Advanced Metrology Solutions

Interview conducted by Will SoutterApr 11 2013

Vamsi Velidandla, VP of Marketing for Zeta Instruments, talks to AZoNano about the applications of their unique metrology technology.

Tell us about Zeta Instruments and the type of products you provide.

Zeta Instruments is dynamic start-up company based in Silicon Valley that specializes in metrology and wafer defect inspection instruments. We combine our innovative optics design with advanced software algorithms in products tailored for the target industries. In addition to innovative technologies, Zeta Instruments is focused on delivering best-in-class hardware and very user-friendly interfaces.

Having launched our first commercial product in early 2010, Zeta Instruments was quickly adopted as the supplier of choice for metrology instruments in the solar cell manufacturing industry, due to our tool’s ability to handle the complicated surface texture of solar cells. More recently, our products have also been adopted in the HB-LED and microfluidics areas.

Zeta’s technology portfolio includes the first truly “multi-mode” metrology and inspection system that incorporates our Z-Dot™ and interferometer based surface profilers, DIC (differential image contrast) based imaging and reflectometry based thin film thickness measurement modes. Zeta Instruments has recently introduced an industry leading wafer inspection and metrology tool aimed at providing an integrated defect inspection, review and metrology tool for the HB-LED (high brightness light emitting diode) industry.

In the last 3 years Zeta Instruments has rapidly grown into a provider of precision microstructure and surface measurement systems that enable manufacturers of green technology and bio-medical products to substantially improve yields and quality control. Zeta’s advanced metrology solutions provide direct benefit to the production of HBLEDs, solar cells, micro-fluidics/bio-technology and magnetic storage media. Our patented Z-Dot™ technology enables manufacturers to quickly and accurately perform 3D measurement of the micron-scale features of these applications, positioning it as a strategic supplier to these high-growth industries.

Catering to the wide range of applications are the different Zeta platforms, from the Zeta-20 desktop system all the way up to the Zeta-580 platform that is capable of automatically handling and measuring 300 mm semiconductor wafers.

Zeta-20 Desktop Optical Profiler

What are the most popular applications of your optical metrology products?

Zeta’s optical profilers have been adopted for a wide variety of applications by leading universities across the world. Our tools enable research on a variety of topics in the fields of science and engineering. A few examples are surface metrology after laser ablation, microfluidics, microwave waveguides, corrosion and electroplating.

Zeta Optical Profilers are also used in the solar cell industry for inspecting incoming wafer roughness, post etch wafer texture (pyramid dimensions), nitride film thickness, contact line and bus bar dimensions. Zeta’s ability to handle very dark (low reflectivity) and very rough surfaces provide a unique solution for characterizing solar cell substrates that are designed to reflect less than 1% of the incident light.

We also have a large customer base in the HB-LED sector - our customers working in this area find that the key to an efficient HBLED is the underlying patterned sapphire substrate (PSS) which is patterned with an array of (typically) conical bumps. Zeta can measure an array of 1µm tall PSS bumps with a repeatability of less than 20nm. The same tool (Zeta-300i) can be used to inspect a full 4-inch wafer for defects within 1.5 minutes.

In the biotech sector, the ability of Zeta’s non-contact optical technique to penetrate through the top cover of an enclosed microfluidic channel has enabled companies like IntegenX to accelerate their microfluidic device development timelines. More recently, Zeta’s ability to use high numerical aperture objectives combined with the ability to resolve very low reflectivity surfaces has made it a key tool for investigating microneedle structures for drug delivery.

This is just a small sample – our technology has applications in many other industries, including forensic investigation of bullet signatures, corrosion analysis on large naval components, analysis of pads for chemical-mechanical polishing machines.

How do the capabilities of your instruments differ from other inspection tools, such as AFMs?

The versatility of the multi-mode optics, combined with the open architecture of the tool, enables users to scan samples requiring sub-nanometer resolution all the way up to millimeters of resolution on the same tool, without any change in optics or tool configuration.

Most university and research labs have AFM (atomic force microscope) and SEM (scanning electron microscope) facilities. While the AFM and SEM provide extremely high lateral and vertical resolution, they lack the ability to scan a large area. The Zeta Optical Profiler is very complementary to these tools, by providing a high resolution large area image. Zeta provides a detailed view of the “forest” while the AFM and SEM can be used to nail down the specifics of one particular “tree”.

Some of the key attributes of Zeta that make it the ideal solution for many tough metrology problems are the true color imaging, the ability to handle very low reflectivity, the ability to handle very high roughness, the large translational and optical dynamic range, and the ability to use multiple measurement tools (ZDot™, interferometer, reflectometer, Nomarski techniques) within the same package.

