JP2006303175A - Method for defining illumination brightness distribution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimally set an illumination brightness distribution on an aligner, and to prevent rework, due to difference in illumination brightness distribution, to contribute to the enhancement of development efficiency and further, the enhancement of accuracy of estimation of the light exposure margin and the depth of focus in lithography, and the like. <P>SOLUTION: A method is for defining an illumination brightness distribution on an illumination light source surface in an aligner so designed that light from the illumination light source surface is guided to the mask pattern on a photomask to form the image of the mask pattern on a substrate surface. The method includes dividing an illumination light source surface into multiple illumination elements, computing an image formed on the substrate surface, with respect to each divided illumination element, selecting an illumination element, based on the performance of the computed image to obtain a design illumination luminance distribution, computing the lithographic performance of the photomask pattern image, formed on the substrate surface using a deformed illumination luminance distribution, and comparing the computed lithographic performance with a preset threshold of lithographic performance, to determine the allowable range of fluctuations in the amount of deformation of illumination brightness distribution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for setting optical conditions of an exposure apparatus for manufacturing a semiconductor element, a liquid crystal display element, and the like, and more particularly to a method for defining an illumination luminance distribution for optimally defining a luminance distribution on an illumination light source surface.

  In recent years, the progress of semiconductor manufacturing technology is very remarkable, and semiconductor elements having a minimum processing dimension of 0.13 μm are mass-produced. Such miniaturization is realized by dramatic progress in fine pattern formation techniques such as a mask process technique, an optical lithography technique, and an etching technique.

  When the pattern size is sufficiently large, the planar shape of the LSI pattern to be formed on the wafer is directly drawn as a design pattern, and a mask pattern faithful to the design pattern is created. Then, this mask pattern was transferred onto the wafer by a projection exposure apparatus, and the base was etched, so that a pattern almost as designed could be formed on the wafer. However, as pattern miniaturization progresses, it has become difficult to faithfully form a pattern in each process, and a problem has arisen that the final finished dimension does not match the design pattern.

  In such a situation, an error caused by the projection exposure apparatus used for transferring the pattern is also a major cause of distorting the finished shape of the pattern. In recent years, due to the aberration of the projection lens of the exposure apparatus, it has been regarded as a problem that the pattern transferred on the wafer may have a dimensional error or misalignment, and the projection lens aberration can be reduced without disassembling the exposure apparatus. A method of measuring has been proposed.

  On the other hand, it has been clarified that the coherence factor (σ) representing the effective size of the illumination optical system varies in dimensions within the exposure region due to variations in shape and light intensity within the exposure region. When the shape and light intensity of the coherence factor vary within the exposure area, the light intensity and direction that illuminate the reticle vary depending on the location. Here, since σ is a parameter that governs the contrast of the image, the above fluctuation of σ means a fluctuation of the exposure performance within the batch exposure region.

  In order to cope with this problem, a technique for inspecting and adjusting the σ of the exposure apparatus without disassembling the projection exposure apparatus has been proposed (see, for example, Patent Documents 1 to 3). In order to prevent the yield reduction of the most advanced devices, to perform precise evaluation of the illumination optical system of the projection exposure system, and to enable precise measurement of aberrations by combining the illumination optical system and the projection optical system These technologies are essential.

  Using the technique for measuring the illumination luminance distribution of the projection exposure apparatus described above, a method for modeling the function by describing the illumination luminance distribution using an analytical function and fitting the measured value of the illumination luminance distribution is proposed. Yes. However, this modeling method is a technique that is realized only when there is an exposure apparatus to be used and there is experimental data of illumination luminance distribution. On the other hand, from the viewpoint of technological development, development always starts one to two years before the device generation, and there may be a case where there is no exposure apparatus for transferring patterns in the early stages of development. .

