Sc-2 based pre-thermal treatment wafer cleaning process

Abstract

Pre heat-treatment processing of a silicon wafer to grow a hydrophilic oxide layer includes an initial step of contacting the wafer with a pre-clean SC-1 bath, thereby producing a silicon wafer surface that is highly particle free. After a deionized water rinse, the wafer is scoured with an aqueous solution containing hydrofluoric acid and hydrochloric acid to remove metallic-containing oxide from the wafer surface. In order to grow a hydrophilic oxide layer, an SC-2 bath (containing hydrogen peroxide and a dilute concentration of metal-scouring HCl) is used. The resulting hydrophilic silicon oxide layer grown on the surface of the silicon wafer using the combined SC-1->AF / HCL->SC-2 wafer cleaning process has a metal concentration no greater than 1x109. The diffusion length of minority carriers is increased from a range on the order of 500-600 microns to a range on the order of 800-900 microns.

Description

[0001] The present invention relates in general to the manufacture of semiconductors, and is particularly directed to a new and improved process for cleaning silicon wafers prior to a heat treatment, so as to minimize the presence of particulates, organics and metallic contaminants that impact minority carrier recombination lifetimes. BACKGROUND[0002] The production of single crystal silicon wafers customarily involves growing a single crystal ingot, slicing the ingot into wafers, and then lapping, etching and polishing the wafers. Based upon the required specifications of a circuit device manufacturer, the silicon wafers may also be subjected to thermal processing, such as, but not limited to, oxygen donor annihilation annealing, thermal processing to control oxygen precipitation, low temperature chemical vapor deposition (CVD) oxidation, epitaxial deposition, and polysilicon deposition.[0003] In the course of such thermal processing, a silicon wafer will typically be exposed to a ...

AI Technical Summary

Benefits of technology

[0009] The HCl in the SC-2 bath serves to mitigate metallic contamination during the chemical oxide growth caused by the H.sub.2O.sub.2 in the SC-2 bath. The SC-2 medium in which the oxide is grown is not itself a source of metallic contaminants. The resulting hydrophilic silicon oxide layer grown on the surface of the silicon wafer using the combined SC-1.fwdarw.HF / HCL.fwdarw.SC-2 wafer cleaning process of the invention has a metal concentration no greater than 1.times.10.sup.9 atoms cm.sup.-2. Measurements have revealed that subsequent to the heat treatment, the diffusion length of minority carriers is increased from a range on the order of 500-600 microns to a range on the order of 800-900 microns, or about a fifty percent improvement in P-type silicon.

Problems solved by technology

Unfortunately, a number of limitations associated with conventional processes for growing hydrophilic surface layers of silicon oxide have made it impractical to grow such a silicon oxide layer at a surface concentration of less than 1.times.10.sup.11 atoms / cm.sup.2 of contaminant metals (minority carrier recombination lifetime killers).

Unfortunately, stripping such oxide layers prior to thermal processing is not without its disadvantages, as silicon wafers that have hydrophobic surface layer can be prone to localized (metal) contamination.

Now although the patentee states that the concentration of contaminant metals on the surface of the oxide-grown wafer at the beginning of the anneal / heating step is less than 1.times.10.sup.9 atoms / cm.sup.2, his use of ozonated water creates several problems that are antithetical to the objective of forming a hydrophilic oxide on the metal free surface of a silicon wafer.

First of all, during the production of ozone in present day commercially available ozone generation equipment, contaminant metals may be leached from the hardware into the ozonated water.

Secondly, ozone concentration in the produced solution is extremely difficult to control.

While silicon is hydrophobic, silicon oxide is hydrophilic and easily wetted by water.

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