JPH06132251A - Etching monitor for plasma etching - Google Patents

Abstract

PURPOSE:To maintain etching property constant so as to prevent the occurrence of inferiority by monitoring the etching processing of a wafer at all times. CONSTITUTION:Amidst the etching processing, the light emission 12 from plasma 6 is monitored with a spectroscope 15, and also the high frequency voltage applied to a wafer 7 is monitored in advance with a voltmeter 17. The power of microwaves inputted into plasma 6 and the pressure of a processing chamber 5 are monitored with a microwave output meter 2 and a pressure gauge 16 in advance. The etching condition after the end of processing is inferred, using the signals from these four pieces of monitors (microwave output meter 2, spectroscope 15, pressure gauge 16, and high frequency voltmeter 17) and data base 19, and in case that it is disqualified for the condition of inspection, the processing condition is modified so that the wafer to be processed next may pass inspection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching apparatus for manufacturing a semiconductor device, and monitors the etching condition and corrects the processing conditions of the apparatus according to the result to maintain a constant etching characteristic to prevent the occurrence of defects. The present invention relates to an etching monitor of a plasma etching apparatus suitable for prevention.

[0002]

2. Description of the Related Art With the high integration of LSI, high precision is required for its processing. In order to perform highly accurate processing, it goes without saying that the performance of each processing device should be improved.
In order to improve productivity, it is important to maintain the performance of each processing device stably for a long time and to prevent defects. Among the processing equipment, when we look at the etching equipment that forms a pattern on the wafer surface by plasmaizing the processing gas in a vacuum container, the resist that is the mask of the pattern decomposes during the etching processing to generate organic matter, which is generated in the processing chamber. Metal that adheres to the inner wall or is the material to be etched (aluminum,
Molybdenum and tungsten) adhere to the inner wall of the processing chamber as a film. When these deposits come into contact with plasma, gas is generated due to the action of ions in the plasma and the temperature rise of the wall of the processing chamber, and the state of microwaves entering the processing chamber changes due to the adhesion of the metal film. As a result, the plasma state in the processing chamber changes. Since the etching process is performed by plasma, the etching characteristics also change due to the change of the plasma state. Further, the O-ring for vacuum sealing may be deteriorated by the etching gas, and a minute leak may occur to change the plasma state. That is, when the etching apparatus is continuously operated for a long time, the etching characteristics change with time, and eventually the inspection pass condition is not satisfied, leading to the occurrence of defects. Further, the adhered matter on the inner wall of the processing chamber is peeled off and becomes a foreign matter when it reaches a certain thickness. This is another plasma processing equipment (CVD equipment, sputtering equipment, etc.)
However, the same is true, which is an obstacle to maintaining its performance stable for a long time.

So far, for example, Japanese Patent Laid-Open No. 63-4212.
As in the plasma etching apparatus shown in FIG. 4, the plasma state is monitored by the light emission during the etching process, but this monitoring result is used only to monitor the end of etching. That is, during etching, the material to be etched (aluminum, etc.) appears in the plasma due to the etching reaction, so the intensity of the light (wavelength peculiar to the substance) emitted by this is monitored, and etching is performed when the intensity of that light becomes zero. Has detected that has ended. Therefore, the time and etching rate required to etch one wafer can be obtained, but even if this value changes, no particular modification of the processing conditions has been made.

[0004]

In the above-mentioned prior art, only the completion of the etching process is monitored, and the result of the etching process (pattern cross-section size, shape, wafer in-plane uniformity of the process, etc.). Does not confirm that they meet the inspection requirements. Therefore, the characteristics of the processing apparatus change, and as a result, even if the etching process fails the inspection condition, the process is continued under the same condition and a defective product is produced. As described in the above-mentioned section of the prior art, since the processing characteristics of the etching processing apparatus change with time, it is necessary to accurately inspect the result every time processing is performed. The present invention monitors the processing status every time one etching processing is completed, and reports the result to the processing apparatus so that the processing apparatus corrects the processing conditions so that an appropriate processing is performed, or (EN) Provided is an etching monitor which prevents the occurrence of defects by maintaining a constant etching characteristic by stopping the processing when a condition cannot be dealt with.

