WO2006057451A1 - オートフォーカス装置および光学測定評価方法 - Google Patents
オートフォーカス装置および光学測定評価方法 Download PDFInfo
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- WO2006057451A1 WO2006057451A1 PCT/JP2005/022138 JP2005022138W WO2006057451A1 WO 2006057451 A1 WO2006057451 A1 WO 2006057451A1 JP 2005022138 W JP2005022138 W JP 2005022138W WO 2006057451 A1 WO2006057451 A1 WO 2006057451A1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/28—Systems for automatic generation of focusing signals
- G02B7/34—Systems for automatic generation of focusing signals using different areas in a pupil plane
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
- G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
- G03F9/7003—Alignment type or strategy, e.g. leveling, global alignment
- G03F9/7023—Aligning or positioning in direction perpendicular to substrate surface
- G03F9/7026—Focusing
Definitions
- the present invention relates to an optical device, for example, a autofocus device used for an overlay measuring machine or the like for detecting a displacement of a circuit pattern formation position when a circuit pattern is laminated on a wafer.
- an optical device for example, a autofocus device used for an overlay measuring machine or the like for detecting a displacement of a circuit pattern formation position when a circuit pattern is laminated on a wafer.
- the present invention also provides, for example, a method of optically measuring a position detection pattern mark or the like used for detecting a misalignment of the formation position of a circuit pattern when a circuit pattern is formed on a wafer in a stacked manner. Relates to an optical measurement evaluation method for obtaining an optimum focus position in this optical measurement. Background art
- a plurality of patterns are laminated one by one using a plurality of reticles each having a pattern corresponding to each process.
- a plurality of pattern layers are stacked and formed, it is necessary to form the lower layer pattern and the upper layer pattern stacked thereon in the correct positional relationship.
- a position detection pattern mark is formed simultaneously with the formation of each pattern layer, and the positional detection of the upper and lower pattern layers is detected by optically detecting the position detection pattern mark. It is known to perform (overlapping detection) (see, for example, Japanese Patent Laid-Open No. 2 0 0 1-3 1 7 9 1 3).
- the positional deviation measurement (overlay measurement) using the position detection pattern mark formed for each layer in this way is performed by optically positioning the position detection pattern mark. This is performed using an optical measuring device for observation. Specifically, a measurement calculation is performed based on the image of the position detection pattern mark obtained by this optical measurement device, and the positional deviation is measured, but such an optical measurement device has an autofocus mechanism. This autofocus mechanism automatically adjusts the focus.
- FIG. 1 An example of such an optical measuring device will be briefly described with reference to FIG.
- the optical measuring device of FIG. 1 is also related to the embodiment of the present invention, the basic configuration is the same as the conventional one, so the configuration of the conventional optical measuring device with reference to FIG. Is described below.
- the detailed configuration of the optical measuring device will be described in the description of the preferred embodiment of the present invention. Here, only the portions necessary for explaining the conventional problems will be described, and the rest will be described very simply.
- the illumination light emitted from the light source 1 is reflected by the first half mirror 6 through the diffusion plate 2, the condenser lens 3, the AF slit plate 4 and the projection lens 5, 1 Illuminate the position detection pattern mark M on the surface of the wafer W held by the wafer stage 3 3 through the objective lens 7.
- Light reflected from the surface of the wafer W by illuminating the position detection pattern mark M passes through the first objective lens 7 and the first half mirror 6 to the second half mirror 8, and is transmitted through the second half mirror 8.
- the light enters the observation optical system 10, and the light reflected by the second half mirror 8 enters the autofocus optical system 20.
- the focusing light reflected by the second half mirror 8 is reflected and divided by the wedge mirror 23 located substantially at the pupil position through the AF second objective lens 21, Subsequently, the AF photoelectric conversion element 26 is irradiated through the focusing imaging lens 24 and the cylindrical lens 25.
- the relay lens 22 is not provided. As a result, in the photoelectric conversion element for AF 26, 8
- a segmented image that is substantially conjugate with the wafer in the autofocus measurement direction and pupil conjugate in the non-measurement direction is captured.
