JPS60105232A - Automatic focusing apparatus - Google Patents

Abstract

PURPOSE:To save the time for measurement and realize accurate and quick focusing by moving the wafer in vertical for the specified distance for focusing during movement in the horizontal direction to the predetermined region by making use of position data of a plurality of detector at the time of preceding focusing. CONSTITUTION:When a wafer 4 moves upward by the drive of piezo-element 23, amount of drive is detected by air sensor nozzles 34, 35, 36, 37 and an eddy current type position detector 22 and then can also be measured. A differential amplifier 45 sequentially compares amount of drive of wafer by piezoelement 23 detected by the eddy current type position detector 22 and amount of drive indicated by a micro processor 40 and drives wafers until such difference is ranged within the range of error. As a result, surface of wafer 4 is accurately located to the predetermined focusing surface position. As a first detector, a photoelectric reflection type displacement member max be used in addition to the air microsensor displacement meter. As a second detector, measurement can be realized with high accuracy even by using an electrostatic capacitance type displacement meter is addition to the eddy current type displacement meter.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a projection printing apparatus for manufacturing semiconductor circuit elements such as ICs, LSIs, and VLSIs, particularly for forming a partial image or an entire image of a mask on a wafer. This technology involves using an imaging optical system and accurately positioning a mask and a wafer at predetermined positions in the optical system.

[Prior art]

The minimum dimensions of the constituent patterns of semiconductor circuit elements are becoming finer, and therefore projection printing apparatuses are also required to have high resolution. To obtain high resolution, the mask position and wafer position of the imaging optics must be precisely positioned at its focal position.

Conventionally, the focusing method for this type of device is to push the top surface of the wafer, which has been flattened by an ultra-flat plate (wafer chuck) with back surface straightening ability, into three claws on a reference surface (wafer disk) at a predetermined position. This was done by hitting it and stopping it. Therefore, the sticky resist coated on the wafer surface adheres to the claws of the reference surface (wafer disk), and when a large number of wafers are processed, the resist adhesion is a major cause of blurring of focus. Furthermore, the photomask image is not projected on the three tabs on the reference surface that abut against the wafer, which is a major factor in reducing the profitability of semiconductor devices.

Furthermore, in steppers and the like, there is a problem in that it is necessary to focus the wafer many times, and therefore it takes a long time to focus.

[Purpose of the invention]

The present invention has been proposed in view of the above points, and is an automatic focusing device that can move a mask, reticle, or wafer to any predetermined position and quickly adjust it to the best focus position. For the purpose of providing.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

First, the overall configuration will be explained with reference to FIG. 1, which depicts the appearance of a reduction projection apparatus according to an embodiment of the present invention. 1o is an illumination optical system for converging the mask illumination light emitted from the light source 10a, and 1 is a mask provided with an integrated circuit pattern. 2 is a mask chuck that holds the mask 1 at a prescribed position with high precision. 6 is a reduction projection lens, 4 is a wafer provided with a photosensitive layer, and 5 is a wafer stage. The wafer stage 5 can move the wafer 4 in a plane XY plane perpendicular to the optical axis of the reduction projection lens 3. The wafer stage 5 has a built-in wafer 2 unit (not shown) that moves the wafer 4 in the optical axis direction (in two directions) of the reduction projection lens.

FIG. 2 is a sectional view showing the arrangement of the reduction projection lens 6 and the wafer 2 unit. 6 is a reduction projection lens, 4 is a wafer on which a projected image is projected, and 20 is a wafer chuck that holds the wafer 4. 26 is a piezo element, one end of which is in pressure contact with the wafer chuck 20° and the other end with the bottom of the container of the piezo element 26. The wafer chuck 20 moves up and down as the piezo element 26 expands and contracts. 27 is pivotally supported on the wafer and chuck holder 24 by a lever, and the wafer chuck base 21 is supported relative to the wafer chuck holder 24.
are moved up and down via the container of the piezo element 26 and the ball. Note that the wafer chuck holder 24 is fixed to the wafer stage 5. Ball bush guides 25 and 26 move the wafer chuck base 21 with respect to the wafer chuck holder 24 with high precision in the z-axis direction.

