As applications for ultraviolet-laser systems broaden in medical, wafer processing, atmospheric detection, and electronics manufacturing, the accompanying rise in performance requirements pushes laser system manufacturers and their suppliers to work together in new ways. Applications requiring higher pulse energy, kilohertz repetition rates, and ever-shorter ultraviolet (UV) wavelengths put particular strain on the laser optics, requiring coated optics with higher laser-induced damage threshold (LIDT), lower scatter, and lower absorption. New applications in a competitive market demand fast prototyping and a new approach to supply-chain management.
Partnerships such as the one between toolmaker Electro Scientific Industries (ESI) and optics-maker CVI Laser are necessary to produce advanced UV-laser-based manufacturing tools for the commercially available electronic devices. Like many OEMs, ESI is moving away from the traditional vendor management role in which delivery fulfills the majority of expectations. Instead, the company is working toward partnerships in which it grows vendors along with the technology. Rapid information exchange and close collaboration of such partners is required to advance the technology.
Companies that prosper will have vendor partnerships in place. The economic environment is forcing equipment manufacturers to re-examine where they add value. The trend is for OEMs to outsource optical assemblies to contract optical manufacturers, allowing the equipment suppliers to focus on system design and customer relationships.
Demands placed on new manufacturing systems come from customers. In the case of ESI, the laser systems are used for creating high-density interconnects in devices such as camcorders, cell-phone cameras, IC packaging for microprocessors, and chipsets. Lasers are the technology of choice for forming microvias in high-density interconnects as well as chip packaging devices. All of these segments are competitive and fast moving, populated with global companies. The technology continually demands higher repetition rates, higher average power, and smaller feature sizes (see Fig. 1).
FIGURE 1. An electron micrograph shows a 75-µm-diameter "blind" microvia in a 45-µm layer of epoxy resin cut by a UV laser system; vias form the interconnect paths between layers in printed circuit boards and may be "through"—cutting through all processing layers, or "blind"—cutting through a controlled number of layers (top). A beam-shaping technique changes the shape of the beam to match the application by taking the total energy of the Gaussian beam and redistributing it to form a beam of uniform intensity; advantages include highly circular vias, high throughput, and excellent bottom copper quality with no resin residue (bottom).
When its customers request modifications, improvements, or price reductions, ESI must evaluate all options and sometimes pass requirements on to its vendors. The speed at which the entire supply chain can partner to meet these modifications or requirements can directly impact the success of new products.
In the case of rapid prototype development with an optics vendor, for example, the relationship can direct the choice of optics toward commonly stocked polished substrate sizes, because the optics vendor knows that coating takes less time than polishing. If the vendor receives accurate, comprehensive, and timely information regarding the application and environment, it can make better choices regarding which particular coating design to provide. Such partnerships create a set of special responsibilities for both parties (see "Partnerhsips bring responsibilities," below).
Challenges to an optics vendor
To meet the rigorous specifications of current and future UV-laser systems, manufacturers of laser optics face many materials issues. These include:
Substrate material. A UV-laser optics manufacturer may have to work with several materials including fluoride compounds. These materials are generally more expensive than crown glasses and can carry processing challenges such as thermal sensitivity.
Surface finish. Since the shorter UV wavelengths are more easily scattered, the surface smoothness on the substrate becomes even more important. Optical manufacturers are motivated to supply "super polished" surfaces, often with average RMS roughness down to 0.1 nm. Measurements of this type of low roughness require sophisticated optical or profile equipment, such as scatter based instruments or atomic force microscopes.
Cleaning. To prepare the optics for coating and in expectation of the highest damage threshold, the surface must be rigorously cleaned. Cleaning methods may include multiple processes of wet chemical, ultrasonic, ion, and plasma processes.
Coating. The antireflection and reflective coatings for laser optics are complex multilayer structures requiring careful material and layer thickness choices to give the proper optical performance, control structural parameters such as stress, and minimize local electrical fields to raise LIDT. The materials themselves also pose challenges. Whereas some oxides, such as hafnia (HfO2) and silica (SiO2), are familiar from their use at moderate UV wavelengths, low-index fluoride materials come into use as the UV wavelengths descend. Coating processes are also changing. Laser-optic manufacturers that found electron-beam deposition or resistive heating adequate for deposition in the past may now use reactive sputtering or ion assist to improve packing density in the coatings.
Measurements. Ultraviolet optics must be measured at UV wavelengths. As 157-nm fluorine (F2) lasers become more prominent for future applications in lithography, measurements of F2 laser optics will need to be made below the absorption wavelength of oxygen, approximately 185 nm. Most existing systems cannot be converted to the vacuum and nitrogen-purged environment needed for these measurements, forcing the purchase of new capital, expansion of work areas, and the training of workers.
These development issues—presented to the optics supplier as UV requirements move to shorter wavelengths—keep laser-optics manufactures in a constant race to improve their products and processes while making the needed infrastructure changes. While it is understandable for an OEM to want the highest performance possible from the optics, both vendor and customer will be better served by working together to determine exactly which specifications are really needed. This is especially true when development time is short, or times such as today when resources are expensive or scarce as we moveto the region below 185 nm.
Perhaps the most important step in the partnering process is deciding what partnerships are beneficial. As always, understanding where the company's core competency lies is key to finding which items are most cost-effective to keep in-house and which should be outsourced.
The authors would like to thank ESI for helpful discussions.
LILIAN HOINES is an application engineer and BOB SOALES is vice president of sales at CVI Laser, 200 Dorado Place, SE, Albuquerque, NM 87047; e-mail: [email protected].
Partnerships bring responsibilities
Increasingly close vendor/OEM partnerships place special demands on both parties involved. These responsibilities include:
· The supplier may be asked to hold excess inventory to assist the OEM in the event of emergency or quick ramp-up.
· Component testing at the system manufacturers site can be eliminated if the supplier can provide optics that are quality tested to ensure performance in the final system. Achieving this requires close work between both parties to develop representative tests and acceptance criteria. In some cases a system or portions of a system may be installed at the vendor site for final qualification tests.
· The OEM may need to expend funds or resources raising the technical quality of a smaller supplier. If prototype systems are often sold as product, the OEM should arrange for all prototype optics to be production worthy.
· Prototype time can be reduced if the vendor carries a variety of production-worthy optics in stock.
· The vendor should identify long lead-time materials or items that the OEM is likely to need and consider keeping some of them in stock.