JP2010199452A - Method of measuring optical characteristic, exposure method, and method of manufacturing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably measure the best focus position of a projection optical system. <P>SOLUTION: Based on imaging signals (pixel data) obtained for an area DE<SB>i</SB>(i=1-M), including a divided area DA<SB>i</SB>in which an image PM' of a mark PM is formed, and a reference area DC<SB>i</SB>, size LH<SB>i</SB>of the image PM' of the mark PM transferred to each divided area DA<SB>i</SB>(i=1-M) is obtained, reliable size LH<SB>i</SB>is extracted, based on the S/N ratio of the imaging signal (pixel data) from the obtained size LH<SB>i</SB>(i=1-M), and the best focus position of the projection optical system is obtained, based on the extracted size. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical property measuring method, an exposure method, and a device manufacturing method, and more specifically, an optical property measuring method for measuring an optical property of a projection optical system, an exposure method using the optical property measuring method, and the exposure. The present invention relates to a device manufacturing method using the method.

  Conventionally, in a lithography process for manufacturing electronic devices (microdevices) such as semiconductor elements and liquid crystal display elements, a step-and-repeat projection exposure apparatus (so-called stepper) or a step-and-scan projection exposure apparatus ( A so-called scanning stepper (also called a scanner)) or the like is mainly used.

  In this type of exposure apparatus, along with the miniaturization of integrated circuits, the resolution of the projection optical system is improved, so that the wavelength of the exposure light is shortened and the numerical aperture of the projection optical system is increased (high NA). It is illustrated. In this type of exposure apparatus, it is also required to improve the overlay accuracy between a pattern to be transferred and a pattern region already formed on an object to be exposed (substrate) such as a wafer. As this premise, it is necessary to accurately measure the optical characteristics (including the imaging characteristics) of the projection optical system such as the best focus position.

  A so-called SMP focus measurement method (see, for example, Patent Document 1) is known as one of the representative measurement methods for the best focus position. In this method, for example, a diamond-shaped mark (wedge mark) as a test pattern is transferred onto a wafer at a plurality of focus positions (wafer positions with respect to the optical axis direction of the projection optical system), and the wafer is formed after development. The size of the wedge mark resist image (for example, the length in the longitudinal direction) is measured, and the best focus position is calculated based on the measurement result and the focus position at the time of the measurement.

  Conventionally, an LSA (Laser Step Alignment) type sensor that irradiates a mark with laser light and measures the position of the mark using diffracted / scattered light has been mainly used for the above-described resist image size measurement. However, in recent projection exposure apparatuses, an FIA (Field Image Alignment) type sensor of an image processing system is mainly used for measuring the size of a resist image in order to shorten the measurement time. In addition, with the passage of time, finer marks tend to be used as test marks. For this reason, recently, the focus area (defocus area) far from the best focus position is larger than the best focus position. Measurement results (noise components) are generated, making it difficult to automatically measure the best focus position.

U.S. Pat. No. 4,908,656

  The present invention has been made under such circumstances. From the first viewpoint, the optical characteristic measurement for measuring the optical characteristic of the projection optical system that projects the image of the pattern on the first surface onto the second surface. In the method, a part of a plurality of exposure conditions including the position of an object with respect to the optical axis direction of the projection optical system is changed in stages, and the mark arranged on the first surface is passed through the projection optical system. A first step of sequentially transferring to different locations on the object arranged on the second surface side of the projection optical system; and imaging a region on the object including a plurality of first regions to which the marks are transferred A second step; obtaining a size of a transfer image of the mark transferred to each of the plurality of first regions from an image pickup signal obtained as a result of the image pickup; and obtaining a size of the first region corresponding to the obtained size of each transfer image Based on the information on the intensity of the imaging signal. An optical characteristic measuring method comprising; third step and obtaining the optical characteristics of the optical system.

  According to this, based on the size of the transferred image of the mark transferred to each of the plurality of first areas obtained from the imaging signal and the information on the intensity of the imaging signal of the corresponding first area, the projection optical system Obtain optical properties. Here, the level of reliability of the measurement result of the size of the transfer image of the corresponding mark corresponds to the magnitude of the intensity of the imaging signal. For this reason, it is possible to handle such as weighting the size of the transferred image of the mark transferred to each of the plurality of first areas according to the information on the intensity of the imaging signal, or excluding the unreliable size. Become. Therefore, the optical characteristics can be obtained more reliably and accurately than in the case where the intensity information of the image pickup signal in the mark transfer region is not taken into consideration.

  According to a second aspect of the present invention, there is provided a step of measuring an optical characteristic of a projection optical system that projects an image of a pattern on the first surface on the second surface using the optical characteristic measuring method of the present invention; In consideration of the measurement result of the optical characteristic, at least one of the optical characteristic of the projection optical system and the position of the object with respect to the optical axis direction of the projection optical system is adjusted, and the pattern formed by the projection optical system Exposing the object disposed on the second surface side with an image.

  According to this, it is possible to perform highly accurate exposure (pattern formation) of the object.

  From a third aspect, the present invention is a device manufacturing method including a step of forming a pattern on an object using the exposure method of the present invention; and a step of developing the object on which the pattern is formed. .

It is a figure which shows schematically the structure of the exposure apparatus which concerns on one Embodiment. FIG. 2A is a plan view of the measurement reticle as viewed from the pattern surface side, and FIG. 2B is an enlarged view of the opening pattern AP portion of FIG. It is a flowchart which simplifies and shows the processing algorithm of the main controller (internal CPU) in the case of the measurement of the optical characteristic of a projection optical system. It is a flowchart which shows the specific example of the subroutine of step 406 of FIG. It is a plan view showing a wafer W _T that evaluation point corresponding region is formed. It is a figure for demonstrating an evaluation score corresponding | compatible area | region. Evaluation points formed on the wafer W _T is a diagram showing an example of a resist image of the corresponding region. It is a flowchart which shows the specific example of the subroutine of step 410 of FIG. Figure 9 (A) is a diagram for explaining the area on the wafer W _T to be captured by the alignment system, shows an example of FIG. 9 (B) region DE _i in the pixel data P _i (Y) FIG. 9C is an enlarged view of the pixel data in the region a in FIG. 10A shows a plot point obtained by plotting the pattern length LH _i (measurement result) with respect to the corresponding focus position Z _i and a curve connecting the plot points, and FIG. 10B shows FIG. 10A. FIG. 10C is a diagram for explaining a state in which a highly reliable pattern length measurement result is extracted based on the magnitude of the S / N ratio. is there.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 10C.

