JP2008070730A - Mask blanks selection method, calculation method for birefringence index, lithographic method, mask blanks selecting device, birefringence index calculation device and program therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress dimensional fluctuation of a transfer pattern within an allowable range and to improve the yield of products and the throughput. <P>SOLUTION: A birefringence index calculation device 11 calculates distribution of RBI as an index representing changes in the polarization state between incident light entering a photomask and exiting light exiting from the photomask, originating from the incident light. Then a selection device 21 selects a mask blanks based on the distribution of the calculated RBI and on the allowable value of dimensional fluctuation in a pattern transferred onto a photoresist film formed on a wafer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mask blank selection method, a birefringence index calculation method, a lithography method, a mask blank selection apparatus, a birefringence index calculation apparatus, and a program thereof, and more specifically, a mask pattern is formed so as to correspond to a design pattern. A mask blank selection method for selecting a mask blank on which a photomask is formed, a birefringence index calculation method, a mask blank selection apparatus, a lithography method, a birefringence index calculation apparatus, and a birefringence index RBI distribution are calculated. Related to the program.

  In manufacturing a semiconductor device, a fine pattern is processed using a lithography technique.

  Here, for example, after a photoresist film made of a photosensitive material is formed on the surface of the wafer on which pattern processing is performed, a photomask on which a mask pattern is formed so as to correspond to the design pattern is illuminated, and the illumination is caused by the illumination. The mask pattern image is exposed and transferred to a photoresist film formed on the wafer. Thereafter, the photoresist pattern on which the transfer pattern is formed by transferring the mask pattern image is developed to form a resist pattern on the surface of the wafer. Then, patterning is performed by performing an etching process using the resist pattern as a mask.

  In the lithography technique, it is required to finely process a pattern with higher resolution in order to meet the demand for higher integration of devices and higher operation speed. As shown in the following formula (A), the resolution R is determined by the wavelength λ of the exposure light irradiated from the light source to the photomask, and the numerical aperture of the projection lens that projects the mask pattern image of the photomask onto the resist film. It is determined by the Rayleigh equation defined by NA. Here, k is a constant and is determined according to the manufacturing process.

  R = k · λ / NA (A)

  As shown in the mathematical formula (A), the resolution R increases as the wavelength λ of the exposure light from the light source is shorter and the numerical aperture NA of the projection lens is larger. For this reason, the resolution R is improved by shortening the wavelength λ of the exposure light and increasing the numerical aperture NA of the projection lens.

  For example, with regard to the light source, the KrF excimer laser having a wavelength of 248 nm is shifted to an ArF excimer laser having a wavelength of 193 nm, thereby improving the resolution.

  On the other hand, the numerical aperture NA of the projection lens is approaching 1 which is the theoretical limit. For this reason, an immersion exposure method has been proposed in which the space between the projection lens and the photoresist film is filled with a liquid such as pure water to increase the effective numerical aperture NA (see, for example, Patent Document 1).

  That is, the numerical aperture NA is expressed by the following formula (B) by the refractive index n of the medium through which the light passes and the angle θ formed by the light. 1. The medium in the space between the projection lens through which the lens passes and the resist film is replaced with air having a refractive index n of 1, for example, by pure water having a refractive index n of 1.44, thereby increasing 1.44 times. The numerical aperture NA is realized, and the resolution R can be improved.

  NA = n × sin θ (B)

  In order to cope with an increase in the degree of contrast degradation due to the polarization state as the numerical aperture NA increases, a method of using polarized illumination as illumination for illuminating a photomask has been proposed (for example, Patent Document 2, Non-Patent Document 1).

  This is because the effect of vector imaging expands from conventional scalar imaging as the numerical aperture NA increases. This is because when line-and-space is exposed in vector imaging, only the component parallel to the pattern contributes to imaging in the electric field vector of exposure light, and the other components reduce contrast. Because it will let you. For this reason, in particular, in the so-called Hyper-NA region where the numerical aperture NA exceeds 1, it has become essential to adjust the polarization state of the exposure light and use the adjusted polarized illumination.

JP 2005-57278 A Japanese Patent Laid-Open No. 2005-5521 D. Flagello et al. , “Challenges with Hyper-NA (NA> 1.0) Polarized Light Lithography for Sub λ / 4 resolution”, Proc. SPIE, vol. 5754, 53 (2004)

  However, when performing a lithography process using polarized illumination as described above, the polarization component of the polarized illumination may be deteriorated by an optical element, so the dimension of the processed pattern is not the reference dimension. Variations may occur. That is, a CD (Critical Dimension) may be formed with a value outside the allowable range.

