JP2006013049A - Sample grounding mechanism, sample grounding method, and electron beam exposure system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an occurrence of particles when a sample is grounded, while reducing a contact resistance between the sample and a ground electrode. <P>SOLUTION: A sample grounding mechanism comprises ground electrodes 37, 38 coming into contact with the surface of a sample 30 to ground the sample 30, ground electrodes 47, 48 coming into contact with the surface of a sample 40 to ground the sample 40, a power supply 61 which flows a surface activating current between the ground electrodes 37, 38 and the sample 30 to reduce a contact resistance between the ground electrodes 37, 38 and the sample 30, and a power supply 71 which flows the surface activating current between the ground electrodes 47, 48 and the sample 40 to reduce the contact resistance between the ground electrodes 47, 48 and the sample 40. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sample grounding mechanism for grounding a sample, and more particularly to a sample grounding mechanism for grounding a mask or wafer used in an electron beam exposure apparatus.

  In recent years, with the need for higher integration of semiconductor integrated circuits, further miniaturization of circuit patterns has been demanded. At present, the limits of miniaturization are mainly limited to exposure apparatuses, and new exposure apparatuses such as an electron beam direct writing apparatus and an X-ray exposure apparatus have been developed.

  Recently, an electron beam proximity exposure apparatus that can be used for ultrafine processing at a mass production level has been disclosed as a new type of exposure apparatus (for example, Patent Document 1 and Patent Document 2 corresponding to Japanese Patent Application). .

FIG. 1 is a diagram showing a basic configuration of an electron beam proximity exposure apparatus disclosed in Patent Document 1. As shown in FIG. The electron beam proximity exposure apparatus will be described with reference to this figure. As shown in the figure, the electron beam proximity exposure apparatus 1 includes an electron optical column (column) 10 and a sample chamber (chamber) 8 whose interior is kept in a high vacuum state.
In the column 10, an electron gun 12 having an electron beam source 14 that generates an electron beam 15, a shaping aperture 18, and an irradiation lens 16 that makes the electron beam 15 a parallel beam, a pair of main deflectors 21 and 22. And scanning means 13 for scanning the electron beam parallel to the optical axis.

  On the other hand, in the chamber 8, a mask 30 having an opening corresponding to a pattern to be exposed, an electrostatic chuck 44, and an XY stage 46 are provided. A sample (semiconductor wafer) 40 has a resist layer 42 formed on the surface thereof and is held on an electrostatic chuck 44.

  The mask 30 has a thin film portion in which an opening is formed at the center of the thick outer edge portion, and the wafer 40 has a surface close to the mask 30 (for example, the distance between the mask 30 and the wafer 40 is 50 μm). To be arranged). In this state, when the electron beam 15 is irradiated perpendicularly to the mask 30, the electron beam 15 that has passed through the opening of the mask 30 is irradiated to the resist layer 42 on the surface of the wafer 40.

  As shown in FIG. 2, the main deflectors 21 and 22 included in the scanning unit 13 are arranged so that the electron beam 15 is kept on the entire surface of the thin film portion of the mask 30 while keeping its optical axis parallel to the optical axis 19 of the electron gun 12. The deflection is controlled so as to scan. Thus, the electron beam 15 scans the entire surface of the thin film portion, whereby the mask pattern of the mask 30 is transferred to the resist layer 42 on the wafer 40 at the same magnification.

  The XY stage 46 moves the wafer 40 to be placed in the horizontal orthogonal two-axis direction (XY direction), and moves the wafer 40 by a predetermined amount every time when the mask pattern is transferred at an equal magnification. A plurality of mask patterns can be transferred to the wafer 40. The XY stage 46 can also rotate the wafer 40 with the vertical direction (Z direction) as the rotation axis.

The sub deflectors 51 and 52 included in the scanning unit 13 control (tilt correction) the incident angle of the electron beam to the mask pattern so as to correct the mask distortion. As shown in FIG. 3, when the incident angle of the electron beam 15 on the mask 30 is α and the distance between the exposure mask 30 and the wafer 40 is G, the shift amount δ of the transfer position of the mask pattern due to the incident angle α is ,
δ = G ・ tanα
The mask pattern is transferred to a position shifted from the normal position by a shift amount δ. Therefore, even if the exposure mask 30 has a mask distortion, the mask distortion can be corrected by controlling the tilt of the electron beam in accordance with the mask distortion at the electron beam scanning position.