  FIG. 1 schematically shows a configuration of an exposure apparatus 100 according to an embodiment. The exposure apparatus 100 is a step-and-repeat projection exposure apparatus (so-called stepper). As will be described later, in the present embodiment, a projection optical system PL is provided. In the following, a direction parallel to the optical axis AXp of the projection optical system PL is set as a Z-axis direction, and in a two-dimensional plane orthogonal to the Z-axis direction. In FIG. 1, the left and right direction on the paper surface is defined as the X axis direction, and the direction orthogonal to the paper surface is defined as the Y axis direction.

  The exposure apparatus 100 holds an illumination system IOP, a reticle stage (reticle holder) RST that holds a reticle R, a projection optical system PL that projects an image of a pattern formed on the reticle R on the wafer W, and a wafer 2. An XY stage 20 that moves on a dimensional plane (within the XY plane), a drive system 22 that drives the XY stage 20, a control system that controls these, and the like are provided.

  The illumination system IOP includes, for example, a light source composed of an ultra-high pressure mercury lamp that outputs an ultraviolet bright line (g-line, i-line, etc.), an elliptical mirror, a reflection mirror, a wavelength filter, a fly-eye integrator, a relay lens system, and a variable field of view. An illumination optical system including a diaphragm (reticle blind), a bending mirror, a condenser lens, and the like is included. A shutter for closing and opening the optical path is disposed in the vicinity of the second focal point of the elliptical mirror. Details of such an illumination system are disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-146732. In the illumination system, the light emitted from the light source passes through the wavelength filter to become the illumination light IL for exposure, and the illumination light IL is adjusted to a luminous flux having a uniform illuminance distribution by a fly eye integrator, and then the variable field of view. By passing through the stop, the rectangular illumination area on the reticle R is illuminated with substantially uniform illuminance.

  Reticle stage RST is arranged below illumination system IOP in FIG. 1 (on the −Z side). On reticle stage RST, reticle R is held by suction via a vacuum chuck (not shown) or the like. Reticle stage RST can be finely driven in a rotation direction (θz direction) around the X axis direction, the Y axis direction, and the Z axis by a drive system (not shown). Thus, reticle stage RST can position reticle R (reticle alignment) in a state where the center of the pattern of reticle R (reticle center) substantially coincides with optical axis AXp of projection optical system PL. FIG. 1 shows a state in which this reticle alignment is performed.

  Projection optical system PL is arranged below reticle stage RST in FIG. 1 (on the −Z side) so that its optical axis AXp is parallel to the Z axis. Here, as the projection optical system PL, a double-sided telecentric reduction system is used, and a refractive optical system including a plurality of lens elements arranged at a predetermined interval along a direction parallel to the optical axis AXp is used. Among the plurality of lens elements, a plurality of specific lens elements are controlled by an imaging characteristic correction controller (not shown) based on a command from the main controller 28, and the projection optical system PL thereby has its optical characteristics. For example, magnification, distortion, coma aberration, and field curvature are adjusted (including imaging characteristics).

  The projection magnification of the projection optical system PL is, for example, 1/5 (or 1/4). Therefore, when the reticle R is uniformly illuminated by the illumination light IL, the pattern image of the reticle R is reduced and projected onto the exposure area on the wafer W coated with the resist. Thereby, a reduced image of the pattern of the reticle R is transferred onto the wafer W.

  The XY stage 20 is disposed below (-Z side) in FIG. 1 of the projection optical system PL, and freely moves in the XY plane along the upper surface of a base (not shown). A wafer table 18 is mounted on the XY stage 20, and a wafer W is held on the wafer table 18 by vacuum suction or the like via a wafer holder (not shown).

  The wafer table 18 is also called a Z / tilt stage, and minutely drives the wafer holder holding the wafer W in the Z-axis direction and the tilt direction with respect to the XY plane. A movable mirror 24 is fixed on the upper surface of the wafer table 18. A laser interferometer 26 is provided facing the reflecting surface of the movable mirror 24. The laser interferometer 26 irradiates the movable mirror 24 with a laser beam and receives the reflected light, thereby measuring the position of the wafer table 18 (XY stage 20) in the XY plane. Actually, an X moving mirror having a reflecting surface orthogonal to the X axis and a Y moving mirror having a reflecting surface orthogonal to the Y axis are provided, and the position in the X axis direction is measured correspondingly. And an X laser interferometer for measuring a position in the Y-axis direction. However, in FIG. 1, these are shown as the moving mirror 24 and the laser interferometer 26. The X laser interferometer and the Y laser interferometer are multi-axis interferometers having a plurality of measurement axes, and rotate the wafer table 18 (rotation around the Z axis (θz rotation), rotation around the X axis (θx rotation)). And rotation around the Y axis (θy rotation) can also be measured. Therefore, the laser interferometer 26 can measure position information of the wafer table 18 in the five-degree-of-freedom directions (X, Y, θz, θy, and θx directions).

  The position information measured by the laser interferometer 26 is supplied to the main controller 28. The main controller 28 positions the wafer table 18 (wafer W) by controlling the XY stage 20 via the drive system 22 based on the position information.

  In addition, the exposure apparatus 100 of the present embodiment is provided with a focus sensor AFS that measures the position and inclination of the surface of the wafer W in the Z-axis direction. The focus sensor AFS includes, for example, an oblique incidence type multipoint focal position detection system having a light transmission system 50a and a light reception system 50b disclosed in US Pat. No. 5,502,311 and the like. The measurement result of the focus sensor AFS is also supplied to the main controller 28. Based on the measurement result, main controller 28 drives wafer table 18 in the Z-axis direction, θx direction, and θy direction via drive system 22 to move wafer table 18 in the optical axis direction of projection optical system PL. Control position and tilt.