28 is a nut that is fixed to the wafer chuck holder 24, 29 is a threaded rod that engages with this, 60 is a gear attached to the threaded rod 29, 61 is an idler gear that is thick in the axial direction, and 62 is the output shaft of the stepping motor. The drive gear 63 attached to the is a stepping motor. When the stepping motor 66 rotates, the threaded rod 29 rotates through the gear train and moves up and down, thereby levering the lever 2.
One end of the wafer 7 is pushed through the ball, and the surface of the wafer 4 is transferred to the imaging plane of the projection lens of the reduction lens.

Reference numeral 22 denotes an eddy current type position detector for detecting the amount of drive by the piezo element 26 attached to the wafer chuck base 21, and measures the distance between the wafer chuck base 21 and the wafer chuck 20. Reference numerals 64 and 65 indicate air microsensor nozzles attached to the reduction projection lens 6, and measure the distance from the sea urchin to the surface by changes in the flow rate or pressure of air blown out from the nozzles.

FIG. 3 shows a top view of the reduction projection lens 6, the nozzle of the air microsensor, and the wafer 4.

Reference numerals 64 to 67 are four air microsensor nozzles attached to the reduction projection lens, and measure the distance to the wafer surface. The distance from the end face of the reduction projection lens to the wafer surface of No. 4 measured by the nozzles 64 to 67 is d1. d2. d3. If d4, the average distance is (d+ + d2+ d3+ d4)/4. The distance between the imaging plane position of the predetermined reduction projection lens B and the end surface of the reduction projection lens B is d. Then, to move the wafer to the imaging plane position, Δd = do7 (d+ + d
It is sufficient to move the wafer 2 mechanism by an amount Δd equal to 2+ d3-1- d+ )/4. As a result, the average plane of the wafer becomes the imaging plane position.

FIG. 4 is a block diagram showing the configuration of a drive control mechanism of an automatic focusing device according to an embodiment of the present invention.

A microprocessor 40 performs various judgment processes and issues commands in accordance with each case. 41 is a register;
Microprocessor-40 to stepper motor 6
It stores command information such as the rotation direction, two rotation amounts, and two rotation speeds. 42 is a stepping motor control circuit;
Based on the command information in the register 41, open loop control of the stepping motor 66 is performed. In the initial state, the surface position of the wafer is separated from the imaging plane position by, for example, 2wn or more. This is to prevent the wafer from colliding with the reduction projection lens B even if the wafer is thicker than the specified thickness.

Note that the range that can be accurately measured with the air sensor nozzle is when the distance from the nozzle end face to the wafer surface is approximately 0.2.
It is within the specified period.

Therefore, assuming that the predetermined focal plane position is from the end surface of the nozzle to the sail IU, accurate measurements can only be made when the wafer surface moves upward and below the imaging plane position o, i.
This is after the distance is within mm.

50 is a circuit that converts changes in the fluid flow rate of the air sensor nozzles 64 to 67 into voltage, and the distance d1. d2. d3. Voltage outputs v, , v2, v3.corresponding to d4. Generates V4.

49 is an analog-to-digital converter (ADC), which outputs the output voltages Vle, V2, V generated in the voltage conversion circuit 50.
3. Convert V4 into a digital signal and send it to the microprocessor-40. Here, since the initial position of Ueno-4 is more than 2'IIU1 away from the imaging plane position, the microprocessor-40 moves the register 41 until the Ueno'i-Z axis rises and enters the measurement range of the air sensor nozzle. Continue to give driving commands to the stepping motor.