The mask 30 and the wafer 40 are constantly exposed to the electron beam 15 irradiation. In the electron beam proximity exposure apparatus in which the distance between the mask 30 and the wafer 40 is small as described above, the thickness of the mask 30 is about 0.6 μm due to the Coulomb force acting between the mask 30 and the wafer 40 when they are charged. The thin film portion may be destroyed.
Further, in the electron beam proximity exposure apparatus, the acceleration voltage of the electron beam is as low as about 2 kV and the beam current is as large as about 20 μA. Therefore, when the mask 30 or the wafer 40 is charged, the electric field generated by charging adversely affects the trajectory of the electron beam 15 Transfer accuracy (exposure accuracy) is deteriorated.

  In order to adversely affect the charging of the mask 30 and the wafer 40 as described above, in the conventional electron beam exposure apparatus, a ground electrode (stylus) 38 for grounding the mask 30 and a ground electrode (contact) for grounding the wafer 40 are used. Needle) 48 is provided to ground the mask 30 and the wafer 40 to prevent the electron beam 15 from being charged by electrons.

  Patent Documents 3, 4 and 5 below disclose electrostatic chucking devices that hold a semiconductor wafer.

U.S. Pat.No. 5,831,272 Japanese Patent No. 2951947 Japanese Patent No. 3123956 Japanese Patent No. 3337762 Japanese Patent Publication No.7-62691

In order to sufficiently exhibit the antistatic effect by the ground electrode 38 or the ground electrode 48, the contact resistance between the mask 30 and the ground electrode 38 is desirably 2 MΩ or less, and between the wafer 40 and the ground electrode 48. The contact resistance is desirably 20 MΩ or less.
However, when an insulating film such as an oxide film or contamination is generated on the surface of the mask 30 or the wafer 40, a high contact resistance is generated between the mask 30 and the ground electrode 38 or between the wafer 40 and the ground electrode 48. The antistatic effect by the ground electrode 38 or the ground electrode 48 is not sufficiently exhibited.

  In order to destroy these insulating films and lower the contact resistance, a method of cutting the insulating film on the surface of the mask 30 or the wafer 40 by forming the ground electrodes 38 and 48, which are styluses, with diamond needles may be considered. However, if the insulating film is removed, particles are always generated, which adversely affects the mask 30 having openings corresponding to fine circuit patterns.

  In view of the above problems, an object of the present invention is to reduce the contact resistance between a sample and a ground electrode while suppressing generation of particles.

  The present inventors have found that the contact resistance between the ground electrode and the sample is reduced by passing a constant current (surface activation current) between the ground electrode and the sample. Table 1 shows experimental values of contact resistance value before applying current, contact resistance value after applying current, and applied voltage value when applying current when a surface activation current of 100 mA is passed through each sample 1 to 3. Indicates. Here, Samples 1 and 2 are mask material samples having sheet resistances of 0.01 to 0.02 Ωcm and 0.6 to 1.2 Ωcm, respectively, and Sample 3 is a bare wafer.

  As can be seen from the experimental data in Table 1, the contact resistance value after application of the surface activation current is greatly reduced (about three orders of magnitude) for any sample. The reason for this is that when a surface activation current flows, a spark occurs between the ground electrode and the sample surface, and the contact portion of the insulating layer on the sample surface with the ground electrode is cleaned (purged). Conceivable.

  The present invention has been made based on these findings, and the sample grounding mechanism according to the first embodiment of the present invention includes a ground electrode that contacts the surface of the sample and grounds the sample, and between the ground electrode and the sample. And a power source for reducing the contact resistance between the ground electrode and the sample by supplying a surface activation current to the electrode.

  In the sample grounding method according to the second embodiment of the present invention, a surface activation current is passed between the ground electrode and the sample to reduce the contact resistance between the ground electrode and the sample.

The ground electrode is selectively connected to a current source for flowing the surface activation current, and a resistance measuring instrument for measuring a contact resistance between the ground electrode and the sample, and grounded. Good. The sample grounding mechanism may include a switch for that purpose.
Then, while alternately applying the surface activation current to the ground electrode and measuring the contact resistance between the ground electrode and the sample, the output of the power supply is increased until the measured value of the contact resistance becomes a predetermined threshold value or less. It is good as well.

  When the sample is held by the sample holding means having the electrostatic chuck, the surface activation current may be passed with a polarity opposite to the voltage applied to the electrostatic chuck holding the sample.

  An electron beam exposure apparatus according to a third embodiment of the present invention includes the sample grounding mechanism according to the first embodiment, and grounds the wafer by the sample grounding mechanism. The electron beam exposure apparatus may be the above-described electron beam proximity exposure apparatus, and the sample grounding mechanism may ground the exposure mask in addition to the wafer.

