Imprint apparatus, method of calibrating correction mechanism, and method of manufacturing article

An imprint apparatus includes a mold holding unit configured to hold a mold, a correction mechanism configured to correct a shape of a pattern formed in the mold to a desired shape by applying a force to the mold held in the mold holding unit, and a controller configured to assume a plurality of mold pattern shapes for a specific mold, calculate a parameter for associating the plurality of assumed mold pattern shapes and a deformation amount of the specific mold by causing the correction mechanism to apply the force to the specific mold to obtain the deformation amount of the specific mold so that the plurality of assumed mold pattern shapes are formed, and calibrate the correction mechanism using the parameter.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an imprint apparatus, a method of calibrating a correction mechanism, and a method of manufacturing an article.

Description of the Related Art

There is microfabrication technology for forming a pattern on a substrate according to an imprint process of molding an imprint material on the substrate according to a mold. This technology is also referred to as imprint technology and enables a pattern (structure) on the order of several nanometers to be formed on the substrate. For example, one type of imprint technology is a photocuring method. In an imprint apparatus adopting the photocuring method, first, a photocurable resin is supplied as an imprint material to a shot region on the substrate. Next, the resin on the substrate is molded using the mold. Then, the resin is cured by radiating light and released to form a pattern of the resin on the substrate. In the imprint technology, for example, there is a thermosetting method for curing a resin according to heat in addition to the photocuring method.

However, in an imprint apparatus adopting the above-described technology, a pattern shape error such as magnification, skew, or a trapezoid occurring in a semiconductor process may be included. Thus, when a base layer (base pattern) formed on the substrate in advance and a concave-convex pattern (pattern region) formed in a mold are superimposed, relative positions of a mark formed in the mold and a mark formed on the substrate are first measured using a detector. Next, the relative positions are corrected by deforming the mold based on a relative position difference. Here, a shape correction apparatus for deforming the mold at a precision of several nanometers or less is required to perform the superimposition of the pattern at high precision.

Therefore, Japanese Patent Laid-Open No. 2009-141328 discloses a shape correction apparatus in which an actuator for applying a compressive force to a side surface of a mold is disposed between the side surface of the mold and a support structure, the compressive force is measured using a force sensor installed between the actuator and the support structure, and feedback is controlled. In addition, the publication of Japanese Patent No. 4573873 discloses a method of obtaining a deformation parameter predicted to occur in a mold to minimize a dimension change between a record pattern on a mold and a reference pattern.

However, in a force sensor such as a load cell or a strain gauge for general use as disclosed in Japanese Patent Laid-Open No. 2009-141328, error sensitivity for an environmental change in temperature or humidity is high and a measurement error due to an offset or a gain change is likely to occur. In addition, because there is also a possibility of a measurement error occurring due to changes over time of an adhesive to be used when the strain gauge or the like is attached, it is difficult to maintain stable precision.

On the other hand, as disclosed in the publication of Japanese Patent No. 4573873, it is possible to correct a mold to a desired shape by measuring a plurality of marks at the time of alignment even when a sensor measurement error occurs. However, because it is difficult to correct the shape of the mold according to a command when the correction is affected by the sensor measurement error, the number of iterations of measurement increases until the residual converges and there is a possibility of the degradation of throughput.

SUMMARY OF THE INVENTION

The present invention, for example, provides an imprint apparatus that is useful for changing a mold to a desired shape at a high precision and a high speed.

According to the present invention, an imprint apparatus for forming a pattern of an imprint material on a substrate using a mold includes a mold holding unit configured to hold the mold; a correction mechanism configured to correct a shape of a pattern formed in the mold to a desired shape by applying a force to the mold held in the mold holding unit; and a controller configured to assume a plurality of mold pattern shapes for a specific mold, calculate a parameter for associating the plurality of assumed mold pattern shapes and a deformation amount of the specific mold by causing the correction mechanism to apply the force to the specific mold to obtain the deformation amount of the specific mold so that the plurality of assumed mold pattern shapes are formed, and calibrate the correction mechanism using the parameter.