- the image information (autofocus detection signal) obtained by the AF photoelectric conversion element 26 in this way is sent to the focus position detection device 31 and measures the distance between the two images divided here. To obtain the focus error signal.
- the focus actuator driving device 32 drives the wafer stage 33 to move the wafer W in the direction of the optical axis (perpendicular to the surface of the wafer W. This direction Is referred to as the Z direction) to adjust the auto focus.
- the wedge mirror 23 in the autofocus optical system 20 performs image division on the pupil plane, so that the center of focus is the just focus position (this is referred to as the “just focus position”).
- Auto focus between the position where the focus shift occurs on the front side referred to as “front focus shift position” and the position where the focus shift occurs on the rear side (referred to as “rear focus shift position”).
- front focus shift position the position where the focus shift occurs on the front side
- rear focus shift position refers the position where the focus shift occurs on the rear side.
- the phenomenon that the detection signal has an asymmetric peak (ringing phenomenon) occurs.
- Figure 2 shows this ringing phenomenon.
- the distance between the two images is measured to obtain the focus error signal.
- the distance between the images is reduced to the peak.
- the focus position is shifted.
- the auto focus adjustment becomes unstable because the peak position reverses from the inside to the outside of the image when the front focus shifts slightly from the just focus position and when the rear focus shift slightly occurs. Or non-linearity with respect to the set autofocus position.
- the inter-image distances obtained by the focus position detection device 31 are indicated by L 1, L 1, L 2, L 3, and L 4.
- the horizontal axis shows the Z-direction position (focus adjustment offset amount A F), and the vertical axis shows the focus error signal ES.
- the focus error signal ES is compared to the amount of deviation from the just focus position (the amount of movement of the wafer W in the Z direction) as shown by the broken line! In this case, accurate and stable autofocus adjustment is possible.
- the problem is that a deviation of the force error signal ES between the characteristic indicated by the broken line and the characteristic indicated by the solid line in FIG. 3 occurs, but this deviation amount ⁇ ES differs depending on the wavelength of the light.
- the horizontal axis indicates the Z-direction position (focus adjustment offset AF), and the vertical axis
- the shift amount ⁇ ES of the focus error signal (that is, the value corresponding to the focus error signal difference between the broken line and the solid line in FIG. 3) is shown for each wavelength.
- the shift amount of the focus error signal in the case of blue light is indicated by a solid line ES 1 (B), and the shift amount of the focus error signal in the case of red light is indicated by a solid line ES 1 (R).
- the offset correction amount for the axial chromatic aberration in the observation optical system 10 is indicated by a broken line
- the offset correction amount in the case of blue light is represented by the broken line ES 2 (B), the red light.
- the amount of offset correction is indicated by a broken line ES 2 (R).
- Red light shift amount ES 1 (R) is greater than blue light shift amount ES 1 (B) (ES 1 (R) is located on the upper side in the vertical axis direction of the reverse) In the region where the force Z is positive (ES 1 (R) is located on the lower side of the vertical axis of the graph).
- the offset correction amount in the observation optical system 10 is such that the red light correction amount ES 2 (H) is larger than the blue light correction amount ES 2 (B) in all regions (in the vertical axis direction of the graph). ES 2 (R) is on the top).
- the magnitude relationship between the shift amount of the focus error signal in blue light and red light is negative with respect to the magnitude relationship of the offset correction amount of the observation optical system with respect to the axial chromatic aberration of blue light and red light.
- the opposite direction is obtained when the forces S and Z in the same direction are positive, and there is a problem that the autofocus adjustment is more likely to become unstable depending on the color of light, that is, the wavelength.
- the semiconductor pattern formed on the wafer has been increasingly miniaturized recently, and the thickness of each pattern has also become thinner. For this reason, the step of the position detection mark formed at the time of forming each pattern has become very small, and accurate focus adjustment is necessary when optically detecting this.
