Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
  • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
  • H01L21/6831—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using electrostatic chucks
  • H01L21/6833—Details of electrostatic chucks
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
  • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
  • H01L21/6831—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using electrostatic chucks
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
  • H02N13/00—Clutches or holding devices using electrostatic attraction, e.g. using Johnson-Rahbek effect
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T279/00—Chucks or sockets
  • Y10T279/23—Chucks or sockets with magnetic or electrostatic means

Definitions

• the present invention relates to semiconductor devices and apparatus for their manufacture. More particularly, the present invention relates to improved apparatus and methods for clamping a semiconductor substrate on a bipolar electrostatic chuck in a plasma processing chamber.
• FIG. 1 illustrates a simplified schematic of a substrate processing chamber known as the TCP 9400 SETM, which is available from Lam Research
• a substrate plasma processing system 100 includes a plasma processing chamber 102. Above chamber 102, there is disposed an electrode 103, which is implemented by a coil in the example of Fig. 1. Coil 103 is typically energized by a RF generator 105 via a matching network (not shown in Fig. 1).
• a gas ring 104 which preferably includes a plurality of orifices for releasing gaseous source materials, e.g., the etchant source gases, into the RF-induced plasma region between above substrate 150, representing for example a semiconductor substrate or a flat panel display.
• gaseous source materials e.g., the etchant source gases
• the gaseous source materials may also be released from ports built into the walls of the chamber itself or from a showerhead-type apparatus disposed above the substrate.
• Bipolar electrostatic chuck 110 typically receives RF power from an RF generator 120 (also typically via a matching network).
• a power supply 152 biases the poles of the bipolar electrostatic chuck to clamp substrate 150 thereon. The mechanism involved in clamping substrate 150 to chuck 110 is discussed subsequently herein.
• RF filters may be disposed between power supply 152 and RF generator 120.
• dc blocking capacitors may be disposed between power supply 152 and RF generator 120.
• Helium cooling gas is introduced under pressure (e.g., about 5-10 Torr in one embodiment) between chuck 110 and substrate 150 to act as a heat transfer medium for accurately controlling the substrate's temperature during processing to ensure uniform and repeatable process results.
• the pressure within chamber 102 is preferably kept low by withdrawing gas through port 160, e.g., between about 5 to 25 mTorr in one embodiment.
• a plurality of heaters may be provided to maintain a suitable chamber temperature for etching (e.g., about 70 °C in one embodiment).
• the chamber wall of chamber 102 is typically grounded.
• Fig. 2 illustrates in greater detail a cross-section of bipolar electrostatic chuck 110 of Fig. 1.
• bipolar chuck 110 is arranged in a configuration commonly known as "donut-and-base.” This configuration is more clearly illustrated in the top view of Fig. 3.
• bipolar electrostatic chuck 110 has two poles: a positive pole 204 and a negative pole 206.
• Bipolar electrostatic chuck 110 is shown in its preferred negative base configuration although the invention is not limited to negative base configurations only.
• a dielectric layer 212 which may be made of any suitable dielectric material such as ceramic, polymer, or the like. Wafer 208 is placed on top of this dielectric layer 212 of the bipolar ESC chuck for processing.
• the poles of the bipolar electrostatic chuck are coupled to a power supply 210.
• power supply 210 When power supply 210 is turned on, negative pole 206 is negatively biased by a power supply 210 relative to the common reference potential level.
• Power supply 210 also biases positive pole 204 positively relative to the common reference potential level.
• the presence of a negative potential on negative pole 206 electrostatically induces the positive charges or holes in wafer 208 to move toward the wafer region overlying negative pole 206.
• electrons in wafer 208 migrate toward the wafer region overlying positive pole 204.
• electrostatic forces between the poles and their respective overlying wafer regions are created to provide the clamping forces required to keep wafer 208 clamped to bipolar electrostatic chuck 110 during processing.
• poles are biased equally with opposite polarities relative to a common reference voltage level, an imbalance in the electrostatic forces over the poles may occur when the plasma is turned on and the wafer becomes biased negatively.
