JP4534376B2 - Exposure mask manufacturing method and exposure mask - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exposure mask manufacturing method and an exposure mask, and more particularly, to an inspection exposure mask manufacturing method for detecting a shift of a focus position of an exposure apparatus used when forming a fine pattern by lithography, and thereby The present invention relates to the formed exposure mask.
[0002]
[Prior art]
An exposure apparatus used in a lithography process in a semiconductor device manufacturing process is configured by using a plurality of lenses A to D as shown in FIG. 8A, and an exposure pattern 103 formed on an exposure mask 101 is a substrate. 105 is projected onto the screen. For this reason, as shown in FIG. 8B, even if one of them (the lens C in the figure) is slightly deviated from the original position, the focus position is deviated, thereby causing the pattern 107 on the substrate 105 to be deviated. Deviation occurs in the formation position and line width of the. Therefore, in the lithography process, it is necessary to routinely manage the focus of the exposure apparatus.
[0003]
As the focus management of the exposure apparatus, an adjustment for focusing on one mark engraved on the stage of the exposure apparatus is routinely performed. However, there is a step on the wafer surface where exposure is actually performed, and such an adjustment method cannot be adjusted in consideration of this step. Therefore, apart from such daily management, management is performed in which an actual pattern is formed by performing a lithography process, and the focus position is adjusted based on the line width and positional deviation amount of the actual pattern. In this case, a dedicated exposure mask is used to perform multiple exposures with the focus position shifted, and then a development process is performed to form an actual pattern for inspection, and the focus on the line width and positional deviation amount of this actual pattern. A curve is created, and focus adjustment is performed based on the obtained focus curve.
[0004]
In recent years, attention has been paid to an inspection method in which inspection exposure using a phase shift mask is performed, and a shift amount of a focus position is detected from a shift amount of a pattern obtained thereby. This method uses the phenomenon that when the phase shift amount is other than nπ, the optical image becomes asymmetric due to defocus and the pattern image moves in the horizontal direction, and the amount of positional deviation of the formed pattern is measured. Thus, the shift amount of the focus position is detected.
[0005]
[Problems to be solved by the invention]
However, in the focus management described above, the method of detecting the amount of shift of the focus position from the focus curve requires many exposures with the focus position shifted every time inspection is performed, which is very laborious. In addition, since the production line is stopped during this period, it is difficult to say that the method is suitable for daily management, and the current state is that it is periodically performed once a week. In this case, a focus shift may be noticed only after the product is completed, and a large number of defective products may remain at hand.
[0006]
On the other hand, in the method of performing inspection exposure using a phase shift mask, the amount of pattern displacement does not necessarily change depending on the focus position. For example, in US Pat. No. 5,300,78, the amount of focus shift is determined from the amount of pattern position shift by using an exposure mask having a phase shift amount of 40 ° to 140 °. The amount of focus shift cannot be accurately detected with any phase shift amount within the range of the phase shift amount.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide an inspection exposure mask manufacturing method and an exposure mask capable of detecting the focus position of an exposure apparatus with ease and accuracy.
[0008]
[Means for Solving the Problems]
An exposure mask manufacturing method of the present invention for achieving such an object is a method of manufacturing a phase shift type inspection exposure mask used when inspecting a focus position of exposure light in an exposure apparatus. It is characterized by being performed. That is, first, a pattern exposure simulation is performed using the phase shift amount and the focus position of the exposure light as factors, and the pattern displacement amount obtained by the simulation is obtained. The focus position and the displacement amount are obtained for each phase shift amount. Detect the relationship with. After that, based on this relationship, a phase shift amount in which the positional shift amount changes depending on the focus position within a range of the phase shift amount shift due to a manufacturing error at the time of manufacturing an exposure mask is selected. Then, an exposure pattern for inspection is formed by applying the selected phase shift amount. The present invention is also an exposure mask obtained by such a manufacturing method.
