JPS61153502A - Height detecting device - Google Patents

Abstract

PURPOSE:To detect the height of a sample surface accurately by composing an interferometer of a measurement optical path which includes the sample surface as a reflecting surface and a reference optical path which includes a reflecting means as a reflecting surface, and then measuring the height of the sample surface from the optical path length of the reference optical path which provides the maximum intensity of interference fringes varying with the optical path length of the reference optical path. CONSTITUTION:Light passed through the measurement optical path formed of a light source 6, a ring-shaped mirror 5, a wafer 3, a condenser lens 11, etc., and light passed through the reference optical path formed of the light source 6, a half-mirror 9, an oscillatory mirror 13, and the condenser lens 11 form white interference fringes on a photodetector 12 and the intensity of the interference is maximum when the measurement optical path and reference optical path are equal in optical path length. The photoelectric conversion signal of the photodetector 12 is amplified 15 and inputted to a peak detecting circuit 16, which outputs a high-level signal when the value exceeds a predetermined threshold level; and the oscillatory mirror 13 which makes a scan within a predetermined range knows the position of the oscillatory mirror 13 where the light incident on the photodetector has the highest intensity from the output signal of the peak detecting circuit 16, so that the height position of a wafer 13 is detected.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a height detection device for detecting the height of a sample surface. It is used to detect.

(Background of the Invention) For example, in an electron beam exposure apparatus, in order to perform highly accurate drawing, the electron optical system must be corrected according to the height of the wafer surface. Conventionally, height measurement using an electron beam exposure apparatus has been performed using an obliquely incident light beam because drawing is performed in a vacuum. That is, a light beam is incident on the wafer surface from an oblique direction, the reflected light beam from the wafer surface is received by the original position detector, and the position of the reflected light beam on the optical position detector is adjusted to the height of the wafer surface. This is a method of matching.

However, in such a height detection device, the wafer 17c
In areas where a pattern exists, accurate measurement is difficult due to the influence of diffraction or the brightness of the pattern, regardless of whether laser beam or rectangular irradiation is used. If the stage is moved using a step-and-repeat method, for example, if the laser is used by one person, measurements should be made on a scribe line without a pattern, or in the case of rectangular irradiation, measurements should be made in an area averaged by a thin pattern, etc., and the problem can be practically avoided. was. However, when writing is performed while the stage is continuously moved in order to increase throughput, a structure that is not affected by the pattern is required.

[Purpose of the invention]

The present invention aims to solve these drawbacks and provide a height detection device that can always accurately detect height regardless of the presence or absence of patterning on the surface of a sample.

(Summary of the invention) Therefore, the present invention provides a measurement optical path using the sample surface 3 as a reflecting surface,
An interferometer is configured with a reference optical path having the reflecting means 13 as a reflecting surface, and the height of the sample surface is measured by the optical path length of the reference optical path that gives the maximum intensity of interference fringes that changes according to changes in the optical path length of the reference optical path. It is characterized by being made to do.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention, in which an electron beam 1 from an electron gun (not shown) passes through an objective lens, a condenser lens, etc., and reaches an objective lens 2. 2 onto the wafer 3. Objective lens 2 and wafer 3
A deflection coil 4 is provided between the wafer 3 and the wafer 3, and a predetermined pattern is drawn on the wafer 3 by controlling the deflection coil 4 by a control circuit (not shown). Various known electronic drawing devices t can be used as they are.

At an appropriate position on the electron beam axis, a ring-shaped mirror 5 having an electron beam passage hole formed in the center so that the electron beam passes through is obliquely provided. Light from an incoherent light source 6 such as a thermal light source passes through a pinhole in a pinhole plate 7 having a pinhole on the optical axis, and is converted into parallel light by a collimating lens 8 having a front focal point at the position of the pinhole. be done. The light emitted from the lens 8 is separated into two lights by a half mirror 9.

The light transmitted through the bar filler 9 passes through a long focal length lens 10, is reflected by the mirror 5, and is focused on the wafer 3. wafer 3
The reflected light is reflected by the mirror 5, passes through the lens 10,
A part of it is reflected by the half mirror 9. This reflected light is focused by a condensing lens 11 onto a photodetector 12 disposed at a focal position on the back side of this lens 11 .

On the other hand, among the parallel light emitted from the lens 8, the half mirror
The reflected light of 9 is perpendicularly incident on the vibrating mirror 13 that vibrates in the optical axis direction, and after being reflected there, a part of the light is reflected by the half mirror 9.
The light passes through and is focused onto the photodetector 2 by the condenser lens 11. The vibration ξ~13 passes through the half mirror 9 and travels to the long focal length lens 10. Ring-shaped mirror 5. Wafer 3. Ring-shaped budgie 5. The optical path length through which the light passes through the long focal length lens 1o and reaches the half mirror 9 is almost equal to the optical path length through which the light reflected from the half mirror 9 is reflected by the vibration roller 13 and reaches the half mirror 9 again. The driving device ft14 drives the wafer 3 around a predetermined reference position of the wafer 3. The scanning amount Δ2 of such a vibration baller 13 is, for example, 100μ.
That's about it.

