JPH0611445A - Light intensity measuring device - Google Patents

Abstract

PURPOSE:To provide a multi-channel light intensity measuring device, which is applied to a thin film fabricating device etc. and senses a plurality of light beams having different wavelengths, wherein the measurement can be made possible even with a weak incoming signal by removing likely influence of the temperature drift. CONSTITUTION:A rotary disc 12 is equipped with a plurality of interfering filters 12a-12d, wherein the space between the filters is used as a light shield part, and a plurality of circuit channels to process the sensing signals given by a photo-sensor 15 having a photoelectric transducing function are furnished in correspondence with respective filters. Each of these channels includes sample hold circuits 31-34 to hold the offset signal when the light shield part lies in the light takein position of the photo-sensor, other sample hold circuits 35-38 to hold the sensing signal when any filter exists in that position, and subtracting devices 39-42 to determine the difference between the two types of sample hold circuits. The light intensity is determined on the basis of the output signals from these subtracting devices.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light intensity measuring device,
In particular, the present invention relates to a light intensity measuring device which is applied to a monitor in a thin film manufacturing technique such as a molecular beam epitaxy device and has a configuration for measuring emission intensity of a plurality of different wavelengths and which can compensate temperature drift due to a circuit element. .

[0002]

2. Description of the Related Art In a thin film forming technique, Japanese Patent Application Laid-Open No. Sho 5-5 has been used as an example of a conventional structure of a light intensity measuring device used for a monitor.
9-9911, JP-A-59-9929, JP-A-61-292538, JP-A-62-2472.
There is one disclosed in each of the 31 publications.

The film quality monitoring method of Japanese Patent Laid-Open No. 59-9911 is configured to measure the light emission amount of a light emitting chemical species and the light emission amount of an ion of a light emitting chemical species in plasma and obtain the ratio thereof. . For this reason, it has a lens for detecting plasma emission, a filter disc, a detector, and an electric circuit system configuration, and while rotating the filter disc with a motor, the detection target is synchronized with the filter disc, and It has a configuration in which it is detected separately and stored in a memory.

The plasma monitor disclosed in JP-A-59-9929 has the same apparatus configuration as that disclosed in JP-A-59-9911. That is, a rotary plate having two types of filters is provided, the rotary plate is rotated by a motor, light passing through the filter is converted into a current by a photoelectric converter, and the light intensity is measured by the current value. Light of different wavelengths obtained by each filter is processed by a common circuit channel.

The plasma monitor disclosed in Japanese Patent Laid-Open No. 61-292538 has three interference filters, separates the light with an optical fiber and guides it to each interference filter, and the light transmitted through each interference filter is converted into the corresponding light. It is configured to detect with a detector.

The plasma monitor of Japanese Patent Laid-Open No. 62-247231 is equipped with a plurality of rotating plates, the light to be measured is guided by an optical fiber to the location where the rotating plates are present, and the light is transmitted by one of the interference filters. A light detector detects the intensity of light. The rotary plate is provided with a plurality of interference filters having different transmission wavelengths along the circumference. The detection signal relating to the light transmitted through any one of the interference filters of the rotating plate is subjected to signal processing in a common circuit channel for the plurality of interference filters.

[0007]

None of the above-mentioned conventional monitor light intensity measuring devices takes into consideration the problem of temperature drift that occurs in circuit elements such as operational amplifiers.
Therefore, the offset voltage is included in the measured signal. As a result, there is a problem particularly in accurately measuring the intensity of weak light. In other words, an operational amplifier or the like is generally used to amplify the output of the photodetector. This operational amplifier has a characteristic of temperature drift. When detecting faint light, the detection signal also becomes small, so it is necessary to increase the multiplication factor of the operational amplifier.
However, the higher the amplification factor of the operational amplifier, the more the temperature drift is amplified, and the greater the influence on the light intensity measurement, which is a problem.

In view of the above problems, an object of the present invention is to eliminate the influence of temperature drift and to measure weak signals in a multi-channel light intensity measurement configuration for detecting a plurality of lights having different wavelengths. An object is to provide a light intensity measuring device.