  As described above, by driving the wafer table 18, the position of the wafer W can be controlled in the directions of five degrees of freedom (X, Y, Z, θx, θy). The position of the wafer W in the remaining θz direction (yawing) is controlled by rotating at least one of reticle stage RST and wafer table 18 in accordance with the yawing of wafer table 18 measured by laser interferometer 26. The

  Further, a reference plate FP is fixed on the wafer table 18 so that the surface thereof is the same height as the surface of the wafer W. On the surface of the reference plate FP, various reference marks including a first reference mark and a pair of second reference marks for reticle alignment used for baseline measurement of an alignment system AS, which will be described later, are formed.

  Furthermore, in the present embodiment, an off-axis alignment system AS is provided on the side surface of the projection optical system PL. As the alignment system AS, for example, an image processing type FIA (Field Image Alignment) system is used. The alignment system AS can measure the position of the reference mark formed on the reference plate FP and the alignment mark formed on the wafer W in the two-dimensional directions (X-axis and Y-axis directions).

  In the present embodiment, the main controller 28 performs fine alignment or the like that accurately measures the position of each exposed region on the wafer using the alignment system AS. In addition, as an alignment system AS, for example, an alignment sensor that irradiates a target mark with coherent detection light and makes two diffracted lights (for example, the same order) generated from the target mark interfere with each other. It can also be used in combination with an FIA system or the like.

  The alignment control device 16 performs A / D conversion on the output signal DS from each alignment sensor constituting the alignment system AS, performs arithmetic processing on the converted signal, and detects a mark position. This detection result is supplied from the alignment controller 16 to the main controller 28.

  In addition, the exposure apparatus 100 of the present embodiment is provided with a pair of reticle alignment systems (not shown) above the reticle R. The pair of reticle alignment systems is, for example, a reticle mark on the reticle R or a reference mark on the reticle stage RST via the projection optical system PL (as disclosed in, for example, US Pat. No. 5,646,413). And a TTR (Through The Reticle) alignment system for simultaneously observing the second reference mark on the reference plate FP. The detection signal of the reticle alignment system is supplied to the main controller 28 via the alignment controller 16.

  The control system is mainly composed of a main control device 28 composed of a microcomputer or the like for comprehensively controlling the entire device.

In the present embodiment, a measurement reticle R _T (hereinafter abbreviated as reticle R _T ) shown in FIG. 2A is used to measure the optical characteristics of the projection optical system PL. FIG. 2A is a plan view of reticle _RT as viewed from the pattern surface side (the lower surface side in FIG. 1). As shown in FIG. 2A, the reticle _RT is composed of a square glass substrate 42, and a square (or rectangular) pattern area PA defined by a light shielding band (not shown) is formed on the pattern surface. In the present example (example in FIG. 2A), almost the entire pattern area PA is a light shielding portion by a light shielding member such as chromium. The center of the pattern area PA (here, coincides with the center of the reticle _RT (reticle center)), for example, a square opening pattern (transmission area) AP having a side of 27 μm is formed, and a measurement mark (hereinafter referred to as a measurement mark) is formed in the opening pattern AP. MP (abbreviated as “mark”) is formed. In this example (the example of FIG. 2A), almost the entire pattern area PA is used as the light shielding part, but the pattern area PA may be used as the light transmitting part.

  The mark MP is composed of a dense pattern, for example, a periodic mark in which five rhombus marks (wedge marks) M as shown in an enlarged manner in FIG. 2B are arranged at a predetermined pitch in the X-axis direction.

  Further, a pair of reticle alignment marks RM1 and RM2 are formed on both sides in the X-axis direction of the pattern area PA passing through the above-described reticle center (see FIG. 2A).

  Next, regarding the method of measuring the optical characteristics of the projection optical system PL in the exposure apparatus 100 of the present embodiment, along with the flowchart of FIG. This will be described with reference to the drawings.

First, in step 402 of FIG. 3, a wafer W _T (see FIG. 5) is loaded onto the wafer table 18 via a wafer loader (not shown). Here, the surface of the wafer W _T, it is assumed that the positive-type resist sensitive layer is coated is formed.

  Next, in step 404, predetermined preparatory work such as reticle replacement and alignment of the reticle with respect to the projection optical system PL is performed.

Specifically, the reticle on reticle stage RST and reticle _RT are exchanged via a reticle exchange mechanism (not shown). If there is no reticle on reticle stage RST, reticle _RT is simply loaded.

Next, a pair of second reference marks (not shown) of the reference plate FP fixed on the wafer table 18 and the reticle on the reticle stage RST (in this case, the reticle R _T ) by the above-described reticle alignment systems 13A and 13B. The wafer table 18 (XY stage 20) is moved based on the measurement value of the laser interferometer 26 so that the pair of reticle alignment marks RM1 and RM2 are detected. Then, the position (including rotation) of reticle stage RST in the XY plane is adjusted based on the detection results of reticle alignment systems 13A and 13B. Thereby, for example, the entire surface of the pattern area PA of the reticle _RT is irradiated with the illumination light IL. In this embodiment, the position at which the projection image (pattern image) of the mark MP is generated in the field of view through the projection optical system PL should measure the optical characteristics (for example, the best focus position) of the projection optical system PL. It becomes an evaluation point. Although there are actually a plurality of evaluation points, it is sufficient that the number of evaluation points (marks MP) is at least one. In this embodiment, in order to simplify the description, the projection optical system PL It is assumed that one evaluation point is set at the center of the exposure area.

  When the predetermined preparation work is completed in this way, the process proceeds to the next step 406 (exposure processing subroutine).

In this subroutine, first, in step 502 of FIG. 4, the amount per unit area of illumination light IL irradiated on wafer W _T (exposure), ie, the target value of the dose (referred to as target dose) For example, it is set to the optimum value of the exposure energy amount obtained in advance by experiment or simulation.

In the next step 504, the target value of the focus position of the wafer W _T (Z-axis direction position) (hereinafter, referred to as a target focus position) to initialize the Z _i. That is, the counter initial value (count value i) is set to "1" sets the target focus position Z _i of the wafer W _T to Z ₁ (i ← 1). In the present embodiment, the counter (count value i), together with the setting of the target focus position of the wafer W _T, used to set the divided area DA _i to be exposed in step 506 to be described later (see FIGS. 5 and 6). In the present embodiment, in step 508 to be described later, for example, around the best known focus position for the projection optical system PL (including design value), the target focus position Z _i of the wafer W _T from Z ₁ in ΔZ increments Z Change to _M (M = 15 as an example) (Z _i = Z _{1 to} Z ₁₅ ).

