JPS62203335A - Etching monitor apparatus - Google Patents

Abstract

PURPOSE:To monitor the etching by comprising a mechanism for squeezing the laser beam to the size less than the scribe line width, a means for detecting reflected reference light intensity for the incident light, an incident light chopper and a predetermined lock-in amplifier. CONSTITUTION:A laser beam emitted from an oscillation tube 1 is chopped 2 by the frequency higher than the noise, it is then squeezed to the width less than the width of scribe line 16 through an expansion and condenser lenses 3 and 6, and the substrate 13 is irradiated with the laser beam through a glass window 12 of a chamber 11. The laser beam is partly extracted by a half-mirror 4, it is then condensed 7, laser beam intensity is sensed by a sensor 8, the reflected reference beams of front and rear surfaces of substrate 13 are extracted with the half-mirror 5, it is then condensed 7, and intensity is sensed by the sensor 9. Both signals are divided in analog 10, relative intensity is sensed, and the light beam is rectified 18, smoothed 19 and monitored through the lock-in amplifier 17. The amplifier 17 outputs only the signal having the same frequency and phase as those of the chopper. The etching comes to the end when reflected reference beam intensity is no longer changed. According to this structure, the etching condition may be monitored by avoiding variation of reflected reference beam intensity or high frequency noise.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an etching monitor device for monitoring the etching state of a semiconductor thin film.

(Prior Art) In recent years, with the demand for higher integration of semiconductor devices, semiconductor devices are moving toward three-dimensional multilayer structures, and etching apparatuses with high etch rates have appeared. When etching a semiconductor thin film under such circumstances, it is important to detect the end point of etching and to control the etching depth to a predetermined value in order to prevent overetching.

Conventionally, as this type of monitoring device, devices using emission spectrometry, gas analysis, impedance measurement, laser interferometry, etc. are known. However, according to emission spectroscopy, gas analysis, and impedance measurement, if the etching area is small.

The amount of change in the measured quantity at the end of etching was small, making it difficult to determine whether etching was complete. On the other hand, the laser interference method does not cause the above problem because it directly monitors the etching state of the laser beam irradiated area.

The laser interferometry described above produces a transparent thin film or a semi-transparent thin film (for example, 5in2.Poly-5i) to be etched, and the light intensity of this reflected interference light changes periodically with respect to the thickness of the thin film, while the thin film is completely etched. This method takes advantage of the phenomenon that once the etching is etched, the above-mentioned interference does not occur, and therefore the light intensity does not change.In other words, the etching depth can be detected by periodic changes in the reflected interference light intensity. The completion of etching can be confirmed when the light intensity stops changing.

Further, if the thin film to be monitored is a transparent film or a semi-transparent film, the end point of etching can be detected with a single laser oscillation tube. Furthermore, by using a laser tube that oscillates a beam with a predetermined intensity, reflected interference light with sufficient light intensity compared to plasma light in a vacuum chamber can be obtained, ensuring that the beam is not affected by noise or disturbance. The etching condition can be monitored.

Conventional monitoring devices that utilize laser interferometry with the above-mentioned characteristics require that a monitoring substrate, on which no pattern is printed, be placed on a sample stage in a vacuum processing chamber in order to obtain the reflected interference light. In addition, a monitor boat was purposely installed on the board.

(Problems to be Solved by the Present Invention) However, since the etching characteristics are different between the above-mentioned monitor substrate and the substrate on which the etching process is actually performed, it is difficult to determine the exact etching depth and end point of etching. The detection of is due to.

In addition, as mentioned above, special processes are required such as placing the monitor board on the sample stage and creating a monitor port on the board, which may require changes to equipment or the need to place the monitor board on the sample stage. However, there was a problem in that throughput deteriorated and productivity decreased.

Furthermore, no measures were taken to prevent fluctuations in the intensity of the laser beam and vibrations and high-frequency noise inherent in the device, which caused detection errors.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional drawbacks and to provide an etching monitor device capable of accurately detecting the etching depth and the end of etching.

(Means for Solving the Problems) In order to achieve the above object, the present invention is an etching monitor device that monitors the etching state of a semiconductor thin film using laser interference method. A beam aperture mechanism that focuses the beam to less than the width of the drawn scribe line.

The configuration includes a light intensity detection mechanism that detects the relative intensity of the reflected interference light with respect to the incident laser beam, and a lock-in amplifier that detects only the reflected interference light that has the same frequency and the same phase as a chopper that chops the incident laser beam. ing.