When the wafer Z-axis rises due to the rotation of the stepping motor 66 and the wafer 4 enters within 0.1 period from the focal plane position, the air sensor nozzle 64-67° voltage conversion circuit 5
0 and the analog-to-digital reversing circuit 49, the microprocessor 40 detects that it has entered the measurement range;
A stop command is sent to the register 41 and stepping motor 66 to stop the Ueno X-4 from rising. Next, the microprocessor 40 again selects the air sensor nozzles 64-67,
Voltage conversion circuit 50 and analog-digital conversion circuit 4
9, the surface position of the wafer 4 is measured, and the movement amount of the wafer z mechanism Δd+ = do (d+ + d2
+ds+d4)/4 is calculated. The movement resolution by the stepping motor 66 is 2 μm, and the microprocessor 40 stores the movement amount Δd1 in units of 2 μm in the register 41.
to raise the wafer's two axes. As a result, wafer 4
The surface position is located with an accuracy of within about 2 μm with respect to the focal plane position. Here, the distance to the surface of the wafer 4 is also measured. If the distances measured by the air sensor nozzles 64 to 67 are d9 to d+2, respectively, the microprocessor 40 stores Δd2'' do (do
A command is issued for the drive direction and drive amount of the piezo element 23, which is 10d+o+do+d+2)/4. The register 43 stores this command and the necessity command for driving the piezo element, and also transmits the command to the digital-to-analog converter 4.
4 and the piezo drive voltage generation circuit 46.

44 is a digital-to-analog converter (DAC), which outputs a command from the microprocessor 40 as an analog voltage as a command voltage for the differential amplifier 45.

46 is a piezo drive voltage generation circuit, and the piezo element 26
A voltage is generated above and below a voltage that is approximately one-half of the maximum voltage (■H) applied to the differential amplifier 45 in accordance with the output of the differential amplifier 45. When the wafer 4 moves up and down due to the drive of the piezo element 26, the amount of drive is determined by the air sensor nozzles 34, 35,
36 , 37 , and the eddy current type position detector 22 . The output of the eddy current type position detector 22 is converted by a displacement voltage conversion circuit 48 into a voltage proportional to the amount of displacement, and is outputted to a differential amplifier 45 and an analog-to-digital converter 47. The differential amplifier 45 successively compares the amount of drive of the wafer 4 by the piezo element 26 detected by the eddy current type position detector 22 with the amount of drive instructed by the microprocessor 40 until the difference falls within the error range. drive

As a result, the surface of the wafer 4 can be accurately positioned with respect to a predetermined focal plane position. Reference numeral 47 denotes an analog-to-digital converter (ADC), which converts the drive amount of the piezo element 26 detected by the eddy current type position detector 22 into a digital amount and transmits the digital amount to the microprocessor 40. Note that the reason why an eddy current type position detector is used as the second detector is because its reaction speed is fast. If an air sensor is used to form a servo loop, it will take longer to converge.

FIG. 5 is a servo circuit diagram according to an embodiment of the present invention. The circuit elements 60 to 86 are the piezo drive voltage generating circuit 4 of FIG.
6 is formed. 60 is a sawtooth wave generation circuit and is approximately 10
KH2 sawtooth wave oscillation is performed. 62 is a comparator (
Comparator) compares the output of the differential amplifier 45 with the sawtooth wave generating circuit 60, and converts the result to 0 or 1.
It is given to an inverter 64 as a digital output.

The comparator 62 compares the differential amplifier 45 and the sawtooth wave generating circuit 6I to obtain a pulse width modulated output.

An inverter 64 inverts the output of the comparator 62 and supplies it to AND circuits 66 and 67.

The contents of the register 46 indicate that the piezo element drive unnecessary output is 0 (
OFF), the outputs of the AND circuits 66 and 67 are set to O regardless of the output of the differential amplifier 45.

This allows the piezo element 23 to be brought into a discharge state. When the piezo element 23 is driven by a servo loop, the microprocessor 40 gives the piezo element drive necessary output 1 (ON) of the register 46. As a result, the AND circuits 66 and 67 pass the output of the differential amplifier 45 in the form of a signal that has been pulse width modulated by the comparator 62, and supplies the signal to optical couplers 70 and 78. When the AND circuit 66 has an output of 0 (OFF), the optical coupler 70 is OFF.

