JPH05102087A - Method for monitoring plasma etching end point - Google Patents

Abstract

PURPOSE:To detect the end point accurately enough to have a sufficient sensitivity for detecting the micro-etching by performing plasma radiation intermittently accompanied with a longer downtime of plasma radiation than the duration required for the radiation start to measurement. CONSTITUTION:Etching gas 6 is regulated by a mask flow meter 7 and introduced into a vacuum chamber 1. The gas in the chamber is led to a mass analyzer 12 through a turbo-molecular pump 10 and rotary pump 10, and the obtained result of mass analysis is collected to be processed arithmetically by a computer 14. Etching is performed through generating intermittent radiation, while the radiation stop time is specified to be longer than the response delay time of signal issued by the analyzer 12 and the radiation connecting time is also specified to be longer than the response raise time. Thus, since the signal change of the mass analyzer accompanied with interlayer composition change can be securely monitored during the downtime, excessive etching can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching end point monitoring method used for precision etching of fine patterns in the manufacturing process of electronic devices such as semiconductors.

[0002]

2. Description of the Related Art In recent years, electronic devices such as semiconductors have become more and more miniaturized, and how to precisely etch a fine pattern has become a very important issue. As a method of forming such a fine pattern,
Liquid-free dry etching techniques such as plasma (mainly radical species) etching, reactive ion etching, and ECR etching are drawing attention. Since such etching is performed in a vacuum chamber, it is necessary to accurately monitor the end point. In general, in the case of electronic devices, in most cases, laminates of different materials are plasma-etched to the interface between layers, so the end point is monitored by observing the difference in the physical and chemical properties between layers. ing.

[0003]

Some optical methods such as light interferometry are used as a monitor for utilizing the above-mentioned physical properties, and when the object to be etched has a large area, it is practically used. Is almost no problem. However, often difficult cases occur with small areas, especially fine patterns.

On the other hand, when utilizing the difference in the chemical properties, a gas chemical analysis method is often used. The reason is,
This is because the gas products differ not only due to the difference in the composition between the layers but also because the plasma etching rate often differs greatly, so that the gas composition in the etching chamber is likely to change. Examples of such gas analysis methods include absorption spectroscopy, emission spectroscopy, mass spectrometry, and the like.

Among them, the absorption spectrophotometry has a technical difficulty that it is necessary to detect a minute change of a large signal (bright transmitted light), and therefore has a drawback that it is not suitable for an ultratrace analysis. ing.

Also, in the case of emission spectroscopic analysis, as a monitor when the reaction rate is low, in the case of an ultrafine pattern, or when the emission spectrum of the etching gas largely covers the emission spectrum of the monitor chemical species, it is not suitable as a monitor. Inadequate ability. In the case of low reaction rate or ultrafine pattern, the concentration of the product substance, that is, the monitor substance, in the chamber is too low.
The point is that the sensitivity of the analyzer is a problem. On the other hand, the case where the emission spectrum of the etching gas largely covers the emission spectrum of the monitor chemical species is, for example, the case of plasma etching of a Si-based semiconductor wafer with a CF-based gas. In this case, the emission of the CF-based gas decomposition product occupies a wide range of 250 to 400 nm, and the emission spectrum of the main etching products such as Si and SiF is hidden, which makes it difficult to use the emission spectroscopy. is there.

On the other hand, in the case of the mass spectrometry, the analytical sensitivity is 10 times or more better than that of the emission spectroscopic method, which is most suitable for this purpose. However, this method does not directly measure the etching state, but requires the time required for the movement of the monitor substance in the pipe from the etching chamber to the mass spectrometer and the signal processing time. Therefore, there is a fatal defect that there is a time lag between the actual end point of etching and its measurement, and the end point is missed. That is, none of the conventional analysis methods has sufficient characteristics without specially expensive incidental equipment.

