From the spindle to the assembly

The polarization filter was specially developed by Steinmeyer for DUV lithography. (Copyright: stock.adobe.com/IM Imagery, number 560372105)

At a height of just 15 mm, three flat filters are housed, which can be moved within the optical system's beam path and positioned independently of each other. (Copyright: Steinmeyer Group)

Ultracompact, highly precise positioning solution for wafer exposure in dry, oxygen-free nitrogen atmosphere. (Copyright: Image: Steinmeyer Group)

The combination of non-rusting stainless steel (spindle) and high-performance plastic PEEK (nut) enables optimal sliding ability, heat dissipation, and mechanical stability in ultra-dry nitrogen. (Copyright: Feinmess Suhl GmbH)

The lead screw has a spindle diameter of 3 mm and a spindle length of 112 mm, making it one of the smallest on the market in this precision. (Copyright: Steinmeyer Group)

When it comes to highly specialized, customer-specific positioning solutions, Steinmeyer is the go-to provider. Even in the semiconductor industry, the Dresden location in "Silicon Saxony" has long been considered an Eldorado for the seemingly impossible, as Saxony's experts master the most demanding challenges with flying colors as Europe's largest ICT/microelectronics center. A prime example of their high solution competence is the complementary polarization filter for miniaturization and automation in DUV lithography. The assembly combines the expertise and experience of the internationally active Steinmeyer Group and sets standards in terms of compactness, reliability, and particle cleanliness. This is engineering at its finest.

Positioning systems in the semiconductor industry impose high demands on purity, reliability, lifespan, ease of maintenance, as well as precision, often requiring customer-specific engineering. It is not uncommon for these to involve very specific requirements close to the limits of what is feasible. Making the impossible possible? No problem for Steinmeyer! The Steinmeyer Group can draw on concentrated know-how with a total of over 400 years of experience in drive, positioning, and precision measurement technology. This unique development, solution, and manufacturing expertise leads to outstanding results that are unmatched in the industry. The Dresden location is among the world's leading manufacturers of highly precise positioning solutions for optical and fine mechanical systems and has especially made a name for itself as a specialist in custom-made special solutions.

Complementary polarization filter for DUV lithography

A prime example of the high innovation power of the Steinmeyer Group is the ultra-compact, highly precise positioning solution for wafer exposure in dry, oxygen-free nitrogen atmosphere. It is a complementary polarization filter for miniaturization and automation in DUV lithography. "DUV lithography uses deep-ultraviolet light with wavelengths of 193 or 248 nm and enables particularly small structure sizes in microchips," explains Elger Matthes, development and product management at Steinmeyer Mechatronics, and continues: "Our task was to develop a retrofittable filter unit for a wafer stepper to adjust the optical properties of the light beam," he says. "Since the assembly was designed as an optional add-on for integration into an existing machine, we had very limited space available. Other requirements included minimal adjustment ranges, stability at standstill – the setting should only need to be changed every few minutes – as well as specific specifications regarding speed, repeatability, and lifespan."

Ultra-compact, highly precise, and dry-running assembly

The polarization filter realized by the Steinmeyer Group is built with dimensions of approximately 120 x 180 x 31 mm, making it extremely compact. Three flat filters are housed within a height of just 15 mm, which can be shifted in the optical path of the system and are independently positionable. The relative positioning of the three filters determines the desired filter property. The drive is implemented via a lead screw drive (stroke 75 mm) and electronically commutated DC motors. Each filter has its own drive train, which is protected from DUV radiation with a steel cover. The system operates dry, achieves accuracies of up to 1.5 µm, and offers maintenance-free, flexible 24/7 operation over many thousands of positioning cycles (spread over 10 years).

Material selection challenge

Material selection poses a particular challenge for semiconductor applications. Smooth surfaces, low outgassing, and minimal particle generation are required. Only certain materials, components, and lubricants meet these requirements. Often, the use of liquid lubricants is not possible – as in this specific application. Elger Matthes also points out another aspect: "In the ultra-dry nitrogen in which the assembly should operate, similar tribological effects occur as in high vacuum. Friction coefficients above 1 are common. This further restricts the material palette – especially if good sliding properties and a meaningful lifespan of the lead screw are to be achieved."

