JPH11354405A - Electron beam lithography device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam lithography device the plotting accuracy of which is not affected by the individual characteristics of a plurality of substrate holders and, in addition, which can be adjusted easily. SOLUTION: At the time of plotting, a stage driving system 28 controls the position of an X-Y stage 9 so as to move the stage 9 to a prescribed position. A storage device 30 is connected to a central processing unit 29 connected to each control system, and the correction parameters corresponding to each substrate holder 8a and 8b are stored in the device 30 and used at the time of calculating correction amounts for plotting and detection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam writing apparatus in the field of semiconductor manufacturing and the like, and more particularly to an electron beam using a plurality of sample holders having an electrostatic attraction mechanism and a sample positioning mechanism in one apparatus. The present invention relates to a drawing device.

[0002]

2. Description of the Related Art Electron beam lithography is one of the main processes for forming an LSI pattern on a semiconductor substrate. Electron beam lithography is a method of controlling the shape and trajectory of an electron beam emitted from an electron gun, and sequentially drawing a pattern on a substrate coated with a photosensitive material.

FIG. 7 is a schematic view 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 rectangle 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. The substrate 7 is fixedly held by a substrate holder 8, and the substrate holder 8 is fixed on an XY stage 9. Thus, even if the deflection amount of the electron beam is about several mm, X
By moving the Y stage, an LSI pattern can be drawn on the entire surface of the substrate. Since the LSI pattern is configured by being stacked on the substrate in a number of layers, writing is performed by accurately positioning the pattern to be a base.

[0004] Here, the substrate holder is provided with Si as a substrate.
When holding the wafer, (a) positioning of the wafer,
(B) Two functions of flattening a wafer are required.
The wafer positioning in (a) is for aligning the axis in which the wafer moves, that is, the XY stage axis, with the arrangement direction of the underlying pattern on the wafer.

[0005] As shown in FIG. 8, if this direction is an angle φ
Considering the case where a rectangular area having a width d is sequentially drawn, the shift amount Δd of the connection portion with the adjacent area is geometrically expressed by Equation 1.

[0006]

Δd = d · φ (1) For example, φ = 5 mrad (1 mm shift between 200 mm), d =
If it is 5 μm, the deviation is 25 nm, which has a great effect on the drawing accuracy. Therefore, as described in JP-A-9-139418, positioning is performed by pressing the side surface of the wafer against a roller or the like so that the rotation of the wafer coincides with the axial direction of the stage. The position of the roller at this time needs to be adjusted in advance using a wafer on which a base pattern is arranged.

[0007] The flattening of the wafer (b) is performed in order to correct the film stress generated in the process of forming a film on the wafer surface and the warpage caused by the clamping force for positioning into a flat surface. As shown in FIG. 9, if the wafer having the thickness t is warped by δ during the distance L, the shift amount Δ
L is geometrically represented by Equation 2.

[0008]

ΔL = 2 · t · δ / L (2) For example, a wafer with a thickness of t = 725 μm and L = 200 mm is
If the projection is warped by 10 μm, the peripheral portion of the base pattern is extended by 75 nm as compared with the central portion, which greatly affects the drawing accuracy. Therefore, as described in Japanese Patent Application Laid-Open No. 9-237827, a method of accumulating electric charges in a dielectric material serving as a holding surface and using the electrostatic force to make the back surface of a wafer flat on the flattened holding surface has been proposed. Used.

Next, the operation of the substrate holder will be described with reference to FIG.
Explanation will be made using 0. FIG. 10 is a schematic diagram showing the configuration of the drawing room and its surroundings. In the figure, the preliminary exhaust chamber 1
The wafer 11 is transferred to the substrate holder 8 placed on the
The wafer 11 is positioned in the atmosphere by clamping the side surface of the wafer 11 with the roller 12. The pre-evacuation chamber 10 is evacuated to vacuum and, when a predetermined degree of vacuum is reached, the first gate valve 14 that separates the pre-evacuation chamber 10 from the exchange chamber 13 is opened, and the pre-evacuation chamber 10 and the exchange chamber 13 become the same space. Thereafter, the substrate holder 8 is transferred to the exchange chamber 13 while clamping the side surface of the wafer 11, and the first gate valve 14 is closed. Further, the substrate holder 8 holds the second gate valve 1
The XY stage 9 is transported to the drawing chamber 31 after the
After mounting on the wafer, the wafer 11 is flattened by electrostatic attraction, and the operation proceeds to electron beam drawing. After the drawing is completed, the wafer 11 is carried out of the apparatus by the flow reverse to the above.

