KR100672691B1 - Method for measuring pattern in semiconductor device - Google Patents

Abstract

A method for measuring a pattern of a semiconductor device is provided to detect various data related to a critical dimension, an angle of a sidewall, and a thickness of a pattern without using an additional device. An optical measurement apparatus including a library for a critical dimension reflection characteristic corresponding to incident rays is prepared. A substrate(10) having a periodical pattern(12) formed on a surface thereof is prepared. The incident rays are irradiated on the pattern. The light scattered from the pattern is detected by using the optical measurement apparatus. A corresponding critical dimension for the scattered light is determined by comparing the scattered light information with the library.

Description

Method for Measuring Pattern of Semiconductor Device {Method for Measuring Pattern in Semiconductor Device}

1A to 1C are cross-sectional views illustrating a method of measuring a critical dimension of a conventional semiconductor device.

2 is a process cross-sectional view showing a pattern measuring method of a semiconductor device of the present invention.

Figure 3 is a signal used in the pattern measuring method of the semiconductor device of the present invention and the critical dimensions analyzed thereby

4A and 4B are cross-sectional views illustrating a pattern after exposure and after etching in a pattern measuring method of a semiconductor device according to the present invention

* Description of symbols on the main parts of the drawings *

10 substrate 11 material layer

12: pattern 20: detector

The present invention relates to a semiconductor device, and more particularly, to a method for measuring a pattern of a semiconductor device using optical equipment.

A method for measuring a critical dimension (CD) of a fine pattern of a conventional semiconductor device is as follows.

That is, after forming a photoresist pattern for forming a pattern of a predetermined structure on the upper surface of the semiconductor lower structure by using a scanning electron microscope (SEM) equipment, the critical dimension of the formed pattern by scanning electrons in the SEM equipment ( Measure CD).

In this case, the principle of measuring the CD of the pattern in the SEM is to first scan the electrons toward the pattern in the SEM, and the scanned electrons are again bounced off the pattern surface. It is measured that the phase is formed by electron).

Hereinafter, a method for measuring a critical dimension of a conventional semiconductor device will be described with reference to the accompanying drawings.

1A to 1C are cross-sectional views illustrating a method for measuring a critical dimension of a conventional semiconductor device.

As shown in FIG. 1A, first, a photoresist pattern 3 having a shape for patterning the lower structure 1 is formed on an upper portion of the lower structure 1.

Subsequently, when Ar plasma is irradiated onto the lower structure 1, the surface of the photoresist pattern 3 is graphitized 5, as shown in FIG. 1B, so that the electrical resistance is reduced and the total pressing force is reduced. (total suppression) is reduced.

At this time, the irradiation time of the Ar plasma is about 20 to 30 seconds so that no damage is generated on the surface of the photoresist pattern 3 by the Ar plasma.

As shown in FIG. 1C, when the electrical resistance of the photoresist pattern 3 decreases due to the irradiation of the Ar plasma, electrons scanned from the scanning electron microscope (SEM) may move freely without being trapped inside the photoresist pattern 3. In this way, the generation of the emission electrons 7 coming out is easily achieved.

Here, the image of the SEM is a detector that detects the secondary electrons 7 ejected from the object, that is, the photoresist pattern 3 and then bounces back from the object by the scanned electrons e-. It is formed by an intensity curve obtained by detection by a detector (not shown).

The measurement of the critical dimension (CD) using the SEM is based on the principle that the second electron is emitted when the electron is scanned. At this time, the incident angle at which the electron is incident is 90 °, at this time, the light source used is a semiconductor laser, the wavelength of the light source is 780nm, using the SEM only the critical dimension of the periodic pattern such as wiring Can be measured.

However, the above-described conventional critical dimension measuring method (measurement method using a SEM) of a semiconductor device has the following problems.

First, in the measurement using SEM (Scanning Electron Microscope), which is a measurement equipment used for measuring the critical dimension of a semiconductor device, a method of monitoring the process result is limited. It is cumbersome to use different equipment for each item (CD (critical dimension), pattern thickness, profile, etc.).

Second, in the SEM for critical dimension measurement using high energy (800-1500 volts), the critical dimension change occurs because the periodic pattern to be measured is deformed by electron charging as the measurement is repeated in the ArF photoresist pattern.

Third, the measurement method using SEM cannot observe the profile of the pattern to be measured by the top-down measurement method.

Fourth, optical probes for measuring thickness are inferior in accuracy in multiple films and thin films.

Fifth, in order to check the cross section of the pattern to be measured, the pattern should be observed using a cross section SEM (hereinafter referred to as X-SEM). In this case, there is a problem of breaking the wafer on which the pattern is formed. have.