Accordingly, in the present embodiment, the projection optical system PL while changing the position of the wafer W _T to an optical axis direction, for sequentially transferring the mark MP on the wafer W _T, M times (where M = 15) Exposure will be performed. In the present embodiment the projected image of the mark MP in projection area of aperture pattern AP _n by the projection optical system PL is generated and aperture pattern AP _n on wafer W _T is transferred by the exposure, transfer image of the mark MP _n A partition region including is formed. Therefore, the area on the wafer W _T that corresponds to the evaluation point in the exposure area of the projection optical system PL (i.e., evaluation point corresponding area DB (see FIG. 5)), 1 × M pieces (M = 15 in this case ) Mark MP is transferred.

Here, description will be back and forth, for convenience, the exposure that will be described later, the evaluation point corresponding area DB on wafer W _T mark MP is transferred will be described with reference to FIG. As shown in FIG. 6, in this embodiment, 1 × M = M (for example, 1 × 15 = 15) virtual arrays arranged in a matrix of 1 row and M columns (for example, 1 row and 15 columns). Mark MP is transferred to each partition area DA _i (i = 1 to M (for example, M = 15)), and evaluation points corresponding to M (for example, 15) partition areas DA _i to which these marks MP are transferred respectively. region DB is formed on the wafer _{W T.} As shown in FIG. 6, the virtual partition area DA _i is arranged so that the + X direction is the column direction (increase direction of i). Further, the subscripts i and M used in the following description have the same meaning as described above.

Returning to FIG. 4, in the next step 506, by moving the XY stage 20 via drive system 22 while monitoring the measurement values of laser interferometer 26, sections of the evaluation point on the wafer W _T of the corresponding area DB virtual area DA _i mark MP to (DA ₁ (see FIG. 5) in this case) is in a position to be transferred respectively to position the wafer _{W T.}

In the next step 508, the wafer table 18 with finely driven in the Z-axis direction and the tilt direction while monitoring the measured values from the multipoint AF system (90a, 90b), setting the position of the Z-axis direction of the wafer W _T The set target focus position Z _i (in this case, Z ₁ ) is set.

In the next step 510, exposure is performed. At this time, as the dose on the wafer W _T is the target dose which is set, performs exposure control. The dose amount can be adjusted by changing the intensity and / or irradiation time of the illumination light IL. Thus, as shown in FIG. 5, the aperture pattern AP is transfer comprising a mark MP in divided area DA ₁ rating point on wafer W _T corresponding area DB.

In the next step 512, check the target focus position of the wafer W _T (counter (count value i)), it determines whether the exposure of the predetermined range (i.e., the target focus position Z ₁ on Z _M) has been completed To do. Here, since only the exposure of the first target focus position Z ₁ is completed, [Delta] Z and proceeds to step 514, along with the count value i is incremented by 1 (i ← i + 1), the target value of the focus position of wafer W _T Are added (Z _i ← Z _{i + 1} = Z _i + ΔZ). Here, after changing the target value of the focus position to Z ₂ (= Z ₁ + ΔZ), the process returns to Step 506. Then, the processing (including judgment) in steps 506, 508, 510, 512, and 514 is repeated until the judgment in step 512 is affirmed. Here, in step 506, for each repetition, the XY stage 20 a predetermined step pitch (in this embodiment, substantially the same (slightly less) and X-axis direction size of the projected image on the wafer W _T of aperture pattern AP It is moved to the set distance of which) XY plane in a predetermined direction (in this case the -X direction), successively, the mark MP in divided area DA _i evaluation point corresponding area DB on wafer W _T is transferred positioning the wafer _{W T} in position. Then, in step 508, positions the wafer _{W T} to a target focus position Z _i, the opening at step 510, including as before, the mark MP in divided area DA _i evaluation point corresponding area DB on wafer _{W T} pattern Transcribe AP. Thus, the wafer _W divided area evaluation point corresponding area DB on _T DA _{i (i} = _2~M) in aperture pattern AP _n that includes a mark MP _n are respectively transferred.

On the other hand, when the exposure to the partition area DA _M (DA _{15 in} this embodiment) of the evaluation point corresponding area DB is completed and the determination in step 512 is affirmed, the processing of this subroutine is terminated, and FIG. Routine (step) 408 (return). The process of step 406, as shown in FIG. 5, the evaluation point on the wafer W _T in the corresponding area DB, the exposure condition (in this embodiment, the focus position of the wafer W _T) M number of different (M is here = 15) A transfer image (latent image) of the mark MP (opening pattern AP) is formed. Incidentally, in practice, as described above, at the stage wafer W M _{to T} on the mark MP transferred image (latent image) is formed (the 15 in this case) pieces of divided areas are formed, the evaluation point corresponding although the area DB is formed, in the above description, for ease of explanation, but the evaluation point corresponding area DB has adopted a description method as if on the previously wafer W _T.

In step 408, the wafer W _T, after unloaded from above the wafer table 18 via a wafer unloader (not shown), is transported to the coater developer (not shown) via the wafer transfer system (not shown). Here, the coater / developer (not shown) is connected to the exposure apparatus 100 in-line.

After transfer of the wafer W _T to the above coater developer, a next step 410, development of the wafer W _T waits for the termination. During the waiting time in step 410, development of the wafer W _T is performed by the coater developer. Upon termination of the development, on the wafer W _T, the resist image of a rectangular evaluation point corresponding area DB, as shown in FIG. 5, the image of the mark MP is formed in each divided area DA _i are formed. Then, the wafer W _T that the resist image is formed as a sample for measuring the optical characteristics of the projection optical system PL. Figure 7 shows an example of a resist image of evaluation point formed on the wafer W _T corresponding area DB is shown.

In FIG. 7, the evaluation point corresponding area DB is configured by M (= 15) partition areas DA _i (i = 1 to 15), and whether a resist image of a partition frame exists between adjacent partition areas. Although this is illustrated, this is done in order to make the individual partition areas easier to understand. However, in practice, there is no resist image of the partition frame between adjacent partition regions. By eliminating the frame in this manner, it is possible to prevent the contrast of the pattern portion from being lowered due to the interference by the frame when the image is captured in the area AA including the evaluation point corresponding area DB by the alignment system AS described later. Therefore, in the present embodiment, it is of the step pitch of the above was set to be equal to or less than the X-axis direction size of the projected image on the wafer W _T of each aperture pattern AP.

