Patent Application
20100225236
The technology disclosed relates to an illumination source including numerous laser diodes. In particular, it relates to extending the duty cycle and/or reducing the frequency of component replacement by detecting failure of one or more individual laser diodes and compensating for the failure, without replacing the laser diodes.
The Micronic Laser development team has pioneered a variety of platforms for microlithographic printing. An established platform for the Sigma machine is depicted in
One printing mechanism designed for these platforms uses swept beams that are modulated as they traverse the surface of the workpiece, applying energy as a paintbrush applies color. Another printing mechanism design freezes the motion of the workpiece with the flash and stamps two dimensional patterns on the workpiece, exposing a radiation sensitive layer in a manner similar to block printing a pattern. Printing with stamps is an intricate process that typically overlaps multiple writing passes.
Illuminators are a major part of the operating cost of many microlithographic printing systems. Accordingly, the opportunity is ever present to develop new illuminators. New illuminator designs may deliver increased power, extended lives, failure tolerance and decreased maintenance.
The technology disclosed relates to an illumination source including numerous laser diodes. In particular, it relates to extending the duty cycle and/or reducing the frequency of component replacement by detecting failure of one or more individual laser diodes and compensating for the failure, without replacing the laser diodes.
The technology disclosed can be used in cases of catastrophic laser diode failure by changing the power of remaining laser diodes to restore illumination to the coherence function similar to the pre-failure illumination field. Particular aspects of the technology disclosed are described in the claims, specification and drawings.
a: Gaussian distribution of light from the plane of the sources.
b: Depicting the coherence function with the failed laser diode.
c: Depicting the solution for a failed laser diode.
The following detailed description is made with reference to the figures. Preferred embodiments are described to illustrate the technology disclosed, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows.
The technology disclosed uses a one or two dimensional array of laser diodes with individually controlled power feeds and radiation outputs as an illumination source. Based on our analysis, we believe that 15 laser diodes is a good minimum number to permit the system to continue operation after catastrophic failure of one or more laser diodes, while continuing to satisfy a selected coherence function and afford a printing fidelity. Our analysis demonstrates that seven or eight laser diodes is too few to permit reduction of output from one of the remaining good laser diodes, to reestablish symmetry. By catastrophic failure, we mean that one or more laser diodes suffers a reduction in output to less than or equal to 20% of its initial output. By continuing to operate, we mean that the array of laser diodes can be used without replacing the failed laser diode. Coupled to an array of 15 or more laser diodes, we describe a detection and recovery method device to avoid the inconvenience of interrupted production and increase the time between replacement of illumination elements or illumination sources.
The coherence function may have an approximately Gaussian or sin(x)/x shape. The exact shape is a compromise between desired imaging properties and technical limitation of the illuminator. An approximately Gaussian shape assumes an approximate Gaussian distribution of light from the plane of the sources. An example is shown in
The laser diodes have a limited life and the cost of the laser diodes is a large part of the cost of ownership of the disclosed laser writer. Typically the laser diodes fade slowly during life, but catastrophic failure also happens. Such a failure is shown in the example in
First, if the deterioration of the coherence function is large enough to affect image properties, the writing system may need to be taken down for repair immediately, upsetting production planning. If the repair cannot be affected immediately, the system may be down for hours or longer until a skilled service person with the proper spare parts arrives.
Second, if the light sources, e.g. laser diodes, are mounted in modules or form part of the same array component, one failed source means changing a whole module or array, incurring higher replacement costs.
In addition, having a tunable fault-tolerant scheme may allow laser diodes or laser diode arrays with less tight specifications to be used. To be able to run the system with laser diode arrays with some laser diodes performing out of spec may save cost and in some cases even make it possible to use lasers which cannot be reproducibly produced, e.g. at shorter wavelengths.
b shows the coherence function with the failed laser diode in the left figure. The figure shows the actual coherence function (“Act”) and the intended one (“Ref”) and the difference magnified ten times (“10*Diff”). The horizontal scale may, in some embodiments, be equal to the number of pixels in the SLM. The difference between intended and actual coherence function translates to errors in the image, e.g. in the balance between the size of small and large features. The figure also shows the phase angle of the complex coherence function in milliradians. A tilted phase angle from mirror to mirror is the same as an apparent tilt in the illumination and will give problems with the landing angle of the light in the image, i.e. the image gets a displacement sideways when focus is changed.
The problem of failing laser diodes or laser diodes out of specification may be solved as shown in
The adjustment of the power to the laser diodes may be done automatically by calculation of the coherence function or even the properties of the image and finding, e.g. by iteration, laser diode currents that minimize the resulting errors.
Another possibility is to specify momenta of different orders for the light intensity and bringing the momenta within bounds by modifying the drive currents to the laser diodes. In some cases it may not be possible to recreate the desired momenta, coherence functions, or image properties at the same total power. In those cases, a lower power may be set and the writing speed of the laser writer reduced, in order to keep it running until a repair can be done. Likewise it may be possible to run some laser diodes beyond their safe power levels in order to keep the system running until a repair can take place, thereby eating into the lifetime of the laser diodes slightly, but avoiding unscheduled downtime.