[0005]

In order to achieve the above object, it is first necessary to accurately monitor the result of etching processing of a wafer. As a method of this, it is possible to know the state of the etching process by, for example, observing the emission spectrum analysis of plasma during the etching process and observing changes in process conditions (processing pressure, bias voltage, etc.). That is, if the relationship between the result of the etching process and the spectroscopic analysis result of the plasma or the variation of the process conditions is checked in advance, the process result can be monitored without directly inspecting the wafer after the etching process. As another method, a method of directly inspecting the wafer after the etching process can be considered. That is, if the depth or width of the pattern is measured by utilizing light interference or the like, the uniformity of processing, dimensional accuracy, shape, etc. can be inspected.

When the result of the etching process obtained by such a method is unacceptable to the inspection condition, the information is sent to a processing apparatus and the processing condition is corrected so that the inspection is passed. It is necessary. For this method,
The relationship between process conditions (pressure, gas flow rate, bias voltage, etc.) and processing results (uniformity, dimensional accuracy, shape, selectivity with respect to the underlying film, etc.) may be investigated in advance. If this relationship is stored in the processing device, it is possible to determine which of the processing conditions (process conditions) should be corrected and to what extent if the inspection fails due to insufficient uniformity, for example. Various modifications can be made to pass the inspection from the next wafer to be processed. Further, when the processing cannot be recovered by only correcting the processing conditions, the processing can be stopped and the administrator can be notified to take appropriate measures.

By the above method, the characteristics of the etching process can be maintained constant and the occurrence of defects can be prevented.

[0008]

When the result of the etching process is indirectly monitored, the processing method is as follows. After the wafer is transferred to the etching processing chamber and set on the mounting table, etching processing gas is introduced, the pressure is adjusted to a predetermined pressure, and plasma discharge is started. A lighting window provided in the processing chamber from the start of discharge (the start of etching processing) to the emission intensity of the material to be etched (aluminum when etching aluminum wiring) in plasma and the emission intensity of active species (eg chlorine radicals) that contribute to etching. Through a spectroscope, and the data of each time change is taken into the monitor.
At the same time, data on the time change of process conditions (processing pressure, bias voltage, etc.) is also captured. These are performed until the end of the etching process. Simultaneously with the end of etching, the monitor arithmetically processes these data, predicts the result of the etching process just finished, and judges whether the inspection condition is passed or failed. If it passes, immediately process the next wafer,
Monitor by the same procedure. If the monitor fails, which item in the inspection conditions (uniformity of processing, dimensional accuracy, shape, selectivity with the underlying film) fails and the condition (for example, if the uniformity is Insufficient) to correct this, the etching processing equipment is instructed which of the process conditions should be modified and to what extent the processing equipment should be modified in accordance with the instruction before the etching processing of the next wafer. Get started. In this case, the previously processed wafer becomes defective, but the next wafer does not become defective. If the degree of failure is too great to correct the processing conditions, the monitor instructs the processing device to stop the processing.

On the other hand, in the case of directly monitoring the result of the etching process, the monitor starts to inspect the wafer at the same time when the process is completed and judges whether the result is a pass or a fail. The subsequent operation is the same as that described above.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. In FIG. 1, the processing chamber 5 is evacuated by a vacuum exhaust system (not shown) through the exhaust pipe 10 and the pressure control valve 9, and the etching gas whose flow rate is adjusted through the gas introduction pipe 14 and the gas flow rate controller 13 is processed in the processing chamber. Introduced in 5 and maintained at a predetermined pressure. Microwave is introduced into the processing chamber 5 from the microwave oscillator 1 through the microwave output meter 2, the waveguide 3 and the microwave transmission window 2 to generate the plasma 6 for processing the wafer 7 and the plasma 6
The wafer 7 is etched by the ions and active species generated therein. A high frequency power supply 18 can apply a high frequency voltage to the electrode 8 on which the wafer 7 is placed in order to attract ions generated in the plasma 6 to the wafer 7. Further, a voltmeter 17 is provided in the high frequency path to monitor the applied voltage at this time. The processing chamber 5 is provided with a daylighting window 11 for taking out the light emitted by the internal plasma 6 to the outside, and the light emission 12 of the plasma 6 passing through the daylighting window 11 can be observed by the spectroscope 15. There is.

