JP3893276B2 - Plasma processing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing apparatus and a processing method, and more particularly, to a plasma processing apparatus and the like that can prevent the occurrence of a plasma processing failure due to abnormalities in plasma discharge (including unstable discharge).
[0002]
[Prior art]
In plasma processing apparatuses such as CVD (Chemical Vapor Deposition) or etching, the permissible width (process window) of process conditions for obtaining uniform processing results within the wafer is increasing year by year in response to the recent miniaturization of semiconductor devices. It is getting narrower. For this reason, the plasma processing apparatus is desired to operate under more complete process conditions. Further, the process conditions are required to be stable over the processing period of a large number of wafers, not just one.
[0003]
In general, the process conditions vary due to adhesion of reaction products generated as processing is repeated. In CVD (Chemical Vapor Deposition) or etching, the state of the chamber changes due to adhesion of reaction products generated as processing is repeated, and the plasma processing conditions gradually change. For example, particles are generated by reaction products adhering to the chamber, and the composition of dissociated species, the potential or density of plasma, and the like change during plasma processing.
[0004]
Hereinafter, the generation of particles will be specifically described. Usually, aluminum or the like whose surface is anodized is used for a vacuum chamber for performing plasma processing. When the plasma treatment is repeated, a deposition film of a reaction product is formed on the alumite layer. The surface of the deposited film is easily charged up by electrons in the plasma, and the amount of electrons on the deposited film surface becomes excessive. When the deposited film is peeled off by releasing these electrons into the bulk plasma, they are released into the plasma as dust. Some of these dusts fly onto the wafer, causing plasma processing defects. In addition, when an abnormal discharge occurs in the plasma, the semiconductor element on the wafer is charged up, and the element may be destroyed due to an excessive current flowing. Furthermore, depending on the deposited film of the reaction product, the electrical resistance or capacitance between the plasma and the chamber may change, or the reaction balance on the chamber surface may change to change the composition of dissociated species in the plasma. In this case, the plasma discharge itself changes to cause instability of the plasma and to cause a defective plasma processing.
[0005]
[Problems to be solved by the invention]
In order to prevent troubles caused by abnormal discharge and plasma instability as described above, maintenance such as cleaning of the vacuum chamber is generally performed before the deposited film exceeds a certain thickness. However, it is difficult to accurately grasp the maintenance timing. Even if maintenance is performed early, depending on the history of plasma processing, there is an unavoidable possibility of processing failure due to abnormal discharge or unstable discharge within the earlier maintenance cycle.
[0006]
The present invention has been made in view of these problems, and provides a plasma processing apparatus capable of stopping plasma processing when abnormal discharge occurs and preventing occurrence of defective plasma processing.
[0007]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
[0008]
A plasma chamber that includes a processing gas introduction unit, an exhaust unit, and a wafer stage on which a semiconductor wafer is placed, and plasma that generates a plasma in the vacuum chamber by supplying high-frequency power to the vacuum chamber via an impedance matching unit In a plasma processing apparatus comprising a generating means for performing plasma processing on a semiconductor wafer placed on the wafer stage,
Inserted into a sensor for measuring reflected wave power of high frequency power supplied into the vacuum chamber, a sensor for measuring traveling wave power of high frequency power supplied into the vacuum chamber, and a circuit for supplying high frequency power into the vacuum chamber A sensor for measuring a variation amount of a matching position in a circuit element constituting the matching circuit, and an abnormal discharge detection circuit for detecting an abnormal discharge of plasma based on the sensor output, the abnormal discharge detection circuit including the traveling wave The power is greater than or equal to a set value, the amount of change in the matching position in the circuit element and the traveling wave power at a predetermined time is less than or equal to the set value, and the differential output of the sensor output that measures the reflected wave power When the maximum value and the minimum value in time are above or below a preset value, it is determined that the plasma discharge is abnormal .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment of the present invention. The plasma processing unit in the plasma processing apparatus 23 includes plasma generating means 1 (for example, an electrode to which a high frequency voltage is supplied) that generates plasma upon receiving power supply from high frequency power generating means (including microwave generating means), The vacuum chamber 2, the means 3 for introducing gas into the vacuum chamber, the exhaust means 6, and the like. Further, a wafer stage 27 is provided in a portion of the vacuum chamber where the plasma is generated, and a wafer carried by a transfer system (not shown) is placed on the wafer stage. In addition, a high frequency power generation means 8 is electrically connected to the plasma generation means 1 via an impedance matching means 7.