The light source may be measured constantly or at short regular intervals using an array of detectors or a camera. The image may be brought to the camera by means of a beam sampling mirror or grating always present in the system.
The tuning of the light source currents may be automated in the background by the following procedure.
In the following paragraphs, we describe systems that use 2D and 1D SLMs that require illumination services.
A generic projection system is illustrated by
The basic projection system in 1a can be realized in many equivalent forms, e.g. with a reflecting object as shown in
The Sigma7300 mask writer made by Micronic Laser Systems AB further includes as an Excimer laser 17, a homogenizer 18, and relay lenses 13 forming an intermediate image 14 between the SLM and the final lens. The pupil of the final lens is normally located inside the enclosure of the final lens and difficult to access, but in
The technology disclosed may be practiced as a method or device adapted to practice the method. The technology disclosed may be an article of manufacture such as media impressed with logic to carry out computer-assisted method or program instructions that can be combined with hardware to produce a computer-assisted device.
One embodiment is a method of extending the life of an illumination source upon catastrophic failure of one or more illumination elements among 15 or more elements. The method includes operating an illuminator that combines radiation output from 15 or more illumination elements. The illuminator distributes initial power to the elements that produces initial radiation output levels from the elements. The illuminator also combines the initial radiation output levels to produce an overall illumination field from the illuminator that satisfies a quality function. Next, there is detection of failure of a first illumination element that reduces output from the first element to less than 20 percent of its initial output level. The power distribution to and output from one or more non-failing illumination elements is reduced to restore symmetry in the overall illumination field. The power distribution to and output from at least some of the illumination elements is increased to restore quality of the overall illumination field, as measured by the quality function.
In alternate embodiments, the illuminator combines radiation from 15 up to 200 illumination elements. The illumination elements can also have varying spatial distribution.
One aspect of the technology disclosed, applicable to any of the embodiments above, is expressing said quality function as an approximately Gaussian distribution. Alternately, the quality function can also be expressed as an approximately sin(x)/x distribution.
Another aspect of the technology disclosed is automatically detecting, reading and increasing power distribution.
In another embodiment, the illuminator operates with the 15 or more illumination elements after the first illumination element fails, without replacing the failed first illumination element.
In yet another embodiment, failure of a second illumination element is detected, applying the reducing and increasing steps to compensate for the failure of the second illumination element, and continuing to operate the illuminator with the 15 or more illumination elements after the first and second illumination elements have failed, without replacing the first or second illumination elements.
Any of the methods described above or aspects of the methods may be embodied in a self correcting illuminator system. The system includes an illuminator that includes 15 or more illumination elements and optics that combine radiation output from the illumination elements, a power supply coupled to the illumination elements that distributes power to the illumination elements, sensors optically coupled to the radiation output, a controller coupled to the sensors and controlling the power supply, the controller including program instructions that set an initial power level for the illumination elements, wherein initial output levels from the illumination elements produce an overall illumination field from the illuminator that satisfies a quality function. The controller also detects failure of a first illumination element that reduces output from the first element to less than 20 percent of its initial output level. The controller is further responsive to the detected failure, reduce power distribution to and output from one or more non-failing illumination elements to restore symmetry in the overall illumination field and also responsive to the detected failure, increase power distribution to and output from at least some of the illumination elements to restore quality of the overall illumination field, as measured by the quality function.
One aspect of the technology disclosed is illumination elements having even spatial distribution. Alternately, the illumination elements can also have varying spatial distribution.
Another aspect of the technology disclosed is expressing said quality function as an approximately Gaussian distribution. Alternately, the quality function can also be expressed as an approximately sin(x)/x distribution.
While the technology is disclosed by reference to the preferred embodiments and examples detailed above, it is understood that these examples are intended in an illustrative rather than in a limiting sense. Computer-assisted processing is implicated in the described embodiments, implementations and features. Accordingly, the disclosed technology may be embodied in methods for reading or writing a workpiece using at least one optical arm that sweeps an arc over the workpiece, systems including logic and resources to carry out reading or writing a workpiece using at least one optical arm that sweeps an arc over the workpiece, systems that take advantage of computer-assisted control for reading or writing a workpiece using at least one optical arm that sweeps an arc over the workpiece, media impressed with logic to carry out, data streams impressed with logic to carry out reading or writing a workpiece using at least one optical arm that sweeps an arc over the workpiece, or computer-accessible services that carry out computer-assisted reading or writing a workpiece using at least one optical arm that sweeps an arc over the workpiece. It is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the disclosed technology and the scope of the following claims.
This application claims the benefit of U.S. Provisional Application No. 61/158,310, filed 6 Mar. 2009, which is hereby incorporated by reference. This application is related to US patent application entitled “Rotor Imaging System and Method with Variable-Rate Pixel Clock”; and US patent application entitled “Variable Overlap Method and Device for Stitching Together Lithographic Stripes”; and US patent application entitled “Lithographic Printing System with Placement Corrections”, all filed contemporaneously. The related applications are incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61158310 | Mar 2009 | US |
