CN102087483B - Optical system for focal plane detection in projection lithography - Google Patents

Abstract

The invention is an optical system for focal plane detection in projection lithography. The focus detection mark and projection imaging system are located between the illumination system and the multiple reflection prism, and the detected surface is located between the multiple reflection prism and the reflection mirror. The focus inspection mark magnification system is located between the reflector and the detection device; the projection imaging system is matched with the illumination system to provide illumination light for the illumination focus inspection mark, and the multiple reflection prism divides the incident light of the illumination focus inspection mark of the illumination system into two beams or There are more than two beams of probe light, and the position of each beam of probe light is different. The focus inspection mark will image the mark of each beam of probe light position on the surface of the detected surface through the projection imaging system and multiple reflection prisms, and then reflect it from the detected surface The final detection light is amplified by the focus detection mark amplification system and then incident on the detection device. The detection device is used to detect the reflected image position amplified by the optical amplification system to detect the focal plane position and focal plane tilt of the lithography projection objective lens.

Description

An optical system for focal plane detection in projection lithography

technical field

The invention relates to an automatic focal plane detection system, which is a technique for measuring the position movement of an imaging plane through an optical triangulation method.

Background technique

Photolithography device (lithography machine) is one of the important equipment for the production of large-scale integrated circuits. The projection lithography machine can image the pattern on the mask plate to the object to be processed (such as a silicon wafer, etc.) in a certain proportion through the imaging exposure device. The silicon wafer here refers to all exposed objects, including substrates, coatings and light Engraving etc. During the exposure process, it is necessary to keep the corresponding surface of the processing object (such as a silicon wafer) within the focal depth range of the exposure device. For this reason, the projection lithography machine adopts a focusing and leveling measurement system (focal plane detection system) for measuring surface position information of a processing object (such as a silicon wafer, etc.). The focusing and leveling measurement system can work with the processing table that clamps the processing object (such as silicon wafer, etc.) to keep the exposed area of the processing object (such as silicon wafer, etc.) within the focal depth of the exposure device of the projection lithography machine, so that Ideally transfer the graphics on the mask to the processing object (such as silicon wafer, etc.).

With the improvement of the resolution of the projection lithography machine and the continuous reduction of the depth of focus of the projection objective lens, the requirements for the measurement accuracy of the focusing, leveling and measurement subsystem of the lithography machine and the ability to measure the exposure area in real time are also increasing. higher. Therefore, the focusing and leveling measurement systems currently used in step-and-scan projection lithography machines are usually photoelectric measurement systems, such as: photoelectric measurement methods based on gratings and four-quadrant detectors (US Patent US5191200), based on slits and four-quadrants Photoelectric measurement method of detector (US patent US6765647B1), photoelectric detection method based on PSD (position sensitive device) (Chinese patent: 200610117401) and photoelectric detection method based on grating Moire fringe (Chinese patent: 200710171968). The measurement position of the above-mentioned focusing and leveling measurement system is a single position, that is, it can only test the average position information of a certain point or a small area on the processing object. In order to realize the two functions of focusing and leveling measurement required by the projection lithography machine, it is necessary to use several sets of focal plane detection systems (such as: Overlay and field leveling in wafersteppers using an advanced metrology system, SPIE Vol.1673) or in a Several marks are adopted in the system (such as US Patent: US5191200), which makes the entire focusing and leveling measurement system very redundant.

Contents of the invention

In order to solve the problem that the above-mentioned set of optical systems can only perform focal plane detection on a certain point or a small area, several sets of focal plane detection systems are required to realize the two functions of focusing and leveling required by projection lithography machines, so the entire Focusing and leveling measurement system is very redundant. The purpose of the present invention is to use a set of optical system to complete the focal plane position and tilt detection in projection lithography, and realize the functions of focusing and leveling measurement.

