This technical information has been contributed by
Resonetics, Inc.

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Excimer Lasers...Unique Manufacturing Tools

Excimer lasers are gas lasers that, when electrically discharged, produce ultraviolet photons. Total powers range up to 200 Watts but most of the installed industrial excimer lasers output about 50 Watts. The gas mixture consists of a buffer gas, used to carry away excess energy; a rare gas; and a halide gas. The three ingredients combine when electronically excited to form the molecule that emits laser energy.

When excimer lasers were first 'discovered' in the late 1970's, their potential for use in micro-machining was almost immediately realized.

It was not until the late 1980's, however, that serious attempts were made to deliver large numbers of excimer laser-based systems to a variety of industries serving many different market segments.

Part of this delay was because time was needed for application development. But the primary reason was that early devices were notoriously unreliable and difficult to use. Recent advances in laser engineering and materials compatibility have produced excellent, highly reliable 'workhorses'. Today, there are many examples of excimer lasers being used in 24 hour per day, seven day per week operation.

Also, laser system integrators now provide packaged 'tools' for manufacturing operations that require only minimal knowledge of laser operation or physics. These systems can be operated by almost anyone with some degree of technical skill.

Excimer lasers have truly become an accepted industrial tool and have taken their place beside the more traditional CO2 and solid state lasers.

Excimer Laser Advancement

In the early 1980's, the typical commercial excimer laser was difficult to use, and had short gas lifetime, high maintenance requirements, and high cost of operation. Gas lifetimes were measured in minutes/hours and thousands of shots.

There was virtually no application development. There was no computer or microprocessor control. Very little thought had gone into material compatibility and, in fact, some of the earliest devices were modified nitrogen or CO2 lasers. The earliest commercial manufacturers were Tachisto (no longer in business), Lambda Physik (which probably holds 90 percent of the world market by units), and Lumonics.

In the mid 1980's, there were some technical advancements. The first commercial installations were made in pioneering companies like IBM and Siemens. Gas lifetimes were measured in hours and hundreds of thousands of shots. The first attempts were made at microprocessor control. Research and applications laboratories were developing new techniques and products to make use of the new technology. Materials compatibility issues were being investigated. Internal filters were developed to keep the gas clean of impurities and metal debris.

By the late 1980's, there were many excimer laser systems in production because of the ongoing development work in both the applications and in laser system engineering. Gas lifetimes were measured in hours/days and millions of shots. Full computer control of all the service, maintenance, and operating parameters allowed easier laser integration into industrial machining tools. Fiber optic communication lines minimized electrical interference, another problem in earlier lasers.

Although excimer lasers were becoming more accepted and reliable, operating costs were still too high, and gas lifetimes were still too short for more than a few well-suited and high value added applications.

Today's excimer laser is quite a different product than the earliest lasers. Full computer control and easy interfacing make the laser quite user friendly. Gas lifetimes now are measured in days/weeks and tens of millions of shots and component lifetimes are surpassing several billion shots.

Operating costs including electrical, cooling, gases, and consumables can be less than $10 per hour. Applications continue to be developed, especially in the microelectronics and medical device industries. Typical industrial laser costs are about $150,000 to $200,000 with a full, class I micro-machining system including laser, vision, motion, etc. costing about $250,000 to $500,000.

Unique Manufacturing Capabilities

The growing use of excimer lasers for micro-machining--whether conducted in-house or contracted through service companies--is providing opportunities for cost effective solutions to many industrial manufacturing problems.

In general, it is fair to say that excimer lasers are best applied to manufacturing processes where precision and quality requirements outweigh bulk material removal requirements. Excimer lasers, because of the nature of ultraviolet light interaction with materials, tend to be best applied to plastics, ceramics, CVD diamond and, in some precision applications, metals.

Because of the very small penetration depth and the low power of the lasers, most successful operations are performed on materials less than one mm thick. Image sizes at the target, which are adjustable from about 0.015 inch to 0.040 inch, depend on the material being processed, and the desired on-target energy density.

Some of the biggest commercial uses of the excimer laser are outside the scope of this article to discuss in detail, but a listing should be made. First, corneal ablation for corrective eye surgery is becoming very popular around the world, and companies such as Summit Technologies and VISX in the U.S. provide complete workstations to the medical industry.

Micro-lithography applications currently use excimer lasers to extend the available mercury lines, used in traditional lithography, to shorter wavelengths. Major players in this market are Cymer and Lambda Physik with a Japanese company, Komatsu, making a play for the expected rapid growth of market share.

