1. A modeling method of an optical proximity correction model is characterized by comprising the following steps:

designing a test pattern, and manufacturing a test photomask according to the test pattern;

transferring the test pattern to a wafer by using the test photomask, forming an actual pattern on the wafer, and collecting first wafer data of the actual pattern;

determining a defocus range through the first wafer data, wherein the specific method comprises the following steps: searching a target point of a pattern wide and sparse area in the test pattern according to the first wafer data, wherein the first wafer data corresponding to the target point meets the process target requirement; drawing a Poisson curve corresponding to the target point of the wide and sparse region of the graph by using simulation software; acquiring a vertex value of the Poisson curve, and determining the defocus range according to the vertex value;

and fitting according to the defocus range to establish an optical proximity correction model.

2. The method of modeling an optical proximity correction model according to claim 1, wherein the defocus amount range is ± 10% of the vertex value.

3. The method for modeling an optical proximity correction model according to claim 1, wherein the method of fitting according to the defocus amount range comprises:

acquiring second wafer data of a target point of the pattern wide and sparse area under a focusing matrix condition;

selecting a plurality of defocus amounts and corresponding actual critical dimensions from the second wafer data, wherein the defocus amounts comprise an optimal exposure defocus amount, at least one defocus amount larger than the optimal exposure defocus amount and at least one defocus amount smaller than the optimal exposure defocus amount, and drawing a trend graph of the actual critical dimensions;

selecting at least three defocusing amounts in the defocusing amount range to respectively perform model calculation and regression processing to obtain corresponding simulated key dimensions, and drawing a trend graph of the simulated key dimensions;

and regulating and controlling the simulated key size by adjusting the defocus amount selected in the defocus amount range until the variation trend of the simulated key size is consistent with that of the actual key size.

4. The method for modeling an optical proximity correction model according to claim 3, wherein the method for obtaining the second wafer data of the target points of the pattern broad and sparse areas under the condition of the focusing matrix comprises:

and photoetching the wafer under the condition of a focusing matrix, and transferring the target point of the wide and sparse graph onto the wafer to acquire the second wafer data.

5. The method of modeling an optical proximity correction model according to claim 3, wherein the number of defocus amounts selected in the second wafer data is equal to the number of defocus amounts selected in the defocus amount range.

6. The method of modeling an optical proximity correction model according to claim 5, wherein the number of defocus amounts selected in the defocus amount range is three.

7. The modeling method of the optical proximity correction model according to claim 6, wherein when the simulated critical dimension is consistent with the variation trend of the actual critical dimension, the defocus amount in the middle of the three defocus amounts selected in the defocus amount range is a defocus amount accurate value.

8. The method of claim 3, wherein the first wafer data and the second wafer data are obtained using a scanning electron microscope for feature size measurement.

9. The modeling method of the optical proximity correction model according to claim 1, wherein when searching for the target point of the pattern wide and sparse region in the test pattern according to the first wafer data, anchor points of the pattern dense region in the test pattern are also searched for as the reference points of the test pattern.

Background

Photolithography is the driving force for the development of integrated circuit fabrication processes and is one of the most sophisticated. Improvements in lithographic technology have made significant progress in the development of integrated circuits relative to other individual fabrication techniques. Before the photolithography process is started, a pattern is firstly copied to a mask plate through a specific device, and then a pattern structure on the mask plate is copied to a silicon wafer for producing a chip through generating light with a specific wavelength through the photolithography device. However, as the size of semiconductor devices is continuously reduced, the diffraction Effect of light becomes more and more obvious, and as a result, the Optical image degradation is finally generated on the design pattern, so that the distortion phenomenon occurs in the process of transferring the pattern on the mask to the silicon wafer, that is, the actual pattern finally formed on the silicon wafer through photoetching is different from the design pattern, and the OPE (Optical Proximity Effect) is generated, and if the distortion phenomenon is not eliminated, the whole manufacturing process can fail.

In order to correct the OPE phenomenon, OPC (Optical Proximity Correction) is generated. The core idea of OPC is to pre-process the reticle before photolithography by modifying the amount of compensation in advance to exactly compensate for the optical proximity effect caused by the exposure system. Specifically, an OPC model is established, and a photomask pattern is designed based on the OPC model, and although an OPE phenomenon occurs in the lithographic pattern after lithography with respect to the photomask pattern, the cancellation of the phenomenon is considered in designing the photomask pattern based on the OPC model, and therefore, the lithographic pattern after lithography is close to a target pattern actually desired by a user.