An object of the present invention is to provide a method for measuring a pattern of a semiconductor device using optical equipment, which has been devised to solve the above problems.

The pattern measuring method of the semiconductor device of the present invention for achieving the above object comprises the steps of preparing an optical measuring equipment having a library for reflection characteristics for each critical dimension in response to incident light, and a substrate having a periodic pattern on the surface Preparing a light source; and irradiating incident light having a predetermined angle of incidence to the pattern, detecting scattered light emitted from the pattern through the optical measuring device, comparing the detected scattered light with the library, and comparing the scattered light. It is characterized in that it comprises the step of determining the corresponding critical dimension of the.

The predetermined angle of incidence is -47 ° to + 47 °.

The incident light is HeNe laser light.

Irradiation of incident light and scattered light of the substrate is performed in-line.

The preparing of the substrate may include depositing an insulating film on the substrate, depositing a material layer on the insulating film, forming a lower anti-reflection film on the material layer, and then having a predetermined period on the lower anti-reflection film. It is made by forming the pattern.

The pattern is a photoresist pattern.

Irradiation of incident light and scattered light of the substrate is performed immediately after exposure / development and etching of the photoresist pattern.

And sequentially etching the lower anti-reflection film and the material layer on the substrate using the pattern as a mask.

Irradiation of incident light and scattered light of the substrate is performed after etching of the material layer.

As the directivity of the semiconductor in the wafer increases, the design rule of the transistor (element) also rapidly decreases. In order to form a device having a half pitch of 130 nm or less, photoresist patterning is possible only when the light source uses an ArF light source of 193 nm instead of KrF of 248 nm, and the equipment for measuring the critical dimension of the pattern is a second electronic device. It is changing from the method using (secondary electron) to the optical method. This is because, in the SEM method, the phenomenon of changing the threshold value occurs every time measured by electron charging in the photoresist pattern. In the semiconductor process, the transistor formation process is an important process that determines the performance of the device, so accurate and stable process control is required. This requires a large amount of process data such as critical dimensions (CDs) and profiles in a short time and a tool capable of measuring them at one time.

Hereinafter, as described above, optical equipment capable of measuring information required from patterns at once and a pattern measuring method of a semiconductor device of the present invention using the same will be described with reference to the drawings.

2 is a cross-sectional view illustrating a method for measuring a pattern of a semiconductor device of the present invention.

As shown in FIG. 2, in the method for measuring a pattern of a semiconductor device according to an embodiment of the present invention, a library of information on scattered light (reflected light) for each critical dimension is stored therein, and a predetermined light is incident on an object, An optical system having an detector 20 for detecting scattered light from which light is scattered is used.

That is, the pattern measuring method of the semiconductor element of this invention is performed as follows.

First, a material layer 11 is formed on the entire surface, and a substrate 10 having a periodic pattern 12 formed on the material layer 11 is prepared.

Subsequently, after irradiating incident light on the substrate 10 at a predetermined incident angle Q, the irradiated light meets a periodic pattern 12 to detect scattered light that is scattered and stored in a library provided in the optical equipment. One of the critical dimensions is selected, and the critical dimension of the periodic pattern 12 is measured.

3 is a signal used in the pattern measuring method of the semiconductor device of the present invention and the critical dimensions analyzed thereby.

As shown in FIG. 3, after detecting the reflectance according to the incident angle from the detector 20, the critical dimension of the periodic pattern is selected by comparing with the graph about the reflectance of the incident angle for each critical dimension through a library provided in the optical equipment.

As shown, it can be seen that when the graph t of the reflectance with respect to the detected incident angle and the graphs l1, l2 and l3 having the critical dimensions of 95 nm, 115 nm and 125 nm, respectively, the threshold is shown at 115 nm. .

As described above, the pattern measuring method of the semiconductor device of the present invention uses an optical critical dimension measuring method or scattering measuring method, and includes a periodic pattern having a constant pitch (line and space) structure ( 12) HeNe laser light with long wavelength (632.8nm) is used to measure the characteristics of reflected light reflected after scanning while changing the angle of incidence at -47 ~ +47 degrees (degree). It is based on an optical method of finding the appropriate matching point. The HeNe light is relatively short wavelength 632.8 nm rather than the wavelength (780 nm) of the semiconductor laser light used in conventional SEM equipment.

