|
|
 |
Home / About Us / Solutions / X-ray Fluorescence / Del-Tron Solutions
New Focusing Method Allows X-Ray
Fluorescence to Resolve Finer Details
|
| Veeco Instruments. |
A new focusing method enables X-ray fluorescent (XRF) thickness and composition measuring tools to measure in much smaller areas. XRF instruments are most commonly used to determine the thickness and composition of interconnect metalizations in microelectronic and data storage devices. The accuracy of conventional X-ray fluorescent instruments is limited by the opening (collimator) used to govern the area of X-rays impinging the sample – as it gets smaller less of the primary beam flux can get through. The new method, called optical collimation, captures and directs the primary beam down to a node, increasing precision by a factor of ten. A key to the development of this new device is the use of linear motion devices that precisely align the beam to the sample.
Continued advances in microelectronics manufacture – including increasing clock speeds, reduction in device size, impedance and capacitance factors and thermal management issues –- have increased the demand on the packaging and interconnect segments to provide smaller, faster and more electrically and thermally conductive interconnect schemes. Sub 100 micron interconnect structures used in ball grid arrays, flip chips and wire bonding techniques on wafers, packages and substrates are common and these structures will continue to decrease in size and increase in density.
|
X-ray fluorescence
This trend raises the need for opaque film metrology tools capable of determining the thickness and composition of interconnect metallurgy. XRF has long been the preferred tool for thickness and composition measurement in the electronics industry. This method relies on the principle that any element, when exposed to a source of high intensity x-rays, will emit x-rays or fluoresce at energy levels unique to that element. To obtain a measurement, the XRF system uses an x-ray source to produce a spectrum of x-rays that are directed at a sample to induce fluorescence.
|
 |
Since the XRF is used to measure very small sample areas, small x-ray beams are required. Erroneous measurements will be obtained if the beam size is larger than the sample, or if the beam is mispositioned in such as way that its perimeter extends beyond the edge of a sample. Most XRFs use collimators, essentially pin hole apertures, to direct the beam. The collimator blocks all but a very small fraction of the generated x-rays, passing only those traveling in a path coincident with the opening. These x-rays emerge in a cone-like beam whose initial diameter is equal to the diameter of the collimator opening.
Detection methods
The XRF detects x-ray emissions from the sample and converts these to electronic pulses. Each pulse is then sorted according to its energy level into a memory location or channel in the XRF’s multichannel analyzer. The analyzer also counts the number of pulses stored in each channel. The data is used by a computer to generate a frequency distribution or histogram displaying channel number or energy level information along the x-axis and number of pulses along the Y-axis. To arrive at a measurement level, the instrument can either compare the spectral data from a sample to a previously stored calibration spectrum or use fundamental parameters to evaluate the sample. Using either of these methods, the instrument can calculate the thickness and composition of a sample.
XRF is a powerful tool but has until recently been taxed to provide fast and precise results on structures smaller than 100 microns. This is because of the mechanical collimators used to govern the exposure area impinging the sample. With mechanical collimation, as the machined openings become smaller to resolve smaller interconnect structures, less of the primary beam can reach the sample. Since XRF systems are counting devices, their precision is proportional to the number of x-rays generated at the sample and subsequently fluoresced back from the sample to the detector. Thus, smaller beams mean reduced precision, longer measurement times and reduced throughput.
q
|
|
Optical collimation
Recently, a new method has been developed to improve the precision of XRF devices. Called optical collimation, rather than governing the flow of primary x-ray beam photons, it redirects them down to a point. This is accomplished by a device called a focusing element that utilizes a monolithic polycapillary optic in conjunction with a beam input array and an exit filter to deliver unprecedented x-ray intensities in areas as small as 50 microns. Countrate gains on the order of 100 times and precision gains of an order of magnitude can be achieved with this new technology. |
The use of a focusing element allows for micro-beam x-ray analysis of structures as small as 50 microns. Typical applications for the new technology include analysis of solder bump composition (Sn-Pb), three-layer under bump metallurgy thickness measurement (such as Au/Ni-P/Cu and Cu/Cr/Ti), wire bond pad metallurgy (Au/Ni/Cu), thickness measurement, ball grid array and flip-chip package metallurgy, package-to-substrate interconnect and current carrying metallurgy.
