Chip quality in semiconductor fabrication processes is typically defined as the reduction of variability around target, or in other words, how well the distribution sets between the lower and upper specified limits. Critical to Quality (CTQ) and conformance to customer requirements also play a significant role. Too high variability in manufacturing quickly turns to product quality issues. To ensure a stable supply of good products to market, thorough quality metrics and process control are needed. One important part of product quality and manufacturing is chemistry. Semiconductor wafer plants consume tons of chemicals throughout the whole fab process. Repeatability and reproducibility of each process is a top concern of fabs, and even the slightest deviation from specification can result in expensive equipment contamination and wafer scrap.
From chemistry’s point of view, there are two distinct operations related directly to product quality: process monitoring and fault detection. In process monitoring applications, the desired chemistry must be maintained over time. In fault detection applications, the system must verify that the correct chemical is being dispensed to the process. With accurate monitoring, fabs know the composition of each given chemical stream. Without monitoring, wafers become the de facto chemical monitors. By that time, wafers have already been lost and large-scale equipment contamination may have occurred.
Vaisala K PATENTS® Semicon Refractometer offers real-time liquid monitoring and prevents wrong chemical concentrations from being dispensed onto wafers, indicates timing for spiking, e.g. for water in EKC at the post-etch residual removal, and indicates bath life and KOH concentration in the etching of silicon. The fully integratable Semicon Refractometer supports intelligent fabs and self-diagnosis.
Vaisala offers in-line, real-time, reliable, precise and cost-effective metrology for wet chemistry concentration measurements which can replace expensive and complex analyzers used in fab chemical process monitoring and fault detection as well as CMP slurry composition and concentration control.
Quality detection of incoming chemicals, such as: HF, IPA, DHF, H2O2, HNO3, HCI, KOH, NaOH, NH4OH.
Real-time concentration monitoring of wet chemicals during silicon wafer fabrication in wet bench or wet process.
Critical process systems: Hydrogen peroxide H2O2 or other oxidizing agent's concentration monitoring during Chemical Mechanical Planarization (CMP) process.
KOH bath concentration monitoring for determining the correct etch end-point.
Water content monitoring in EKC® for spray solvent tools.
Instant switch of wafer cleaning chemicals hydrofluoric acid (HF), deionized water (DIW), SC-1 (H2O2, NH3).
Lactic acid CH3CHOHCOOH or acetic acid CH3COOH bath concentration monitoring.
In-line refractive index (RI) measurements are the technique of choice for qualifying the hydrogen peroxide content in CMP slurries. However, peroxide content is not the only slurry metric of interest. Typically, slurries are delivered from the manufacturer in concentrated form, then diluted with water and peroxide at the fab. Though slurry density is a critical parameter for CMP performance, incoming density can vary from batch to batch.
Refractive index measurements have established themselves as the technique of choice for qualifying peroxide content in slurries for CMP of tungsten. Many emerging process flows use CMP as a critical tool for building circuit structures, dramatically increasing the number of CMP steps — and thus the number of opportunities for yield loss if slurry composition deviates from the specification. While auto-titration measurements can give extremely accurate results, they impose large capital equipment and ongoing maintenance costs and offer only discrete sampling at specified intervals. Refractive index, a continuous, non-slurry-consuming measurement, helps fabs identify slurry composition faults quickly, reducing the number of wafers at risk.
Inline refractive index measurements have established themselves as the technique of choice for detecting faults in the CMP slurry blending and dispense systems of leading fabs. Refractive index, a continuous, non-sampling measurement, helps fabs identify slurry composition changes quickly.
Once calibrated to a specific slurry’s temperature/refractive index characteristics, refractive index measurements can determine the concentration of hydrogen peroxide in slurry with a precision to within ±0.02% by weight, for both copper and tungsten slurries. In long-term studies at this leading edge fab, measurements for low node technology CMP processes detected slurry compositions reliably for three years, with no instrument maintenance beyond routine flushing of the slurry blender tank.
In-coming chemical quality has been left to the chemical suppliers. Semiconductor fabricators have very limited or no capability to detect problems with process chemistries from their suppliers. It was found that product is exposed to any incoming chemical changes, no matter what the cause, supplier, mechanical or human. In fact it can be said that the product is used as a monitoring method for the chemicals. This paper will discuss a variety of different monitoring methodologies; suggest the best practices for a cost efficient application for a wide variety of semiconductor chemistries. The solution to the overall problem is not a single device or scheme, but rather a set of devices and a change to fundamental thinking in the chemical distribution area. Supporting data and other relevant experimental results will also be discussed to support and reinforce the findings.
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