Under the existing photoetching process conditions, the conventional method for establishing the OPC model comprises the following steps: firstly, designing a test pattern; secondly, manufacturing a test photomask; then, collecting wafer data (wafer data) on the test photomask, and checking and sorting the collected wafer data; and finally, establishing an OPC model by using effective and reasonable wafer data. When the OPC model is established, calculation and regression are carried out on optical term parameters and non-optical term parameters, and the process is continuously circulated until the OPC model finds the most suitable parameters. If the parameters of the optical item and the non-optical item are many, each parameter can set a range, if a process is finished, the data weight or the number and the like used for building the model are adjusted, the parameters need to be fitted again, so that a long time is needed for fitting, the production plan of the product is stressed, and a large amount of system resources and manpower are wasted.

Disclosure of Invention

The invention aims to provide a modeling method of an optical proximity correction model, which is used for shortening the modeling time of the optical proximity correction model and improving the modeling efficiency.

In order to achieve the above objects and other related objects, the present invention provides a modeling method of an optical proximity correction model, which includes at least the following steps:

designing a test pattern, and manufacturing a test photomask according to the test pattern;

transferring the test pattern to a wafer by using the test photomask, forming an actual pattern on the wafer, and collecting first wafer data of the actual pattern;

determining a defocus range through the first wafer data, wherein the specific method comprises the following steps: searching a target point of a pattern wide and sparse area in the test pattern according to the first wafer data, wherein the first wafer data corresponding to the target point meets the process target requirement; drawing a Poisson curve corresponding to the target point of the wide and sparse region of the graph by using simulation software; acquiring a vertex value of the Poisson curve, and determining the defocus range according to the vertex value;

and fitting according to the defocus range to establish an optical proximity correction model.

Optionally, in the modeling method of the optical proximity correction model, the defocus range is ± 10% of the vertex value.

Optionally, in the modeling method of the optical proximity correction model, the method of fitting according to the defocus range includes:

acquiring second wafer data of a target point of the pattern wide and sparse area under a focusing matrix condition;

selecting a plurality of defocus amounts and corresponding actual critical dimensions from the second wafer data, wherein the defocus amounts comprise an optimal exposure defocus amount, at least one defocus amount larger than the optimal exposure defocus amount and at least one defocus amount smaller than the optimal exposure defocus amount, and drawing a trend graph of the actual critical dimensions;

selecting at least three defocusing amounts in the defocusing amount range to respectively perform model calculation and regression processing to obtain corresponding simulated key dimensions, and drawing a trend graph of the simulated key dimensions;

and regulating and controlling the simulated key size by adjusting the defocus amount selected in the defocus amount range until the variation trend of the simulated key size is consistent with that of the actual key size.

Optionally, in the modeling method of the optical proximity correction model, the method for obtaining the second wafer data of the target point of the wide and sparse region of the graph under the condition of the focusing matrix includes:

and photoetching the wafer under the condition of a focusing matrix, and transferring the target point of the wide and sparse graph onto the wafer to acquire the second wafer data.

Optionally, in the modeling method of the optical proximity correction model, the number of defocus amounts selected in the second wafer data is equal to the number of defocus amounts selected in the defocus range.

Optionally, in the modeling method of the optical proximity correction model, the number of defocus amounts selected in the defocus range is three.

Optionally, in the modeling method of the optical proximity correction model, when the variation trend of the simulated critical dimension is consistent with that of the actual critical dimension, a defocus amount in the middle of three defocus amounts selected in the defocus amount range is a defocus amount accurate value.

Optionally, in the modeling method of the optical proximity correction model, the first wafer data and the second wafer data are acquired by using a scanning electron microscope for measuring a feature size.

Optionally, in the modeling method of the optical proximity correction model, when the target point of the pattern wide and sparse region in the test pattern is searched according to the first wafer data, the anchor point of the pattern dense region in the test pattern is also searched to serve as the reference point of the test pattern.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

in the modeling method of the optical proximity correction model provided by the invention, the defocus range is determined in advance, and the optical proximity correction model is built by fitting according to the defocus range, namely, in the process of fitting the optical proximity correction model, the defocus amount is set in the determined defocus range, so that the time and the times of regression processing can be reduced, the modeling time of the optical proximity correction model is shortened, and the modeling efficiency is improved.

Drawings

FIG. 1 is a block diagram of a method of modeling an optical proximity correction model;

FIG. 2 is a block diagram of a modeling method of an optical proximity correction model according to an embodiment of the present invention;

FIG. 3 is a Poisson curve corresponding to a target point of a pattern broad and sparse region according to an embodiment of the present invention;

FIG. 4 is a graph of actual CD trend and a graph of simulated CD trend, in accordance with an embodiment of the present invention.

Detailed Description

Referring to fig. 1, a conventional method for creating an optical proximity correction model includes: firstly, designing a test pattern; secondly, manufacturing a test photomask according to the test pattern; then, transferring the test pattern to a wafer by using the test mask, forming an actual pattern on the wafer, collecting wafer data of the actual pattern (i.e. collecting wafer data), and checking and sorting the collected wafer data (i.e. performing data sorting on the collected wafer data); and finally, establishing an OPC model by using effective and reasonable wafer data. When the OPC model is established, calculation and regression processing are carried out on optical term parameters and non-optical term parameters, and the process is continuously circulated until the OPC model finds the most suitable parameters. If there are many optical parameters and non-optical parameters, each parameter will set a range, if a process is finished, the weight or number of data used for modeling is adjusted, i.e. the parameters are new, then the parameters need to be fitted again, and thus it takes a long time to fit. Pressure is placed on the production plan of the product, and a large amount of system resources and manpower are wasted.

In order to shorten the modeling time of the optical proximity correction model and improve the modeling efficiency, the invention provides a modeling method of the optical proximity correction model. By determining the defocus range in advance and setting the defocus amount within the determined defocus range in the fitting process of the optical proximity correction model, the time and times of regression processing can be reduced, the modeling time of the optical proximity correction model can be shortened, and the modeling efficiency can be improved.

The following describes the modeling method of the optical proximity correction model according to the embodiment of the present invention in further detail with reference to fig. 2 to 4 and the specific embodiment. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.

Referring to fig. 2, the method for modeling an optical proximity correction model provided by the present invention specifically includes:

step S1: designing a test pattern, and manufacturing a test photomask according to the test pattern;

step S2: transferring the test pattern to a wafer by using the test photomask, forming an actual pattern on the wafer, and collecting first wafer data of the actual pattern;

step S3: determining a defocus range through the first wafer data;

step S4: and fitting according to the defocus range to establish an optical proximity correction model.

In step S1, the mask may be selected from various types, such as chrome plate, dry plate, film, and relief plate, specifically, in this embodiment, taking chrome plate as an example, a quartz substrate is first fabricated, and more specifically, a blank substrate is first provided, the size and thickness of which may be selected according to actual needs, and this embodiment is not limited, for example, the blank substrate has a size of 6 inches square and a thickness of 0.25 inches, and is made of pure fused silica, for example, and the surface of the substrate is flat and defect-free. And depositing a light blocking layer on the blank substrate, wherein the light blocking layer is a chromium layer, for example, the light blocking layer can block exposure from a photoetching machine, the light blocking layer can be a chromium layer deposited on one side of the blank substrate by a sputtering method, a test pattern is formed on the chromium layer, a chromium oxide layer or a chromium nitride layer can be further deposited on the chromium layer to increase the adhesion between the chromium layer and the substrate, and a photoresist layer is further deposited on the chromium oxide layer or the chromium nitride layer by sputtering to form a photomask, wherein the photoresist layer is chromium sesquioxide, for example. Test patterns are then formed on the reticle by a reticle writer, and the original patterns stored by electrons can be drawn into a layout by e-beam lithography, for example. Specifically, a high resolution pattern is transferred to the reticle surface by electron beam lithography in which an electron source generates a plurality of electrons that are accelerated and focused to form a pattern projected onto the reticle surface, the electron beam may be focused magnetically or electrically, the photoresist is exposed, data of a test pattern is presented on the photoresist, the exposed photoresist is baked, an image of the photoresist is developed using a developer, rinsed and dried to remove residues. The developed reticle is placed in an etcher that can precisely etch away the light blocking layer material, for example, by plasma, and the etched reticle is loaded into a cleaning machine that strips the photoresist layer, for example, using a dry plasma or wet chemical process.

In step S2, the test pattern is transferred onto a wafer by using the test mask, so as to form an actual pattern on the wafer, and wafer data obtained by the actual pattern, i.e. first wafer data, is collected. Specifically, first, a mask layer (for example, a photoresist layer) is formed on the wafer; then, using the test photomask to execute a photoetching process to form a patterned mask layer; then, etching the wafer by using the patterned mask layer as an etching mask so as to form the actual pattern on the wafer; and finally, removing the patterned mask layer and collecting the wafer data of the actual graph. After the wafer data is collected (i.e., the first wafer data is collected), data interpretation is also performed to determine the defocus range. Illustratively, the first wafer data of the actual pattern may be collected with a scanning electron microscope (CDSEM) through feature size measurement.

