JP2008209663A - Method for correcting optical proximity effect - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an method for correcting optical proximity effect for obtaining high accuracy, close to that of three-dimensional simulation by taking influences of the three-dimensional structure of a mask into consideration, while maintaining a high speed close to that of two-dimensional simulation. <P>SOLUTION: The optical proximity effect correction method includes steps of computing a threshold of light intensity on a wafer surface, at which a target dimension can be obtained on the wafer surface and computing the mask pattern dimension 1 at the threshold of the light intensity by three-dimensional simulation; computing the sum of light intensities of all the diffracted lights collected by a projection lens in the mask pattern dimension 1 by the three-dimensional simulation; computing the sum of the light intensities of the whole diffracted lights collected by the projection lens, when the mask pattern dimension is varied, by two-dimensional simulation; computing a mask pattern dimension 2 by two-dimensional simulation, where the sums of the light intensities of all the diffracted lights by the three-dimensional simulation and by the two-dimensional simulation become equal to each other; and determining the difference between the mask pattern dimension 2 and the mask pattern dimension 1 as a bias value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, when a mask pattern of a photomask (hereinafter referred to as a mask) is transferred onto a wafer surface through a projection lens, the optical proximity improves the transfer fidelity so that a desired dimension can be obtained on the wafer surface. The present invention relates to an effect correction method.

  Along with the high integration and miniaturization of LSIs, when the mask pattern is transferred onto the wafer surface, degradation of pattern transfer fidelity such as a decrease in pattern dimension controllability and pattern shape deformation has become a problem. As a method for preventing such deterioration, a design that takes into account the correction amount at the time of transfer onto the wafer surface on the mask is adopted. Such a process is called optical proximity correction (hereinafter also referred to as OPC). The optical proximity effect correction method is roughly divided into a so-called rule-based OPC method in which correction is performed based on a correction rule obtained in advance as shown in FIG. 5, and an exposure process as shown in FIG. There is a model-based OPC method using a simulator that models a phenomenon.

  In LSIs with a line width of 65 nm or more on the wafer surface, model-based OPC that expresses optical phenomena by simulation and calculates corrections is the mainstream, but high-speed processing is applied to apply optical simulation to full chips. A simplified simulation model that can be used is adopted. A major feature of this simulation is a two-dimensional simulation that employs a method of handling a mask pattern as a planar model that expresses only the transmittance and the phase difference. For example, the Kirchhoff method is used.

  However, in lithography using the current mainstream ArF excimer laser, the mask pattern size becomes equal to or smaller than the light source wavelength of 193 nm, so that the mask three-dimensional structure cannot be ignored. For this reason, a three-dimensional simulation considering the three-dimensional structure of the mask is also used in part. In the three-dimensional simulation, for example, light propagation in a mask is guided using an approximate expression of Maxwell's equation, and an FDTD method (also called a time domain difference method or a finite difference time domain method) is used (for example, , See Patent Document 1 and Patent Document 2).

  FIG. 7 shows a mask CD having a mask pattern size including a bias value (correction value) of OPC obtained by processing in a two-dimensional simulation (Kirchhoff method; Kirchhoff) of a conventional planar model that does not consider the three-dimensional structure of the mask. It is a figure which shows (Critical Dimension). In FIG. 7, the pattern pitch of the mask of 45 nm node (minimum half pitch 65 nm) is shown on the horizontal axis, the mask CD which is an important dimension of the mask after the OPC processing is shown on the vertical axis, and the mask CD is changed for each pattern pitch. The mask CD is thickened as the pitch increases. Henceforth, in this specification, all the dimension notations are shown on a wafer scale.

FIG. 8 is a diagram showing a wafer CD (vertical axis) that is an important dimension of the wafer when the pattern is transferred onto the wafer surface by using the above-mentioned mask subjected to OPC by simulation, and the horizontal axis is the pattern pitch. . In the case of using a two-dimensional simulation (hereinafter also referred to as 2D) (upper straight line in FIG. 8; 2D), the wafer CD can be seen as almost constant without depending on the pattern pitch in the simulation. . However, in actual transfer, there arises a problem that the accuracy of OPC is lowered. On the other hand, when a stricter three-dimensional simulation (hereinafter also referred to as 3D) is used (the lower straight line in FIG. 8; 3D), an error as much as 5 nm is maximum between the two-dimensional simulation and the three-dimensional simulation of the wafer CD. Has occurred. This error is caused by the three-dimensional structure of the mask. Although the two-dimensional simulation has an advantage that the calculation is quick and the number of parameters is small, the mask three-dimensional pattern is not used in the mask transfer having a fine pattern of 65 nm node or later. This is due to the problem that the OPC error due to the structure becomes considerably large and can be ignored. Therefore, in order to improve the accuracy of OPC, there is a need for an OPC technique that incorporates the influence of the three-dimensional structure of the mask.
JP 2006-39594 A JP 2006-22941 A