As can be seen in FIG. 2, the light scattering phenomenon is used, and the reflected light is inherently different due to the difference in the amount of the light source HeNe refracted and reflected by the material and structure of the material layer 11. Signal can be generated and analyzed to obtain various information about the periodic pattern 12 (thickness, CD, angle, etc.). This method consists of two methods: horizontal and vertical signals (S, P polarized light) measured at the wafer in a measurement system, and analysis setups that analyze the simulations and produce meaningful results. Use at the same time.

Signal analysis by simulation uses Maxwell's equation, which is the most common analysis method. This technique determines the accuracy of the measured diffraction signal by matching the signal generated by the theoretical model. When scattered signal on the wafer is measured, the periodic pattern (12) is determined. Based on the information on the film stack of the C) film, the ideal signal from the library is matched to determine whether it is correct by using the root mean square error (RMS) value. . The smaller this value is, the more reliable the library setup and the data value obtained are judged to be reliable. The smaller the% RMSE, the better the reliability of the data to be set up in the library setup, but consider the general evaluation criteria below 5. At this time, compare the S and P signals on the wafer with the signal graphs in the library to improve the accuracy of the results. You can check it.

4A and 4B are process cross-sectional views illustrating patterns after exposure and after etching in the pattern measuring method of the semiconductor device of the present invention.

In the method for measuring a pattern of a semiconductor device of the present invention, after the exposure and development processes are carried out on an inline process, as shown in FIG. 4A, the thicknesses and the CDs (critical dimensions) and the like of the material layers on the substrate are measured. After the etching process, as shown in Figure 4b, to measure the thickness and the CD for the changed material layers.

At this time, in the initial state of the substrate, the substrate 10, the oxide film 21, the material layer 11, the bottom anti-reflective coating (BARC) 22 and the photoresist film (the same layer as 12) The photoresist pattern 12 is periodically formed after the exposure and development processes are performed on the photoresist.

Here, the material layer 11 is a polysilicon layer for forming a gate or data electrode of a semiconductor device.

As shown in FIG. 4B, when the lower material layer 11 is etched using the photoresist pattern 12 as a mask, the lower anti-reflection film 22 and the material layer 11a are formed on the photoresist pattern 12. Is patterned along the shape, and the oxide film 21a corresponding to the region where the photoresist pattern 12 is not formed is etched together with a predetermined thickness so that only a part thereof remains.

After etching, the photoresist pattern 12 and the lower anti-reflection film 22 are removed together.

Hereinafter, based on a predetermined library condition, values such as CD (threshold dimensions) after gate exposure / development and gate etching are compared by using a measurement device and an optical measurement device.

Table 1 shows the libraries used to analyze the signals measured on the wafer. Such a library is very important as it can lead to incorrect process results if not set up correctly.

Process information Post-development inspection Inspection after etching n, k value Initial value increase step Initial value increase step n k Library model Trapezoidal Trapezoidal Gate oxide thickness 20Å One One 20Å One One 1.456 0.000 Poly thickness 1700 yen 15 16 1700 yen 5 81 4.000 0.040 BARC thickness 550 yen 10 21 1.578 0.000 KrF PR thickness 2700 yen 25 21 1.537 0.000 Bottom critical dimension 100 nm 2 26 90 nm 0.5 92 - Sidewall angle 84 ° 0.25 21 84 ° 0.25 25 -

In addition, Tables 2 and 3 below show the measurement results after gate exposure and the measurement results after etching completion using the library conditions set up in Table 1. This is a table comparing the measured values.

item Thickness CD (μm) Angle (°) % RMSE Poly PR Optical CD data 1700 3583 0.1254 85.5 3.7 Offset (Inline Instrument Measurement-OCD Measurement) -27 -293 0.0145 -0.0002 1.4 matching % 98.3 91.1 89.6 99.8 98.4 Matching device Thickness measuring instrument CD SEM Cross section SEM Cross section SEM

item Poly thickness CD (μm) Angle (°) % RMSE Optical CD data 1847 0.1010 85.5 3.7 Offset (Inline Instrument Measurement-OCD Measurement) -50 0.0030 0.0025 -1.6 matching % 97.0 97.1 97.6 98.1  Matching device Thickness measuring instrument CD SEM Cross section SEM Cross section SEM

These results show that the measurement results using optical measuring instruments show the same performance as the various measuring instruments currently used inline.

Here, the photoresist pattern (KrF PR) was formed in a periodic pattern with a line and a space having a value of 0.130 / 0.180 μm, and the measurement experiment was performed.

In addition, n and k which are not demonstrated mean reflection coefficient n and absorption coefficient k, respectively.

