Elevated temperature measurement of the minority carrier lifetime in the depletion layer of a semiconductor wafer

• US 5,977,788 A
• Filed: 07/11/1997
• Issued: 11/02/1999
• Est. Priority Date: 07/11/1997
• Status: Expired due to Fees

• Current Assignee: Jacek Lagowski
• Original Assignee: Jacek Lagowski
• Inventors: Lagowski, Jacek
• Primary Examiner(s): Nguyen, Vinh P.
• Assistant Examiner(s): SUNDARAM, T R
• Application Number:
  US08/893,857
• Time in Patent Office: 844 Days
• Field of Search: 324/765, 324/766, 324/767, 324/752
• US Class Current: 324/750.03
• CPC Class Codes: G01R 31/2648 Characterising semiconductor materials testing of materials or semi-finished products G01R31/2831; testing during manufacture H01L22/00
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A method for determining the depletion layer minority carrier lifetime τ_o in a depletion layer of a semiconductor wafer includes the following. A depletion layer is induced on a surface of the wafer. The wafer is heated to a temperature T₁. A surface photovoltage is induced on the surface of the wafer with modulated light. A surface photovoltage ΔV_o1 is measured at a selected point of the wafer, at T₁ and at a low light modulation frequency where the surface photovoltage is substantially independent of frequency. A surface photovoltage ΔV₁ is measured at the selected point, at T₁ and at a higher light modulation frequency ω which is within a frequency range where the surface photovoltage is inversely proportional to frequency. A surface photovoltage response time τ_max1 is determined by the relationship: τ_max1 =ω₁^-1 [(ΔV_o1 /ΔV₁)² -1]^1/2. The wafer is heated to a temperature T₂, greater than the temperature T₁. A surface photovoltage ΔV_o2 is measured at the selected point, at T₂ and at the low light modulation frequency. A surface photovoltage ΔV₂ is measured at the selected point, at T₂ and at a frequency ω₂ in a range where the photovoltage is inversely proportional to frequency. A surface photovoltage response time τ_max2 is determined by the relationship τ_max2 =ω₂^- 1[(ΔV_o2 /ΔV₂)² -1]^1/2. The room temperature depletion layer lifetime τ_o is determined by the relationship:

τ.sub.o =τ.sub.max2 ·exp [(T.sub.2 -T.sub.0)E.sub.A

/kT_o ·T₂ ],

where T_o is room temperature.

Claims

1. A method for determining a depletion layer minority carrier lifetime τ

_o in a depletion layer within a semiconductor wafer comprising;

a) measuring a first surface photovoltage Δ

V_o1 at a selected point of the wafer, at a temperature T₁ in a range between 303°

K-373°

K and at a low light modulation frequency;

b) measuring a second surface photovoltage Δ

V₁ at the selected point, at a temperature T₂ and at a frequency ω

within the frequency range where the surface photovoltage is inversely proportional to frequency;

c) determining a surface photovoltage response time τ

_max1 of the selected point by;

space="preserve" listing-type="equation">τ

.sub.max1 =ω

.sup.-1 {(Δ

V.sub.o1 /Δ

V.sub.1).sup.2 -1}.sup.1/2;

and

d) determining the depletion layer lifetime τ

_o by;

space="preserve" listing-type="equation">τ

.sub.o =τ

.sub.max1 ·

exp [(T.sub.2 -T.sub.0)E.sub.A /kT.sub.o ·

T.sub.2 ]

where

T_o is room temperature,

k=8.6×

10^-5 eVK^-1,

E_A =k(ln τ

₁ /τ

₂)·

(T₁ ·

T₂)/(T₂ -T₁),

where τ

₁ and τ

₂ are the values of τ

_max1 at temperatures T₁ and T₂.

2. A method for determining a depletion layer minority carrier lifetime τ

_o in a depletion layer within a semiconductor wafer comprising;

a) inducing a depletion or inversion layer on a surface of the semiconductor wafer;

b) heating the semiconductor wafer to a first temperature T₁ in a range between 303°

K-373°

K;

c) inducing a surface photovoltage on the surface of the semiconductor wafer with modulated light;

d) measuring a first surface photovoltage Δ

V_o1 at a selected point of the wafer, at T₁ and at a low light modulation frequency where the surface photovoltage is independent of frequency;

e) measuring a second surface photovoltage Δ

V₁ at the selected point, at T₁, at a higher light modulation frequency ω

which is within a frequency range where the surface photovoltage is inversely proportional to frequency;

f) determining a first surface photovoltage response time τ

_max1 of the selected point by;

space="preserve" listing-type="equation">τ

.sub.max1 =ω

.sub.1.sup.-1 {(Δ

V.sub.o1 /Δ

V.sub.1).sup.2 -1}.sup.1/2;

g) heating the semiconductor wafer to a second temperature T₂ in the range between 303°