  However, the conventional 3D simulation has the advantage of being highly accurate and capable of supporting the three-dimensional structure of the mask. However, even if consideration is given to improving the processing capability of future simulation equipment, 3D simulation can be applied to all LSI full chips. Adopting and performing OPC processing has a problem that it is almost impossible because it requires an increase in parameters and enormous processing time.

  On the other hand, as another method for correcting the above OPC error, a solution using a comparison experiment with actual transfer has also been proposed. However, when actual transfer is performed, errors due to processes are included in the error. Therefore, there is a problem that due to the difficulty of convergence, a decrease in the accuracy of the optical model leads to a decrease in the accuracy of the final OPC.

  The present invention has been made in view of the above problems, and its object is to maintain the high speed close to that of a two-dimensional simulation and to take into account the influence of the three-dimensional structure of the mask. Is to provide an optical proximity effect correction method.

  In order to solve the above problems, the optical proximity correction method according to the first aspect of the present invention is such that when a mask pattern is transferred onto a wafer surface via a projection lens, a target dimension can be obtained on the wafer surface. In the optical proximity effect correction method for improving the transfer fidelity, a) a light intensity threshold value on the wafer surface at which the target dimension is obtained at a specific pitch of the mask pattern on the wafer surface by three-dimensional simulation; Obtaining a mask pattern dimension (mask pattern dimension 1) at a specific pitch of the mask pattern at the light intensity threshold; and b) the projection lens at the mask pattern dimension 1 at the specific pitch by a three-dimensional simulation. Calculating the sum of the light intensities of all diffracted light that can be captured by c, and c) A step of obtaining a sum of light intensities of all diffracted lights that can be taken in by the projection lens when the mask pattern dimension is changed at the same pitch as the constant pitch; and d) the total diffracted light of step b) in the mask pattern dimension 1 Obtaining a mask pattern dimension (mask pattern dimension 2) of the two-dimensional simulation in which the sum of the light intensities and the sum of the light intensities of all the diffracted lights in step c) are equal; e) the mask pattern dimension 2 and the And a step of setting a dimensional difference from the mask pattern dimension 1 as a bias value.

  The optical proximity effect correction method according to claim 2 is the optical proximity effect correction method according to claim 1, wherein f) a threshold value of light intensity on the wafer surface at which the target dimension can be obtained with the mask pattern dimension 2. And g) two-dimensional simulation is performed on the basis of the threshold value of light intensity set in step f), and the target dimensions are obtained for all the pitches used in the mask pattern. The step of determining the mask pattern size at each pitch as described above, and h) uniformly applying the bias value of step e) to the entire mask pattern size determined in step g). It is what.

  The optical proximity effect correction method according to the invention of claim 3 is the optical proximity effect correction method according to claim 1 or 2, wherein the specific pitch is a pitch having the strictest manufacturing conditions on the wafer surface, or is frequently used. Pitch.

  According to the optical proximity correction method according to claim 1 of the present invention, a three-dimensional simulation considering the influence of the mask three-dimensional structure for considering the influence of the mask three-dimensional structure while using a high-speed two-dimensional simulation. It is possible to find a correction rule for performing optical proximity effect correction that can achieve high accuracy close to.

  According to the optical proximity correction method according to claim 2 of the present invention, the influence of the mask three-dimensional structure can be taken into account while using a high-speed two-dimensional simulation, and the target dimension can be obtained over the entire pitch of the mask pattern. The high-precision optical proximity effect correction can be performed at high speed.

  According to the optical proximity correction method according to claim 3 of the present invention, it is necessary to set the main object of the OPC processing of the mask pattern to a pitch with the most severe manufacturing conditions on the wafer surface or a frequently used pitch. It is possible to accurately perform the OPC processing with the pitch of

  Hereinafter, an optical proximity effect correction method according to an embodiment of the present invention will be described in detail based on the drawings.

