|ExpertTM is designed for the integration with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) base on the experience of ultratrace metal analysis by ICP-MS.
Analysis of metallic impurities in Si wafer is one of important items in semiconductor manufacturing. The concentration of metallic impurities to be controlled has been lower and lower as the integration has been higher. Total Reflection X-Ray fluorescence (TRXRF) has been used in a production line (FAB) because of its non-destructive technique. However, the detection limit of TRXRF could not satisfy the requirement, and VPD (Vapor Phase Decomposition) technique was developed as a sample pre-concentration method. As a result, the detection limit was improved around two orders of magnitude, but TRXRF is no longer a non-destructive technique. In addition, the chemical solution prepared by VPD can be directly analyzed by ICP-MS with much lower detection limit including lighter masses such as Li, Na and Mg. Consequently, ICP-MS with VPD becomes a common technique to control metallic impurities in Si wafer.
There are several VPD equipment in the market, but they are developed for preparation of TRXRF and not designed for ICP-MS analysis.
ExpertTM was developed for integration with ICP-MS and has the following features:
A special gas is introduced into the VPD chamber together with HF vapor, which allows etching of bulk-Si, and poly-Si, WSi and Ti films that cannot be etched by only HF.
Using this function, metallic impurities diffused into Si substrate from deposited films can be analyzed and profile measurement of dopant and metallic impurities in implanted wafer are available.
The etching speed and depth can be controlled by optimizing the amount of HF vapor and special gas. The maximum etching speed is over 1.5 um/hr with +/- 10% uniformity.
A scan nozzle holds scan solution and scans desired area of wafer to collect metallic impurities remained on a wafer after VPD. However, surface of wafer becomes hydrophilic after the bulk etching or dry etching because the wafer surface gets rough after the bulk etching and organic residue remains on a wafer after the dry etching. As a result, it is difficult to hold the scan solution with the conventional scan nozzle.
The Dual scan nozzle with vacuum can hold the scan solution inside the nozzle very well and allows the scan of hydrophilic surface.
The Expert can do various scan patterns such as full, radial, sector, radial-sector and bevel as a standard function. Expert can also do the edge scan that scans around 1mm from edge of backside wafer together with the bevel part.
The drying module is used to dry a wafer before returning to a cassette. The Expert measures the volume of recovered scan solution, and if the recovered volume is smaller than the original volume, the scan solution may remain on the wafer and it is dangerous if the wafer returns to the cassette with the remaining scan solution. To avoid such a risk, the wafer is transferred to the drying module before returning to the cassette.
The drying module can also be used for a local bulk etching and preparation for TRXRF measurement. Multiple VPD, scan and analyses can be combined in one recipe. For example, the full scan and analysis are repeated consecutively 3 times after only one VPD, and a 0.1 um depth bulk etching and analysis can be repeated 20 times automatically. The Expert has two load port positions and various combinations of wafer size such as 300mm (12") FOUP or FOSB, 200mm (8") SMIF, 150mm (6") or 200mm adaptor are available. The Expert has SEMI-S2 and S8, CE certificates to meet with strict safety regulations required for FAB use.
Presentation by one of our users is available as below: