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Method for detecting positively charged metallic impurities in virgin and processed heavily boron-doped Si wafers

IP.com Disclosure Number: IPCOM000013533D
Publication Date: 2003-Jun-18
Document File: 3 page(s) / 74K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for detecting positively charged metallic impurities in virgin and processed heavily boron-doped silicon (Si) wafers. Benefits include improved performance, improved throughput, and improved cost effectiveness.

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Method for detecting positively charged metallic impurities in virgin and processed heavily boron-doped Si wafers

Disclosed is a method for detecting positively charged metallic impurities in virgin and processed heavily boron-doped silicon (Si) wafers. Benefits include improved performance, improved throughput, and improved cost effectiveness.

Background

� � � � � The detection of metallic impurities in heavily boron doped Si wafers is a challenging task. Conventionally, the detection method includes the surface analytical technique (TXRF or ICP-MS) following annealing of a wafer at low/moderate temperatures (120oC to 400oC) for an extended time to stimulate impurity out-diffusion. This technique is known as the hot-plate technique. The effectiveness of impurity out-diffusion is determined by the impurity solid solubility, diffusivity, and the thermal stability of boron pairs with impurities, i.e., Cu, Fe, Cr, and possibly Ni.� This makes sensitivity of the hot plate method strongly dependent on annealing temperature and cooling conditions. The major limitation of this method is poor impurity recovery, especially for low impurity concentration (<1012 cm-3).

� � � � � The other conventional technique utilizes an application of a surface charge to oxidized wafers followed by annealing at a low/moderate temperature. This technique has improved sensitivity, however its accuracy may be reduced due to possible cross-contamination in the oxidation furnace. In addition, this method� requires a significantly longer turn-around-time and substantially increased cost.

General description

� � � � � The disclosed method detects process-induced metallic impurities (Cu, Ni, Fe, Li) in the bulk of heavily boron-doped Si wafers. Corona charging of the hot (200oC to 400oC) wafer surface with negative ions (CO3- ) stimulates impurity out-diffusion, which is followed by the measurement of the impurities pulled to the surface with standard analytical tools, see Fig.1 .

        � � � � � The key elements of the method include:

•        � � � � Applying a negative charge onto the Si wafer surface to create an electric field directed toward the surface

•        � � � � During surface charging, maintaining the wafer temperature at 200oC to 400oC to break imp...