  This defect occurs, for example, because the refractive index of the medium is different in the vibration direction of the electric field of light. That is, it is mainly caused by the occurrence of the birefringence phenomenon. This is partly because, for example, thermal stress in the manufacturing process and mechanical stress when holding the element are unevenly distributed in an optical element such as a mask blank. For example, in the case of a birefringence of 5 nm / cm, a dimensional error of a transfer pattern of 2 nm may occur. When a synthetic quartz is used as a glass material in a mask blank, the birefringence is about 10 to 20 nm / cm. In some cases, the above-mentioned problems become apparent.

  As described above, since variations in pattern dimensions after processing may exceed the allowable range, the product yield may be reduced, and it may be difficult to improve the throughput.

  Therefore, the present invention provides a mask blanks selection method, a birefringence index calculation method, a lithography method, and a mask blanks selection device that can suppress variations in the dimensions of transfer patterns within an allowable range, improve product yield, and improve throughput. Another object of the present invention is to provide a program for calculating the distribution of the birefringence index RBI and the birefringence index RBI.

In order to solve the above problems, a mask blank selection method of the present invention is a mask blank selection method for selecting a mask blank on which a photomask is manufactured by forming a mask pattern so as to correspond to a design pattern. , A birefringence measuring step for measuring the distribution of the birefringence B and the azimuth angle θ when the incident light incident on the photomask is birefringent, and the polarization state of the incident light incident on the photomask The incident light polarization state measuring step, the outgoing light polarization state calculating step for calculating the distribution of the polarization state of the outgoing light emitted from the photomask, and the outgoing light being transferred to the photoresist film. A transfer pattern dimension calculating step for calculating a distribution of a transfer pattern dimension, and the birefringence measured in the birefringence measuring step; And RBI calculation step for calculating the distribution of the birefringence index RBI represented by the following equation (1) by the azimuth angle θ, the transfer pattern size distribution calculated in the transfer pattern size calculation step, and the RBI calculation step. And a selection step of calculating a correlation between the variation of the transfer pattern dimension and the RBI based on the calculated distribution of the RBI and selecting the mask blanks based on the correlation.
RBI = B | sin (2θ) | (1)

In order to solve the above-described problem, the birefringence index calculation method of the present invention provides a birefringence index RBI in a mask blank in which a photomask is manufactured by forming a mask pattern corresponding to a design pattern. A birefringence index calculating method for calculating a distribution, a birefringence measuring step for measuring a distribution of a birefringence index B and an azimuth angle θ when incident light incident on the photomask is birefringent; An RBI calculating step of calculating a distribution of RBI which is a birefringence index represented by the following formula (1) defined by the birefringence index B and the azimuth angle θ measured in the birefringence measuring step. It is characterized by that.
RBI = B | sin (2θ) | (1)

In order to solve the above problems, a lithography method according to the present invention selects a mask blank on which a photomask is manufactured by forming a mask pattern so as to correspond to a design pattern, and applies the mask pattern to the mask blank. Forming the photomask, exposing and transferring a transfer pattern onto a photoresist film formed on the wafer by the photomask, developing the photoresist film to which the transfer pattern has been transferred, and developing the photoresist; A lithography method for performing an etching process using a film as a mask, a birefringence measuring step for measuring a distribution of a birefringence index B and an azimuth angle θ when incident light incident on the photomask is birefringent, An incident light polarization state measuring step for measuring a polarization state of the incident light incident on the photomask; and An exit light polarization state calculation step for calculating a polarization state distribution of the exit light emitted from the photomask by the incident light, and a size distribution of a transfer pattern transferred to the photoresist film by the exit light. A transfer pattern dimension calculating step, and an RBI calculating step of calculating a distribution of a birefringence index RBI represented by the following formula (1) based on the birefringence index B and the azimuth angle θ measured in the birefringence measuring step. Based on the distribution of the transfer pattern dimension calculated in the transfer pattern dimension calculation step and the distribution of the RBI calculated in the RBI calculation step, the correlation between the variation of the transfer pattern dimension and the RBI is calculated, and the correlation A selection step for selecting the mask blanks based on the relationship, and the mask blank selected by the mask blank selection step. The mask pattern is exposed to the photoresist film formed on the wafer by the photomask forming step of drawing the mask pattern on the nux and forming the photomask, and the photomask formed by the photomask forming step And a pattern exposure step.
RBI = B | sin (2θ) | (1)