In the wait state of step 410, when confirming that the development of wafer W _T is completed by a notice from the control system of the coater developer (not shown), the process proceeds to step 412.

In step 412, instructs the wafer loader (not shown), after loading the wafer W _T already developed in the same manner as step 402 described above on the wafer table 18, the process proceeds to the subroutine of the best focus position measurement step 414 .

In the subroutine of step 414, first, in step 606 of FIG. 8, the wafer W a predetermined area including the evaluation point corresponding area DB on _T, for example, FIG. 9 (A) to the detectable area AA is in alignment system AS shown moving the wafer W _T to a position. This movement, i.e. positioning, the main controller 28, an alignment mark of a plurality of positions on the wafer W _T is detected by using the alignment system AS, and the measurement values of laser interferometer 26 when the detection result and the detection, based on the position information of the design on the wafer W _T of the evaluation point corresponding area DB, XY stage 20 is performed by being driven via a drive system 22 while monitoring the measurement values of laser interferometer 26.

In the next step 608, the area AA including the evaluation point corresponding area DB on wafer W _T, and imaged using the alignment system AS, captures the captured data. The alignment control device 16 divides the imaging target into pixel units of the imaging device (CCD or the like), and supplies the density of the imaging target corresponding to each pixel to the main control device 28 as 8-bit digital data (pixel data), for example. . That is, the imaging data is composed of a plurality of pixel data. In this case, it is assumed that the pixel data value decreases as the density of the imaging target increases (closes to black). In this case, it is assumed that the area AA can be simultaneously (collectively) imaged by the alignment system AS. Here, the area AA includes an evaluation point corresponding area DB, an evaluation point corresponding area DB in which no image of the mark PM that is a predetermined distance away from the evaluation point corresponding area DB exists (the mark PM is not transferred), and it is a rectangular area on wafer W _T that includes a region DD of the same size of the rectangle. That is, the area DD is a region on the risk-free wafer W _T to resist the wafer WT surface is photosensitive by illumination light IL in the transfer mark PM.

In the next step 610, the following a. ~ E. In this procedure, the image data obtained above is processed (image processing).
a. First, the main control device 28 performs image processing on the captured data by a method disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-146702, US Patent Application Publication No. 2004/0179190, and the like in the evaluation point corresponding region DB. Detect the outer edge.
b. Next, main controller 28 is based on the outer edge of evaluation point corresponding region DB detected above, and is a rectangular region DD having the same shape as evaluation point corresponding region DB that is separated from evaluation point corresponding region DB in the predetermined distance −Y direction. (Position information) is obtained.

c. Next, main controller 28 obtains a rectangular area BB (see FIG. 9A) that is in contact with evaluation point corresponding area DB and area DD, and extracts imaging data in the area BB.
d. Next, the main control device 28 divides the extracted imaging data into M equal parts in the X-axis direction, and the imaging data is divided between the partitioned area DA _i and the reference area DC _i (and the areas DA _i , DC _i paired therewith). The data is divided into data for each area), that is, data for each area DE _i represented by a dotted line in FIG.
e. The main controller 28 further region DE pixel data in the _i-addition with respect to the X-axis direction (or averaging) the one-dimensional data, i.e. a function of the Y position within the region DE _i pixel data P _i ( Y).

  In the next step 612, the following f. ~ J. In this procedure, the best focus position of the projection optical system PL is calculated.

FIG. 9B shows an example of pixel data P _i (Y) in the area DE _i . With respect to the pixel data P _i (Y), a signal waveform (indented (or valley-shaped) waveform) derived from the formation of the resist image (resist pattern) PM ′ of the mark PM in the partition area DA _i is formed. , Appearing in the Y area corresponding to the partition area DA _i .

FIG. 9C shows an enlarged view of pixel data (pixel data in the area a in FIG. 9B) P _i (Y) in the reference area DC _i that is paired with the partition area DA _i . Has been. As described above, as the reference area DC _{i (i} = 1~M), measuring marks or the like, the area on the wafer W _T that has not been any image formation is selected. Accordingly, only the noise is included in the pixel data P _i (Y) in the reference area DC _i .
f. First, the main controller 28 determines the length (pattern) of the resist pattern PM ′ in the Y-axis direction from the width of the recesses for the resist patterns PM ′ respectively formed in the partition areas DA _i (i = 1 to M). Long) LH _i and signal strength (indentation depth) S _i are determined. In FIG. 10A, the obtained pattern length LH _i is plotted against the corresponding focus position Z _i . As an example, four results are shown.
g. Next, the main controller 28 determines noise intensity (or simply referred to as noise) N for the reference area DC _i (i = 1 to M) from the variation (standard deviation or the like) of the pixel data P _i (Y) therein. _i is determined.
h. Next, the main controller 28 obtains the S / N ratio (unit: [dB]) between the corresponding signal intensity S _i and noise N _i based on, for example, the following equation (1).

S / N = 20 · log ₁₀ (S _i / N _i ) (1)
In FIG. 10B, S / N ratios corresponding to the four pattern lengths LH _i shown in FIG. 10A are plotted with respect to the focus position Z _i . In calculating the S / N ratio, noise N _i obtained for the reference area DC _i (i = 1 to M) individually corresponding to the partition area DA _i (i = 1 to M) may be used. You may use the noise N calculated | required only about any one reference area DC.
i. Next, main controller 28 corresponds to an S / N ratio exceeding a predetermined threshold (see FIG. 10B) from the obtained M (for example, M = 15) S / N ratio groups. The pattern length LH _i is extracted. This reason will be described in detail later. The threshold for the S / N ratio is set to an appropriate value (for example, 20 dB) in advance.

