Using Ellipsometers in the Semiconductor and Liquid Crystal Display Industries

By AZoNano

Table of Contents

Introduction
The UNECS – 3000A Spectrometer
Principle of UNECS-3000A Spectroscopic Ellipsometer
Overview of the UNECS-3000A Spectroscopic Ellipsometer
Applications of UNECS – 3000A
Conclusion
About ULVAC Technologies

Introduction

Ellipsometers are based on the principles of ellipsometry. This measurement instrument measures the film thicknesses and refractive indexes of transparent or semi-transparent thin films with high precision without physical contact and is used in many industries including the semiconductor and liquid crystal display industries. Generally, ellipsometers are classified into the following:

  • Single wavelength type whose light sources are lasers
  • Spectroscopic type, which uses halogen, xenon, or other such lamps.

Spectroscopic ellipsometers can study multi-layer films or other complexly structured thin films because this type of ellipsometer can measure the polarized light reflected off thin films in certain wavelength bands.

There are two categories of measurement methods

  • The optical device rotation method – This controls the polarization properties by mechanically rotating optical devices.
  • The phase modulation method – This controls the polarization properties of the polarization device electrically

The UNECS – 3000A Spectrometer

The automated high-speed spectroscopic ellipsometer, "UNECS-3000A' is described here and benefits from the spectrums obtained from the polarization interference occurring between two multiple-order retarders to instantly snapshot the wavelength distribution of the sample's spectroscopic polarization parameters. The UNECS-3000A is equipped with compact sensors and has rapid measurement features and does not require the conventional complex rotational mechanisms or electric-control functions for the sensor head.

This product integrates the measuring capabilities of "UNECS-2000" launched in 2010 for substrates up to 200 mm in diameter with an automated mapping function that can handle substrates up to 300 mm in diameter, thus enabling greatly enhanced measurement of film thickness distribution.

Principle of UNECS-3000A Spectroscopic Ellipsometer

Ellipsometry is an optical measurement technique, which is based on measuring changes in the light polarized by reflecting it off of samples. The first value is the phase difference of polarized light called p-polarized and s-polarized light. The second value is the angle determined by the amplitude ratio.

Figure 1. Basic structure of UNECS-3000A

Spectroscopic ellipsometers determine spectrums corresponding to (?,?) in certain wavelength bands. The UNECS-3000A spectroscopic ellipsometer, which uses multiple-order retarders, basically consists of a polarizer, two multiple-order retarders (retarders 1 and 2), an analyzer, and a spectroscope as shown in Figure 1.

It benefits from the spectrums obtained from the polarization interference occurring between two multiple-order retarders to snapshot the wavelength distribution of the sample's spectroscopic ellipsometric parameters. This eliminates the need to use rotation mechanisms. Since the sensor does not have any drive unit or electric wire, this ellipsometer is much smaller and performs measurement at a higher speed than conventional spectroscopic ellipsometers, and is excellent in cost performance.

Overview of the UNECS-3000A Spectroscopic Ellipsometer

With an automated stage that is capable of handling samples up to 300 mm diameter as well as high speed measuring capabilities and the automated mapping function, the ellipsometer offers high-precision measurement with easy operation, including quick evaluation of the distribution of thin-film thicknesses and optical constants. It can be used in a broad range of applications ranging from research and development to production line applications. The UNECS-3000A is compact due to its innovative design. The spectroscopic polarization method using multiple-order retarders made it possible for the emitter and receiver to be small. In addition, all of the peripherals, including controllers and the light source unit are built into the system.

Figure 2 shows the appearance of the UNECS-3000A.

Figure 2. NECS-3000A main measuring unit (right) and controller (left)

The equipment required to operate the UNECS-3000A is supplied with the main measuring unit and the controller as standard equipment. This includes the control PC and the analysis software. The UNECS-3000A spectroscopic ellipsometer boasts excellent cost performance. It is possible to edit or add material table files easily, which are essential for data analysis. The thickness of each layer can be measured using parallel measurement. Up to six layers are measurable at the same time. Table 1 shows the basic specifications of the UNECS-3000A.

Figure 3 shows an example of in-plane distribution (2D mapping) measurement results obtained by using the UNECS-3000A. It took about 100 seconds to take measurements at 99 points on a substrate 300 mm in diameter.

Figure 3. Example of in-plane distribution measurement results obtained by the UNECS-3000A

Table 1. Basic specifications of UNECS-3000A

Item Specification
Data measurement time 20 ms or longer
Reproducibility of film thickness measurement (1σ) 0.1 nm(Ten continuous measurements of a standard SiO2/Si sample with a film thickness of 100 nm)

 

Range of film thickness measurement 1 nm∼2μm
Range of measurement wavelength 530∼750 nm
Maximum sample size &phi300 mm
Outer dimensions Main unit:450 (W) x 620 (D) x 370 (H) [mm]
Controller:204 (W) x 500 (D) x 509 (H) [mm]

Figure 4 shows the result of measuring a resist film deposited on a Si wafer substrate. The fitting result completely matches the measured data, showing high credibility. Calculation of the results of ten continuous measurements also shows excellent reproducibility.

Figure 5 shows the result of comparing measured values between the UNECS-3000A spectroscopic ellipsometer and a stylus surface roughness tester. The objects being measured are microcrystal silicon µc-Si (lower) and SiO2 (upper) layers deposited on a glass substrate for thin-film solar cells. The result shows the coefficient of correlation to be as high as 99.9%. This proves the very high measurement precision of the UNECS-3000A.

Figure 4. Measurement result of a resist film on a Si wafer substrate

Figure 5. Result of comparing measured values between the UNECS-3000A and a stylus surface roughness tester

Applications of UNECS – 3000A

The applications of UNECS-3000A are:

  • Evaluation in thin-film formation processes
  • Etching
  • Oxidization
  • Thermal processing and other processes

Conclusion

Adopting multiple-order retarders, "UNECS-3000A" is the realization of a compact and high-speed spectroscopic ellipsometer, which was difficult to achieve by conventional methods. The sensor unit of the UNECS-3000A is also mounted on the MPEC-1300, a composite measurement system for thin-film solar cell panels. Thanks to its compact design and high-speed measurement features, the sensor unit is highly appreciated as a very effective measurement tool.

We are planning to expand its applications, including integrating it into deposition systems, to displays, solar cells, storage, communications, chemical and other industries, as well as offer measuring instruments utilized in research and development and on production lines.

About ULVAC Technologies

Founded in Japan in 1952, ULVAC is an international corporation that designs, manufacturers and markets equipment and materials for industrial applications of vacuum technology. Today, ULVAC is a leading global supplier of production systems, instrumentation, pumps and vacuum components used in the semiconductor, flat panel display, disk/magnetic media, and industrial manufacturing markets.

The corporation is comprised of some 36 individual companies engaged in all sectors of the vacuum industry. The ULVAC name is derived from the company's conceptual foundation - "The ULtimate in VACuum Technology".

This information has been sourced, reviewed and adapted from materials provided by ULVAC Technologies.

For more information on this source, please visit ULVAC Technologies.

Date Added: Jun 13, 2013 | Updated: Jun 14, 2013
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