As described above, a certain amount of time is required for operations for drawing preparation such as wafer transfer and vacuum evacuation.
In order to minimize this waste time, a method of mounting a plurality of substrate holders in the apparatus is used as described in Japanese Patent Application Laid-Open No. 2-163927. This makes it possible to draw on a wafer on another substrate holder even during wafer transfer or vacuum evacuation, thereby improving throughput.

[0011]

However, when a plurality of substrate holders are used in one apparatus, the following problems occur because the characteristics are different for each substrate holder.

1) In order to accumulate electric charges in the dielectric on the holding surface of the wafer, it is necessary to apply an electric field to the dielectric. For this reason, a DC voltage of several hundred volts is applied between the planar electrode formed on the dielectric and the wafer (described with reference to FIG. 11). Since a dielectric having a volume resistivity of 10 ⁸ to 10 ¹² Ω · cm is used for the dielectric 16, several tens to several hundreds μ
A leakage current is flowing. Here, the wafer 11 and the peripheral parts of the substrate holder are connected to the ground potential so as to suppress the generation of an unnecessary electric field on the wafer 11 so that the trajectory 17 of the electron beam as a negative charge is not affected. However, since the wafer 11 is a semiconductor, a contact resistance of several kΩ is generated at the connection portion 18 with the ground potential, and the wafer 11
Generates an electric potential, that is, an electric field.

The relationship between the wafer potential and the trajectory of the electron beam is described by M.
Journal of Physics E by Miyazaki et al .:
Scientific Instruments (J.Phys.E:
Sci. Instrum) 14, 194 (1981). Assuming that the wafer potential is V, the acceleration voltage of the electron gun is U, and the deflection amount of the electron beam is R, the deviation amount of the electron beam due to this potential is Δ
R is represented by Equation 3.

[0014]

ΔR = −V / (4 · U) · R (3) For example, if V = + 2 V, U = 50 kV, and R = 2.5 mm, the image is drawn by reducing by ΔR = 25 nm.

The magnitude of the deviation greatly changes depending on the leakage current for generating the potential, that is, the characteristic of the dielectric 16 at the time of manufacture, and thus becomes a value unique to the substrate holder. Therefore, when a plurality of substrate holders are used in one apparatus, the accuracy may be varied.

2) As described above, the wafer is positioned by the rollers on the substrate holder in order to suppress the displacement of the connection portion between the adjacent drawing areas. The position of this roller is set so that the wafer exposed to the pattern by the reference device is placed on the substrate holder, and rotated so that the pattern arrangement on the wafer coincides with the XY axes of the electron beam lithography system on which the substrate holder is mounted. Is adjusted. When using a plurality of substrate holders, not only rotation but also wafer center position
It is necessary to match between each substrate holder.

This is for the following reason. Immediately before the start of drawing, a specific mark of a pre-registered base pattern is detected by an optical microscope or an electron microscope, and how much the mark position is shifted from a reference position is grasped by image recognition. The rotation and shift are corrected at the time of mark detection and drawing. When detecting the specific mark, if the deviation from the reference position is large, the detection range (for example, 100
μm) and an error occurs. Alternatively, in the method of partially detecting a wide area sequentially, there is a possibility that detection takes a long time or another similar mark is detected.

For this reason, the adjustment must be strictly performed, but since this adjustment is performed manually, an adjustment error occurs for each substrate holder. Even when the same wafer and substrate holder are used, the position of the wafer changes every clamping operation due to the eccentricity of the roller.
Deviation may occur. Therefore, when a plurality of substrate holders are used in one apparatus, the range of deviation from the reference position becomes large, which causes a decrease in stability in apparatus operation such as a mark detection error.