If of FIG. 10 (B), as is apparent from the figure, since the S / N ratio in the region b ₂ exceeds the threshold value, only the measurement result of the pattern length LH _i in the region b ₂ is extracted (See FIG. 10C).
j Next, the main controller 28 (in FIG. 10 (C), the focus position _Z 8 for the maximum pattern length LH ₈₎ focus position extracted above pattern length LH _i becomes maximum, or extracted The pattern length LH _i is approximated using a least square method or the like, and the evaluation point corresponding to the evaluation point corresponding region DB (exposure area center of the projection optical system PL (light The best focus position Z _best at the position of the axis AXp) is obtained, and the main controller 28 stores the obtained result in a storage device (not shown), whereby the processing of step 612 in FIG. Step 410) is finished, and the series of processes is finished.

Here, from M S / N ratio group obtained it will be described the reason for extracting the pattern length LH _i corresponding to the S / N ratio exceeding a predetermined threshold (threshold The).

In the actual measurement result, as is clear from FIG. 10A, in the region b ₂ in the vicinity of the best focus position Z _best (= Z ₈ ), the curve connecting the plot points of the pattern length LH _i is a mountain shape. Shows the ideal profile. On the other hand, in areas (defocus areas) b ₁ and b ₃ away from the best focus position Z _best (= Z ₈ ), the curve connecting the plot points of the pattern length LH _i shows an irregular behavior.

On the other hand, as is clear from FIG. 10B, the S / N ratio is such that the pattern length LH _i is larger than the threshold value in the region b ₂ where the curve connecting the plot points shows an ideal profile, that is, the noise N In contrast, the signal intensity S is large. Therefore, it can be said that the measurement result of the pattern length LH _i of in the region b ₂ is sufficiently reliable. On the other hand, in the defocus regions b ₁ and b ₃ , in which the curve connecting the plot points has an irregular shape, the S / N ratio is smaller than the threshold, that is, the signal intensity S with respect to the noise N is small. In this case, for example, a signal buried in noise is detected from pixel data P _i (Y) as shown in FIG. Therefore, the measurement result of the pattern length LH _i of in the defocus regions _b 1, _{b 3} is unreliable. Therefore, only the measurement result of the pattern length LH _i in the region b ₂ corresponding to the S / N ratio exceeding the threshold shown in FIG. 10B is extracted as being sufficiently reliable, and the extracted pattern using only the measurement result of the length LH _i, it is obtained by the performing the subsequent processing.

Therefore, as long as it can extract only the measurement result of the sufficiently reliable pattern length LH _i, not only the S / N ratio, it may be used other strength information obtained from the pixel data. For example, with respect to the maximum intensity _{S MAXp} of signal intensity _{S i} for divided area _DA i (i = 1~M), is a signal strength _{S i} is more than a certain percentage (e.g., 1/4 or more _{S MAXp)} In this case, the pattern length LH _i corresponding to the signal intensity S _i may be determined to be reliable (to be extracted). In this case, the signal intensity S _i is used as the intensity information.

In the present embodiment, for simplification of explanation, exposure of wafer W _T by using the reticle R _T mark MP only in the center of the pattern area PA is formed, the wafer W _T after the development as a sample Only the best focus position at the center of the exposure area (position of the optical axis AXp) of the projection optical system PL is measured by the above-described procedure. However, the present invention is not limited to this. The wafer is exposed not only to the center of the pattern area PA but also to a reticle having measurement marks formed at a plurality of different positions in the pattern area. As described above, the best focus position at a plurality of evaluation points (corresponding to positions in the pattern area of each measurement mark) in the exposure area of the projection optical system PL can be obtained by the same procedure as described above. In this case, the curvature of field of the projection optical system PL is calculated based on the best focus position at the plurality of evaluation points. Further, the depth of focus at each evaluation point in the exposure area may be obtained. Further, a reticle having a set of periodic marks whose periodic directions are orthogonal as measurement marks is used to expose a wafer, and the wafer is obtained as a set of resist images whose periodic directions are orthogonal after development. Astigmatism at each evaluation point may be obtained from the obtained best focus position. Further, for each evaluation point in the exposure area of the projection optical system PL, the astigmatism in-plane uniformity is obtained by performing an approximation process by, for example, the least square method based on the astigmatism calculated as described above. It is also possible to obtain a total focal difference from astigmatism in-plane uniformity and field curvature.

  The main controller 28 controls a specific lens element via an imaging characteristic correction controller (not shown) based on the optical characteristics of the projection optical system PL including at least the best focus position obtained as described above. The optical characteristics (including the imaging characteristics) of the projection optical system PL are adjusted. Then, main controller 28 transfers the pattern formed on reticle R onto wafer W in a step-and-repeat manner through projection optical system PL with adjusted optical characteristics. Further, the main controller 28 performs focus / leveling control (setting of the Z position and the tilt of the wafer W) on the basis of the best focus position using the focus sensor AFS at the time of exposure. The occurrence of exposure failure due to defocusing can be effectively suppressed. This makes it possible to transfer a fine pattern onto the wafer with high accuracy. The main controller 28 may calibrate the focus sensor AFS with the best focus position as a reference prior to exposure.

As described in detail above, according to the optical characteristic measurement method performed in exposure apparatus 100 of the present embodiment, a plurality of divided area DA obtained from the imaging signal of the wafer W _T after development the mark MP is transferred The pattern length LH _i (size) of the transfer image (resist pattern) MP ′ of the mark MP transferred to each _i and the S / N ratio which is a kind of information on the intensity of the imaging signal of the corresponding partition area DA _i Based on this, the optical characteristics of the projection optical system PL are obtained. Here, the level of reliability of the measurement result of the size of the transfer image of the corresponding mark corresponds to the magnitude of the intensity of the imaging signal.

  Specifically, in the present embodiment, only the pattern length of the transfer image (resist pattern) MP ′ of the mark MP having a high S / N ratio (high reliability) is extracted (transfer image of the mark MP having low reliability). (Resist pattern length is excluded), and based on the extracted pattern length, at least one evaluation point in the field of view of the projection optical system PL on the same principle as the conventional SMP measurement or CD focus method Is automatically measured by the exposure apparatus 100 (main controller 28), and optical characteristics such as field curvature are calculated based on the measurement result of the best focus position. Therefore, the optical characteristics can be obtained more reliably and accurately than in the case where the intensity information of the image pickup signal in the mark transfer region is not taken into consideration.

