JP4690837B2 - Temperature control method and temperature control apparatus for sample mounting electrode - Google Patents

Description

  The present invention relates to a plasma processing technique, and more particularly to a plasma processing technique capable of suppressing a change with time in a plasma processing apparatus.

  In the plasma etching apparatus, anisotropic etching is performed by applying high-frequency power to a sample (wafer) mounting electrode and drawing ions from plasma. At this time, a coolant is circulated through the sample mounting electrode for the plasma etching apparatus to keep the sample (wafer) at a constant temperature. In an electrostatic chuck type mounting electrode, an insulating layer is provided on the surface of the mounting electrode, and the sample is electrostatically adsorbed by applying a DC voltage to the mounting electrode in a state where plasma is generated on the sample. Yes. At this time, the mounting electrode and the plasma are insulated.

Further, heat conduction gas (He) is supplied to the gap between the sample and the mounting electrode, and the heat is transferred from the sample to the mounting electrode by maintaining a constant pressure of several hundred Pa or more. In many cases, a ceramic sprayed film such as Al ₂ O ₃ is used as an insulating layer on the surface of the mounting electrode. Further, a sealing agent is often applied to the sprayed film in order to seal the pores generated between the ceramic particles forming the sprayed film and increase the insulation.

In addition, in order to maintain the pressure of the gas for heat conduction over the entire back surface of the sample, a width in the radial direction is set so that the entire periphery of the sample is in contact with the portion of the mounting electrode facing the vicinity of the periphery of the sample back A convex portion is formed to prevent leakage of the gas. In addition, the inner part of the mounting electrode forms a part having a certain gap so that gas can easily flow and a part to be held in contact with the sample. In addition, when such a sample mounting electrode is used, a change with time in which the sample temperature gradually decreases occurs, and such a change with time is improved by changing the sealing agent. It is known (see Patent Document 1).
JP 2003-45752 A

  By the way, when performing the plasma etching process using the sample mounting electrode whose ceramic is sprayed on the surface of the mounting electrode as described above, the sample is not mounted on the sample mounting electrode in order to improve the throughput. Plasma cleaning may be performed. In such a case, the sample mounting electrode is frequently exposed to plasma.

  When such an operation is performed, it has been found that, unlike the case described in Patent Document 1, a change with time in which the sample temperature gradually rises appears.

  The present invention has been made in view of such problems, and provides a plasma processing technique capable of keeping a sample temperature constant by suppressing a change in the sample temperature based on a change with time of the plasma processing apparatus. is there.

  In order to solve the above problems, the present invention employs the following means.

A vacuum processing container; a gas supply means for supplying a processing gas into the vacuum processing container; a sample mounting electrode disposed in the vacuum processing container for mounting and holding a sample; and the sample mounting The vacuum processing container comprising: a cooling gas supply means for supplying a cooling gas to a gap between the electrode and the sample; and an electrode temperature controller for supplying a temperature-adjusted refrigerant to a refrigerant channel provided in the sample mounting electrode. In the method for controlling the temperature of the sample mounting electrode in the plasma processing apparatus for supplying a high frequency power into the plasma to generate plasma in the vacuum vessel and performing plasma processing on the sample,
The previously acquired relationship between the flow rate of the cooling gas supplied to the gap and the temperature rise relative to the initial state of the sample temperature accompanying the time-dependent change of the mounting electrode due to the plasma cleaning of the mounting electrode, and the plasma cleaning As a result, the temperature rise value of the sample is estimated based on the flow rate of the cooling gas that is supplied to the gap between the mounting electrode and the sample that has changed over time and is required to keep the pressure in the gap constant. The value obtained by subtracting the temperature increase value from the mounting electrode temperature specified by the recipe is set as the target temperature of the mounting electrode, and the temperature or flow rate of the refrigerant supplied to the refrigerant flow path is adjusted to adjust the temperature of the sample. The temperature is kept constant at the sample temperature before the aging of the mounting electrode.

