KR100194619B1 - Wafer autofocusing device and autofocusing method using external optical feedback method of semiconductor laser - Google Patents

Abstract

The present invention relates to a wafer autofocusing apparatus and an autofocusing method using an external optical feedback method of a semiconductor laser.

The wafer autofocus apparatus of the present invention includes an autofocus module comprising a semiconductor laser 21, a collimating lens 22, a light splitter 23, and a focus lens 24; And a slit 32, a collimating lens 32, a diffraction grating 33, a focusing lens 34, and a PSD 35, which are reflected by the above-described wafer 25 and are semiconductor laser ( And a spectroscope 40 and a PSD signal processor 50 for converting a change in light intensity of the feedback light of the semiconductor laser 21 oscillated by the external light feedback of the signal 21 into a voltage change.

In addition, the wafer autofocusing method of the present invention comprises the steps of making the laser light from the semiconductor laser into parallel light and incident it on the wafer through a light splitter; Changing the output wavelength of the laser light by a change in light intensity due to external light feedback of the semiconductor laser according to a change in position of the wafer in a vertical direction; And converting the change of the output wavelength into the change of the output voltage through the PSD and the PSD signal processing unit.

Description

Wafer autofocusing device and autofocusing method using external optical feedback method of semiconductor laser

1 is a view for explaining the basic principle of the external optical feedback of the semiconductor laser used as a basic principle of the micro-distance measurement for the autofocus in the autofocus apparatus according to the present invention.

FIG. 2 is a graph showing experimental results of measuring a change in output wavelength caused by external light feedback of a semiconductor laser using the experimental apparatus shown in FIG.

3 is a schematic diagram showing an embodiment of an autofocusing apparatus of the present invention using the above-described external optical feedback principle of a semiconductor laser.

FIG. 4 is an explanatory diagram for explaining that the light intensity fed back to the semiconductor laser in the wafer autofocus apparatus of FIG. 3 varies with the relative distance between the focus lens and the wafer.

FIG. 5 (a) is a schematic block diagram of an embodiment in which the wafer autofocusing apparatus of the present invention is applied to a wafer stepper by external light feedback of a semiconductor laser.

Figure 5 (b) is a detailed view of the connection portion with the autofocus device module and the spectroscopic portion of Figure 5 (a).

* Explanation of symbols for main parts of the drawings

1,21 semiconductor laser 2,22,32 collimating lens

3,23: optical splitter 4: variable optical attenuator

5: Reflective mirror 6,7,26,34,37: Focusing lens

8,28: optical sensor 9,29: wafer stage

10,30: power meter 11: spectrometer

12: Optical multichannel analyzer 13,60: PC for control

24: focusing lens 25: wafer

31: slit 33: diffraction grating

35: PSD 38: Optical Fiber

40: spectrometer 50: PSD signal processor

70: auto focusing device module 80: main optical system

The present invention relates to a wafer autofocusing apparatus and an autofocusing method using an external optical feedback method of a semiconductor laser.

More specifically, the present invention is an automatic focusing apparatus in a wafer stamper that can improve the accuracy of the automatic focusing apparatus by measuring the vertical position change of the wafer using an external feedback method of the semiconductor laser. And an autofocusing method.

In lithography equipment, such as wafer steppers used in semiconductor manufacturing processes, an optical non-contact wafer auto-focus system is used for the wafer surface relative to the top surface of the main optical system, the exposure reference position of the wafer used in the stepper system. A device that finds relative positional information out of the vertical direction of a focusing system, which focuses an object within a depth of focus of sub-micron size to obtain a clear image with the resolution of a stepper system. Is an essential device.

In particular, in recent years, a method of reducing the wavelength of an exposure light source or increasing the NA (numerical aperture) of a reduction projection lens is a major issue in order to increase the resolution of exposure equipment such as a wafer stepper according to high integration of semiconductor devices. .

However, as the N.A. of the main optical system increases, the depth of focus of the main optical system becomes smaller, and such a decrease in the focus depth of the main optical system is a serious problem in the actual lithography process.

That is, the size of the depth of focus of the main optical system must include an error factor such as a process, a design rule, and an exposure system optical system.