There are probably hundreds of lasers in manufacturing environments around the globe using the excimer to provide a very tiny, high contrast and quality, indelible mark that will not cause surface micro-cracking or change the capacitive properties of the material.

Two general applications are good examples of success stories in our experience. The first is the contract manufacture of disposable medical devices. This usually involves a simple operation (for example drilling small holes in plastics for drug delivery) and involves very high volume (hundreds of thousands or millions of pieces per year).

The value added by the excimer laser can be to provide a technology that allows completely unique processing unattainable in any other way. Or, it can be reducing cost associated with existing manufacturing techniques; for example, making a multi-step operation into a one step operation and reducing both labor and material costs.

Dealing with the medical market may require a significant investment in infrastructure that may not already exist, such as setting up and maintaining a clean room, routine quality audits, certificates of compliance sent with deliveries, and lot tracking and document control that may be more stringent than in other industries. Per piece margins may be lower than in higher value added processes, but volumes can be quite high. We see the medical device market as one of the most promising for future growth.

Another example of high volume, lower margin work is the processing of flexible circuits to remove dielectric insulation from contact points or to create small holes.

The second type of application involves very high value added applications with perhaps lower unit numbers. For example, a particular processing job may have a requirement for only several hundred pieces per year. But if this job involves a high cost (and margin) product, and each piece takes ten or more hours of laser time, the total laser on-time in one year can be quite high.

These types of applications are not normally found in the medical industry, but are more common in the microelectronics and semiconductor industries. Currently, these industries are very strong users of UV lasers.

Continued developments in excimer laser systems have made the technology a viable commercial processing tool, with applications in R&D, prototyping, short-run or low-volume production, and high-volume, high-throughput manufacturing. Through familiarization with the technology, manufacturers can cross the comfort threshold and use excimer laser processing as a valuable enhancement to traditional manufacturing techniques.

Job Shop or In-House System?

A very important decision for the manufacturer is whether to incorporate laser systems into existing manufacturing environments, or to rely on the use of laser contract manufacturing services or 'job shops'. This choice is usually based primarily on the portability of the product and the relative costs involved.

For instance, very high volume products could justify capital equipment purchases (assuming that operating costs are also acceptable), whereas lower volume jobs, perhaps requiring only a fraction of available machine time, would not. Unless there are good reasons for capital purchases, such as a proprietary process or simply to retain full control of manufacturing, consideration should be given to contract manufacturing.

There are a large number of contract manufacturers using CO2 or solid state lasers, but only a few shops capable of using excimer lasers in any reasonable volume. It is sometimes difficult for the job shops using red lasers to transition to excimer lasers because of the large number of differences in the operation and maintenance required. This also includes facilities preparation and having the proper analytical instrumentation to 'see' what you are doing.

Resonetics, Inc. specializes in laser micro-machining services and turn key systems for micro-machining applications. The company can work with plastics, metals, ceramics, glass, sapphire, and diamond. They are a full service facility capable of providing feasibility studies, prototyping, and high volume production.

The importance of selecting a reputable contract manufacturer with a long history of involvement in contract manufacturing cannot be emphasized enough.

COMPARISON OF COMMON INDUSTRIAL LASERS
CO2 Nd:YAG EXCIMER
Processing Plane Focal Focal Image
Relative Operating Cost per Photon Low Low High
Wavelength (μm) 9.6 - 10.6 1.06 0.19 - 0.35
Average Power 0.3 to 20 KW 0.1 to 2 KW < 200 W
Penetration Depth (μm) > 10 1 to 10 0.1 to 1
Ultimate Feature Resolution (μm) 10 > 1 0.2
Practical Feature Resolution (μm) ~ 50 ~ 25 ~ 1
Material Interaction Thermal Thermal Photochemical/
Thermal
Types CW, Pulsed CW, q-switched,
Pulsed
Pulsed


COMMON EXCIMER LASER GAS MIXTURES
MIXTURE WAVE-
LENGTH
GAS
LIFETIME
AVG.
POWER
COMMENTS
ArF 193 nm ~106 pulses
Gas processing
required
~30 Watts Requires high grade optics
Requires purged BDS
Good for low power, high
resolution industrial applications
KrF 248 nm >107 pulses
Gas processing
recommended
50 to 150 Watts Good optical transmission
Aggressive on materials
Good industrial wavelength
XeCl 308 nm >2x107 pulses
Gas processing
not required, but
can be used
50 to 200 Watts Easy on optics
Absorbed well by many materials
Good industrial wavelength,
especially for marking

This technical information has been contributed by
Resonetics, Inc.

Click here to find suppliers

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