• power supply 210 biases positive pole 204 at +350 V and negative pole 206 at -350 V relative to the common reference voltage level.
• the wafer potential is at 0 V relative to the common reference voltage level, and the potential differences between the poles of bipolar chuck 110 and their overlying wafer regions are + 350 V and -350 V respectively.
• the wafer bias voltage may be -100 V when the plasma is turned on.
• the potential difference between the positive pole and the negatively biased substrate is increased to + 450 V, i.e., (+ 350 V- (-100 V)).
• the potential difference between the negative pole and the negatively biased wafer is decreased to only - 250 V, i.e., (-350 V- (-100 V)).
• the reduction in the potential difference reduces the electrostatic holding force between the negative pole and the wafer. Consequently, some heat-exchange gas may escape, resulting in inadequate temperature control and/or process variations.
• the electrostatic force holding the wafer to the bipolar chuck may become so weak that it is insufficient to resist the force exerted on the wafer by the pressure differential between the helium cooling pressure and the low pressure within the chamber, resulting in the wafer "popping off” the chuck's surface.
• the plasma-induced negative wafer bias may unduly increase the potential difference between the negatively-biased wafer and the positive pole of the bipolar chuck.
• An excessively high potential difference may cause arcing, i.e., sparking, between the lower surface of the wafer and the upper surface of the chuck, resulting in pit mark damage.
• the surface of the chuck may be damaged to the point where it becomes impossible to keep the heat-exchange gas properly sealed.
• Heat-exchange gas leakage is found to be exacerbated in negative-edged bipolar chucks, such as that shown in Fig. 2 wherein the edge of bipolar electrostatic chuck 110 is negatively charged. This is because there is less electrostatic force over the edge region of the negative- edged bipolar electrostatic chuck 110 when the plasma is turned on and the wafer is negatively biased.
• Positive-edged bipolar electrostatic chucks while being more effective at clamping the wafer's edge against the chuck and therefore reducing helium leakage, are nonetheless not favored since they tend to create conditions wherein large leakage currents between the plasma and the chuck's edge may occur.
• Positive-edged bipolar electrostatic chucks also exacerbate wafer sticking, further contributing to their unpopularity.
• the prior art technique of producing static offset voltages requires the use of a second power supply, other than the power supply employed to bias the chuck's poles, to offset the voltage levels supplied to the chuck's poles.
• the requirement of this second power supply is disadvantageous since it renders the resulting static offset power supply more expensive and cumbersome.
• Dynamic feedback systems attempt to vary the voltages supplied to the chuck's poles responsive to the inferred wafer DC bias.
• the reference voltage i.e., the inferred wafer DC bias
• the voltage supplied to the negative pole becomes correspondingly more negative
• the voltage supplied to the positive pole becomes correspondingly less positive. Since the differences between the reference voltage (hence the wafer DC bias) and the voltage levels of the chuck's poles does not change, theoretically speaking, there should be no difference in the level of helium flow when the plasma is turned on.
• the inferred wafer DC bias is typically less than the real wafer DC bias in magnitude.
• the reference voltage is typically less than the wafer real DC bias in magnitude. Accordingly, the potential difference between the chuck's negative pole, which is referenced to the reference voltage, and the wafer DC bias actually lowers when the plasma is turned on. As mentioned earlier, the reduction in the ⁇ V between the negative pole and the wafer reduces the electrostatic force therebetween and undesirably increases the helium flow.
• the present invention relates, in one embodiment, to a method of providing unbalanced voltages to a bipolar electrostatic chuck of a substrate processing chamber.
• the method includes providing a variable balanced voltage power supply, which is configured for producing, responsive to a control signal, balanced differential output voltages on a first and second terminals of the variable balanced voltage power supply.
• the method further includes coupling the first terminal of the variable balanced voltage power supply to a first node.
• the first node is coupled to a first resistive element of a resistor bridge;
• the method also includes coupling the second terminal of the variable balanced voltage power supply to a second node.
• the second node is coupled to a second resistive element of the resistor bridge.