[0010]
Between the high-frequency power generating means 8 and the matching means 7, a directional coupler 9 for detecting the transmitted high-frequency traveling wave power and reflected wave power is installed. The directional coupler outputs a voltage waveform proportional to the traveling wave power and the reflected wave power of the frequency generated by the high frequency power generating means. The voltage waveforms proportional to the traveling wave power and the reflected wave power are detected by the detection circuits 10 and 11, respectively. Next, these detection outputs are amplified to an appropriate voltage by the amplifier circuits 12 and 13, respectively, and then the progress is output as a voltage signal 14 proportional to power and the reflection as a voltage signal 15 proportional to power.
[0011]
Here, FIG. 2 is a diagram showing a waveform 50 of the reflected wave power output from the directional coupler, and FIG. 3 is a diagram showing a waveform 55 after detection of the reflected wave power.
[0012]
The directional coupler 9, the detection circuits 10 and 11, and the amplifier circuits 12 and 13 are normally built in a power supply system 22 including a high frequency power generation means 8, and the signals 14 and 15 are output as analog outputs. There are many.
[0013]
FIG. 4 is a diagram showing a waveform 60 after detection when abnormal discharge occurs in the plasma. As shown in the figure, various noises are included. Therefore, a signal 65 as shown in FIG. 5 is obtained by removing high-frequency components and noise by the first low-pass filter 16.
[0014]
Next, the signal 65 is supplied to the differentiating circuit 17 to perform first order differentiation. There are various methods for obtaining the first derivative, and the Savitzky-Golay smoothed differential method described in SJ Orfanidis: “Introduction to Signal Processing”: Prentice Hall (1996) is used, and is shown in FIG. Thus, it is possible to obtain a primary differential value signal 70 that is relatively less affected by noise.
[0015]
Since the primary differential signal 70 includes some noise fluctuation, by applying the second low-pass filter 18, a signal 75 finally used for discrimination of abnormal discharge as shown in FIG. 7 is obtained.
[0016]
The abnormal discharge detection circuit 19 for detecting abnormal discharge indicates a signal obtained by processing the signal 15 indicating the reflected wave power by the low-pass filters 16 and 18 and the differentiating circuit, the signal 14 indicating the traveling wave power, and the fluctuation of the impedance matching means. A signal 20 is input.
[0017]
Although the form of the impedance matching means 7 differs depending on the frequency to be processed, the high frequency band or UHF band matching unit has two or three variable capacitors inside, and changes the capacitance of these variable capacitors. Impedance matching is achieved. Accordingly, the signal 20 indicating the fluctuation of the impedance matching means can be a signal indicating the capacitance of the variable capacitor in a high frequency band or UHF band matching unit.
[0018]
Note that the entire plasma processing apparatus 23 including the power supply system 22 is controlled by the control system 4, and plasma processing is sequentially performed on the wafers placed on the wafer stage 27.
[0019]
FIG. 8 is a flowchart showing the operation of the abnormal discharge detection circuit 19. First, the detection circuit constantly monitors the traveling wave power signal Pf (signal 14), and when the signal 14 is larger than a preset value Pf0, the operation starts on the assumption that plasma processing has started (step 1). ). The detection circuit checks the maximum variation ΔCmax of the capacitance of the three variable capacitors built in the matching unit and the variation ΔPf of the traveling wave power signal Pf at regular intervals (in this case, every 5 seconds) (step 2). ) If these fluctuations are larger than the preset values ΔC0 and ΔPf0, the abnormal discharge detection process is not performed because it is immediately after the ignition of the plasma or during the switching of the processing step (step 4). Otherwise, it is determined that the plasma is stable to some extent (not meaning that there is no abnormal discharge or instability), and detection of abnormal discharge is started (step 5). First, the reflected wave signal for 5 seconds is processed by the low-pass filter 16, the Savitzky-Golay smoothing differentiation circuit 17, and the second low-pass filter 18 as described with reference to FIGS. 4 to 7 (steps 5, 6, 7, 8). ), And a signal 75 (a signal finally used for detecting abnormal discharge) as shown in FIG. 7 is obtained.