In order to solve the above problems, a mask blank selection device of the present invention is a mask blank selection device that selects a mask blank on which a photomask is manufactured by forming a mask pattern so as to correspond to a design pattern. A birefringence measurement data acquisition unit for measuring the distribution of the birefringence B and the azimuth angle θ when the incident light incident on the photomask is birefringent, and the polarization state of the incident light incident on the photomask Incident light polarization state measurement data acquisition unit for measuring the incident light polarization state calculation unit for calculating the polarization state distribution of the emitted light emitted from the photomask, and the photoresist film by the emitted light Measured by a transfer pattern size calculation unit that calculates the distribution of the size of the transfer pattern transferred to the surface and the birefringence measurement data acquisition unit RBI calculation unit for calculating the distribution of the birefringence index RBI represented by the following formula (1) by the birefringence index B and the azimuth angle θ, and the transfer pattern dimension calculated by the transfer pattern dimension calculation unit A selection unit configured to calculate a correlation between the variation of the transfer pattern size and the RBI based on the distribution and the distribution of the RBI calculated by the RBI calculation unit, and to select the mask blanks based on the correlation; It is characterized by that.
RBI = B | sin (2θ) | (1)

In order to solve the above-described problem, the birefringence index calculating apparatus according to the present invention distributes the birefringence index RBI in a mask blank in which a photomask is manufactured by forming a mask pattern corresponding to a design pattern. A birefringence index calculating device for calculating a birefringence measurement data acquisition unit for measuring a distribution of a birefringence index B and an azimuth angle θ when incident light incident on the photomask is birefringent; An RBI calculating unit that calculates a distribution of RBI that is a birefringence index represented by the following formula (1) defined by the birefringence index B and the azimuth angle θ measured by the birefringence measurement data acquisition unit; It is characterized by having.
RBI = B | sin (2θ) | (1)

In order to solve the above problems, the program of the present invention causes a computer to calculate the distribution of the birefringence index RBI in a mask blank in which a photomask is manufactured by forming a mask pattern corresponding to a design pattern. A birefringence measurement data acquisition unit for measuring a distribution of a birefringence index B and an azimuth angle θ when incident light incident on the photomask is birefringent, and the birefringence measurement data acquisition unit The computer functions as each of the RBI calculation unit that calculates the distribution of RBI that is a birefringence index represented by the following formula (1) defined by the birefringence index B and the azimuth angle θ measured by It is characterized by making it.
RBI = B | sin (2θ) | (1)

  In the present invention, the distribution of RBI, which is a birefringence index, is an index indicating the change in the polarization state of incident light incident on a photomask and the polarization state of outgoing light after the incident light has passed through the photomask. To do. Then, mask blanks are selected based on the calculated RBI distribution.

  According to the present invention, a mask blank selection method and birefringence index calculation capable of improving the product yield and improving the throughput by selecting the mask blank so as to suppress the variation in the dimension of the transfer pattern within an allowable range. A method, a lithography method, a mask blank selection apparatus, a birefringence index calculation apparatus, and a program for calculating the distribution of the birefringence index RBI can be provided.

  Embodiments according to the present invention will be described.

  FIG. 1 is a block diagram of a mask blank selection apparatus according to an embodiment of the present invention.

  The mask blank selection device 1 is configured to include a computer and a memory that stores a program that causes the computer to execute a predetermined operation. Further, the mask blank selection device 1 selects a mask blank on which a photomask is manufactured by forming a mask pattern so as to correspond to the design pattern. In the present embodiment, the mask blank selection device 1 stores a program memory that causes a computer to execute as each of the birefringence index calculation device 11 and the mask blank selection device 21 as shown in FIG. . Each part will be described sequentially.

  The birefringence index calculating device 11 will be described.

  The birefringence index calculating device 11 calculates a birefringence index indicating changes in the polarization state of incident light incident on the photomask and the polarization state of outgoing light transmitted through the photomask.

  In the present embodiment, the birefringence index calculation device 11 includes a birefringence measurement data acquisition unit 111, an incident light polarization state measurement data acquisition unit 112, an outgoing light polarization state calculation unit 113, and a transfer pattern dimension calculation unit. 114 and an RBI calculation unit 115, and a memory stores a program for causing the computer to execute in each unit.

  Each part will be described.

  The birefringence measurement data acquisition unit 111 acquires data measured as described later for the distribution of the birefringence B and the azimuth angle θ when the incident light is birefringent in the photomask into which the incident light is incident. Remember.

  The incident light polarization state measurement data acquisition unit 112 acquires and stores data measured as described later regarding the polarization state distribution of incident light incident on the photomask.