The present invention overcomes the drawbacks of the conventional plasma etching end point detection method described above, has sufficient detection sensitivity even for etching of a small area, and can detect the end point accurately. It is an object to provide an etching end point monitoring method.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have paid attention to the good analytical sensitivity of a mass spectrometer, and are keen to improve the above-mentioned drawbacks of this spectrometer. It was obtained as a result of the investigation, when performing plasma etching of a layered laminate of different materials, the composition change of the etching object and the change of the etching rate related to the end point of the etching change of the gas phase component concentration in the plasma etching chamber As a change, in the end point monitoring method of the plasma etching observed by the mass spectrometer, the time required for transfer of the monitor substance in the pipe from the plasma etching chamber to the mass spectrometer, the signal processing time, etc. The feature is that intermittent plasma discharge is performed with a plasma discharge pause time that is sufficiently longer than the time. It is an.

[0010]

With the above means, a plasma discharge pause time is sufficiently longer than the time required from the start of discharge to the measurement, such as the time required to move the monitor substance in the pipe from the chamber to the mass spectrometer and the signal processing time. By performing the intermittent plasma discharge, the change in the signal of the mass spectrometer accompanying the change in composition between layers can be observed without fail during the down time, and therefore excessive etching can be prevented.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First, FIG. 1 shows an outline of the plasma etching apparatus used in the present invention. The vacuum chamber 1 for etching has a volume of 8 liters and has an area of 4 in the center.
0 cm ² It has a pair of parallel plate electrodes 2 and 3, and the lower electrode 2 used also as a sample stand has an oscillation frequency of 13.56 MH.
high frequency power of z is applied to bring the upper electrode 3 to the ground potential,
The so-called RIE mode plasma etching can be performed. The high frequency power is generated by the RF power source 4, and is applied to the lower electrode 2 by impedance matching through the automatic tuning type matching box 5. The etching gas 6 is introduced into the vacuum chamber 1 with its flow rate controlled by a mask flow meter 7. The pressure in the vacuum chamber 1 is controlled by the rotary pump 8 and the butterfly valve 9 having an evacuation speed of 340 l / min. Further, the gas in the chamber is passed through a SUS pipe having a length of 1 m and an inner diameter of 1/4 inch to a mass spectrometer 12 by a turbo molecular pump 10 and a rotary pump 11 (displacements are 300 liter / sec and 340 liter / min, respectively). lead. Adjust the sampling gas flow rate with the needle valve 13, and set the operating pressure upper limit of the mass spectrometer to 2 × 10 ⁻⁵ T.
The pressure was reduced so as not to exceed orr. The results of mass spectrometry can be collected and arithmetically processed by the computer 14, and the results can be output to the CRT 15 and the printer 16.

Using this apparatus, the silicon oxide film (SiO ₂ ) was etched under the following conditions. CF ₄ gas having a purity of 99.99% is used as the etching gas 6 for 10 seconds.
The mass flow meter 7 is used so that the flow rate is ccm, and the pressure in the vacuum chamber 1 is 0.50 Torr.
The pressure was automatically controlled by the butterfly valve 9 so as to be r. Input power is 1 during plasma discharge
At 00 W, the fluctuation of the power and the reflected power were controlled to 1% or less. The sample used for etching is 70
17m in size with 0 nm thick silicon oxide film
A silicon wafer of mx 17 mm, a stripe-shaped opening with a width of 3 μm was partially formed on the part by a photoresist.
Those with a cut of 00 (the total exposed area of the oxide film is about 0.
004 cm ² ). Conventional example 1

For comparison, FIGS. 2 (a) and 2 (b) show conventional time-dependent change charts of the output of the mass spectrometer at the time of continuous discharge. As shown in this figure, the mass spectrometer signal started to increase approximately 23 seconds after the start of discharge (called signal delay time), and became a constant value approximately 16 seconds after the increase started (signal Called rise time).
In addition, the discharge was stopped and the sample was taken out because a decrease in the signal was observed about 3 minutes and 20 seconds after the signal became a constant value.
The cross section of the etching groove of the sample was observed with a scanning electron microscope to examine the etching condition. As a result, overetching of the 15 nm silicon layer was observed.

As described above, in the conventional example, overetching is performed even if the etching is stopped immediately after the change in the signal of the mass spectrometer for detecting the end point. In this example, it is considered that at least the signal delay time of about 23 seconds is over-etched. Example 1

An etching experiment by intermittent discharge was conducted under the same conditions as in Conventional Example 1. However, the discharge stop time was set to 30 seconds longer than the response delay time of the signal of the mass spectrometer, and the discharge duration was set to 20 seconds longer than the response rise time. As a result, FIG. 3 (a), (b), (c)
As shown in FIG. 5, the chart has a substantially constant value in about 16 seconds after starting to rise, begins to decrease in about 20 seconds, and draws a waveform locus having a constant value 18 seconds after the decrease starts. From the beginning to the 10th discharge, almost the same waveform was obtained,
Regarding the 11th discharge, the value of the peak of the signal did not change much, but the decrease started before 20 seconds (about 17 seconds) from the start of rising. Although the results of calculating the areas of these output waveforms are also shown in the same figure, the area of the 11th waveform was a smaller value than the waveforms before that. After the eleventh discharge based on these facts, the discharge was stopped, the sample was taken out, and the state of the etching groove was examined. As a result, it was found that the over-etching on the silicon layer was as small as 2 nm.

As described above, by setting the one-time discharge duration to be shorter than the discharge delay time, overetching could be reduced. In the worst case, overetching is less than the discharge duration. It is considered that over-etching in this example was only about 3 seconds. Since the discharge stop time needs to be at least longer than the signal delay time of the mass spectrometer, it is better to shorten the signal delay time as much as possible in order to improve productivity. In the apparatus used in this experiment, the signal delay time was 20 seconds or more because the distance from the vacuum chamber to the mass spectrometer was long, but this signal delay time can be improved depending on the position of the mass spectrometer. Example 2

Subsequently, the discharge time interval was shortened in order to further reduce the etching depth of the silicon layer. That is, first, after continuously discharging for 2 minutes and 30 seconds,
The discharge for 3 seconds and the rest for 30 seconds were repeated. The results are shown in FIGS. 4 (a), 4 (b) and 4 (c). Ie 1
After performing intermittent discharge 5 times, the discharge was stopped at the 16th time because a peak having a value lower than the peak height of each previous cycle was obtained. In the sample obtained in Example 2, it was revealed that the etching almost stopped between the silicon oxide film layer and the silicon layer.

In the second embodiment, the discharge duration is set to be a fraction of the signal rise time, so the signal output has not reached a certain value, but the end point is sufficiently detected. ing. According to this method, the signal output is reduced, but the worst overetching amount can be reduced. Further, as in Example 2, performing etching by continuous discharge until just before the etching time expected to be completed in advance, and finally repeating small intermittent discharge to detect the end point shortens the entire etching time. Is effective for. The duration of the intermittent discharge does not necessarily have to be a constant time as long as appropriate reading is performed, but a constant value is preferable for ease of data analysis.

In order to determine the end point more easily, the average value and standard deviation of the end point detection signals due to each intermittent discharge are sequentially calculated, and the signal intensity obtained during the latest stop time of the intermittent plasma discharge is calculated. When the end point was determined to be a value equal to or less than the average value−3 × standard deviation value, it was possible to eliminate an artificial judgment error. In order to improve the accuracy of the average value and the standard deviation value, it is desirable to set the continuous discharge time, the intermittent discharge duration, etc. so that the end point determination is performed after performing the intermittent discharge of at least about 8 points. In this case, it is important that the high frequency plasma input is stable, and the variation is preferably 3% or less. Further, as the numerical value of the end point detection signal at this time, the absolute value of the signal intensity after a lapse of a certain time from the start of the increase of the signal related to the monitor substance of the mass spectrometer may be used, and the area of the signal intensity during that period may be used. The calculation result (integral value) may be selected. For example, FIG.
In (c) and FIGS. 4A to 4C, the solid line shown in the area calculation result of the signal intensity is the average value, and the broken line shows the range of the average value ± 3 × standard deviation. Fig.3 (a)-
In the case where there is no large difference in the peak value of the signal strength as in the example of (c) and it is necessary to detect a slight time difference,
Since the signal strength itself is small as in the examples of (a) to (c), it is particularly effective to use the area calculation result when the influence of noise needs to be removed.