  Since the present invention has the above-described configuration, it is possible to keep the sample temperature constant by suppressing the sample temperature change based on the change with time of the plasma processing apparatus.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram for explaining a plasma processing apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining details of a sample mounting electrode shown in FIG. Hereinafter, description will be given with reference to these drawings. The plasma processing apparatus includes a plasma processing chamber 101 formed of a vacuum processing container. An upper portion of the plasma processing chamber 101 includes an antenna 103 connected to a high-frequency power source 102a for generating plasma and a power source 102b for bias, and a gas supply system 104 for supplying an etching gas. In addition, an exhaust system 105 for maintaining the processing chamber at a predetermined pressure and a sample mounting electrode 107 for mounting a sample are provided below the plasma processing chamber 101.

  Details of the sample mounting electrode 107 will be described with reference to FIG. The portion of the sample mounting electrode where the sample is not mounted (the outermost peripheral portion) is covered with a quartz cover 108 or the like in order to insulate from the plasma. The sample mounting electrode 107 includes an electrostatic chuck mechanism using an electrostatic attraction power source 109.

That is, a dielectric sprayed film 110 made of a mixture of Al ₂ O ₃ and TiO ₂ is applied to the surface of the mounting electrode 107 facing the sample 106. Further, the surface of the sprayed film 110 that comes into contact with the sample has a surface roughness (Ra) of 0.8 μm or less by polishing. As described above, the surface of the outer peripheral portion (bank portion 111) of the mounting electrode 107 and the outermost peripheral portion of the sample are in contact with each other as described above. Further, He gas is supplied from the cooling gas supply system 112 to the back surface of the sample 106. The control computer 116 monitors the pressure of the supplied He gas with the pressure gauge 113 and adjusts the flow rate so as to be a constant pressure of 1.5 kPa.

  As described above, since the outermost peripheral portion of the sample is in contact with the sprayed film 110 of the mounting electrode on the entire periphery, the conductance is the smallest at this contact portion (bank portion 111). For this reason, the leakage amount of the cooling gas is almost determined by the sealing performance of this portion. Thus, the cooling gas always leaks slightly from the gap between the sample and the mounting electrode due to the roughness of the surface of the sprayed film 110. This leakage amount can be recorded by monitoring the supply flow rate from the cooling gas supply system 112 corresponding to the leakage amount.

Connected to the sample mounting electrode 107 are a DC power source 109 for electrostatic adsorption, a bias high frequency power source 114 for performing anisotropic etching, and an electrode temperature controller 115 for controlling the temperature of the mounting electrode 107. ing. The electrode temperature adjuster 115 adjusts the temperature or flow rate of the refrigerant supplied to the refrigerant flow path formed in the mounting electrode 107. The plasma processing chamber 101 shown in FIG. be able to. The unit includes, for example, two cassettes storing 25 samples, and samples are sequentially transferred from these cassettes to the processing chamber for processing. Further, each power source 102a, 102b, cooling gas supply system 112, electrode temperature controller 115, electrostatic adsorption power source 109, gas supply system 104, and pressure gauge 113 of the plasma processing apparatus are connected to a control computer 116. Various settings and setting values can be saved. The control computer 116 includes an operation computer (not shown) and a display device that perform recipe setting, display, processing history storage, calculation, and the like.

  Next, the change with time of the sample temperature in the plasma processing apparatus will be described.

  FIG. 3 is a diagram showing a change in the flow rate of the cooling gas (He) with respect to the processing time (total processing time), and FIG. 4 explains the relationship between the leakage amount (supply amount) of the cooling gas and the temperature rise of the sample (wafer). FIG.

In the plasma processing apparatus, a reaction product is deposited in the processing chamber every time one sample is etched. For this reason, cleaning is performed with O ₂ plasma every time the etching process is performed. Further, in order to improve the throughput, the cleaning performs plasma discharge by applying a wafer bias of 50 to 200 W without placing a sample on the placement electrode.