[0009]
In the above-described exposure mask manufacturing method, a phase shift amount that can be found to be dependent on the pattern displacement amount with respect to the focus position of the exposure light is selected based on the simulation result of the pattern exposure. At this time, a phase shift amount having a margin for manufacturing errors is selected. Therefore, in this exposure mask manufactured by applying the selected phase shift amount, even if the phase shift amount is deviated from the design value due to a manufacturing error in exposure mask manufacturing, this exposure mask is used. The focus position at the time of pattern exposure can be detected from the amount of positional deviation of the pattern subjected to pattern exposure.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The exposure mask manufacturing method described here is used to detect the focus position of an exposure apparatus when adjusting the focus of the exposure apparatus in a lithography process for forming a fine pattern such as a semiconductor device. It is a method of manufacturing an exposure mask. In the following embodiment, a method of forming a phase shift type exposure mask for use in inspection of an exposure apparatus will be described based on the flowchart shown in FIG. 1 and referring to other drawings as necessary.
[0011]
Step S1
First, in step S1, a pattern exposure simulation is performed using the phase shift amount of the exposure mask and the focus position of the exposure light as factors. Here, the target line width of the pattern formed by lithography is set, and various exposure conditions for pattern exposure, such as the numerical aperture (NA) of the exposure apparatus, numerical aperture ratio (σ), exposure wavelength (λ), exposure A simulation is performed in which the transmittance of the oblique light film in the mask is set in the same manner as the actual pattern exposure.
[0012]
At this time, for example, as shown in FIG. 2, the oblique film pattern 2 is formed on the glass substrate 1, and one glass substrate 1 in the width direction of the light shielding film pattern 2 is engraved to a predetermined depth d. An exposure mask 3 is set. The phase shift amount of the exposure light passing through the exposure mask 3 is changed in a wide range (for example, a range of 70 ° to 180 °) by setting the engraving depth d. The focus position is changed within a predetermined range of plus or minus (for example, ± 0.3 μm), with the optimum focus position being 0 μm. Although the phase shift amount may be changed to 180 ° or more, it is preferable to change the phase shift amount within a range of 180 ° or less in consideration of the manufacturing process of the exposure mask, and to select the phase shift amount from this range later.
[0013]
In addition to the above, in this simulation, as an example, the numerical aperture (NA) = 0.6, the numerical aperture ratio (σ) = 0.53, the exposure wavelength (λ) = 248 nm of the exposure apparatus, and the oblique film pattern For pattern 2, chromium (Cr) having a light transmittance of 0 is used, and pattern exposure is set in which the central portion of the exposure light source is blocked (1 / 2annular).
[0014]
Step S2
Next, with respect to each pattern obtained as a result of the simulation in step S1, the positional deviation amount of the formation position is obtained, and a focus curve of the positional deviation amount obtained by plotting the positional deviation amount with respect to the focus position is created. This focus curve is created for each phase shift amount (70 °, 80 °,...) As shown in FIG. It is assumed that the pattern displacement amount (Image Placement Error) with respect to the focus position (Focus) is the displacement amount with respect to the design position.
[0015]
Step S3
On the other hand, the line width of each pattern obtained as a result of the simulation in step S1 is obtained, and a focus curve having a line width obtained by plotting the line width with respect to the focus position is created. This focus curve is created for each phase shift amount (70 °, 80 °,...) As shown in FIG.
[0016]
Step S4
Next, based on the focus curve of the position shift amount for each phase shift amount obtained in step S2, the position shift amount depends on the focus position within the range of the phase shift amount shift due to the manufacturing error when manufacturing the exposure mask. Select the amount of phase shift that changes. For example, when the shift in the phase shift amount due to the manufacturing error is about the target phase shift amount ± 5 °, the phase shift amount changes most greatly depending on the focus position within the range of the manufacturing error of the phase shift amount. Select the range of shift amount.
[0017]
Here, it is confirmed from the focus curve in FIG. 3 that the change in the amount of positional deviation with respect to the focus position becomes the largest in the range of the phase shift amount of 70 ° to 80 °. select.
[0018]
Step S5
Next, based on the focus curve of the line width for each phase shift amount obtained in step S3, the fluctuation of the line width in the vicinity of the optimum value of the focus position within the range of the phase shift amount selected in the fourth step is allowed. It is determined whether or not there is. Here, the allowable state indicates a value in which the amount of change in the line width is smaller and the line width in the range of the selected phase shift amount is closer in the vicinity of the optimum value (0) of the focus position in the focus curve. Suppose that it is a state.
