A Contamination Wafer Standard is a NIST traceable, silica wafer standard.

A Contamination Wafer Standard is a NIST traceable, silica wafer standard, which is deposited from 40 nm to 2000 nm with a typical size distribution width of 3% or less. A NIST Traceable, Size Certificate is included. Silica Contamination Standards are used to calibrate the size response of SSIS wafer inspection systems using a high powered laser. There are two advantages when using silica contamination standards with size calibration of SSIS tools, such as KLA-Tencor SP3, KLA-Tencor SP5 and KLA-Tencor SP5xp . The capacity of the silica particles to withstand high levels of heat without particle shrinkage is a distinct advantage over PSL spheres. And the silica nano-particles have a wavelength nearly identical to PSL spheres, therefore the size response curves of silica is close to a size calibration using traditional PSL spheres. There are slight variations between PSL Sphere calibration and Silica Particle calibration. This Silica Wafer Standard is deposited with a full deposition across the wafer with a single particle size. The particle wafer standard can also be deposited as a SPOT Deposition with 1 or more silica nano-particle sizes and particle sizes located at precise locations around the wafer standard.
 

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For many years, the semiconductor industry has focused on using PSL spheres to produce particle wafer standards to calibrate wafer inspection tools, which are now technically defined as surface scanning inspection systems, SSIS. Over the years, particle detection needed to improve in size detection sensitivity. In order to achieve this, laser power was increased over the years. Simultaneously, the laser beam width was decreased to improve particle resolution. In 1990, particle sensitivity was around 1/2 micron, but was progressively decreased towards 100nm by 2000. All the while as laser power was increased and beam width decreased, the energy per micron squared increased in orders of magnitude. This energy is directed onto the wafer surface to locate and size particles on the wafer surface, which cause device failure during the manufacture of semiconductor chips.

PSL spheres have been used for size calibration in the semiconductor industry for many years. But as that energy per micron squared increased on the wafer surface, the PSL spheres used for size calibration, began to encounter a shrinkage phenomena. It has long been known that spherical polystyrene latex particles are not representative of particle contamination on the wafer surface; however, the use of PSL spheres for calibration became a common and accepted use. However, as the energy coefficient of scanning lasers on the silicon wafer  increased, silicon came of interest to Metrology managers in the semiconductor facilities. Silicon is a common defect found on silicon wafers, thus using silica nano-particles had a common reference for size calibration. Particles are inherently non-uniform in size and non-uniform in shape; i.e. a true particle. The value of silica nanoparticles is that the particle can be produced in a spherical package, and the wavelength of silica particles is very close to PSL spheres, thus when calibrating with silica nano-particles the calibration curves of silica are similar to PSL, but have the distinct advantage of being able to calibrate SSIS tools down to 40nm with no difficulty. That is a distinct advantage that PSL calibration does not offer. Contamination Wafer Standards deposited at 100 nano-meters diameter and above are typically scanned by a KLA-Tencor Surfscan SP1 and SP2 tools. Contamination Wafer Standards deposited from 40nm and above are typically scanned by KLA-Tencor Surfscan SP3, SP5 and SP5xp.

Contamination Wafer Standard, Spot Deposition, 100nm

Contamination Wafer Standards with a full deposition or spot deposition.
Silica particles at 100nm are deposited with two spot deposition above.

Deposition of Silica Nano-Particles

Silica nano-particles are produced to specification with a typical 5% size distribution, and are deposited on a 200mm or 300mm, prime silicon wafer using a 2300XP1 system. The 2300XP1 uses a DMA to isolate a narrow portion of the starting silica particle distribution, while also filtering out unwanted back ground particles from the wafer deposition. A differential mobility analyzer is able to isolate a narrow particle size peak out of an aerosol particle input. Mass flow controllers are used to provide a very high degree of sir flow control. The DMA also incorporates a high degree of electrical voltage control. Air pressure and temperature is also monitored; each of the parameters directly affect particle size accuracy, which is the precise goal of the differential mobility analyzer. Airflow is introduced to the DMA using mass flow controllers. Silica nano-particles are mixed with a deionized water solution, and converted to a particle aerosol stream using an atomizer. The silica nano-particle distribution generated by the atomizer has a typical 5% distribution width, and there are unwanted background particles in the airstream generated by the atomizer. Another element in the particle distribution are unwanted Haze particles, which is a combination of particles created from the remaining mass of material in the filtered water.  The purpose of the DMA is to filter out the left side of the unwanted particle mass from the silica nano-particle size peak, as well as the right side of the silica size peak, which are agglomerates (doublets, triplets, etc.). The end result is a typical 3% narrow size distribution of silica nao-particles deposite4d on the wafer surface. The deposition is accomplished as a full deposition of silica nano-particles at one distinct size peak, deposited across the wafer surface.  Or, it can be deposited as a SPOT Deposition of 1 particle size between 40nm and 2000nm; or multiple size distributions deposited as spot locations around the 200mm or 300mm wafer surface.

Silica Contamination Wafer Standard on a 300mm Prime Silicon Wafer: 125 nm, 147 nm, 204 nm, 304 nm, 350 nm Size Peaks