In order to achieve the purpose of the present invention, the present invention provides an optical system for focal plane detection in projection lithography. The technical solutions adopted by the optical system to solve technical problems include: illumination system, focus detection mark, projection imaging system, multiple Reflecting prism, detected surface, reflecting mirror, focusing mark magnification system and detection device; focusing marking and projection imaging system are located between the illumination system and the multiple reflecting prism, and the detected surface is located between the multiple reflecting prism and the reflecting mirror , the focus inspection mark magnification system is located between the reflector and the detection device; the projection imaging system is matched with the illumination system to provide illumination light for the illumination inspection mark, and the multiple reflection prism divides the incident light of the illumination inspection mark of the illumination system into two beams Or more than two beams of probe light, and the position of each beam of probe light is different, the focus inspection mark will image the mark of the position of each beam of probe light onto the surface of the detected surface through the projection imaging system and multiple reflection prisms, and pass through the detected surface The reflected detection light is amplified by the focus detection mark amplification system and then incident on the detection device, and the detection device is used to detect the position of the reflected image amplified by the optical amplification system, and detect the focal plane position and focal plane tilt of the lithography projection objective lens .

The optical system for focal plane detection in projection lithography can also be applied to other occasions where it is necessary to detect the position difference between the actual imaging surface of the imaging objective lens and the ideal focal plane, for the detection of the focal plane of the imaging objective lens and can also be applied to Where precise position detection is required.

Beneficial effects of the present invention: In the present invention, by introducing multiple reflection prisms, only one set of optical system is used, and the focal plane position detection and focal plane tilt detection are realized at the same time, which not only reduces the complexity of the system, but also reduces the source of errors , which improves the detection accuracy. The present invention can realize the inclination detection of the detected surface through the position detection of multiple points. Since all the detection lights are emitted by the same light source and the same detection mark, each detection light is strictly consistent, and these detection lights pass through the same optical system, so the differences caused by factors such as optical system processing and assembly can be eliminated; comprehensive With the above advantages, such a structural arrangement can increase the accuracy of leveling and focusing detection.

Description of drawings

Figure 1 is a schematic diagram of a projection lithography machine.

FIG. 2 is a schematic diagram of the optical system for focal plane detection in the projection lithography machine of the present invention of the focal plane detection optical system in FIG. 1 .

Figure 3 is a schematic diagram of multiple reflections.

FIG. 4 is a schematic diagram of the reflected light path of the detection light path on the surface to be detected.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Figure 1 shows a schematic diagram of a projection lithography machine, which includes an optical axis 1a, a mask plate 2a, a lithography projection objective lens 3a, and a leveling and focusing detection system 4a composed of multiple focal plane detection optical systems , Processing object 5a and loading platform 6a. The mask plate 2a is placed on the object plane of the lithography projection objective lens 3a, and the processing object 5a (such as silicon wafer, etc.) is placed on the object loading platform 6a. During lithography exposure, the object loading platform 6a needs to be moved so that the exposure surface of the processing object 5a is on the focal plane of the lithography projection objective lens 3a. In order to accurately transfer the image on the mask plate 2a to the processing object 5a, it is necessary to accurately detect and adjust the relative position (including distance and inclination) of the exposure surface of the processing object 5a and the lithography projection objective lens 3a, so that the processing object The entire area to be exposed of 5a is within the focal depth range of the lithographic projection objective 3a. In order to achieve this goal, the leveling and focusing detection system 4a composed of multiple focal plane detection optical systems is required to precisely detect the position of the area to be exposed on the processing object 5a, and to give the focusing and adjustment of the loading platform 6a. Ping execution system feedback.

What Fig. 2 shows is the improvement to the optical system of focal plane detection in Fig. 1, the optical system of focal plane detection in the projection lithography machine provided by the present invention is to utilize triangulation method, the optical system of the present invention comprises: illumination system 1, detection The focus mark 2, the projection imaging system 3, the multiple reflection prism 4, the detected surface 5, the mirror 6, the focus mark magnification system 7 and the detection device 8, the focus mark 2 and the projection imaging system 3 are located in the illumination system 1 and Between the multiple reflection prisms 4, the detected surface 5 is located between the multiple reflection prisms 4 and the reflector 6, and the focus detection mark amplification system 7 is located between the reflector 6 and the detection device 8; the projection imaging system 3 and the illumination system 1 Matching provides illumination light for the illumination focus inspection mark 2, and the multiple reflection prism 4 divides the incident light of the illumination focus inspection mark 2 of the illumination system 1 into two beams or more than two beams of detection light, and the position of each beam of detection light is different , the focus detection mark 2 images the mark of the position of each beam of detection light onto the surface of the detected surface 5 through the projection imaging system 3 and the multiple reflection prism 4, and the detection light reflected by the detection surface 5 passes through the focus detection mark amplification system 7 is amplified and incident on the detection device 8, and the detection device 8 is used to detect the position of the reflected image amplified by the optical amplification system 7, and detect the focal plane position and focal plane tilt of the lithography projection objective lens 3a.