Further, when product patterning is performed after device development is started, the lateral development of the exposure apparatus (changing the exposure apparatus that performs patterning according to the processing capability of the exposure apparatus and the product scale) is performed. There is. An exposure apparatus (referred to as exposure apparatus A) that first performs product processing at the present time acquires a dimensional characteristic curve (referred to as characteristic curve A) of the test pattern, and then performs exposure processing (referred to as exposure apparatus B). The illumination luminance distribution is adjusted so that the dimensional characteristic curve A is reproduced. In this case, since the dimensional characteristic curve is acquired again after the exposure apparatus B is adjusted, there is a problem that it takes time for patterning and dimension measurement necessary for curve acquisition.
JP 2000-21732 A JP 2002-33269 A JP 2004-72114 A

  As described above, in the conventional method, it is difficult to accurately predict the illumination luminance distribution of the exposure apparatus at the initial stage of device development, an error occurs with respect to the actual illumination luminance distribution, and the need for rework due to the difference in the illumination luminance distribution. As a result, there was a problem that the efficiency of development was reduced. Furthermore, there has been a problem that the exposure accuracy margin of lithography and the prediction accuracy of the focal depth are lowered due to the influence of the dimensional deviation due to the error of the illumination luminance distribution.

  The present invention has been made in consideration of the above circumstances, and the object of the present invention is to optimally set the illumination luminance distribution of the exposure apparatus and prevent rework due to the difference in the illumination luminance distribution, thereby improving development efficiency. Another object of the present invention is to provide a method for defining an illumination luminance distribution that can contribute to improvement, further improvement of lithography exposure dose margin and focus depth prediction accuracy, and the like.

  In order to solve the above problems, the present invention adopts the following configuration.

  That is, one embodiment of the present invention is an exposure apparatus that forms an image by guiding light from an illumination light source surface to a mask pattern on a photomask and guiding light emitted from the photomask to a substrate surface through an optical system. On the other hand, a method for defining an illumination luminance distribution on an illumination light source surface, the step of dividing the illumination light source surface into a plurality of illumination elements, and when the mask pattern is illuminated to each of the divided illumination elements Calculating an image formed on the substrate surface, selecting the illumination element based on the calculated performance of the image to obtain a designed illumination luminance distribution, deforming the illumination luminance distribution, The step of calculating the lithography performance of the mask pattern image formed on the substrate surface using the deformed illumination luminance distribution and the threshold of the lithography performance of the mask pattern are set. Comparing the calculated lithography performance and the set threshold value of the lithography performance to obtain an allowable variation range of the deformation amount of the illumination luminance distribution, and the design of the illumination luminance distribution and deformation amount in the design. Defining an illumination luminance distribution from an allowable variation range.

  Another embodiment of the present invention is an exposure for forming an image by guiding light from an illumination light source surface to a mask pattern on a photomask and guiding light emitted from the photomask to a substrate surface through an optical system. A method for defining an illumination luminance distribution on an illumination light source surface for an apparatus, the step of dividing an illumination light source surface of a first exposure apparatus into a plurality of illumination elements, and for each of the divided illumination elements, Calculating an image formed on the substrate surface of the first exposure apparatus when the mask pattern is illuminated, selecting the illumination element based on the performance of the calculated image, and obtaining a design illumination luminance distribution; A step of deforming the illumination luminance distribution, a step of calculating a lithography performance of a mask pattern image formed on the substrate surface of the first exposure apparatus using the deformed illumination luminance distribution, and the mask pattern Setting a threshold value of the lithography performance of the screen, a step of obtaining an allowable variation range of the deformation amount of the illumination luminance distribution by comparing the calculated lithography performance and the threshold value of the set lithography performance, The step of defining the illumination luminance distribution in the first exposure apparatus from the designed illumination luminance distribution and the allowable variation range of the deformation amount, and the first exposure of the mask pattern using the illumination luminance distribution defined in the first exposure apparatus The step of obtaining the dimensional characteristics when the exposure is performed by the apparatus, and the illumination luminance distribution of the second exposure apparatus so as to satisfy the design illumination luminance distribution and the allowable variation range of the deformation amount used in the first exposure apparatus. A step of defining, a step of obtaining dimensional characteristics when the mask pattern is exposed by the second exposure apparatus using the illumination luminance distribution defined by the second exposure apparatus, The dimensional characteristics obtained by the optical apparatus are compared with the dimensional characteristics obtained by the second exposure apparatus, and the coincidence between these is confirmed to finally determine the allowable variation range of the illumination luminance distribution and deformation amount of the second exposure apparatus. And a step of determining.