  According to the present invention, it is possible to reduce the contact resistance between the sample and the ground electrode without generating particles. In order not to damage the sample surface and generate particles, the tip portion where the ground electrode comes into contact with the sample is preferably rounded (dulled) by, for example, a chamfering process and is not sharp.

  In addition, it is considered that a sample having a higher contact resistance before surface activation needs to pass a stronger surface activation current for surface activation. Therefore, by increasing the output of the power supply while alternately applying the surface activation current and measuring the contact resistance, it becomes possible to apply the necessary surface activation current in a short time.

  By causing the surface activation current to flow with a polarity opposite to the voltage applied to the electrostatic chuck holding the sample, it is possible to prevent the adsorption force of the electrostatic chuck from being reduced by the application of the surface activation current.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 4 is a schematic block diagram of an electron beam exposure apparatus including a sample grounding mechanism according to an embodiment of the present invention. In the following description, an electron beam proximity exposure apparatus 1 of a proximity exposure system is exemplified as the electron beam exposure apparatus 1, but the electron beam exposure apparatus of the present invention exposes a wafer with an electron beam as well as an electron beam proximity exposure apparatus. Any electron beam exposure apparatus that exposes a pattern can be used for other types of electron beam exposure apparatuses such as an electron beam direct drawing apparatus.

  In the following drawings, when a plurality of elements having the same configuration are provided, the same reference numbers may be indicated with alphabets, and in the description of each element, only the reference numbers may be used. The basic configuration of the electron beam proximity exposure apparatus has a configuration similar to the configuration shown in FIG. 1 and the configuration disclosed in Document 1 above. Therefore, the same functional parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown in FIG. 4, the electron beam proximity exposure apparatus 1 includes a column 10 and a chamber 8, and the inside of the column 10 and the chamber 8 is maintained in a high vacuum state (10 ⁻⁵ Pa level) by a vacuum pump 9. The column 10 includes an electron beam source 14 that generates an electron beam 15, an electron gun 12 having an irradiation lens 16 that makes the electron beam 15 a parallel beam, and a shaping aperture 18, a main deflector 20, and a sub deflector 50. Scanning means 13 for deflecting the electron beam 15 so as to scan the beam 15 parallel to the optical axis 19 is provided. In FIG. 4, each of the main deflector 20 and the sub deflector 50 is shown as a single deflector, but actually has a two-stage configuration as shown in FIG.

  On the other hand, the electron beam proximity exposure apparatus 1 holds a mask 30 having an opening corresponding to a pattern to be exposed in a chamber 8 and a mask stage that holds the mask 30 and moves it at least in the horizontal orthogonal biaxial direction (XY direction). 31 is provided. Here, the mask stage 31 includes an electrostatic chuck, and a voltage is applied from the mask chuck power source 35 to the internal electrode 33 embedded in the housing formed of a dielectric material, whereby the mask stage 31 and the dielectric layer 33 are electrically connected. An electrostatic force is generated between the body cases to hold the mask.

  The chamber 8 includes an electrostatic chuck 44 that supports the wafer 40 and an XY stage 46. The electrostatic chuck 44 applies an electrostatic force between the wafer 40 and the dielectric casing by applying a voltage from the wafer chuck power supply 45 to the internal electrode 43 embedded in the casing formed of a dielectric. Generate and hold the mask.

  Further, the electron beam proximity exposure apparatus 1 includes a ground electrode 37 that contacts the surface of the mask 30, a current source 61 that supplies a surface activation current that is a current of a predetermined intensity between the ground electrode 37 and the mask 30, A power supply controller 62 that controls the current applied by the current source 61, a digital multimeter (hereinafter referred to as DMM) 63 that is a resistance measuring instrument for measuring the contact resistance between the ground electrode 37 and the mask 30, and a switch 64. Further, another ground electrode 38 that contacts the surface of the mask 30 and grounds the mask 30 is also provided.

The power supply controller 62 controls the intensity at which the surface activation current is applied, the application time, and the applied waveform (pattern).
On the other hand, the DMM 63 has a contact resistance between the ground electrode 37 and the mask 30, an electric resistance of the mask 30 itself from a contact position with the ground electrode 37 to a contact position with the ground electrode 38, and the mask 30 and the ground electrode 38. Measure the series resistance of the contact resistance between.
Further, the switch 64 selectively connects the ground electrode 37 to the current source 61 and the DMM 63, and grounds it. It should be noted that the current passed through the ground electrode 37 by the current source 61 is applied with a polarity opposite to the polarity of the voltage applied to the internal electrode 33 by the mask chuck power source 35. As a result, a current is applied to the current source 61 to increase the potential of the mask 30 and prevent the suction force of the electrostatic chuck from decreasing.

