Case Study: SiMPore Inc.

SiMPore is a nanotechnology company that develops ultrathin specialty membranes for biological and semiconductor applications. (Figure 1) However, SiMPore's unique technology presents a characterization challenge for measuring membrane thickness. "The thickness of the membrane is critical because it determines performance and yield," explained Dr. Christopher Striemer, VP of Membrane Development for SiMPore.

As a startup company with initial capital focused on product development, SiMPore needed an economical way to obtain some thickness measurements before receiving the funds to purchase an instrument.

Although spectroscopic ellipsometry is an established technology for measuring thin film properties, Striemer realized it could not adequately measure a very small spot size on his company's ultrathin membranes.

The limitations of spectroscopic ellipsometry for SiMPore's ultrathin-film measurement needs include the following:

• Spectroscopic ellipsometry uses non-perpendicular light to measure film thickness, and the light splays across the sample instead of concentrating on a single spot.
• Spectroscopic ellipsometry cannot measure an actual membrane. Instead, it requires preparation of a separate witness sample, which may produce different measurement results.
• Many spectroscopic ellipsometry systems do not have an attached microscope, which makes it difficult to pinpoint what area on the sample is actually being measured. "You need a live image to see what you're measuring and to make sure you are hitting the right spot on the membrane," said Striemer.
• SiMPore employees need to travel to use a spectroscopic ellipsometry system in an open user laboratory.

Additionally, Striemer wanted to find a thin-film thickness measurement solution that could be purchased by SiMPore when the company received the necessary funds, either through small business grants or loans, or other capital investment. "Spectroscopic ellipsometry systems are very expensive, and unlikely to be affordable for a small private company by any funding mechanism. In academia, such tools must be acquired through special instrument grants and typically must be placed in a facility that is open to other researchers," said Striemer.

Striemer found the solution he needed in the Filmetrics^® F40-UV system and Filmetrics professional services for film measurement. "The Filmetrics instrument directs light onto the membrane sample," said Striemer. "This means you can easily take the spectrum from a very defined area (33µmx33µm) and know exactly what you're measuring, even on a membrane that isn't completely flat."

"For our tests, this was the first time we were able to directly confirm the thickness of a single isolated membrane since our current ellipsometric measurements require larger unpatterned areas," noted Striemer. This precise measurement allows SiMPore to provide more accurate performance information about the membrane thickness based on a customer's intended application.

The measurements were made by Striemer working with Filmetrics engineers as part of Filmetrics professional services. These services offer companies and researchers a cost-conscious way to obtain film thickness measurements without buying or renting an instrument.

Each service project includes a report with images and data for the test results. (Figure 2) "The Filmetrics report not only gave us the information we wanted, it increased our confidence levels for measurement accuracy," said Striemer.

With the Filmetrics F40-UV, Striemer also found an economical measurement instrument for SiMPore to purchase when funding becomes available. The inexpensive cost means an F40-UV purchase is far more realistic for a small company.

SiMPore expects to buy a Filmetrics unit in the future for ongoing product development and quality control. "Spectroscopic ellipsometry is very complex and modeling-intensive, which makes many people uncomfortable in using those systems," said Striemer. "With the Filmetrics instrument, all of my technicians would gladly use it because it's so easy."