Implementing smaller device dimensions requires cleaner chemicals and, more importantly, cleaner production processes. One example of a potential contamination source is polymeric seals often found in process chambers. Over time, in aggressive environments such as plasmas, these materials can break down and release metals that can become incorporated in the product processed in that chamber. Low levels of metals such as Na, K, Li, Cu, Zn, Fe, and Ti, can alter the electrical characteristics and affect long term reliability of semiconductor devices. Here at Cerium Labs, we regularly use a technique called Vapor Phase Decomposition Inductively Coupled Plasma Mass Spectroscopy (VPD-ICPMS) to measure the trace metals on silicon wafers and identify the source of contamination.
The 3 process steps are:
Step 1: Vapor phase decomposition
Step 2: Wafer surface impurity collection using a scanning solution
Step 3: Analysis by ICP-MS
The procedure starts with the vapor phase decomposition sample preparation technique, by which trace metals on the surface of a silicon wafer are released so that they can be collected. The silicon wafer (from 75 up to 300 mm) is exposed to hydrofluoric acid vapor in a sealed chilling chamber. The hydrofluoric acid vapor forms a condensate on the chilled wafer surface. This condensate etches the surface silicon dioxide layer on the wafer surface along with any metals that are present.
After this, the condensate is collected by carefully scanning the entire wafer surface with a droplet of ultra-pure scanning solution. This solution is typically a dilute mixture of hydrogen peroxide, nitric acid, and hydrofluoric acid. The scanning process is done by either our automated scanning system or manually by a certified chemist. The droplet is then transferred from the wafer surface into a clean sample vial. Once the droplet is collected, it is diluted and analyzed on the ICPMS.
Our VPD-ICPMS technique is capable of measuring metallic contaminants at concentrations ranging from 1E6 to 1E14 atoms/cm2. It is particularly useful in measuring light elements on bare silicon or in hydrofluoric acid soluble thin films where TXRF analysis falls short.
The advantages of using this procedure are numerous in semiconductor manufacturing. Metal contamination comes from numerous sources and can lead to catastrophic failures and loss. VPD-ICPMS and Cerium Laboratories can help you identify the source and improve your wafer yield.