• the first resistive element is lower in resistance value than the second resistive element.
• coupling the first resistive element and the second resistive element to a common reference terminal, thereby producing, without employing a power supply other than the variable balanced voltage power supply, the unbalanced voltages at the first node and the second node when the variable balanced voltage power supply is turned on.
• the invention in another embodiment, relates to an unbalanced differential voltage power supply configured for supplying unbalanced voltages to a bipolar electrostatic chuck of a substrate processing chamber.
• the unbalanced differential voltage power supply includes a variable balanced voltage power supply, which is configured for producing, responsive to a control signal, balanced differential output voltages on a first and second terminals of the variable balanced voltage power supply.
• the unbalanced differential voltage power supply includes a first node, which is coupled to the first terminal of the variable balanced voltage power supply.
• a resistor bridge having a first resistive element coupled in parallel to a second resistive element. The first resistive element is coupled to the first node.
• the unbalanced differential voltage power supply also includes a second node, which is coupled to the second terminal of the variable balanced voltage power supply and the second resistive element.
• the first resistive element is lower in resistance value than the second resistive element.
• a common reference terminal coupled to the first resistive element and the second resistive element, whereby the unbalanced voltages are produced, without employing a power supply other than the variable balanced voltage power supply, at the first node and the second node when the variable balanced voltage power supply is turned on.
• Fig. 1 illustrates, to facilitate discussion, a typical plasma substrate processing system.
• Fig. 2 is a cross-sectional illustration of a bipolar electrostatic chuck.
• Fig. 3 illustrates a donut-and-base configuration of a bipolar electrostatic chuck.
• Fig. 4 illustrates, in accordance with one embodiment of the present invention, an static unbalanced bipolar electrostatic chuck power supply.
• Figs. 5A and 5B illustrate the effect unbalancing the supply voltages has on the potential difference between the negative pole of the bipolar ESC chuck and the substrate when the plasma is turned on.
• Fig. 6 illustrates, in accordance with one embodiment of the present invention, another embodiment of an unbalanced bipolar electrostatic chuck power supply.
• Figs. 7A and 7B illustrate the effect that combining dynamic feedback and unbalanced supply voltages has on the potential difference between the negative pole of the bipolar ESC chuck and the substrate when the plasma is turned on.
• Fig. 8 illustrates, in accordance with one embodiment of the present invention, an static unbalanced bipolar electrostatic chuck power supply.
• the helium leakage would be acceptable. It is further realized that for minimizing helium leakage, balanced voltages on the two poles of the bipolar ESC chuck are not essential. It is realized that unbalanced voltages on the poles of the bipolar ESC chuck may indeed confer advantages even when dynamic feedback is employed.
• the voltages supplied to the two poles of the bipolar ESC chuck can be deliberately unbalanced (i.e., making the magnitude of the negative potential supplied to negative pole of the bipolar electrostatic chuck larger than the magnitude of the positive potential supplied to the positive pole of the bipolar electrostatic chuck), it is possible to ensure that the potential difference between the wafer and the negative pole always exceeds a minimum level, even when the wafer becomes negatively biased and its inferred DC voltage is employed as a reference to the power supply.
• the unbalanced ESC power supply is employed together with dynamic feedback, it becomes possible to maintain a stable cooling helium flow, even when a high bias power is applied to the chuck's poles.
• the present invention achieves the goal of supplying unbalanced voltages to the bipolar ESC chuck's poles without requiring the use of complicated control circuitries or additional power supplies.
• it is possible to provide fixed negative offset voltages to the ESC chuck's electrodes without requiring the use of a second power supply (i.e., an offset power supply).
• a second power supply i.e., an offset power supply.
• the present invention represents a significant advance since it furnishes fixed offset voltages to the bipolar ESC chuck using only a single power supply.
• the ability to employ only a single power supply to obtain fixed offset voltages offers significant cost and reliability advantages.
• Fig. 4 illustrates, in accordance with one embodiment of the present invention, an unbalanced differential voltage power supply 400 for supplying unbalanced voltages to the poles of a bipolar electrostatic chuck, e.g., chuck 110 of Fig. 1.