Zeta-300 Surface Metrology System

The Zeta-300 is your flagship product - when was it launched, and what features does it offer over the other products in the line?

The Zeta-300 was launched in early 2012. The Zeta-300 offers a platform with integrated acoustic isolation as well as a base designed to reduce seismic vibrations. This makes the tool inherently stable, increasing the accuracy and repeatability of mission critical measurements such as PSS bump measurements, nanoscale defect sizing in the data storage industry and microwire measurements for MEMS applications.

The Zeta-300i also adds in the ability to run a defect inspection scan over the entire wafer. This unique combination of wafer inspection, defect review and metrology in the same tool offers HBLED manufacturers huge savings in terms of time, equipment cost and process development time. The Zeta-300i offers the industry’s fastest wafer inspection time by inspecting a full 4-inch sapphire wafer in just 1.5 minutes.

The Zeta-300 is advertised as capable of Angstrom-scale resolution of surface defects on a wafer. How critical is this level of detail to a manufacturing process? Do defects that small have an impact on the performance of the device?

In modern terabyte-scale storage media, the hard disk drives have to hold very large volumes of information on very tiny magnetic bits. In order to read and write data to a hard drive, the read-write head has to literally ‘fly’ a few nanometers above the disk surface. This is the equivalent of a large jumbo jet flying a few feet above the ground.

In such a dynamic situation, even a defect that is 5 nm tall can cause a significant fault in the hard drive, possibly causing the drive to fail. Detecting nanometer and Angstrom scale defects is critical not only in the disk drive manufacturing process, but also holds true for a variety of semiconductor device manufacturing processes.

So clearly high performance devices, such as high-end data storage media, have a much lower tolerance to defects than something like a photovoltaic panel, due to the stresses they are subject to, and the ever-increasing data density. What additional problems do the surfaces in these devices face, and how does the Zeta-300 help to deal with them?

Apart from the sensitivity to defects, disks also have to be polished down to a few Angstroms of roughness. At the edge of the disk, the transition between the top surface and side wall must have a smooth chamfer profile, otherwise the turbulence at the edge of the disk may cause the read-write head to suffer a fatal crash on the disk.

Any contaminants or particles that are on the side walls of the disk can be transferred to the top surface. Therefore, in the recent past our customers have also started programs aimed at reducing contamination on the side walls of the disks. The Zeta-300 is a versatile instrument with a large working range – from nanometers all the way up to millimeters, which enables our customer to inspect the monolayer (Å scale) organic contaminants as well as the macro scale side wall chamfer profiles (100s of micrometers) on the same instrument.

Zeta Instruments offers tools capabale of analyzing Angstrom-scale organic contaminants, all the way up to sidewall chamfer profiles, making them ideal inspection tools for high-density data storage media.

How does Zeta Instruments' nVision technology work, and what value does it add to the inspection and analysis process?

Zeta’s nVision mode is specifically designed to detect very thin film defects such as monolayer film contaminants on a disk substrate or a wafer. These defects may be caused by leftover chemical stains after a wash cycle or a cross contamination of organic material used in other parts of the manufacturing process.

The nVision mode uses a special Nomarski optics configuration that works in conjunction with optimized data acquisition electronics and image processing algorithms that minimize noise and maximize the signal from transparent thin film layers. This makes the nVision mode a vital tool to look for very small material differences and defects. A normal optical profiler or microscope would be blind to the texture, defects and thin film contaminants that the nVision mode allows our tools to see.

Are there any major new developments planned for Zeta Instruments in 2013, or in the near future?

Starting in 2010 with the release of ZDot™ technology, Zeta’s dedicated R&D team has added multiple metrology and inspection modes to our tools. In 2013 we have targeted the release of additional products and measurement modes optimized for applications in the data storage, bio-tech, HBLED and semiconductor industries.

Where can we find more information about the Zeta-300 and your other products?

Your readers can reach us through our website. Our USA offices and demo facilities are located at 2528 Qume Drive, Suite 12, San Jose, CA 95131. Our international partners and our Shanghai China office details are also available on our website. We look forward to hearing from your readers and to helping solve the tough metrology and inspection problems that they face.

About Vamsi Velidandla

Vamsi Velidandla is the VP of Marketing for Zeta Instruments, where he has worked since 2009. Prior to Zeta Instruments, Vamsi was at KLA-Tencor, where he was involved in the development and release of a variety of metrology and inspection products. Vamsi has a Masters in Mechanical Engineering from Arizona State University, USA.