Extremely particle-free running precision lead screw from Feinmess Suhl

The choice for the lead screw was a combination of stainless steel (spindle) and high-performance plastic PEEK (nut), which was reinforced with lubricating fillers. This innovative material pairing enables optimal sliding, heat dissipation, and mechanical stability even under the extreme environmental conditions of DUV lithography. "Due to its molecular structure, PEEK is chemically and physically very stable. The high-performance plastic has very low outgassing values and is considered an ideal choice for the demanding applications of the semiconductor industry," says Detlef Rode, development manager at Feinmess Suhl. "Of course, we proved the concept for this material pairing, so the customer had absolute certainty regarding feasibility." The system operates without liquid lubricants and is therefore ideal for dry operation up to cleanroom class ISO 3 and 10E-9 mbar.

The material pairing of PEEK plus stainless steel for the linear drive is also reflected in the guide system. The V-shaped guide grooves are made of stainless steel, and the sliding elements, i.e., the bearings, are made of PEEK. Aluminum parts are coated with a deep-ultraviolet-absorbing anodized layer.

Unique development and manufacturing expertise

The extremely particle-free running linear drive was developed specifically by Feinmess Suhl for this application. With a spindle diameter of only 3 mm and a spindle length of 112 mm, it is among the smallest on the market in this precision class. "Linear drives are perfect for DUV polarization filters. Size plays an important role because such small dry-running ball screws are currently not technically feasible," explains Detlef Rode. Additionally, the linear drive (thread size M3x1P0.5, pitch 1 mm, load 2 N) offers further advantages. It is relatively simple in design, extremely robust, and characterized by high stiffness, precise form and dimensional accuracy, and low wear. An additional benefit: linear drives have a self-locking feature, meaning the nut position on the spindle is maintained by static friction. No separate braking component is needed. This is ideal for increased stability requirements over a long period. Since the three filters in the assembly are moved rarely and only slowly when they are moved, this setup was perfect. Feinmess Suhl manufactures the two-start dry-running linear drives using thread rolling or thread rolling processes. This chipless process creates the thread form by cold forming. The result is a high-quality surface finish at an extremely economical price-performance ratio.

Small, compact, precise, dry-lubricated, reliable, durable, low-maintenance: the polarization filter fully meets the demanding requirements of DUV lithography. The linear drive proved to be the key component during development and design. It is the heart of the assembly and makes the small dimensions possible. "We developed the linear drive for a specific customer project, but of course, other high-end applications in semiconductor technology also benefit from the unique properties of the spindle. A wide range of options allows for individual customization," emphasizes Detlef Rode.

Broad spectrum of drive options

The development of customer-specific linear drives is one of Feinmess Suhl's core competencies. The Steinmeyer Group also has an experienced partner in August Steinmeyer for the development and manufacturing of highly precise ball screws. With appropriate special lubrication and coatings, these can also be used in the semiconductor industry. Which technology is right – dry-lubricated linear drive or liquid-lubricated ball screw – ultimately depends on the application requirements and is individually determined by Steinmeyer specialists for each case.

Popular partner for the semiconductor industry

Whether handling, inspection, or assembly, whether HV, UHV, or EUV positioning: thanks to its broad technological expertise, comprehensive engineering know-how, deep application understanding, and extensive experience, Steinmeyer Mechatronics is a sought-after partner in designing, developing, and manufacturing demanding positioning solutions for wafer and chip production. The proven systems are customized to meet application-specific requirements – from test laboratories to automated semiconductor factories, up to ISO 14644-1 Class 1. All components are designed for vacuum compatibility and are cleaned separately after manufacturing. Assembly takes place in a certified ISO Class 6 cleanroom. Variable cleanroom capacities of over 3,900 m² ensure exceptional flexibility. A cleanroom-compatible packaging with nitrogen inert gas filling protects the finished product during transport.

"We have decades of experience in designing and manufacturing positioning systems for semiconductor applications and possess special expertise in tribology and lubrication in dry, oxygen-free atmospheres such as vacuum and pure nitrogen. This enables us to reliably and economically implement solutions even for challenging tasks," emphasizes Elger Matthes. He adds: "The three competence centers of drive technology, positioning technology, and precision measurement technology of the Steinmeyer Group combine an incredibly broad range of services. This allows us to optimize synergies and quickly and straightforwardly realize specific customer requirements." The joint development of the DUV polarization filter is the best example.