  When the sample processing is continued by such an operation method, the cooling gas flow rate gradually increases as shown in FIG. Further, the temperature of the sample gradually increases as shown in FIG. 4 corresponding to the increase in the cooling gas flow rate. As shown in FIG. 4, the temperature rise with respect to the initial state of the cooling gas leakage amount and the sample temperature is in a proportional relationship.

  For this reason, the temperature of the sample can be kept constant by lowering the temperature of the mounting electrode in accordance with the leakage amount of the cooling gas.

  As described above, the flow rate (leakage amount) of the cooling gas is almost determined by the surface roughness of the bank portion 111 of the mounting electrode in contact with the outermost peripheral portion of the sample. Further, the surface roughness of the bank portion represents a change in the surface roughness of other portions. For this reason, a change (increase) in surface roughness caused by exposing the sprayed surface of the mounting electrode to plasma causes an increase in the flow rate of the cooling gas and a decrease in the cooling capacity of the sample. For this reason, the time-dependent change of sample temperature can be monitored by monitoring the cooling gas flow rate.

  FIG. 5 is a diagram for explaining a method for controlling the temperature of a sample. First, the control computer stores data (cooling gas flow rate, electrostatic adsorption voltage, wafer bias voltage (Vpp: peak-to-peak voltage), wafer bias power) acquired during past wafer processing as history data. (Step S1). Next, based on the history data, the trend of the cooling gas flow rate converted into the reference condition is analyzed and grasped (step S2). Next, the reference cooling gas flow rate is calculated based on the monitoring value of the current cooling gas flow rate (step S3). The current flow rate of the cooling gas may be estimated based on the trend grasped in step S2 and the plasma processing time (cumulative value).

  Next, the temperature rise value of the sample is predicted based on the correlation between the cooling gas flow rate acquired in advance and the sample temperature rise (FIG. 4) (step S4) and the estimated cooling gas flow rate (step S5).

  Next, a value obtained by subtracting the temperature rise is set as the target temperature of the mounting electrode from the mounting electrode setting temperature (step S6) designated by the recipe, and control is started (step S7, step S8).

  Although the proportionality constant representing the correlation (step S4) shown in FIG. 4 varies depending on the mounting electrode and the sample back pressure, in the present embodiment, ΔT = 4 (Q (ml / min) −1). When grasping the long-term trend of the cooling gas flow rate, the cooling gas flow rate varies from wafer to wafer, so it is desirable to determine from the results of wafer processing of 10 lots or more.

  In step S7 and step S8 of FIG. 5, in this embodiment, the sample temperature is controlled to be constant by lowering the mounting electrode temperature. However, instead of changing the mounting electrode temperature, the cooling gas pressure is changed. Alternatively, by changing the sample bias power, the sample temperature can be kept constant as long as the relationship between these and the sample temperature is known. However, it is easy to use and adjust the mounting electrode temperature.

In this embodiment, the Al ₂ O ₃ film is used as the sprayed film of the mounting electrode, but a Y ₂ O ₃ sprayed film can be used. The back pressure can be set to 1 kPa to 2 kPa. A gas other than He gas can be used as the cooling gas. In addition, although an example in which Ra = 0.8 μm or less is shown as the initial surface roughness, the initial value of Ra is not limited to this. In addition, since the seal portion formed by the bank portion is in contact with the sample on the surface of the mounting electrode and the flow rate is controlled, the correlation between the cooling gas flow rate and the sample temperature rise can be obtained. It does not need to be arranged on the outermost periphery. Further, the correlation is a relationship required for each mounting electrode and condition from the relationship between the surface roughness, the cooling gas leakage flow rate, and the sample temperature rise, and is not limited to the proportional relationship.

  As described above, according to the present embodiment, the temperature of the sample is kept constant by controlling the temperature of the mounting electrode based on the flow rate of the cooling gas supplied between the sample and the mounting electrode. Etching characteristics can be stabilized over a long period of time. In addition, it is possible to suppress a change in the sample temperature with time due to a change in the surface of the mounting electrode, and to obtain etching characteristics that are stable over a long period of time.

