JP2010050178A - Plasma processing device and plasma processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma processing operating method that suppresses temporal deterioration in processing dimensional accuracy caused by temporal variations in wafer temperature so as to maintain high-accuracy etching. <P>SOLUTION: Concerning a heater-temperature control electrode, a change waveform of controlled heater power after the start of the plasma processing is logged and a controlled temperature or fill pressure of heat-transfer gas, filled in the wafer rear-face, is adjusted so as to suppress a change of the waveform with respect to a reference value. Concerning a refrigerant-temperature control electrode, a change waveform of a temperature sensor signal after the start of the plasma processing is logged and the controlled temperature or the fill pressure of the heat-transfer gas, filled in the wafer rear-face, is adjusted by temporal changes of the waveform. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma processing apparatus and a plasma processing method, and more particularly to a plasma processing apparatus and a plasma processing method suitable for a transistor gate etching process requiring high processing line width accuracy.

  In the prior art, generally, a temperature-controlled refrigerant is circulated in the refrigerant groove of the electrode substrate, and the wafer temperature is indirectly controlled by the temperature adjustment temperature of the refrigerant. Alternatively, as shown in Patent Document 1, a heater is built in between the coolant circulation groove and the electrode surface, and the wafer temperature is indirectly controlled by adjusting the temperature at a position close to the wafer, and etching is performed in a temperature sensitive process. The machining dimensional accuracy was maintained.

  During the plasma processing, due to heat input to the wafer generated by plasma and bias or chemical reaction, a temperature difference is generated between the point controlled by the refrigerant or the heater and the wafer. Since this temperature difference is determined by the amount of heat input and the thermal resistance between the wafer and the control point, if both the amount of heat input and the thermal resistance are constant, the wafer temperature is kept equal when performing the same process.

  However, among the elements that form the thermal resistance, in particular, the thermal resistance between the wafer and the electrode changes over time as the state of the electrode surface accumulates the etching process. Despite the fact that the wafer temperature is changed, the wafer temperature may change over time, and the dimensional accuracy of the etching process may decrease.

  With the progress of miniaturization, semiconductor integrated circuits are required to have high-speed operation of transistor elements, and high processing dimensional accuracy is required particularly for etching of gate electrodes. The dimensional accuracy of the etching process is greatly affected by the temperature of the wafer as well as the gas chemistry and plasma conditions to be used. Regarding the wafer temperature, the temperature of the electrode is controlled to maintain the dimensional accuracy of the process.

  On the other hand, the heat generated on the wafer surface by the chemical reaction and charged particles during the plasma treatment is transferred from the wafer to the interface between the wafer back surface and the electrode filled with the heat transfer gas and flows to the electrode. Although the heat transfer gas is filled on the back surface of the wafer, its heat resistance is relatively large, and the temperature of the wafer becomes higher than the control temperature of the electrode due to the temperature difference generated in this portion. In particular, when etching is performed with a high bias voltage applied, a large temperature difference occurs between the wafer temperature and the electrode control temperature.

  The heat transfer rate between the wafer back surface and the electrode is affected not only by the filling gas pressure but also by the state of the electrode surface or the state of the wafer back surface. The rate is not constant, and as a result, the wafer temperature may fluctuate despite the electrode temperature and the heat input by the plasma treatment being kept constant.

As a result, in the processing process that is easily affected by the wafer temperature, the processing dimensions fluctuate due to the accumulation of plasma processing, resulting in variations in transistor element characteristics.
JP 2007-88411 A

  An object of the present invention is to provide a plasma processing operation method capable of suppressing a decrease in processing dimension accuracy over time caused by a change in wafer temperature with time and maintaining a highly accurate etching process.

  The plasma processing apparatus of the present invention is a plasma processing apparatus having an electrode with a temperature control function, and monitors the output monitor value of the temperature control means of the electrode during plasma processing, and the history is monitored by the monitoring means. And a calibration means for calibrating the back surface filling gas or the control temperature set value of the substrate to be processed when the monitor value changes more than a predetermined value.

  The plasma processing method of the present invention is a plasma processing method using a plasma processing apparatus having an electrode with a temperature control function, and has a maintenance sequence for temperature control calibration. A step of adjusting the temperature with a temperature adjustment setting in which a temperature gradient is generated in the wafer surface, a step of logging (historic monitoring) the output monitor of the temperature adjusting means and comparing it with a reference value, and a processing target depending on the comparison result Calibrating the back surface filling gas or the control temperature set value of the substrate.