- the position detection pattern mark formed on the wafer corresponding to the pattern formed on the wafer is formed in a rectangular shape formed together with the lower layer pattern. The first mark and the second mark that is formed to extend in parallel with the first mark when the upper layer pattern is formed on the lower layer pattern.
- the step of the position detection pattern mark formed for each layer is determined according to the thickness of the pattern provided for each layer, and the step of the position detection pattern mark is different for each layer. It is common.
- such misalignment measurement (overlapping measurement) using the position detection pattern mark is performed using an optical measurement device that optically observes the position detection pattern mark. Specifically, a measurement calculation is performed based on the image of the position detection pattern mark obtained by this optical measuring device, and the positional deviation is measured.
- Such an optical measurement apparatus has an autofocus mechanism, and automatic focus adjustment is performed by this autofocus mechanism.
- the step of the position detection pattern mark formed for each layer is different.
- the focus position adjusted by the auto focus may be focused on the pattern mark of a specific layer, and defocus may occur with respect to the pattern mark of another layer.
- the present invention has been made in view of the above-described problems, and provides an autofocus device that improves the non-linear characteristics caused by ringing phenomenon in an autofocus optical system and enables stable autofocus adjustment. For the purpose.
- the present invention further provides an optical measurement evaluation method that can be used to determine an optimum condition for adjusting the focus position when optically shifting the position detection pattern marks formed in a plurality of layers.
- the purpose is to provide
- the first aspect of the present invention provides an illumination optical system that irradiates an observation target with illumination light (for example, the light source 1, the diffusion plate 2, the condenser lens 3, and the AF slit plate in the embodiment). 4, an illumination optical system composed of a projection lens 5 and a first half mirror 6) and an observation optical system that obtains an image of the observation object by receiving reflected light from the observation object (for example, the second pair in the embodiment) An observation optical system 10) having an object lens 11, an observation imaging lens 12 and a two-dimensional photoelectric conversion element 13), and using the reflected light from the observation target, An autofocus device that performs focus adjustment, An imaging unit that divides a pupil of the observation optical system and detects an image of the observation target that passes through one area of the pupil and an image of the observation target that passes through the other area of the pupil (for example, an embodiment) Shield / divider placed at approximately pupil position in the optical path from the second half mirror 8 to the photoelectric conversion element 26 for AF (a wedge mirror
- a focus position detector for calculating, and a focus actuator for adjusting the relative position of the observation target in the optical axis direction based on the focus error signal calculated by the focus position detector (for example, A correction optical system (for example, the relay lens 22 in the embodiment in the direction of arrow A) that shifts the imaging position of the image captured by the imaging device by a predetermined amount.
- a correction optical system for example, the relay lens 22 in the embodiment in the direction of arrow A
- the magnitude relationship of the shift amount of the focus error signal for each wavelength of the reflected light is the same as the magnitude relationship of the offset correction amount in the observation optical system with respect to axial chromatic aberration for each wavelength of the reflected light. It is preferable that the imaging position is shifted so as to be in the direction.
- the focus position detecting means is configured to calculate the focus error signal from an inter-image distance between the two images, and the correction optical system is configured to generate the focus error signal due to a ringing phenomenon that occurs in the two images. It is preferable that the focus position is shifted so as to avoid the non-linear portion occurring in the lens.
- the second aspect of the present invention includes an illumination optical system that irradiates the observation target with illumination light, and an observation optical system that receives the reflected light from the observation target and obtains an image of the observation target.
- An autofocus device that adjusts the pupil of the observation optical system, and an image of the observation target that passes through one area of the pupil and an image of the observation target that passes through the other area of the pupil
- An imaging means for detecting the focus, a focus position detection means for calculating a focus error signal based on an image picked up by the image pickup means, and a focus error signal calculated by the focus position detection means.
- a focus actuator that adjusts the relative position in the optical axis direction, sets a predetermined focus error signal, and sets the focus actuator until the focus position detection means detects the predetermined focus error signal. Control, and then control the inversion of the focus actuator by an amount corresponding to the predetermined focus error signal. Constituted by a that control means.