3) When measuring the position of a mark on a wafer, particularly when an optical microscope is used, the position of the measurement surface in the height direction of the wafer becomes important. This is because the depth of focus of the optical microscope is as small as several tens of μm, and if the height of the measurement surface changes and deviates from the focal length, the image of the mark becomes blurred and cannot be identified. For this reason,
As described in 1), the structure is such that the wafer is corrected to a flat holding surface by electrostatic attraction, and the height deviation is suppressed.
However, when a plurality of substrate holders are used in one apparatus, the height of the holding surface changes for each substrate holder, causing a mark detection error. In addition, it is difficult to make the holding surfaces of all the substrate holders uniform in height in units of μm, which makes the substrate holder expensive.

An object of the present invention is to provide an inexpensive substrate holder in which, when a plurality of substrate holders are used in one apparatus, the drawing accuracy is not affected by the characteristics of the individual substrate holders and the adjustment is easy and inexpensive. An object of the present invention is to provide a usable electron beam drawing apparatus.

[0021]

Means for Solving the Problems In the present invention, the following means are used to solve the above problems. First, when a plurality of substrate holders that attract and hold a wafer by electrostatic force are used, the amount of deviation from a predetermined irradiation position during electron beam deflection is individually corrected for each substrate holder to perform drawing. Also, when measuring the reference mark position of the base pattern on the wafer with a microscope, the focal length of the microscope is individually corrected for each substrate holder based on the amount of deviation from the reference in the height direction of the wafer and measured. .

Further, when a plurality of substrate holders for positioning pins by pressing the pins against the side surface of the wafer are used to measure the reference mark position of the underlying pattern on the wafer with a microscope, the amount of rotation and the amount of horizontal displacement of the wafer are individually determined. Is individually corrected for the substrate holders.

Further, these deviation amounts are measured and stored in advance for each substrate holder, the substrate holder is identified in the apparatus, and the deviation amount corresponding thereto is used for correction. When electrostatic attraction is used, the relationship between the amount of deviation and the leakage current is measured and stored, and the amount of deviation corresponding to the leakage current measured during drawing is used for correction.

Further, a unique shape such as a step or a hole is formed in each substrate holder, and the substrate holder is identified by a contact or transmission type detector.

[0025]

FIG. 1 is a schematic view of an electron beam drawing apparatus showing 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 rectangle by the shaping deflector 4 controlled by the deflection control system 20. Further, by controlling the electron lens 5 to which the lens power supply 21 is connected and the deflector 6, an image is formed at an arbitrary position on the wafer 11. The wafer 11 is fixedly held by a substrate holder 8, and the substrate holder 8 is fixed on an XY stage 9. The wafer holding surface of the substrate holder 8 is formed of the dielectric 16, and a power supply terminal 23 is provided so that a DC voltage can be applied to the internal electrode 22, and a DC power supply 24 and an ammeter 25 are connected.

The wafer 11 and peripheral components of the substrate holder 8 are connected to the ground potential, and the wafer 11 is attracted to the surface of the dielectric 16 by electrostatic force. XY stage 9 has reflector 2
6 is fixed, and the position of the XY stage 9 is measured by the laser interferometer 27. At the time of drawing, the position of the stage 9 is controlled by the stage drive system 28 in order to move the XY stage 9 to a predetermined position. A storage device 30 is further connected to the central processing unit 29 connected to each control system, and correction parameters corresponding to each substrate holder 8 are stored. Based on this, a correction amount calculation process in drawing and detection is performed.

Here, a method of correcting each substrate holder will be described. Now, a substrate holder A (8a) holding a wafer 11a before drawing is placed on the XY stage 9, and a substrate holder B (8) is placed in an exchange room adjacent to the drawing room.
b) stands by while holding another wafer 11b before drawing. For both the substrate holders A and B, the potential of the wafer when the electrostatic chuck is performed is measured in advance outside the apparatus. The potential of the wafer can be measured by using a high-resolution electrostatic meter or a voltmeter having a high input impedance. The displacement when this potential is generated is a value proportional to the deflection distance according to Equation 3 described above. Therefore, the deviation can be corrected using the deflection distance as a parameter. Specifically, in the design of the pattern, the deflection distance is m
Is drawn at the position of m 'represented by the equation (4).

