JP2738769B2 - End point judgment method - Google Patents

Description

The present invention relates to a method for determining an end point of dry etching using plasma.

[Prior Art] The conventional end point determination method is to change the gain / offset of an amplifier for amplifying the amount of plasma emission converted into an electric signal with an increase in the number of processed pieces, and to determine the end point dead time, sampling time, and the like. The time factor of was fixed. This is because the change with time of the optical system is considered to be caused by the fact that the change with time of the plasma light emission amount is caused by the obstruction of the observation window for determining the light emission amount due to the deposition in the etching chamber.

However, in practice, there is a phenomenon such as a decrease in etching rate due to a temporal change due to deposition or the like. In such a case, an accurate end point determination may not be performed by the conventional method.

In addition, as for this kind, for example,
No. 63-254732.

[Problems to be solved by the invention]

In the prior art, as described above, there is a problem that it is not possible to cope with a change in the light intensity of the emission spectrum in the time axis direction due to a phenomenon that the etching rate decreases due to an increase in the number of processed wafers.

For example, in an apparatus for performing an etching process by generating plasma in a quartz chamber by the action of a microwave electric field and a magnetic field as shown in FIG. 2, when a process having a large number of deposits is used, deposits adhere to the quartz chamber. However, the light emission amount decreases with an increase in the number of processed images. In addition, if this is the only case, it can be corrected by the auto gain function.
The etching rate also changes, in this case, it decreases.
Therefore, as shown in FIGS. 4 (a) to 5 (a), the rate of change of the waveform near the end point also changes gradually as the rate decreases. FIG. 4 shows the one during the processing of the first sheet, and FIG. 5 shows the one during the processing of the n-th sheet. 1 sheet of change width in auto gain (V ₁₎ and the n-th change width (V _n) is adjusted to become equal, but the time required for the change is changed (T ₁ → T _n) for, d ² The value of V / dt ² (secondary difference) decreases. Therefore, there is no other way to correct this than reducing the determination value or increasing the difference interval.

In recent years, a plurality of wafers are used, and a multilayer film is often etched by one etching. The emission intensity waveform in such a case is, for example, as shown in FIG. In order to detect the just etch of the second layer with such a waveform, the etching of the second layer is started,
It is necessary to provide a dead time at a place where the waveform is stable.
However, when the etch rate decreases and the dead time is always constant, a dead time occurs during the etching of the first layer as shown in FIG. 6B, and the end point is reached at the boundary between the first layer and the second layer. May be detected.

SUMMARY OF THE INVENTION An object of the present invention is to provide an end point determination method capable of reliably determining the end point of etching even when the etching rate changes as the number of samples processed increases.

[Means for solving the problem]

In order to achieve the above object, the ratio of the end point determination time of the first sample to the end point determination time of the nth sample is calculated, and the time for all end point determinations such as the end point determination sampling interval, dead time, and difference interval is calculated. The constant corrected by multiplying the constant by the ratio is used for the end point determination of the (n + 1) -th processing.

In order to achieve the above object, an interval between a peak interval of the secondary difference value of the light emission amount at the time of processing the first sample and a peak interval of the secondary difference value of the light emission amount at the time of processing the nth sample is set. The time is compared to calculate a ratio, and the ratio is used to correct the end-point determination sampling interval, dead time, difference interval, and other time constants relating to all end-point determinations, and the end-point determination for the (n + 1) th processing is performed. Things.

[Action]

Now, the just-etch time of the _first wafer is t ₁ , the just-etch time of the _n-th wafer is t _n , and the plasma emission spectrum waveform is expanded and contracted in the time axis direction for the first and n-th wafers. When a similar fashion, the ratio between the t ₁ and t _n is considered the ratio of the etch rate.

In the present invention, based on such a concept, the above t ₁ and t _n
Using the ratio t _n / t ₁ , each time constant for end point determination is corrected.
The time constant indicates a sampling interval, a dead time, a difference interval, and the like for the end point determination. In the end point determination of the (n + 1) th, the time constant of the first sheet, using a multiplied by t ₁ / t _n. In this manner, the end point determination can be corrected in the time axis direction, and accurate etching end point determination can be performed even when the etching rate decreases as the number of processed wafers increases.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 2 shows an end point determination system. In this case, the inside of the etching chamber 1 is supplied with an etching gas and is evacuated and reduced to a predetermined pressure, and plasma is generated by the action of the electric field and the magnetic field of the microwave. The emission spectrum of the plasma when the wafer 2 is etched in the etching processing chamber 1 passes through the spectroscope 3 and is guided to the photoelectric conversion element 4 only at a specific wavelength. The amount of emission spectrum converted into an electric signal by the photoelectric conversion element 4 is amplified by the amplifier 5 and input to the computer 6. Hereinafter, all the processing is software processing in the computer 6.

FIG. 1 shows a principle diagram of the present invention. FIG. 1 (a),
(B) and (c) show the number of processed sheets, the first, n, and n, respectively.
This is the + 1st emission spectrum amount.