It is a figure explaining the plasma processing apparatus which concerns on embodiment of this invention. It is a figure explaining the detail of the sample mounting electrode shown in FIG. It is a figure which shows the change of the cooling gas flow rate with respect to process time. It is a figure explaining the relationship between the leakage amount of a cooling gas, and the temperature rise of a sample. It is a figure explaining the temperature control method of a sample.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Plasma processing chamber 102a High frequency power supply for plasma generation 102b High frequency power supply for bias 103 Antenna 104 Gas supply system 105 Exhaust system 106 Sample (sample)
107 Sample mounting electrode 108 Quartz cover
DESCRIPTION OF SYMBOLS 109 Electrostatic adsorption power source 110 Thermal spray film 111 Placement electrode outer peripheral part 112 Cooling gas supply system 113 Pressure gauge 114 Bias high frequency power supply 115 Electrode temperature controller 116 Control computer

Claims (3)

A vacuum processing container; a gas supply means for supplying a processing gas into the vacuum processing container; a sample mounting electrode disposed in the vacuum processing container for mounting and holding a sample; and the sample mounting The vacuum processing container comprising: a cooling gas supply means for supplying a cooling gas to a gap between the electrode and the sample; and an electrode temperature controller for supplying a temperature-adjusted refrigerant to a refrigerant channel provided in the sample mounting electrode. In the method for controlling the temperature of the sample mounting electrode in the plasma processing apparatus for supplying a high frequency power into the plasma to generate plasma in the vacuum vessel and performing plasma processing on the sample,
The previously acquired relationship between the flow rate of the cooling gas supplied to the gap and the temperature rise relative to the initial state of the sample temperature accompanying the time-dependent change of the mounting electrode due to the plasma cleaning of the mounting electrode, and the plasma cleaning As a result, the temperature rise value of the sample is estimated based on the flow rate of the cooling gas that is supplied to the gap between the mounting electrode and the sample that has changed over time and is required to keep the pressure in the gap constant. The value obtained by subtracting the temperature increase value from the mounting electrode temperature specified by the recipe is set as the target temperature of the mounting electrode, and the temperature or flow rate of the refrigerant supplied to the refrigerant flow path is adjusted to adjust the A temperature control method for a sample mounting electrode, characterized in that the temperature is maintained at a constant sample temperature before the time-dependent change of the mounting electrode. In the temperature control method of the sample mounting electrode according to claim 1,
A method for controlling a temperature of a sample mounting electrode, characterized in that a plasma cleaning process is performed without placing a sample on a sample mounting electrode every time a sample is subjected to plasma processing. A vacuum processing container; a gas supply means for supplying a processing gas into the vacuum processing container; a sample mounting electrode disposed in the vacuum processing container for mounting and holding a sample; and the sample mounting The vacuum processing container comprising: a cooling gas supply means for supplying a cooling gas to a gap between the electrode and the sample; and an electrode temperature controller for supplying a temperature-adjusted refrigerant to a refrigerant channel provided in the sample mounting electrode. In a plasma processing apparatus for supplying a high-frequency power into the plasma to generate plasma in the vacuum vessel and subjecting the sample to plasma processing,
For each processed sample, the relationship between the flow rate of the cooling gas supplied to the gap and the temperature rise relative to the initial state of the sample temperature due to the time-dependent change of the mounting electrode due to the plasma cleaning of the mounting electrode was stored. With a database,
The sample is supplied based on the flow rate of the cooling gas required to keep the pressure in the gap constant, which is supplied to the gap between the database and the mounting electrode that has changed with time due to the plasma cleaning and the sample. The temperature or flow rate of the refrigerant supplied to the refrigerant flow path is set as a target electrode temperature set by subtracting the temperature increase value from the mounting electrode temperature specified by the recipe. The temperature of the sample is kept at the sample temperature before the time-dependent change of the placement electrode by adjusting the temperature of the sample placement electrode.

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