(Function) The laser beam chopped by the chopper 2 has a spot diameter narrowed down to a width of 16 scribe lines or less by the beam expander 3 and the condensing lens 6, and then the laser beam is chopped by the chopper 2.
3 is irradiated. The intensity of the incident light is detected by the photo sensor 8 via the half mirror 4 and the condensing lens 7, while the reflected interference light from the substrate 13 is reflected and interfered by the photo sensor 9 via the half mirror 5 and the condensing lens 7'. The light intensity of the light is detected. The above two detection signals are then input to an analog divider circuit 10, which monitors periodic changes in light intensity via a lock-in amplifier 17 that detects only reflected interference light having the same frequency and phase as the chopper 2. I can do it.

(Example) FIG. 1 shows an embodiment of the present invention.

1 is a laser oscillation tube (for example, a He-Ne laser),
2 is a chopper, 3 is a beam expander 14, 5 is a half mirror, 16, 7, 7' are condensing lenses, 8, 9 are photosensors, 1o is an analog divider circuit, 11 is a process chamber, 12 is a chamber wall 13 is a substrate, 14 is a layer to be etched, and 15 is a resist mask.

16 is a scribe line.

The laser oscillation tube 1 is oscillated, and the laser light emitted from it is set at a frequency sufficiently higher than the frequency of noise (comparatively low frequency in normal equipment) that is vibrating at an amplitude harmful to measurements in the equipment. Chimiping is performed using chopper 2.

The chopper 2 has the effect of shortening the irradiation time of the laser beam onto the substrate 13, and can prevent the photoexcitation effect from promoting etching in the irradiated areas more than in the non-irradiated areas. However, if the optical excitation effect adversely affects the determination of etching completion or etching depth, the wavelength of the laser used may be changed.

And the laser beam chopped as above is 2
The spot diameter is narrowed down to the middle or below of the scribe line 16 drawn on the substrate 13 by the combination of the beam expander 3 consisting of two lenses and the condensing lens 6.
For example, the light is irradiated toward the substrate 13 through a glass window 12 installed in the process chamber 11 with a diameter of 50 μm.

On the other hand, among the half mirrors 4 and 5 disposed between the beam expander 3 and the condensing lens 6, the half mirror 4 has a fixed proportion of the emitted laser light that is transmitted to the photosensor 8.
The laser beam is arranged so as to be reflected toward the laser beam, and the reflected beam is condensed by a condenser lens 7, and a photosensor 8 detects the light intensity of the laser beam. on the other hand.

The half mirror 5 reflects reflected interference light generated by interference between the laser beam reflected on the surface of the substrate 13 and the reflected light from the back surface of the substrate, and sends the reflected interference light to the photo sensor 9 via the condenser lens 7'.
The light intensity of the reflected interference light is detected.

Then, by inputting the above two signals to the analog division circuit 9, it becomes possible to detect the relative intensity of the reflected interference light with respect to the intensity of the incident laser light, and monitor it via the lock-in amplifier 17. This makes it possible to avoid erroneous measurements of the etching state due to fluctuations in the intensity of laser radiation.

In addition, when the laser beam is chopped by the chopper 2 as described above, the same frequency as that of the chopper 2
A lock-in amplifier 17, which is adjusted to output only signals of the same phase, performs signal processing in synchronization with the chopper 2.

This makes it possible to avoid erroneous measurements caused by relatively low-frequency device vibrations, and also avoid erroneous measurements caused by high-frequency noise.

In addition, the output of the lock-in amplifier 17 is rectified by 18 degrees and smoothed by 19.
What is doing is converting the output from the lock-in amplifier 16 to DC
This is to facilitate the subsequent processing.

FIG. 2 shows an etching monitor device 22 according to the present invention.
is assembled into a parallel plate type dry etching chamber, and FIG. 3 is an enlarged view of the main part thereof.

Reference numeral 20 in the figure indicates an X disposed in the process chamber 11.
- Y stage, and the etching monitor device 22 is
It is placed on the XY stage 2o.

A scribe line 16 is drawn on the substrate 13,
In order to position the laser beam irradiation section on the line 16, the following operation is performed.

That is, the substrate 13 is irradiated with a laser beam narrowed down to a spot diameter of, for example, 50μ, and then the X-Y stage 20 is driven by the stepping monitor 21°21'.
A laser beam is scanned over an area several meters square or wide, which corresponds to the size of a chip.

Based on the difference in the intensity of the reflected interference light at that time, we found a sedge fly plan (approximately 100 μm in width) that was uniformly etched over a relatively wide area on the substrate 12, and the X-Y stage 2° was stopped directly above it. let

After performing the above operations and positioning the laser beam, etching is started.