  Similarly, the electron beam proximity exposure apparatus 1 includes a ground electrode 47 that contacts the surface of the wafer 40, a current source 71 that supplies a surface activation current between the ground electrode 47 and the wafer 40, and an application by the current source 71. A power supply controller 72 that controls current, a digital multimeter (hereinafter referred to as DMM) 73 that is a resistance measuring device for measuring contact resistance between the ground electrode 47 and the wafer 40, and a switch 74 are provided. In addition, another ground electrode 48 that contacts the surface of the wafer 40 and grounds the wafer 40 is also provided.

The power supply controller 72 controls the intensity at which the surface activation current is applied, the application time, and the applied waveform (pattern).
On the other hand, the DMM 73 is configured such that the contact resistance between the ground electrode 47 and the wafer 40, the electrical resistance of the wafer 40 itself from the contact position with the ground electrode 47 to the contact position with the ground electrode 48, and the contact between the wafer 40 and the ground electrode 48. Measure the series resistance of the contact resistance between.
Further, the switch 74 selectively connects the ground electrode 47 to the current source 71 and the DMM 73, and grounds it. It should be noted that the current flowing from the current source 71 to the ground electrode 47 is applied with a polarity opposite to the polarity of the voltage applied to the internal electrode 43 by the wafer chuck power supply 45.

The tip portions where the ground electrodes 37 and 38 are in contact with the mask 30 and the ground electrodes 47 and 48 are in contact with the wafer 40 are preferably rounded (blunted) by, for example, a chamfering process and not sharp.
Furthermore, the electron beam proximity exposure apparatus 1 includes switching control of the switches 64 and 74, application intensity, application time and application pattern control of the current source 61 based on the measured value of the DMM 63, and current source based on the measured value of the DMM 73. 71 is provided with a controller 81 for controlling application intensity 71, application time, and application pattern.
Further, the electrical resistance of the mask 30 itself from the contact position between the ground electrode 37 and the mask 30 to the contact position between the ground electrode 38 and the mask 30, and the ground electrode 48 and the wafer 40 from the contact position between the ground electrode 47 and the wafer 40. The electrical resistance of the wafer 40 itself up to the contact position is obtained in advance by experiments or by calculation from the product specifications of the mask 30 and the wafer 40 and stored in a storage means (not shown) so that it can be used by the controller 81. Is done.

FIG. 5 is a flowchart of the sample grounding method according to the embodiment of the present invention. Hereinafter, a method for grounding the mask 30 will be described.
In step S91, the mask 30 is transferred into the chamber 8, and in step S92, the mask 30 is set on the mask stage 31. A chuck voltage is applied to the built-in electrode 33 of the electrostatic chuck of the mask stage 31 by the mask chuck power source 35, and the mask 30 is attracted to the mask stage 31. In step S93, the ground electrodes 37 and 38 are brought into contact with the back surface (upper surface) of the mask.

  In step S94, the controller 81 switches the switch 64 so that the ground electrode 47 is connected to the current source 61. The current source 61 applies a constant surface activation current to the ground electrode 47 with a predetermined intensity. As a result, the surface activation current flows through the path of the current source 61, the ground electrode 47, the mask 30, the ground electrode 48, and GND. At this time, the current source 61 applies a voltage having a polarity opposite to the voltage applied to the built-in electrode 33 of the electrostatic chuck to the ground electrode 47 so that the suction force of the electrostatic chuck of the mask stage 31 does not decrease.

In step S95, the controller 81 switches the switch 64 so that the ground electrode 47 is connected to the DMM 63. The DMM 63 determines the contact resistance between the ground electrode 37 and the mask 30 and the contact position between the ground electrode 37 and the ground electrode 38. The electrical resistance of the mask 30 itself up to the contact position and the series resistance value of the contact resistance between the mask 30 and the ground electrode 38 are measured.
The DMM 63 transmits the measurement value to the controller 81, and the controller 81 subtracts the known electrical resistance of the mask 30 itself from the contact position with the ground electrode 37 to the contact position with the ground electrode 38 from the received measurement value. The series resistance values of the contact resistance between the mask 37 and the mask 30 and the contact resistance between the mask 30 and the ground electrode 38 are obtained.