  As a specific means for solving the above-mentioned problem, for example, in the case of a heater temperature control electrode, a change waveform of the control heater power after starting plasma processing is logged (history monitoring), and a change from the reference value of the waveform is performed. The control temperature is adjusted so as to suppress this, or the filling pressure of the heat transfer gas filled on the back surface of the wafer is adjusted.

  Furthermore, in the case of the refrigerant temperature control electrode, the change waveform of the temperature sensor signal after the start of plasma processing is logged (history monitoring), and the control temperature is adjusted by the change of the waveform over time, or the back surface of the wafer is filled. Adjust the heat transfer gas filling pressure.

  The present invention has been made for the purpose of solving the above problems, and the configuration, implementation method, and the like will be described below with reference to the drawings.

  FIG. 1 shows an etching apparatus in which Example 1 of the present invention is implemented. The microwave output from the microwave source 101 is transmitted through the waveguide 104. A vacuum exhaust system (not shown) and a gas introduction system (not shown) are connected to the processing chamber 111 and can be maintained at an atmosphere and pressure suitable for plasma processing. A gas in the processing chamber 111 is turned into plasma by the input microwave, and a predetermined plasma processing can be performed on the sample to be processed (hereinafter referred to as a wafer) 112. Note that the plasma generation means is not microwaves, but may be plasma generation means based on inductive coupling using high frequency or electrostatic coupling using high frequency.

  The wafer 112 is set on a circular mounting surface disposed on the sample mounting electrode 113 having a substantially cylindrical shape. The sample mounting electrode 113 is electrically connected to a bias power source 115 via an automatic matching unit 114, and a bias potential can be formed on the upper surface of the wafer 112 by power supplied therefrom. As a result, ions in the plasma are drawn into the substrate to be processed, and plasma etching is performed. The mounting surface, which is the upper surface of the sample mounting electrode 113, is composed of a dielectric film, and heat transfer gas is applied to the surface of the mounting surface in order to improve heat conduction between the surface and the back surface of the wafer 112. A He introduction system 116 having an opening for supply is arranged in the sample mounting electrode 113.

  In addition, electric power is supplied to the dielectric film to heat the wafer 112 and the electrostatic chuck having a film-like electrode to which electric power is supplied to attract and hold the wafer 112 on the mounting surface. A film-shaped heater is disposed, a DC power source 117 for operating the electrostatic chuck, a heater power source 118 for operating the heater to control the temperature of the wafer 112, and further disposed inside the sample mounting electrode 113 and above it. A temperature controller 119 for temperature-regulating and circulating a refrigerant flowing in a concentric or spiral passage arranged to cool a metal base material having a shape that can be regarded as a cylindrical shape with a dielectric film disposed on the surface. Is connected.

  Furthermore, a temperature sensor 121 that detects and outputs the temperature at a plurality of locations inside the sample mounting electrode 113, and a wafer that determines an output command value to the heater power supply 118 based on the output from the temperature sensor 121. A temperature control unit 120 is connected.

  The wafer temperature control unit 120 may be configured by a single semiconductor device having an arithmetic unit such as a CPU and a storage device therein, or a plurality of semiconductor devices each constituting the arithmetic unit and the storage device. You may comprise from the combination of a connector, an interface, etc. Further, the wafer temperature control unit 120 may constitute a part of a control device that is connected to a DC power source 117, a temperature controller 119, and the like so as to be able to send and receive signals and adjusts the operation of the etching apparatus.

  In order to clarify the malfunction phenomenon to which the present invention is applied, a wafer with a resist pattern was etched, and the change in the processing dimension was compared before and after the plasma was irradiated on the electrode surface. Here, the plasma irradiation to the electrode is intended to be performed by simulating acceleration of the state change of the electrode surface caused by the cumulative processing of the wafer.

  As shown in FIG. 2, it can be seen that the processing dimension becomes thinner every time the plasma irradiation is repeated once or twice as shown in FIG. 2. This is because the fine shape of the electrode surface is changed by the long-time irradiation of plasma, and the heat transfer coefficient between the wafer and the electrode is lowered, thereby increasing the wafer temperature and increasing the etching rate of the pattern side wall. Variations in processing dimensions have a significant effect on performance, particularly in transistor gate electrode processing, and must be minimized.

  With respect to this problem, a method of applying the first embodiment of the present invention and the result thereof will be described below. In this embodiment, the heater temperature control power of the heater power supply 118 is always logged (history monitoring), and the power fluctuation waveforms of the heater control of the current process and the past process are compared at a constant cycle. That is, in this embodiment, the value of power, current or voltage output from the heater power supply 118 is periodically detected at predetermined intervals and recorded as data in the storage device in the wafer temperature control unit 120.

