Exposure apparatus and method

According to one embodiment, an exposure apparatus performs exposure to transcribe a circuit pattern onto each of a plurality of sections on a wafer. The exposure apparatus includes a measurement device and a control device. The control device sets, on each of a first section and a second section adjacent to each other among the plurality of sections, a measurement point at a position offset from a reference position of each section. The control device causes the measurement device to measure surface information at each measurement point. The control device executes focus leveling control for exposure on the basis of the surface information measured at each measurement point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-176886, filed on Sep. 14, 2017; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an exposure apparatus and a method.

BACKGROUND

When a resist film applied on a wafer is exposed with a projection image of a circuit pattern drawn on a reticle, a topography (level difference) at a position where the projection image is formed is measured to prevent defocusing. An exposure apparatus performs focus leveling control on the basis of the measured topography.

DETAILED DESCRIPTION

According to the embodiment, an exposure apparatus performs exposure to transcribe a circuit pattern onto each of a plurality of sections on a wafer. The exposure apparatus includes a measurement device and a control device. The control device sets, on each of a first section and a second section adjacent to each other among the plurality of sections, a measurement point at a position offset from a reference position of each section. The control device causes the measurement device to measure surface information at each measurement point. The control device executes focus leveling control for exposure on the basis of the surface information measured at each measurement point.

Exemplary embodiments of an exposure apparatus and a method will he explained below in detail with reference to the accompanying drawings. The present invention is not limited to the following embodiments.

Embodiment

In recent years, miniaturization has been faced with a limit thereof in the technical field of fabrication of NAND flash memory having a two-dimensional structure. Hence, there is a concept that a capacity of a nonvolatile memory device is increased not by miniaturization but by stacking. Here, in terms of a nonvolatile memory device having a vertical NAND structure where NAND strings are arranged vertically, the number of steps of forming insulation films and wiring layers is dramatically increased for integration by stacking as compared to the two-dimensional NAND structure. Level differences on the wafer surface tend to be increased with increasing the number of steps. The level differences on the wafer surface may bring about defocusing in a lithography step. Hence, it is important to measure level differences, that is, topographies of the wafer surface with high accuracy when exposure. In the embodiment, a description is given of an exposure apparatus that can measure topographies easily and with high accuracy.

FIG. 1is a schematic diagram illustrating an example of the configuration of the exposure apparatus of the embodiment. The direction to the front side with respect to a normal to the paper surface is expressed as the X-axis direction, the direction to the right with respect to the paper surface as the Y-axis direction, and the upward direction with respect to the paper surface as the Z-axis direction. The upward direction with respect to the paper surface corresponds to the upward direction in the height direction of an exposure apparatus1. The X-axis, the Y-axis, and the Z-axis are orthogonal to each other. The exposure apparatus1described here is an apparatus that has employed a step-and-scan system. However, the embodiment can also be applied to an exposure apparatus that has employed another system.

The exposure apparatus1includes an illumination system2, a reticle stage3, a first interferometer4, a first drive device5, a projection unit6, a focus sensor7, a wafer stage8, a second interferometer9, and a control device10.

The reticle stage3supports a reticle30provided with a circuit pattern. The first drive device5includes, for example, a motor. The first drive device5can move the reticle stage3along at least an X-Y plane. The reticle stage3is moved to move the reticle30. The position of the reticle stage3is measured by the first interferometer4. The measurement result by the first interferometer4is inputted into the first drive device5. The first drive device5executes position control on the reticle stage3on the basis of the result of the measurement by the first interferometer4.

The wafer stage8supports a wafer40in a movable manner. Specifically, the wafer stage8includes a wafer chuck11on which the wafer40is mounted, and a second drive device12that moves the wafer chuck11. The second drive device12includes, for example, a motor. The second drive device12can move the wafer chuck11in the X-, Y-, and Z-axis directions. Moreover, the second drive device12can control the inclination of the wafer chuck11. The inclination is, for example, inclination (Ry) in the X direction with the Y-axis as the axis of rotation, and inclination (Rx) in the Y direction with the X-axis as the axis of rotation. The position of the wafer chuck11is measured by the second interferometer9. The measurement result by the second interferometer9is inputted into the second drive device12. The second drive device12executes position control on the wafer chuck11by using the result of the measurement by the second interferometer9. The wafer chuck11is moved to move the wafer40mounted on the wafer chuck11.