  According to the present invention, it is possible to accurately predict the illumination luminance distribution of the exposure apparatus at the initial stage of device development. Accordingly, it is possible to minimize errors with respect to the actual illumination luminance distribution, prevent rework due to the difference in the illumination luminance distribution, and increase the development efficiency. Furthermore, it is possible to eliminate the influence of dimensional deviation due to an error in the illumination luminance distribution, and to accurately predict the lithography exposure amount margin and the focal depth.

  The details of the present invention will be described below with reference to the illustrated embodiments.

(First embodiment)
FIG. 1 is a flowchart for explaining a method for defining an illumination luminance distribution according to the first embodiment of the present invention.

  In the present embodiment, among the effective light sources on the pupil plane of the exposure apparatus, an illumination element necessary for forming an image is determined using an illumination light source shape optimization method. That is, the effective light source of the exposure apparatus is divided into each element, the contrast of the image when each effective light source element is illuminated is monitored, and the effective light source element that provides the contrast necessary to form an image is selected. This is the illumination luminance distribution required value (S2). FIG. 2 shows the required illumination luminance distribution value at this time. This is an example of annular illumination or second illumination.

  The illumination element is preferably selected based on the performance of the optical image of the photomask pattern. The performance of the optical image of the photomask pattern is, for example, a differential value of the image at a predetermined position on the surface of the substrate.

  Next, the obtained illumination luminance distribution required value was transformed (S3). The required value of the illumination luminance distribution is a rectangle as shown in FIG. 2, but the illumination luminance distribution in an actual apparatus has a distribution in which the rectangle is deformed. Therefore, by convolving the Gaussian function shown in FIG. 3 with the required illumination luminance distribution value, a distribution in which a rectangle is deformed as shown in FIG. 4 is reproduced. At this time, the parameter (illumination luminance distribution deformation parameter: S4) for deforming the required illumination luminance distribution value is set to 5 nm in the present embodiment as the full width at half maximum (301) of the Gaussian function.

  As shown in FIG. 5, in the deformation using the convolution of the Gaussian function, the degree of deformation from the original illumination luminance distribution predicted value (501) increases as the width of the Gaussian function increases (502 to 504). Therefore, it is possible to control the deformation of the illumination luminance distribution required value using the full width at half maximum of this Gaussian function as a parameter.

  Two patterns shown in FIGS. 6A and 6B are prepared as mask patterns for defining the illumination luminance distribution, and in this embodiment, a 55 nm pitch pattern shown in FIG. 6A is used ( Evaluation pattern: S1). As a result of calculating the exposure amount margin of this pattern under the exposure conditions NA = 0.915, σ = 0.9, exposure wavelength = 193 nm, 5% was obtained (calculation of margin: S5). Here, the surface of the substrate of the exposure apparatus is set to the best focus position.

  Then, the obtained exposure amount margin was compared with a predetermined margin threshold 3% (margin specification: S6) (S7). At this time, since the obtained margin of 5% is larger than the threshold of 3%, the illumination luminance distribution was modified with the deformation parameter value set to 7 nm, and the exposure amount margin was calculated again. The relationship between the deformation parameter and the exposure allowance is as shown in FIG.

  As a result of comparing the exposure amount margin threshold value with the calculated exposure amount margin value while changing the size of the deformation parameter in accordance with the flowchart of FIG. The thickness was 10 nm. Then, the illumination brightness distribution is defined using the range of the variation parameter that satisfies the used illumination brightness distribution required value and the exposure amount margin threshold.