  The value of the data recorded in this way is a waveform indicating the fluctuation of the power value when the time is shown as a graph on one axis and the output value is shown as a graph on the other axis. The recorded data becomes the past history of the output of the heater power supply 118, and the etching apparatus of this embodiment has a function of comparing the recorded past history with the history of the output of the heater power supply 118 of the current process. Yes. For the past history, a storage device outside the wafer temperature control unit 120 may be used, a storage device disposed at a location remote from the etching device may be used, or the storage device may be configured to be detachable. good. The waveform (history monitoring) to be compared is a waveform obtained at the timing of step execution of the same etching recipe shown in FIG.

  FIG. 4 shows a case where there is a change in the monitor waveform of the heater control power from the heater power supply 118 due to accumulated wafer processing without using the calibration control portion of the present invention. The heater control power starts to decrease from the time of plasma ignition and stabilizes after a certain period of time. However, the level at the time of stabilization does not change due to the accumulation of wafer processing, but the rate of change until stabilization decreases as shown by the dotted line in FIG. You can see that This decrease in the change speed corresponds to a change in the heat transfer coefficient between the wafer and the electrode, and further corresponds to a change in the processing dimension with time.

  In the configuration for performing the calibration control in the present invention, when the change rate is lowered so that the change rate is kept within a certain value, the He (helium) supply system 116 is controlled according to the change amount, and the wafer back surface is controlled. The He (helium) filling pressure is increased to control cooling. As a result, the decrease in the change rate can be suppressed within a certain range, and the variation in wafer processing dimensions can be suppressed within the required accuracy.

  Next, FIG. 5 illustrates, as a second embodiment, an example in which a method of shifting a control temperature set value is used as a calibration unit configured to perform calibration control in the present invention. In the case of this method, the control temperature set value is converted in the processing apparatus by the controller 120 in accordance with the amount of change in the change speed, and shifted to a lower level. As the change ratio, a value determined by a test conducted in advance is used.

  As a result, the control power monitor waveform does not change, but the variation of the processed dimension of the processed pattern wafer is reduced and can be suppressed within the specified value. In this method, it is not necessary to control the He (helium) supply system to increase the pressure of the filling He (helium) gas on the backside of the wafer, and calibration can be performed under the control of the controller 120. It works effectively when used when there is no margin in the adsorbing power.

  FIG. 6 illustrates a case where an electrode that can independently control the heaters of a plurality of zones is used as a third embodiment of the present invention. In this embodiment, unlike the first and second embodiments, the calibration work is performed as an independent maintenance work different from the actual wafer processing. Here, the case of an electrode using electrodes in which the control zone is divided into three areas, center / middle / edge, from the wafer center will be described.

  First, a dummy wafer was placed on the electrode before plasma long-time irradiation, and the temperature of the heater was set by the controller 20 so as to have a temperature distribution of a relationship of center> middle> edge. This temperature setting may be any setting that allows heat to flow through the wafer, and it is desirable that the temperature difference be set as large as possible for accurate calibration. At this time, the dummy wafer used is the same as the wafer to be actually processed and the back surface state. However, if the influence is small, a normal dummy wafer may be used.

In the data acquisition, the temperature control is started with the above settings, and the controller 20 acquires the average heater power of each of the center, the middle, and the edge in a state where the temperature control reaches a steady state. This data was compared with reference data obtained and stored in the same way in the past. The results are summarized in Table 1.

  It can be seen that the power difference between the heaters is smaller after the plasma irradiation than before the irradiation. This is because the heat flow rate flowing in the temperature gradient direction in the wafer decreases due to a decrease in the heat transfer coefficient between the wafer and the electrode. When the patterning wafer was etched in this electrode state, the processing dimensions were narrower than before the plasma irradiation. Here, the method of the present invention was applied, and the He (helium) supply system 116 was controlled so that the steady power was equal to the reference data, and the He filling pressure on the back surface of the wafer was adjusted. After the adjustment, the patterning wafer was etched again, and it was found that the processing dimension was almost the same as that before the plasma irradiation.

  Next, an etching apparatus according to Example 4 of the present invention will be described with reference to FIG. In this embodiment, not the heater temperature control power of the heater power supply 118 but the waveform change of the temperature sensor signal of the temperature sensor 121 that monitors the temperature at a plurality of locations in the electrode is logged (history monitoring).

  The temperature sensor 121 that monitors the temperature at a plurality of locations in the electrode may be included in the controller 120, but may be installed separately from the controller 120 as shown in FIG.

  In the present embodiment, the temperature at a plurality of locations in the electrode is monitored by the temperature sensor 121, and the waveform change of the temperature sensor signal in the electrode of the current process and the past process is logged (history monitoring).