K-373°

K, the second temperature T₂ greater than the first temperature T₁ ;

h) measuring a third surface photovoltage Δ

V_o2 at the selected point, at T₂ and at the low light modulation frequency;

i) measuring a fourth surface photovoltage Δ

V₂ at the selected point, at T₂ and at a frequency ω

₂ within the frequency range where the surface photovoltage is inversely proportional to frequency;

j) determining a second surface photovoltage response time τ

_max2 of the selected point by;

space="preserve" listing-type="equation">τ

.sub.max2 =ω

.sub.2.sup.-1 {(Δ

V.sub.o2 /Δ

V.sub.2).sup.2 -1}.sup.1/2 ; and

k) determining the depletion layer lifetime τ

_o by;

space="preserve" listing-type="equation">τ

.sub.0 =τ

.sub.max2 ·

exp {(T.sub.2 -T.sub.0)E.sub.A /kT.sub.o ·

T.sub.2}

where T_o is room temperature.

3. The method of claim 2 further comprising, between steps j) and k), determining a response time activation energy E_A by:

space="preserve" listing-type="equation">E.sub.A =k(ln τ

.sub.max1 /τ

.sub.max2)(T.sub.1 ·

T.sub.2)/(T.sub.2 -T.sub.1),

the value of E_A indicating the validity of the depletion layer minority carrier lifetime measurement.

4. The method of claim 2 wherein temperature T₁ is in a range between about 40 to 60°

C.

5. The method of claim 2 wherein temperature T₂ is in a range between about 60 to 80°

C.

6. The method of claim 2 wherein the low light modulation frequency is in a range between 0.1 to 100 Hz.

7. The method of claim 2 wherein frequency ω

is in a range between 100 to 5 KHz.

8. The method of claim 2 further comprising, between steps a) and b), adjusting the surface barrier to ensure that it is within an optimal range defined by:

##EQU4##

9. The method of claim 8 further comprising depositing a positive corona on the wafer in doses of about 2×

10¹⁰ charge/cm² per dose, if;

until V_s is within the optimal range.

10. The method of claim 8 further comprising depositing a negative corona on the wafer in doses of about 2×

10¹⁰ charge/cm² per dose, if;

##EQU5## until V_s is within the optimal range.

11. A system for determining a depletion layer minority carrier lifetime τ

_o in a depletion layer within a semiconductor wafer, the system comprising a measurement device configured to measure a series of surface photovoltages including;

a first surface photovoltage Δ

V_o1 at a first temperature T₁ and at a low light modulation frequency where the surface photovoltage is independent of frequency;

a second surface photovoltage Δ

V₁ at T₁ and at a frequency ω

which is higher than the low light modulation frequency and where the surface photovoltage is inversely proportional to frequency;

a third surface photovoltage Δ

V_o2 at a second temperature T₂ and at the low light modulation frequency;

a fourth surface photovoltage Δ

V₂ at T₂ and at the frequency; and

a controller which receives electrical signals representative of the first, second, third and fourth photovoltages and determines;

a first surface photovoltage response time τ

_max1 by;

space="preserve" listing-type="equation">τ

.sub.max1 =ω

.sub.1.sup.-1 [(Δ

V.sub.o1 /Δ

V.sub.1).sup.2 -1].sup.1/2;

a second surface photovoltage response time τ

_max2 by;

space="preserve" listing-type="equation">τ

.sub.max2 =ω

.sub.2.sup.-1 [(Δ

V.sub.o2 /Δ

V.sub.2).sup.2 -1].sup.1/2 ; and

a depletion layer lifetime τ

_o by;

space="preserve" listing-type="equation">τ

.sub.0 =τ

.sub.max2 ·

exp [(T.sub.2 -T.sub.0)E.sub.A /kT.sub.o ·

T.sub.2 ]

where T_o is room temperature.

12. The system of claim 11 further comprising a first variable-temperature wafer stage configured to support and heat the semiconductor wafer at temperature T₁ and a second variable-temperature wafer stage configured to support and heat the semiconductor wafer at temperature T₂.

13. The system of claim 11 further comprising a charge deposition device configured to induce a depletion or inversion layer on a surface of the semiconductor wafer.

14. The system of claim 11 further comprising a charge deposition device configured to induce a depletion or inversion layer on a surface of the semiconductor wafer.