Laser-Based System Monitors Polishing Equipment

Ruth A. Mendonsa

The integrated circuit manufacturing process imposes stiff requirements on makers of chemical mechanical planarization equipment. Planarization of the insulating oxide layers and formation of the tungsten, aluminum and copper interconnect layers are the equipment's primary functions. Its manufacturers need to provide accurate measurements of multiple film stacks on all the film types that are used for integrated circuit manufacturing. They also must be able to monitor the effectiveness of their equipment.

To meet these requirements, Strasbaugh Inc., a maker of chemical mechanical planarization polishers, turned to Therma-Wave Inc., which uses proprietary laser-based technology to design and manufacture nondestructive metrology and inspection systems for film-thickness measurement and ion-implant monitoring of advanced semiconductor devices.

Therma-Wave's Opti-Probe 3260 monitors the performance of Strasbaugh Inc.'s planarization equipment.

Therma-Wave's Opti-Probe 3260 fulfilled Strasbaugh's twofold requirement: The system enables the measurement of all film types, including some that the company previously couldn't measure, and supplies a means of monitoring the polishing equipment's performance.

Chemical mechanical polishing can be a challenge to control. Residual material tends to be removed from less dense areas more quickly, causing slopes on the film stacks. Also, to ensure accurate global planarity, the polish rate on small selected areas of wafers needs to be closely monitored.

The Opti-Probe employs advanced robotics, Pentium-speed processing, a spectrometric light source and pattern recognition. The system's small spot size is useful in determining localized planarization by detecting height differences in areas as small as 7 × 7 µm. Using both UV and 675-nm laser light sources, the Opti-Probe combines beam profile reflectometry, beam profile ellipsometry, spectrophotometry, spectroscopic ellipsometry and absolute ellipsometry to provide deep-UV, thickness, index-of-refraction and extinction-coefficient measurements down to 190 nm.

Because Strasbaugh works with many integrated circuit manufacturers worldwide, it needed a tool that provided an industry standard. After it began using the same measurement system as its customers, the company could simply upload the measurement recipes.