TWI421908B - Method for constructing opc model - Google Patents

Description

Method for establishing optical proximity correction model

The present invention relates to a lithography process, and more particularly to a method of establishing an optical proximity correction model.

With the rapid development of semiconductor process technology, in order to improve the speed and performance of components, the size of the entire circuit components must be continuously reduced, and the accumulation of components must continue to increase. In general, lithography processes play a pivotal role in the overall process as semiconductors tend to shrink the design of circuit components.

In the semiconductor process, the patterning of the layers of the film or the implantation of the doped regions is defined by the lithography process and determines the size of the critical dimension (CD). The lithography process first forms a layer of photosensitive photoresist on the surface of the wafer. Then, the photoresist exposure step and the development step are sequentially performed to transfer the desired pattern to the photoresist material layer on the surface of the wafer by using the pattern on the photomask to form a desired photoresist pattern. As components continue to shrink and accumulate, and the design of integrated circuits becomes more complex, the transfer of reticle patterns onto wafers plays an important role. If the pattern transfer is not as expected, it will affect the critical dimensions on the wafer.

In the tendency of the line width of the element and the pitch to be reduced, it is easy to cause a deviation in the pattern transfer in the exposure step, that is, a so-called optical proximity effect (OPE). Since the accuracy of lithography imaging directly affects the yield of the product, in order to solve this problem, some methods for improving the resolution of the reticle are constantly being proposed. For example, using light The correction of the mask pattern by the optical proximity correction (OPC) is mainly used to eliminate the key dimensional deviation caused by the optical proximity effect, that is, to reduce the photoresist pattern and the mask pattern. Deviation between.

The conventional optical proximity correction method obtains the deviation value by comparing the original drawing material having the line layout pattern with the photoresist pattern formed by pattern transfer using the reticle, and collects related data of different patterns to establish optical proximity correction. model. However, in the process of fabricating the reticle, when the original drawing data is written on the reticle, the pattern on the reticle may be rounded due to the characteristics of the writing tool, resulting in formation on the reticle. The pattern does not exactly match the original drawing material. Therefore, the optical proximity correction model established by the conventional method based on the original drawing data cannot correct the layout design of the component for the pattern actually formed on the reticle.

The present invention provides a method of establishing an optical proximity correction model that can facilitate pattern transfer.

The invention proposes a method for establishing an optical proximity correction model. First, a test pattern is provided. Next, the test pattern is written on a reticle. The pattern on the reticle is measured to obtain a modified pattern. Thereafter, an optical proximity correction model is established based on the modified pattern.

In one embodiment of the invention, the method of obtaining the correction pattern is by simulating the contour of the pattern on the reticle.

In one embodiment of the invention, the method of obtaining the correction pattern is to obtain an image by a scanning electron microscope (SEM).

In an embodiment of the invention, the establishing the optical proximity correction model further includes input physical parameters, such as a numerical aperture (NA), a numerical aperture ratio (sigma, a ratio of a numerical aperture of the light source to a numerical aperture of the lens). , illuminator shape or film stack properties.

In an embodiment of the invention, the establishing the optical proximity correction model further includes inputting a statistical parameter, such as a pattern density or an aerial image slope.

In an embodiment of the present invention, after obtaining the correction pattern and before establishing the optical proximity correction model, the method further includes transferring the pattern on the reticle to a photoresist layer to form a plurality of photoresist patterns correspondingly, and measuring and The data of each photoresist pattern is collected to construct a database, and then an optical proximity correction model is established based on the modified pattern and the data of the database.

In an embodiment of the invention, the method further comprises correcting the test pattern according to the optical proximity correction model.

In an embodiment of the invention, the method further includes converting the modified pattern into a digitized format.

In an embodiment of the invention, the test pattern is the original drawing material.