For example, a reduction projection lens with a NA of 0.5 and a wavelength of 248 nm has a depth of focus of about 0.5 μm, within which the warpage of the wafer itself, the topology of the circuit, and the top surface curvature ( Since errors due to field curvature, wafer chuck flatness, etc. must be included, the actual positional accuracy of the wafer must be maintained at 0.1 μm or less, and thus the accuracy and stability of the wafer autofocusing device. More improved performance is required for stability.

As a result, an object of the present invention is to improve the accuracy of the autofocusing apparatus used in the lithography equipment such as the wafer stepper and to auto-focus the apparatus using an external optical feedback method of a semiconductor laser which can be easily mounted on an existing exposure equipment system. And an autofocus method.

A wafer autofocusing apparatus using an external optical feedback method of a semiconductor laser according to an embodiment of the present invention to achieve the above object,

A semiconductor laser, a collimating lens for converting the laser light emitted by the semiconductor laser to the parallel light, a light splitter for splitting the laser light through the collimating lens, and a laser beam passing through the light splitter to the wafer on the wafer stage. An automatic focusing device module composed of a focusing lens for incident; And,

A slit, a collimation lens for collimating the light incident on the slit to the diffraction grating, a diffraction grating for diffracting the incident beam at a predetermined angle according to the wavelength of the incident beam collimated by the collimation lens, and diffracted by the diffraction grating A voltage change of the light intensity of the feedback light of the semiconductor laser, which is composed of a focusing lens for focusing light onto a position sensitive detector (PSD) and the PSD, which is reflected by the wafer and oscillated by an external light feedback of the semiconductor laser. It includes a spectroscope and a PSD signal processing unit for converting to.

In addition, a wafer autofocusing apparatus using an external optical feedback method of a semiconductor laser according to another embodiment of the present invention,

An autofocusing device module mounted below the main optical system of the wafer stepper and composed of a semiconductor laser, a collimating lens, a light splitter, a reflecting mirror and a focus lens;

A spectroscope for controlling the stage by measuring a change in stage according to an output wavelength of the semiconductor laser by the spectroscope according to the vertical positional change of the wafer by the autofocusing module; And,

It includes a focusing lens and an optical fiber for connecting the autofocus device module with the spectroscope.

In addition, the wafer autofocus method using the external optical feedback method of the semiconductor laser according to the present invention,

Making laser light emitted from the semiconductor laser into parallel light and incident it on the wafer through a light splitter;

Changing the output wavelength of the laser light by a change in light intensity due to external light feedback of the semiconductor laser according to a change in position of the wafer in a vertical direction; And,

And converting the change in the output wavelength into a change in output voltage through the PSD and PSD signal processing units.

Hereinafter, a wafer autofocusing apparatus and an autofocusing method according to a preferred embodiment of the present invention will be described in more detail with reference to the accompanying drawings.

In general, the external feedback technology of semiconductor lasers is already being applied in various fields, such as to reduce the line width of the laser, to stabilize the oscillation frequency, or to convert the laser frequency.

1 is a view for explaining the basic principle of the external light feedback of the semiconductor laser used as a basic principle of the micro-distance measurement for the automatic focusing in the automatic focusing apparatus according to the present invention, a part of the output light from the semiconductor laser The schematic diagram of the experimental apparatus for returning to the active area of the laser and measuring the change in the output wavelength of the laser according to the amount of light returned is shown.

As shown in FIG. 1, the light emitted from the semiconductor laser 1 applied by the laser drive la is converted into parallel light through the collimation lens 2 and through the beam splitter 3. It enters into the reflection mirror 5 attached to the micro-movement stage 9 like PZT.

The light reflected by the reflective mirror 5 is returned to the optical path again and enters the semiconductor laser 1. At this time, the intensity of the reflected light reflected by the reflective mirror 5 and returned to the semiconductor laser 1 is variable. It is controlled through a variable attenuator (4), input to an optical sensor (8) such as a photodiode, and fed back to the semiconductor laser (1) using a power meter (10) connected to the optical sensor (8). Measure the light intensity.

