Novel technique for contamination analysis around the edge, the bevel, and the edge exclusion area of 200 and 300mm silicon wafers

Abstract

Contamination around the edge exclusion area and bevel of silicon wafers is becoming an increasingly important area to control in semiconductor manufacturing. This is especially relevant in any manufacturing line where portions of the process toolset, e.g. metrology or lithography, are shared between multiple types of materials processed. This could be materials like copper versus aluminum for interconnect lines or more recently the newer high-k gate dielectrics and alternate metal electrodes. There are numerous pathways for contamination; for example, one source could be incomplete etching of a film at the edge during a backside-cleaning process. Also, the move to edge handling of wafers along with wafer alignment and centering pins is a contamination pathway. Even the direct contact between the wafer's edge and the cassette it is in can be a source of cross contamination. Historically, it has been difficult or impossible to quantify metal contamination in the bevel and edge exclusion region of silicon wafers by traditional analytical methods. Total reflection x-ray fluorescence spectroscopy cannot operate close to the edge of a wafer due to scattering affects of the incident radiation and typically has a built in edge exclusion area of 10 mm. Vapor phase decomposition would expose the entire wafer to hydrofluoric acid vapor, which would not be desired on a patterned wafer or a wafer with a film that would reacted with the vapor. Direct acid drop decomposition and vapor phase decomposition both employ a scanning technique where it is impossible to include the bevel area for analysis. Time of flight secondary ion mass spectrometry is also not easily done on the angled bevel edge of a wafer. The relative sample size of a time of flight mass spectrometer analysis is also quite small and therefore would require many analyses to achieve a sampling set that is representative of the entire edge of a wafer. We have developed a technique that will allow us to precisely measure the metallic contamination in this difficult region on both 200 mm and 300 mm wafers. This procedure calls for exactly positioning the wafer in a mechanical jig and collecting the contamination via chemical extraction. The amount of the wafer's edge exclusion analyzed is controllable as well as the ability to analyze the entire circumference of the wafer or any portion thereof. The solution sample is then analyzed for trace metals by inductively coupled plasma mass spectrometry. Knowing the concentration of the metals in solution, the mass of the solution, and the area of the wafer analyzed we will calculate the area concentration in atoms/cm^2 for comparison to the traditional techniques mentioned in the previous paragraph. We will show the development of this technique along with data highlighting contamination control in a manufacturing line that processes multiple types of material. Detection limits of this technique and current challenges under development will be discussed. This technique is likely to become an indispensable part of any semiconductor fabÕs analytical capabilities.