During the etching process, the light emission 12 from the plasma 6 is observed by the spectroscope 15 and the high frequency applied voltage to the wafer 7 is monitored by the voltmeter 17. Further, the microwave power input to the plasma 6 and the pressure in the processing chamber 5 are monitored by the microwave output meter 2 and the pressure gauge 16, respectively. These four monitors (microwave output meter 2, spectroscope 15, pressure gauge 16,
Signal from high frequency voltmeter 17) and database 19
Is used to estimate the etching state after the process is completed, and pass / fail is determined for the inspection conditions. If it fails, the processing conditions are corrected so that the next wafer to be processed is passed, and the corrected conditions are instructed to the microwave oscillator 1, the gas flow rate regulator 13, the pressure regulating valve 9 and the high frequency power source 18. , And subsequent etching processing is performed. If the processing conditions cannot be corrected, the subsequent processing is stopped.

Next, a method of estimating the uniformity of the etching process from the monitor items will be described with reference to FIGS.
The case of etching the aluminum wiring pattern will be described. Since aluminum, which is a reaction product, is present in the plasma during the etching process, the emission of aluminum can be observed with the spectroscope. FIG. 2 shows the emission intensity of aluminum on the vertical axis and the time on the horizontal axis. The emission intensity of aluminum increases at the same time when the etching process is started, and becomes 0 when the etching is completed. As shown in FIG. 2, the emission intensity of aluminum is almost constant while the entire surface of the wafer is being etched, but the emission intensity depends on when the etching end portion appears on the wafer (t _{1 in} FIG. 2). Becomes 0 when the etching of the entire surface is completed (t _{2 in} FIG. ₂ ). Therefore, if the etching process is completed on the entire surface of the wafer at the same time, t ₁ becomes equal to t ₂ . On the other hand, if the uniformity of the etching process is not good, this time lag becomes large. Therefore, it is considered that a dimensionless version of this time shift (t ₂ −t ₁ ), that is, (t ₂ −t ₁ ) / (t ₂ + t ₁ ) is proportional to the uniformity of the etching process. If the correlation between the etching uniformity and the uniformity obtained from t ₁ and t _{2 is} investigated by a preliminary experiment prior to the actual treatment (Fig. 3), t ₁ and t ₂
The uniformity can be estimated from

Next, a method for estimating the side etching amount and the size and shape of the etching process will be described with reference to FIGS. In the etching process, there is a side etching phenomenon in which the side wall of the pattern is etched, and it is preferable that the side etching amount is small. In order to prevent the side-etch phenomenon, a resist mask decomposition product is used as a pattern mask. That is, during etching, the resist is decomposed by the ions from the plasma, and the decomposed product serves as a protective film to cover the surface of the aluminum, which is the material to be etched, to prevent the progress of etching. Although the etching reaction proceeds on the bottom surface of the pattern even if there is a protective film due to the impact of ions, the etching reaction does not proceed so much on the side surface (side wall) of the pattern because the collision of ions is small. Therefore, the side etch amount is determined by the thickness of the protective film formed on the side wall and the amount of active species that promotes the etching reaction. The thickness of the protective film is determined by the rate at which the resist is decomposed, which is determined by the energy of the ions incident on the wafer. Since the energy of ions incident on the wafer is proportional to the bias voltage as shown in FIG. 4, the thickness of the protective film can be calculated from the value of the bias voltage. On the other hand, the amount of active species that contributes to etching may be determined by examining the intensity of light having a specific wavelength emitted by the active species with a spectroscope. The rate of etching reaction can be estimated from this emission intensity.

From the above, the side etch amount can be estimated from the bias voltage and the emission intensity of the active species. For example, if the emission intensity of the active species is constant as shown in FIG. 5, there is a correlation between the bias voltage and the side etch amount. Comes out. If this correlation is obtained by preliminary experiments before the actual processing,
The side etch amount, that is, dimensional accuracy and shape can be indirectly monitored.

