film-forming surface was 0.19 µm, the load length ratio (tp) at 50% of the cut level was 72.2%, and the curvature was 100 mm. , The frequency change during thermal shock was measured under the same conditions as in Experimental Example 1. As a result of the measurement, the frequency change amount (ΔF) was about 300 Hz. The thermal shock properties of sample 5M-3 are shown in FIG. 10 .

(Experimental Example 4)

The surface roughness (Ra) of the film-forming surface is 0.28 µm, the load length ratio (tp) at 50% of the cutting level is 76.9%, the cut angle θ = 35°15'±20' (the cutting direction with respect to the r-plane is 2°58 Except for '±20'), a crystal oscillator sample 5M-4 having the same configuration as in Experimental Example 1 was prepared, and the frequency change during thermal shock was measured under the same conditions as in Experimental Example 1. As a result of the measurement, the frequency change amount (ΔF) was about 330 Hz. The thermal shock properties of sample 5M-4 are shown in FIG. 11 .

(Experimental Example 5)

The surface roughness (Ra) of the film-forming surface is 0.25 µm, the load length ratio (tp) at 50% of the cutting level is 99.0%, the cut angle θ = 35°15'±20' (the cutting direction with respect to the r-plane is 2°58 Except for '±20'), a crystal oscillator sample 5M-5 having the same configuration as in Experimental Example 1 was prepared, and the frequency change during thermal shock was measured under the same conditions as in Experimental Example 1. As a result of the measurement, the frequency change amount (ΔF) was about 280 Hz. The thermal shock properties of sample 5M-5 are shown in FIG. 12 .

It was confirmed that the crystal oscillators according to samples 5M-1 to 5M-5 had a small frequency change at the time of thermal shock compared with the crystal oscillator having a fundamental frequency of 6 MHz described above (see Tables 1 and 2).

Further, according to samples 5M-1, 5M-2, and 5M-5, the surface roughness (Ra) of the film-forming surface is 0.4 µm or less, and the load length ratio (tp) at 50% of the cut level is 95% or more, Compared with 5M-3 and 5M-4, the frequency change amount (ΔF) is small. Among these, according to samples 5M-1 and 5M-2 having a surface roughness (Ra) of 0.23 μm or less, it is confirmed that the frequency change amount (ΔF) can be further reduced and suppressed to half the size of that of sample 5M-5 became

Among these, the load length ratio tp at 50% of the cut level of the film-forming surface is preferably 97% or more, and the surface roughness Ra of the film-forming surface is preferably 0.25 µm or less.

Here, when sample 5M-4 and sample 5M-5 having almost similar surface roughness (Ra) are compared, from the ratio of ΔF of both (280/330:85%), sample 5M-5 is An improvement in ΔF of about 15% is recognized. This is because the load length ratio tp of the sample 5M-5 is higher than that of the sample 5M-4, and from this, the advantage of reducing the ΔF of the load length ratio tp is recognized.

In addition, when comparing sample 5M-1 and sample 5M-3 having the same cutting orientation, from the ratio of ΔF of both (140/300:47%), sample 5M-1 has a ΔF of about 53% with respect to sample 5M-3 improvement is recognized. In this example, a remarkable effect on the reduction in ?F of the load length ratio tp is recognized.

On the other hand, in the sample 5M-1, the ΔF is improved by 50% compared to the sample 5M-5, although the load length ratio tp is deteriorated. This is due to the difference in the cutting orientation of the two samples, and from this, the superiority of the crystal vibrator with a cut angle θ of 35°08'±03' (3°05'±03' with respect to the r-plane) is recognized. do.

As described above, according to the present embodiment, it is possible to obtain a film thickness sensor excellent in thermal shock characteristics. Thereby, for example, high-precision film-forming rate measurement or film-thickness measurement that is less affected by thermal radiation when the crystal oscillator is switched or the shutter of the deposition source is opened is attained.

Further, according to the present embodiment, by managing the load length ratio tp of the film-forming surface of the crystal vibrator, it is possible to stably manufacture a crystal vibrator having desired vibration characteristics. In particular, a quartz crystal vibrator excellent in thermal shock properties can be manufactured relatively inexpensively without mirror-finishing the film-forming surface or using an expensive quartz plate such as an SC-cut substrate.

As mentioned above, although embodiment of this invention was described, this invention is not limited only to embodiment mentioned above, It goes without saying that various changes can be added.

For example, in the above embodiment, as the crystal vibrator 20, a plano convex crystal vibrator was described as an example, but the present invention is not limited thereto, and the present invention is also applicable to a crystal vibrator composed of flat surfaces.

In addition, in the above embodiment, although the vacuum vapor deposition apparatus was mentioned as an example and demonstrated as a film-forming apparatus, it is not limited to this, This invention is applicable also to other film-forming apparatuses, such as a sputtering apparatus. In the case of a sputtering apparatus, the organic material source is constituted by a sputtering cathode including a target made of an organic material.

10 … film forming device
11 … vacuum chamber
12 … vapor source
13 … substrate holder
14 … behind the scenes sensor
16 … shutter
17 … measuring unit
20 … crystal oscillator
W … Board

Claims (8)

An AT-cut crystal oscillator having a film-forming surface with a surface roughness (Ra) of 0.19 µm in the lower limit and 0.4 µm in the upper limit, and a load length ratio (tp) of 95% lower limit and 99.0% upper limit at 50% cut level.
A behind-the-scenes sensor comprising a. According to claim 1,
When the surface roughness (Ra) of the film-forming surface is 0.25 μm,
The load length ratio (tp) at 50% of the cut level of the film-forming surface is 99.0%
behind the scenes sensor. According to claim 1,
When the surface roughness (Ra) of the film-forming surface is 0.23 μm,
The load length ratio (tp) at 50% of the cut level of the film-forming surface is 98.4%
behind the scenes sensor. 4. The method of claim 3,
The crystal oscillator is composed of a crystal oscillator having a cutting orientation of 3°05'±03' with respect to the r-plane of the crystal.
behind the scenes sensor. 4. The method according to any one of claims 1 to 3,
The fundamental oscillation frequency of the crystal oscillator is 5 MHz or 6 MHz
behind the scenes sensor. 4. The method according to any one of claims 1 to 3,
The film-forming surface is composed of a metal film
behind the scenes sensor. 7. The method of claim 6,
The metal film is an Ag film or an Au film
behind the scenes sensor. 4. The method according to any one of claims 1 to 3,
The crystal oscillator has a plano-convex shape in which the film-forming surface is a flat surface.
behind the scenes sensor.

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