On the other hand, in order to measure the output wavelength of the laser oscillated by the external light feedback in the experimental apparatus, the laser output beam is incident to the spectrometer 11 through the focusing lens 6 through the light splitter 3, the spectrometer Numeral 11 measures the change in wavelength through an optical multi-channel analyzer 12 and sends the value to the controlling PC 13.

Then, the controlling PC 13 compares the relationship between the change in the output wavelength of the laser and the light intensity fed back to the laser and outputs the result.

FIG. 2 is a graph showing an experimental result of measuring a change in output wavelength caused by external light feedback of a semiconductor laser using the experimental apparatus shown in FIG. 1. FIG. 2 is a graph illustrating a single mode semiconductor laser. Is a graph showing the change of the laser output wavelength according to the light intensity fed back to the semiconductor laser.

As can be seen from FIG. 2, the wavelength variation range of a general single mode semiconductor laser is about 10 nm, and the output wavelength of the laser varies within the wavelength variation range of the laser according to the light intensity fed back from the outside of the semiconductor laser. Can be.

That is, when the feedback light intensity is small, the laser output wavelength oscillates at the smaller wavelength, and as the feedback intensity gradually increases, the wavelength shifts to the larger wavelength.

3 is a schematic diagram showing an embodiment of the autofocusing apparatus of the present invention using the external optical feedback principle of the semiconductor laser, and the variation of the laser output wavelength according to the light intensity fed back to the semiconductor laser as described above. Is actually a device configuration for applying a change in the position of the wafer in the vertical direction as a change in the output voltage.

The wafer autofocus apparatus of the present invention shown in FIG. 3 is a schematic block diagram showing an embodiment of the autofocus apparatus of the present invention using the principle of external light feedback of a semiconductor laser. The spectrometer and optical multi-channel analyzer are shown as the spectrometer and the PSD signal processing circuit. Also, the power meter for measuring the intensity of the feedback light is used only for monitoring, and the output of the power meter is not input to the control PC.

As shown in FIG. 3, in the wafer autofocusing apparatus of the present invention, the laser light emitted from the semiconductor laser 21 is converted into parallel light by the collimating lens 22, and through the light splitter 23, the focus lens. Incident on the semiconductor wafer 25 located on the precision stage 29 via the (24).

At this time, the light intensity of the feedback light reflected from the wafer 25 and returned to the semiconductor laser 21 changes depending on the relative distance between the focus lens 24 and the wafer 25.

On the other hand, the spectroscopic section for converting the change in the output wavelength of the semiconductor laser 21 oscillated by the external light feedback into the change in voltage includes a slit 31, a collimating lens 32, a diffraction grating 33, a focusing lens ( 34) and a position senaitive detector (PSD) 35, which is a position detecting element, the light incident on the slit 31 is collimated by the collimating lens 32 to be incident on the diffraction grating 33, and the incident beam Light diffracted at a predetermined angle according to the wavelength is incident on the PSD 35 by the focusing lens 34.

At this time, when the angle of the diffraction grating 33 is constant, the position of the light incident on the PSD 35 is changed according to the wavelength of the incident beam, so that the change in the oscillation wavelength of the laser is directly in the PSD signal processor 50. It appears as a change in the output voltage, from which the position information of the wafer can be obtained.

In FIG. 3, reference numerals 27, 28, and 30 denote focusing lenses, optical sensors, and power meters, respectively, for measuring the light intensity of the feedback light, and 60 denotes output voltages of the PSD signal processor 50 described above. The control PC for controlling the wafer stage 29 by the change value is shown.

4 (a) to 4 (c) are explanatory diagrams for explaining that the light intensity fed back to the semiconductor laser in the wafer autofocus apparatus of FIG. 3 varies with the relative distance between the focus lens and the wafer. The laser part is shown on the right side of the splitter, and the arrows are deleted in the figure.

In general, since the width of the active region in which the laser is oscillated in the semiconductor laser is about 20, the laser light must be incident to the active region of the semiconductor laser.

As shown in FIG. 4 (a), when the wafer 25a is exactly positioned at the focal length of the focus lens 23a, the light reflected from the wafer 25a returns to the optical path, and thus the light splitter 24a and collimating lens ( It is returned to the active region of the semiconductor laser 21a exactly through 22a), and the amount of light fed back is maximum.