Now, the first wafer as shown in FIG. (A), sampling interval S _1, performs end point detection in the dead time t _a1, t ₁
It is assumed that the end point is detected by. Further, it is assumed that the end point is detected at t _n on the _n-th wafer as shown in FIG. this,
The ratio of t ₁ and t _n is considered to be the ratio of 1 sheet and the n-th etching rate.

Next, when etching the (n + 1) th sheet, the above-mentioned ratio t _n / t is applied to all the time constants such as the sampling interval, the dead time, and the difference interval (not shown).
_{Use one} multiplied by one. That is, the sampling interval as shown in FIG. (C) becomes _{S n + 1 = t n /} t 1 × S 1, the dead time _{t an + 1 = t n /} t 1 × t a1. However, the second sheet has the same data as the first sheet because there is no data for correction.

By correcting the constants for various times of the end point determination by the above method, it is possible to cope with the fluctuation of the emission spectrum in the time axis direction.

Note that, in the present embodiment, the method of correction when determining the etching end point has been described. However, when the above ratio t _n / t ₁ becomes a certain value or more, a warning or maintenance is performed by an instruction from a computer. By displaying the information, the inside of the etching processing chamber 1 may be cleaned and the maintenance of the apparatus may be performed.
Further, the maintenance display at this time may be a warning by a lamp or the like, or may be displayed on a CRT.

As a method of notifying the maintenance time, the above ratio may be displayed on a CRT as a graph, and the user may be informed of the tendency to perform the maintenance.

In addition, if a dummy wafer is provided in the etching apparatus and a maintenance time is detected by a computer, the signal is sent to a higher-level computer, the processing of the wafer is managed by a higher-level computer, and a time when cutting is good, for example, a lot. It is also possible to automatically stop the wafer processing at the time when the temperature changes, carry the dummy wafer into the etching chamber, perform plasma cleaning, and return to the normal etching processing. When restarting the etching process, the time constant for performing the etching end point is returned to the constant for the first sheet.

When correcting the time constant, the reference time may be kept constant, and the counting time may be lengthened or corrected, as shown in FIG.
The clock cycle of the computer that performs the end point determination may be changed. In this case, reference numeral 6 denotes a microcomputer for judging the end point, 7 denotes a clock control circuit for adjusting the cycle of the clock 8 serving as a reference for judging the end point, and 9 denotes a real-time counter for managing time as a base. is there.

Further, in the present embodiment, the ratio is obtained by comparing the time until the just etch, but the secondary difference value of the light intensity at the time of processing the first wafer shown in FIG. 'and the peak spacing t _n secondary difference values of FIG. 5 (b) n-th processing time of the light emission amount shown in the' peak interval t ₁ be calculated the ratio by comparing the time interval between the The same effects as those of the above embodiment can be obtained.

〔The invention's effect〕

According to the present invention, the fluctuation of the emission spectrum in the time axis direction can be corrected, and the end point can be determined in response to a decrease in the etching rate due to an increase in the number of processed wafers.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in generated intensity for explaining a method of correcting a constant with respect to time in an end point determination method according to an embodiment of the present invention, and FIG. 2 is an etching apparatus for performing the method of FIG. FIG. 3 is a schematic view showing an example of a configuration for performing time correction in the apparatus shown in FIG. 2, and FIG. 4 is a view showing the light emission intensity and the light emission intensity at the time of processing the first wafer. FIG. 5 is a diagram showing the light emission intensity at the time of processing the n-th wafer and the secondary difference of the light emission intensity. FIG. 6 is a diagram showing light emission accompanying an increase in the number of processed wafers in the case of two-stage etching. It is a figure showing a change of intensity. DESCRIPTION OF SYMBOLS 1 ... Etching chamber, 2 ... Wafer, 3 ... Spectroscope, 4 ... Photoelectric conversion element, 5 ... Amplifier, 6 ... Computer

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor ▲ Yoshi ▼ Motohiko Kaiyo Katsumatsu City, Yamaguchi Prefecture

Claims (5)

(57) [Claims] In a method for determining the end point of dry etching by emission spectroscopy, a ratio of an end point determination time of a first sample to an end point determination time of an nth sample is calculated, and an end point determination sampling interval, a dead time, and a difference are calculated. An end point determination method, characterized in that a constant corrected by multiplying a time constant relating to all end point determinations such as intervals by the ratio is used for the end point determination of the (n + 1) th processing. 2. The end point judging method according to claim 1, wherein an alarm or maintenance is displayed when the ratio becomes equal to or more than a certain value. 3. The end point judging method according to claim 1, wherein the ratio is displayed on a CRT as a graph to notify a user of a tendency and a maintenance time. 4. The end point judging method according to claim 1, wherein said time constant is determined by changing a clock cycle of a microcomputer for judging the end point. 5. A method for determining an end point of dry etching by emission spectroscopy, wherein a peak interval of a secondary difference value of a light emission amount during processing of a first sample and a secondary difference of light emission during processing of an n-th sample. By comparing the interval time with the peak interval of the value, the ratio is calculated, and the time constant relating to the end point determination such as the end point determination sampling interval, dead time, difference interval, and the like is corrected by the ratio, and the processing of the (n + 1) -th sheet is performed. An end point determination method, wherein an end point is determined.