  Further, according to the exposure apparatus 100 according to the present embodiment, the best focus position (and other optical characteristics) of the projection optical system PL is measured by the above-described optical characteristic measurement method, and the projection optical system PL is taken into consideration in the measurement result. At least one of the above optical characteristics and the focus position of the wafer W is adjusted, step-and-scan exposure is performed, and the pattern of the reticle R is transferred onto the wafer W via the projection optical system PL. As a result, the wafer W can be exposed with high precision (pattern formation).

In the above-described embodiment, the case where only the pattern length of the transfer image (resist pattern) of the highly reliable mark MP is extracted according to the size of the S / N ratio has been described. The size of the transfer image of the mark MP transferred to each of the plurality of partition areas DA _i may be weighted according to information on the signal intensity, for example, the S / N ratio. In this case, when the S / N ratio is smaller than the threshold, the weight corresponding to the S / N ratio is set to a weight about 1/100 of the weight when the S / N ratio is larger than the threshold. good. In this way, by obtaining the best focus position of the projection optical system using the weighted size in the same manner as in the above embodiment, the same effect as in the above embodiment can be obtained.

In the above embodiment, the pattern length LH _i of the highly reliable resist pattern MP ′ is obtained by using the S / N ratio obtained from the one-dimensional data P _i (Y) obtained by converting the two-dimensional pixel data. Although the case of extracting has been described, the present invention is not limited to this. For example, when two-dimensional pixel data is used as it is without being converted, the contrast ratio of the internal pixel data between the partition area DA _i and the reference area DC _i is set to the S / N ratio. instead, it may be used as the information relating to the intensity of the image signal divided area DA _i.

Incidentally, in the exposure apparatus 100 of the above embodiment, the surface anti-reflection film of the wafer _{W T} that the pattern of the mark MP is transferred (ARC: Antireflection Coating), for example, sometimes BARC (Bottom ARC) is formed, Depending on the presence or absence of BARC, the intensity of reflected light differs when a resist image is captured by the alignment system AS. Therefore, the S / N ratio threshold, the signal intensity _Si constant ratio, or the contrast ratio threshold is changed according to the presence or absence of BARC. Specifically, when BARC is present, there is no BARC. Since the reflected light intensity is lower than in the case, it is desirable to lower the threshold value or ratio. Instead of changing the threshold of the S / N ratio, the logarithmic coefficient (20) in the above equation (1) may be changed according to the presence or absence of BARC.

  Further, instead of or in addition to the presence or absence of BARC, the above-described threshold value or ratio may be adjusted according to the minimum line width of the line pattern constituting the mark MP.

In the above embodiment, the entire area AA described above is imaged simultaneously. However, for example, the area AA may be divided into a plurality of areas and imaged separately. At this time, for example, the entire area AA may be set within the detection area of the alignment system AS, and a plurality of parts of the area AA may be imaged at different timings, or a plurality of parts of the area AA may be sequentially captured by the alignment system AS. It may be set within the detection area and imaged. For example, an area DEi including a partition area DA _i and a reference area DC _i provided corresponding to the partition area DA _i may be sequentially set in the detection area of the alignment system AS and imaged. However, at least one reference area (that is, the second area on the object to which the mark is not transferred) is sufficient. In this case, using the imaging signal (pixel data) for the M partition areas DA _{i and} the imaging signal (pixel data) for the one reference area, the projection optical system is similar to the above embodiment. The best focus position can be obtained.

  Furthermore, in the above embodiment, the plurality of partitioned areas DA constituting the evaluation point corresponding area DB are formed adjacent to each other. For example, a part (at least one partitioned area) of the alignment area AS described above is formed. They may be formed apart by a distance corresponding to the size of the detection area. That is, the arrangement (layout) of a plurality of partition regions may be determined according to the size of the detection region of the alignment system AS so that the entire evaluation point corresponding region can be imaged simultaneously.

In the above embodiment, for simplification of explanation, it has been illustrated for the case of forming on the wafer W _T by conventional exposing the resist image of diamond mark (wedge mark), not limited to this, for example, JP-2002 As disclosed in JP-A-169266, etc., diamond marks (by a double exposure using a set of line and space patterns symmetrically inclined at a predetermined angle with respect to a predetermined axis (for example, the Y axis) on a reticle ( A wedge mark) resist image may be formed, or as disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-029372, a set of symmetry on a reticle with respect to a predetermined axis (for example, Y axis). A resist image of a rhombus mark (wedge mark) may be formed by double exposure using a long-shaped pattern. In these cases, it is possible to effectively suppress the occurrence of a resist defect at the pointed tip of the resist image of the diamond mark (wedge mark).

  Moreover, in the said embodiment, the mark which consists not only of a dense pattern but an isolated pattern can also be used as a measurement mark. When a periodic pattern is used as the measurement mark, the periodic direction may be arbitrary.

  In the above-described embodiment, the sensitive layer may be formed on the wafer using not only a positive type but also a negative type resist. However, the signal waveform of the above one-dimensional signal (pixel data) may differ depending on the type of resist. In the above embodiment, the dent (valley) appears in the signal waveform of the one-dimensional signal, but a ridge may appear instead. In addition, a depression (valley shape) or a mountain shape with bumps may appear. It is desirable to define the pattern length and signal intensity as appropriate according to the situation.

In the above embodiment, by changing the position of the wafer W _T to optical axis AXp direction (Z axis direction) of the projection optical system PL stepwise, the mark MP of the reticle R _T, via the projection optical system PL wafer has been described for the case of sequentially transferring at different locations on the W _T, not limited thereto, in addition to the Z position of the wafer W _T, for example, other such exposure dose (irradiation dose of the illumination light IL per unit area) These exposure conditions may be changed in stages.

  In the above embodiment, for example, the object to be imaged may be a latent image formed on a resist at the time of exposure. The wafer on which the image is formed is developed, and the wafer is further etched. An obtained image (etched image) or the like may be used. In addition, the sensitive layer on which an image on an object such as a wafer is formed is not limited to a resist, and any layer can be used as long as an image (latent image and visible image) is formed by irradiation with light (energy). It may be a recording layer, a magneto-optical recording layer, or the like.