The illumination system 1 shapes the light emitted by the light source to illuminate the focus detection mark 2; the focus detection mark 2 is imaged on the detected surface 5 after the projection imaging system 3 and the multiple reflection prism 4; the upper surface of the multiple reflection prism 4 has Spectroscopic characteristics, and the lower surface of the multiple reflection prism 4 has reflection characteristics, so after the incident light is reflected by the multiple reflection prism 4, a reflected light will be formed, that is, the focus detection mark 2 will form a plurality of images with reproduction characteristics, these images The shape and position relationship are strictly consistent without being affected by the manufacturing process of the focus detection mark; the image of the focus detection mark 2 is reflected by the detected surface 5 and the mirror 6 and then enlarged and imaged by the focus detection mark amplification system 7 onto the detection device 8 , the optical signal obtained by the detection device 8 will be converted into an electrical signal, and the detection signal will be read out by the corresponding circuit system. The ideal imaging focal plane position of the lithographic projection objective lens 3a is obtained through process experiments, and the focal plane detection system is calibrated. After calibration, the focal plane detection system can measure the position difference between the actual imaging plane of the lithographic projection objective lens 3a and the ideal focal plane in real time. .

The lighting system 1 adopts broadband or monochromatic light sources, including halogen lamps, xenon lamps, LEDs or lasers and other commonly used light sources in engineering technology;

The focus inspection mark 2 is a light and dark mark that is easy to be detected by the detection device, wherein the light and dark mark is one of crosses, straight lines, gratings, dots and circles.

The surface of the external reflection medium of the multiple reflection prism 4 is a spectroscopic surface. According to actual needs, the partial reflection of the surface of the reflection medium or through methods such as coating can be used to achieve a certain splitting ratio. The multiple reflection prism 4 converts the incident detection light Divided into two beams of probe light or more than two beams of probe light. The light-splitting property of the external reflection surface of the multiple reflection prism 4 can be color-splitting or neutral light-splitting. The chief ray reflected by the outer surface of the multiple reflection prism 4 and the chief ray reflected by the inner surface and then refracted by the outer surface may be parallel rays or rays at an angle.

The detected surface 5 is a plane or a curved surface with specular reflection, diffuse reflection or scattering properties located on the image plane of the lithography projection objective lens 1a.

The detection device 8 is not limited to the CCD area detector 8, and can also be a CMOS device, a two-quadrant detector, a four-quadrant detector, a position detector (PSD) and a photoelectric detection device sensitive to optical signals. A sort of.

As shown in Figure 3, after the light is incident on the multiple reflection prism 4, part of the light is reflected by the front surface of the multiple reflection prism 4, and part of the light passes through the front surface of the multiple reflection prism 4 and is reflected by the front surface of the multiple reflection prism 4. Reflection from the rear surface exits through the front surface. If the transmittance and reflectance of the front and rear surfaces of the multiple reflection prism 4 are reasonably designed, the incident light can be divided into two or more than two beams. These rays are all emitted by the same light source and the same focus inspection mark 2, and have strict reproduction characteristics.

As shown in FIG. 4 , the detection light projected by the focus inspection mark 2 through the focus inspection mark projection imaging system 3 is divided into two or more beams, and then incident on the detected surface 5 respectively. These detection lights have an X offset along the horizontal direction, that is to say, the detected position also has an X offset. Through the position detection of multiple points, the tilt detection of the detected surface can be realized. Since all the probe lights are emitted by the same light source and the same focus mark 2, each probe light is strictly consistent; and these probe lights all pass through the same optical system, so the differences caused by factors such as optical system processing and assembly can be eliminated ; Based on the above advantages, such a structural arrangement can increase the accuracy of leveling and focusing detection.