When the thin film is a transparent or semi-transparent film such as 5in2 or Po1y-5i, the laser beams reflected from the front and back surfaces of the thin film cause interference, and the intensity varies with the film thickness as shown in Figure 4. changes periodically with respect to When this device is used as an etching end detection device, etching may end when the intensity of the reflected interference light no longer changes. Furthermore, since the change period of reflection interference is (laser wavelength)/(2X refractive index), it is also possible to calculate the etching rate during etching. Furthermore, according to the following formula, ΣRti-tj・(ti-tj) = etching depth R
ti-tj: The etching depth can be determined from the etching rate during the time ti-tj or the total amount of phase change from the start of etching. Through the above operations,
The lock-in amplifier 17 has the same frequency as the chopper 2.
Adjusted to output only signals of the same phase.

In FIG. 4, a rotatable reflecting mirror is used to control the direction of the laser beam.

The same reference numerals are used for the same components as in FIGS. 1 to 3, and the explanation thereof will be omitted.

The laser beam emitted from the laser oscillation tube 1 is totally reflected by the parallel and rotatable reflection mirror 23 and is incident on the substrate 13 . The irradiation position of the laser beam is
It is determined by adjusting the angle and position of the reflecting mirror 23. The reflected light from the substrate 13 is totally reflected by a reflecting mirror 24 that can be moved in parallel and rotated, and is focused on a photosensor 9 via a condensing lens 7'. Then, the laser beam irradiation section can be positioned on the scribe line 16 based on the difference in intensity of the detected reflected interference light.

The above purpose can be achieved even if the reflection mirrors 23 and 24 are moved only by rotation on one side.

Note that the analog division circuit 10 described above may digitize the output from the photosensor 8 or 9 and process it with a microcomputer.

In addition, if reflection on the front and back surfaces of the glass window 12 into which the laser beam is incident will complicate data analysis, it is advisable to apply anti-reflection treatment to the laser beam used on both surfaces of the glass.

In addition, laser light or reflected interference light is transmitted to photosensors 8 and 9.
Although the half mirrors 4 and 5 reflect the light in the same direction, they do not necessarily have to be half mirrors, and may be any mirror that can transmit and reflect incident light at a constant rate.

The etching monitor device described above is applicable not only to dry etching but also to monitoring the state of thin film formation in sputtering, which is a thin film forming process, such as CVD.

(Effects of the Invention) According to the configuration of the present invention, it is possible to monitor the etching state by laser interference method without placing a monitor wafer or providing a part of the monitor on the wafer, and at the same time, it is possible to monitor the etching state by laser interference method, and at the same time, it is possible to monitor the etching state by the laser interference method. This makes it possible to avoid misjudgments based on vibrations of devices, high frequency noise, etc.

[Brief explanation of drawings]

FIG. 1 is a principle explanatory diagram of the main structure of the first embodiment of the present invention, and FIG. 2 shows a state in which the apparatus according to the present invention mounted on an X-Y stage is installed in a dry etching apparatus. Fig. 3 is an enlarged view of the main part of Fig. 2, Fig. 4 is a schematic diagram of S i
FIG. 5 is a diagram showing the correlation between the thickness of the O2 film and the intensity of the reflected interference light. FIG. 5 is a diagram explaining the principle of the main structure of the present invention, showing the state in which the direction of the laser beam is controlled using a reflecting mirror. 1-11-Ser oscillator tube, 2----Chopper, 3
-111 beam expander, 4.5---half mirror 16,7,7'---1 condensing lens, 8.9---
--Photo sensor, 10---Analog division circuit,
11-111 process chamber, 12----glass window. 13---One substrate, 14---One layer to be etched, 15
-1 resist mask, 16 scribe lines,
1 '7----o Twin-in amplifier, 20----
X - Y stage, 21.21' ---- Stepping motor, 23.24 - One reflection mirror. FIG, 2 (Fubo Tsuru) Procedural amendment (spontaneous) October 1986 270 1985 Patent Application No. 45991 2 Name of the invention Etching monitor device 3 Relationship with the case of the person making the amendment Patent applicant address 5-8-1 Yotsuya, Fuchu-shi, Tokyo Name: Nichiden Anelva Co., Ltd. (1 other person) Representative: Yasu 1) Susumu 4, Agent address: 5-8-16 Yotsuya, Fuchu-shi, Tokyo, Page 5 of the specification subject to amendment The first line says "Change of equipment".
Changes in board patterns and equipment" should be corrected.

Claims (2)

[Claims] (1) In an etching monitor device that monitors the etching state of a semiconductor thin film using laser interferometry, there is a beam diaphragm mechanism that narrows the spot diameter of the laser beam to less than the width of the scribe line drawn on the substrate, and a reflection mechanism for the incident laser beam. Etching characterized by comprising a light intensity detection mechanism that detects the relative intensity of interference light, and a lock-in amplifier that detects only reflected interference light having the same frequency and phase as a chopper that chops incident laser light. Monitor device. (2) The etching monitor device according to claim 1, further comprising a direction control mechanism for controlling the direction of incidence or reflection of the laser beam having a narrowed spot diameter.