The transistor 76 is ON, and the Langistav 5 is also ON.

Transistor 76 is turned off and piezo element 26 is not charged. Further, when the AND circuit 66 has an output of 1 (ON), the optical coupling circuit 10 is ON and the transistor 76 is OFF.
, ) Langistav 5 is QFF, ) Langistav 6 is O
The N lipiezo element 26 is charged.

On the other hand, when the AND circuit 67 has an output of 0 (OFF'), the optical coupler 78 is turned off, and the range nut 81 is turned on.

Transistor 82 is turned on and piezo element 26 is discharged. When the AND circuit 67 has an output of 1 (ON), the optical coupler 78 is ON, and the transistor 81 is OFF.
) The transistor 82 is turned off and the piezo element 23 is not discharged. Here, the only combinations of outputs from the AND circuits 66 and 67 are O and 0 or 1 and 1, so these combinations are summarized in Table 1.

Table 1 Here, the piezo element 26 used is what is called a piezo stack. Piezo stack is approximately 0.5 wL thick
It is made up of about 100 different layers of piezo elements.
If a voltage of several hundred volts is applied, a displacement of 30 μm can be obtained. Also, the piezo element is expressed as a condenser (condenser) in any electrical circuit, and with this size, it has a capacity of 01 μF. When the transistor 76 is ON and the transistor 86 is OFF, the piezo element 26 is charged from the power source 1H through the resistor 76 and extends in the optical axis direction. Further, when the transistor 76 is OFF and the transistor 86 is ON, the charges stored through the resistor 86 are discharged, and the potential is lowered and the optical axis is shrunk in the optical axis direction. Here, the voltage power supply vH is, for example, 4
At 00V, the resistor 68 is a voltage drop resistor.

Zener diode 69 is a constant voltage source to prevent excessive voltage from being applied to optical couplers 70 and 78, and resistors 71, 72, and 74
・79 and 80 are collector resistances of each transistor.

The resistor 77 is a resistor for charging the piezo element, and the resistor 86 is a resistor for discharging.The resistor 77 is a resistor for charging the piezo element, and the resistor 86 is a resistor for discharging the piezo element.

Next, the operation of the servo circuit according to the embodiment will be explained.

In the initial state, a control unnecessary signal is output from the register 43,
The piezo element 26 is completely discharged. Next, a control necessary signal is output from the register 46, and a driving amount corresponding to one-half of the maximum driving amount, ie, 15 μm, is applied to the digital-to-analog converter 44. The digital-to-analog converter 44 outputs an analog voltage of 5 V corresponding to a drive amount of 15 μm, and supplies it to the differential amplifier 45 . On the other hand, the output of the eddy current type position detector 22 is adjusted so that a voltage of 5V is output from the displacement voltage conversion circuit 48 when a displacement of 15 μm is detected.

However, near the initial state, the piezo element 26 is still in a discharge state and there is no elongation displacement, so the displacement voltage converter 48 outputs an output OV and supplies it to the differential amplifier 45. Therefore, the differential amplifier 45 generates a large positive voltage as an output since the amount of feedback from the displacement voltage converter 48 is small. Since the output voltage of the differential amplifier 45 is larger than the output voltage of the sawtooth wave generation circuit 60, the comparator 62 generates almost an O (OFF) output. Continue charging. Piezo element 26
is charged and generates an elongated displacement, so the displacement voltage conversion circuit 48 generates a voltage proportional to the displacement, and eventually the displacement approaches 15 μm, and the displacement voltage conversion circuit 48 generates a voltage close to 5V.

When a voltage close to the output (drive command voltage) of the digital-to-analog converter 44 is fed back from the output (displacement voltage) of the displacement voltage conversion circuit 48, the output of the differential amplifier 45 approaches OV. When the output of the differential amplifier 45 approaches Ov, it becomes approximately the center voltage of the output voltage of the sawtooth wave generation circuit 60, and the comparator 62 outputs O (OFF) and t (O
N) Repeat the output and generate/JE at the oscillation frequency of the sawtooth wave generation circuit 60. When the output of the comparator 62 becomes a repetition of 0 and 1 signals with almost equal time width, the piezo element 2
The charging amount and the discharging amount of the piezo element 26 become equal, and the terminal voltage of the piezo element 26 converges.