DESCRIPTION OF THE EMBODIMENTS

First, an imprint apparatus according to the first embodiment of the present invention will be described.FIG. 1is a schematic diagram illustrating a configuration of the imprint apparatus100according to the embodiment of the present invention. The imprint apparatus100is used to manufacture a semiconductor device or the like serving as an article, molds an uncured resin (imprint material) coated on a wafer7(on a substrate) and a mold2by bringing the uncured resin and the mold2in contact with each other, and forms a pattern of a resin on the wafer7. Also, the imprint apparatus100, for example, is assumed to adopt a photocuring method. In addition, in the following drawings, a Z axis is defined as an upward/downward direction (vertical direction) and X and Y axes orthogonal to each other within a plane perpendicular to the Z axis are defined. The imprint apparatus100includes an illumination system1, a mold holding mechanism3, a wafer stage8, a coating unit10, an alignment measuring unit11, and a controller14.

The illumination system1is a resin curing means for adjusting ultraviolet light emitted from a light source (not illustrated) to light suitable for curing the resin and radiating the light to the mold2. The light source is not limited to the ultraviolet light and it is only necessary that it emit light of a wavelength which is transmitted through the mold2and at which the resin is cured. Also, for example, when the thermosetting method is adopted, a heating means for curing a thermosetting resin is installed in the vicinity of the wafer stage8as a resin curing means in place of the illumination system1.

The mold2is a mold in which a plane shape is a rectangle and which has a concave-convex pattern (pattern region)21such as a circuit pattern three-dimensionally formed in the center of a surface opposed to the wafer7. The material of the mold2is a material such as quartz capable of transmitting ultraviolet light. The surface of the concave-convex pattern21is processed at a high degree of flatness. In addition, the mold2has a plurality of alignment marks22in a perimeter region of the concave-convex pattern21(seeFIG. 2). Plane coordinates of each of the plurality of alignment marks22are measured in advance and saved as coordinate data including a drawing error when a mark is formed, for example, in a storage apparatus included in the controller14, within the imprint apparatus100.

The mold holding mechanism (mold holding unit)3has a mold chuck4for holding the mold2, a mold driving mechanism (not illustrated) for supporting and moving the mold chuck4, and a shape correction mechanism5capable of deforming the concave-convex pattern21(mold2). The mold chuck (mold base)4holds the mold2by attracting an outer circumferential region of an irradiation surface of the ultraviolet light in the mold2according to a vacuum suction force or electrostatic force. In addition, the mold chuck4and the mold driving mechanism have an opening region in a center (inner side) so that the ultraviolet light radiated from the illumination system1is transmitted through the mold2and directed to the wafer7. The mold driving mechanism moves the mold2in a Z-axis direction to selectively bring the mold2and the resin on the wafer7in contact with each other or separate them from each other. Also, the contact or separation operation at the time of an imprint process may be implemented by moving the mold2in the Z-axis direction. In addition, the contact or separation operation may be implemented by driving the wafer stage8and moving the wafer7in the Z-axis direction or both the mold2and the wafer7may be relatively moved. The shape correction mechanism (correction mechanism)5corrects the shape of the concave-convex pattern21to a desired shape by applying a force (external force or compressive force) to the mold2held in the mold chuck4and changing the shape of the mold2.

FIG. 2is a schematic plan view illustrating a configuration of the shape correction mechanism5when viewed from a negative side of the Z-axis direction (the side of the wafer stage8). The shape correction mechanism5has a plurality of driving units30opposed to any of side surfaces (surfaces (XZ surfaces or YZ surfaces) perpendicular to the XY surface in which the concave-convex pattern21is formed) of four directions of the mold2and disposed to surround the entire side surface corresponding to an outer circumferential portion of the mold2. Also, in the shape correction mechanism5illustrated inFIG. 2, for example, four driving units30are assumed to be disposed for each side surface (one side) of one direction of the mold2. Each driving unit30is supported by the mold chuck4and includes an actuator for generating a compressive force to the side surface of the mold2and a sensor (detector)6for measuring the compressive force applied to the side surface of the mold2. As the actuator, a piezoelectric actuator having a small heating value and excellent responsiveness can be adopted. The driving unit30has a driving stroke necessary to generate a desired compressive force and a driving stroke including a predetermined idle running distance in which a non-contact state is provided for the mold2. The sensor6is a force sensor such as a load cell or a strain gauge individually continuously provided in each of a plurality of driving units30. Also, as the sensor6, a non-contact displacement sensor supported by the mold chuck4may be designated as another compressive force measuring means and detect a relative position of the side surface of the mold2may be provided.