Next, a method of estimating the etching selection ratio will be described with reference to FIG.
Will be described. When the wiring pattern is processed by etching, there is always an insulating film under the wiring. At present, silicon oxide (SiO ₂ ) is often used for this insulating film. When the etching process is performed, the process is continued for a while even after the entire surface etching is completed in order to remove the etching residue of the stepped portion (called overetching). At this time, since the lower insulating film is in contact with plasma, this insulating film is also etched. The ratio of the etching rate of the material to be etched (e.g. aluminum) to the etching rate of the insulating film (e.g. silicon oxide) is called the selection ratio, but processing conditions that increase this selection ratio are necessary. In order to monitor this selection ratio, it is utilized that the etching of the insulating film is not physical etching by active species but physical etching by incident ions (sputter etching). Sputter etching with ions is determined by the amount and energy of incident ions. As shown in FIG. 4, if the bias voltage is monitored, the energy of the ions can be found, and the etching rate of the insulating film can be found from the result (quantity of light emission) of the spectral analysis of plasma. Since the etching rate of aluminum is proportional to its emission intensity, the selection ratio is proportional to the aluminum emission intensity divided by the product of plasma emission intensity and bias voltage. Therefore, the correlation as shown in FIG. 6 is obtained, and thereby the selection ratio can be estimated.

Since the result of the etching process can be indirectly monitored by the above method, the pass / fail can be determined by comparing this with the pass condition of the inspection. Parameters that affect etching characteristics (processing conditions)
If it is clarified by a preliminary experiment and stored as a database, the next process can be passed if the processing condition is corrected according to the database even if it fails, and the defect is judged to be one. You can keep it in one sheet.

Further, by examining the time change of the etching characteristics collected by the method of the present invention, it is possible to estimate the time when the characteristic deterioration which cannot be coped with by the modification of the processing conditions (maintenance is required). Therefore, maintenance can be minimized.

[0018]

According to the present invention, since the etching process of the wafer of the plasma etching apparatus can be constantly monitored and the processing characteristics thereof can be maintained constant, the occurrence of defects can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a uniformity estimation method according to the first embodiment of this invention.

FIG. 3 is an explanatory diagram of a uniformity estimation method according to the first embodiment of this invention.

FIG. 4 is an explanatory diagram of a dimension accuracy estimation method according to the first embodiment of this invention.

FIG. 5 is an explanatory diagram of a dimension accuracy estimation method according to the first embodiment of this invention.

FIG. 6 is an explanatory diagram of a selection ratio estimation method according to the first embodiment of this invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Microwave oscillator, 2 ... Microwave output meter, 3 ... Waveguide, 4 ... Microwave transmission window, 5 ... Processing chamber, 6 ... Plasma, 7 ... Wafer, 8 ... Wafer mounting electrode, 9 ... Pressure control Valve, 10 ... Exhaust pipe, 11 ... Lighting window, 12 ... Plasma light emission optical path, 13 ... Gas flow rate controller, 14 ... Gas introduction pipe, 1
5 ... Spectrometer, 16 ... Pressure gauge, 17 ... High-frequency voltmeter, 18
… High frequency power supply, 19… Etching database, 20…
Arithmetic controller.

Claims (5)

[Claims] 1. A wafer etching process in an etching monitor of a plasma etching apparatus having a processing chamber having a structure for holding a vacuum, a means for introducing an etching gas into the processing chamber, and a means for generating and maintaining plasma in the processing chamber. An etching monitor for a plasma etching apparatus, which is provided with means for monitoring characteristics. 2. The etching monitor for a plasma etching apparatus according to claim 1, further comprising means for judging whether the monitoring result of the etching process is acceptable or unacceptable with respect to the inspection condition of the etching process. 3. The etching monitor for a plasma etching apparatus according to claim 1, further comprising means for instructing the plasma etching apparatus to modify the processing conditions based on the monitoring result of the etching processing. 4. The etching monitor of the plasma etching apparatus according to claim 1, further comprising means for instructing the plasma etching apparatus to stop the processing based on the monitoring result of the etching processing. 5. An etching monitor for a plasma etching apparatus according to claim 1, further comprising means for estimating a maintenance time of the plasma etching apparatus based on a change over time based on a monitoring result of the etching processing.