JP2001257158A - Electron beam lithography system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable electron beam lithography system which suppresses wafer potential regardless of the grounded state of the wafer when the system electrostatically attracts the wafer. SOLUTION: The electrode in an electrostatic chuck 9 is divided into two electrodes (10a and 10b) which are respectively connected to DC power sources 16a and 16b having different polarities. The wafer 14 is grounded by pressing an earth pin 12 against the wafer 14 and made to be electrostatically attracted to the surface of the chuck 9. Since the current flowing to the pin 12 can be reduced, the rise of the wafer potential can be suppressed even when the wafer 14 is defectively grounded. Consequently, the current flowing to the pin 12 can be reduced and, accordingly, the rise of the wafer potential can be suppressed and highly reliable electron beam lithography becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electron beam lithography apparatus used in the field of semiconductor manufacturing, and more particularly to drawing while holding a semiconductor substrate by means of an electrostatic chuck mechanism (hereinafter referred to as an electrostatic chuck). The present invention relates to an improvement in an electron beam lithography apparatus that performs the following.

[0002]

2. Description of the Related Art Electron beam lithography is one of the main processes for forming LSI patterns on a semiconductor substrate. Electron beam lithography is a method in which a cross-sectional shape and a trajectory of an electron beam emitted from an electron gun are controlled to sequentially draw a pattern on a substrate coated with a photosensitive material (electron beam resist). .

FIG. 5 shows a schematic configuration of a drawing chamber in a conventional electron beam drawing apparatus. In the figure, an electron beam 2 emitted from an electron gun 1 is shaped into a rectangular cross section by a stop 3 and a shaping deflector 4, and is imaged at an arbitrary position on a substrate 7 by an electron lens 5 and a deflector 6. Is done. The substrate 7 is sucked and held on a substrate holder 8 provided with an electrostatic chuck, whereby the substrate 7 is flattened. This is because if the substrate 7 is in a warped state, the pattern formation surface is distorted, and high-precision drawing cannot be performed. The substrate holder 8 is provided with a dielectric 9 for adsorbing and holding the substrate 7 and an electrode 10 for applying a voltage to the dielectric 9, and a DC power supply 11 is connected to the electrode 10. Further, a ground pin 12 for grounding is pressed against the substrate 7. When a DC voltage is applied to the dielectric 10, the dielectric charge is generated in the dielectric 10 while maintaining the substrate 7 at the ground potential. 10 can be held by suction. Also,
The substrate holder 8 is fixed on an XY stage 13 having a long moving stroke. Thus, even if the deflection range of the electron beam is about several mm square, the LSI pattern can be drawn on the entire surface of the substrate 7 by moving the XY stage. Since the LSI pattern is formed by being stacked on a substrate in a number of layers, it is necessary to accurately align the pattern to be a base when drawing.

[0004] Here, the substrate 7 is grounded by the earth pin 12, but strictly speaking, does not reach 0V. This is due to the leak current I flowing when a voltage is applied to the dielectric 10 and the contact resistance R generated at the pressed portion of the ground pin 12. The potential V generated at this time is expressed by the following equation (1) according to Ohm's law. V = I × R (1) For example, assuming that the volume resistivity of a dielectric material of a general electrostatic chuck is about 10 ⁹ Ω · cm, the leakage current I varies depending on the contact state of the surface. Flows about 200 μA. Here, assuming that the contact resistance R of the ground pin is 20 kΩ, a potential of 4 V is generated on the substrate. The generated potential disturbs the trajectory of the electron beam having a negative charge, causing a problem that the drawing accuracy is deteriorated. Regarding the relationship between the potential of the substrate (wafer) and the trajectory of the electron beam, see M.S.
J. Phys.E: Sci. Instrum. By Miyazaki et al.
14, 194 (1981), and the deviation ΔL of the beam position at this time is represented by the following equation (2), assuming that the deflection distance L and the acceleration voltage U are: ΔL / L = −V / (4 × U) (2) Therefore, if L = 2.5 mm and U = 50 kV, a displacement of as much as 50 nm occurs when the above-described substrate potential 4V is generated. Become. As the miniaturization of semiconductor devices progresses,
When drawing a pattern line width of 80 nm or less,
This beam position shift amount is a value that cannot be ignored.

Therefore, conventionally, (a) a method of reducing the contact resistance by positively taking the ground by increasing the hardness of the earth pin and increasing the pressing force against the substrate, and (b) an electron beam by an amount corresponding to the generation of the substrate potential (C) a method of increasing the resistance of a dielectric to suppress a leak current.