In step S96, the controller 81 determines whether or not the obtained series resistance value is less than or equal to a predetermined threshold (for example, 2 MΩ). If the obtained series resistance value is not less than or equal to the predetermined threshold, the controller 81 in step S97. Instructs the power supply controller 62 to increase the applied intensity of the current source 61 and repeats steps S94 to S97.
In step S97, the controller 81 increases the application time of the current source 61 or changes the application pattern of the current source 61 instead of instructing the power supply controller 62 to increase the application intensity of the current source 61 (for example, The power supply controller 62 may be instructed to change from a direct current to a sawtooth wave or a square wave, or from a sawtooth wave to a square wave or a direct current.

  If it is determined in step S96 that the series resistance value obtained in step S95 is equal to or less than a predetermined threshold value, the controller 81 switches the switch 64 to ground the ground electrode 47 in step S98.

  The wafer 40 is also grounded by a sample grounding method similar to the flowchart shown in FIG. In the description of the grounding method of the mask 30 with reference to FIG. 5 above, the mask 30 is attached to the wafer 40, the electrostatic chuck of the mask stage 31 is attached to the electrostatic chuck 44, the built-in electrode 33 is placed on the built-in electrode 43, and the ground electrode 37 is placed By replacing the ground electrode 47, the ground electrode 38 with the ground electrode 48, the current source 61 with the current source 71, the power controller 62 with the power controller 72, the DMM 63 with the DMM 73, and the switch 64 with the switch 74, respectively. Easy to understand.

  The present invention is applicable to an electron beam exposure apparatus that irradiates a sample with an electron beam.

It is a basic block diagram of an electron beam proximity exposure apparatus. It is explanatory drawing of electron beam scanning. It is explanatory drawing of inclination correction | amendment of an electron beam. 1 is a basic configuration diagram of an electron beam proximity exposure apparatus including a sample grounding mechanism according to an embodiment of the present invention. It is a flowchart of the sample grounding method which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron beam proximity exposure apparatus 8 ... Chamber 30 ... Mask 31 ... Mask stage 33, 43 ... Built-in electrode 35, 45 ... Electrostatic chuck power supply 37, 38, 47, 48 ... Ground electrode 40 ... Wafer,
44 ... Electrostatic chucks 61, 71 ... Current sources 63, 73 ... Digital multimeters 64, 74 ... Switching devices

Claims (11)

  A ground electrode that contacts the surface of the sample and grounds the sample; and a power source that reduces a contact resistance between the ground electrode and the sample by causing a surface activation current to flow between the ground electrode and the sample. A sample grounding mechanism comprising:   The sample grounding mechanism according to claim 1, further comprising a switch that selectively connects and grounds the ground electrode to the power source. A resistance measuring instrument for measuring a contact resistance between the ground electrode and the sample;
The sample grounding mechanism according to claim 1, further comprising a switch for selectively connecting the ground electrode to the power source and the resistance measuring device and grounding the ground electrode. A sample holding means for holding the sample having an electrostatic chuck;
The sample grounding mechanism according to claim 1, wherein the power supply causes the surface activation current to flow with a polarity opposite to a voltage applied to the electrostatic chuck.   An electron beam exposure apparatus comprising the sample grounding mechanism according to claim 1, wherein the wafer is grounded by the sample grounding mechanism. The sample grounding mechanism according to any one of claims 1 to 4,
An electron gun that generates an electron beam;
A mask provided in a path of the electron beam and having an opening corresponding to an exposure pattern;
An electron beam exposure apparatus that exposes the exposure pattern on the surface of a wafer with the electron beam that has passed through the opening,
An electron beam exposure apparatus wherein the wafer and / or the mask are grounded by the sample grounding mechanism.   A sample characterized by reducing a contact resistance between the ground electrode and the sample by passing a surface activation current between the sample and a ground electrode that contacts the surface of the sample and grounds the sample. Grounding method.   The sample grounding method according to claim 7, wherein the ground electrode is selectively connected to and grounded to a power source for allowing the surface activation current to flow.   Selectively connecting the ground electrode to a power source for flowing the surface activation current and a resistance measuring instrument for measuring a contact resistance between the ground electrode and the sample, and grounding the ground electrode; The sample grounding method according to claim 7, wherein:   While alternately applying the surface activation current to the ground electrode and measuring the contact resistance between the ground electrode and the sample, the output of the power supply until the measured value of the contact resistance becomes a predetermined threshold value or less. The sample grounding method according to claim 9, wherein the sample is grounded.   The sample grounding method according to claim 7, wherein the surface activation current is caused to flow with a polarity opposite to a voltage applied to an electrostatic chuck holding the sample.

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