[0020]
Next, the maximum value α (positive) and the minimum value β (negative) of the signal 75 in the 5 seconds are used as a criterion for determination, and the maximum value α and the minimum value β are α with respect to the preset values α0 and β0. When> α0 and β <β0 are satisfied, it is considered that the fluctuation of the reflected wave is abnormally large, and it is determined that the discharge is abnormal (steps 9 and 10). Here, α> α0 and β <β0 are used to determine the presence or absence of abnormal discharge because the reflected wave is “increased and decreased” or “decreased and increased”. This is because the wave fluctuation pattern. For example, if it decreases significantly during the 5 seconds, β <β0 is satisfied, but α> α0 is not satisfied, so that stable discharge can be determined (step 11).
[0021]
In the flowchart shown in FIG. 8, the presence / absence of abnormal discharge is determined at regular intervals of 5 seconds, but as shown in FIG. 7, the first 5 seconds of processing is performed first, and then the next 5 seconds. Processing may be performed, or as shown in FIG. 9, processing for continuously determining the presence or absence of abnormal discharge may be performed using a history of signals from a certain time to a time going back for 5 seconds.
[0022]
When the abnormal discharge detection circuit 19 determines that an abnormal discharge has occurred, an abnormal discharge detection signal 21 is output to the control system 4. The control system 4 can immediately stop the plasma processing. Depending on the degree of abnormal discharge that has occurred, the plasma processing may not be significantly affected. Therefore, the plasma processing is performed on the wafer being processed as it is, and the plasma processing on the subsequent wafers may be interrupted. Good. Alternatively, an alarm may be issued.
[0023]
In the above description, a reflected wave of high-frequency power for plasma generation is used as a signal for detecting an abnormal discharge of plasma. However, the present invention is not limited to the reflected wave, and the electrical state indicating the plasma processing state is used. Alternatively, all optical signals can be used.
[0024]
Further, as a signal for detecting an abnormal discharge of plasma, a detection signal from other means can be used in combination with the reflected wave of the plasma generating high frequency power.
[0025]
For example, a signal 20 (a signal indicating the capacitance of the variable capacitor) indicating the fluctuation of the impedance matching means 7 can be used. In this case, it is determined that an abnormal discharge has occurred when the degree of temporal fluctuation of the reflected wave of the detected high-frequency power is large and the degree of temporal fluctuation of the signal 20 indicating the fluctuation of the matching means is small. Can do.
[0026]
FIG. 10 is a diagram showing another embodiment. In the figure, the same parts as those shown in FIG. In the plasma processing apparatus, a high frequency power source 31 (hereinafter referred to as a bias power source) different from the plasma generating power source is connected via the bias matching unit 30 in order to control the ion energy incident on the workpiece. It is connected to a wafer stage 27 on which an object to be processed is placed. In FIG. 10, instead of the reflected wave of the high frequency power for plasma generation, signals relating to the bias power source such as the peak voltage 32, the DC component 33, and the reflected power 34 of the bias power source 31 are sent to the first low-pass filter 16. Supply. The low-pass filter 16, the differentiating circuit 17 and the second low-pass filter 18 apply these signals to the abnormal discharge detection circuit 19 after filtering and differentiating them. The abnormal discharge detection circuit detects the reflected wave of the plasma generation power by using these signals, or these signals and the signal 20 (signal indicating the capacitance of the variable capacitor) indicating the fluctuation of the impedance matching means 7. It is possible to detect plasma instability and abnormal discharge in the same way as in the case of performing.
[0027]
Further, the plasma emission obtained by the photodetector 28 provided in the vacuum chamber is detected, and the detected plasma emission is dispersed through the spectral and signal amplification unit 29, and the spectral signal is converted into the first low-pass filter 16 and the differential. Even if it is supplied to the abnormal signal detection circuit via the circuit 17 and the second low-pass filter 18, it is possible to detect an abnormal discharge of plasma in the same manner as described above.
[0028]
FIG. 11 is a diagram showing still another embodiment. In the figure, the same parts as those shown in FIG.
[0029]
In the figure, a data collection unit 25 receives a process recipe data signal 26 from the control system 4 to constantly collect process recipe data necessary for plasma processing, such as a gas flow rate, power, and gas pressure supplied to the vacuum chamber. Similarly, signals indicating fluctuations in traveling wave power, reflected wave power, and impedance matching means are also collected.