[0028]

M ′ = {1 + V / (4 · U)} · m (4) Since the acceleration voltage U is a fixed value in the apparatus, if the potential V of each substrate holder is stored in the storage device. It is possible to draw while always correcting by the formula (4). For example, assuming that the potentials of the two substrate holders are 3 V and 1 V, respectively, when drawing the substrate holder A, a correction coefficient of 1.5 × 10 ⁻⁵ as shown in the correction table of FIG. 2 is used. When performing drawing by replacing with the substrate holder B, a correction coefficient of 5 ×
^M ′ is calculated by using 10 ⁻⁶ and corrected. Thus, even when a plurality of substrate holders having different characteristics are used, it is possible to perform drawing without deteriorating accuracy.

FIG. 3 is a correction table showing another embodiment of the present invention. As shown in the figure, both the substrate holders A and B measure the potential of the wafer and the leakage current when the electrostatic chuck is performed outside the apparatus in advance. The wafer potential is proportional to the leakage current according to Ohm's law. Therefore, the potential of the wafer on the stage can be grasped by measuring the leakage current when the wafer to be actually written is electrostatically attracted in the writing apparatus. In particular, when an insulating film is deposited on the back surface of the wafer, the leakage current becomes smaller than that of a normal wafer due to its resistance, and the potential of the wafer also decreases. As a result, it is possible to perform a more accurate correction than the above-described correction. More specifically, a reference wafer is electrostatically attracted, and at this time, the leakage current I and the wafer potential V are stored in a storage device. If the leakage current measured at the time of writing is I ', the wafer potential at the time of writing is I' / I
By multiplying by two, drawing may be performed using the correction formula represented by Expression 5.

[0030]

M ′ = {1 + V / (4 · U) · I ′ / I} · m (5) For example, the potential / leakage current of the substrate holder is 3V / 3, respectively.
Suppose that it was 00 μA, 1 V / 50 μA. Here, when the drawing current is measured to be 5 μA on the wafer to be drawn when drawing on the substrate holder A, a correction coefficient of 2.5 × 10 ⁻⁷ as shown in the correction table of FIG. 3 is used. In addition, when the drawing current is measured to be 45 μA on the drawing target wafer when drawing is performed by replacing the substrate holder B, the correction coefficient is set to 4.
Use 5 × 10 ^-6 . As a result, even when a plurality of substrate holders having different characteristics are used and a wafer having different characteristics is drawn, drawing can be performed without deteriorating accuracy.

FIG. 4 is a schematic view of an electron beam lithography apparatus showing another embodiment of the present invention. In the figure, an optical microscope 32 is attached to the container wall surface above the wafer 11, and two marks 33 at specific positions on the wafer 11 are detected, and their coordinate positions are measured. The objective lens 34 in the optical microscope 32 is operated in a direction perpendicular to the optical axis by an actuator such as an electromagnetic motor or an ultrasonic motor, so that the focal length can be adjusted. When detecting the mark, the XY stage 9 is moved so that the mark 33 is included in the detection visual field of the optical microscope.

Although the displacement of the wafer 11 is caused by the individual substrate holders 8 as described above, the position can be corrected by the parameters for each substrate holder stored in the storage device 30. Specifically, using a wafer on which a certain reference pattern is arranged, the amount of rotation from the reference position and the amount of shift of the center position of the wafer in the X and Y directions are measured in advance by the drawing apparatus for each substrate holder. Keep it. Assuming that the rotation amount φ, the X-direction shift amount ΔX, and the Y-direction shift amount ΔY, the reference mark position coordinates (X1,
Since the displacement of Y1) is geometrically expressed by Equations 6 to 9, even if the position coordinates of the reference mark are changed each time,
The stage may be moved to the calculated position coordinates (X, Y).

