JPH066797B2 - Etching end point detection method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an etching end point detection method, and more particularly to an end point detection method suitable for highly accurate end point detection.

[Background of the Invention]

Conventionally, in this type of apparatus, as described in Japanese Patent Laid-Open No. 53-138943, the material to be etched is irradiated with light or polarized light to detect the reflected light, and the change in the reflected light is detected to perform etching. There is a control to stop the reflected light, but since the reflected light change is captured in the entire surface to be etched, the diffraction of light due to the miniaturization of the element (device)
No consideration was given to the influence of reflected light due to scattering and interference.

In addition, JP-A-54-97371 and JP-A-55.
As described in Japanese Patent Publication No. 3634, there is a control in which etching is stopped by visual observation of the color of a substance to be etched by light in an etching gas atmosphere. There was no consideration given to the effects of fluctuations in equipment and automation of equipment.

Further, as described in JP-A-55-104482, the layer being etched is irradiated with a light beam, and the reflected light is monitored by an appropriate detector to automatically detect the end point. Although some are configured, no consideration was given to the case where the allowable overetching time is as short as several seconds or the case where the etching discharge is stopped at the just etch point.

[Object of the Invention]

An object of the present invention is to provide an etching end point detection method which eliminates the above-mentioned drawbacks of the prior art and can detect the end point of reproducibly with high accuracy and automatically with respect to etching of devices that are becoming finer. To do.

[Outline of Invention]

In order to achieve the above object, the present invention takes in a pattern of a wafer surface during etching as an image signal by an image sensor, extracts only an image signal of a scribe line on the wafer from the image signal, and extracts the image signal waveform Is a method for determining the etching end point based on the change in the monitor signal by obtaining the integrated value of the etching process and monitoring it according to the etching process.The detection signal with a high SN ratio is used to detect the end point with high accuracy and reproducibility. It is a thing.

Example of Invention

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the apparatus used in this embodiment.
A parallel plate electrode composed of a lower electrode 2 and an upper electrode 3 is installed in the etching processing chamber 1. A high frequency power source 4 is connected to the lower electrode 2, and the opposing upper electrode 3 is at ground potential. Further, a part of the upper electrode 3 is a mesh 3a, and a transparent glass window 6 is provided in a part of the etching processing chamber 1 so that the wafer 5 placed on the lower electrode 2 can be observed from above. is there. Further, the surface of the wafer 5 is imaged on the image sensor 11 through the lens 7, the half mirror 8, the color filter 9, and the cylindrical lens 10 which are installed above the glass window 6.

The image signal from the image sensor 11 is input to the etching end point determination control device 14. The etching end point determination control device 14 includes an analog-digital converter (A / D converter) 14
a, a memory 14b, and a computer 14c. The image signal from the image sensor 11 is converted into a digital signal by the A / D converter 14a and stored in the memory 14b.
The computer 14c has a function of determining the end point of etching from this digital signal and outputting an end detection signal.

The output of the etching end point determination control device 14, that is, the end point detection signal is input to the high frequency power source 4,
Control the output to control the etching. On the other hand, it is arranged so that the light emitted from the illumination lamp 12 is spread by the lens 13 and is irradiated onto the surface of the wafer 5 via the half mirror 8.

In the above-described configuration, an etching gas is supplied to the etching processing chamber 1 from a gas supply device (not shown), and the inside of the etching processing chamber 1 is exhausted by an exhaust device (not shown) while maintaining a constant pressure (0.5 High frequency power supply 4
When high frequency power (for example, 13.56 MHz) is applied to the lower electrode 2 to generate glow discharge between the lower electrode 2 and the upper electrode 3, the surface of the wafer 5 is etched by ion radicals in the plasma.

Next, a method for monitoring the progress of etching on the wafer surface will be described with reference to FIG. Fig. 2 (a)
Shows the surface of the wafer 5, and the chips 5c are partitioned by the scribe lines 5a and 5b for dicing. Reference numeral 21 denotes a field of view, which is an area of the wafer surface that can be observed through the glass window 6 and has a size that allows observation of a plurality of chips. Further, 22 is a detection region, which is an image of the wafer surface in the field of view 21 and is a cylindrical lens.
It is an area for image compression at 10. The x direction of the detection area 22 is
The direction is orthogonal to the scribe lines 5a and 5b, and the wafer surface is compressed in the y direction by the cylindrical lens 10 to give a contrast-enhanced image signal as shown in FIG. 2 (b). In this image signal, the sections 5a ', 5c', and 5 shown respectively
b'corresponds to the scribe line, the chip, and the scribe line in the detection area 22.

Now, for example, in the etching of aluminum, the reflection intensity from the scribe line before etching is very strong.
However, in the process of etching, the uncoated portion of the photoresist on the wafer is scraped off, and when the etching of the material to be etched is completed, the underlayer, for example, SiO _2, is exposed and the reflection state changes, resulting in an image of the image sensor 11. The signal changes according to the reflection intensity. In this case, the chip 5c has a complicated device pattern on the order of micron, and is therefore affected by diffraction, interference, and scattering. On the other hand, since the scribe lines 5a and 5b are flat over a relatively wide range (50 to 100 μm),
Insensitive to diffraction, interference and scattering. Therefore, in the present embodiment, in the above configuration, the end point determination control device 14 takes in all the image signals from the image sensor 11 and A / D converts them by the A / D converter 14a to store the digital signals in the memory 14b.
In the digital signal stored in the computer 14a, only the signals corresponding to the scribe lines 5a and 5b are extracted and monitored to determine the etching end point.