  The outgoing light polarization state calculation unit 113 calculates and stores data as will be described later regarding the distribution of the polarization state of outgoing light emitted from the photomask on which incident light is incident.

  The transfer pattern dimension calculation unit 114 will be described later with respect to a distribution of CD (Critical Dimension), which is the dimension of the transfer pattern transferred to the photoresist film formed on the wafer by the emitted light emitted from the photomask on which the incident light is incident. Calculate and store as follows.

  The RBI calculation unit 115 calculates the distribution of RBI that is a birefringence index of the photomask defined by the birefringence index B and the azimuth angle θ in the photomask measured and stored by the birefringence measurement data acquisition unit 111. And remember.

  Next, the selection device 21 will be described.

  The selection device 21 calculates the CD variation (CD-Range) based on the distribution of the CD calculated by the transfer pattern dimension calculation unit 114 and the distribution of the RBI calculated by the RBI calculation unit 115, and allows the CD to be allowed. Mask blanks are selected based on the variation.

  In the present embodiment, the selection device 21 includes a correlation calculation unit 211, an RBI upper limit calculation unit 212, and a mask blank specification selection unit 213, and a memory stores a program that causes a computer to be executed in each unit. . Each part will be described.

  The correlation calculation unit 211 calculates a first correlation which is a correlation between the CD and the RBI which is a birefringence index in the photomask on the photoresist film formed on the wafer calculated by the transfer pattern dimension calculation unit 114. Then, based on the calculated first correlation, a second correlation that is a correlation between the CD variation and the RBI is calculated. Here, the CD variation corresponds to the CD difference at the same RBI value.

  The RBI upper limit calculation unit 212 calculates the upper limit value of the RBI for the allowable CD variation based on the second correlation between the CD variation calculated by the correlation calculation unit 211 and the RBI.

  The mask blank specification selection unit 213 selects a mask blank specification based on the RBI upper limit value calculated by the RBI upper limit calculation unit 212.

  Hereinafter, an operation when the mask blank selection device 1 according to the present embodiment selects a mask blank will be described.

  FIG. 2 is a flowchart showing a main part of the operation of the mask blank selection device according to the embodiment of the present invention.

  As shown in FIG. 2, first, a distribution of a birefringence index, which is an index indicating changes in the polarization state of incident light and the polarization state of outgoing light, is calculated (S11).

  Here, the birefringence index calculating device 11 calculates RBI, which is an index indicating the birefringence of the photomask.

  FIG. 3 shows a birefringence index that is an index indicating a change in the polarization state of incident light incident on the photomask according to an embodiment of the present invention and the polarization state of the emitted light emitted from the photomask. It is a flowchart at the time of calculating.

In order to calculate the birefringence index, first, as shown in FIG. 3, the birefringence of the photomask is measured (S111).
Here, the distribution of the birefringence B and the azimuth angle θ when the incident light is birefringent is measured in the photomask on which the incident light is incident. For example, this measurement is performed using an Exicor system manufactured by HINDS.

  Then, the birefringence measurement data acquisition unit 111 acquires data measured for the distribution of the birefringence B and the azimuth angle θ when the incident light is birefringent in the photomask on which the incident light is incident. And remember.

FIG. 4 is a diagram showing an example of the distribution of the birefringence B and the azimuth angle θ measured in the photomask. A frame in FIG. 4 represents a photomask.
4A shows the distribution of the birefringence B in the photomask, and FIG. 4B shows the distribution of the azimuth angle θ in the photomask. The direction of the arrow in FIG. 4B indicates the azimuth angle θ of each point in the photomask. For example, when the arrow is parallel to the X axis and facing right in FIG. 4, θ = 0 ° and the Y axis 4 and upward in FIG. 4, θ = 90 °.

Next, as shown in FIG. 3, the polarization state of incident light is measured (S121).
Here, as the polarization state of incident light incident on the photomask, the ellipticity, the azimuth angle, and the degree of polarization (DOP: Degree of Polarization) are measured, and the incident light polarization state measurement data acquisition unit 112 sets the Stokes parameters. Seek and remember.

  In the present embodiment, for example, an ellipticity of 0.18, an azimuth angle of 90 °, and a polarization degree of 0.95 were measured, and a Stokes parameter was calculated as shown in the following formula (1). Note that a Stokes parameter such as Equation (1) can be regarded as a kind of vector. This is called a Stokes vector.

Next, as shown in FIG. 3, the distribution of the polarization state of the emitted light is calculated (S131).
Here, the outgoing light polarization state calculation unit 113 calculates the distribution of the polarization state of the outgoing light emitted from the photomask on which the incident light is incident.

