PSL Wafer Standard, Calibration Wafer Standards
A Calibration Wafer Standard with polystyrene latex nanoparticles) is a certified, NIST Traceable, particle size standard deposited on a prime silicon wafer with a monodisperse, polystyrene latex sphere size and narrow size distribution. Monodisperse calibration sizes are available from 40nm to 10um. A PSL Wafer Standard can be provided with a spot deposition with one or more calibration sizes deposited on the wafer surface with controlled particle count between 1000 and 2500 per size deposited. A Full Deposition is a single size deposition across the entire wafer surface with a PSL count between 5000 and 25,000 count on the wafer surface, depending on diameter of wafer standard. These PSL Wafer Standards are used to calibrate the size accuracy response of scanning surface inspection systems (SSIS) using low powered lasers, such as Tencor Surfscan 6200, 6220, Tencor Surfscan 6400, 6420, as well as KLA-Tencor Surfscan SP1 and SP2 tools.
Calibration Wafer Standard to calibrate the size accuracy of KLA-Tencor Surscan SP1, SP2, SP3, SP5, SP5xp toolsApplied Physics provides Calibration Wafer Standards to calibrate the size accuracy of the KLA-Tencor Surfscan SP1, KLA-Tencor Surfscan SP2, KLA-Tencor Surfscan SP3, KLA-Tencor Surfscan SP5, KLA-Tencor Surscan SP5xp, Surfscan 6420, Surfscan 6220, Surfscan 6200, ADE, Hitachi and Topcon SSIS tools and wafer inspection systems. Our 2300 XP1 Particle Deposition System can deposit on 150mm, 200mm and 300mm wafers using PSL Spheres and SiO2 particles. These PSL contamination wafer standards are used by Semiconductor Metrology Managers to calibrate the size response curves of Scanning Surface Inspection Systems (SSIS) manufactured by KLA-Tencor, Topcon, ADE and Hitachi. PSL Wafer Standards are also used to evaluate how uniform a Tencor Surfscan tool scans across the silicon or film deposited wafer.
Calibration Wafer Standard, Full Deposition, 5um - Calibration Wafer Standard, Spot Deposition, 100nm
PSL Wafer Standards come in two types of depositions: Full Deposition (Full Deposition above left) and Spot Deposition (Spot Deposition above right).
Either PSL Spheres or Silica particles can be deposited.
Full Deposition - Request a Quote
A Calibration Wafer Standard is used to identify two aspects of an SSIS tool: size accuracy of each size deposited and size accuracy across a wide dynamic range of the SSIS tool. Uniformity of scan across the wafer is generally analyzed in a FULL Wafer Deposition. The surface of the wafer is deposited with a specific PSL size, leaving no portion of the wafer not deposited with PSL Spheres. During the scan of the PSL Wafer Standard, The SSIS tools detects the peak of the PSL size distribution, which should be the size deposited on the wafer. The uniformity of scan across the wafer should indicate the SSIS is not overlooking certain areas of the wafer during the scan. Count accuracy on a Full Deposition wafer is subjective, since the Count Efficiency of two different SSIS tools (Deposition site and Customer site) are different, sometimes as much as 50 percent. Thus, the same Particle Wafer Standard deposited with a highly accurate size peak of 204nm at 2500 counts and counted by SSIS tool 1, may be scanned by SSIS 2 at customer site and the count of the same 204nm peak may be counted anywhere between 1500 count to 3500 count. This count difference between the two SSIS tools is due to the count efficiency of each PMT (photo Multiplier Tube) operating in the two separate SSIS tools.
Spot Deposition - Request a Quote
PSL Wafer Standards with a Spot Deposition are used for size accuracy calibration of the SSIS.
A Calibration Wafer Standard with a Spot Deposition has the advantage in that the spot of PSL Spheres deposited on the wafer is clearly visible as a spot, and the remaining wafer surface around the spot deposition is left free of any PSL Spheres. The advantage is that over time, one can tell when the Calibration Wafer Standard is too dirty to use as a size reference standard. Spot Deposition forces all the desired PSL Spheres onto the wafer surface at a controlled spot location; thus very few PSL spheres and much higher count accuracy is the result. Applied Physics uses a Model 2300XP1 using DMA (Differential Mobility Analyzer) technology to ensure the NIST traceable PSL size peak to be deposited is accurate. A CPC is used to control count accuracy. The DMA size control minimizes unwanted Haze, Doublets and Triplets from being deposited on the wafer surface. Several companies in the industry use Direct PSL Deposition to deposit Wafer Standards, as discussed below; which is not able to prevent Haze, doublets and triplets from being deposited on the wafer surface. However, the Direct Deposition, Particle Deposition System is less expensive to produce PSL wafer Standards from 40nm to 5 microns.
Applied Physics is able to use both DMA Deposition control and Direct Deposition control. DMA control provides the most size accuracy below 150nm by providing very narrow size distributions with minimal Haze, doublets and triplets deposited in the background. Excellent count accuracy is also provided. PSL Direct Deposition provides good depositions from 80nm and above, all the way up to 5 microns.
PSL Direct Deposition
The PSL Direct Deposition method uses a PSL Sphere source, diluted to the appropriate concentration, mixed with a highly filtered (20nm) airflow or dry nitrogen flow and uniformly deposited over a silicon wafer or blank photo mask as a full deposition or a spot deposition. The Direct Deposition, Particle Deposition System is less expensive, and best used for Peak PSL Size depositions from 80nm to 5 mircons.
If several companies producing the same size of PSL spheres are compared, for example at 204nm, one may measure a difference in the peak size of the two PSL depositions from the companies, possibly as much as 3 percent. Manufacturing methods, measuring instruments and measuring techniques cause this delta. However, this means that any Wafer Deposition tool using only PSL Direct Deposition to deposit PSL Spheres directly from a PSL bottle relies on the accuracy of the PSL size peak in the bottle source.
DMA Deposition Control
The second method, DMA (Differential Mobility Analyzer) Deposition Control, applies more control over the PSL Spheres. The DMA is calibrated to NIST Standards at 60nm, 102nm, 269nm and 895nm. The PSL spheres are diluted with DI Water to the desired concentration, aerosolized into an air stream, mixed with a Dry Air or Dry Nitrogen to evaporate the DI water surrounding each PSL sphere and nuetralized to remove double and triple charges. The air stream and PSL spheres are then processed through the DMA, which strips away the left and right side of the size peak to provide a narrow PSL Size peak, which is then directed down to the wafer surface as a FULL Deposition of SPOT Deposition, while simultaneously being counted for size accuracy. The DMA calibration to NIST SRM accuracy ensure the DMA peak is highly accurate and narrow, so as to provide superb calibration for a KLA-Tencor SP1 and KLA-Tencor SP2.
If for example, 204nm PSL Spheres from two different manufacturers were used in a DMA controlled, Particle Deposition System, the DMA would ensure that a precise 204nm would be deposited onto the wafer surface.
A DMA controlled, Particle Deposition System is also able to provide much better count accuracy, as well as computer recipe control over the entire deposition. IN addition, a DMA based system can deposit real process particles, such as Si3N4, SiO2, W, etc.