Design challenge
When Veeco Industrial Measurement Division, Ronkonkoma, New York, first integrated the optical collimator into their XRF tools the company faced a challenging task in commercializing this technology. The biggest obstacle was the fact that the optical collimator is considerably more complicated from a mechanical standpoint, yet Veeco wanted the new instrument to be exactly the same size as the old one. The primary complexity is the need for two-axis positioning of the focusing element. At the same time, engineers wanted to fit the case inside the existing product structure because of tight space requirements in the clean rooms where the devices are normally used and in order to reduce design and manufacturing costs.
Veeco engineers selected the R201XY roller slide positioning stage from Del-Tron Precision, Inc., Bethel, Connecticut, because it was the smallest linear motion device they could find that fit their requirements. This stage easily fit within the confines of the existing product packaging. The stage also meets the accuracy requirements of the application without difficulty. It incorporates a spring loaded micrometer drive that allows precise repeatable adjustments with low friction and zero backlash. The slides provide accuracy to .0001"/inch of travel and repeatability of .0001". Over 60 models, support load capacities to 160 lb.
Spring-loaded drive
This device incorporates a spring-loaded micrometer drive that allows precise repeatable adjustments with low friction and zero backlash. It also features a positive locking capability consisting of a steel shim and extended micrometer bracket secured by a screw mounted to the side of the stage carriage. This allows the user to positively lock the position of the carriage during use. Locking micrometer heads are also available to lock the micrometer setting. Del-Tron makes more than 60 models of the ball slide positioner with load capacities of up to 60 pounds. Used for gauging and positioning light and medium loads, applications include measuring instruments and optical assemblies. The firm’s full line includes the subminiature series with the smallest commercially available positioner, the standard series, ideal for most gauging and positioning applications, and our heavy duty series providing high load capacities with the same high accuracy and repeatability.
Veeco incorporated the slide into its MXR XRF metrology tool that delivers 40 to 300 times the X-rays and 10 times the precision of mechanically collimated XRF systems with equivalent beam sizes. The detection column of the MXR instrument features an electrically cooled solid state detector for optimum sensitivity required for thin (100-500Å) depositions, multilayer metal stacks and elemental peak overlap applications. Veeco has also introduced a VXR instrument that utilizes vacuum technology to extend the elemental measurable range of the MXR to elements from aluminum to scandium, in addition to the titanium to uranium range of the MXR. This instrument also incorporates an evacuated conduit design that allows measurement of the sample in the air while retaining the accuracy of vacuum measurement. Since chamber evacuation is not required, throughput is dramatically improved. Both of these instruments have experienced excellent success in the market, demonstrating the validity of this new technology.
|
| |
|
|
Del-Tron Precision began operations in 1974 supplying original equipment manufacturers with the world’s first commercially available subminiature ball slide. Since then, thousands of Del-Tron ball slides have been incorporated into medical analyzing and testing machines, semiconductor processing equipment, computer peripherals, assembly systems, scientific instruments and many other machines. Del-Tron’s modern corporate campus boasts highly automated computer controlled equipment and final inspection of 100% of all products has been Del-Tron’s policy since its inception. For more information, contact Del-Tron by phone at 800-245-5013, by fax at 203-778-2721 or by email: deltron@deltron.com. |
| |
|
| |
|
|
|
 |
Receive Our Newsletter |
 |
 |
|
|
| Free up-to-date product information, specials, industry news and more . . . |
|
| Sign up now >> |
 |
|
 |
|
Save 10% |
|
|
|
|
| Save at least 10% on any written quote issued by one of our competitors . . . |
|
| Details here >> |
|
|
|
|
Special Modifications? |
|
|
|
|
| See the Del-tron Product you want, but want something changed slightly? |
|
| Info on prototypes >> |
|
|
|
|