[0030]
The abnormal discharge detection circuit 19 constantly monitors all these data. In the exact same process recipe, when the newly performed plasma processing signal is significantly different from the history signal of these processing signals for the already processed wafer, this is detected and an abnormal signal is sent to the control system 4 to the user. Issue a warning. Alternatively, the plasma processing of the wafer being processed or the plasma processing of the wafer subsequent to the wafer being processed is stopped.
[0031]
In the example shown in FIG. 1, it is necessary to set appropriate parameters (α0, β0) for determining abnormal discharge in advance, but in this example, the process recipe data and the reflected wave power, for example, It is possible to detect or predict the occurrence of abnormal discharge by accumulating signal data indicating fluctuations and comparing the history data when normal processing is performed with the currently processed signal.
[0032]
As described above, the abnormal discharge accompanying the deposition of the reaction product in the vacuum chamber can be quickly detected. Further, based on this detection, for example, the plasma processing can be interrupted to prevent plasma processing defects due to particles, charge-up damage, process shifts, and the like. Therefore, the plasma processing performance as a whole and the operating rate of the apparatus are improved, and fine etching processing, high-quality film formation processing, surface treatment processing, and the like are possible.
[0033]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a plasma processing apparatus capable of stopping plasma processing when abnormal discharge occurs and preventing the occurrence of defective plasma processing.
[Brief description of the drawings]
FIG. 1 is a diagram showing a plasma processing apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing a waveform of reflected power output from a directional coupler.
FIG. 3 is a diagram showing a waveform after detection of reflected power.
FIG. 4 is a diagram showing a waveform after detection when abnormal discharge occurs in plasma.
FIG. 5 is a diagram illustrating a waveform after processing by a low-pass filter.
FIG. 6 is a diagram showing a primary differential signal.
FIG. 7 is a diagram showing a waveform of a signal used for discrimination of abnormal discharge.
FIG. 8 is a flowchart showing the operation of the abnormal discharge detection circuit.
FIG. 9 is a diagram for explaining determination of abnormal discharge performed using a history.
FIG. 10 is a diagram illustrating another embodiment.
FIG. 11 is a diagram illustrating still another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma production | generation means 2 Vacuum chamber 3 Gas introduction means 4 Control system 5 of plasma processing apparatus Semiconductor wafer 6 Exhaust means 7 Impedance matching device 8 High frequency electric power generation means 9 Directional coupler 10, 11 Detection circuit 12, 13 Amplifier circuit 16 1 low-pass filter 17 primary differential circuit 18 second low-pass filter 19 abnormal discharge detection circuit 22 power supply system 23 plasma processing device 25 data collection unit 27 wafer stage 28 photodetector 29 spectral and signal amplification unit 30 bias matching unit 31 bias High frequency power supply

Claims (3)

A vacuum chamber provided with a processing gas introducing means, an exhaust means, and a wafer stage on which a semiconductor wafer is placed;
Plasma generating means for generating high-frequency power in the vacuum chamber through impedance matching means to generate plasma in the vacuum chamber;
In a plasma processing apparatus for performing plasma processing on a semiconductor wafer placed on the wafer stage,
Inserted into a sensor for measuring reflected wave power of high frequency power supplied into the vacuum chamber, a sensor for measuring traveling wave power of high frequency power supplied into the vacuum chamber, and a circuit for supplying high frequency power into the vacuum chamber A sensor that measures the amount of variation in the matching position in the circuit elements that constitute the matching circuit, and an abnormal discharge detection circuit that detects abnormal discharge of plasma based on the sensor output,
In the abnormal discharge detection circuit, the traveling wave power is not less than a set value, and the amount of change in the matching position in the circuit element and the traveling wave power in a predetermined time is not more than a set value,
Further, it is determined that the plasma discharge is abnormal when the maximum value and the minimum value of the differential output of the sensor output for measuring the reflected wave power are greater than or less than a preset value, respectively. apparatus. The plasma processing apparatus according to claim 1 ,
The plasma processing apparatus, wherein the abnormal discharge detection circuit stops the plasma processing when detecting abnormal discharge. The plasma processing apparatus according to claim 1 ,
An abnormal discharge detection circuit for detecting an abnormality in plasma discharge includes data collection means for collecting the sensor output signal, and the generation of abnormal discharge is detected by comparing the sensor output with the collected data during normal discharge collected in the collection means. A plasma processing apparatus characterized by predicting.

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