(First embodiment)
FIG. 1 is a conceptual diagram of a mask (FIG. 1-1) for performing the OPC process of the present invention, and an explanatory diagram showing the light intensity on the wafer surface when transferred onto the wafer surface using this mask (FIG. 1-2). ). FIG. 1-1 is a plan view of a mask pattern, showing a state in which patterns (shaded portions) having a pattern dimension 1 are arranged at a specific pitch. FIG. 1-2 shows the light intensity (vertical axis) on the wafer surface with respect to the pattern position (horizontal axis) on the wafer surface.

  The optical proximity effect correcting method according to the present invention is based on a target dimension (hereinafter referred to as a target dimension) on a wafer surface that is a transfer object at a specific pitch of a mask pattern, as shown in FIG. The threshold value of the light intensity on the wafer surface, which is the target dimension, is obtained. As shown in FIG. 1-2, the light intensity on the wafer surface is uniquely determined from the mask pattern size. When the threshold value is increased, the wafer surface size increases, and when the threshold value is decreased, the wafer surface size decreases. . Therefore, the threshold value of the light intensity is determined so that the target dimension is obtained when the light intensity is cut at a certain threshold value, and the mask pattern dimension at a specific pitch of the mask pattern at this light intensity threshold value (referred to as mask pattern dimension 1 in the present invention). (Step a)). At this time, it is also checked whether or not the obtained mask pattern dimension is a dimension that can be manufactured by an actual process. Alternatively, it may be determined whether it is advantageous to use the determined mask dimensions in the process on the wafer surface. In the simulation, the light intensity threshold and the mask pattern size 1 can be obtained almost simultaneously.

  As an example of general optical proximity correction after the mask pattern dimension 1 is determined, when the specific pitch of the mask pattern is 130 nm, a threshold value of the light intensity at which the target dimension is 65 nm is obtained on the wafer surface. At this time, the mask pattern dimension (mask pattern dimension 1) is set to 65 nm, and the threshold value of the light intensity is set so that the target dimension is obtained on the wafer surface. However, when the mask pattern pitch is increased to 260 nm, the dimension on the wafer surface is reduced to 33 nm at the same mask pattern dimension and light intensity threshold as described above, and the target dimension cannot be obtained. In the case of this pitch of 260 nm, by adjusting the mask pattern dimension, the mask pattern dimension for obtaining the target dimension of 65 nm on the wafer surface is 95 nm with the same threshold value of light intensity as described above. As described above, on the simulation, mask dimensions with various pitches are adjusted according to a constant slice level based on a threshold value.

  FIG. 2 is a diagram in which the sum of the light intensities of all the diffracted light that can be captured by the projection lens when the mask pattern dimension (mask CD) is changed at a specific pitch is obtained by a three-dimensional simulation. It is also a figure which calculated | required the sum of the light intensity of all the diffracted lights which a projection lens can take in when a mask pattern dimension (mask CD) is changed by the same pitch as said specific pitch.

  In FIG. 2, as an example, the mask CD (horizontal axis) when the specific pitch is 100 nm and the sum (vertical axis) of the light intensity of all diffracted light are shown, and the lower dotted line is the light of all diffracted light in the three-dimensional simulation. The sum of the intensities is shown, and the upper straight line shows the sum of the light intensities of all diffracted lights in the two-dimensional simulation. The total diffracted light is assumed as 0th order light and 1st order light.

  As an example of this embodiment, a case where the mask pattern dimension 1 is 40 nm will be described with reference to FIG. By the three-dimensional simulation, the sum of the light intensities of all the diffracted lights that can be taken in by the projection lens at the above-mentioned specific pitch and mask pattern size 1 is obtained (step b)). The intersection (point P) between the mask pattern dimension 1 (dashed line with mask CD of 40 nm) and the straight line (3D) indicating the sum of the light intensities of all diffracted light is the light intensity of all diffracted light with mask pattern dimension of 40 nm. Indicates the sum. In FIG. 2, for convenience of explanation, the sum of the light intensities of all diffracted lights that can be taken in by the projection lens when the mask pattern dimension is changed at the specific pitch is obtained. In the present embodiment, the mask pattern dimension is obtained. Find only one.