- the correction optical system arranged in the autofocus optical path shifts the imaging position of the image captured by the imaging means in the autofocus optical system by a predetermined amount.
- the detection means calculates the focus error signal based on the image picked up by the image pickup means, it is possible to adjust the autofocus of the observation optical system while avoiding the non-linear part caused by the ringing phenomenon that occurs in this image. And stable autofocus control.
- a third aspect of the present invention is a method for performing a measurement evaluation when performing optical measurement of a focus position of a pattern formed on each of two or more layers formed in a stacked manner, and the state in which the layers are formed
- a third step of calculating a correlation function with a comparison pattern for each region a fourth step of calculating an evaluation value indicating a peak length of the correlation function for each region, and for each region.
- the calculated evaluation value And a sixth step for calculating an optimal force position based on the total index. It consists of.
- the correlation function can be calculated using the self-folding pattern as a comparison pattern.
- the correlation function can be calculated using a template pattern as a comparison pattern.
- the evaluation value indicating the sharpness of the correlation function can be calculated using the peak value of the correlation function and the correlation function values adjacent to the position indicating the peak value.
- the equation E V p— ⁇ V ( The evaluation value E indicating the length of the correlation function can be calculated from a) + V (b) ⁇ Z 2.
- the sum of the reciprocals of the evaluation values calculated for each region can be calculated as the comprehensive index.
- the first to fifth steps are performed while changing the offset position of the pattern in the optical axis direction when the pattern is optically photographed to acquire an image in the first step.
- the change characteristic of the comprehensive index is obtained, and the offset position that becomes the optimum focus position can be obtained in the sixth step from the change characteristic thus obtained.
- the optimum value can be evaluated using the evaluation value extracted from the image, so that the optimum condition can be calculated efficiently in a short time.
- the optimum evaluation can be automatically performed, so that the measurement accuracy can be improved.
- the contrast of the position detection pattern marks for each layer is different and the contrast is compatible.
- the optimum condition for adjusting the focus position can be determined easily and accurately.
- FIG. 1 is a schematic configuration diagram of an optical measuring device having an autofocus device according to the present invention.
- FIG. 2 is a diagram showing a relationship between two images photographed by the AF photoelectric conversion element 2 6 and the focus position shift in the conventional autofocus device.
- FIG. 3 is a graph showing the focus error signal characteristic with respect to the focus position offset amount in the conventional autofocus device.
- Fig. 4 is a graph showing the relationship between the amount of shift of the focus error signal relative to the focus position offset amount in a conventional autofocus device and the amount of offset correction corresponding to axial chromatic aberration in the observation optical system for blue light and red light. It is.
- FIG. 5 is a diagram showing the relationship between the two images taken by the photoelectric conversion element 26 for AF and the focus position shift in the autofocus device of the present invention.
- FIG. 6 is a graph showing the focus error signal characteristic with respect to the focus position offset amount in the auto focus apparatus of the present invention.
- FIG. 7 shows the relationship between the focus error signal shift amount with respect to the focus position offset amount and the offset correction amount corresponding to the longitudinal chromatic aberration in the observation optical system in the case of blue light and red light. It is a graph to show.
- FIG. 8 is a plan view and a cross-sectional view showing an example of a position detection pattern mark to be measured by an optical measuring device having the autofocus device according to the present invention.
- FIG. 9 is a flowchart for explaining the auto focus adjustment according to the second embodiment. Yat.
- FIG. 10 is a schematic configuration diagram showing the configuration of an optical measurement apparatus that is an object of the optical measurement evaluation method according to the present invention.
- FIG. 11 is a flowchart showing the contents of the measurement method using the optical measurement evaluation method according to the present invention.
- FIG. 12 is a graph showing an example of an evaluation function calculated in the optical measurement evaluation method according to the present invention.
- FIG. 13 is a graph showing an example of a comprehensive index calculated in the optical measurement evaluation method according to the present invention.