  As described above, according to the present embodiment, the required illumination brightness distribution value by selecting the illumination element is deformed by convolution of a Gaussian function, and the exposure allowance is calculated using the deformed requested illumination brightness value, and this is used as an exposure. By comparing with the margin of the amount margin, the illumination luminance distribution of the exposure apparatus can be accurately predicted. For this reason, it is possible to minimize errors with respect to the actual illumination luminance distribution, prevent rework due to the difference in the illumination luminance distribution, and increase the development efficiency. Furthermore, it is possible to eliminate the influence of dimensional deviation due to an error in the illumination luminance distribution, and to accurately predict the lithography exposure amount margin and the focal depth.

(Second Embodiment)
In this embodiment, the variation range of the deformation parameter satisfying the common exposure amount margin of these two patterns is obtained by using both patterns of FIGS. 6A and 6B described in the first embodiment. . The required illumination luminance distribution values for each pattern were the same. The method for obtaining the variation range of the deformation parameter is the same as the method shown in the first embodiment, as shown in the flowchart of FIG. The variation range of the deformation parameter of the required illumination luminance distribution value of the pattern shown in FIG. 6A was 10 nm. On the other hand, the variation range of the deformation parameter of the pattern shown in FIG. 6B was 7 nm. From the two results, the variation range of the deformation parameter satisfying the exposure margin of the two patterns in FIGS. 6A and 6B was 7 nm.

  As described above, when the variation range of the illumination luminance distribution is determined for a plurality of patterns as in the present embodiment, each variation range may be obtained and the common part thereof may be obtained.

  The required illumination luminance distribution value used in each of the above embodiments may not be based on the method shown in the embodiment. For example, the design data itself of the lens of the exposure apparatus or the experimental data of the illumination luminance distribution measured by some method can be used.

  Further, the method of changing the required illumination luminance distribution value is not limited to the method shown in the embodiment. For example, a method of tilting the outside of the required illumination luminance distribution value stepwise or a method of curving may be used. In each of the above embodiments, the range of the variation parameter is defined by the pattern exposure amount threshold. However, this threshold is not limited to the exposure amount margin, but the focus depth margin, the exposure amount margin, and the focus depth. Any factor that is affected by the change in the shape of the illumination luminance distribution, such as both of the margin of the image, may be used.

  It goes without saying that mask patterns other than those used in the embodiments are also possible. Furthermore, the Gaussian function used in the embodiment has one full width at half maximum as a parameter, but the convolution function is not limited to this, and convolution is performed by combining two types of Gaussian functions. May be. Furthermore, the convolution is not necessarily limited to a Gaussian function, and various analytical functions that modify the required illumination luminance distribution value can be used.

(Third embodiment)
In the present embodiment, the required value of the illumination luminance distribution is defined when the exposure apparatus is laterally expanded (the exposure apparatus that performs patterning is changed according to the processing capability of the exposure apparatus and the product scale). First, a dimensional characteristic curve using a test pattern was obtained with an exposure apparatus (exposure apparatus A) that processed the product. The test pattern at this time is shown in FIG. 8, and the obtained dimensional characteristic curve is shown in FIG.

  Next, the illumination luminance distribution of the exposure apparatus was defined according to the flow of FIG. The required value of the illumination luminance distribution at that time and the variation amount of the deformation parameter of 10 nm were obtained. Since this product was processed by the exposure apparatus B, the illumination brightness distribution of the exposure apparatus B was adjusted so that the illumination brightness distribution of the exposure apparatus B was between the illumination brightness distribution of the exposure apparatus A and the parameter fluctuation range. Then, after matching the illumination brightness distribution of the exposure apparatus B with the illumination brightness distribution defined by the exposure apparatus A, when the dimensional characteristic curve of the exposure apparatus B is acquired using the test pattern of FIG. 8, as shown in FIG. The two dimensional characteristic curves almost coincided. In the figure, 1001 is a dimensional characteristic curve acquired by the exposure apparatus A, and 1002 is a dimensional characteristic curve acquired by the exposure apparatus B.

  The processing flow of this embodiment and the conventional processing flow are shown in comparison with FIG. (A) is the conventional processing flow, (b) is the processing flow of this embodiment.

