Calibration Wafer Standard
A Calibration Wafer Standard is a NIST traceable, PSL wafer standard with Size Certificate included, deposited with monodisperse polystyrene latex beads and narrow size peak between 50nm and 10 microns to calibrate the size response curves of Tencor Surfscan 6220 and 6440, KLA-Tencor Surfscan SP1, SP2 and SP3 wafer inspection systems. A Calibration Wafer Standard is deposited as a FULL Deposition with a single particle size across the wafer; or deposited as a SPOT Deposition with 1 or more particle size standard peaks, precisely located around the wafer standard.

Our company provides Calibration Wafer Standards using Particle Size 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 100mm, 125mm, 150mm, 200mm and 300mm silicon wafers using NIST Traceable, PSL Spheres (polystyrene latex particle size standards) and Silica particle size standards.

These PSL calibration 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.

A Calibration Wafer Standard is used to verify and control two specifications of an SSIS tool: size accuracy at specific particle sizes and uniformity of scan across the wafer during each scan. The Calibration wafer is most often provided as a full deposition at one particle size, typically between 50nm and 12 microns. By depositing across the wafer, i.e, a full deposition, the wafer inspection system keys in on the particle peak, and the operator can easily determine if the SSIS tool is in specification at this size. For example, if the wafer standard is 100nm, and the SSIS tool scans the peak at 95nm or 105nm, then the SSIS tool is out of calibration and can be calibrated using the 100nm PSL Wafer Standard. Scanning across the wafer standard also tells the technician how well the SSIS tool detects across the PSL Wafer Standard, looking for similarity of particle detection across the uniformly deposited wafer standard. The surface of the wafer standard 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 uniformity of scan across the wafer should indicate the SSIS tool 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 3000 count. This count difference between the two SSIS tools is due to the laser efficiency of each PMT (photo Multiplier Tube) operating in the two separate SSIS tools. Count accuracy between two different wafer inspection systems are normally different due to the laser power differences and laser beam intensity of the two wafer inspections systems.

PSL Calibration Wafer Standards come in two types of depositions: Full Deposition and Spot Deposition shown above.

Either polystyrene latex beads (PSL Spheres) or silica nanoparticles can be deposited.

PSL Wafer Standards with a Spot Deposition are used to calibrate the size accuracy of an SSIS tool at one size peak or multiple size peaks.
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 improved 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 deposited is accurate and referenced to NSIT Size Standards. A CPC is used to control count accuracy. The DMA is designed to remove unwanted particles such as Doublets and Triplets from the particle stream. The DMA is also designed to remove unwanted particles on the left and right of the particle peak; thus ensuring a monodispersed particle peak deposited on the wafer surface. Depositing without DMA technology allows unwanted doublets, triplets and background particles to deposit on the wafer suraface, along with the desired particle size.