  Specifically, the distribution of the polarization state of the outgoing light is calculated using the data of the birefringence distribution in the photomask calculated as described above and the polarization state of the incident light. Here, after obtaining the birefringence distribution in the photomask so as to correspond to the Mueller matrix M as shown in the following formula (2), it is obtained from the Mueller matrix M and the Stokes parameters of the incident light. The distribution of the polarization state of the emitted light is obtained by calculating the product of the Stokes vector to be obtained. For example, when the birefringence B at a certain point in the photomask is 14.87 nm / cm and the azimuth is 135.69 °, the Mueller matrix M as shown in Equation (2). Therefore, by multiplying this Mueller matrix M by the Stokes parameter of the incident light calculated as shown in Equation (1), the polarization state of the emitted light is changed as shown in Equation (3) below. Calculated as Stokes parameter.

  For this reason, it was calculated from the result of the equation (3) that the polarization state of the outgoing light transmitted through the photomask has an ellipticity of 0.32, an azimuth angle of 89.87 °, and a polarization degree of 0.95.

Next, as shown in FIG. 3, the distribution of dimensions of the transfer pattern transferred to the photoresist film is calculated (S141).
Here, based on the distribution of the polarization state of the outgoing light calculated by the outgoing light polarization state calculation unit 113 as described above, the transfer pattern transferred on the photoresist film when incident light enters the photomask. The transfer pattern dimension calculation unit 114 calculates the distribution. For example, the distribution of the CD is calculated by performing a lithography simulation in consideration of the polarization state of the emitted light after passing through the photomask. For example, KLA-Tencor's Prolith ver. The distribution of CD is calculated using 9.0.
FIG. 5 is a diagram showing an example of the distribution of CD calculated at each point where the birefringence B in the photomask is measured.

  Specifically, as described above, when the birefringence B at a certain point in the photomask is 14.87 nm / cm and the azimuth angle θ is 135.69 °, the ellipticity is 0.18, the azimuth The incident light having an angle of 90 ° and a degree of polarization of 0.95 was transmitted through the photomask after being transmitted through the photomask, and was in a polarization state having an ellipticity of 0.32, an azimuth angle of 89.87 °, and a degree of polarization of 0.95. By performing lithography simulation under transfer conditions as shown in Table 1 below as an argument, a line pattern extending in the y direction with a width of 65 nm is repeated in the x direction via a space with a width of 65 nm. The CD is calculated when a 1: 1 line and space (L / S) pattern is used as a mask pattern.

  As a result of the transfer, the post-transfer CD was calculated to be 66 nm. The CD distribution is calculated by sequentially performing this process at each point where the birefringence B in the photomask is measured.

  The CD shown in FIG. 5 deviates from the pattern dimension of 65 nm in the vicinity of the corner in the photomask and from 65 nm near the corner in the direction of 45 degrees with respect to the X axis from the center of the photomask. It is deviated to the higher side, and deviated to the lower side of 65 nm near the corner in the direction of 135 degrees with respect to the X axis. From this, it can be seen that DC in the vicinity of the corner in the photomask deviates from the design pattern.

Next, as shown in FIG. 3, the distribution of RBI, which is a birefringence index in the photomask, is calculated (S151).
Here, the distribution of RBI, which is an index indicating the birefringence of the photomask, is calculated from the birefringence B and the azimuth angle θ of the photomask measured and stored by the birefringence measurement data acquisition unit 111.
FIG. 6 is a diagram showing an example of the distribution of RBI calculated at each point where the birefringence index B in the photomask is measured.

  Specifically, RBI defined by the equation (4) is calculated as an index indicating birefringence from the birefringence B and the azimuth angle θ in the photomask. Here, B is a birefringence (nm / cm), and θ is an azimuth angle.

In the present embodiment, the RBI was calculated to be 14.86 as shown below from the birefringence index B and the azimuth angle θ at a certain point in the photomask described above.
RBI = 14.87 × | sin (2 × 135.69 °) | = 14.86
This process is sequentially performed at each point where the birefringence B in the photomask is measured. The result is shown in FIG.

  As described above, in the present embodiment, the birefringence B and the azimuth angle θ in the photomask are measured, and the RBI distribution is calculated from the measured birefringence B and the azimuth angle θ. Further, the polarization state of the incident light incident on the photomask is measured, and the polarization state of the outgoing light emitted from the photomask is calculated from the birefringence distribution in the photomask and the polarization state of the incident light incident on the photomask. Then, the CD distribution is calculated from the polarization state of the emitted light emitted from the photomask.