The wafer7, for example, is a processed substrate including single crystal silicon. Also, when the substrate is used to manufacture an article other than a semiconductor device, for example, optical glass such as quartz can be adopted as the material of the substrate if an optical element is manufactured and GaN, SiC, or the like can be adopted as the material of the substrate if a light-emitting element is manufactured.

The wafer stage (substrate holding unit)8is capable of moving within the XY plane while holding the wafer7and performs position alignment of the mold2and the wafer7when in contact with the mold2and the resin on the wafer7. In addition, the wafer stage8has a reference mark9for aligning the mold2and the wafer stage8.

FIG. 3is a schematic plan view illustrating shapes and installation positions of the wafer stage8and the reference mark9when viewed from a positive side of the Z-axis direction (the side of the mold holding mechanism3). A plurality of reference marks9are provided to be symmetrical with respect to a plurality of alignment marks22(seeFIG. 2) installed (formed) in the mold2. In addition, plane coordinates of each of the plurality of reference marks9are measured in advance and saved as coordinate data including a drawing error at the mark formation time, for example, in a storage apparatus included in the controller14, within the imprint apparatus100.

The coating unit (dispenser)10coats an uncured resin in a desired coating pattern on a shot region (pattern formation region) preset on the wafer7. The resin serving as the imprint material has mobility when filled between the mold2and the wafer7and a solid for maintaining a shape after molding is required. In particular, in this embodiment, the resin is an ultraviolet curable resin (photocurable resin) having a property of being cured by receiving ultraviolet light, but a thermosetting resin, a thermoplastic resin, or the like can be used in place of the photocurable resin according to various types of conditions such as article manufacturing processes.

The alignment measuring unit11includes a measurement light source12for use in a wavelength band in which no resin is cured such as a He—Ne laser, a detector13such as a charge coupled device (CCD) camera, and an optical element (not illustrated). The alignment measuring unit11radiates measurement light in a state in which the alignment mark22and the alignment mark on the wafer7overlap when the concave-convex pattern21and the base layer (base pattern) formed in advance on the wafer7are superimposed and the detector13detects an interference fringe. Thereby, the alignment measuring unit11can measure relative positions of the alignment mark22of the mold2and the alignment mark of the wafer7. Likewise, the alignment measuring unit11can detect the alignment mark22of the mold2and the reference mark9installed on the wafer stage8. Further, based on a detection result, it is possible to measure relative positions of the alignment mark22(mold2) and the reference mark9(wafer stage8).

The controller14, for example, includes a computer or the like, is connected to each component of the imprint apparatus100via a line, and can control an operation, adjustment, or the like of each component according to a program or the like. In particular, in this embodiment, the controller14can perform control related to calibration of the shape correction mechanism5as follows. Also, the controller14may be configured to be integrated with another part of the imprint apparatus100(within a common housing) or configured to be separated from another part of the imprint apparatus100(within a separate housing).

Next, shape correction of the concave-convex pattern21formed in the mold2will be described. First, the controller14superimposes the alignment mark of the base layer formed in advance on the wafer7and the alignment mark22of the mold2and causes the alignment measuring unit11to measure mutually relative positions of the marks. Here, a relation between alignment precision and a measurement time becomes the trade-off according to the number of alignment marks22to be measured. Therefore, the controller14selects the alignment mark22to be measured from among a plurality of alignment marks22according to use conditions of the imprint apparatus100. Next, the controller14calculates a shape error of the concave-convex pattern21from information related to the relative positions obtained by the alignment measurement and obtains a shape correction amount decomposed into a shape component such as magnification, skew, a trapezoid, a bow shape, or a spool shape. In this manner, it is possible to obtain a shape difference between a pattern region of the mold2and an imprint region formed in the wafer7from a result of detecting the alignment mark. Next, the controller14derives a compressive force input to each driving unit30by applying the obtained shape correction amount to Formula (1) and performs shape correction by adding the derived compressive force to a target value (compressive force or displacement) of a control system of each driving unit30.