- the observation optical system 10 has a second objective lens 1 1, an observation imaging lens 1 2 and a two-dimensional photoelectric conversion element 1 3, and the light transmitted through the second half mirror 8 is the second object lens 1 1 and
- the observation imaging lens 12 passes through the two-dimensional photoelectric conversion element 13, and an image of the position detection pattern mark M is taken by the two-dimensional photoelectric conversion element 13. Then, based on the image captured by the two-dimensional photoelectric conversion element 13 in this way, the displacement measurement is performed.
- the autofocus optical system 20 includes an AF second objective lens 21 and a relay lens 22, a wedge mirror 23, a focusing imaging lens 24, a cylindrical lens 25, and an AF.
- a photoelectric conversion element 26 is provided.
- the divided image obtained by the photoelectric conversion element 26 for AF is located at the just focus position due to the ringing phenomenon.
- a peak occurs on the inner or outer edge of the image and the focus position shifts.
- the optical measurement apparatus of the present embodiment is configured by slightly moving the position of the relay lens 22 in the autofocus optical system 20 from the just focus position in the optical axis direction (arrow A direction). ing.
- the primary imaging plane 2 8 exists between the AF system second objective lens 2 1 and the relay lens 2 2, but by moving the relay lens 2 2 in the direction of arrow A, the photoelectric conversion element 2 for AF
- the focus position of the image taken in step 6 will be shifted by the corresponding amount.
- the movement of the relay lens 22 may be achieved by manual operation along the lens guide mechanism, or may be achieved by electric operation by a motor.
- FIG. 5 shows an example of a divided image taken by the A / F photoelectric conversion element 26 when the focus position is thus shifted.
- a peak appears on the outside. That is, as can be seen by comparing FIG. 2 and FIG. 5, the divided image shifted to the rear focus shift position as a whole is taken by the AF photoelectric conversion element 26. Adjustments are made.
- the characteristics when no ringing occurs are indicated by broken lines, and the actual characteristics (characteristics when ringing occurs) in the present embodiment are indicated by solid lines.
- the relay lens 22 is slightly moved in the direction of the arrow A.
- the solid line ES 1 (B) and the solid line ES 1 ( The deviation indicated by R) changes as if the line in Fig. 4 was shifted to the right.
- the magnitude relationship between the shift amount of the focus error signal in light and the magnitude relationship between the offset correction amounts of the observation optical system are the same. Therefore, stable and good autofocus control is performed for both blue light and red light.
- Example 1 In this embodiment, an example in which the focus error signal is obtained from the distance between the images divided into two using the wedge mirror 23 and the auto focus control is performed. However, it is of course possible to use a configuration in which the focus error signal is obtained using a knife edge, a split prism, or the like instead.
- Example 1
- FIG. 8 shows an example of the force position detection pattern mark M in which the position shift detection is performed based on the position detection pattern mark M formed on the surface of the wafer W.
- the first pattern layer L 1 is formed on the surface of the wafer W, and the first mark M 1 is formed when the first pattern layer L 1 is formed.
- the second mark M 2 is formed as a part of the second pattern layer L 2.
- a large number of reticle (photomask) patterns are reduced and projected onto the wafer W, and a plurality of position detection pattern marks M are formed adjacent to each projection pattern. It is possible to detect misalignment for each transfer pattern.
- an image of the position detection pattern mark M is taken by the two-dimensional photoelectric conversion element 13 in the observation optical system 10, and the first pattern is based on the taken image.
- a displacement of the second pattern layer L 2 with respect to the layer L 1 is detected.
- the wafer stage 33 is driven using the photofocus optical system 20, The auto focus control is performed by moving the wafer W in the Z-axis direction.
- the auto focus control The just focus position to be adjusted is often set to one of the two marks M l and M 2. However, for the measurement of misalignment, both marks M 1 and M 2 are required to be photographed well, and the focus position is adjusted so that equal contrast is obtained for both marks M l and M 2 ( Focus adjustment is performed.
