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US5216362A
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Contactless technique for measuring epitaxial dopant concentration profiles in semiconductor wafers
Assignee: International Business Machines Corp
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Filing: 1991-10-08
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Granted: 1993-06-01
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Expires: 2011-10-08
Abstract
Abstract The dopant concentration of a semiconductor wafer is determined using a contactless technique. First, a temporary P-N junction is formed in the surface of the semiconductor wafer using corona discharge. Then, the area of the junction is measured, and the depletion region is deepened, again by corona discharge. The depletion region is collapsed using light, and as the depletion region collapses, the surface potential is measured as a function of time. The charge which drains as the depletion layer collapses is directly proportional to the change in time. Since the total charge is known from the original corona discharge used to establish the depletion layer, as are the unit area and the surface voltage, the dopant profile is directly calculatable as a function of the surface voltage and the charge per unit area.
Inventors
- 👤 Roger L. Verkuil
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 11:00
CPC Classifications
G; G01; G01R; G01R31/00; G01R31/28; G01R31/282; G01R31/2831
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
105 words
A contactless method for measuring dopant concentration in an epitaxial layer of a semiconductor wafer comprising the steps of: forming a temporary P-N junction in the surface of the semiconductor wafer by corona discharges; measuring the surface area of the temporary P-N junction; deepening, by corona discharge, the depletion region under the temporary P-N junction; collapsing the depletion layer using a low intensity light while measuring the surface potential of the semiconductor wafer above the temporary P-N junction; and calculating the dopant concentration at each vertical point in the depletion layer region as a function of the surface voltage and charge drained per unit area.
Claim 2
Dependent Claim
105 words
A contactless method for measuring dopant concentration in an epitaxial layer of a semiconductor wafer comprising the steps of: forming a temporary P-N junction in the surface of the semiconductor wafer by corona discharges; measuring the surface area of the temporary P-N junction; deepening, by corona discharge, the depletion region under the temporary P-N junction; collapsing the depletion layer using a low intensity light while measuring the surface potential of the semiconductor wafer above the temporary P-N junction; and calculating the dopant concentration at each vertical point in the depletion layer region as a function of the surface voltage and charge drained per unit area.
Claim 3
Dependent Claim
65 words
The method recited in claim 1 wherein the step of forming a temporary P-N junction comprises the steps of: depositing charges of a first polarity over an area having a first radius; and depositing charges of a second polarity, different from said first polarity, of a second area concentric with said first area, said second area having a second radius different from said first radius.
Claim 4
Dependent Claim
35 words
The method recited in claim 2 wherein the step of measuring the surface area of the temporary P-N junction comprises the step of performing a surface photovoltage scan of a portion of said epitaxial layer.
Claim 5
Dependent Claim
40 words
The method recited in claim 3 further comprising the step of allowing a surface potential of said temporary P-N junction to come to equilibrium in complete darkness before the step of deepening the depletion region under the temporary P-N junction.
Claim 6
Dependent Claim
39 words
The method recited in claim 4 wherein the step of measuring the surface potential above the temporary P-N junction comprises the step of measuring the time decay rate of a surface potential transient due to the collapsing depletion layer.
Claim 7
Dependent Claim
22 words
The method recited in claim 5 further comprising the step of plotting a profile of the dopant concentration in the epitaxial layer.
References Cited (Backward Citations)
US3995216A
Cited
US4812756A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1996-05-31 | 1996-11-30 | 1997-06-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2000-05-31 | 2000-11-30 | 2001-06-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2004-05-31 | 2004-11-30 | 2005-06-01 | $7700.00 | Window Closed / Lapsed |