And transferring the test pattern to a wafer by using the test mask under the optimal exposure condition. The optimal exposure conditions are: the wafer is exposed according to a plurality of exposure conditions in advance to obtain an actual pattern, and the finally obtained exposure condition corresponding to the actual pattern, such as a process window, a critical dimension (namely a CD value), pattern density and the like which can best meet the design requirements, is the optimal exposure condition.

In step S3, the method for determining the defocus range from the first wafer data includes:

step S31: searching a target point of a pattern width sparse area in the test pattern according to the first wafer data;

step S32: drawing a Poisson curve corresponding to the target point of the wide and sparse region of the graph by using simulation software;

step S33: and acquiring a vertex value of the Poisson curve, and determining the defocus range according to the vertex value.

In step S31, after the first wafer is collected, data sorting is performed on the first wafer, and a target point of a pattern sparsely and widely distributed region in the test pattern is searched according to the first wafer data. The target point of the pattern wide sparse region in the test pattern is a point at which the pattern wide sparse region in the test pattern reaches a target, that is, the first wafer data corresponding to the target point meets the process target requirement, and further, the difference value between the key size formed by the target point of the pattern wide sparse region on the test pattern and the key size formed by the target point of the pattern wide sparse region transferred to the wafer is smaller than a threshold value. The threshold value can be set according to the process requirements, and further, the threshold value is preferably 1. And when searching for the target point of the pattern wide and sparse area in the test pattern according to the first wafer data, searching for the anchor point of the pattern dense area of the test pattern to serve as the reference point of the test pattern. The anchor points of the pattern dense area of the test pattern also need to meet the target, namely, the first wafer data corresponding to the anchor points of the pattern dense area meet the process target requirement. The graph density of the graph dense area is greater than that of the graph wide and sparse area, and anchor points of the graph dense area can also be used as technical nodes of the photoetching process.

In step S32, a poisson curve (Bossung curve) corresponding to the target point of the wide and sparse region of the graph is drawn by using simulation software, and referring to fig. 3, the simulation software plots a graph of key dimensions corresponding to different defocus amounts.

In step S33, a vertex value of the poisson curve is obtained, and the defocus range is a relatively stable value at a position where the poisson curve is close to the vertex, referring to fig. 3, a value of the change amount of a CD (critical dimension) to the left or right at the vertex of the parabola is the smallest and relatively stable, and the slope of the parabola is relatively large at other places and the CD change amount is also relatively large. Preferably, the defocus range is ± 10% of the vertex value. For example, in fig. 3, the defocus amount corresponding to the vertex value of the poisson curve is 75, and the defocus amount range is 75 ± 10%, that is, the defocus amount value is 75 ± 10%.

In step S4, the method of fitting according to the defocus amount range includes:

step S41: acquiring second wafer data of a target point of the pattern wide and sparse area under a focusing matrix condition;

step S42: selecting a plurality of defocus amounts and corresponding actual critical dimensions from the second wafer data, wherein the defocus amounts comprise an optimal exposure defocus amount, at least one defocus amount larger than the optimal exposure defocus amount and at least one defocus amount smaller than the optimal exposure defocus amount, and drawing a trend graph of the actual critical dimensions;

step S43: selecting at least three defocusing amounts in the defocusing amount range to respectively perform initial model calculation and regression processing of the optical proximity correction to obtain corresponding simulated key dimensions, and drawing a trend graph of the simulated key dimensions;

step S44: and regulating and controlling the simulated key size by adjusting the defocus amount selected in the defocus amount range until the variation trend of the simulated key size is consistent with that of the actual key size.

In step S41, the method for acquiring the second wafer data of the target points of the pattern broad and sparse regions under the condition of the focusing matrix includes: and photoetching the wafer under the condition of a focusing matrix, and transferring the target point of the wide and sparse graph onto the wafer to acquire the second wafer data. And second wafer data of the actual pattern may be collected with a scanning electron microscope (CDSEM) through feature size measurement.