The method of the present invention can obtain the pattern contour (ie, the correction pattern) actually formed on the reticle by using the existing equipment, and establish an optical proximity correction model according to the correction pattern by using the existing software package, thereby improving the lithography process. Reliability and cost savings.

In order to make the above features and advantages of the present invention more obvious, the following DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments, together with the drawings, are described in detail below.

Since the process of fabricating the reticle may cause a difference between the pattern written on the reticle and the original design drawing pattern, the present invention simultaneously considers the process error and optics of forming the reticle pattern when establishing the correction model of the reticle pattern. The influence of the proximity effect on the component layout pattern actually formed on the wafer, after the completion of the fabrication of the reticle, the variability in the reticle process is appropriately modified for the subsequent optical proximity correction model to be established, thereby effectively increasing The credibility of the lithography process.

The method for establishing the optical proximity correction model of the embodiment of the present invention is to obtain a digitized correction pattern according to a pattern actually formed on the reticle, and add all parameter conditions (such as physical parameters, statistical parameters, etc.) in the process, and The optical proximity correction model is established by a database established with data actually collected from the photoresist layer on the wafer, and the originally designed layout pattern can be corrected according to the optical proximity correction model. Next, an embodiment of the present invention will be further described in the form of a flowchart, and FIG. 1 is a flow chart showing the steps of correcting the mask pattern according to an embodiment of the present invention.

Referring to FIG. 1, step S100 is performed to provide a test pattern. This test pattern is the original drawing of the original designed line layout pattern, which is, for example, a geometric pattern used to describe the integrated circuit layout to be transferred to the wafer. In one embodiment, the test pattern includes information such as geometric patterns of different critical dimensions, different pattern densities, and different line width spacings.

Next, in step S110, the test pattern is written on the photomask to produce a mask having a pattern. A method of writing a test pattern on a reticle, for example A writing step is performed, which includes performing an electron beam or a laser beam.

Step S120 is performed to measure the pattern on the reticle to obtain a correction pattern. In detail, since the process of the reticle is affected by the process equipment, the pattern actually formed on the reticle is not completely identical to the test pattern originally written. That is to say, the pattern formed on the reticle may be inaccurate with the originally designed test pattern, so it is necessary to obtain the actual reticle pattern (ie, the correction pattern) by measuring the reticle. The method of obtaining the correction pattern is, for example, by using an analog method or using a scanning electron microscope to obtain an image, and drawing a pattern feature such as a contour and a key size of the pattern on the reticle. After the correction pattern is obtained, the correction pattern can be further converted into a digitized data file to facilitate the establishment of a subsequent optical proximity correction model. In an embodiment, the format of the digitized data file is not particularly limited, and includes the outline of the pattern on the reticle, the critical size, and the like.

Then, in step S130, the pattern on the photomask is transferred to the photoresist layer to form a plurality of photoresist patterns correspondingly in the photoresist layer. The method of transferring the pattern on the photomask to the photoresist layer is, for example, an exposure step and a development step, and this step is a technique well known to those skilled in the art, and thus will not be described herein.

Step S140 is performed to measure each of the photoresist patterns formed in step S130, and collect data to establish a database. A method of measuring the photoresist pattern and collecting its data is, for example, using a scanning electron microscope to measure the critical dimensions of the photoresist pattern. Generally, when the pattern on the reticle is transferred to the photoresist layer through the exposure and development steps, the light used in the exposure step is received. The interference of the source and the photoresist of the photoresist layer cause problems such as rounding of the corners of the photoresist pattern and changes in line width, that is, optical proximity effects occur. Therefore, the formed photoresist pattern does not coincide with the pattern on the photomask. The method for establishing a database is, for example, calculating a deviation value between a measurement result of each photoresist pattern and a corresponding correction pattern thereof, and collecting various design patterns to form a photoresist pattern and a correction pattern. The deviation value, and then store the relevant data to establish a database.

