Optical systems and methods of characterizing high-k dielectrics

Patent metadata

Field	Value
Publication number	US-10989664-B2
Application number	US-201615256442-A
Country	US
Kind code	B2
Filing date	Sep 2, 2016
Priority date	Sep 3, 2015
Publication date	Apr 27, 2021
Grant date	Apr 27, 2021

Abstract

The disclosed technology generally relates to characterization of semiconductor structures, and more particularly to optical characterization of high-k dielectric materials. A method includes providing a semiconductor structure comprising a semiconductor and a high-k dielectric layer formed over the semiconductor, wherein the dielectric layer has electron traps formed therein. The method additionally includes at least partially transmitting an incident light having an incident energy through the high-k dielectric layer and at least partially absorbing the incident light in the semiconductor. The method additionally includes measuring a nonlinear optical spectrum resulting from the light having the energy different from the incident energy, the nonlinear optical spectrum having a first region and a second region, wherein the first region changes at a different rate in intensity compared to the second region. The method further includes determining from the nonlinear optical spectrum one or both of a first time constant from the first region and a second time constant from the second region, and determining a trap density in the high-k dielectric layer based on the one or both of the first time constant and the second time constant.

First claim

What is claimed is:

1. A method of characterizing a semiconductor structure, the method comprising:
providing a semiconductor structure comprising a semiconductor and a high-k dielectric layer formed over the semiconductor, wherein the high-k dielectric layer has electron traps formed therein;
at least partially transmitting incident light having an incident energy through the high-k dielectric layer and at least partially absorbing the incident light in the semiconductor,
wherein the incident energy is sufficient to cause electrons to be transported from the semiconductor to the electron traps such that some of the electrons are temporarily trapped by the electron traps, and
wherein the incident energy is sufficient for the electron traps filled with temporarily trapped electrons to cause generation of light having an energy different from the incident energy resulting from nonlinear optical effects;
obtaining a nonlinear optical spectrum resulting from the light having the energy different from the incident energy, the nonlinear optical spectrum having a first time dependent region and a second time dependent region, wherein the first time dependent region changes at a different rate in intensity compared to the second time dependent region;
determining from the nonlinear optical spectrum a first time constant from the first time dependent region or a second time constant from the second time dependent region; and
determining a trap density in the high-k dielectric layer based on the the first time constant or the second time constant.

2. The method of claim 1 , wherein providing the semiconductor structure comprises providing an Hf-based high-k dielectric layer on a silicon substrate.

3. The method of claim 2 , wherein electron traps comprise oxygen vacancies.

4. The method of claim 3 , wherein providing the semiconductor structure further comprises providing a silicon dioxide layer interposed between the silicon substrate and the Hf-based high-k dielectric layer.

5. The method of claim 4 , wherein a combined physical thickness of the silicon dioxide layer and the Hf-based high-k dielectric layer is less than 4 nm such that the electrons are capable of being transported from the silicon substrate to the oxygen vacancies by tunneling from the silicon substrate to the electron traps within a time duration of measuring the nonlinear optical spectrum.

6. The method of claim 1 , wherein the electron traps have a median trap energy level that is between a conduction band of the high-k dielectric layer and a conduction band of the semiconductor substrate.

7. The method of claim 1 , wherein the first time constant in the first time dependent region is associated at least with a trapping rate of electrons by the electron traps, and wherein the second time constant in the second time dependent region is associated at least with a detrapping rate of electrons from the electron traps.

8. The method of claim 1 , comprising determining from the nonlinear optical spectrum both the first time constant from the first time dependent region and the second time constant from the second time dependent region, and determining the trap density in the high-k dielectric layer based on both the first time constant and the second time constant.

9. The method of claim 8 , wherein determining the trap density comprises numerically solving a partial differential equation relating a rate of change of filled traps with inverses of the first time constant and the second time constant.

10. The method of claim 9 , wherein the partial differential equation is expressed as:

∂

n
t

⁡

(

x
,
t

)

∂
t

=

[

N
t

-

n
t

⁡

(

x
,
t

)

]

τ
1

-

n
t

⁡

(

x
,
t

)

τ
2

,

wherein n t (x,t) is a filled electron trap concentration in the high-k dielectric layer, N t is a total electron trap concentration, τ 1 is the first time constant and τ 2 is the second time constant.

11. The method of claim 1 , wherein the incident energy is sufficient for the electron traps filled with temporarily trapped electrons to cause second harmonic generation (SHG), and wherein measuring the nonlinear optical spectrum comprises measuring a second harmonic spectrum having the first time dependent region and the second time dependent region.

12. The method of claim 1 , wherein the first time dependent region changes at a faster rate in intensity compared to the second time dependent region.

13. The method of claim 1 , wherein the electron traps are within the bulk of the high-k dielectric layer.

14. The method of claim 1 , wherein the incident light has a wavelength between 700 nm and 2000 nm.

15. The method of claim 1 , wherein the first time constant is associated at least with a trapping rate of the electrons in the electron traps, and wherein the second time constant is associated at least with a detrapping rate of the electrons from the electron traps.

16. A system for characterizing a semiconductor structure, the system comprising:
a light source configured to emit incident light having an incident energy that is at least partially transmitted through a high-k dielectric layer formed on a semiconductor and at least partially absorbed by the semiconductor, wherein the high-k dielectric layer has electron traps formed therein,
wherein the incident energy is sufficient to cause electrons to be transported from the semiconductor to the electron traps such that some of the electrons are temporarily trapped by t

Assignees

• California Inst Of Techn

Inventors

• Adell Philippe C
• Atwater Harry A

Classifications

• H10P74/203

  Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects · CPC title

• G01R31/302

  Contactless testing {(G01R31/66 takes precedence)} · CPC title

• G01R31/2656

  using non-ionising electromagnetic radiation, e.g. optical radiation · CPC title

• G01R31/2648

  Characterising semiconductor materials (testing of materials or semi-finished products G01R31/2831; testing during manufacture H10P74/00) · CPC title

• G01R29/24

  Arrangements for measuring quantities of charge · CPC title