Next, a method of determining the etching end point from the change of the signal waveform in the etching process will be described. In FIG. 3, the image signal from the image sensor 11 is converted into an A / D converter 14
Of the digital signal digitally changed by a, the waveform corresponding to the scribe line is shown. When determining the etching end point, it is important to reduce sudden noise (irregular noise) of the monitor signal and obtain a signal with essentially high SN ratio in order to improve detection accuracy and reproducibility. Therefore, in this embodiment, signal processing is performed as follows.

The digital signal obtained by A / D converting the image signal from the image sensor 11 has a continuous signal waveform of the output of the adjacent pixel as shown in FIG. FIG. 3 (a) shows a signal waveform before etching. In the figure, the average of all pixel levels in the detection area 22 captured by the image sensor 11 When selected, the selected portion is always the section including the scribe line. The number of pixels in this section is n, and the level of each of the n pixels is V ₁ (0), , And the sum over the entire section Then, S (0) represents the shaded area 31 in FIG. 3 (a). Here, Vmin (0) is the output level of the lowest level pixel in the section, Then determine the pixel section as above before etching,
When a similar operation is performed when a time t has elapsed from the start of etching, the signal waveform becomes as shown in FIG. 3 (b), and the shaded portion 32 is the same as the equation (1). Becomes

As described above, the value of S (t) is set to the shaded portion (third part) of the image signal waveform.
When calculated as the integrated value in FIG. 3 (b), the temporal change of S (t) becomes like the curve A in FIG. 3 (c), and a monitor signal with a high SN ratio can be obtained. By the way, if only the change of the pixel level Vmax (t) at the peak point in the section is taken as the monitor signal,
The change over time of the value is as shown by the curve B in FIG. 3 (c), and since the noise signal appears as it is, the signal has a poorer SN ratio than the curve A.

To determine the end point of etching, the monitor signal with a waveform of S (t) is sampled at regular intervals of Δt, and the slope of S (t) is calculated. The change point (inflection point) is calculated in real time while obtaining the values such as In order to have certainty of the decision point, the change point is usually delayed by several sampling times, and (t + hΔt) (h = 3 to
Although it is determined at the time of 6), when the SN ratio of the monitor signal S (t) is high as in the present embodiment, the change point can be clearly caught, and therefore one sampling time Δt (for example, 1 second). ), That is, at the time of t + Δt, it becomes possible to detect the end point (detection of just etch point) with high accuracy.

As described above, in the present embodiment, the pixel section including the scribe line is determined before etching, and the integrated value of the level of each pixel in the pixel section is continuously obtained and monitored at regular time intervals during the etching process. Since a monitor signal having a high ratio can be obtained, it is possible to detect the etching end point with high accuracy and high reproducibility.

〔The invention's effect〕

As described above, according to the present invention, since the etching end point detection monitor signal having a high SN ratio can be obtained, it is possible to detect the etching end point (just etch point) with high accuracy and with good reproducibility. It is possible to etch even a fine device pattern having an allowable overetching time of about 5 seconds without damaging the material, which greatly contributes to the improvement of wafer yield.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus used in an embodiment of the present invention, and FIG.
FIG. 3 is an explanatory view of a wafer to be etched and its image signal in the embodiment, and FIG. 3 is an explanatory view showing an image signal waveform corresponding to a scribe line of the wafer. DESCRIPTION OF SYMBOLS 1 ... Etching process chamber, 2 ... Lower electrode, 3 ... Upper electrode, 4 ... High frequency power supply, 5 ... Wafer, 6 ... Glass window, 7 ... Lens, 8 ... Half mirror, 9 ... Color filter, 10 ... Cylindrical lens, 11 ... Image sensor, 12 ... Illumination lamp, 13 ... Lens, 14 ... Etching end point determination control device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Aiuchi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Hitachi, Ltd. Institute of Industrial Science (72) Inventor, Etsuro Watanabe 292 Yoshida-cho, Totsuka-ku, Yokohama Address Company, Hitachi, Ltd., Institute of Industrial Science (56) References JP-A-59-147433 (JP, A) JP-A-58-19478 (JP, A)

Claims (1)

[Claims] 1. A method for detecting an etching end point in a wafer etching process in which a scribe line is provided on a surface, wherein reflected light from the wafer surface is detected to obtain an image signal of a wafer surface pattern, and the image signal is obtained. The image signal corresponding to the scribe line is taken out from the image signal, the sum of the output signals of all the pixels of the image signal corresponding to the scribe line is calculated at regular time intervals, and the sum of the output signals of all the pixels is temporally calculated. A method for detecting an etching end point, which comprises determining an etching end point based on a change.