The above drawings and specific implementation are only an embodiment of the present invention. On the premise of not departing from the spirit of the present invention and the scope of the invention defined by the claims, the present invention can have various additions, modifications and substitutions. Therefore, the above-mentioned embodiments are used to illustrate and illustrate the present invention rather than to limit the scope of the present invention, which is defined by the claims and their legal equivalents, and not limited by the foregoing description. The claims are intended to cover all such equivalents.

Claims (8)

1. an optical system that is used for the projection lithography focal plane is characterized in that: be comprised of illuminator (1), focusing test mark (2), projection imaging system (3), Multi reflection prism (4), detected face (5), catoptron (6), focusing test mark amplification system (7) and sensitive detection parts (8); Focusing test mark (2) and projection imaging system (3) are positioned between illuminator (1) and the Multi reflection prism (4), detected face (5) is positioned between Multi reflection prism (4) and the catoptron (6), and focusing test mark amplification system (7) is positioned between catoptron (6) and the sensitive detection parts (8); Projection imaging system (3) provides illumination light with illuminator (1) coupling for illumination focusing test mark (2), Multi reflection prism (4) is divided into two bundles or the above detection light of two bundles with the incident light of the illumination focusing test mark (2) of illuminator (1), and it is not identical that every bundle is surveyed the position of light, the mark that focusing test mark (2) is surveyed optical position by projection imaging system (3) and Multi reflection prism (4) with every bundle is imaged onto on detected face (5) surface, through the detection light after detected face (5) reflection, after amplifying, focusing test mark amplification system (7) incides on the sensitive detection parts (8), utilize sensitive detection parts (8) to survey reflected image position after focusing test mark amplification system (7) is amplified, position of focal plane and the focal plane of photoetching projection objective lens (3a) tilted to detect; The reflective outer surface of described Multi reflection prism (4) is light splitting surface, described light splitting surface is to utilize the part reflection on reflecting medium surface or make light splitting surface reach the splitting ratio of setting by film plating process, and Multi reflection prism (4) is divided into two bundles or the above detection light of two bundles with the detection light of incident.

2. the optical system for the projection lithography focal plane according to claim 1 is characterized in that: described illuminator (1) adopts broadband or monochromatic source, and described broadband or monochromatic source comprise Halogen lamp LED, xenon lamp, LED or laser instrument.

3. the optical system for the projection lithography focal plane according to claim 1, it is characterized in that: described focusing test mark (2) has the mark that sensitive detection parts are surveyed of being convenient to of light and shade form, and wherein the mark of light and shade form is a kind of in spider, straight line, grating, round dot and the circle.

4. the optical system for the projection lithography focal plane according to claim 1 is characterized in that: the spectroscopic property of the reflective outer surface of described Multi reflection prism (4) can be the color separation light splitting, also can be neutral light splitting.

5. the optical system for the projection lithography focal plane according to claim 1, it is characterized in that: described Multi reflection prism (4) can be parallel light through the outside surface chief ray that reflects and the chief ray that reflects through outside surface again through internal surface reflection, also can be light at angle.

6. the optical system for the projection lithography focal plane according to claim 1, it is characterized in that: described detected face (5) is the plane with mirror-reflection, diffuse reflection or scattering nature, the curved surface that is positioned at photoetching projection objective lens (3a) image planes.

7. the optical system for the projection lithography focal plane according to claim 1, it is characterized in that: described sensitive detection parts (8) are not limited to the CCD planar array detector, can also be a kind of in cmos device, two quadrant detectors, the 4 quadrant detector.

8. utilize the optical system for the projection lithography focal plane claimed in claim 1, can also be applied to other poor occasions of needs detection image-forming objective lens actual imaging face and desirable position of focal plane, be used for the image-forming objective lens focal plane and can also be applied to the occasion that needs Precision positioning.

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