- the pattern layer formed on the surface of the wafer W has a different layer thickness (film thickness), and the spectral characteristics from the marks M l and M 2 may differ depending on the film thickness. . That is, the wavelength (color) of the reflected light from the first mark M 1 may be different from the wavelength (color) of the reflected light from the second mark M 2. In this example, the wavelength is set as shown in Fig. 7. Thus, stable focus adjustment is possible even when the reflected light wavelength of each mark is different.
- FIG. 9 shows a modification of the above-described embodiment, and shows a flowchart of the apparatus excluding the relay lens 22 from FIG.
- the other configurations are the same as those in FIG. 1, so the description is omitted here, and different configurations are described in detail.
- the wafer stage 33 is moved to a predetermined differential in the Z-axis direction.
- Drive to the orcas position that is, drive to the default position where ringing does not occur and drive control is completed at a position with good linearity
- step S2 when the focus position detection device 31 detects a predetermined amount of defocus, the signal output to the focus actuator drive device 3 2 is stopped, and the wafer stage 3 3 is driven in the Z-axis direction. Is stopped.
- step S 3 when it is confirmed that the driving of the wafer stage 33 is stopped, the focus actuator driving device 3 2 forcibly prohibits reception of the focus error signal from the focus position detecting device 31.
- the focus actuator driving device 32 drives the driving amount corresponding to the predetermined defocus amount set in step S 1 in the direction opposite to the driving direction in step S 2.
- step S4 the focus actuator driving device 32 determines whether or not the reverse driving corresponding to the predetermined defocus amount has been completed.
- step S5 when the inversion driving in step S4 is completed, the optical measurement apparatus (for example, semiconductor manufacturing apparatus) in FIG. 1 enters the sequence of the next inspection process.
- the optical measurement apparatus for example, semiconductor manufacturing apparatus
- This optical measuring device includes a light source 1001, a diffuser plate 102, a condenser lens 10.03, an AF slit plate 10.04, a projection lens 10.05, and a first half mirror 1. And an illumination optical system consisting of six.
- this illumination optical system the illumination light emitted from the light source 101 is made uniform by the diffuser plate 102 and condensed by the condenser lens 103, and auto-focused by the AF slit plate 1004.
- a slit-shaped luminous flux is formed, and an appropriate illumination magnification is given by the projection lens 1 0 5 to reach the first half mirror 1 0 6.
- the slit illumination light reflected by the first half mirror 106 and irradiated vertically downward passes through the first objective lens 107 and the surface of the wafer W gripped by the wafer gripping device 1 33 Illuminate the position detection pattern mark M.
- the light reflected from the surface of the wafer W by illuminating the position detection pattern mark M in this way passes through the first objective lens 10 7 and the first half mirror 1 0 6 and the second half mirror 1 0. Up to 8.
- the light transmitted through the second half mirror 110 8 enters the observation optical system 110, and the light reflected by the second half mirror 10 108 enters the autofocus optical system 120.
- the observation optical system 1 1 0 has a second objective lens 1 1 1, an observation imaging lens 1 1 2 and a two-dimensional photoelectric conversion element 1 1 3, and the light transmitted through the second half mirror 1 0 8 is The second objective lens 1 1 1 and the observation imaging lens 1 1 2 pass through to the two-dimensional photoelectric conversion element 1 1 3 and the two-dimensional photoelectric conversion element 1 1 3 takes an image of the position detection pattern mark M. The Then, based on the image photographed by the two-dimensional photoelectric conversion element 113 as described above, the positional deviation measurement is performed.
- the auto-focus optical system 1 2 0 includes a relay lens 1 2 1, a total reflection mirror 1 2 2, a knife edge 1 2 3 (a splitting prism can be used instead), and a focusing imaging lens 1 2 4, cylindrical lens 1 2 5, and AF photoelectric conversion element 1 2 6.
- the light reflected by the second half mirror 1 0 8 and incident on the autofocus optical system 1 2 0 passes through the relay lens 1 2 1 and is totally reflected by the total reflection mirror 1 2 2, and is almost at the pupil position.