  As the three-dimensional simulation in the above steps a) and b), for example, EM-Suite (trade name: manufactured by Panoramic Technology) is used as simulation software, and FDTD by TEMPESTpr2 (EM-Suite option) is used for the three-dimensional simulation. The method (also referred to as a time domain difference method or a finite difference time domain method) can be used.

  Next, the sum of the light intensities of all diffracted light that can be taken in by the projection lens when the mask pattern size is changed at the same pitch as the specific pitch is obtained by two-dimensional simulation (step c)). The upper straight line (2D) in FIG. 2 indicates the sum of the light intensities of all diffracted light in the two-dimensional simulation. In this case, the total diffracted light is the 0th order light and the first order light.

  As the two-dimensional simulation in step c), for example, EM-Suite (trade name: manufactured by Panoramic Technology) is used as simulation software, and the two-dimensional simulation can be used.

  Next, the mask pattern dimension (mask pattern dimension) of the two-dimensional simulation in which the sum of the light intensities of all diffracted light in step b) in the mask pattern dimension 1 is equal to the sum of the light intensities of all diffracted lights in step c). 2) is obtained (step d)). That is, in FIG. 2, a Q point indicating the sum of the light intensities of all diffracted light by a two-dimensional simulation in which the light intensity of the P point and the total diffracted light is equal is obtained. Ask.

  Next, the dimensional difference (−8 nm) of the mask pattern dimension 1 (40 nm) with respect to the mask pattern dimension 2 (48 nm) is set as the bias value of OPC (step e)). As described above, an OPC correction rule can be established by setting the mask CD to 48 nm with a pattern pitch of 100 nm in a two-dimensional simulation.

  As described above, in this embodiment, by making the sum of the light intensities of all diffracted light in the two-dimensional simulation of the mask pattern size of a specific pitch and the sum of the light intensities of all diffracted light in the three-dimensional simulation, In other words, by finding the mask pattern dimension 2 by matching the diffracted light intensity, the optical proximity effect can be obtained with high accuracy close to the three-dimensional simulation considering the influence of the three-dimensional structure of the mask while maintaining the high speed close to the two-dimensional simulation. A correction rule for performing correction can be found. In the present embodiment, the three-dimensional simulation has only to be applied to one point (40 nm in the above example) as the pattern size, so the load by the three-dimensional simulation is small and the high speed of the OPC process is maintained.

(Second Embodiment)
In the first embodiment described above, the construction of the OPC correction rule at the specific pitch of the mask has been described. However, as the second embodiment, in the case of the through pitch over the entire used pitch including other pattern pitches of the mask. The optical proximity effect correction method will be described.

  In the present embodiment, a two-dimensional simulation is performed, and a threshold value of light intensity on the wafer surface at which a target dimension is obtained with the mask pattern dimension 2 of the specific pitch is newly set (step f)).

  Next, a two-dimensional simulation is performed on the basis of the threshold value of the light intensity set in step f) above, and the mask at each pitch is obtained so that the above target dimensions are obtained for the entire pitch used in the mask pattern. The pattern dimension is determined (step g)). For this process, the same process as in the example shown in paragraph (0019) of the first embodiment is used.

  In this embodiment, step f) and step g) are performed over a sufficiently wide range including the mask pattern dimension 2 described above, but not necessarily after step e) but after step d). Step e) may be performed after Step f) and Step g).

  FIG. 3 is a diagram showing the mask pattern dimension (mask CD) when the mask pattern pitch is changed, and the upper solid line (2D) is obtained by two-dimensional simulation. When the pattern pitch is 100 nm, the mask pattern dimension 2 in the first embodiment is shown. The lower dotted line (3D) is a mask CD obtained by a three-dimensional simulation published simultaneously for OPC accuracy verification. When the pattern pitch is 100 nm, the mask pattern dimension 1 in the first embodiment is shown. ing. As shown in FIG. 3, the tendency of the mask CD for each pitch obtained by the two-dimensional simulation approximates the mask CD obtained by the three-dimensional simulation.

  Next, as shown in FIG. 4, the bias value obtained in step e) is uniformly applied to the entire mask pattern dimension obtained by the two-dimensional simulation shown in FIG. 3 (step h)), and the OPC process is performed. I do. In FIG. 4, the bias value is set to −8 nm, and the entire pattern dimension is reduced to 8 nm.