[0019]
In order to make this determination, for example, an allowable value of the change amount of the line width and an allowable value of the shift amount of the line width in the variation range of the shift amount are set, and the range of the phase shift amount selected in step S4 is It is determined whether or not it is in an allowable state depending on whether or not these allowable values are satisfied. And when it is judged that it is not an allowable state (No), it progresses to step S6. On the other hand, if it is determined that it is in an allowable state (Yes), the process proceeds to step S7. Since the focus curve of the line width at the phase shift amount of 180 ° has a maximum value at the focus position of 0 °, the determination in step S5 is the behavior of the change of the line width near the optimum value (0) of the focus position. However, it may be determined by how close to the behavior of the phase shift amount 180 °.
[0020]
Step S6
On the other hand, if it is determined in step S5 that the state is not an allowable state (No), the phase shift amount range (for example, 70 ° to 80 °) selected in the previous step S4 is not selected again. Thus, the setting for limiting the selection range is performed, and the process returns to step S4 again.
[0021]
In step S4, a phase shift amount range different from the previous one is selected, and step S4, step S5, and step S7 are repeated until it is determined in step S5 that the variation in line width is smaller than a predetermined value. Here, for example, the phase shift amount range of 90 ° to 100 ° is selected as the optimum phase shift amount range, and the process proceeds to step S7.
[0022]
Note that the method of selecting the phase shift amount here is not limited to the procedure shown in Step 4, Step S5, and Step S7, but within the range of the phase shift amount deviation due to the manufacturing error in manufacturing the exposure mask. The position shift amount changes depending on the focus position, and the change amount of the line width is smaller near the optimum value (0) of the focus position, and the line width in the range of the selected phase shift amount is closer. The range of the phase shift amount that indicates is sufficient to be selected.
[0023]
Step S7
After selecting the optimum phase shift amount range as described above, an exposure mask is produced using the median value (95 °) of the phase shift amount range as a design value.
[0024]
The exposure mask produced in this way has a phase shift amount that can find the dependence of the pattern displacement amount on the focus position of the exposure light based on the simulation result of the pattern exposure.
[0025]
That is, when the phase shift amount of 95 ° is set as the design value, there is a possibility that an exposure mask having a phase shift amount in the range of 90 ° to 100 ° is manufactured due to the manufacturing error of the exposure mask. However, in the embodiment described above, the phase shift amount is selected in advance with a margin for this variation (manufacturing error). Since an exposure mask is produced using the selected phase shift amount as a design value (using the median value of the range of the phase shift amount as a design value), even if the phase shift amount varies due to manufacturing errors at this time, this exposure mask is used. Thus, it becomes possible to reliably detect the focus position at the time of pattern exposure from the amount of positional deviation of the pattern formed by pattern exposure using.
[0026]
Hereinafter, the management of the exposure apparatus using the exposure mask manufactured as described above will be described. Here, first, preparation for focus management in the exposure apparatus will be described using the flowchart of FIG. 5, and then routine focus management of the exposure apparatus will be described using the flowchart of FIG.
[0027]
Step S11
First, an actual pattern is formed on a substrate by performing pattern exposure using the exposure mask produced as described above and subsequent development processing. In this pattern exposure, exposure is performed a plurality of times using a focus position as a factor using an exposure apparatus that performs inspection, and a plurality of actual patterns corresponding to each exposure are formed. Note that the lithography conditions here are set in the same manner as in the simulation in step S1.
[0028]
Step S12
Next, the positional deviation amount with respect to the design position is measured for the plurality of actual patterns formed in step S11.
[0029]
Step S13
Next, as shown in FIG. 6, a focus curve for the positional deviation amount is created from the measured positional deviation amount and the focus position at the time of pattern exposure in step S11. This focus curve is used as a reference focus curve.
[0030]
The above steps S11 to S13 are performed as preparations for managing the exposure apparatus. Then, the exposure apparatus is managed as follows using the reference focus curve created in this preparation (see FIG. 7).
[0031]
Step S21
First, inspection exposure using an exposure mask is performed, and further development processing is performed to form an actual pattern for inspection. Here, using an exposure apparatus that performs inspection, pattern exposure is performed once in a state where the focus position seems to be optimal, thereby forming an actual pattern. Note that the lithography conditions here are set in the same manner as in the simulation in step S1.
