JP2005285893A - Original plate inspection method, exposure method and electron beam exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an original plate inspection method for precisely correcting deformation of sub-fields on an original plate and reducing overlap errors and stitching errors much more during exposure. <P>SOLUTION: An L-type position detection mark (measuring mark) 55 is formed in a part 53' between the adjacent position detection sub-fields 53 on an Si substrate 50 of a reticle. Three or above marks 55 are placed at the periphery of the sub-field 53. The position of the mark 55 is measured and the position is compared with device pattern design data, and errors of rotation, magnification, perpendicularity and the position at every sub-field 53 are obtained. Since a deformation (distortion) correction value at every sub-field 53 can be obtained by obtaining the errors of rotation, magnification, perpendicularity and the position at every sub-field 53, correction precision can be improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for inspecting an original (reticle, mask) used for lithography using an electron beam, an exposure method for transferring an entire device pattern by joining images of the original on a sensitive substrate, and the like The present invention relates to an electron beam exposure apparatus to which such a method is applied.

  In recent semiconductor lithography technology, demands for higher resolution and larger exposure field are increasing. In response to the demand for higher resolution, development of an exposure apparatus using an electron beam has been performed. In the electron beam exposure of the divided transfer method, the design pattern to be transferred is divided into a large number of small pattern areas (subfields) and formed on an original (reticle), and an electron beam is transmitted through each subfield for sensitivity. Subfields are projected and exposed collectively on a substrate (wafer), and images of the subfields are connected on the wafer to transfer the entire design pattern.

  In order to connect the images of the subfields on the wafer with high accuracy, a reticle stage on which the reticle is placed and moved / positioned, a wafer stage on which the wafer is placed and moved / positioned, and a pattern on the reticle The projection lens that projects the image onto the wafer needs to be positioned with high accuracy. Alternatively, when the upper layer pattern is superimposed on the lower layer pattern already formed on the wafer, high-precision positioning between the stage and the lens is required. If an error occurs in such joining and overlaying, the pattern transferred onto the wafer will change in shape, which can be a very large defect for a fine pattern (for example, the gate portion of a transistor circuit). is there.

  By the way, in such a divided transfer type electron beam exposure, a stencil reticle composed of a membrane or thin film in which a hole for transmitting an electron beam is finely processed and a strut supporting the hole is being widely used as an original. . The stencil film is a silicon wafer formed in a thin film shape, and a subfield pattern is formed on the thin film. This type of reticle is manufactured by a process such as (1) thinning a silicon wafer → (2) applying a resist → (3) a chuck of a drawing apparatus → (4) pattern etching → (5) resist peeling. In the manufacturing process, deformation such as distortion may occur in the reticle. When exposure is performed using a deformed reticle, a distorted pattern is projected on the wafer, which may cause a problem that pattern overlay accuracy and joining accuracy are reduced. Therefore, managing the reticle deformation is extremely important in terms of maintaining accuracy.

  Therefore, it has been proposed to measure the amount of deformation of the reticle and perform exposure while correcting the deformation based on the measurement data. For example, a method of providing a position measurement mark on a strut portion of a reticle (a portion between each thin film region), measuring the position measurement mark with an inspection device such as a coordinate measuring device, and correcting distortion using the measurement data (See Patent Document 1 etc.). In this method, the center position error of each subfield in the entire reticle area is obtained from the obtained measurement data, and corrected in accordance with the alignment result of the reticle, thereby reducing overlay errors and stitching errors due to reticle deformation. Can do. Alternatively, when the amount of deformation inside the subfield can be measured, in addition to the correction of the center position error described above, it is also possible to correct it by adjusting parameters such as the magnification, rotation, and position of the projection optical system.

JP 2003-77804 A

Incidentally, since the inside of the subfield of the reticle is a normal pattern region, it is impossible to provide position measurement marks in all the subfields. Therefore, a subfield dedicated to measurement is formed in the non-exposure area on the reticle (portion not directly involved in exposure), and pattern resolution and distortion are measured using this subfield for measurement. As a representative value, a method for correcting distortion of all subfields, and a method for correcting the magnification of subfields using a result obtained from reticle alignment have been proposed.
However, the deformation of the reticle is not isotropic, and there is a possibility that the amount of distortion varies depending on the location of each subfield. Therefore, it is conceivable that such a method cannot sufficiently correct the deformation.

  The present invention has been made in view of such problems, and an original inspection that can accurately correct the deformation of each subfield on the original and further reduce overlay errors and stitching errors during exposure. It aims to provide a method. It is another object of the present invention to provide an exposure method and an electron beam exposure apparatus to which such an inspection method is applied.