The illumination system2applies exposure light to an area of a region20on the reticle30. The projection unit6projects the exposure light which has passed through the reticle30onto an area of a region21on the surface of the wafer40. Consequently, the circuit pattern drawn on the reticle30is transcribed onto the wafer40. The projection unit6can also be called a projection optical system. The region21can also be called an exposure slit.

A resist film is formed on the surface of the wafer40. Hence, specifically, the exposure light is applied to the resist film. A projection image of the circuit pattern is formed on the surface of the resist film. The surface of the wafer40indicates the surface of the resist film formed on the wafer40below unless otherwise specified.

The focus sensor7is a device that measures topographies of the surface of the wafer40. The focus sensor7includes a projection system7aand a detection system7b. The projection system7aapplies a luminous flux to the wafer40. The wavelength and the application angle of the luminous flux are set in such a manner that the luminous flux is reflected from the surface of the wafer40. The detection system7bdetects the reflected luminous flux and acquires the topographies of the surface of the wafer40on the basis of the detected luminous flux.

The projection system7aand the detection system7bare each provided therein with a grating71.FIG. 2is a diagram illustrating an example of the grating71. The grating71is provided with five openings72according to the example ofFIG. 2. The five openings72are spaced evenly in one direction. Here, as an example, each opening72has a rectangular shape. Luminous fluxes applied through the different openings72belonging to the grating71of the projection system7aare applied to different positions on the surface of the wafer40, and then reflected therefrom. The detection system7hreceives the luminous fluxes reflected at the positions through the different openings72belonging to the grating71of the detection system7b, and acquires measurement data of topographies for each of the individual openings72. In other words, the focus sensor7can acquire measurement data of topographies from the five measurement points in one process.

FIG. 3is a diagram illustrating an example of spots of luminous fluxes applied by the projection system7ato the surface of the wafer40. Luminous fluxes emitted from the projection system7aform five spots51on the surface of the wafer40. The position and the attitude of the projection system7aare set in such a manner as to arrange the five spots51in the X-axis direction. The width of each spot51in the X-axis direction is expressed as W, and the pitch of the five spots51as P. Moreover, among the five spots51, the spot51corresponding to the center of the focus sensor7may be expressed as the spot51c. Moreover, the five spots51may be collectively referred to as the measurement area50.

The focus sensor7may be configured in such a manner as to be able to acquire surface information from measurement points, the number of which is other than five, in one process by causing each grating71to include one to four, or more than five openings72. Moreover, the opening72is not necessarily rectangular in shape. For example, each opening72may be divided into a plurality of (here four) segments73as illustrated by example inFIG. 4.

The control device10controls the illumination system2, the focus sensor7, the first drive device5, and the second drive device12.

For example, the control device10controls the first drive device5and the second drive device12to move the reticle stage3and the wafer chuck11for exposure.

FIG. 5is a schematic diagram for explaining an example of a method for moving the reticle stage3and the wafer chuck11for exposure.FIG. 5illustrates a state before exposure of a hatched section41a. As illustrated inFIG. 5, the wafer40is divided into a plurality of sections41. The circuit pattern formed on the reticle30is transcribed onto each section41in one exposure. Each section41can be called a shot area. The control device10drives the reticle stage3and the wafer chuck11in synchronisation to move the reticle30relatively to the region20in a direction indicated by an arrow22(the positive direction of the Y axis) and move the wafer40relatively to the region21in a direction indicated by an arrow23(the negative direction of the Y axis). Consequently, a circuit pattern31drawn on the reticle30is transcribed onto the section41where the region21has been scanned. The control device10repeatedly makes an exposure on each section41, and transcribes the circuit pattern31onto each of the plurality of sections41.

The control device10performs the measurement topography by using the focus sensor7before the exposure. The exposure apparatus1moves the wafer chuck11to move a measurement area on the wafer40relatively to the wafer40.

FIG. 6is a diagram for explaining an example of a method for moving a measurement area for measurement of topographies.FIG. 7is an enlarged view of a part ofFIG. 6. InFIGS. 6 and 7, dotted lines indicate boundaries of the sections41, and dot-and-dash lines indicate center lines of the sections41in the X-axis direction.