In step S42, an actual critical dimension corresponding to a plurality of defocus amounts including an optimal exposure defocus amount, at least one defocus amount larger than the optimal exposure defocus amount, and at least one defocus amount smaller than the optimal exposure defocus amount is selected from the second wafer data, and a trend graph of the actual critical dimension is drawn. Preferably, an actual critical dimension corresponding to 3 defocus amounts is selected from the second wafer data, where the 3 defocus amounts are a first defocus amount, a second defocus amount, and a third defocus amount, respectively, and the second defocus amount is an optimal exposure defocus amount, such as a vertex value 75 corresponding to fig. 3. The first defocus amount is smaller than the second defocus amount, the third defocus amount is larger than the second defocus amount, the first defocus amount and the third defocus amount are selected within the bearing range of the machine table, preferably, the first defocus amount is as small as possible, the second defocus amount is as large as possible, and therefore the variation trend of the actual critical dimension is obvious. And forming a two-dimensional coordinate system by taking the defocus amount as an abscissa and the key size as an ordinate, and drawing the defocus amounts selected from the second wafer data and the key size corresponding to the defocus amount in the two-dimensional coordinate system. For example, referring to fig. 4, the first defocus amount, the second defocus amount, the third defocus amount, the actual critical dimension corresponding to the first defocus amount, the actual critical dimension corresponding to the second defocus amount, and the actual critical dimension corresponding to the third defocus amount are plotted in the two-dimensional coordinate system, so as to obtain a trend graph of the actual critical dimension (L1).

At step S43, at least three defocus amounts are arbitrarily selected in the defocus amount range, and preferably, the number of defocus amounts selected in the second wafer data is equal to the number of defocus amounts selected in the defocus amount range. For example, three defocus amounts are selected within the defocus amount range. Three defocus amounts are selected in a defocus range to be a group and are respectively calculated and regressed with other parameters, a simulated key size is output after each regression processing, and the accurate value of the defocus amount is determined by comparing the variation trend of the simulated key size with the actual key size. The parameters of the optical proximity correction model include: exposure Beam focal length (Beam Focus), defocus, pupil attenuation radius, and pupil edge transmittance, among others.

In step S44, the simulated critical dimension is adjusted by adjusting the defocus amount selected in the defocus amount range until the simulated critical dimension and the actual critical dimension have a variation trend consistent. For example, when the three defocus amounts selected in the defocus amount range have a variation trend consistent with that of the actual key size, the defocus amount (arranged according to the defocus amount) in the middle of the three defocus amounts selected in the defocus amount range is an accurate defocus amount value. The three defocus amounts selected in the defocus range are set in the parameters of the machine (i.e. in software), and the defocus amounts in the trend graph output by the machine correspond to the defocus amounts in the parameter setting of the machine one by one, but are not completely the same. Referring to fig. 4, the defocus amount in the simulated critical dimension trend graph (L2) is the defocus amount output by the machine, and when the simulated critical dimension trend is consistent with the actual critical dimension trend, the defocus amount (also the middle defocus amount) in the machine parameter setting corresponding to the middle defocus amount (arranged by the defocus amount) in the defocus amounts output by the machine is the accurate value of the defocus amount. Namely, when the variation trend of the simulated key size obtained by fitting the three defocus amounts selected in the defocus range is consistent with the variation trend of the actual key size, the middle defocus amount of the three defocus amounts selected is the accurate defocus amount.

The optical proximity correction model is a purely optical model. The process of fitting of modeling requires that each parameter be uniformly calculated and regressed. In the modeling process of the optical proximity correction model in the embodiment, the defocus amount is directly set in the defocus amount range, so that the time and times of regression processing can be reduced, the modeling time of the optical proximity correction model is shortened, and the modeling efficiency is improved. In the optical proximity correction model in the prior art, the range of the defocus parameter is set in combination with other parameters, each group of parameters can obtain an evaluation function, the lower the evaluation function is, the better the evaluation function is, but the evaluation function is sometimes inaccurate, parameter setting errors can occur, and the finally obtained model and the simulated critical dimension are not correct. The defocus range in the modeling process is directly set in the defocus range, and the defocus of the optical proximity correction model is determined by simulating the variation trend of the critical dimension and the actual critical dimension, so that the finally established optical proximity correction model can be ensured to be correct, and the critical dimension obtained by the model is also correct.

When the weight or number of the data of the model is adjusted to obtain new data, the adjusted parameters (i.e. the new data) and the defocus amount set in the defocus amount range are only required to be calculated and regressed, so that the fitting time can be shortened, and the modeling efficiency can be improved.

Therefore, the invention provides a method for determining the defocus range in advance, which sets the defocus in the defocus range during fitting, can reduce the time and times of regression processing, shorten the time of OPC modeling, and improve the modeling efficiency.

The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.