KR100930383B1 - How to measure pattern line width of photomask - Google Patents

Abstract

After forming a mask pattern on the transparent substrate and attaching a pellical membrane layer protecting the mask pattern on the substrate, the measurement light passing through the pellicle membrane film is used for the wavelength band of the exposure light to be used for transfer on the wafer of the mask pattern. The present invention provides a method for measuring pattern line width of a photomask including irradiating using a longer wavelength band and measuring a change in reflectance of reflected light to measure a line width (CD) of a mask pattern with a spectrophotometer.

Description

Method for estimating critical dimension of patterns in photomask

1 is a view for explaining a pattern line width measuring method of a photomask according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining measurement modeling of a method for measuring a pattern line width of a photomask according to an embodiment of the present invention.

3 is a graph showing the distribution of refractive index (n) and extinction coefficient (k) according to a measurement wavelength band of a spectrophotometer according to an embodiment of the present invention.

4 is a graph illustrating a reflectance (R) distribution according to a measurement wavelength band of a spectrophotometer according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to microlithography technology, and more particularly, to a method of measuring a critical dimension (CD) of a photomask.

Microlithography technology is used to implement circuit patterns of semiconductor devices on wafers. After designing a circuit pattern to be implemented on the wafer, forming a photomask having a designed pattern layout, and performing an exposure process using a photomask, a wafer such as a photoresist pattern following the pattern layout on the wafer is formed. It forms a pattern. The line width (CD) measurement of the mask pattern of the photomask during the process of manufacturing the photomask is performed after the pattern etch and resist strip processes are completed.

Line width measurement is mainly used for measuring the line width (CD) using a scanning electron microscope (SEM). However, after the line width (CD) measurement, the line width of the pattern may vary as further processes such as cleaning and pattern defect repair are performed. For example, in the case of wet cleaning, sulfuric acid (H ₂ SO ₄ ), hydrogen peroxide (H ₂ O ₂ ), ammonia (NH ₄ OH), and / or ozone water (O ₃ -DI) are used. Due to wet chemistry, the mask pattern of the photomask may be lost and line width variation may occur. For example, the thickness of chromium (Cr), chromium oxide (CrO or CrO ₂ ), chromium nitride (CrON), or the like, or the thickness of molybdenum silicon nitride (MoSiN) constituting a phase shift layer, The line width CD may be changed. In addition, after such wet cleaning, different etching rates may be generated according to areas in which the pattern is dense and isolated, thereby causing a difference in line width (CD) between the areas.

The line width (CD) information of the mask pattern at the time of shipping the photomask is provided based on the line width (CD) measurement result measured before the progress of this subsequent process. Therefore, when setting exposure conditions in a subsequent exposure process using such line width information, a wafer exposure error may be caused. After the photomask fabrication process including the subsequent process is completed, a method of measuring the final line width (CD) using a CD-SEM may be considered. Nevertheless, the SEM measurement process takes place in a vacuum chamber, which requires an additional cleaning process due to particle contamination after the measurement. Therefore, there is a limit to measuring and verifying the final line width (CD) excluding any further processing.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method for more accurately measuring a line width (CD) of a mask pattern on a photomask.

One aspect of the present invention for the above technical problem, forming a mask pattern on a transparent substrate, attaching a pellical membrane layer (pellical membrane layer) to protect the mask pattern on the substrate, and the pellicle membrane A method for measuring a pattern line width of a photomask, comprising measuring a line width (CD) of the mask pattern with a spectrophotometer by irradiating the measurement light passing through the film and measuring a change in reflectance of the reflected light.

The measurement light proposes a photomask pattern line width measuring method for inducing the measurement of the change in reflectance according to the change in the wavelength band by using a wavelength band longer than the wavelength band of the exposure light to be used for transferring the mask pattern on the wafer.

The measurement light suggests a photomask pattern linewidth measuring method irradiated at a wavelength range of 190 nm to 1000 nm when the pellicle membrane film is for an ArF light source.

According to the present invention, a method for more accurately measuring the line width (CD) of a mask pattern on a photomask can be provided.

In an embodiment of the present invention, a mask pattern is formed on a transparent substrate of a photomask, a pellicle is attached on the substrate, and then a CD mean to target of a target of the photomask line CD. (MTT)) and global CD uniformity are measured by optical linewidth measurements using spectrophotometers, i.e., reflected light using a spectrophotometer.