The sections41located inside the edge of the wafer40(for example, a section41b) have a rectangular shape. In contrast, the sections41including the outer peripheral end of the wafer40(for example, a section41c) have shapes whose part is missing. In terms of the sections41including the outer peripheral end of the wafer40, center lines are drawn assuming that they have the rectangular shape. The sections41of the rectangular shape located inside the edge of the wafer40may be expressed as perfect sections41. The sections41including the outer peripheral end of the wafer40, the sections41having the shapes whose part is missing, may be expressed as defect sections41. A forbidden zone with a constant width may be set along with the edge of the wafer40. If the forbidden zone is included in a certain section41, the area of the forbidden zone within the section41is treated as a missing part.

A path60is set in such a manner that the measurement area50crosses each section41in a direction (the positive or negative direction of the Y axis) different from an arrangement direction (the X-axis direction) of the spots51. The control device10performs a measurement at intervals of a predetermined time, or in each scan of a predetermined amount while scanning the measurement area50in such a manner that the spot51cmoves along the path60. Consequently, the control device10can set measurement points at five different positions in the X-axis direction at one measurement timing, and also can set measurement points at a plurality of different positions in the Y-axis direction at different timings respectively for the spots51.

Here, in the embodiment, the path60is set in such a manner as to pass a position offset by a distance D in the positive or negative direction of the X axis from the center line of each section41. In two sections41that are adjacent to each other in the X-axis direction, the path60is offset in different directions from reference positions being the center lines of the two sections41. For example, among columns of the sections41arranged in the Y-axis direction, the path60is set at a position offset by the distance D in the negative direction of the X axis for a column including the section41b, and is set at a position offset by the distance D in the positive direction of the X axis for a column including the section41c.

Furthermore, in the embodiment, the control device10uses, as data representing a topography of one section41, not only measurement data at each measurement point set on the one section41but also measurement data at each measurement point set on a section41adjacent to the one section41. More specifically, the control device10interpolates the measurement data in one section41with measurement data of another section41adjacent to the one section41.

An example of an interpolation process of an embodiment is described with reference toFIGS. 8 to 10. InFIGS. 8 to 10, a description is given of an example where measurement data at each measurement point set on the section41cis interpolated with measurement data at each measurement point set on the section41b.

As illustrated inFIG. 8, measurement data at measurement points61ato61lis obtained from the section41bby the measurement of a topography. Moreover, measurement data at measurement points61mto61uis obtained from the section41c.

The spot51cpasses the measurement points61dto6famong the measurement points61ato61l. Hence, the group of the measurement points61ato61lis offset by the distance D in the negative direction of the X axis from a reference position being the center line of the section41b. Moreover, the spot51cpasses the measurement points61sto61uamong the measurement points61mto61u. Hence, the group of the measurement points61mto61uis offset by the distance D in the positive direction of the X axis from a reference position being the center line of the section41c.

The control device10excludes measurement data that is not suitable for use from the measurement data obtained at these measurement points61. For example, the control device10does not use measurement data at a measurement point61located on the boundary of the section41. Moreover, the control device10does not use measurement data at measurement point61that is partly included in a missing part of the defect section41.FIG. 9shows measurement points61except for the points61from which measurement data to be excluded is obtained.

InFIG. 10, relative positions f positions62dto62iwith reference to the center line of the section41ccorrespond to relative positions of the measurement points61dto61iwith reference to the center line of the section41b. The control device10varies the offset direction of the path60between the column of the section41band the column of the section41cto prevent the positions62dto62ifrom coinciding with the measurement points61in the section41c. The control device10uses measurement data at the measurement points61dto61iin the section41b, as data measured at the positions62dto62i. In other words, the control device10interpolates measurement data at the measurement points61pto61rand61uwith the measurement data at the measurement points61dto61lin the section41b.

The control device10executes focus leveling control for exposure on the basis of the interpolated topography. The focus leveling control is to obtain focusing at an exposure position as accurately as possible by, for example, moving the wafer chuck11in the Z-axis direction and controlling the inclination of the wafer chuck11. In the embodiment, the amount of effective measurement data presenting a topography of each section41is increased by interpolation. Accordingly, for example, even if the defect section41(such as the section41c) having a small number of measurement points is exposed, it is possible to prevent a focus error (defocusing) due to a lack of measurement data. Moreover, also in terms of the perfect section41, the data mount of measurement data is increased. Accordingly, the focus leveling control can be executed with higher accuracy than in the case where interpolation is not performed.