In this way, feedback is performed to the circuit, and the voltage becomes stable when the drive command voltage and the displacement voltage become equal, and the piezo element 26 is driven by the desired drive amount (15 μrn).

By initially setting 15 μm, which is one half of the maximum drive amount, subsequent adjustments can be made more quickly. Here, the surface position of the wafer 4 is measured again using the air sensor nozzles 64 to 67, and the distances at that time are d9 to d.
12, the new set drive amount of the piezo element 23 is Δd
2-do (do+d+o + d++ + du)/
It is given as 4. Here, as mentioned above, Δd2 is 2
Already positioned within μm. Therefore, the microprocessor 40 provides the register 43 with a value obtained by adding a new driving amount Δd2 to the initial driving amount (15 μm) that has already been driven. The register 46 generates a new drive command voltage, and the differential amplifier 45 performs error amplification. Displacement voltage converter! When the output (displacement voltage) of 1848 becomes equal to the drive command voltage, the piezo terminal voltage converges and the predetermined drive ends.

FIG. 6 is a signal waveform diagram for explaining a state in which the signal output from the sawtooth wave voltage generating circuit 6° shown in FIG. 5 is pulse width modulated by the comparator 62. FIG. 6(a) shows a case where the elongation of the piezo element is smaller than the drive command value.

Since the displacement voltage is lower than the drive command voltage, the differential amplifier 45
generates a high voltage and the comparator generates an output with a narrow Lebel time width compared to the sawtooth voltage. In the logic circuit, this signal is inverted and becomes a signal with a wide Lebel time width, that is, a signal that charges the piezo element. FIG. 6(b) shows a case where the elongation of the piezo element almost matches the drive command value. Since the drive command voltage and the displacement' voltage are almost equal, the differential amplifier generates an intermediate voltage, and the comparator compares it with the sawtooth wave voltage and generates an output with approximately equal time widths for the level and the O level. The AND circuit inverts this signal, but since the difference in time width between the level and the O level is small, it becomes a signal that balances charging and discharging of the piezo element. FIG. 6(c) shows a case where the elongation of the piezo element is larger than the drive command value. Since the displacement voltage is higher than the drive command voltage, the differential amplifier generates a low voltage, and the comparator generates an output with a wider Lebel time width than the sawtooth wave voltage. In the AND circuit, this signal is inverted and becomes a narrow Lebel signal, that is, a signal that discharges the piezo element.

FIG. 7 is a diagram showing the shot arrangement of the wafer 4'', the arrangement of the reduction projection lens 6 and the air sensor nozzles 34 to 67. The area indicated by P in the figure is a pattern area exposed by one shot. The pop-and-repeat type projection printing machine thus performs divisional printing by moving the wafer 4 placed on the wafer stage 5 in the XY-axis directions.

By the way, when printing the area Q, the reduction projection lens 6 and the air sensor nozzles 64 to 67 are located relative to the wafer 4 as shown in the figure.
- The air sensor nozzle 67 can detect and measure the wafer surface position, but the air sensor nozzle 64 cannot detect and measure the wafer surface position. That is, when the wafer 4 is brought closer to the reduction projection lens 6, the microprocessor 40 can detect that the air sensor nozzles 65, 36, and 67 are sufficiently within the measurement range; No response input. Therefore, the microprocessor-40 determines that the air sensor nozzle 34 is unable to measure, takes out the measured values d2, d3, and d4 of the air sensor nozzles 65, 66, and 67, averages them, and calculates the average distance to Ueno-4. (
Calculated as d2+d3+d4)/3. Focus positioning is performed based on this calculated value.

