Calibration Wafer Standards are produced with polystyrene latex spheres and polystyrene latex beads, which are NIST Traceable, particle size standards.

Calibration Wafer Standards are produced with polystyrene latex spheres, deposited over the wafer surface as a full deposition across the wafer or as multiple spot depositions around the wafer. The particle size standards are NIST Traceable and the Size Certificate of the Calibration Wafer Standard is based on that NIST Traceability. Polystyrene latex beads are deposited on the wafer surface, each size with a monodisperse size peak. The sizes deposited are available between 40nm and 12 microns. The resulting PSL Wafer Standard is used to calibrate the size response curves of Tencor Surfscan 6220 and 6440 wafer inspection systems; as well as KLA-Tencor Surfscan SP1, SP2, SP3, SP5 and SP5xp wafer inspection systems. Full Deposition is where the polystyrene latex particles with a single, narrow size peak are deposited uniformly across the full surface of the wafer. Spot Deposition means the polystyrene latex beads are deposited as a single, narrow size peak, but deposited as a small spot at one location on the wafer; or deposited as multiple sizes around the wafer. Call Applied Physics at 720-635-3931.

Calibration Wafer Standard – Request a Quote

Applied Physics produces Calibration Wafer Standards to your specifications:

Wafer Size:           100mm, 125mm, 150mm, 200mm or 300mm

Type Deposition:  FULL Deposition or SPOT Deposition

Wafer Surface:     Prime Silicon, Customer Si Wafer, Customer Glass Wafer, Customer Bare Mask

PSL Size:              between 40nm and 12 microns

Particle Count:     count is approximate and depends on size of wafer, count is typically between 2500 and 20000 count, as measured by our wafer inspection system

Type of Particle:   Polystyrene Latex (PSL) spheres or Silica particles

Certification:        NIST Traceable

Wafer Inspection Systems, now called a surface scanning Inspection System (SSIS), are used to scan non-patterned wafers during device manufacture, so as to monitor the cleanliness of the starting wafers prior to device manufacture. The SSIS tool uses a laser beam to scan across the wafer surface. The laser beam width limits the particle size resolution. For example, if the beam width is 1 micron wide, then a particle smaller than 1 micron in diameter would be hard to size. The basic particle detection concept of the SSIS tool uses an overlapping scan to layout a scan map, which then locates the detected particles on a scan map, assigned in particle size and X/Y location on the wafer surface. As the laser scans across the wafer, when a particle is detected, the particle emits a light signature, which is detected by a solid state diode (SSD).  The laser beam power, beam width and uniformity of power across the laser beam width are all elements, which control the wafer inspection systems accuracy in correctly sizing surface particles. In addition, the Solid State Detector or photo multiplier tube detector affects particle sizing.

The primary purpose of a Calibration Wafer Standard is to calibrate an SSIS tool with NIST traceable size standards, calibrated across the size range of the SSIS tool. SSIS tools today typically offer 40nm minimum size detection. This would be KLA-Tencor SP3 and SP5 tools, and some of these tools are now under 20nm particle size detection. Older SSIS tools, such as KLA-Tencor SP1 and SP2 detect at 85nm and above. The older Tencor 6200, Tencor 6220, Tencor 6400 and Tencor 6420 are typically able to detect around 150nm and above.

Each one of these tools may use 3 to 8 different calibration wafer standards that help to calibrate size accuracy at the minimum particle sensitivity, maximum particle sensitivity and a number of calibration points between the min and max points, forming a calibration curve for that wafer inspection tool. Once calibrated the SSIS tool is then able to respond consistently to different particles detected on non-patterned wafers.

Calibration Wafer Standard, Full Deposition, 5um – Calibration Wafer Standard, Spot Deposition, 100nm

Full Wafer Deposition – Request a Quote

Full Deposition, Calibration Wafer Standards are also called PSL Wafer Standards. A Full Deposition wafer is normally deposited with a uniform particle count per centimeter squared across the wafer. This is a general count uniformity across the wafer, but is not exact. Count accuracy between two different wafer inspection tools can differ as much as 50% because the two wafer inspections may have two different lasers with different laser power, different beam widths, different laser power uniformity, etc. All of these elements affect count accuracy; thus count accuracy can not be a specification. The function of a FULL Deposition wafer standard is to calibrate size accuracy at one particle size, and to see how uniformly the SSIS tools scans across the wafer. For example, if a wafer standard has an average count of 100 particles per centimeter squared at 0.1 microns, then if the SSIS tool provides a similar, uniform detection of particles across the wafer, it is describing the uniform detection response of the calibration. On the other hand, if the SSIS tool has a blank spot or blank spots, where no detection is noted, then a FULL Deposition wafer standard helps to describe a poor scan response of the SSIS tool.

calibration wafer standard

Calibration Wafer Standard is often referred to as a PSL Wafer Standard. Full Deposition shown above.