- the knife edge 1 2 3 is reached, and then the AF photoelectric conversion element 1 2 6 is irradiated through the focusing imaging lens 1 2 4 and the cylindrical lens 1 2 5.
- the photoelectric conversion element 126 for AF captures an image that is substantially conjugate with the wafer in the autofocus measurement direction and pupil-conjugated in the non-measurement direction.
- the image information (signal) obtained by photographing with the A / F photoelectric conversion element 1 26 in this way is sent to the focus position detection device 1 31, where the optimum focus position is obtained.
- a drive control signal is sent from the focus position detection device 1 3 1 to the focus actuator drive device 1 3 2 to obtain the optimum focus position and to set the obtained optimum focus position.
- the focus actuator driving device 1 3 2 receives this drive control signal and drives the wafer gripping device 1 3 3.
- the focus position detecting device 1 3 1 performs based on the image information obtained by photographing with the photoelectric conversion element 1 2 6 for AF.
- the control contents optical measurement evaluation method and optical measurement condition setting method
- step S 11 global alignment (detection and correction of the rotational position of the wafer W) of the wafer W held by the wafer holding device 1 33 and placed on the stage is performed.
- step S 11 global alignment (detection and correction of the rotational position of the wafer W) of the wafer W held by the wafer holding device 1 33 and placed on the stage is performed.
- step S 11 global alignment (detection and correction of the rotational position of the wafer W) of the wafer W held by the wafer holding device 1 33 and placed on the stage is performed.
- step S 11 global alignment (detection and correction of the rotational position of the wafer W) of the wafer W held by the wafer holding device 1 33 and placed on the stage is performed.
- the position detection pattern mark M is, for example, the same as that shown in FIG. It has the composition of.
- an image of the position detection pattern mask M is taken by the two-dimensional photoelectric conversion element 1 13 in the observation optical system 110, and based on the taken image.
- the displacement of the second pattern layer L 2 with respect to the first pattern layer L 1 is detected.
- the following is used using the auto focus optical system 1 2 0. Control is performed.
- an A F offset value (initial value) is set in step S13.
- the autofocus adjustment is performed by moving the wafer W in the optical axis direction (the direction perpendicular to the surface of the wafer W, this direction is called the Z direction) by the wafer gripping device 1 3 3. In 3, it is set to a position offset by a predetermined amount in advance from the autofocus position.
- evaluation values for the first mark M 1 and the second mark M 2 are calculated from the image of the position detection pattern mark M photographed by the two-dimensional photoelectric conversion element 1 1 3 in the offset state (step) S 1 4).
- the evaluation value calculation in step S 14 will be described in detail below.
- the image area of the first mark M 1 and the image area of the second mark M 2 are separated from the image of the position detection pattern mark M photographed by the two-dimensional photoelectric conversion element 112. This region separation may be performed based on the design value of the pattern, or may be performed by teaching. Then, for each of the first and second marks M 1 and M 2, the folding correlation function in the horizontal direction (X direction in FIG. 8) and the vertical direction (Y direction in FIG. 8) is calculated. In this example, a method of calculating the correlation function based on the self-folding pattern is adopted, but the correlation function may be calculated using a template pattern.
- the X direction of each of the first and second marks M 1 and M 2 The correlation values V (p + 2) and V (p-2) at positions two pixels away from the position of this signal peak value V ⁇
- the evaluation value E indicating the sharpness of the peak is calculated by the following formula (1).
- the evaluation value E is calculated from equation (1) using the correlation values V (p + 2) and V (p-2) on both sides. This is because, even if the correlation value is slightly small, the measured value is considered to be stable when the difference from the adjacent correlation value is large (when the peak is sharp), and the difference between the correlation value and the adjacent correlation value In view of the above, an evaluation value E (an evaluation value indicating the sharpness of the peak) is calculated, where the measured value is most stable. In this example, since the evaluation values from different images are compared, normalization is not performed when calculating the evaluation values.
- the evaluation value E based on the equation (1) is calculated in the X direction and the Y direction of the first and second marks M1 and M2, respectively, and these evaluation values are expressed as E (X1), Let E (Y1), E (X2), and E (Y2).