However, a matrix [r] is a deformation amount (shape correction amount) including elements of n shape components. A matrix [f] is a target value (compressive force) for a feedback control system of each driving unit30including m elements corresponding to the number of axes of the driving unit30. In addition, a matrix [A] is a matrix which includes m×n elements and determines a target value [f] from a deformation amount [r].

Here, the matrix [A] is a parameter determined according to the shape of the mold2, Young's modulus and Poisson's ratio of the material, a friction force at the time of suction holding of the mold2, etc., and is obtained through simulation in advance. Specifically, first, the controller14obtains the deformation amount [r] of the concave-convex pattern21when the compressive force corresponding to the target value [f] is applied to the side surface of the mold2using a known technique such as finite element analysis (FEA). Next, the controller14iterates this process while sequentially changing a plurality of types of compressive forces (target values [f]) assumed in advance. Then, the controller14calculates the matrix [A] using a least squares method or the like from elements {[r]} of a matrix of a deformation amount obtained through the simulation and elements {[f] } of a matrix of a plurality of types of target values assumed in advance. Also, Formula (1) corresponds to simultaneous linear equations, but the order may be increased by further developing Formula (1) to precisely perform shape correction.

Then, the controller14can finally perform desired superimposition by iteratively performing alignment measurement and shape correction until a shape error converges in an allowed range.

Next, initial calibration will be described as a method of calibrating the shape correction mechanism5. The matrix [A] in the above-described Formula (1) is obtained through the simulation, and thus there is a possibility of occurrence of an error if the matrix [A] is directly applied to the shape correction mechanism5. This error results from a dimension error of the mold2, a processing/assembly error of the shape correction mechanism5, a measurement error of the sensor6, or the like. Therefore, in this embodiment, initial calibration of the shape correction mechanism5is performed as described below to implement more precise shape correction.

FIG. 4is a flowchart illustrating a flow of an initial calibration process of the shape correction mechanism5. First, when the controller14starts the initial calibration process, a mold (calibration mold) to be used to perform calibration different from the mold (production mold) to be used in actual production is set as the mold2and installed in the mold holding mechanism3(setting process: step S101). It is desirable that the calibration mold be constantly provided within the imprint apparatus100and the calibration mold be appropriately automatically conveyed with the mold holding mechanism3based on a conveyance command from the controller14.

Next, the controller14calibrates an offset error of the sensor6(step S102). Each driving unit30included in the shape correction mechanism5is movable by a given stroke in a non-contact state with the mold2. Therefore, here, the controller14first drives the driving unit30until all the driving units30are in the non-contact state. In this non-contact state, the mold2is held in only an absorption force by the mold chuck4and the compressive force for the side surface of the mold2is not generated. Accordingly, at this time, it is desirable that the measured value of each sensor6be zero or match a predetermined reference value. Based on this, the controller14designates the measured value of each sensor6or a difference from the reference value as an offset error and processes a result obtained by adding the offset error to an actually measured value (output value) as a measured value. Also, the information related to the offset error is saved, for example, in the storage apparatus included in the controller14, within the imprint apparatus100.

Next, the controller14moves the wafer stage8to the measurement position for performing alignment measurement in the following step S105by superimposing the alignment mark22of the mold2and the reference mark9installed on the wafer stage8(step S103). In addition, the controller14lowers the mold chuck4so that the alignment mark22and the reference mark9are close to the mold driving mechanism. Also, in order to perform initial calibration in a state close to a state of an actual imprint process, a resin or a fluid other than a resin may be coated on the reference mark9in advance.

Next, the controller14inputs elements {[f]} of a matrix of a predetermined desired target value (driving command) to each driving unit30and deforms the concave-convex pattern21of the mold2(step S104).

Next, the controller14causes the alignment measuring unit11to perform alignment measurement and calculates the shape of the concave-convex pattern21of the mold2, that is, elements {[r]} of a matrix of an actual deformation amount of the concave-convex pattern21, based on a measurement result (deformation amount derivation process: step S105).

Next, the controller14determines whether the elements {[r]} of the matrix of the actual deformation amount are obtained for the elements {[f]} of the matrix of all the target values (step S106). Here, when it is determined that the elements {[r]} are not obtained (No), the controller14iterates the process of steps S104and S105. On the other hand, the controller14proceeds to the following step S107when the elements {[r]} are obtained (Yes).