On the other hand, the optical measuring equipment used in the present invention, in the measurement of the critical dimension (CD) in the in-line process for the etching process control as well as the exposure and development process control with the advantage of high measurement with high accuracy. It is more advantageous. Because at the same time, it can give a large amount of data and information about the gate poly (material layer) profile. Such information can help predict and understand the yield of devices in semiconductor devices.

In order to achieve accurate and consistent measurement results from these optical measurement instruments, stable models and libraries are very critical because of indirect measurement characteristics. For example, defining substrate conditions, modeling of a range of parameters, target values and model types, if you do not use the same data criteria, you will get different results. The library disclosed in Table 1 above shows an optimal example in obtaining accurate and stable result values.

The light source used above was an optical measuring device capable of irradiating a HeNe laser light source from -47 ° to + 47 °, and used an Accent CDS 200 angular scatterometry system.

In such optical measuring equipment, the input signal uses light scattered by a diffraction grating in which lines and spaces are repeated, as in the pattern 12 shown in FIG.

Usually, scattering means light that is reflected at irregular angles when the light is irradiated on an uneven surface. Scattered light in a very periodic structure can be described as diffraction behavior in the physical sense.

When light is irradiated to the periodic diffraction grating, the reflected light is dispersed in a plurality of states. The mathematical relationship of the reflected light can be explained by the diffraction equation shown in terms of angle of incidence, wavelength and diffraction period (pitch of diffraction). This means that we can obtain diffraction information when we analyze the diffracted light. However, in the fine pattern of gate or data poly currently running in semiconductor processes, there is only one diffracted light for incident light because of the diffraction dimension smaller than several hundred nanometers, which produces pure diffraction efficiency. This is a simple reflection.

Therefore, to obtain diffraction information, one must have a signal as a function of one or more variables. Such a variable may be wavelength or incident light of light.

Therefore, the optical measuring equipment used in the critical dimension measuring method of the present invention can be divided into two different devices. One is to change the wavelength and the other is to change the incident light. Usually, when we change the angle of incidence, we use two different polarizations, S polarization and P polarization. This is because it can give more accurate diffraction information.

In the above experiments, the Accent CDS200 angular scatterometry system, which can rotate the HeNe light source from -47 ° to + 47 °, was used. In this device, HeNe laser (632.8 nm) monochromatic light at various incidence angles is exposed to a targeted periodic pattern on the wafer.

Here, the measurement using the optical measuring equipment is performed for all patterns formed on the substrate, in which case, the move and measure (MAM) time for each pattern is within 2 to 3 seconds in a very short time. Is done.

The pattern measuring method of the semiconductor device of the present invention as described above has the following effects.

First, since the pattern of the semiconductor device is measured by using an optical measuring device, not only the critical dimension (CD) but also various information related to the pattern such as the angle of the sidewall and the thickness of the pattern are provided separately. We can judge at a time without using.

Secondly, the technique for measuring the critical dimension using the optical measuring device of the present invention is faster than other measuring devices currently in use, with the movement and measurement time of the optical measuring device being within 2 to 3 seconds. Therefore, the measurement can be made quickly and easily for all the patterns formed on the wafer to facilitate the measurement of the highly integrated device.

Third, there is a problem in that the wafer has to be broken in order to check the profile of the conventional semiconductor device, that is, the information of the cross-section. Analysis can yield the desired measurements.

Claims (9)

Preparing an optical measuring device having a library for reflection characteristics for each critical dimension in response to incident light; Preparing a substrate having a periodic pattern on the surface; Irradiating incident light on the pattern in-line to detect scattered light emitted from the pattern on the in-line through the optical measuring equipment; And comparing the detected scattered light information with the library to determine a corresponding critical dimension of the scattered light. The method of claim 1, The incident angle of the incident light is -47 ° to +47 ° method of measuring a pattern of a semiconductor device. The method of claim 1, The incident light is HeNe laser light, the pattern measuring method of a semiconductor device. delete The method of claim 1, Preparing the substrate Depositing an insulating film on the substrate, depositing a material layer on the insulating film, forming a lower antireflection film on the material layer, and then forming the pattern having a predetermined period on the lower antireflection film. The pattern measuring method of the semiconductor element characterized by the above-mentioned. The method of claim 5, The pattern is a pattern measuring method of a semiconductor device, characterized in that the photosensitive film pattern. The method of claim 6, Irradiation of incident light and detection of scattered light of the substrate is performed immediately after the exposure and development of the photosensitive film pattern or immediately after etching. The method of claim 5, And sequentially etching the lower anti-reflection film and the material layer on the substrate using the pattern as a mask. The method of claim 8, Irradiation of incident light from the substrate and detection of scattered light are performed after etching of the material layer.

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