Unlike the measurement in CD-SEM equipment, which uses a vacuum chamber to irradiate an electron beam and obtain signals from secondary electrons emitted from the specimen, the spectrophotometer, an optical measuring instrument, is not an vacuum but an atmosphere. The measurement may proceed in the middle. Therefore, it is possible to measure the pattern line width of the photomask with the pellicle attached, thereby protecting the mask pattern from particle contamination during the measurement. Thus, additional wet cleaning for decontamination after measurement and the like can be ruled out. In addition, since the pellicle membrane has a transmittance of substantially 99% or more with respect to the optical measurement wavelength, it is possible to measure CD with high reproducibility and accuracy of substantially 1 nm or less in the presence of the pellicle membrane. Therefore, in contrast to the CD measurement measured immediately after the patterning, it is possible to measure the minute CD change width after the completion of the final process.

1 is a view for explaining a pattern line width measuring method of the photomask according to an embodiment of the present invention. FIG. 2 is a diagram for explaining measurement modeling of a method for measuring a pattern line width of a photomask according to an embodiment of the present invention. 3 is a graph showing the distribution of refractive index (n) and extinction coefficient (k) according to a measurement wavelength band of a spectrophotometer according to an embodiment of the present invention. 4 is a graph illustrating a reflectance (R) distribution according to a measurement wavelength band of a spectrophotometer according to an embodiment of the present invention.

Referring to FIG. 1, in the method for measuring a pattern line width of a photomask according to an embodiment of the present invention, after the mask pattern 120 is formed on the transparent substrate 110, the pellicle membrane layer 140 is formed on the substrate 110. It is carried out with attached. Therefore, before the line width measurement, for example, the mask pattern 120 of the phase inversion layer such as MoSiN and the light shielding layer pattern 130 such as chromium (Cr) are patterned on the quartz substrate 110. Subsequently, the mask pattern 120 may be cleaned, and the pellicle membrane 140 may be attached to the light shielding layer pattern 130 using a frame 150.

Thereafter, the line width CD of the mask pattern 120 is measured using an optical measuring device such as a spectrophotometer 170. The spectrophotometer 170 irradiates the measured incident light passing through the pellicle membrane film 140 and measures the reflected reflected light to change the refractive index n and extinction coefficient k of the measurement target. By measuring, the line width CD of the mask pattern 120 is extracted. Since the optical measurement value is different between the region where the mask pattern 120 is located and the region where the mask pattern 120 is not located, the line width CD is measured using the difference for each region.

Referring to FIG. 2, as shown in FIG. 1, the surface of the photomask in which all the manufacturing processes are completed may include a first region 210 and a first layer that may be classified into a stack of different media in the case of a phase inversion mask (PSM). It may be divided into two regions 220. The first region 210 may be formed of the first quartz layer 111 used as the substrate 110 and the thickness of the recess layer 113 etched and recessed together when the mask pattern 120 is etched. It may be composed of a stack of two quartz layers 112 and a molybdenum silicon nitride (MoSiN) layer that is a mask pattern 120. The second region 220 may be formed of a single layer of the remaining first quartz layer 111 except for the thickness of the recessed recess layer 113. Optical linewidth (CD) measurement using a spectrophotometer is performed on these two regions 210 and 220.

Optical linewidth (CD) measurements are performed using reflected light, as shown in FIG. 1. At this time, it is preferable that the measurement light uses light of a wavelength band having a wavelength of less than 193 nm in the case of an ArF phase inversion mask. This is to prevent damage of the pellicle membrane film (140 in FIG. 1) by the measured incident light. Since the phase inversion mask for ArF adopts a pellicle membrane film 140 having characteristics suitable for the ArF exposure light source used in actual exposure, the pellicle membrane film 140 is irradiated when low-energy measurement light of a longer wavelength is applied. Damage can be suppressed. Therefore, the measurement light can use a band of approximately 193 nm to 1000 nm. For this reason, in the case of the KrF phase inversion mask, measurement light having a wavelength range of approximately 248 nm to 1000 nm can be used.

Even in the case of a binary mask in which a mask pattern is composed only of a chromium (Cr) light shielding layer, not a phase inversion mask, the pellicle membrane to be attached has a different film quality component depending on the wavelength of light used during exposure. Damage to the pellicle membrane film can be prevented by using the measurement light having a wavelength band longer than that of the light source.