After calculating the CD distribution and the RBI distribution as described above, mask blanks are selected as shown in FIG. 2 (S21).
Here, mask blanks are selected based on the correlation between the CD calculated by the transfer pattern dimension calculation unit 114 and the RBI calculated by the RBI calculation unit 115.
FIG. 7 is a flowchart when selecting mask blanks according to an embodiment of the present invention.
FIG. 8 is a diagram showing a graph in which CD and RBI according to an embodiment of the present invention are plotted. Here, the CD difference at the same RBI value corresponds to the CD variation in FIG.
FIG. 9 is a diagram illustrating an example of a graph plotting CD variation and RBI according to an embodiment of the present invention.

When selecting mask blanks, as shown in FIG. 7, the correlation between CD and RBI is calculated (S211).
Here, the correlation calculation unit 211 obtains a first correlation which is a correlation between the distribution of the CD calculated by the transfer pattern dimension calculation unit 114 in the photomask and the distribution of the RBI calculated by the RBI calculation unit 115. calculate. Then, based on the calculated first correlation, the correlation calculation unit 211 calculates a second correlation that is a correlation between the CD variation and the RBI.

  Specifically, based on the CD distribution calculated by the transfer pattern dimension calculation unit 114 shown in FIG. 5 and the RBI distribution calculated by the RBI calculation unit 115 shown in FIG. Thus, a graph in which CD and RBI are plotted is calculated, and the first correlation is calculated. Then, based on the calculated first correlation, a graph in which CD and RBI are plotted as shown in FIG. 9 is calculated, and a second correlation is calculated.

Next, as shown in FIG. 7, the upper limit value of RBI is calculated (S221).
Here, based on the CD variation, the RBI upper limit value calculation unit 212 calculates the maximum RBI that gives an allowable value of the CD variation.

  In the present embodiment, when the allowable value of CD variation due to the birefringence is 1 nm, RBI is calculated to be 10 nm / cm from FIG. This value (10 nm / cm) is the maximum RBI.

Next, as shown in FIG. 7, the specification of mask blanks is selected (S231).
Here, a mask blank specification for forming a photomask is selected by the mask blank specification selection unit 213 based on the maximum RBI that gives an allowable value of CD variation calculated as described above.

  In the present embodiment, since the maximum RBI at which the CD variation is 1 nm is calculated as 10 nm / cm, the RBI at which the RBI in the mask blanks is less than 10 nm / cm is selected.

Thereafter, mask blanks are selected based on the specifications of the selected mask blanks.
Here, mask blanks exhibiting the selected RBI are selected.

  As described above, the present embodiment calculates the relationship between CD variation and RBI, and calculates the maximum RBI that gives an allowable value of CD variation from the calculated relationship. Then, by selecting a mask blank that exhibits less than the calculated maximum RBI, it is not necessary to select a mask blank that severely restricts CD variation more than necessary, and a mask blank that provides desired CD variation can be selected. Therefore, the cost can be reduced.

  In the following, the operation during lithography according to the present embodiment will be described.

FIG. 10 is a flowchart for forming a transfer pattern on a wafer by lithography according to an embodiment of the present invention.
Steps S11 and S21 in the operation during lithography are the same as steps S11 and S21 in the operation when selecting mask blanks. Therefore, description is abbreviate | omitted about the location which overlaps.

As shown in FIG. 10, first, a birefringence index, which is an index indicating changes in the polarization state of incident light and the polarization state of outgoing light, is calculated (S11).
Next, mask blanks are selected (S21).

Next, as shown in FIG. 10, a photomask is formed (S31).
Here, a photomask is formed by drawing a design pattern on the mask blank selected in the selection step (S21).

  For example, a photomask is formed by drawing a pattern on the mask blank by an electron beam drawing apparatus that draws a design pattern by scanning the mask blank with an electron beam or a laser drawing apparatus that draws a design pattern by scanning the laser beam.

Next, as shown in FIG. 10, the transfer pattern is exposed (S41).
Here, the transfer pattern is exposed to the photoresist film formed on the wafer by the photomask formed in the photomask forming process.

  For example, a photomask on which a mask pattern is drawn is illuminated, and a mask pattern image generated by the illumination is exposed and transferred to a photoresist film formed on the wafer.

Next, as shown in FIG. 10, the transfer pattern is developed (S51).
Here, the transfer pattern is developed on the photoresist film formed on the wafer.

  For example, a photoresist film to which the transfer pattern is transferred is developed by a developing device such as a spin developer to form a transfer pattern on the surface of the wafer.