[0009]

A light intensity measuring device according to the present invention converts a light transmitted through one of a plurality of interference filters having a rotating plate having a plurality of interference filters having different transmission wavelengths into a current. A photodetector, which has a configuration for obtaining the intensity of light of each wavelength based on the detection signal of the photodetector, the rotating plate has a light shielding portion between the plurality of interference filters,
A plurality of circuit channels for processing the detection signal output by the photodetector are provided corresponding to each of the interference filters, and each of the plurality of circuit channels has an offset signal when the light shielding part is present at the light receiving position of the photodetector. And a second sample and hold circuit that holds a detection signal when an interference filter is present at the light receiving position, and a subtractor that finds the difference between the first and second sample and hold circuits. And is configured to obtain the light intensity based on the output signal of the subtractor.

In the above configuration, preferably, a switching circuit for selecting and extracting a signal obtained in each of the plurality of circuit channels and transmitting it to an arithmetic processing circuit for calculating the light intensity, and a rotating operation of the rotating plate. A timing signal generating circuit for generating a timing signal synchronized with the first and second sample and hold circuits, a switching circuit, etc., to give a predetermined operation timing for measuring a plurality of lights having different wavelengths. Configured to give.

[0011]

The light intensity measuring device according to the present invention comprises a plurality of interference filters arranged along the circumference in the configuration of a rotary type filter, and the space portion between the interference filters on the rotary plate is used as a light shielding part. , A circuit channel for processing each detection signal corresponding to each interference filter is individually provided, and the detection signal corresponding to the light transmitted through each circuit channel and the offset signal in the light-shielded state are held, and the difference between the two signals is held. The component related to the temperature drift is removed from the measurement signal corresponding to the light of each wavelength.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The light intensity measuring device according to the present embodiment is included in the structure of the vapor deposition rate monitor in the quaternary vapor deposition device. This vapor deposition rate monitor employs an optical filter rotation method in which measurement is performed in a time-division method when measuring four channels.

In the vapor deposition apparatus shown in FIG. 1, 1 is a vacuum container, 2 is a quadruple electron gun, and 3 to 6 are power supplies for electron guns. Reference numeral 7 is a sensor for monitoring the state of vacuum vapor deposition. As an example of the sensor 7, for example, the sensor disclosed in Japanese Patent Publication No. 3-59140 by the present applicant is used. In the following description, the sensor 7 is a CCES sensor (Cold Cathode discharged induced Emission Spectroscopy).
scopy). The CCES sensor 7 is used for the purpose of strictly controlling the composition ratio of the multi-component system. A hollow pipe 8 guides the excitation light generated by the CCES sensor 7 to a target position. The pipe 8 extends through the observation window 9 of the vacuum container 1 to the filter rotary detector 10.

The filter rotation type detector 10 has two rooms 10A and 10B. The two rooms 10A and 10B are kept in a dark room state, and the respective internal spaces are connected via a hole 11. The room 10A is provided with a rotary plate 12 having a plurality of interference filters, a DC servo motor 13 for rotating the rotary plate 12, and a rotary encoder 14 for measuring the amount of rotation of the DC servo motor 13. The pipe 8
The leading end of the is inserted into the room 10A and is arranged so as to face the rotary plate 12. The rotation operation of the DC servo motor 13 is
It is controlled by a controller (not shown). Room 10B
A photodetector 15 and a current / voltage converter 16 are arranged in the photodetector. A photomultiplier tube is used for the photodetector 15, and converts the incident light into an electric current. The position of the interference filter on the rotary plate 12, the position of the hole 11 and the position of the photodetector 15 are arranged on the same straight line, and are set in a corresponding relationship. Pipe 8
The light transmitted by (1) can be transmitted through one of the interference filters of the rotary plate 12 and can enter the photodetector 15.

A front view of the rotary plate 12 is shown in FIG. The rotary plate 12 includes, for example, four interference filters 12a to 12d.
Are provided at equal intervals. The transmission wavelength of each interference filter is designed to be different. Interference filters 12a-12
d is arranged on a line along the circumference of the rotary plate 12, and the space between the interference filters is used as a light shield.