Then, the controller14calculates a matrix [A′] for associating the elements {[r] } of the matrix of the actual deformation amount and the elements {[f]} of the matrix of the target values (calculation process: step S107). Here, the matrix [A′] is calculated using a least squares method as in the case in which the matrix [A] in Formula (1) is obtained.

Hereinafter, when the calibration mold is used, it is only necessary for the controller14to perform shape correction using Formula (2) to which the matrix [A′] obtained in step S107is applied as a calibration process.

In this manner, when the calibration of the shape correction mechanism5in the imprint apparatus100is performed, the matrix [A′] which is a parameter obtained using the calibration mold is used. Therefore, because it is only necessary to use a parameter obtained in advance while installing the calibration mold at the time of subsequent calibration, it is possible to perform calibration at a high speed without having to obtain a parameter for calibration again. In addition, the parameter for use in the calibration is not obtained by simulation, but is obtained by actual measurement. Accordingly, for example, it is possible to perform highly precise calibration because a parameter reflecting the measurement error is used even when a measurement error occurs in the sensor6.

As described above, according to this embodiment, it is possible to provide an imprint apparatus and an imprint method that are useful for stably changing the concave-convex pattern formed in the mold to a desired shape at a high precision and a high speed.

Next, the imprint apparatus according to the second embodiment of the present invention will be described. In the first embodiment, an example in which initial calibration is particularly performed in relation to calibration of the shape correction mechanism5was shown. Meanwhile, the imprint apparatus according to this embodiment is characterized in that the imprint apparatus can be applied to calibration for changes with time, that is, the case in which the calibration is performed at a desired time interval in relation to a calibration method of the shape correction mechanism5. Also, because each component of the imprint apparatus according to this embodiment is the same as each component of the imprint apparatus100according to the first embodiment, the same reference signs are assigned to the same components and description thereof will be omitted.

A main factor of the changes with time of the shape correction mechanism5includes a measurement error of the sensor6. The measurement error of the sensor6is classified into a linearity error and an offset error. In particular, when a function of the linearity error is generated, a high-order approximation function may be used. However, for simplification of description, only a linear gain error will be mentioned.

Here, a matrix [f′ ] which is an actual compression amount for a matrix [f] of a target value of each driving unit calculated using the above-described Formula (1) is expressed by Formula (3).

However, a matrix [gain] is a gain error of each sensor6including m elements. In addition, a matrix [ofs] is an offset error of each sensor6including m elements.

FIG. 5is a flowchart illustrating a flow of a calibration process for changes with time of the shape correction mechanism5. Also, because the process of steps S201to S206after the calibration process for the changes with time inFIG. 5starts is the same as the process of steps S101to S106inFIG. 4illustrating an initial calibration process described in the first embodiment, description thereof will be omitted.

After completion of step S206, the controller14obtains a gain correction coefficient as a second parameter (step S207). At this time, the controller14obtains the elements {[f′]} of a matrix of a target value of each driving unit30by substituting the elements {[r′]} of a matrix of an actual deformation amount obtained in alignment measurement in step S205into the above-described Formula (2). Here, the matrix [A′] serving as the parameter in Formula (2) becomes an invariable parameter by using the alignment mark22of the same mold2and the reference mark9of the wafer stage8. Thus, a coefficient for which a ratio between the element {[f′]} and the element {[f]} is 1 becomes a gain correction coefficient of the sensor6. Also, if another mold2is used when the gain correction coefficient is obtained, the gain correction coefficient is calculated as a value including a difference of the matrix [A′]. As a result, improvement of the same degree is obtained for precision of the shape correction, but there is no improvement for the other mold2. Accordingly, calibration is performed using the same mold2as described above, and it is desirable that two parameters, that is, the matrix [A′ ] and the gain correction coefficient of the sensor6, be separately managed. In addition, because the gain correction coefficient obtained here is strictly a coefficient including an error factor of a transfer mechanism or the like present in the driving unit30, the gain correction coefficient is also referred to as a gain correction coefficient in the entire driving unit30.

Also, when the gain error serving as the linearity error is calibrated, the number of elements of the shape (shape pattern) {[r] } of the concave-convex pattern21is sufficient when there are several elements. In particular, it is desirable to use a combination of shape patterns in which measured values of the sensor6are significantly different. In addition, when a high-order linearity error is calibrated, it is only necessary to calculate each coefficient using a least squares method or the like by increasing the number of elements of the shape {[r] } of the concave-convex pattern21and applying a relation between the element {[f′ ] } and the element {[f] } of the matrix of the target value to a high-order approximation function.