An original plate inspection method according to the present invention is a method for inspecting an original plate in which a device pattern to be transferred on a sensitive substrate is divided into a plurality of subfields. A mark is provided, the position of the mark is measured, and the position and device pattern design data are compared to obtain rotation, magnification, orthogonality, and position error for each subfield.
According to this inspection method, since the deformation (distortion) correction value for each subfield can be obtained by obtaining the rotation, magnification, orthogonality, and position error for each subfield, the correction accuracy can be improved. it can.

In the exposure method of the present invention, a device pattern to be transferred onto a sensitive substrate is divided into a plurality of subfields, formed on an original, and sequentially irradiated with an energy beam for each subfield. An exposure method for transferring the entire device pattern by joining on the sensitive substrate, wherein three or more marks are provided around each subfield of the original plate, and the positions of the marks are measured, The position and device pattern design data are compared to determine rotation, magnification, orthogonality, and position errors for each subfield, and exposure and transfer are performed while correcting these errors.
According to this exposure method, a deformation (distortion) correction value for each subfield can be obtained and the correction accuracy can be improved, so that the overlay error and stitching error of the drawn pattern can be further reduced. Can do.

  An electron beam exposure apparatus according to the present invention includes an electron beam source that generates and accelerates an electron beam, an original plate formed by dividing a device pattern into a plurality of subfields, and illuminates the electron beam at a desired position on the original plate An optical system for limiting an illumination beam limiting aperture for limiting the electron beam irradiated to the original, an original stage for holding the original, and the original stage so that the electron beam is irradiated to a desired position of the original An optical stage for transferring and joining a device pattern on the original plate to a desired position on a sensitive substrate, a sensitive substrate stage for holding the sensitive substrate, and a sub-field of the subfield A sensitive substrate stage drive mechanism for moving the sensitive substrate stage so that an image is formed at a desired position on the sensitive substrate, and Corrects the rotation, magnification, orthogonality, and position errors for each subfield obtained by measuring the positions of three or more marks arranged around the subfield and comparing the positions with device pattern design data. However, exposure and transfer are performed.

  According to the present invention, it is possible to provide an original inspection method and the like that can accurately correct deformation of each subfield on the original and further reduce overlay errors and stitching errors during exposure.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, it demonstrates, referring drawings.
First, the outline of the divided transfer type electron beam projection exposure technique will be described with reference to the drawings.
FIG. 1 is a diagram showing an outline of an imaging relationship and a control system in the entire optical system of a divided transfer type electron beam projection exposure apparatus.
The electron gun 1 arranged at the uppermost stream of the optical system emits an electron beam downward. Below the electron gun 1, two-stage condenser lenses 2 and 3 are provided. The electron beam emitted from the electron gun 1 is converged by the condenser lenses 2 and 3, and the crossover C.D. O. Is imaged.

  A rectangular opening 4 is provided below the second-stage condenser lens 3. This rectangular aperture (illumination beam shaping aperture) 4 allows only the illumination beam that illuminates one subfield (pattern small area that becomes one unit of exposure) of the reticle 10 to pass. The image of the illumination beam shaping aperture 4 is formed on the reticle 10 by the lens 9. A blanking deflector 5 is disposed below the illumination beam shaping opening 4. The blanking deflector 5 deflects the illumination beam when necessary and hits the non-opening portion of the blanking opening 7 so that the beam does not hit the reticle 10.

  An illumination beam deflector 8 is disposed below the blanking opening 7. The deflector 8 mainly scans the illumination beam in the horizontal direction (X direction) in FIG. 1 to illuminate each subfield of the reticle 10 in the field of view of the illumination optical system. An illumination lens 9 is disposed below the illumination beam deflector 8. The illumination lens 9 images the illumination beam shaping aperture 4 on the reticle 10.

  The reticle 10 of the present embodiment is actually spread in the optical axis vertical plane (XY plane) (described later with reference to FIG. 2), and has a large number of subfields. A pattern (chip pattern) forming one semiconductor device chip as a whole is formed on the reticle 10. Of course, a pattern forming one semiconductor device chip may be divided and arranged on a plurality of reticles.

  The reticle 10 is placed on a reticle stage 11 that can be moved and positioned. By moving the reticle 10 on the reticle stage 11 in the direction perpendicular to the optical axis (XY direction in FIG. 1), it is possible to illuminate each subfield on the reticle 10 that extends over a wider range than the field of view of the illumination optical system. The reticle stage 11 is provided with a position detector 12 using a laser interferometer, so that the position of the reticle stage 11 can be accurately grasped in real time.

  Projection lenses 15 and 19 and a deflector 16 are provided below the reticle 10. The electron beam that has passed through one subfield of the reticle 10 is imaged at a predetermined position on the wafer 23 by the projection lenses 15 and 19 and the deflector 16. An appropriate resist is applied on the wafer 23, and an electron beam dose is given to the resist, and the pattern on the reticle is reduced and transferred onto the wafer 23. The point at which the space between the reticle 10 and the wafer 23 is internally divided by the reduction ratio is the crossover C.I. O. Is formed. This crossover C.I. O. A contrast opening 18 is provided at the position. The contrast opening 18 blocks the electron beam scattered by the non-pattern part of the reticle 10 from reaching the wafer 23.

  A backscattered electron detector 22 is disposed immediately above the wafer 23. The reflected electron detector 22 detects the amount of electrons reflected by the exposed surface of the wafer 23 or the mark on the stage. For example, the relative positional relationship between the reticle 10 and the wafer 23 can be known by scanning the mark on the wafer 23 with a beam that has passed through the mark pattern on the reticle 10 and detecting the reflected electrons from the mark at that time. it can.

  The wafer 23 is placed on a wafer stage 24 that can be moved and positioned in the XY directions via an electrostatic chuck (not shown). By synchronously scanning the reticle stage 11 and the wafer stage 24 in opposite directions, each part in the chip pattern extending beyond the field of view of the projection optical system can be sequentially exposed. The wafer stage 24 is also equipped with a position detector 25 similar to the reticle stage 11 described above.

  The lenses 2, 3, 9, 15, 19 and the deflectors 5, 8, 16 are controlled by a controller (control unit) via the coil power supply control units 2a, 3a, 9a, 15a, 19a and 5a, 8a, 16a. Part) 31. Further, the reticle stage 11 and the wafer stage 24 are also connected to the controller 31 via the stage controllers 11a and 24a. The stage position detectors 12 and 25 send signals to the controller 31 via interfaces 12a and 25a including amplifiers and A / D converters. The backscattered electron detector 22 also sends a signal to the controller 31 via the same interface 22a.

  The controller 31 grasps the control error of the stage position and corrects the error by the image position adjusting deflector 16. Thereby, the reduced image of the subfield on the reticle 10 is accurately transferred to the target position on the wafer 23. Then, the subfield images are joined on the wafer 23, and the entire chip pattern on the reticle is transferred onto the wafer.

Next, a detailed example of the reticle used in the divided transfer type electron beam projection exposure will be described with reference to FIG.
FIG. 2 is a diagram schematically showing a configuration example of a reticle for electron beam projection exposure. (A) is a plan view of the whole, (B) is a partial perspective view, and (C) is a plan view of one small membrane region.
Such a reticle can be manufactured, for example, by performing electron beam drawing / etching on a silicon wafer.

  FIG. 2A shows an entire pattern division arrangement state in the reticle 10. A region indicated by a large number of squares 41 in the drawing is a small membrane region (thickness 0.1 μm to several μm) including a pattern region corresponding to one subfield. As shown in FIG. 2C, the small membrane region 41 is composed of a central pattern region (subfield) 42 and a peripheral frame-shaped non-pattern region (skirt 43). The subfield 42 is a portion where a pattern to be transferred is formed. The skirt 43 is a portion where no pattern is formed and hits the edge portion of the illumination beam. As a form of pattern formation, there are a stencil type in which perforations are provided in the membrane and a scattering membrane type in which a pattern layer made of a high scatterer of electron beams is formed on the membrane.

  One subfield 42 currently has a size of about 0.5 to 5 mm square on the reticle. Assuming that the reduction ratio of the projection is 1/5, the size of the projected image obtained by reducing and projecting the subfield onto the wafer is 0.1 to 1 mm square. A portion 45 called an orthogonal lattice-shaped glage around the small membrane region 41 is, for example, a beam having a thickness of about 0.5 to 1 mm for maintaining the mechanical strength of the reticle. The width of the glage 45 is, for example, about 0.1 mm. Note that the width of the skirt 43 is, for example, about 0.05 mm.

  As shown in FIG. 2A, a large number of small membrane regions 41 are arranged in the horizontal direction (X direction) in FIG. 2 to form one group (electrical stripe 44). Such an electrical stripe 44 is shown in FIG. One mechanical stripe 49 is formed side by side in the vertical direction (Y direction). The length of the electrical stripe 44 (the width of the mechanical stripe 49) is limited by the size of the deflectable field of view of the illumination optical system. A method in which a non-pattern region such as a skirt or a gray area is not provided between adjacent subfields in one electrical stripe 44 has been studied.

  A plurality of mechanical stripes 49 exist in parallel in the X direction. A thick beam shown as a strut 47 between adjacent mechanical stripes 49 is to keep the deflection of the entire reticle small. The strut 47 is integral with the grage 45. According to the method considered to be dominant at present, the columns of the subfields 42 in the X direction (electrical stripes 44) in one mechanical stripe (hereinafter simply referred to as a stripe) 49 are sequentially exposed by electron beam deflection. On the other hand, the columns in the Y direction in the stripes 49 are sequentially exposed by continuous stage scanning.

Next, the reticle error correction method according to the present invention will be described in comparison with the current method.
FIGS. 3A and 3B are plan views schematically showing an example of position detection mark arrangement around one subfield of the reticle according to the present embodiment.
FIG. 4 is a plan view schematically showing an example of the present reticle position detection mark arrangement.
The reticle Si substrate 50 used in this method is circular and has two rectangular pattern regions 51 formed thereon. Each pattern region 51 includes a large number of small membrane regions 53 including subfields arranged vertically and horizontally. The small membrane region is also referred to as a subfield. The diameter of the Si substrate 50 is 200 mm as an example, and the dimension of each pattern region 51 is 132.57 mm in length × 54.43 mm in width as an example.

  In the pattern region 51, each outermost subfield (position detection subfield) 53a is formed as a dedicated region for position detection marks. The position detection subfield 53a does not have a pattern for device formation, and only an alignment mark (not shown) is formed. The position of the alignment mark is detected using an electron beam in the exposure apparatus. On the other hand, the inner subfield 53b excluding the position detection subfield 53a has a normal pattern for device formation.

  As shown on the lower side in FIG. 4, another position detection mark (measurement mark) 55 is formed in a portion 53 ′ between adjacent position detection subfields 53. The measurement mark 55 has an L shape and is formed by vapor-depositing Cr, Ta or the like on the surface of the Si substrate 50. The position of the measurement mark 55 is detected outside the exposure apparatus using an inspection apparatus (for example, a light wave interference type coordinate measuring machine 6i type manufactured by Nikon Corporation). Although not shown, a measurement mark for defining the origin is also formed at the center of the Si substrate 50.

The center (P _n , Q _n ) (where n = N _sf −1, N _sf is the number of subfields to be exposed) of the position detection subfield 53a is the coordinate (x _m , y _m ), (x _{m + 1} , y _{m + 1} ) (where m = N−1, N is the total number of measurement marks) (P _n = (x _m + x _{m + 1} ) / 2, Q _n = (y _m + y _{m + 1} ) / 2). The origin of this coordinate is a measurement mark (not shown) formed at the center of the Si substrate 50 described above.

ただし、「数１」において、Ｓ_x、Ｓ_yは縦・横方向の倍率誤差のパラメータであり、θ、ωはそれぞれサブフィールド配列の回転、直交度誤差のパラメータであり、Ｏ_x、Ｏ_yはサブフィールド中心位置のずれのパラメータである。 In the current reticle error correction method, the distortion of the subfield caused by the rotation error, the orthogonality error, and the magnification error of the Si substrate 50 is corrected. Therefore, the measured mark position (x _m , y _m ) and the distortion are not present. From the ideal mark position (X _m , Y _m ), these errors are expressed by the following equation (1), and the linear distortion component is calculated by the following equation (2) using the least square method. :

In “Equation 1”, S _x and S _y are parameters of magnification error in the vertical and horizontal directions, θ and ω are parameters of rotation and orthogonality error of the subfield arrangement, respectively, and O _x , O _y. Is a parameter of the deviation of the center position of the subfield.

  The current method using the “Expression 1” is that a linear distortion component having substantially the same direction / size among a plurality of adjacent subfields and a non-linear distortion component (error amount) having a different direction / size for each point. The position of each subfield is calculated from (the amount obtained by subtracting the linear distortion component from the deviation from the design data) and the reticle distortion data obtained by reticle alignment, and correction is performed during exposure. However, in this method, it may be considered that the subfield joining accuracy and the overlay accuracy cannot be sufficiently ensured. Therefore, in this embodiment, the following correction is performed.

FIG. 3 is a plan view schematically showing an example of the position detection mark arrangement of the reticle according to the present embodiment. (A) is a diagram showing an example in which four position detection marks are arranged around each subfield, and (B) is a diagram showing an example in which six position detection marks are arranged around each subfield.
When six L-shaped marks (position detection marks) as shown in FIG. 3B are arranged, six measurement data are obtained by measuring three L-shaped marks in the X and Y directions. Can do. In this case, (u _j , v _j ) (where j = 1, 2, 3) is the measured position coordinates of each L-shaped mark, and (U _j , V _j ) (where j = 1, 2, 3). When the the ideal position coordinates of each L-shaped marks, the rotational theta _n of n-th sub-field by the following respective formulas, magnification Sx _n, Sy _n, perpendicularity omega _n, the position error Ox _n, be obtained Oy _n Yes (however, the suffix n is omitted for both measured and ideal values):
θ _n = (v ₃ −v ₁ ) / (u ₃ −u ₁ )
ω _n = (u ₂ −u ₁ ) / (v ₂ −v ₁ ) −θ _n
Sx _n = (u ₃ −u ₁ ) / (U ₃ −U ₁ ) −1
_{Sy n = (v 2 -v 1} ) / (V 2 -V 1) -1
Ox _n = (u ₃ + u ₁ ) / 2− (U ₃ + U ₁ ) / 2
Oy _n = (v ₁ + v ₂ ) / 2− (V ₁ + V ₂ ) / 2

そして、得られた線形誤差成分を電子光学系にてサブフィールドごとに補正して、ウェハ上に露光する。 Alternatively, as described above, linear error components may be calculated using J position detection marks (J> 3: J = 4 in FIG. 3A and J = 6 in FIG. 3B). Yes (J is the number of L-shaped marks per subfield). In this case, from the measured mark position (u _m , v _m ) and the ideal mark position (U _m , V _m ) without distortion, these errors are expressed by the following equation (3), The linear distortion component is calculated by the following equation (4) using the least square method:

Then, the obtained linear error component is corrected for each subfield by the electron optical system and exposed on the wafer.

  According to these methods, the deformation (distortion) correction value for each subfield can be obtained and the correction accuracy can be improved, so that the overlay error and stitching error of the drawn pattern can be further reduced. Can do.

It is a figure which shows the outline of the imaging relationship in the whole optical system of the electron beam projection exposure apparatus of a division | segmentation transfer system, and a control system. It is a figure which shows typically the structural example of the reticle for electron beam projection exposure. (A) is an overall plan view, (B) is a partial perspective view, and (C) is a plan view of one small membrane region. FIG. 6 is a plan view schematically showing an example of position detection mark arrangement around one subfield of the reticle according to the embodiment. It is a top view which shows typically the example of the mark arrangement | positioning for position detection of the present reticle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron gun 2, 3 Condenser lens 4 Rectangular opening (illumination beam shaping opening) 5, 8, 16 Deflector 7 Blanking opening 9 Lens 10 Reticle 11 Reticle stage 15, 19 Projection lens 18 Contrast opening 23 Wafer 24 Wafer stage 31 Controller (Control unit) 50 Si substrate 51 Pattern region 53 Small membrane region 53a Subfield for position detection 55 Position detection mark (measurement mark)

Claims (3)

A method for inspecting an original plate formed by dividing a device pattern to be transferred onto a sensitive substrate into a plurality of subfields,
Three or more marks are set around each subfield of the original,
Measure the position of the mark,
An original plate inspection method, wherein the position and device pattern design data are compared to determine rotation, magnification, orthogonality, and position error for each subfield. The device pattern to be transferred onto the sensitive substrate is divided into a plurality of subfields and formed on the original plate.
Sequential irradiation with an energy beam for each subfield,
An exposure method for transferring the entire device pattern by joining the images of the subfields on the sensitive substrate,
Three or more marks are provided around each subfield of the original plate,
Measure the position of the mark,
Compare the position and device pattern design data, find the rotation, magnification, orthogonality, position error for each subfield,
An exposure method comprising performing exposure and transfer while correcting these errors. An electron beam source for generating and accelerating an electron beam;
An original plate formed by dividing a device pattern into a plurality of subfields;
An optical system for illuminating an electron beam at a desired position on the original;
An illumination beam limiting aperture for limiting the electron beam applied to the original;
An original stage holding the original, and
An original stage drive mechanism that moves the original stage so that an electron beam is irradiated to a desired position of the original;
An optical system for transferring and joining the device pattern on the original plate to a desired position on the sensitive substrate;
A sensitive substrate stage for holding the sensitive substrate;
A sensitive substrate stage driving mechanism for moving the sensitive substrate stage so that the image of the subfield is formed at a desired position of the sensitive substrate;
Comprising
The rotation, magnification, orthogonality, and position of each subfield obtained by measuring the positions of three or more marks arranged around each subfield of the original plate and comparing the positions with device pattern design data. An electron beam exposure apparatus that performs exposure and transfer while correcting an error.

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