  As shown in FIG. 4, the optical proximity correction method of the present invention mainly based on a two-dimensional simulation is almost identical to the optical proximity effect correction processing by the three-dimensional simulation, and is a high-level determining mask pattern size at each pattern pitch. It is verified that accurate OPC processing is performed.

(Third embodiment)
As described above, in the optical proximity correction method of the present invention, only one point may be used for the above three-dimensional simulation. Therefore, optical proximity effect correction can be performed at high speed.

  In the present invention, an arbitrary pitch can be selected as the above-mentioned specific pitch. However, as the third embodiment, it is preferable to select a pitch having the strictest manufacturing conditions on the wafer surface or a frequently used pitch. For example, a pitch having the strictest manufacturing conditions is selected as the specific pitch, and a reference mask pattern dimension 1 is set. On the other hand, the optical proximity effect correction method described in the above (first embodiment) or (second embodiment) is performed in the same manner, thereby realizing an OPC process with good wafer manufacturability and high accuracy. can do. Alternatively, the manufacturing efficiency can be expected to be improved by determining the most frequently used pitch as the specific pitch and setting the mask pattern dimension 1.

FIG. 2 is a conceptual view of a mask (FIG. 1-1) for performing OPC processing of the present invention, and an explanatory view (FIG. 1-2) showing light intensity on the wafer surface when this mask is used for transfer onto the wafer surface. It is a figure which shows adjustment of the sum of the light intensity of all the diffracted lights by the three-dimensional simulation and two-dimensional simulation of this invention. It is a figure which shows the mask pattern dimension (mask CD) at the time of performing the OPC process of this invention and changing the pattern pitch of a mask. It is a figure which shows the OPC process result which gave said bias value uniformly to the whole mask pattern dimension obtained by the two-dimensional simulation shown in FIG. It is a schematic diagram which shows the conventional rule-based OPC method. It is a schematic diagram which shows the conventional model base OPC method. It is a figure which shows mask CD containing the bias value (correction value) of OPC for every pattern pitch obtained by the two-dimensional simulation of the conventional plane model. It is a figure which shows wafer CD for every pattern pitch by the simulation when pattern transfer is carried out on the wafer surface using the mask which carried out the OPC process shown in FIG.

Explanation of symbols

2D 2D simulation 3D 3D simulation Kirchoff One method of 2D simulation Rigorous One method of 3D simulation P point Sum of light intensity of all diffracted light at mask pattern size 1 by 3D Q point All diffracted light equal to P point by 2D Sum of light intensity

Claims (3)

In the optical proximity correction method for improving the fidelity of transfer so that a target dimension can be obtained on the wafer surface when the mask pattern is transferred onto the wafer surface via a projection lens,
a) a threshold of light intensity on the wafer surface at which the target dimension is obtained at a specific pitch of the mask pattern on the wafer surface by three-dimensional simulation, and a mask at a specific pitch of the mask pattern at the threshold of light intensity Obtaining a pattern dimension (mask pattern dimension 1);
b) obtaining a sum of light intensities of all diffracted lights that can be captured by the projection lens in the mask pattern size 1 at the specific pitch by a three-dimensional simulation;
c) obtaining a sum of light intensities of all diffracted lights that can be taken in by the projection lens when the mask pattern size is changed at the same pitch as the specific pitch by two-dimensional simulation;
d) The mask pattern size (mask pattern) of the two-dimensional simulation in which the sum of the light intensity of all the diffracted light in step b) in the mask pattern size 1 is equal to the sum of the light intensity of all the diffracted light in step c). Determining dimension 2);
e) a step of setting a dimensional difference between the mask pattern dimension 2 and the mask pattern dimension 1 as a bias value;
The optical proximity effect correction method characterized by including. In the optical proximity correction method according to claim 1,
f) newly setting a threshold value of light intensity on the wafer surface for obtaining the target dimension at the mask pattern dimension 2;
g) A two-dimensional simulation is performed on the basis of the threshold value of the light intensity set in step f), and the mask pattern at each pitch is obtained so that the target dimension can be obtained for the entire pitch used in the mask pattern. Determining the dimensions;
h) uniformly applying the bias value of step e) to the entire mask pattern size determined in step g);
The optical proximity effect correction method characterized by including.   3. The optical proximity correction method according to claim 1, wherein the specific pitch is a pitch having the strictest manufacturing conditions on the wafer surface or a frequently used pitch.

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