  In the configuration for performing the calibration control in the present embodiment, the He (helium) supply system 116 is controlled according to the amount of change when the rate of change is lowered so that the rate of change of the temperature sensor signal is kept within a certain value. Then, the He (helium) filling pressure on the back surface of the wafer is increased to control cooling. As a result, the decrease in the change rate can be suppressed within a certain range, and the variation in wafer processing dimensions can be suppressed within the required accuracy.

Alternatively, similarly to the second embodiment, the controller 120 can convert the control temperature set value in the processing apparatus and shift it to a lower level in accordance with the amount of decrease in the change rate.
Similarly to the fourth embodiment, it is also possible to place a dummy wafer on the electrode before plasma long-time irradiation, and the controller 20 can set the temperature of the heater so that the temperature distribution has a relationship of center>middle> edge.

  As described above, according to the four embodiments, according to the present invention, it is possible to suppress the change with time of the pattern processing dimension caused by the change of the electrode surface state due to the accumulation of the wafer processing, so that the high yield of the semiconductor circuit production can be maintained. As a result, it is possible to extend the electrode replacement cycle, thereby reducing the production cost.

  In the future, the device structure will become deeper due to the progress of miniaturization, and the process of applying a high bias will increase in order to improve productivity, but the effect of the present invention is effective when the heat input to the wafer is large. Since it becomes remarkable, it is thought that usefulness will increase further in the future.

1 is a schematic cross-sectional view of a plasma etching apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram showing the processing dimension variation due to the plasma irradiation to the electrodes. FIG. 3 is a diagram showing fluctuations in the heater power control waveform before and after plasma ignition. FIG. 4 is a diagram showing a change in the heater control waveform due to accumulated wafer processing. FIG. 5 is a schematic cross-sectional view of a plasma etching apparatus according to the second embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a plasma etching apparatus according to Embodiment 3 of the present invention. FIG. 7 is a schematic cross-sectional view of a plasma etching apparatus according to Embodiment 4 of the present invention.

Explanation of symbols

101 Microwave source 104 Waveguide 111 Processing chamber 112 Substrate (wafer)
113 Sample Placement Electrode 114 Automatic Matching Device 115 Bias Power Supply 116 He Supply System 117 DC Power Supply 118 Heater Power Supply 119 Temperature Controller 120 Controller 121 Temperature Sensor

Claims (8)

  A plasma processing apparatus having an electrode with a temperature control function, the monitoring means for monitoring the output monitor value of the temperature control means of the electrode during plasma processing, and the monitor value history monitored by the monitoring means exceeds a specified value A plasma processing apparatus comprising calibration means for calibrating a back surface filling gas or a control temperature set value of a substrate to be processed when a change occurs. The plasma processing apparatus according to claim 1,
A plasma processing apparatus characterized by monitoring a history of a fluctuation waveform of a heater temperature control power of a heater power source as an output monitor value of the temperature control means. The plasma processing apparatus according to claim 1,
A plasma processing apparatus characterized in that a history of fluctuation waveforms of temperature sensor signals at a plurality of locations in the electrode is monitored as an output monitor value of the temperature control means. The plasma processing apparatus according to claim 2 or 3,
After controlling the heaters in the plurality of zones of the electrodes independently to set the temperature distribution in the plurality of zones in advance, the output monitor value of the temperature adjusting means is monitored in history, and the back surface filling gas of the substrate to be processed or the control temperature set value is set. A plasma processing apparatus characterized by performing calibration.   A plasma processing method using a plasma processing apparatus having an electrode with a temperature control function, comprising a maintenance sequence for temperature control calibration, the sequence processing including a step of transporting and placing a wafer on an electrode, and a temperature within the wafer surface The step of adjusting the temperature by the temperature adjustment setting in which the gradient is generated, the step of monitoring the output monitor of the temperature adjustment means and comparing it with the reference value, and calibrating the back surface filling gas or the control temperature setting value of the substrate to be processed based on the comparison result And a plasma processing method. In the plasma processing method of Claim 5,
A history of monitoring a fluctuation waveform of a heater temperature control power of a heater power source as an output monitor value of the temperature control means. In the plasma processing method of Claim 5,
A plasma processing method characterized in that a history of fluctuation waveforms of temperature sensor signals at a plurality of locations in the electrode is monitored as an output monitor value of the temperature control means. In the plasma processing method of Claim 6 or 7,
After controlling the heaters in the plurality of zones of the electrodes independently to set the temperature distribution in the plurality of zones in advance, the output monitor value of the temperature adjusting means is monitored in history, and the back surface filling gas of the substrate to be processed or the control temperature set value is set. A plasma processing method comprising calibrating.

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