Regarding the electric circuit system, 21 to 24 are variable gain amplifiers, and 25 is a timing signal generator. Each of the variable gain amplifiers 21 to 24 includes a current / voltage converter 16
Output signal is input. The pulse signal output from the rotary encoder 14 is input to the timing signal generator 25. 31 to 34 are offset voltage holding circuits, and 35
˜38 are interference filter transmission signal holding circuits. All of these circuits 31 to 38 are sample and hold circuits. 39 to 42 are subtractors, 43 is a switch, 44 is A
A / D converter, 45 is an arithmetic processing circuit. The holding operation of each of the offset voltage holding circuits 31 to 34 and the interference filter transmission signal holding circuits 35 to 38, and the switching operation of the switch 43 are performed by receiving a timing signal from the timing signal generator 25 and performing predetermined timing.

The operation of the light intensity measuring device having the above configuration will be described. Four kinds of substances evaporated from the quadruple electron gun installed in the vacuum container 1 pass through the CCES sensor 7. During this passage, the CCES sensor 7 is excited based on the magnetron discharge phenomenon and emits light peculiar to the substance. CCES
The excitation light generated by the sensor 7 is guided through the hollow pipe 8 to the location where the rotary plate 12 of the filter rotary detector 10 is present. The rotary plate 12 has the four interference filters 12a to 12d as described above. The transmission wavelengths of the interference filters 12a to 12d are different from each other. The light guided to the location of the rotary plate 12 by the pipe 8 is transmitted or blocked by the rotation of the DC servomotor 13 in accordance with the location of the rotary plate 12 that reaches the position corresponding to the tip of the pipe 8. . That is, the excitation light is in any one of a state in which it is transmitted by any one of the plurality of interference filters and dispersed, or a state in which the excitation light is blocked by any light shielding portion between the interference filters. The photodetector 15 outputs an amount of current corresponding to the amount of incident light according to each of the transmitted state and the blocked state.

Therefore, when the light that has been transmitted through the interference filters 12a to 12d and separated into the light enters the photodetector 15, the photodetector 15 outputs a current corresponding to the amount of incident light. On the other hand, when the light is blocked by the light blocking portion of the rotary plate 12, no light is incident on the photodetector 15, so
In principle, no current is output from the photodetector 15. However, when the light is shielded by the light shielding portion, a current flows in the electric circuit portion of the signal processing due to the temperature drift of the circuit element.

The current output from the photodetector 15 is converted into a voltage by the current / voltage converter 16. The output voltage of the current / voltage converter 16 is amplified to an appropriate level by any of the variable gain amplifiers 21 to 24 corresponding to each interference filter. The gains set in the variable gain amplifiers 21 to 24 are different from each other. After that, the output signals of the variable gain amplifiers 21 to 24 are given to the offset voltage holding circuits 31 to 34 and the interference filter transmission signal holding circuits 35 to 38 respectively corresponding thereto. As is clear from the circuit configuration, a set of offset voltage holding circuit and interference filter transmission signal holding circuit are associated with each of the variable gain amplifiers 21 to 24. In other words, each interference filter is provided with a variable gain amplifier and a circuit channel for processing a detection signal by the pair of offset voltage holding circuit and interference filter transmission signal holding circuit.

The timing signal generation circuit 25, which receives the pulse signal from the rotary encoder 14, generates a command for data acquisition, and the command is supplied with the offset voltage holding circuits 31-34 and the interference filter transmission signal holding circuits 35-3.
Give to each of the eight. Each of the holding circuits 31 to 38 that received the data fetching command sequentially holds a light-shielding signal and a light-receiving signal in a set of one offset voltage holding circuit and one interference filter transmission signal holding circuit. To do. Regarding a set of one offset voltage holding circuit and one interference filter transmission signal holding circuit, the output signal of each holding circuit is input to the corresponding subtractor of the subtracters 39 to 42, and the subtractor subtracts the offset voltage holding circuit. The difference between the output of the circuit and the output of the interference filter transmission signal holding circuit is obtained. Therefore, each of the subtractors 39 to 42 subtracts the light-shielding signal from the light-incident signal for the light of the corresponding wavelength, whereby the temperature of the current / voltage converter 16 and the variable gain amplifiers 21 to 24 is reduced. The offset voltage caused by the drift can be removed.

