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Thermal Photovoltage Decay

IP.com Disclosure Number: IPCOM000050642D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Fung, M: AUTHOR

Abstract

A method of determining trapping centers or metallic contaminants in semiconductor wafers is provided which is rapid and non-destructive. The method determines trapping centers or metallic contaminants in, e.g., silicon wafers with a PN junction by the thermal behavior of open-circuit photovoltage decay through non-contact inductive or capacitive sensing techniques and is an alternative to the methods disclosed in (1, 2).

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Thermal Photovoltage Decay

A method of determining trapping centers or metallic contaminants in semiconductor wafers is provided which is rapid and non-destructive. The method determines trapping centers or metallic contaminants in, e.g., silicon wafers with a PN junction by the thermal behavior of open-circuit photovoltage decay through non-contact inductive or capacitive sensing techniques and is an alternative to the methods disclosed in (1, 2).

PN junction leakage I(o) depends on the temperature (T) and trap density (N(t)) by the relation: (1) I h hN e g ~ for the diffusion leakage,

- 4E/kT,

h N e for the impurity (trap) leakage where k = Boltzmann's constant, E(g) = semiconductor energy band gap, and

DE = trap energy level E(t) from conduction band or valence

band, and approx. is the symbol for

"is proportional to".

The junction photo-induced voltage decay time Tau is inversely related to the junction leakage I(o) by (2) Tau= CkT/qI(o), where C is the junction capacitance.

Non-contact inductive sensing or capacitive sensing is applied to detect the photo junction decay time Tau. Based on equations (1) and (2),

(See Original) for diffusion leakage,

(3) (See Original) for impurity leakage.

The photovoltage decay time Tau of a wafer is measured by inductive sensing or capacitive sensing at various temperatures. A plot is made of 1n Tau versus l/T( degrees K). From equation (3), the slope of the plot is equal to DE/k, while the decay time level at any temperature is related to (N(t))/-1/2/ or (N(t))/-1/ for diffusion or impurity leakage.

To identify the trapping center via DE, DE is found from the slope of the plot by DE = k (slope), wh...