When the exposure pattern area R is to be exposed next after the exposure of the exposure area Q is completed, the wafer surface position of the exposure area R is detected in advance by the air sensor nozzle 65 and the distance is measured at the end of the exposure of the Q area. , this value is given by the microprocessor 40 to the register 46 as a drive command amount. The piezo element 26 starts driving before or immediately after the Ueno-4 moves and the exposure area R is located under the reduction lens B, and after confirming the driving operation with the eddy current type position detector 22, the driving ends. let In this way, the wafer 4 is exposed to the exposed area Q.
Focusing at the next exposure area R can be completed while moving from the exposure area R to the next exposure area R.

Therefore, it is possible to achieve an exposure apparatus that utilizes other operating time and has less wasted time. Furthermore, if the nozzle does not enter the next exposure region R due to the arrangement of the air sensor nozzle, the closest nozzle may be used instead.

Although the embodiment describes a wafer, it can also be applied to a mask or a reticle, and instead of moving the wafer up and down, the projection optical system may be moved up and down. As the first detector, in addition to the air microsensor displacement meter used in the embodiment, a photoelectric reflection type displacement meter or the like may be used. As the second detector, in addition to the eddy current type displacement meter, a capacitance type displacement meter or the like may be used for accurate measurement.

In addition, if the drive source is directly driven using a linear motion drive source such as the piezo element or linear motor of the embodiment, there is no need for a mechanical link mechanism and dead zones such as backlash are eliminated, allowing precise position control and fast response speed. However, it is of course possible to use a rotational motion source.

〔Effect of the invention〕

As explained above, according to the present invention, one of the position data of a plurality of detectors at the time of previous focusing is used to move vertically by a predetermined distance while moving horizontally to a predetermined area. Since the focus adjustment can be done by 1", the time required for special focusing or measurement can be omitted, allowing accurate and quick focusing. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the external appearance of a reduction projection apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view showing the arrangement of a reduction projection lens and wafer 2 unit according to an embodiment of the invention,
The figure is a top view of a reduction projection lens, a nozzle of an air microsensor, and a wafer according to an embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of a drive mechanism of an automatic focusing device according to an embodiment of the present invention, FIG. 5 is a servo circuit diagram according to an embodiment of the present invention, and FIG. 6 is a sawtooth shown in FIG. A signal waveform diagram illustrating a state in which the signal output from the wave voltage generation circuit 60 is pulse width modulated by the comparator 62,
FIG. 7 is a diagram showing the shot arrangement of the wafer 2, the arrangement of the reduction lens and the air sensor 7 nozzles. 6...Reducing projection lens 4...Wafer 5...Wafer stage 20...
・・・・・・Wafer chuck 21 ・・・・・・・・・
・・・Wafer chunk base 22 ・・・・・・・・・
... Eddy current type position detector 26 ...... Piezo element 24 ...... Wafer chuck holder 27 ...... Lever 66・・・・・・・・・ Stepping motor 6
4-67... Air micro sensor nozzle 40...
・・・・・・・・・Microprocessor-41・46・
...Register 42...Stepping motor control circuit 44...Digital-to-analog converter 45... Differential amplifier 46・
・・・・・・・・・Piezo element drive voltage generation circuit 4
7.49...Analog-digital converter 48...
...Displacement voltage conversion circuit 50...
...Voltage conversion circuit 60...Sawtooth wave voltage generation circuit 62...Comparator 64... Inverters 66, 67...AND circuits 68-86...Constituent circuit elements (1) (8) of piezo element drive voltage generation circuit 46 Fig. 6 Fig. 7

Claims (1)

[Claims] A planar object is moved stepwise in the horizontal direction and also in the vertical direction (optical axis direction), and each region of the object surface is sequentially aligned with the image plane of the projection optical system. The automatic focusing device includes a plurality of position detecting means for measuring the distance between the image forming plane of the projection optical system and the object plane, and a position detecting means for measuring the distance between the image forming plane of the projection optical system and the object plane; and a drive means for driving the object or the projection optical system in the optical axis direction, using position information obtained by one of the nearby position detection means as a set drive amount, so as to perform focusing of the next area. An automatic focusing device characterized by: