CN112904681A - Photoacid diffusion length measuring method based on Fourier transform - Google Patents
Photoacid diffusion length measuring method based on Fourier transform Download PDFInfo
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- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70425—Imaging strategies, e.g. for increasing throughput or resolution, printing product fields larger than the image field or compensating lithography- or non-lithography errors, e.g. proximity correction, mix-and-match, stitching or double patterning
- G03F7/70433—Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
- G03F7/70441—Optical proximity correction [OPC]
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Abstract
The invention provides a method for measuring a photo-acid diffusion length based on Fourier transform, which measures the line edge roughness of a developed photoresist by using an SEM (scanning electron microscope) machine; carrying out Fourier transform on the line width value to obtain a power spectral density function; determining the spatial frequency of a turning point between the low frequency region and the middle frequency region according to the power spectral density function; calculating the spatial frequency at different temperatures, providing a group of photoacid diffusion length values actually measured at different temperatures, and establishing a functional relation between the photoacid diffusion length values and the spatial frequency at different temperatures; and calculating the photo-acid diffusion length at the required temperature according to the function. According to the method, measurement original data are obtained by optimizing an LER measurement mode, and then the turning point between the low-frequency region and the medium-frequency region is determined through a Fourier transform pair, so that the photoacid diffusion length is finally determined. Compared with the traditional measuring method, the method is easier to realize the monitoring of the actual process end on the acid diffusion length, and is beneficial to timely acquiring the influence of the photoetching process condition on the acid diffusion length.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a method for measuring a photoacid diffusion length based on Fourier transform.
Background
In the field of photolithography, photoacid diffusion is a relatively complex physicochemical process. The characterization of the diffusion length of the photoacid has great significance for the simulation of the photoetching process and the correction of the optical proximity effect. The prior art methods of measuring acid diffusion length typically include: after exposure, the photoresist spun on the substrate is brought into intimate contact with the same photoresist that was not exposed. And (3) carrying out Post-Exposure baking (Post Exposure Bake, PEB) on the two tightly attached photoresists, wherein the photoacid can diffuse into the unexposed photoresists in the process. The photoresist in the photoacid diffusion region is removed by development, and the photoacid diffusion length can be obtained by measuring the thickness of the photoresist film.
A large number of experimental results show that the diffusion length of acid in the glue has strong correlation with the Edge Roughness (LER) of the photoresist pattern. In the photolithography process, fig. 1 is a schematic diagram illustrating a process of forming line edge roughness in the prior art. The method comprises the following steps: first, a light source irradiates a photoresist through a mask plate, and photons react with a Photo Acid Generator (PAG) in the photoresist to generate Acid radical ions. The acid ions then react with the polymer resin. Because the molecular chain of the polymer resin is suspended with acid-labile groups, the reaction product is new acid radical ions and the polymer resin which can be dissolved in a developing solution. Under the action of PEB, acid radical ions diffuse to the non-irradiated area, and the diffusion process mainly generates the reaction of the acid radical ions and the polymer resin. The polymer resin, which is soluble in the developer solution, is washed away during the development process to form a photolithographic pattern.
The photo-acid diffusion length is one of important parameters in the photoetching process, and the accurate measurement of the photo-acid diffusion length has significance for optical simulation and optical proximity effect correction. The traditional measuring method for the diffusion length of the photoacid is relatively complex and is difficult to measure in FAB, so that the influence of the diffusion length on the photoetching process cannot be effectively monitored in real time.
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide a method for measuring a photoacid diffusion length based on fourier transform, which is used to solve the problem in the prior art that when a process parameter changes, a corresponding photoacid diffusion length after the process parameter changes cannot be obtained in time.