[0033]

X = r · cos (α + φ) + ΔX (6)

[0034]

Y = r · cos (α + φ) + ΔY (7)

[0035]

R = √ (X1 ² + Y1 ² ) (8)

[0036]

Α = tan ⁻¹ (Y1 / X1) (9) This correction equation is effective not only when detecting a mark with an optical microscope but also when measuring a smaller mark using an electron microscope. It is.

Although the focus shift of the optical microscope 32 occurs due to the difference in the height of the wafer holding surface of the substrate holder 8, the focal length can be adjusted by the parameters of each substrate holder stored in the storage device 30. is there. Specifically, using a certain reference wafer, the height of the wafer at the time of electrostatic attraction is measured for each substrate holder, and these are grasped as deviations from a certain reference position. At the time of mark detection, the actuator may be controlled so as to correct the amount of displacement corresponding to the substrate holder used.

[0038] With this arrangement, it is possible to reduce the trouble of adjusting the position of the roller for positioning the wafer, and to eliminate the need for an expensive auto-focus mechanism and precision processing for aligning the heights of the wafer holding surfaces of a plurality of substrate holders. It has become possible to stably detect the mark position on the wafer.

FIG. 5 is a schematic view of a substrate holder identifying mechanism of an electron beam lithography apparatus showing another embodiment of the present invention. In the figure, three steps 35 are provided on the back surface of the substrate holder 8, and when the substrate holder 8 is placed on the XY stage 9, a micro switch 36 for detecting contact is provided at a position facing the step 35. The same number of steps 35 as the three steps are provided on the holder mounting surface on the XY stage 93. The step 37 has a structure in which a block 37 is attached. The microswitch 36 does not work without the block 37, but the position is adjusted so as to work with the block 37.

Here, by mounting the block at a position unique to each substrate holder, it is possible to identify the combination of the block mounting positions, that is, eight substrate holders. For example, it is assumed that a substrate holder in which a central step is closed by a block among three steps is transported to an XY stage. Micro switch is OFF-OFF-
From OFF, an OFF-ON-OFF signal is output. By storing the correspondence table between the ON-OFF pattern and the substrate holder in advance in the storage device, the central processing unit determines that the substrate holder is, for example, the substrate holder B, and corrects the corresponding displacement. As a result, the substrate holder can be automatically identified, and a simple and reliable correction operation can be performed.

FIG. 6 is a schematic view of a substrate holder identifying mechanism of an electron beam lithography apparatus showing another embodiment of the present invention. In the figure, the substrate holder 8 has three through holes 38.
When the substrate holder 8 is placed in the preliminary exhaust chamber 10, the same number of photoelectric switches 39 as the number of the through holes 38 and the number of the transmission windows 40 are set at the same position as the through holes 38.
And provided in the preliminary exhaust chamber 10. The through hole 38 is structured so as to be closed by a cover 41.
The position is adjusted so that the photoelectric switch 39 works without the switch and does not work when the cover 41 is attached.

Here, by attaching the cover to a position unique to each substrate holder, it is possible to identify the combination of the cover attachment positions, that is, eight substrate holders. The operation and function are the same as those in the above-described embodiment.

[0043]

According to the present invention, even when a plurality of substrate holders are used in one drawing apparatus, pattern drawing with high accuracy can be performed without being affected by the characteristics of the individual substrate holders.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electron beam drawing apparatus showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a correction table according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a correction table according to another embodiment of the present invention.

FIG. 4 is a schematic diagram of an electron beam drawing apparatus showing another embodiment of the present invention.

FIG. 5 is a schematic view of a substrate holder identifying mechanism of the electron beam lithography apparatus according to the embodiment of the present invention.

FIG. 6 is a schematic view of a substrate holder identification mechanism of an electron beam lithography apparatus according to another embodiment of the present invention.

FIG. 7 is a schematic diagram of a conventional electron beam drawing apparatus.

FIG. 8 is a schematic diagram showing a position shift at the time of writing due to rotation of a wafer.

FIG. 9 is a schematic diagram showing a positional deviation at the time of writing due to the warpage of the wafer.

FIG. 10 is an operation diagram of a substrate holder in a conventional electron beam drawing apparatus.