- E (X1) is the evaluation value of the first mark M1 in the X direction
- E (Y1) is the evaluation value of the first mark M1 in the Y direction
- E (X2) is the second mark M2
- E (Y2) is the evaluation value of the second mark M2 in the Y direction.
- a comprehensive index TE is calculated from the sum of the reciprocals of these four evaluation values E (XI), E (Y1), E (X2), and E (Y2) (step S15). Since each evaluation value E (XI), E (Y1), E (X2), E (Y2) is a desired characteristic, the overall index TE is a desired characteristic. As a result, the total index TE is calculated using the above four evaluation values so that the specific gravity is placed on the layer whose measurement accuracy is relatively limited. Then, the process proceeds from step S16 to step S17, where the increment value of the AF offset value is added, and the AF offset value is calculated in step S13. The position of the wafer W in the Z direction is corrected so that only the increment value is changed (drive control of the wafer gripping device 1 33 is performed so as to move in the Z direction corresponding to the increment value).
- step S4 and step S15 are performed, and the evaluation values E (X1), E (Y1), E (X2), E (Y2) And the overall index TE.
- iterative calculation is performed while changing only the increment value, and each evaluation value E (X1), E (Y1), E (X2) at the AF offset position corresponding to each increment value change , E (Y2) and overall index TE.
- step S 16 the process proceeds from step S 16 to step S 18 and the optimum A F optimum value is calculated.
- the horizontal axis shows the AF offset value
- the vertical axis shows the evaluation values E (XI), E (Y1), E (X2), and E (Y2) obtained as described above.
- Fig. 13 shows a grab showing the total index TE on the vertical axis. 'The calculated total index is indicated by the broken line TE (a) in Fig. 13.
- the AF offset position at which the total index TE is the minimum is the optimal focus position, but the calculation total index TE (a) has a large fluctuation as shown in the figure, so its approximate value is obtained by a predetermined polynomial calculation.
- the indicator is indicated by the solid line TE (b).
- the position of A F offset value 0.2, which is the minimum value of this approximate value index TE (b), is the current optimum focus position.
- step S19 the wafer gripping device 133 is driven to perform setting control so as to reach this AF offset position. Do. After that, position shift detection is performed from the image of the position detection pattern mark M photographed by the two-dimensional photoelectric conversion element 113 (step S20).
- the comprehensive index TE (a) or TE (b) obtained as described above The measurement reproducibility is shown by the solid line TE (c) in Fig. 13. However, the overall index TE (a) and TE (b) has a good correlation with the measurement reproducibility TE (c). I understand that
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Automatic Focus Adjustment (AREA)
- Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
- Microscoopes, Condenser (AREA)
Abstract
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JP2004-344401 | 2004-11-29 | ||
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JPH11167060A (ja) * | 1997-12-03 | 1999-06-22 | Nikon Corp | 合焦検出装置及び方法 |
JP2002164266A (ja) * | 2000-11-22 | 2002-06-07 | Nikon Corp | 光学的位置ずれ測定装置の調整装置および方法 |
JP2002190439A (ja) * | 2000-12-21 | 2002-07-05 | Nikon Corp | 位置計測方法及びその装置、露光方法及びその装置、並びにデバイス製造方法 |
JP2004102064A (ja) * | 2002-09-11 | 2004-04-02 | Nikon Corp | 画像測定装置 |
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JPH11167060A (ja) * | 1997-12-03 | 1999-06-22 | Nikon Corp | 合焦検出装置及び方法 |
JP2002164266A (ja) * | 2000-11-22 | 2002-06-07 | Nikon Corp | 光学的位置ずれ測定装置の調整装置および方法 |
JP2002190439A (ja) * | 2000-12-21 | 2002-07-05 | Nikon Corp | 位置計測方法及びその装置、露光方法及びその装置、並びにデバイス製造方法 |
JP2004102064A (ja) * | 2002-09-11 | 2004-04-02 | Nikon Corp | 画像測定装置 |
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