Thereafter, the output signals of the subtractors 39 to 42 are input to the switch 43. The switch 43 receives the timing signal from the timing signal generation circuit 25, sequentially selects the channels for which the sample and hold have been completed, and brings the switch circuit into the conductive state. The analog signal passed through the switch 43 is converted into a digital signal by the A / D converter 44. The obtained digital signal is input to the arithmetic processing unit 45. The arithmetic processing unit 45 calculates the vapor deposition rate based on the measurement data regarding the intensity of light of each wavelength.
The calculated result is displayed on a display device (not shown) as numerical data of vapor deposition rate.

As is clear from the above description, in the light intensity measuring device applied to the deposition rate monitor, by removing the offset voltage generated in the current / voltage converter 16 and the variable gain amplifiers 21 to 24 from the measurement signal, The temperature drift component contained in the measurement signal can be removed. Therefore, the accuracy of the measurement signal can be improved.

Further, in the configuration of this embodiment, the variable gain amplifier, the offset voltage holding circuit, the interference filter transmission signal holding circuit, and the subtractor are provided in a set corresponding to each of the four interference filters. Therefore, considering that there is a difference in the intensity of the light emitted by the CCES sensor 7 depending on the type of the vaporized substance, the interference filters 12a to 12a.
The measurement cycle can be shortened by changing the gain of the corresponding variable gain amplifier according to the amount of light passing through d. That is, when there is only one set of the variable gain amplifier, the offset voltage holding circuit, the interference filter transmission signal holding circuit, and the subtractor, the rotary plate 1
While it is necessary to change the gain of the variable gain amplifier in synchronism with the rotation operation of No. 2 and to wait for the measurement signal to stabilize after changing the gain, in the configuration of this embodiment as described above, No need arises. As a result, it is possible to measure light emission with a relatively low response speed, which is suitable for a vapor deposition rate monitor or the like.

[0024]

As is apparent from the above description, according to the present invention, the temperature is controlled by the action of the light shielding portion of the rotary plate having a plurality of interference filters, which is constituted by being applied to a multi-source deposition rate monitor or the like. Since the offset voltage caused by the drift is measured and the offset voltage is removed from the measurement signal corresponding to each channel, the weak signal can be accurately measured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a vapor deposition rate monitor including a light intensity measuring device according to the present invention.

FIG. 2 is a front view of a rotating plate including a plurality of interference filters.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum container 2 ... 4 electron guns 3-6 ... Electron gun power supply 7 ... CCES sensor 8 ... Pipe 10 ... Filter rotation type detector 12 ... Rotation plate 13 ... DC servo motor 14 ... Rotary encoder 15 ... Photodetector 16 ... Current / voltage converter 21-24 ... Variable gain amplifier 31-34 ... Offset voltage holding circuit 35-38 ... Interference filter transmission signal holding circuit 39-42 ... Subtractor 43 ... Switcher

Claims (2)

[Claims] 1. A rotating plate provided with a plurality of interference filters having different transmission wavelengths, a photodetector for converting light transmitted through any one of the plurality of interference filters into an electric current, and a detection signal of the photodetector. In the light intensity measuring device for obtaining the intensity of light of each wavelength based on, the rotating plate has a light shielding part between the plurality of interference filters, the circuit channel for processing the detection signal of the photodetector the interference. A plurality of circuit channels provided corresponding to each of the filters, each of the plurality of circuit channels holding a offset signal when the light shielding portion is present at the light receiving position of the photodetector;
A second sample and hold circuit that holds the detection signal when the interference filter is present at the light receiving position; and a subtractor that finds the difference between the first and second sample and hold circuits. A light intensity measuring device, wherein the light intensity is obtained based on an output signal. 2. The light intensity measuring device according to claim 1, wherein a switching circuit for selecting and extracting a signal obtained in each of the plurality of circuit channels and transmitting the signal to an arithmetic processing circuit, and a rotating operation of the rotating plate. A timing signal generating circuit for generating a timing signal in synchronization with each other, and applying the timing signal to the first and second sample-hold circuits and the switching circuit, and a predetermined operation timing for measuring operation of a plurality of lights having different wavelengths. A light intensity measuring device characterized in that it is configured to give.