Method for the vapour phase etching of a semiconductor wafer for trace metal analysis
The surface layer of a semiconductor wafer lying on a rotatable plate within an etching chamber is etched by a process whereby homogeneous etching of the surface is obtained by introducing an etching gas into the etching chamber in such a way that the flow of the etching gas is not directed directly to the wafer but is allowed first to distribute within the etching chamber before coming into contact with the surface of the semiconductor wafer to be etched.
1. A method for etching the surface of a semiconductor wafer lying on a rotatable plate in an etching chamber for analyzing trace metal impurities on said surface, the etching chamber comprising a bottom, above which the rotatable plate, is located, a cover which fits to the bottom, and sidewalls between the bottom and cover, comprising introducing an etching gas comprising hydrogen fluoride and ozone through a valve or nozzle located beside the rotatable plate into the etching chamber, the valve or nozzle arranged such that gas flowing into the etching chamber does not flow directly in the direction of the semiconductor wafer but is directed towards the sidewall, and not in the direction of an exhaust opening,
etching the surface of the silicon wafer lying on the rotatable plate in the etching chamber, wherein the etching chamber comprises at least one exhaust opening in the cover or between the lower edge of the cover and the bottom as allowing the emission of gaseous reaction products out of the chamber;
introducing an etching gas comprising a mixture of hydrogen fluoride and ozone into the etching chamber through the opening of the nozzle or valve and then drying the etched wafer surface of the silicon wafer with nitrogen gas introduced through a drying nozzle or valve,
rotating the rotatable plate with the silicon wafer lying thereon during etching and drying, and
scanning with a liquid droplet moved over the etched and dried surface of the silicon wafer thereby dissolving and collecting into said droplet metal ions, and analyzing the liquid droplet for trace metals.
2. The method of claim 1 , wherein the time over which etching gas is introduced into the etching chamber is between 3 and 60 seconds.
3. The method of claim 1 , wherein the rotatable plate can be cooled or heated.
4. The method of claim 1 , wherein the rotatable plate is rotated at a rotational speed of 5 to 15 rpm during the etching process.
5. The method of claim 1 ,
wherein the method is repeated multiple times on the same wafer.
6. The method of claim 1 , further comprising
hydrophobizing the silicon wafer with HF gas prior to scanning to make the etched and dried surface of the silicon wafer hydrophobic.
7. The method of claim 1 , wherein the wafer surface is a bare wafer surface.