FIG. 11is a diagram illustrating an example of the hardware configuration of the control device10. As illustrated inFIG. 11, the control device10includes a processing device101, a storage device102, an IO device103, and a bus104. The processing device101, the storage device102, and the10device103are electrically connected to the bus104, and can exchange information via the bus104.

The processing device101is, for example, a CPU (Central Processing Unit). The processing device101achieves a function as the control device10on the basis of a program105stored in advance in the storage device102.

The IO device103is an interface device for communicating with other devices (the illumination system2the focus sensor7, the first drive device5, and the second drive device12). The processing device101can transmit control signals to the other devices via the10device103, and receive data from the other devices (for example, measurement data from the focus sensor7).

The storage device102is a memory that can hold various pieces of information. The kind of memory configuring the storage device102is not limited to a specific kind. For example, the storage device102is configured of a combination of a nonvolatile memory and a volatile memory. For example, a ROM (Read Only Memory), an HDD (Hard Disk Drive), a flash memory, a magneto-optical disk, or a combination thereof can be employed as the nonvolatile memory. Various RAMs (Random Access Memories) can be employed as the volatile memory.

The program105is stored in advance in, for example, the nonvolatile memory, and is loaded into the volatile memory from the nonvolatile memory at startup of the control device10. The processing device101executes the program105loaded in the volatile memory. Intermediate data and the like during the execution of the program105can be stored in the volatile memory.

The program105can be stored in advance in the nonvolatile memory, and distributed. Moreover, the program105can be stored in a recording medium in a computer connected to a network such as the Internet, then can be provided or distributed by being downloaded from the computer via the network.

FIG. 12is a flowchart explaining the operation of the exposure apparatus1of the embodiment. Firstly, the processing device101controls the focus sensor7and the second drive device12to measure topographies of the surface of the wafer40(S101). In other words, the processing device101acquires measurement data of a topography with the focus sensor7at intervals of a predetermined time, or in each scan of a predetermined distance, while scanning (causing relative movement of) the measurement area50along the path60relative to the wafer40. The processing device101temporarily stores the obtained measurement data at each measurement point in, for example, the storage device102.

Next, the processing device101interpolates measurement data on the basis of the obtained measurement data at each measurement point, for each section41(S102). As described with reference toFIGS. 8 to 10, the processing device101interpolates, for example, the measurement data of the section41cwith the measurement data of the section41b.

The processing device101may interpolate, for example, the measurement data of the section41bwith the measurement data of the section41adjacent to the section41bon a side opposite to the section41c. As long as the section41whose measurement data is interpolated is adjacent to the section41from which measurement data used for interpolation is acquired, a method for selecting the section41from which measurement data used for interpolation is acquired can be freely selected.

After the interpolation of the measurement data is completed, the processing device101controls the illumination system2, the first drive device5, and the second drive device12to perform an exposure on each section41(S103). In S103, the processing device101performs an exposure on each section41to transcribe the circuit pattern onto the section41. At this point in time, the processing device101executes the focus leveling control on the basis of the interpolated measurement data of each section41.

After exposures all the sections41are completed, the operation is completed.

In the above description, the control device10measures topographies of the surface of the wafer40by using the focus sensor7. The topography is an example of surface information used in the focus leveling control. Any information can be employed as the surface information as long as it is information that can be used for the focus leveling control. For example, the control device10may cause the focus sensor7to measure the position and the inclination in the z-axis direction (that is, the optical axis direction) as the surface information.

Moreover, the control device10excludes the measurement data of the measurement points61located on the boundaries of the plurality of the sections41as illustrated inFIG. 9. A method for determining the use/non-use of measurement data at each measurement point61is not limited to this.

Moreover, the control device10offsets a group of the measurement points61from a reference position being the center line of each section41. A method for setting a reference position is not limited to this.

Moreover, the control device10offsets a group of the measurement points61in the X-axis direction. The control device10may offset the position of each measurement point61in the Y direction by putting some thought into measurement timings during scanning of the measurement area50. For example, a group of the measurement points61may be offset in the positive direction of the Y axis for the column of the section41b, and a group of the measurement points61may be offset in the negative direction of the Y axis for the column of the section47c.