[0032]
Step S22
Next, with respect to the actual pattern formed in step S21, the amount of displacement with respect to the design position is measured.
[0033]
Step S23
Next, the positional deviation amount measured in step S22 is collated with the reference focus curve (FIG. 6) created in step S13, and the focus position is detected from this positional deviation amount.
[0034]
Step S24
Thereafter, the height and tilt of the stage are adjusted based on the detected shift amount of the focus position so that the focus position of the exposure apparatus becomes an optimum value (focus 0), and it contributes to other focus position fluctuations. Adjust the factors.
[0035]
According to the above inspection method, since the actual pattern for inspection is formed by pattern exposure using the exposure mask produced by the above-described method, the amount of misalignment of the actual pattern can be used for pattern exposure. The focus position can be reliably detected. Since this misalignment amount occurs in the same manner throughout the entire exposure surface, the focus position within the exposure surface can be detected by measuring this misalignment amount. At this time, if the focus curve (FIG. 6) of the positional deviation amount is created once, the focus position can be detected by only one exposure and development without creating the focus curve every time. Therefore, it can be applied to daily focus management without difficulty, and the frequency of focus management can be increased as compared with the conventional method in which a focus curve is created each time management is performed.
[0036]
As a result, it is possible to cause a risk that a large number of defective products are manufactured without noticing the shift of the focus position, and it is possible to improve the yield productivity.
[0037]
【The invention's effect】
As described above, according to the exposure mask manufacturing method and the exposure mask of the present invention, the exposure mask is manufactured by using a phase shift amount in consideration of tolerance for manufacturing errors in advance. It is possible to reliably detect the focus position of the exposure apparatus used for pattern exposure from the amount of positional deviation of the pattern formed by the pattern exposure.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a method for manufacturing an exposure mask.
FIG. 2 is a cross-sectional view of a phase shift type exposure mask.
FIG. 3 is a focus curve of a positional deviation amount of a pattern obtained from a simulation result.
FIG. 4 is a focus curve of a line width of a pattern obtained from a simulation result.
FIG. 5 is a flowchart for explaining the creation of a reference focus curve using the produced exposure mask.
FIG. 6 is a reference focus curve related to the amount of pattern displacement.
7 is a flowchart for explaining focus management using the focus curve of FIG. 6;
FIG. 8 is a block diagram of an exposure apparatus used in a lithography process in a semiconductor device manufacturing process.
[Explanation of symbols]
3. Exposure mask

Claims (4)

A method of manufacturing a phase shift type inspection exposure mask used when inspecting a focus position of exposure light in an exposure apparatus,
Perform pattern exposure simulation with phase shift amount and exposure light focus position as factors,
Obtain the amount of positional deviation of the pattern obtained by the simulation,
Based on the relationship between the focus position and the positional deviation amount for each phase shift amount, the positional deviation amount depends on the focus position within the range of the phase shift amount deviation due to a manufacturing error when manufacturing an exposure mask. Select the amount of phase shift to change,
An exposure mask manufacturing method, wherein an inspection exposure mask is manufactured by applying the selected phase shift amount. In the manufacturing method of the exposure mask of Claim 1,
Obtain the line width of the pattern obtained by the simulation,
When selecting the phase shift amount, the exposure mask manufacturing method is characterized in that a phase shift amount with a smaller variation in the line width is selected in the vicinity of the optimum value of the focus position. A phase shift type inspection exposure mask used when inspecting a focus position of exposure light in an exposure apparatus,
Perform pattern exposure simulation with phase shift amount and exposure light focus position as factors,
Obtain the amount of positional deviation of the pattern obtained by the simulation,
Based on the relationship between the focus position and the positional deviation amount for each phase shift amount, the positional deviation amount depends on the focus position within the range of the phase shift amount deviation due to a manufacturing error when manufacturing an exposure mask. An exposure mask characterized in that a changing phase shift amount is selected. The exposure mask according to claim 3.
The exposure mask characterized in that the phase shift amount is selected such that the variation in the line width of the pattern obtained by exposure becomes smaller near the optimum value of the focus position of the exposure light.

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