Light source 6 mentioned above. Pinhole plate 7. Collimating lens 8. Half Badgee 9. Long fi point Len, (io.

Ring-shaped baggie 5, wafer 3. The optical path formed by the focusing lens 11 is a measurement optical path, and the light source 6. pinhole plate 7
．． Collimating lens 8. Half mirror 9, vibrating mirror 1
3. The optical path formed by the condensing lens 11 is a reference optical path, and the above measurement optical path and reference optical path constitute a so-called white interferometer.

That is, the light from the measurement optical path and the light from the reference optical path form white interference fringes on the photodetector 12, and the interference light intensity reaches its maximum when the optical path length of the measurement optical path and the optical path length of the reference optical path are equal. .

A photoelectric conversion signal from the photodetector 12 is amplified by an amplifier 15 and input to a peak detection circuit 16 . Peak detection circuit 1
6 has a predetermined threshold level, and when the signal from amplifier 5 exceeds the threshold level, it outputs a high level signal. Therefore, the vibration baller 13 scans within a predetermined range.

The position of the vibration i-lar 13 where the light incident on the photodetector 12 has a maximum value can be determined by the output signal of the peak detection circuit I6. Since the position of the vibration ε roller 13- at which the light incident on the photodetector 12 has a maximum value corresponds one-to-one to the height position of the wafer 3, the wafer 3
The height position can be detected.

White interference fringes are generated as long as there is specularly reflected light from the wafer 3, regardless of the presence or absence of a pattern on the wafer 3.
Accurate height detection is possible regardless of the presence or absence of a pattern. A signal related to the height variation of the wafer 3 detected in this way is fed back to the control circuit of the objective lens, and adjustment is performed so that the electron beam 1 is focused on the surface of the wafer 3.

Next, see the electrical block diagram in Figure 2 and I! An example of the processing circuit will be described in detail with reference to FIG. 3, which is a time chart of FIG.

Note that (a) to ω) shown in FIG. 2 correspond to (a) to ω) in FIG.
It corresponds to (g). Height detection is started by a pulse from the command device 17 (FIG. 3(a)).

The pulse (a) is input to a one-shot pulse generator 18 that generates a pulse (FIG. 3(b)) with a pulse width corresponding to the scan amount of the vibration i-lar 13, and to a set terminal S' of a flip-flop 19. be done. The pulse (b) of the one-shot pulse generator 18 is applied to the coil 20 which scans the vibration 9-13, and the pulse (b) of the first antagonist 2).
1 is applied to one input terminal of 1. 1st and gate 2
Since the clock pulse (Fig. 3(e)) from the clock pulse generator 22 is input to the other input terminal of the clock pulse generator 1, the clock pulse (e) is generated only while the pulse (b) is occurring. Pass through the 1-AND gate 21. The pulse output from the first AND gate 21 (FIG. 3(f)) is
It is counted by the first counter 23 and applied to one input terminal of the second AND gate 24 . ] The count value of the counter 23 corresponds to the position of the vibration dler 13. The output terminal of the flip-flop 19 is connected to the other input terminal of the second AND gate 2. The flip 70 knob 19 is set by the pulse (a), and since the output terminal of the peak detection circuit 16 is connected to the reset terminal R, it is reset by the high level signal output from the peak detection circuit 16. That is, the flip-flop 19 is set for the time period from when the vibration baller 13 starts scanning until the output signal of the peak detection circuit 16 becomes high level. Therefore, the second AND gate 24 receives the clock pulse (f) only while the flip-flop J9 is set.
) (Figure 3 (g)).

The count value of the second counter 25 that counts the pulses (g) from the second AND gate 24 corresponds to the position of the vibration dler 13 where the light incident on the photodetector 12 has a maximum value.

The calculation circuit 26 inputs the count value of the first counter 23 and the count value B of the second counter 25. Then, find the peak position (%) for the total scan amount of the vibration baller 13,
A focus position correction signal corresponding to the amount of deviation between this value and the reference position (for example, !/2) is output. This correction signal is D
-A converter 27 converts it into an analog value, and inputs it to the control circuit 28 of the objective lens 2. The control circuit 28 changes the focal position so that the electron beam l is focused on the wafer 3 based on the correction signal.

In this way, the electron beam l can be focused on the wafer 3.

Note that if the command device 17 generates command pulses at a cycle sufficiently faster than the moving speed of the wafer 3, it is possible to continuously and automatically follow the height fluctuations of the wafer 3.

9. FIG. 4 shows the mechanical part of the drive device that drives the vibrating i-no 13. The vibrating mirror 13 is fixed to the lid of a support tube 29 which has a structure similar to a cylinder with a lid.
A coil 20 is wound around the outer periphery of the coil 9. A U-shaped yoke 30 for sandwiching this coil 20 and generating magnetic flux.
30' and magnets 31 and 31' are provided at opposing positions of the support tube 29. The support tube 29 is normally located at a reference position by a support member (spring) not shown, and receives a force in the optical axis direction from a magnetic field by applying current to the coil, and moves by a certain amount depending on the current application time.