[0006]

However, even if the ground pin is strongly pressed against the substrate (wafer or the like), there is a limit in reducing the contact resistance, and several kΩ remain. In particular, in a process wafer, it is difficult to ground with good reproducibility because a thick insulating film is deposited on the surface of the substrate. Also,
Since the contact resistance also increases due to wear and deterioration of the earth pin, the generated potential varies, and the deflection correction of the electron beam cannot cope with it. Also, in increasing the resistance of the dielectric, the leakage current is reduced and the effect on the ground failure is high. However, the higher the resistance value of the dielectric, the more difficult it is for accumulated charges to escape, resulting in a problem of residual adsorption. . For example, when a dielectric substance of the order of 10 ¹² Ω · cm is used, it has been confirmed by experiments that a residual adsorption force of ³ gf / cm ² is generated even after 2 minutes from turning off the voltage. It may cause trouble. In addition, since the residual charge produces a dust collecting effect, there is a problem that the flatness at the time of wafer suction is deteriorated due to dust suction and pinching.

Accordingly, an object of the present invention is to provide an electrostatic chuck capable of suppressing a potential generated on a substrate and reducing residual adsorption, thereby realizing a highly reliable electron beam drawing apparatus. It is in.

[0008]

In order to achieve the above-mentioned object, in the present invention, the electrode inside the electrostatic chuck is divided into two, and each of them is connected to a DC power supply having a different polarity. Electron beam drawing is performed with a ground pin pressed against the surface of the substrate. By adopting this method, the current flowing through the ground pin can be reduced, and the potential of the generated substrate can be suppressed. Therefore, it is possible to prevent a beam position shift caused by the potential of the generated substrate, and to achieve highly reliable electron beam writing. Can be realized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an entire electron beam lithography apparatus according to an embodiment of the present invention. In the figure, a high-voltage power supply 19 is connected to an electron gun 1 and an electron beam 2 is emitted. The electron beam 2 passes through the stop 3 and is shaped into a rectangular cross section by a shaping deflector 4 controlled by a deflection control system 20. Further, by controlling the electron lens 5 and the deflector 6 to which the lens power supply 21 is connected, the electron beam 2 is imaged at an arbitrary position on the substrate (wafer) 14. The wafer 14 is fixed and held on the substrate holder 8, and the substrate holder 8 is fixed on the XY stage 13. The wafer holding surface of the substrate holder 8 is composed of a dielectric material 9, and two half-moon-shaped electrodes 10a and 10b embedded in the dielectric body 9 are provided with a power supply terminal 15 so that a DC voltage can be applied. ing. Each power supply terminal 1
5 is connected via a switch 17 to two DC power supplies 16a and 16b which output DC voltages having different polarities and the same absolute value. When the switch 17 is turned off, each electrode has a ground potential. Have been. Ground pins 12 are incorporated in the grounded substrate holder 8, and a mechanism for pressing the ground pins 12 onto the wafer 14 is provided. Thereby, the wafer 1
4 is at ground potential, and switch 17 is set to O
By setting N, the wafer 14 is suction-held on the upper surface of the dielectric 9. The reflecting mirror 22 is fixed to the XY stage 13, and the position of the XY stage 13 is measured by the laser interferometer 23. During drawing, the position of the stage 13 is controlled by the stage drive system 24 in order to move the XY stage 13 to a predetermined position. Each control system is connected to the central processing unit 25 to perform overall control in drawing.

Here, the principle of reducing the generated substrate potential in the present invention will be described. FIG. 2 shows a schematic configuration diagram of the electrostatic chuck portion in FIG. 1 and an electrical equivalent circuit thereof. The generated wafer potential Vw is obtained by solving the closed circuit equation of this equivalent circuit. The result is shown in the following equation (3). Vw = (Va / Ra−Vb / Rb) × (1 / Ra + 1 / Rb + 1 / Rw) ⁻¹ (3) where + Va, −Vb... Voltages applied by the power supplies 16a and 16b Ra, Rb. Resistance components Rw on the 10a, 10b side Contact resistance of earth pin 12 In other words, the generated wafer potential Vw is the product of the current value flowing through the ground pin 12 and the combined resistance value of each resistance component in parallel, but Ra, Rb >> Rw, the combined resistance value ≒ Rw
Becomes Therefore, as compared with the conventional case, the generated potential is reduced by an amount corresponding to the reduction in the current flowing through the ground pin. For example,
Ra = Rb = 4MΩ, Rw = 50kΩ, Va = 405V, V
If b = −395V, the conventional method requires 1
Since a current of 00 μA flows, a potential of Vw = 5 V is generated. However, in the present invention, since only 2.5 μA flows through the ground pin, the generated wafer potential is also about 1/4 of Vw = 0.12 V.
It becomes 0. As a result, the amount of displacement of the electron beam is reduced to 1/40, and high-precision drawing is enabled.

Embodiment 2 FIG. 3 shows a schematic configuration of an electrostatic chuck portion in an electron beam lithography apparatus according to a second embodiment of the present invention. In the figure, a concentric 2
Two electrodes 10a and 10b are embedded, and a DC power supply 16a and 16b is connected to each power supply terminal 15. The diameter of each of the electrodes 10a and 10b is 120 mmφ, 2
00 mmφ, and the area ratio is about 1.8: 1. Therefore, by setting the voltage ratio of the DC power supplies 16a and 16b to the reciprocal of 1: 1.8, that is, 300 V and -540 V, the current flowing through each electrode becomes equal, and the current flowing through the ground pin can be suppressed. Thus, the generated wafer potential can be suppressed. However, if the applied voltage differs, the attraction force also changes. Therefore, it is more preferable to make the area ratio close to 1: 1.

Embodiment 3 FIG. 4 shows a schematic configuration of an electrostatic chuck section in an electron beam lithography apparatus according to a third embodiment of the present invention. In the figure, two electrodes 10a and 10b having a comb shape are embedded in a dielectric 9 and a DC power supply 16a, 16
b and ammeters 18a and 18b are connected. One of the DC power supplies 16a is a variable DC voltage power supply capable of adjusting the output voltage, and its output voltage value can be adjusted so that the indicated current values of the two ammeters 18a and 18b become equal. is there. Thus, the current flowing through the ground pin 12 can be sufficiently reduced even if there is a difference in the shape of the interdigital electrode or the distribution of the resistance of the dielectric material 9. For example, by suppressing the difference between the values of the currents flowing through the two electrodes to 1 μA or less, the amount of beam misalignment that would otherwise occur when a current of 100 μA was applied can be reduced to 1/100 or less, and the drawing failure problem due to a ground defect can be effectively reduced. It became possible to solve.

[0014]

According to the present invention, when electrostatically attracting a substrate (wafer), the potential of the generated substrate can be effectively reduced without being influenced by the contact condition of the ground pin, and thus highly reliable electron beam drawing can be performed. Become.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an electron beam lithography apparatus according to a first embodiment of the present invention.

FIG. 2 shows a generating substrate (wafer) in the embodiment shown in FIG.
FIG. 4 is a diagram illustrating a schematic configuration of an electrostatic chuck unit and an equivalent circuit thereof for explaining a principle of reducing a potential;

FIG. 3 is a diagram illustrating a schematic configuration of an electrostatic chuck unit in an electron beam lithography apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of an electrostatic chuck section in an electron beam lithography apparatus according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a drawing chamber in a conventional electron beam drawing apparatus.

[Explanation of symbols]

1 ... Electron gun, 2 ... Electron beam, 3
... Aperture, 4 ... Shaping deflector, 5 ... Electronic lens,
6: deflector, 7: substrate, 8: substrate holder, 9: dielectric, 10: electrode,
11 DC power supply 12 Ground pin 13
XY stage, 14 wafer, 15 power supply terminal, 16 DC power supply, 17 switch,
18 ... ammeter, 19 ... high voltage power supply, 20 ...
Deflection control system, 21: lens power supply, 22: reflecting mirror,
23: laser interferometer, 24: stage drive system, 25: central processing unit.

Claims (5)

[Claims] An electrostatic chuck for attracting and holding the semiconductor substrate on the dielectric upper surface by applying a voltage between an electrode formed on the lower surface of the dielectric and a semiconductor substrate mounted on the upper surface of the dielectric. An electron beam lithography apparatus comprising a substrate holder of the system, wherein the electrodes are divided into two electrode portions, and DC voltages having different polarities are applied to each electrode portion, and An electron beam lithography apparatus configured to perform pattern drawing on the semiconductor substrate while grounding the semiconductor substrate by grounding means. 2. The apparatus according to claim 1, further comprising a voltage varying means for adjusting a value of the DC voltage applied to at least one of the two electrode portions. Electron beam drawing equipment. 3. The electrode areas of the two electrode portions are substantially equal to each other, and the DC voltages of different polarities applied to the two electrode portions have substantially equal absolute values. The electron beam lithography apparatus according to claim 1, wherein: 4. An electrode area ratio between the two electrode portions is set substantially equal to a reciprocal of a ratio between absolute values of the DC voltage applied to each of the two electrode portions. 3. The electron beam lithography apparatus according to claim 1, wherein: 5. The DC voltage applying means according to claim 1, wherein said DC voltage applied to at least one of said two electrode portions is such that current values flowing through said two electrode portions are substantially equal to each other. 3. The electron beam writing apparatus according to claim 2, wherein the value of the voltage is adjusted.