Next, as shown in FIG. 10, etching is performed (S61).
Here, an etching process is performed using the transferred pattern developed on the photoresist film as a mask to form a transferred pattern.

  For example, an etching process such as dry etching or wet etching is performed using a transfer pattern developed on a photoresist film as a mask, and a pattern is formed on a processing layer stacked on the wafer.

  According to the above lithography method, it is not necessary to select mask blanks that restrict transfer pattern dimension variation more strictly than necessary, and mask blanks that provide desired transfer pattern dimension variations can be selected. A semiconductor device in which a dimension of a pattern formed in the semiconductor device is within an allowable range can be manufactured by using a photomask formed of blanks.

  In implementing the present invention, the present invention is not limited to the above-described embodiment, and various modifications can be employed.

For example, in the above description, the case where the transfer pattern dimension is calculated using the lithography simulation has been described. However, the present invention is not limited to this. For example, data obtained by actually performing exposure and actually measuring the dimensions of a transfer pattern formed by performing the exposure may be used.
In the step S11 of calculating the birefringence index in the above-described embodiment, the step S151 of calculating the RBI that is the birefringence index in the photomask is the last step in the step S11 of calculating the birefringence index. However, the present invention is not limited to this, and may be performed anytime after step S111 for measuring the birefringence of the photomask.

FIG. 1 is a block diagram of a mask blank selection apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing a main part of the operation of the mask blank selection device according to the embodiment of the present invention. FIG. 3 is a flowchart for calculating a birefringence index, which is an index indicating changes in the polarization state of incident light incident on the photomask and the polarization state of outgoing light transmitted through the photomask according to an embodiment of the present invention. FIG. FIG. 4 is a diagram showing an example of the distribution of the birefringence B and the azimuth angle θ measured in the photomask. FIG. 5 is a diagram showing an example of the distribution of CD calculated at each point where the birefringence B in the photomask is measured. FIG. 6 is a diagram showing an example of the distribution of RBI calculated at each point where the birefringence index B in the photomask is measured. FIG. 7 is a flowchart when selecting mask blanks according to an embodiment of the present invention. FIG. 8 is a diagram illustrating an example of a graph in which CD and RBI according to an embodiment of the present invention are plotted. FIG. 9 is a diagram illustrating an example of a graph in which CD variation and RBI according to an embodiment of the present invention are plotted. FIG. 10 is a flowchart for forming a transfer pattern on a wafer by lithography according to an embodiment of the present invention.

Explanation of symbols

1: mask blanks selection device, 11: birefringence index calculation device, 21: mask blanks selection device, 111: birefringence measurement data acquisition unit, 112: incident light polarization state measurement data acquisition unit, 113: outgoing light polarization state Calculation unit 114: Transfer pattern dimension calculation unit 115: RBI calculation unit 211: Correlation calculation unit 212: RBI upper limit calculation unit 213: Mask blank specification selection unit

Claims (7)