Step S150 is performed to calculate an optical proximity correction model based on the data of the database and according to the digitized correction pattern. The method of establishing the optical proximity correction model can utilize the existing software package and input the data of the database, and then calculate and correct the model. In an embodiment, establishing the optical proximity correction model further comprises inputting physical parameters and statistical parameters into the software package described above. Physical parameters include numerical aperture (NA), numerical aperture ratio (sigma, ratio of source numerical aperture to lens numerical aperture), illuminator shape or film stack properties. Statistical parameters include pattern density or aerial image slope.

Herein, in the above step, the optical proximity correction model is established by mutually comparing the actually formed correction pattern obtained from the reticle with the photoresist pattern formed by the lithography process using the reticle. Therefore, the optical proximity effect caused by the exposure step can be effectively improved, and the error between the mask pattern and the photoresist pattern can be reduced.

After that, the optical proximity correction model established by the above method can be used to correct the configuration of the original design test pattern, and the modified pattern data is subjected to subsequent processing so that the component pattern formed on the photoresist layer can be It is enough to conform to the original expected pattern, and those skilled in the art can know the application, and therefore will not be described again.

In summary, the optical proximity correction model of the present invention establishes a correction pattern formed on the reticle by means of an analog method or an image of a scanning electron microscope, and establishes an optical proximity correction model based on the correction pattern. Therefore, the optical proximity correction model constructed by the method of the present invention can correct the pattern actually formed on the reticle to make the pattern formed on the photoresist layer more suitable for the desired pattern, and effectively improve the lithography process. Reliability and yield.

In addition, the method of the present invention utilizes existing equipment and software packages to obtain a correction pattern formed on the reticle and establish an optical proximity correction model, thereby eliminating complicated computational inferences, thereby reducing the credibility of the lithography process and reducing Establishing the computational time of the optical proximity correction model can help save process costs.

Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

S100, S110, S120, S130, S140, S150‧‧ steps

1 is a flow chart showing the steps of establishing an optical proximity correction model in accordance with an embodiment of the present invention.

S100, S110, S120, S130, S140, S150‧‧ steps

Claims (12)

A method for establishing an optical proximity correction model, comprising: providing a test pattern; writing the test pattern on a reticle; measuring the pattern on the reticle to obtain a correction pattern; and establishing the correction pattern according to the correction pattern An optical proximity correction model. The method for establishing an optical proximity correction model according to claim 1, wherein the method of obtaining the correction pattern is by simulating a contour of a pattern on the reticle. The method for establishing an optical proximity correction model according to claim 1, wherein the method of obtaining the correction pattern is to obtain an image by a scanning electron microscope. The method for establishing an optical proximity correction model according to claim 1, wherein the establishing the optical proximity correction model further comprises inputting a physical parameter. The method of establishing an optical proximity correction model according to claim 4, wherein the physical parameter comprises a numerical aperture, a numerical aperture ratio (sigma), a light source shape, or a film lamination property. The method for establishing an optical proximity correction model according to claim 1, wherein the establishing the optical proximity correction model further comprises inputting a statistical parameter. The method for establishing an optical proximity correction model according to claim 6, wherein the statistical parameter comprises a pattern density or a spatial image oblique rate. The method for establishing an optical proximity correction model according to claim 1, after the obtaining the correction pattern and before establishing the optical proximity correction model, further comprising: transferring the pattern on the mask to a photoresist layer, Correspondingly forming a plurality of photoresist patterns; and measuring each of the photoresist patterns, and collecting data of the photoresist patterns to construct a database. The method for establishing an optical proximity correction model according to claim 8 further includes establishing the optical proximity correction model according to the correction pattern and the database. The method for establishing an optical proximity correction model according to claim 1, further comprising correcting the test pattern according to the optical proximity correction model. The method for establishing an optical proximity correction model as described in claim 1 further includes converting the modified pattern into a digitized format. The method for establishing an optical proximity correction model according to claim 1, wherein the test pattern is an original drawing material.