Phillip Chapados

In-situ monitoring of submicron polysilicon linewidths using diffraction gratings

The measurement of pattern integrity is performed as a part of process control in all wafer manufacturing environments. Typically this measurement is performed off-line on pilot material using a top down scanning electron microscope (SEM). With the advent of sub- micron geometries and small lot wafer fabrication centers, it has become important to monitor the processes on a wafer by wafer basis. An in situ technique using diffraction grating test patterns has been used to monitor the pre-etch and post-etch linewidths on a polysilicon etch chamber. The technique is capable of linewidth measurements to 0.25 microns with pitches as small as 0.7 microns. A comparison of the in situ polysilicon linewidth measurements with off-line SEM measurements shows measurement differences of less than 10% indicating a measurement accuracy on that order. The repeatability of the diffraction technique is shown to be approximately 0.01 micron in comparison to the typical SEM repeatability of 0.025 micron.

Diffraction image processing algorithms for in-situ monitoring of submicron polysilicon linewidths

A technique using diffraction grating test patterns has been used to monitor in situ the pre and post etch linewidths on a polysilicon etch chamber. The technique is capable of linewidth measurements to 0.25 microns with pitches as small as 0.7 microns. A comparison of in situ polysilicon linewidth measurements with off-line SEM measurements shows measurement differences of less than 10% indicating a measurement precision on that order. The repeatability of the diffraction technique is shown to be approximately 0.01 micron in comparison to the typical SEM repeatability of 0.025 micron. The implementation of this technique on a production etch chamber required the design of specialized optics and image processing systems. The optics system allows the monitoring of one and a half dimensions of the diffraction pattern. It consists of a CCD camera and some reflective optics for the focusing of the diffraction patterns. The image processing system uses a commercially available frame grabber and several image processing algorithms to record these patterns and extract the linewidth information. Algorithms unique to this application include an image indexing scheme used to store the diffraction images, a blob classification scheme based on a rigorous examination of the three dimensional vector field problem, and a non-linear iterative modeling algorithm used to fit the data to Fourier theory predictions. The resulting system is capable of linewidth measurements on each wafer with an overall reduction in product cycle time relative to the previously used SEM and pilot monitoring schemes.

Practical use of an in-line vacuum metrology cluster in a minifactory environment

A single wafer metrology module capable of performing a variety of wafer property measurements under vacuum is presented. This metrology module was built by Texas Instruments for use in the Microelectronics Manufacturing Science and Technology programs 0.35 micrometers , single wafer processing factory. The primary measurement tools incorporated in our metrology module are a phase modulated spectral ellipsometer and a critical dimension sensor based on laser diffraction. The spectral ellipsometer was originally developed for real-time in situ film thickness measurements for process control. Using the speed of phase modulation, multichannel detection, and digital signal processing techniques, this ellipsometer is capable of measuring the thicknesses of dielectric films in multilayer stacks with a typical solution time of a few seconds. The critical dimension sensor is an in situ diffraction pattern measurement and analysis system capable of measuring sub-micron device dimensions down to 0.15 micrometers . Other sensors included on the machine are a microbalance, a scatter sensor for measuring surface roughness, and an optical microscope.

Monitoring of submicrometer linewidths using diffraction gratings

For a typical fabrication facility, linewidth control is done after the patterning and etch processes by means of a scanning electron microscope (SEM). Several techniques using diffraction gratings have been proposed as in-line or in situ replacements for the SEM linewidth measurement. One such system was developed for use in the Microelectronics Manufacturing Science and Technology (MMST) mini- factory. The system used in the MMST factory was capable of measuring the critical dimensions needed for factory control. This critical dimension diffraction measurement system consists of optics and processing algorithms necessary to measure a series of gratings in an etch processor or directly after processing in a metrology chamber. The optics allow the measurement of a full diffraction pattern with one image. The processing algorithms convert this image to a list of diffraction orders and intensities for each grating in the set. These are then used by the pattern matching algorithms to determine grating linewidth.