In order to achieve the above and other related objects, the present invention provides a method for measuring a diffusion length of an optical acid based on fourier transform, the method at least comprising the steps of:
measuring line edge roughness LER of the developed photoresist by using an SEM (scanning electron microscope) machine; the value range of the measurement sampling length L is 500 nm-4 μm; when the SEM machine measures, the distance between two lines of electron beams scanned by the SEM machine is delta x; measuring to obtain L/delta x line width values of the photoresist;
step two, carrying out Fourier transform on the L/delta x line width values from 1/L to 1/delta x space frequency domain to obtain a power spectral density function PSD;
step three, according to the function PSD of the low frequency area in the power spectral density function PSDLFDetermining low frequency lg (PSD)LF) C; function PSD according to medium-frequency region in power spectral density function PSDMFDetermining the intermediate frequency lg (PSD)MF) Alff + B, where a, B, C are constants and f is the spatial frequency; when C is Algf + B, obtaining the spatial frequency f corresponding to the low-intermediate frequency conversion pointT；
Step four, calculating the spatial frequency f at different temperaturesTProviding a group of photo-acid diffusion length values actually measured at different temperatures, and establishing the photo-acid diffusion length values and the spatial frequency f at different temperaturesTFunctional relationship L ofDiff＝g(fT)；
Step five, according to the functional relation LDiff＝g(fT) The photoacid diffusion length at the desired temperature was calculated.
Preferably, the method for measuring the line edge roughness of the photoresist by using the SEM machine in the first step includes: scanning the photoresist lines from top to bottom at equal intervals by using an electron beam of an SEM (scanning Electron microscope) machine, and obtaining one line width value in each scanning.
Preferably, the length of the measurement sample in step one is 2 μm.
Preferably, when scanning the line of the photoresist from top to bottom at an equal interval by using an electron beam of an SEM station in the first step, the electron beam is two electron beams located at two sides of the line of the photoresist, and a value range of a distance Δ x between the two electron beams is 0.3nm to 10 nm.
Preferably, the distance Δ x between the two electron beams in step one is 1 nm.
Preferably, the photoresist in the first step is a chemically amplified photoresist.
Preferably, the number of the photoacid diffusion length values actually measured in step four at different temperatures is greater than 10.
Preferably, the value of the measurement sampling length L in the first step is 1.312 μm.
Preferably, the distance Δ x between the two electron beams in the first step is 3.32 nm.
As described above, the method for measuring the photoacid diffusion length based on fourier transform according to the present invention has the following advantageous effects: according to the method, the measurement original data is obtained by optimizing an LER measurement mode, the data is analyzed through Fourier transform to determine the turning point between the low-frequency region and the medium-frequency region, and finally the photoacid diffusion length is determined through calculation. Compared with the traditional measuring method, the method is easier to realize the monitoring of the actual process end on the acid diffusion length, and is beneficial to timely acquiring the influence of the photoetching process condition on the acid diffusion length.
Drawings
FIG. 1 is a schematic diagram illustrating a prior art process for forming line edge roughness;
FIG. 2a is a schematic view of an SEM measurement in accordance with the present invention;
FIG. 2b shows an exploded view of the LER of the present invention;
FIG. 3 is a graph of a power spectrum function of the present invention;
FIG. 4 is a flow chart of the Fourier transform-based photoacid diffusion length measurement method of the present invention.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 4. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
The invention provides a method for measuring the diffusion length of an optical acid based on Fourier transform, as shown in FIG. 4, FIG. 4 is a flow chart of the method for measuring the diffusion length of the optical acid based on Fourier transform, and the method at least comprises the following steps:
measuring line edge roughness LER of the developed photoresist by using an SEM (scanning electron microscope) machine; the value range of the measurement sampling length L is 500 nm-4 μm; when the SEM machine measures, the distance between two lines of electron beams scanned by the SEM machine is delta x; measuring to obtain L/delta x line width values of the photoresist;
LER is measured by Scanning Electron Microscope (SEM), wherein the Electron beam scans the object from top to bottom at equal intervals, each scanning results in a value, and the LER is obtained by calculating the standard deviation of the series of values, and the SEM is shown in FIG. 2 a. Factors affecting LER include photoresist composition uniformity, photon shot noise, etc., in addition to photoacid diffusion. The uniformity of the photoresist components and the photon shot noise are random factors, have no autocorrelation and have no periodicity on LER. On the molecular level, acid radical ions react with acid-labile groups in a high molecular polymer one by one, the migration process of the acid radical ions has the influence of the structure and distribution of the high molecular polymer, and the acid radical ions have autocorrelation and periodicity on LER. The LER can therefore be broken down into two parts, LER affected by random factors and LER affected by periodic factors, as shown in figure 2 b.
Further, the method for measuring the line edge roughness of the photoresist by using the SEM machine in the first step of this embodiment includes: scanning the photoresist lines from top to bottom at equal intervals by using an electron beam of an SEM (scanning Electron microscope) machine, and obtaining one line width value in each scanning.
Further, in the first step of this embodiment, when scanning the line of the photoresist from top to bottom at an equal interval by using an electron beam of an SEM station, the electron beam is two electron beams located at two sides of the line of the photoresist, and a value of an interval Δ x between the two electron beams is in a range of 0.3nm to 10 nm.
In some embodiments, the measurement sampling length L in step one is 2 μm and the separation Δ x between the two electron beams is 1 nm. Further, the value of the measurement sampling length L in the first step of this embodiment is 1.312 μm. Still further, in the first step of this embodiment, the distance Δ x between the two electron beams is 3.32 nm. The pitch of the two electron beams refers to the two electron beams in fig. 2a that are located on the same horizontal line on both sides of the line of the photoresist.
Still further, the photoresist in the first step of this embodiment is a chemically amplified photoresist.
Step two, carrying out Fourier transform on the L/delta x line width values from 1/L to 1/delta x space frequency domain to obtain a power spectral density function PSD; that is, fourier transform is performed on the LER result measured by SEM with respect to the measurement interval (1/L to 1/Δ x, where L is the total scan length and Δ x is the interval between two electron beams), so as to obtain a corresponding Power spectral Density function (PSD), as shown in fig. 3, where fig. 3 is a Power spectral function diagram according to the present invention. The LERs affected by random factors and LERs affected by periodic factors can be distinguished from the PSD spectrogram. The LER PSD spectrogram comprises three frequency bands: a low frequency range, a mid frequency range, and a high frequency range. The low-frequency area is a platform area, which indicates that LER is irrelevant to the size of the sampling length and is influenced by random factors; the intermediate frequency region is the region where the PSD drops significantly as the sampling length is shortened. In this embodiment, the two pairs of 800 data points measured in the first step are analyzed, and fourier transform is performed on the data points at a spatial frequency of 0.8 to 301.2 to obtain a PSD spectrogram.
Step three, according to the function PSD of the low frequency area in the power spectral density function PSDLFDetermining low frequency lg (PSD)LF) C; function PSD according to medium-frequency region in power spectral density function PSDMFDetermining the intermediate frequency lg (PSD)MF) Alff + B, where a, B, C are constants and f is the spatial frequency; when C is Algf + B, obtaining the spatial frequency f corresponding to the low-intermediate frequency conversion pointT(ii) a From Fourier transformIndicates that the interval enters a period transition interval. The high frequency region is the measurement noise introduced by the electron beam. And determining the photo-acid diffusion length according to the sampling length corresponding to the low-intermediate frequency turning point.
This embodiment determines a low frequency lg (PSD) from data in a low frequency regionLF) Determining an intermediate frequency lg (PSD) according to the intermediate frequency data (1.80)MF) The spatial frequency f corresponding to the low-intermediate frequency conversion point can be obtained by combining the two formulas as-1.4 lgf +3.13T＝8.91。
Step four, calculating the spatial frequency f at different temperaturesTProviding a group of photo-acid diffusion length values actually measured at different temperatures, and establishing the photo-acid diffusion length values and the spatial frequency f at different temperaturesTFunctional relationship L ofDiff＝g(fT)；
Further, in the fourth step of this embodiment, the number of the photoacid diffusion length values actually measured at different temperatures is greater than 10. Four data volumes suggested to be greater than 10 according to a set of actually measured photoacid diffusion lengths provided by the manufacturer, and f of the actual measurement of FABTEstablishing photoacid diffusion Length and fTFunctional relationship L ofDiff＝g(fT)。
Step five, according to the functional relation LDiff＝g(fT) The photoacid diffusion length at the desired temperature was calculated. That is, according to the functional relationship LDiff＝g(fT) The photoacid diffusion length under different lithographic conditions (different temperatures) can be calculated.