[0021]

As described above, according to the present invention, it is possible to accurately detect the end point even for a wafer having a very small exposed area. Good etching is possible. Therefore, the use of the present invention dramatically improves the manufacturing accuracy of electronic devices such as semiconductors, and thus the industrial utility value of the present invention is extremely high.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an example of an apparatus used for detecting a plasma etching end point according to the present invention.

FIG. 2 is a characteristic diagram showing an example of detecting an end point of plasma etching by a conventional method.

FIG. 3 is a characteristic diagram showing an example of plasma etching end point detection according to the present invention.

FIG. 4 is a characteristic diagram showing another example of the end point detection of plasma etching according to the present invention.

[Explanation of symbols]

1 ... Vacuum chamber, 2, 3 ... Pair of parallel plate electrodes, 4
... RF power source, 5 ... Matching box, 6 ... Etching gas, 7 ... Mass flow meter, 8 ... Rotary pump, 9 ... Butterfly valve, 10 ... Turbo molecular pump,
11 ... Rotary pump, 12 ... Mass spectrometer, 13 ... Needle valve, 14 ... Computer, 15 ... CRT, 1
6 ... Printer.

Claims (7)

[Claims] 1. When a layered laminate of different materials is subjected to plasma etching, the composition change of the object to be etched and the change of the etching rate, which are related to the end point of the etching, are taken as the change of the gas phase component concentration in the plasma etching chamber and the mass spectrometry is performed. In the method of monitoring the end point of plasma etching observed by a meter, the time required for the movement of the monitor substance in the pipe from the plasma etching chamber to the mass spectrometer, the signal processing time, etc. A method for monitoring the end point of plasma etching, which comprises performing intermittent plasma discharge with a plasma discharge pause time. 2. The signal intensity value is measured after a lapse of a period of approximately intermittent discharge from the beginning of the increase in the signal related to the monitor substance of the mass spectrometer related to the start of each intermittent plasma etching, and the measured value. 2. The method for monitoring the end point of plasma etching according to claim 1, wherein the decrease of the end point is used as the end point of the plasma etching. 3. The signal intensity relating to the monitor substance of the mass spectrometer is measured during each intermittent plasma etching stop time, and an integrated value of the measured value with respect to time is calculated.
2. The plasma etching end point monitoring method according to claim 1, wherein the decrease of the calculated value is set as the end point of the plasma etching. 4. The method for monitoring the plasma etching end point according to claim 1, wherein the intermittent plasma discharge is performed after the continuous discharge is performed for a time shorter than the time expected to be the end point in advance. .. 5. A signal intensity value of continuously 8 points or more after a lapse of substantially intermittent discharge duration from the beginning of the increase of the signal related to the monitor substance of the mass spectrometer related to the start of each intermittent plasma etching. 3. The plasma etching end point according to claim 2, wherein the end point of the plasma etching is measured when the last measured value becomes equal to or lower than the lower limit value of the 3σ limit method by the statistical processing of the previous data. Monitoring method. 6. The signal intensity of the monitored substance of the mass spectrometer is continuously measured at 8 or more points during each intermittent plasma etching stop time, and an integrated value of the measured value with respect to time is calculated, and finally, 4. The plasma etching end point monitoring method according to claim 3, wherein the end point of the plasma etching is set when the calculated value of <3> is less than or equal to the lower limit value of the 3 [sigma] limit method by statistical processing of data before that. 7. The intermittent plasma discharge is carried out after the continuous discharge is carried out for a time sufficient to allow the intermittent plasma discharge to be carried out at least eight times before the end point. Item 7. A plasma etching end point monitoring method according to Item 5 or 6.