On the other hand, as shown in FIGS. 4 (b) and 4 (c), when the wafers 25b and 25c are closer or farther away from the focal lengths of the focus lenses 24b and 24c, the amount of light fed back is small. You lose.

Therefore, according to the present invention, since the amount of light fed back to the semiconductor laser can be changed according to the relative distance between the focus lens and the wafer, the positional information of the wafer can be obtained by converting the change in the amount of returned light into the output voltage change. It becomes possible.

FIG. 5 (a) is a schematic block diagram showing an application example for mounting the wafer autofocusing apparatus of the present invention to a wafer stepper by external light feedback of a semiconductor laser, and FIG. 5 (b) is a diagram of FIG. This is a detailed view of the connection with the autofocus module and the spectroscope.

As shown in FIG. 5 (a), the autofocusing device module 70 of the present invention is placed under the main optical system 80 of the wafer stepper, wherein the autofocusing device module described above performs the measurement of the auto-horizontality. Plural can be laid in order to.

As shown in FIG. 5 (b), the autofocusing device module 70 may be configured to have a compact and simple configuration.

That is, as shown in FIG. 5 (b), the autofocus module 70 uses a prism 36 to mount the autofocus apparatus of the present invention in a limited space (lower part of the main optical system) of the stepper. The incident light is refracted and used. In this case, the semiconductor laser 21, the collimating lens 22, and the light splitter 23 are used to transmit the light output from the semiconductor laser to the spectroscope through the fiber according to the direction of the light splitter. , Consisting of a reflecting mirror 36 and a focusing lens 24, measuring the change in the output wavelength of the semiconductor laser 21 according to the vertical positional change of the wafer 25 by the auto focusing device module 70. In order to do so, the autofocus module 70 is simply connected to the spectroscope 40 via focusing lenses 37, 26 and optical fiber 38.

As described in detail above, the wafer autofocusing apparatus and the autofocusing method of the present invention can improve the precision of the autofocusing apparatus used in lithography equipment such as a wafer stepper by using an external optical feedback method of a semiconductor laser. It has been confirmed that it can be easily mounted on the exposure system.

Claims (3)

A laser splitter 23 for splitting the semiconductor laser 21, the collimating lens 22 for converting the laser light emitted from the foregoing semiconductor laser 21 into parallel light, and the laser beam passing through the collimating lens 22 into light splitter 23 And a focusing lens 24 for injecting the laser light that has passed through the light splitter 23 into the wafer 25 on the wafer stage 29; And an incident beam according to the wavelength of the incident beam collimated by the slit 32, the collimating lens 32 for collimating the light incident on the slit 32 on the diffraction grating 33, and the collimating lens 32. A diffraction grating 33 for diffracting the light at a constant angle, a focusing lens 34 for focusing the light diffracted by the diffraction grating 33 on the PSD 35, and the PSD 35. A spectroscope 40 and a PSD signal processor for converting a light intensity change of the feedback light of the semiconductor laser 21 reflected by one wafer 25 and oscillated by an external light feedback of the semiconductor laser 21 into a voltage change. Wafer autofocusing apparatus using an external optical feedback method of a semiconductor laser comprising a 50). An autofocusing device module 70 which is installed under the main optical system 80 of the wafer stepper and is composed of a semiconductor laser 21, a collimating lens 22, a light splitter 23, a reflection mirror 36, and a focus lens 24. ); Spectroscope for controlling the stage by measuring the change of the stage according to the output wavelength of the semiconductor laser 21 by the spectroscope according to the vertical position change of the wafer 25 by the autofocusing device module 70 ( 40); And an external optical feedback method of a semiconductor laser including focusing lenses 37 and 26 and an optical fiber 38 for connecting the auto focusing module 70 to the spectroscope 40. . Making laser light emitted from the semiconductor laser into parallel light and incident it on the wafer through a light splitter; Changing the output wavelength of the laser light by a change in the light intensity due to the external light feedback of the semiconductor laser according to the change in the vertical position of the wafer; and the change of the output wavelength through the PSD and PSD signal processing units. A wafer autofocusing method using an external optical feedback method of a semiconductor laser comprising the step of converting the output voltage change.