In summary, the invention obtains the measurement original data by optimizing the LER measurement mode, analyzes the data by fourier transform to determine the turning point between the low frequency region and the medium frequency region, and finally determines the photoacid diffusion length by calculation. Compared with the traditional measuring method, the method is easier to realize the monitoring of the actual process end on the acid diffusion length, and is beneficial to timely acquiring the influence of the photoetching process condition on the acid diffusion length. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (9)
1. A method for measuring the diffusion length of photoacid based on Fourier transform is characterized by at least comprising the following steps:
measuring line edge roughness LER of the developed photoresist by using an SEM (scanning electron microscope) machine; the value range of the measurement sampling length L is 500 nm-4 μm; when the SEM machine measures, the distance between two lines of electron beams scanned by the SEM machine is delta x; measuring to obtain L/delta x line width values of the photoresist;
step two, carrying out Fourier transform on the L/delta x line width values from 1/L to 1/delta x space frequency domain to obtain a power spectral density function PSD;
step three, according to the function PSD of the low frequency area in the power spectral density function PSDLFDetermining low frequency lg (PSD)LF) C; function PSD according to medium-frequency region in power spectral density function PSDMFDetermining the intermediate frequency lg (PSD)MF) Alff + B, where a, B, C are constants and f is the spatial frequency; when C is Algf + B, obtaining the spatial frequency f corresponding to the low-intermediate frequency conversion pointT；
Step four, calculating the spatial frequency f at different temperaturesTProviding a group of photo-acid diffusion length values actually measured at different temperatures, and establishing the photo-acid diffusion length values and the spatial frequency f at different temperaturesTFunctional relationship L ofDiff＝g(fT)；
Step five, according to the functional relation LDiff＝g(fT) The photoacid diffusion length at the desired temperature was calculated.
2. The method for measuring a photoacid diffusion length based on fourier transform according to claim 1, characterized in that: in the first step, the method for measuring the line edge roughness of the photoresist by using the SEM machine comprises the following steps: scanning the photoresist lines from top to bottom at equal intervals by using an electron beam of an SEM (scanning Electron microscope) machine, and obtaining one line width value in each scanning.
3. The method for measuring a photoacid diffusion length based on fourier transform according to claim 2, characterized in that: in the first step, the length of the measurement sample is 2 μm.
4. The method for measuring a photoacid diffusion length based on fourier transform according to claim 3, characterized in that: when scanning the photoresist line from top to bottom at equal intervals by using an electron beam of an SEM (scanning electron microscope) machine, the electron beam is two electron beams positioned at two sides of the photoresist line, and the value range of the interval delta x between the two electron beams is 0.3nm-10 nm.
5. The method for measuring a photoacid diffusion length based on fourier transform according to claim 4, characterized in that: in the step one, the distance delta x between the two electron beams is 1 nm.
6. The method for measuring a photoacid diffusion length based on fourier transform according to claim 1, characterized in that: the photoresist in the first step is chemically amplified photoresist.
7. The method for measuring a photoacid diffusion length based on fourier transform according to claim 1, characterized in that: and in the fourth step, the number of the photo-acid diffusion length values actually measured at different temperatures is more than 10.
8. The method for measuring a photoacid diffusion length based on fourier transform according to claim 1, characterized in that: the value of the measurement sampling length L in the first step is 1.312 μm.
9. The method for measuring a photoacid diffusion length based on fourier transform according to claim 8, characterized in that: the distance Δ x between the two electron beams in step one is 3.32 nm.
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