Moreover, the control device10increases the amount of effective measurement data by interpolation. The control device10does not necessarily perform an interpolation.

FIG. 13is a diagram for explaining an example of a method for setting an offset amount (the distance D offset). InFIG. 13, two dotted lines42indicate boundaries of one section41in the X-axis direction. Moreover, a cross or circle is displayed at each measurement point61. Each cross indicates a measurement point61from which measurement data obtained is to be excluded. Each circle indicates a measurement point61from which measurement data obtained is to be used.

As illustrated inFIG. 13, when the distance D is zero, that is, when a group of the measurement points61is not offset, the spots51located at both ends among the five spots51included in the measurement area50lie off the boundaries of the section41. Hence, measurement data measured from the spots51located at both ends among the five spots51is excluded. Also when the distance D is greater than zero and less than W/2, the amount of usable measurement data is the same as the case where the distance D is zero.

When the distance D is W/2, or when the distance D is (P−W/2), measurement data measured by using the spot51located at the right end among the five spots51included in the measurement area50is excluded.

When the distance D is greater than (P−W/2), measurement data measured by using two spots51at the right end among the five spots51included in the measurement area50is excluded.

In this manner, the distance D is set to a value equal to or greater than W/2 and equal to or less than (P−W/2), and accordingly the amount of measurement data representing a topography of each section41can be increased. Hence, the control device10may perform an offset on a group of the measurement points61without interpolation.

As described above, according to the embodiment, the control device10sets, on two sections41adjacent to each other, measurement points61at positions offset from reference positions of the two sections41, and causes the focus sensor7to measure surface information at the measurement points61. The control device10then executes the focus leveling control for exposure on the basis of the surface information obtained at the measurement points61.

With this configuration, the amount of effective measurement data of each section41can be increased. Accordingly, it is possible to prevent defocusing due to a lack of measurement data. In other words, the convenience of the exposure apparatus1can be increased.

Moreover, according to the embodiment, the control device10makes a relative position of a measurement point61set on a first section41with reference to a reference position of the first section41and a relative position of a measurement point61set on a second section41with reference to a reference position of the second section41different from each other. The first section41is one section41of the two sections41adjacent to each other, and the second section41is the other section41of the two sections41adjacent to each other.

With this configuration, it is possible to interpolate measurement data of the one section41with measurement data obtained in the other section41.

In the above description, the measurement points61of the two sections41are offset by the distance D in directions opposite to each other. In this case, a difference between a relative position of the measurement point61set on the one section41with reference to a reference position of the one section41and a relative position of the measurement point61set on the other section41with reference to a reference position of the other section51corresponds to 2*D. If the value of 2*D is, for example, less than P, measurement data obtained in the one section41can be interpolated with measurement data obtained in the other section41.

The directions in which the measurement points61are offset are not limited to the above-mentioned directions. The measurement points61may be offset in the same direction in the two sections41. In such a case, the difference between the relative positions may be set greater than zero and less than P, and accordingly the measurement data of the one section41can be interpolated with the measurement data obtained in the other section41.

Moreover, according to the embodiment, the control device10executes the focus leveling control for exposure on the one section41of the two sections41by using measurement data obtained in the one section41and measurement data obtained in the other section41. More specifically, the control device10regards measurement data obtained at a measurement point in the other section41as measurement data obtained at a measurement point located at a position offset a relative position of the one section41by an offset amount of the measurement point in the other section41.

With this configuration, the amount of the measurement data in the one section41is increased. Accordingly, it is possible to prevent defocusing due to a lack of the measurement data.

In an inexpensive or old-type exposure apparatus, the pitch P of each spot51may be greater than that of the latest exposure apparatus. According to the above-mentioned configuration, the number of measurement points can be increased in a pseudo manner. Therefore, if the above-mentioned configuration is applied to the exposure apparatus where the pitch P is not fine, the accuracy of the focus leveling control can be improved.

Moreover, according to the embodiment, the control device10can interpolate measurement data of a defect section41like the section41cwith measurement data of a perfect section41like the section41b. Hence, the highly accurate focus leveling control is possible also in the defect section41from which less measurement data is obtained than the perfect section41.

Moreover, the control device10can increase the amount of measurement data representing a topography of each section41by using a value equal to or greater than W/2 and equal to or less than (P−W/2) as the distance D, as described with reference toFIG. 13.