Next, a second embodiment of the present invention will be explained with reference to FIG. In FIG. 5, the same members as in FIG. 1 are given the same reference numerals, and their explanations will be omitted. The difference between FIG. 5 and FIG. 1 is that the long focal length lens 1O is omitted in the reference optical path and parallel light is made incident on the wafer 3, and that the distance between the half mirror 9 and the ring-shaped vane 5 in the reference optical path is A half-band no. 50 is arranged to branch the reflected light from the wafer 3, and a half-no.
The reflected light is guided to a photodetector 52 by a condensing lens 51. The photodetector 520 photoelectric conversion signal corresponds to the amount of reflected light from the wafer 3.

Therefore, depending on the surface condition of the wafer 3, the amount of reflected light from the wafer 3 may be small. In such a case, if the threshold 7 hold level of the peak detection circuit 16 is constant, accurate peak detection cannot be performed. Although it is possible, if the output signal of the photodetector 12 is normalized by dividing the output signal of the photodetector 52 as a reference, accurate peak detection can be performed even with a constant threshold 7 hold level. Ru.

Although the long focus lens 5 is omitted in FIG. 5, if the surface of the wafer 3 is not tilted, interference fringes can be obtained in the same way, but if the surface of the wafer 3 is tilted, In this case, a round blade that condenses light as shown in FIG. 1 is preferable because it is free from the influence of inclination. Further, the half vane 9 and the vibrating mirror 13 may be used as a condensing system.

Further, the plate 5 does not need to be round as long as it has a hole through which the electron beam passes. Furthermore, two plate-shaped ξ
The holes may be installed diagonally with sufficient spacing for the electron beam to pass through.

In this case, the space between the two plate-shaped i-nos becomes a passage hole for the electron beam.

Although the above embodiments are examples in which the present invention is applied to an electron beam exposure device, it is also possible to use an exposure device that uses an ion beam instead of an electron beam (that is, an exposure device that uses a charged beam), or an exposure device that uses light in a narrow wavelength range. The same can be applied to the exposure apparatus used. However, in the case of an exposure apparatus that uses light, it is necessary to cut the wavelength range of the exposure light from the light emitted from the light source 6 by using an optical filter or the like. Even if such light with a specific wavelength range cut is used, sufficient interference fringes can be obtained, and the incoherent light of the present invention includes such light. At this time, it is preferable to use a beam splitter that transmits the exposure light and reflects the height detection light instead of the ring-shaped minnow 5.

Furthermore, the vibrating vane 13 may be replaced with a fixed mirror, and an optical member for varying the optical path length may be inserted between the fixed mirror and the half vane 9. In any case, the height of the sample surface can be detected since the change in the optical path length of the reference optical path formed by the reflected optical path of the half mirror 9 corresponds to the change in the intensity of the interference fringes.

(Effects of the Invention) As described above, according to the present invention, by forming an interferometer, height detection can be performed without being influenced by the pattern on the sample surface. Therefore, if the present invention is applied to an exposure device using a charged beam, it becomes possible to perform writing while continuously moving the stage and measuring the height, which was difficult in the past, increasing throughput and achieving high precision writing. It became possible to do this.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the first embodiment of the present invention, Fig. 2 is an electrical block diagram of the first embodiment of the invention, Fig. 3 is a time chart explaining the operation of Fig. 2, and Fig. 4 is a block diagram of the first embodiment of the present invention. FIG. 5 is a cross-sectional view showing the mechanical part of the vibration-absorbing drive device, and FIG.
It is a block diagram of an Example. (Explanation of symbols of main parts) 5... Ring-shaped no. 6. ...White light source, 7...
·Pinhole! , 8... Collimator lens, 9 River half mirror, 11... Condensing lens, 12... Photodetector, 13... Oscillating mirror.

Claims (1)

[Claims] A device for detecting the height of a sample surface includes a light source that emits incoherent light, a pinhole placed in front of the light source, and a focal point at the pinhole, and the light from the pinhole is a collimating lens that converts the light into parallel light; a half mirror that splits the light from the collimating lens into two; In order to make the light incident on the collimating lens, a reflecting member installed obliquely in one of the optical paths branched by the half mirror, and when the sample surface is at a reference position, reciprocate between the half mirror, the reflecting means, and the sample surface. a reflecting means disposed perpendicularly to the optical axis in the other optical path of the half mirror in order to form an optical path with an optical path length approximately equal to the optical path length in the other optical path of the half mirror; the half mirror; a means for changing the optical path length of the optical path formed by the reflecting means; and receiving and condensing the reflected light from the sample surface and the reflected light from the reflecting means through the half mirror. and a photoelectric conversion means for photoelectrically converting the light condensed by the condensing lens, the substance of the electric signal obtained from the photoelectric conversion means according to the change in the optical path length by the changing means is provided. A height detection device characterized in that the height of the sample surface is determined from the peak position of the sample.