• unbalanced differential voltage power supply 400 includes a variable balanced voltage power source 402.
• variable balanced voltage power source 402 receives as its inputs a control signal (typically a dc signal between 0V and 5V) and a reference voltage (about 24V in one example), and outputs at its output terminals 404 and 406 positive and negative voltages of equal magnitudes.
• variable balanced voltage power source 402 represents a power supply (model number SF-12) of American High Voltage of El Cajon, California. Of course, any other conventional power source may also be employed (whether or not variable).
• Resistor bridge 408 includes resistive elements 410 and 412, which are coupled at their ends to output terminals 404 and 406 and a common reference terminal 414 as shown.
• common reference terminal 414 is coupled to ground although, as will be shown in a subsequent figure, common reference terminal 414 may alternatively be coupled to a dynamic feedback signal to dynamically modify the voltages output by unbalanced differential voltage power supply
• unbalanced voltages may be produced at outputs 420 and 420 of unbalanced differential voltage power supply 400 simply by unbalancing the resistive values of resistive elements 410 and 412.
• resistive element 410 has a higher resistive value than resistive element 412, for example, an offset voltage may be created whereby the positive voltage at terminal 404 is made less positive by the offset voltage, while the negative voltage at terminal 406 is made more negative by the same offset voltage.
• unbalanced differential voltage power supply 400 outputs unbalanced voltages at its outputs 420 and 422, which may then be employed as biasing voltages to the bipolar ESC chuck's poles.
• balanced voltage power source 402 is configured to output, in the absence of resistor bridge 408, +350 V at terminal 404 and -350 V at terminal 406.
• resistive element 412 having a resistive value of about 1.001 M ⁇ is coupled to terminal 404
• Resistor 430 represents a load resistor to present a finite load to balanced voltage power source 402 (since the chuck to which unbalanced differential voltage power supply 400 is coupled at outputs 420 and 420 typically has a very high impedance). In one embodiment, resistors
• Resistors 432 and 434 are current limiting resistors and leakage sensor resistors. In one embodiment, resistors 432 and 434 may have a value of about 51 k ⁇ each.
• the differential voltages at outputs 420 and 422 may then be employed to bias the poles of the bipolar ESC chuck (e.g., chuck 110 of Fig. 2) with positive and negative voltages of different magnitudes. Since the negative output voltage is made more negative relative to common ground, the invention advantageously maintains a large potential difference between the substrate and the negative pole even when the plasma is turned on and the substrate becomes negatively charged.
• Fig. 5A the poles of the bipolar ESC chuck are biased equally at +350 V and -350 V, as were done in the prior art.
• RF power is turned on at point 502
• the substrate DC bias lowers to -100 V and the potential difference ( ⁇ V) between the negatively charged wafer and the negative pole is lowered to 250 V.
• the poles of the bipolar ESC chuck are biased unequally at +240 V and - 460 V using the unbalanced differential voltage power supply of Fig. 4.
• the substrate DC bias again lowers to -100 V.
• the potential difference ( ⁇ V) between the negatively charged wafer and the negative pole is lowered from a higher ⁇ V (i.e., 460 V prior to the turning on of the RF power) and is advantageously maintained at a potential difference of 360V instead.
• the higher potential difference provided by the present invention translates into a higher electrostatic force clamping the wafer's edge to the chuck's negative base, thus advantageously maintaining a stable flow of cooling helium even when the plasma is turned on.
• resistive elements 410 and 412 represent suitable conventional resistors, or combinations of suitable conventional resistors having off-the-shelf values.
• the exact values of resistors representing resistive elements 410 and 412 vary depending primarily on the parameters of balanced voltage power source 402 and the desired offset voltage value.
• the values of resistors representing resistive elements 410 and 412 may be obtained for a particular offset voltage using a software modeling tool known as "Electronics WorkBench" (version 4) by Interactive Image Technologies, Ltd. (I l l Peter Street, Suite 801 of Toronto, Ontario, Canada) or similarly suitable modeling tools.
• unbalanced differential voltage power supply 400 of Fig. 4 supplies fixed unbalanced voltages to the bipolar ESC chuck's poles without requiring the use of an additional power supply to offset more negatively the negative output voltage and to offset more positively the positive output voltage. This is highly advantageous since it substantially lowers the cost and complexity of the ESC power supply.
• Fig. 6 illustrates, in accordance with another embodiment of the present invention, the unbalanced differential voltage power supply of Fig. 4 in which the common reference terminal 414 is coupled to a wafer bias sensor output instead of ground.
• the unbalanced differential voltage power supply of Fig. 6 allows the output voltages on outputs 420 and 422 to be dynamically changed responsive to the inferred substrate DC bias value.
• Wafer bias sensors and the use of their outputs as reference signals may be found in, for example, the aforementioned co-pending patent application S/N 08/624,988.
• Fig. 7A the voltages supplied to the poles of the chuck are balanced, e.g., at +350V and -350V.
• Vdc the DC bias of the substrate
• Vref i.e., the inferred substrate DC bias
• Vdc the actual substrate DC bias
• the poles of the bipolar ESC chuck are initially unbalanced, e.g., supplied with +240 V and -460 V respectively.
• this potential difference ⁇ V2 is still sufficiently large to maintain an adequate level of electrostatic attraction force between the substrate and the negatively charged wafer (and concomitantly a stable helium flow).
• ⁇ V may change from about 460 V prior to point 704 (when the plasma is turned on) to slightly less than 460 V afterwards (due to the underestimation of the substrate DC bias by the RF peak detector circuit).
• the dynamic feedback unbalanced power supply advantageously maintains the potential difference higher than this required value to keep the helium flow stable.
• Fig. 8 illustrates another embodiment of the invention wherein resistor bridge 408, in addition to unbalancing the voltages at outputs 420 and 422 to be supplied to the chuck's poles, further functions as a voltage divider circuit to divide down the potential difference across nodes 418 and 416.
• a signal representing a fraction of the potential difference across nodes 416 and 418, may be obtained at node 812.
• An analog- to-digital I/O circuit may be coupled to node 812, for example, to provide the user with data pertaining to the voltages being input into the poles of the ESC chuck. This data may then be employed in monitoring the process being performed on the substrate, for example.
• the invention advantageously improves the clamping of a substrate to a bipolar electrostatic chuck, particularly a negative-base bipolar electrostatic chuck, during the time the plasma is turned on and the substrate is negatively charged.
• the invention advantageously increases the magnitude of the negative voltage supplied to the negative pole to increase the magnitude of the electrostatic force such that an adequate level of electrostatic force between the substrate and the negative pole of the chuck still remains even after the substrate becomes negatively biased due to the plasma.
• the present invention achieves the foregoing without requiring the use of complicated control circuitries or the use of one or more additional power supplies. With dynamic feedback, an adequate level of clamping force is assured even if the bias power (as well as the magnitude of the wafer's negative voltage) is greatly increased.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Container, Conveyance, Adherence, Positioning, Of Wafer (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)

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• 1997
  • 1997-03-26 US US08/824,104 patent/US5835335A/en not_active Expired - Lifetime
• 1998
  • 1998-03-24 DE DE69834716T patent/DE69834716T2/de not_active Expired - Lifetime
  • 1998-03-24 WO PCT/US1998/005676 patent/WO1998043291A1/en not_active Ceased
  • 1998-03-24 JP JP54588298A patent/JP4169792B2/ja not_active Expired - Fee Related
  • 1998-03-24 AT AT98911954T patent/ATE328365T1/de not_active IP Right Cessation
  • 1998-03-24 EP EP98911954A patent/EP0970517B1/en not_active Expired - Lifetime
  • 1998-03-24 KR KR10-1999-7008778A patent/KR100538599B1/ko not_active Expired - Fee Related
  • 1998-03-26 TW TW087104757A patent/TW432464B/zh not_active IP Right Cessation

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