  Conventionally, since it is necessary to newly acquire a dimensional characteristic curve of the exposure apparatus B every time the illumination luminance distribution of the exposure apparatus B is adjusted, much effort is required for exposure of the test pattern and dimension measurement. On the other hand, in the present embodiment, after adjusting the illumination luminance distribution, only the dimensional characteristic curve is acquired for confirmation, so that it is possible to save the trouble of exposure and dimensional measurement that has been performed every time adjustment is performed. , Labor has been greatly reduced.

  That is, the illumination luminance distribution of the exposure apparatus A that has acquired the characteristic curve A is obtained using the same method as in the first and second embodiments, and when adjusting the exposure apparatus B, the illumination luminance distribution of the exposure apparatus A is The exposure apparatus B is adjusted so as to be reproduced by the exposure apparatus B. Thereby, it is possible to perform the adjustment for reproducing the characteristic curve A without newly acquiring the characteristic curve by the exposure apparatus B, and the time required for the adjustment can be saved greatly.

  Although there are two types of exposure apparatuses used in this embodiment, a plurality of exposure apparatuses can be combined using the same method. Further, the test pattern used for adjustment is not limited to FIG. 8, and various patterns can be used.

(Modification)
The present invention is not limited to the above-described embodiments. In the embodiment, the method for defining the illumination luminance distribution has been described, but the present invention can also be applied to other categories. For example, as a category other than the illumination luminance distribution definition method, an illumination light source distribution definition system, a mask produced using the illumination light source distribution definition method, a program for realizing the illumination light source distribution definition method, and an illumination light source distribution definition method are used. It can also be applied to a semiconductor device manufactured in this way.

  Further, preferred embodiments of the invention described in claim 1 include the following.

(1) The substrate surface of the exposure apparatus must be set to the best focus position.
(2) The illumination element should be selected based on the optical image performance of the photomask pattern.
(3) The optical image performance of the photomask pattern is the differential value of the image at a predetermined position on the surface of the substrate.

(4) The threshold of the lithography performance of the photomask pattern image should be determined based on the dimensional accuracy required for the photomask pattern generation.
(5) The dimensional accuracy is distributed among all the factors that change the dimension of the photomask pattern image formed on the substrate surface of the exposure apparatus.
(6) The dimensional accuracy of the pattern includes the uniformity of the dimensions of a plurality of types of photomask patterns and the uniformity of the dimensions within the exposure field of the exposure apparatus.

  Furthermore, preferable embodiments of the invention described in claim 6 include the following in addition to the above (1) to (6).

(7) Defining the illumination brightness distribution of the plurality of exposure apparatuses in accordance with the illumination brightness distribution of the first exposure apparatus by performing the process of defining the illumination brightness distribution of the second exposure apparatus with the plurality of exposure apparatuses. .
(8) Obtaining a dimensional characteristic curve using a pattern whose pitch changes continuously.

  In addition, various modifications can be made without departing from the scope of the present invention.

The flowchart for demonstrating the prescription | regulation method of the illumination luminance distribution concerning 1st Embodiment. The figure which shows the illumination luminance distribution required value of the exposure apparatus used in 1st Embodiment. The figure which shows the example of the Gaussian function for deform | transforming illumination luminance distribution request value. The figure which shows the example which deform | transformed the illumination luminance distribution request value of FIG. The figure which shows a mode that the illumination luminance distribution of FIG. 2 is changing in steps. The figure which shows the example of the pattern for evaluation for prescribing illumination luminance distribution. The figure which shows the relationship between the deformation | transformation parameter which deform | transforms illumination luminance distribution, and exposure amount margin. The figure which shows the example of the test pattern used in 3rd Embodiment. The figure which shows the dimensional characteristic curve acquired using the pattern of FIG. The figure which compares and shows each dimensional characteristic curve of exposure apparatus A and B. FIG. It is a flowchart for demonstrating 3rd Embodiment, and is a figure which shows the operation | movement of adjustment of the illumination luminance distribution between exposure apparatuses A and B. FIG.