Spot Deposition Around the Wafer Standard – Request a Quote 

Calibration Wafer Standards with a single SPOT Deposition, permits size calibration of the SSIS tool, and the bare portion of the wafer standard should be relatively clear of particle counts. So a SPOT Dep wafer standard provides calibration at a single size peak, and over time, the technician can evaluate if the wafer standard remains free of external contamination, by monitoring the clean surface. If the clean surface begins to get particle adders, scratches, etc., then one can determine the wafer standard is becoming overly contaminated for proper size calibration.

SPOT Deposition, Calibration Wafer Standards with 2 or more spot sizes around the wafer are even more beneficial for size calibration of the SSIS tool. A Metrology Engineer might want to use 6 FULL Dep wafer standards to calibrate his SSIS tool, which has the advantage of 6 distinct size peaks, while verifying scanning uniformity across the wafer at each calibration size. Or, he may prefer a SPOT Deposition, Calibration Wafer Standard with 6 spot sizes deposited around the single wafer standard, which offers the advantage of lower cost, and offers the second advantage of ensuring the SSIS tool can see all six sizes in one scan across the wafer. This particular Spot Dep Wafer Standard is far more useful, since it designed to calibrate the SSIS tool across a broad size range, but it simultaneously challenges the SSIS tool by showing how accurate the SSIS tool is with multiple size peaks on one wafer standard. Most companies producing wafer inspection tools, SSIS tools, prefer to calibrate with single sizes, rather then multiple sizes on one wafer standard, because multiple size peaks on one scan can point out to weaknesses in the scanning size accuracy of an SSIS tool.

Calibration Wafer Standards are used to measure size accuracy of KLA, Hitachi and the previous KLA-Tencor SSIS tools.

PSL Wafer Standards are deposited as a full deposition wafer standard or a spot deposition wafer standard. Each type of deposition offers a unique advantage for the Metrology Engineer, as he calibrates his SSIS tools.

Applied Physics uses a particle deposition tool that incorporates a differential mobility analyzer (DMA) to deposit a single particle peak with narrow size width. Although there are a number of elements that require control, the end result is depositing the specified peak on the surface of the wafer with NIST Traceability. Calibration wafer standards deposited between 40nm and 1 micron uses a DMA control to ensure size accuracy. Elements such as atmospheric pressure and temperature are control elements that are monitored during particle deposition to ensure the correct size is deposited on the wafer surface. Count is also monitored by sampling the particle counts just prior to deposit on the wafer surface.

polystyrene latext spheres

 

What Affects the Particle Counts by a Wafer Scanning System?
When a calibration Wafer Standard is produced, customers will ask for a desired count, example 10000 count on a 300mm PSL Wafer Standard. Our Particle Deposition System uses a Condensation Nucleus Counter (CNC) to count particles in the air stream just before deposition on the wafer standard. The CNC samples the PSL air stream and when the desired count is achieved, the deposition automatically stops. When scanning the wafer standard using the customer’s SSIS tool, the wafer standard may be scanned by any of 20 different types of scanning tools, so the counts derived by each wafer inspection system will differ due to technical design of the different SSIS systems, due to different light physics and different scanning techniques used by each SSIS system. For this reason, particle count is not a specification, since 20 different wafer inspection systems can scan the same calibration wafer standard, and generate 20 different counts. Particle Count then is a desired goal during deposition of a Calibration Wafer Standards.

How does a Differential Mobility Analyzer control the deposition of Particle Size Standards on the Calibration Wafer Standard?
A Differential Mobility Analyzer, DMA, is special particle size control device using a high degree of airflow control, a high degree of electrical voltage control; while monitoring atmospheric air pressure, atmospheric temperature, both which affect particle size accuracy selected for deposition by the DMA. For example, depositing particle size standards at ocean level versus elevations of 6000 feet has two different atmospheric pressures, thus size accuracy has to account for change in air pressure. Temperature in the clean room may vary by as much as several degrees, thus affecting the accuracy of the DMA. Therefore, the DMA has to account for these changes which influence the velocity of the particle size standard being desired for deposition. Airflow is drawn into the DMA, PSL spheres are introduced to the upstream side of the DMA. The PSL spheres on the upstream side of the DMA are actually a composite of a broad size peak, combined with unwanted background particles generated by the atomizer; thus the upstream side of the PSL sphere size peak is wide with unwanted background particles. As the PSL aerosol or silica particle aerosol travels thru the DMA, a very narrow size peak is allowed to escape the DMA, using airflow velocity and voltage to select the desired size peak to be deposited. A DMA controlled, Calibration Wafer Standard is able to deposit a highly accurate size peak, narrow in size distribution and NIST Traceable for use by the Device Metrology Engineer as a calibration wafer standard for monitoring and calibrating the size response of KLA-Tencor SP1, SP2, SP3, SP5 and KLA-Tencor SP5xp wafer inspection systems.