  In the above embodiment, the position information of the XY stage 20 (wafer table 18) is measured using the laser interferometer 26. However, the present invention is not limited to this, for example, US Patent Application Publication No. 2008/0088843. An encoder system for detecting a scale (diffraction grating) provided on the upper surface of the wafer table, as disclosed in US Pat. No. 2006/0227309, or the like. An XY stage 20 (wafer table) is provided using an encoder system in which an encoder head is provided and a scale on which a one-dimensional or two-dimensional grating (for example, a diffraction grating) is formed is disposed above the wafer table. The position information of 18) may be measured. In this case, it is preferable that a hybrid system including both the interferometer system and the encoder system is used, and the measurement result of the encoder system is calibrated using the measurement result of the interferometer system. Further, the position control of the XY stage 20 (wafer table 18) may be performed by switching between the interferometer system and the encoder system or using both.

  Further, in the above-described embodiment, the case where the present invention is applied to a stepper has been described. Can be applied to. In the case of a scanner or the like, the mark MP may be transferred onto the wafer by scanning exposure. In this case, dynamic optical characteristics can be obtained.

  In the above-described embodiment, the case where the present invention is applied to a dry type exposure apparatus that exposes a wafer without using liquid (water) has been described. No. 49,504, European Patent Application Publication No. 1,420,298, International Publication No. 2004/055803, US Pat. No. 6,952,253, etc. The present invention can also be applied to an exposure apparatus that forms an immersion space including an optical path of illumination light between the wafer and exposes the wafer with illumination light through the projection optical system and the liquid in the immersion space. Further, the present invention can be applied to an immersion exposure apparatus disclosed in, for example, US Patent Application Publication No. 2008/088843.

Furthermore, the light source of the exposure apparatus to which the present invention is applied is not limited to an ultra-high pressure mercury lamp that outputs an emission line in the ultraviolet region (g-line, i-line, etc.), but a KrF excimer laser (wavelength 248 nm), ArF excimer laser (wavelength 193 nm), F ₂ laser (wavelength 157 nm), or other pulse laser light source in the ultraviolet region. In addition, as the illumination light for exposure, for example, a fiber doped with erbium (or both erbium and ytterbium), for example, an infrared or visible single wavelength laser beam oscillated from a DFB semiconductor laser or fiber laser. Harmonics that are amplified by an amplifier and wavelength-converted to ultraviolet light using a nonlinear optical crystal may be used.

  Further, the projection optical system may be any of a refractive system, a catadioptric system, and a reflective system, and may be any of a reduction system, an equal magnification system, and an enlargement system.

  The present invention also provides an exposure apparatus for transferring a device pattern onto a glass plate, a thin film magnetic head, which is used not only for exposure apparatuses used for manufacturing semiconductor elements but also for displays including liquid crystal display elements and plasma displays. Also used in the manufacture of exposure equipment used to manufacture device patterns, exposure devices used to transfer device patterns onto ceramic wafers, imaging devices (CCDs, etc.), micromachines, DNA chips, etc., and masks or reticles can do.

  A semiconductor device includes a step of designing a function / performance of a device, a step of manufacturing a reticle based on the design step, a step of manufacturing a wafer from a silicon material, and an image of a reticle pattern by the exposure apparatus of the above-described embodiment. The wafer is manufactured through a step of generating the wafer, a step of developing the wafer, a step of etching the developed wafer, a device assembly step (including a dicing process, a bonding process, and a package process), an inspection step, and the like. In this case, in the lithography step, the exposure method described above is executed using the exposure apparatus of the above embodiment, and a device pattern is formed on the wafer. Therefore, a highly integrated device can be manufactured with high productivity.

  The optical property measurement method of the present invention is suitable for measuring the optical property of a projection optical system. The exposure method of the present invention is suitable for forming a pattern on an object. The device manufacturing method of the present invention is suitable for manufacturing an electronic device such as a semiconductor element or a liquid crystal display element.

  28 ... Main controller, 100 ... Exposure device, AS ... Alignment system, PL ... Projection optical system, PM ... Mark, W ... Wafer.

Claims (8)

An optical property measurement method for measuring optical properties of a projection optical system that projects an image of a pattern on a first surface onto a second surface,
A part of a plurality of exposure conditions including the position of the object with respect to the optical axis direction of the projection optical system is changed in stages, and the mark arranged on the first surface is transferred to the projection optical system via the projection optical system. A first step of sequentially transferring to different locations on the object disposed on the second surface side of the object;
A second step of imaging a region on the object including a plurality of first regions to which the mark has been transferred;
The size of the transfer image of the mark transferred to each of the plurality of first regions is obtained from the image pickup signal obtained as a result of the image pickup, and the strength of the image pickup signal of the first region corresponding to the obtained size of each transfer image A third step of obtaining optical characteristics of the projection optical system based on the information;
An optical characteristic measuring method including: In the third step, based on the information on the intensity of the imaging signal, the first region in which the transfer image of the mark using the size for calculating the optical characteristic of the projection optical system is selected and selected. The optical characteristic measuring method according to claim 1, wherein the optical characteristic of the projection optical system is obtained based on a relationship between a size of a transfer image of the mark transferred to each first region and a corresponding exposure condition to be changed. The optical characteristic measuring method according to claim 2, wherein in the third step, the relationship is approximated by a curve, and the optical characteristic is calculated based on a profile of the curve. The imaging signal is a one-dimensional signal about a uniaxial direction in a plane on which the mark on the object is transferred,
The optical characteristic measurement method according to any one of claims 1 to 3, wherein the information related to the intensity of the imaging signal is information related to a ratio between the intensity of the imaging signal in the first region and a reference intensity. The optical characteristic measurement method according to claim 4, wherein the reference intensity is an intensity of an imaging signal of a second region on the object where the mark is not transferred. The optical characteristic measuring method according to any one of claims 1 to 5, wherein a rhombus mark is used as the mark. Measuring optical characteristics of a projection optical system for projecting an image of a pattern on the first surface onto the second surface using the optical property measuring method according to any one of claims 1 to 6;
In consideration of the measurement result of the optical characteristic, at least one of the optical characteristic of the projection optical system and the position of the object with respect to the optical axis direction of the projection optical system is adjusted, and the pattern formed by the projection optical system Exposing the object disposed on the second surface side with an image. Forming a pattern on the object using the exposure method according to claim 7;
Developing the object on which the pattern is formed.