Explanation of symbols

301: Full width at half maximum of Gaussian function 501: Shape of original required value of illumination luminance distribution 502: Illumination luminance distribution when the full width at half maximum of Gaussian function is changed to 5 nm 503: When the full width at half maximum of Gaussian function is changed to 10 nm Illumination luminance distribution 504... Illumination luminance distribution when the full width at half maximum of the Gaussian function is changed to 15 nm. 1001... Dimension characteristic curve acquired by the exposure apparatus A 1002.

Claims (5)

Illumination luminance distribution on the illumination light source surface for an exposure device that forms an image by guiding the light from the illumination light source surface to the mask pattern on the photomask and guiding the light emitted from the photomask to the substrate surface via the optical system A method of defining
Dividing the illumination light source surface into a plurality of illumination elements;
For each of the divided illumination elements, an image formed on the substrate surface when the mask pattern is illuminated is calculated, and the illumination element is selected based on the performance of the calculated image to design illumination. Obtaining a luminance distribution;
Deforming the illumination luminance distribution;
Calculating the lithography performance of the mask pattern image formed on the substrate surface using the deformed illumination luminance distribution; and
Setting a threshold for lithography performance of the mask pattern;
A step of obtaining an allowable variation range of the deformation amount of the illumination luminance distribution by comparing the calculated lithography performance and a threshold value of the set lithography performance;
Defining the illumination brightness distribution from the designed illumination brightness distribution and the allowable variation range of the deformation amount;
An illumination luminance distribution defining method characterized by comprising:   2. The method of defining an illumination luminance distribution according to claim 1, wherein, as the step of deforming the illumination luminance distribution, the illumination luminance distribution is analytically deformed by a Gaussian function.   2. The method of defining an illumination luminance distribution according to claim 1, wherein the lithography performance of the mask pattern is exposure margin, depth of focus, and dimensional characteristic curve.   The regulation of the allowable variation range of the deformation amount of the illumination luminance distribution is performed by comparing the calculated lithography performance with the threshold value of the set lithography performance, and while the calculated lithography performance is larger than the set lithography performance, illumination is performed. The variation amount of the luminance distribution is further changed, and when the calculated lithography performance becomes smaller than the set lithography performance, the variation amount of the illumination luminance distribution is defined as an allowable range of the deformation amount of the illumination luminance distribution. 2. The method for defining an illumination luminance distribution according to claim 1. Illumination luminance distribution on the illumination light source surface for an exposure device that forms an image by guiding the light from the illumination light source surface to the mask pattern on the photomask and guiding the light emitted from the photomask to the substrate surface via the optical system A method of defining
Dividing the illumination light source surface of the first exposure apparatus into a plurality of illumination elements;
For each of the divided illumination elements, an image formed on the substrate surface of the first exposure apparatus when the mask pattern is illuminated is calculated, and the illumination element is selected based on the performance of the calculated image. To obtain a design illumination brightness distribution,
Deforming the illumination luminance distribution;
Calculating the lithography performance of a mask pattern image formed on the substrate surface of the first exposure apparatus using the deformed illumination luminance distribution;
Setting a threshold for lithography performance of the mask pattern;
A step of obtaining an allowable variation range of the deformation amount of the illumination luminance distribution by comparing the calculated lithography performance and a threshold value of the set lithography performance;
Defining the illumination luminance distribution in the first exposure apparatus from the designed illumination luminance distribution and the allowable variation range of the deformation amount;
Obtaining a dimensional characteristic when the mask pattern is exposed by the first exposure apparatus using the illumination luminance distribution defined in the first exposure apparatus;
Defining an illumination luminance distribution of the second exposure apparatus so as to satisfy an allowable variation range of the designed illumination luminance distribution and deformation amount used in the first exposure apparatus;
Obtaining a dimensional characteristic when the mask pattern is exposed by the second exposure apparatus using the illumination intensity distribution defined in the second exposure apparatus;
The dimensional characteristics obtained by the first exposure apparatus are compared with the dimensional characteristics obtained by the second exposure apparatus, and the coincidence between these is confirmed to determine the allowable variation range of the illumination luminance distribution and deformation amount of the second exposure apparatus. A final decision process;
An illumination luminance distribution defining method characterized by comprising:

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