Determining composition of mixed dielectrics

Details Determining composition of mixed dielectrics Determining composition of mixed dielectrics

2003-07-14

2004-11-09

Zarneke, David (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S717000

Reexamination Certificate

active

06815974

ABSTRACT:

TECHNICAL FIELD
This invention relates to semiconductor wafer testing, and more particularly to determining the composition of a dielectric layer.
BACKGROUND
Thin dielectric layers (e.g., less than about 10 nm thick, such as about 2.0 nm thick or less) are widely used in semiconductor devices that are the building blocks of integrated circuits. For example, a thin dielectric typically separates a gate electrode from a channel region in a field effect transistor (FET).
The ever-shrinking dimensions of semiconductor devices demand increasingly thin dielectric layers. Presently, advanced devices use dielectric layers with a 1.3 nm effective thickness, however, industry analysts expect that devices will use 1.0 nm thick dielectric layers in 2006, and 0.5 nm in 2014 (see International Technology Roadmap for Semiconductors 2002 Update, available at the website public.itrs.net).
Dielectric layers are commonly formed from silicon dioxide (SiO
2
), which can exhibit large leakage current when the layers are very thin. Such leakage is undesirable in most semiconductor devices. In FET's, for example, thin dielectric layers with large leakage currents could cause computer microprocessors to overheat and/or batteries in portable electronic equipment (e.g., notebook computers, PDA's, and mobile phones) to drain rapidly.
One solution to leakage problems associated with thin dielectric layers is to replace SiO
2
with other dielectric materials, called high-k dielectrics, which have a higher dielectric constant than SiO
2
. Candidate high-k dielectrics that show promise in applications demanding thin dielectric layers include mixed dielectrics, such as “oxynitrides,” which include silicon, oxygen, and nitrogen. In order to reliably manufacture high-k mixed dielectric layers at high production yields, manufacturers will most likely desire metrology methods compatible with their manufacturing techniques that can accurately and rapidly characterize the layers.
SUMMARY
In general, in a first aspect, the invention features a method for determining a composition of a dielectric layer on a semiconductor substrate, which includes monitoring a voltage across the dielectric layer under conditions where substantial leakage current flows across the dielectric layer, determining a leakage voltage for the dielectric layer from the monitored voltage, and determining the composition of the dielectric layer by comparing the leakage voltage to a reference voltage corresponding to the leakage voltage of a dielectric layer of known composition.
Implementations of the method may include one or more of the following features and/or features of other aspects.
The conditions where substantial leakage current flows across the dielectric layer can be achieved by depositing an electric charge on a surface of the dielectric layer using a corona discharge. The voltage across the dielectric layer can be monitored using a vibrating probe placed in proximity to the surface of the dielectric layer.
The dielectric layer can include first and second component materials, and the voltage across the dielectric layer can be monitored for a polarity at which current-voltage characteristics for the first and second component materials differ the most.
In general, in another aspect, the invention features a method for determining a composition of a test dielectric layer on a semiconductor substrate, which includes measuring a leakage voltage, V
T
, at a first polarity for the test dielectric layer, comparing V
T
to a reference leakage voltage, V
R
, corresponding to a leakage voltage at the first polarity for a reference dielectric layer having the same thickness as the test dielectric layer, wherein the reference dielectric layer comprises substantially none of a first material, and determining a value, X
T
, indicative of a concentration of the first material in the test dielectric layer based on a relationship between V
T
and V
R
.
Implementations of the method may include one or more of the following features and/or features of other aspects.
The method can include determining the thickness of the test dielectric layer. The method can also include determining the reference leakage voltage from the thickness of the test dielectric layer. Determining the thickness of the test dielectric layer can include measuring a leakage voltage, V
T2
, at a second polarity opposite the first polarity, proportional to the test dielectric layer thickness. The thickness of the test dielectric layer, T, can be determined according to the equation
T
=(
V
T2
−B
R2
)/A
R2
,
wherein B
R2
and A
R2
are predetermined parameters relating a reference leakage voltage, V
R2
, corresponding to a leakage voltage at the second polarity for a reference dielectric layer comprising substantially none of the first material to a thickness of the reference dielectric layer, T
R
. In some embodiments, V
R2
=A
R2
×T
R
+B
R2
.
The reference dielectric layer can include a reference dielectric material having a conduction band energy, E
R
C
, and a valence band energy, E
R
V
, and the first material can have a conduction band energy, E
T
C
, and a valence band energy, E
T
V
, and wherein measuring V
T
includes selecting the first polarity based on E
R
C
, E
R
V
, E
T
C
, and E
T
V
. The first polarity can be negative when
|
E
R
C
−E
T
C
|<|E
R
V
−E
TV
|.
The first polarity can be positive when
E
R
C
−E
T
C
|>|E
R
V
−E
T
V
|.
Measuring V
T
can include depositing an ionic charge having the first polarity onto a surface of the test dielectric layer in an amount sufficient to cause a measurable leakage current to flow across the test dielectric layer, monitoring a voltage of the dielectric layer after depositing the ionic charge, and determining V
T
based on the monitored voltage.
X
T
can be proportional to a difference between V
T
and V
R
. For example, X
T
can be determined according to the formula
X
T
=(
V
T
−V
R
)/(
V
T2
−B
R2
),
wherein V
T2
is a leakage voltage of the test dielectric layer at a second polarity opposite the first polarity and B
R2
is a predetermined parameter relating a reference leakage voltage, V
R2
, corresponding to a leakage voltage at the second polarity for a reference dielectric layer comprising substantially none of the first material to a thickness of the reference dielectric layer, T
R
.
The method can also include calculating the concentration, [X], of the first material in the test dielectric layer from X
T
. [X] can be calculated according to the formula
[
X]=C
CAL
×X
T
+D
CAL
,
wherein C
CAL
and D
CAL
are predetermined parameters relating [X] to X
T
.
The first material can include nitrogen. The reference dielectric layer can include SiO
2
.
In general, in a further aspect, the invention features a method for determining a composition of a test dielectric layer on a semiconductor substrate, which includes depositing an ionic charge of a first polarity onto a surface of the dielectric layer using a corona discharge, monitoring a voltage of the dielectric layer with a non-contact probe after depositing the ionic charge, determining a leakage voltage, V
T
, for the test dielectric layer based on the monitored voltage, and calculating a value, X
T
, indicative of a concentration of a first material in the test dielectric layer based on a difference between V
T
and a reference leakage voltage, V
R
.
Implementations of the method can include one or more of the following features and/or features of other aspects.
V
R
can correspond to a leakage voltage at the first polarity for a reference dielectric layer having the same thickness as the test dielectric layer, wherein the reference dielectric layer comprises substantially none of the first material.
Calculating X
T
can include first determining V
R
from a thickness of the test dielectric layer. The thickness of the test dielectric layer can be determined by measuring a leakage vo

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