The spectrophotometer 170 measures the reflected light and optically measures the line width (CD) using the refractive index (n) and the extinction coefficient (k) of the measurement target medium. Therefore, modeling of the film structure constituting the photomask is performed first. Specifically, as shown in FIG. 2, the phase inversion mask includes a quartz substrate 110 and a mask pattern 120 of a phase inversion film MoSiN, and the binary mask includes a chromium layer. Unique information on the refractive index (n) and extinction coefficient (k) that the film layers have basically is obtained. The refractive index n according to the measurement wavelength band may be obtained by the first graph 310 shown in FIG. 3, and the extinction coefficient k may be obtained by the second graph 330 shown in FIG. 3. The obtained unique information is input as basic information for the spectrophotometer 170 to analyze the line width (CD). In addition, thickness information of each of the film layers is also input as basic information. Each thickness starts from the prediction information and is shown as a real value from the measurement spectrophotometer 170 after the measurement.

After the input of the tomographic information is completed, the patterns to be measured are divided and set according to regions 210 and 220 of FIG. 2. The object to be measured may be divided into two regions. In the first region 210, the first region 210 may be etched from the first quartz layer 111 used as the substrate 110 and the mask pattern 120. The second quartz layer 112 having the thickness of the recess layer 113 etched and recessed together and the molybdenum silicon nitride (MoSiN) layer of the mask pattern 120 may be formed. The second region 220 may be formed of a single layer of the remaining first quartz layer 111 except for the thickness of the recessed recess layer 113. Optical linewidth (CD) measurement using a spectrophotometer is performed on these two regions 210 and 220. In this case, all of the layers representing the second quartz layer 112 and the mask pattern 120 in the first region 210 may be set as an air region.

After the modeling of the measurement target is completed, the measurement of the main line width (CD) is started. The spot size of the reflected light source may be about 40 μm, and the average line width CD for the repetitive pattern present in the present spot area is calculated as a measurement result. Reflectance of each wavelength of the measurement target pattern is measured by using wavelengths in a broad band that do not inhibit the pellicle membrane (140 in FIG. 1) in the wavelength band of approximately 190 nm to 1000 nm. The measured reflectance (%) can be obtained with the reflectance graph 410 shown in FIG.

The measured reflectivity (410 in FIG. 4) and the layer-specific information for each region input in the initial stage, that is, the refractive index n information (310 in FIG. 3) and extinction coefficient for each layer in each region (210 and 220 in FIG. 2). (k) A scalar operation is performed using the information 330 of FIG. 3 to calculate line width CD for each area and thickness information for each tomography layer. The optical CD value calculated in this way may have a difference in absolute value due to the difference in measurement method compared with the measured value by CD SEM, but has a constant linearity relationship. Therefore, it can be used for actual CD measurement by setting an offset according to each pattern design.

Optical CD measurements can be performed in the air, unlike SEM devices using vacuum chambers. Therefore, the photomask can be safely protected from particle contamination only through environmental management inside / outside the measuring device. Thus, final CD verification without contamination of the surface of the pattern as well as the pellicle membrane is possible.

According to the present invention described above, the conventional method of determining the quality of the mask by CD MTT (Mean To Target) and CDU (CD Uniformity) measured after completing the patterning process of exposure, development and etching during the photomask manufacturing process; Alternatively, in the present invention, the patterned CD MTT and CDU can be measured after the patterning process, and all subsequent processes prior to shipping the mask, including the subsequent wet cleaning and modification process and pellicle deposition. Accordingly, the small CD change exhibited by the post process can be verified and the final CD quality of the mask can be determined using the measured CD results. Therefore, by using the CD measurement as reference data when setting the wafer exposure conditions, it is possible to prevent in advance the wafer line width error (CD error) that may appear in the subsequent process.

As mentioned above, although this invention was demonstrated in detail through the specific Example, this invention is not limited to this, It is clear that the deformation | transformation and improvement are possible by the person of ordinary skill in the art within the technical idea of this invention.

Claims (3)

Forming a mask pattern on the transparent substrate; Attaching a pellical membrane layer protecting the mask pattern on the substrate; And The measurement light transmitted through the pellicle membrane film is irradiated using a wavelength band longer than the wavelength band of the exposure light to be used for transferring the mask pattern on the wafer, and the change in reflectance of the reflected light according to the wavelength band is measured to measure the line width (CD) of the mask pattern. Method for measuring the pattern line width of the photomask comprising the step of measuring with a spectrophotometer (spectrophotometer). delete The method of claim 1, The measurement light is a photomask pattern linewidth measuring method is irradiated in the wavelength range of 190nm to 1000nm when the pellicle membrane film is for the ArF light source.

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