FIG. 11 is a schematic diagram illustrating a principle of generation of a potential when electrostatically attracting a wafer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron beam, 3 ... Aperture, 4 ... Shaping deflector,
5 electron lens, 6 deflector, 7 substrate, 8 substrate holder, 9 XY stage, 10 preliminary exhaust chamber, 11 wafer, 12 positioning roller, 13 exchange chamber, 14 first
Gate valve, 15: second gate valve, 16: dielectric, 17: electron beam orbit, 18: ground potential contact portion, 19 ...
High voltage power supply, 20: deflection control system, 21: lens power supply, 22
... internal electrode, 23 ... power supply terminal, 24 ... DC power supply, 25 ...
Ammeter, 26 ... Reflector, 27 ... Laser interferometer, 28 ...
Stage drive system, 29 central processing unit, 30 storage device, 31 drawing room, 32 optical microscope, 33 wafer mark, 34 objective lens, 35 step for identification, 36 microswitch, 37 identification Block 38: through hole for identification, 39: photoelectric switch, 40: transmission window, 41: cover for identification, 42: focal length control system for optical microscope.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasunari Hayata 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. Central Research Laboratory

Claims (7)

[Claims] An electrode is formed on a dielectric, and a voltage is applied between the electrode and the semiconductor substrate on the dielectric, thereby providing a sample holder for adsorbing and holding the semiconductor substrate on the dielectric. An electron beam lithography system comprising: at least two sample holders used sequentially or irregularly to draw a pattern on the semiconductor substrate, wherein a deviation from a predetermined irradiation position at the time of electron beam deflection is provided. An electron beam lithography apparatus, wherein the amount is individually corrected for each of the sample holders and drawn. 2. A semiconductor device comprising a sample holder for positioning the semiconductor substrate by pressing a side surface of the semiconductor substrate against a reference pin, wherein at least two or more of the sample holders are used sequentially or irregularly. An electron beam drawing apparatus that draws in accordance with an underlying pattern on a semiconductor substrate, wherein when detecting a reference pattern of the underlying pattern formed on the semiconductor substrate by a microscope, the electron beam writing apparatus performs The rotation and horizontal displacement of the semiconductor substrate
An electron beam lithography apparatus wherein correction is performed individually. 3. A sample holder for forming an electrode on a dielectric and applying a voltage between the electrode and the semiconductor substrate on the dielectric, thereby adsorbing and holding the semiconductor substrate on the dielectric. An electron beam lithography apparatus comprising: using at least two or more of the sample holders sequentially or irregularly to draw in accordance with a base pattern on the semiconductor substrate,
When detecting the reference pattern of the underlying pattern formed on the semiconductor substrate by a microscope, the focal length of the microscope is individually determined from the amount of displacement of the semiconductor substrate with respect to each sample holder in the height direction. An electron beam lithography apparatus for performing correction. 4. The apparatus according to claim 1, further comprising: a storage device for separately measuring the amount of displacement of each of the sample holders in advance, and storing the measured values, and identification means for the sample holder. 4. The electron beam lithography apparatus according to claim 1, wherein the correction is performed using a shift amount corresponding to the sample holder. 5. A storage device for separately measuring in advance the relationship between the amount of deviation and the leakage current at the time of applying the voltage to each of the sample holders and storing the measured values, 2. The apparatus according to claim 1, further comprising: means for identifying a holder, and means for measuring the leakage current, wherein the correction is performed using the identified sample holder and a deviation amount corresponding to the measured leakage current. Electron beam drawing equipment. 6. The identification means has a structural step unique to a portion other than the holding surface of each of the sample holders, and the contact detection means provided outside the sample holding portion includes the number of the steps,
6. The electron beam lithography apparatus according to claim 4, wherein the sample holding device is identified by determining a shape or presence or absence. 7. The identification means has a unique through-hole at a part other than the holding surface of each of the sample holders, and the transmitted light detection means provided outside the sample holding part has the number, shape, or number of holes. 6. The electron beam lithography apparatus according to claim 4, wherein presence / absence is determined and the sample holding device is identified.