Hereinafter, the controller14can calibrate the measured value of the sensor6if the gain correction coefficient obtained in step S207is multiplied by the measured value of the sensor6.

As described above, according to this embodiment, similar effects to the first embodiment are exhibited and calibration precision can be stably maintained, in particular, even when an error due to changes with time related to the sensor6occurs.

Also, in the above description, the calibration mold is assumed to be prepared separately from a production mold. However, the calibration mold is not limited to a dedicated mold for calibration as described above. For example, if the initial calibration described in the first embodiment is performed using a specific production mold, a specific production mold may be reused by regarding the specific production mold as a calibration mold at a subsequent calibration time. In this case, because an installation process of the calibration mold in step S201is unnecessary, a calibration time can be shortened.

In addition, calibration may be performed, for example, after predicting a time at which precision is degraded from an actual value of calibration, as a time at which calibration for changes with time can be performed, the calibration may be performed at the beginning of a production lot, or the calibration may be performed at the timing at which the mold2is replaced. Further, one shape of the concave-convex pattern21in which a measurement error of the sensor6is predicted to be significantly shown may be measured by only an alignment mark of several points, production may continue when the error is within an allowed range of values, and calibration may be configured to be performed when the error exceeds the allowed range of values. In this case, because the calibration time is shortened, it is possible to minimize the degradation of throughput even when a process of checking whether a gain error is within an allowed range of values every time wafer processing is performed is added to the calibration process. In addition, because the calibration time is short for calibration of the offset error, the calibration of the offset error may be frequently performed separately from the calibration of the gain error. For example, the calibration may be performed in parallel with wafer replacement or performed in parallel with coating (supplying) of a resin by the coating unit10between shot regions.

Next, the imprint apparatus according to the third embodiment of the present invention will be described. The imprint apparatus according to this embodiment is characterized in that the mold2serving as the production mold is calibrated using the shape correction mechanism5. Also, because each component of the imprint apparatus according to this embodiment is the same as each component of the imprint apparatus100according to the first embodiment, the same reference signs are assigned to the same components and description thereof will be omitted.

FIG. 6is a flowchart illustrating a flow of a calibration process of a production mold. First, the controller14installs the calibration mold as the mold2in the mold holding mechanism3(step S301). Next, the controller14performs calibration of the shape correction mechanism5along the flow of the flowchart ofFIG. 5described in the second embodiment using the calibration mold (step S302). Next, the controller14transports the calibration mold from the mold holding mechanism3and continuously installs the production mold as the mold2(step S303). Then, the controller14can perform the calibration of the production mold by obtaining the matrix [A′] along the flow of the flowchart ofFIG. 4described in the first embodiment using the production mold and updating Formula (2) (step S304).

Also, it is desirable to calibrate the production mold for every type of the mold2and manage the matrix [A′] serving as the obtained calibration value in association with the mold2serving as a calibration target. In addition, the gain correction coefficient and the offset correction value of the shape correction mechanism5are managed separately from the matrix [A′] of the correction parameter due to the mold, so that the matrix [A′] becomes an invariable parameter and it is not necessary to perform calibration thereafter. In addition, even when the shape correction mechanism5is replaced, it is possible to maintain calibration precision without depending upon the mold2only by performing the calibration described in the second embodiment.

A method for manufacturing a device (semiconductor integrated circuit element, liquid display element, or the like) as an article may include a step of forming a pattern on a substrate (wafer, glass plate, film-like substrate, or the like) using the imprint apparatus described above. Furthermore, the manufacturing method may include a step of etching the substrate on which a pattern has been formed. When other articles such as a patterned medium (storage medium), an optical element, or the like are manufactured, the manufacturing method may include another step of processing the substrate on which a pattern has been formed instead of the etching step. The device manufacturing method of the present embodiment has an advantage, as compared with a conventional method, in at least one of performance, quality, productivity and production cost of an article.

This application claims the benefit of Japanese Patent Application No. 2014-235282 filed Nov. 20, 2014, which is hereby incorporated by reference herein in its entirety.