A mask blank selection method for selecting a mask blank on which a photomask is manufactured by forming a mask pattern corresponding to a design pattern,
A birefringence measuring step of measuring the distribution of the birefringence index B and the azimuth angle θ when the incident light incident on the photomask is birefringent;
An incident light polarization state measuring step for measuring a polarization state of the incident light incident on the photomask;
An incident light polarization state calculating step for calculating a polarization state distribution of the emitted light emitted from the photomask by the incident light; and
A transfer pattern dimension calculating step for calculating a distribution of dimensions of a transfer pattern transferred to the photoresist film by the emitted light;
An RBI calculating step of calculating a distribution of a birefringence index RBI represented by the following formula (1) based on the birefringence index B and the azimuth angle θ measured in the birefringence measuring step;
Based on the distribution of the transfer pattern dimension calculated in the transfer pattern dimension calculation step and the distribution of the RBI calculated in the RBI calculation step, the correlation between the variation of the transfer pattern dimension and the RBI is calculated, and the correlation And a selection step of selecting the mask blanks based on the method.
RBI = B | sin (2θ) | (1) The selection process includes
A first correlation between the distribution of transfer pattern dimensions calculated in the transfer pattern dimension calculation step and the distribution of RBI calculated in the RBI calculation step is calculated, and the transfer is performed based on the first correlation. A correlation calculating step of calculating a second correlation between variation in pattern dimensions and the RBI;
An RBI upper limit value calculating step of calculating an upper limit value of the RBI based on the second correlation;
A mask blank specification selecting step for selecting a mask blank specification based on the upper limit value of the RBI calculated in the RBI upper limit value calculating step;
The mask blank selection method according to claim 1, wherein mask blanks are selected based on specifications of the mask blanks. A birefringence index calculating method for calculating a distribution of birefringence index RBI in a mask blank in which a photomask is manufactured by forming a mask pattern corresponding to a design pattern,
A birefringence measuring step of measuring the distribution of the birefringence index B and the azimuth angle θ when the incident light incident on the photomask is birefringent;
An RBI calculating step of calculating a distribution of RBI that is a birefringence index represented by the following formula (1) defined by the birefringence index B and the azimuth angle θ measured in the birefringence measuring step. A birefringence index calculation method characterized by the above.
RBI = B | sin (2θ) | (1) A mask blank on which a photomask is manufactured by selecting a mask pattern corresponding to a design pattern is selected, the mask pattern is formed on the mask blank, the photomask is manufactured, and a wafer is formed using the photomask. A lithography method in which a transfer pattern is exposed and transferred to a photoresist film formed on the photoresist film, the photoresist film to which the transfer pattern is transferred is developed, and an etching process is performed using the photoresist film as a mask,
A birefringence measuring step of measuring the distribution of the birefringence index B and the azimuth angle θ when the incident light incident on the photomask is birefringent;
An incident light polarization state measuring step for measuring a polarization state of the incident light incident on the photomask;
An incident light polarization state calculating step for calculating a polarization state distribution of the emitted light emitted from the photomask by the incident light; and
A transfer pattern dimension calculating step for calculating a distribution of dimensions of a transfer pattern transferred to the photoresist film by the emitted light;
An RBI calculating step of calculating a distribution of a birefringence index RBI represented by the following formula (1) based on the birefringence index B and the azimuth angle θ measured in the birefringence measuring step;
Based on the transfer pattern dimension distribution calculated in the transfer pattern dimension calculation step and the RBI distribution calculated in the RBI calculation step, a correlation between the variation of the transfer pattern dimension and the RBI is calculated, and the correlation A selection step of selecting the mask blanks based on:
A photomask forming step of drawing the mask pattern on the mask blank selected by the mask blank selection step to form the photomask;
And a pattern exposure step of exposing the mask pattern to the photoresist film formed on the wafer by the photomask formed by the photomask formation step.
RBI = B | sin (2θ) | (1) A mask blank selection device for selecting a mask blank on which a photomask is manufactured by forming a mask pattern corresponding to a design pattern,
A birefringence measurement data acquisition unit for measuring the distribution of the birefringence B and the azimuth angle θ when the incident light incident on the photomask is birefringent;
An incident light polarization state measurement data acquisition unit for measuring a polarization state of the incident light incident on the photomask;
An outgoing light polarization state calculation unit for calculating a distribution of a polarization state of the outgoing light from which the incident light is emitted from the photomask;
A transfer pattern dimension calculation unit for calculating a distribution of dimensions of a transfer pattern transferred to the photoresist film by the emitted light;
An RBI calculation unit that calculates a distribution of the birefringence index RBI represented by the following formula (1) based on the birefringence index B and the azimuth angle θ measured by the birefringence measurement data acquisition unit;
Based on the transfer pattern dimension distribution calculated by the transfer pattern dimension calculation unit and the RBI distribution calculated by the RBI calculation unit, the correlation between the transfer pattern dimension variation and the RBI is calculated, and the correlation A mask blanks selection device comprising: a selection unit that selects the mask blanks based on
RBI = B | sin (2θ) | (1) A birefringence index calculating device that calculates a distribution of birefringence index RBI in a mask blank in which a photomask is manufactured by forming a mask pattern so as to correspond to a design pattern,
A birefringence measurement data acquisition unit for measuring the distribution of the birefringence B and the azimuth angle θ when the incident light incident on the photomask is birefringent;
An RBI calculating unit that calculates a distribution of RBI that is a birefringence index represented by the following formula (1) defined by the birefringence index B and the azimuth angle θ measured by the birefringence measurement data acquisition unit; A birefringence index calculating apparatus characterized by comprising:
RBI = B | sin (2θ) | (1) A program for causing a computer to calculate a distribution of birefringence index RBI in a mask blank in which a photomask is manufactured by forming a mask pattern corresponding to a design pattern,
A birefringence measurement data acquisition unit for measuring the distribution of the birefringence B and the azimuth angle θ when the incident light incident on the photomask is birefringent;
An RBI calculating unit that calculates a distribution of RBI that is a birefringence index represented by the following formula (1) defined by the birefringence index B and the azimuth angle θ measured by the birefringence measurement data acquisition unit; Each of the programs causes the computer to function.
RBI = B | sin (2θ) | (1)