Electricity: measuring and testing – Magnetic – With temperature control of material or element of test circuit
Reexamination Certificate
2000-12-06
2002-10-08
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
With temperature control of material or element of test circuit
C324S222000, C324S225000, C324S230000, C324S234000, C324S765010, C427S008000, C438S010000, C438S017000
Reexamination Certificate
active
06462538
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sheet resistance meters which measure the electrical resistance of a metal or alloy thin film formed by sputtering, vapor deposition, or another thin film formation technique without contacting the thin film, and also to methods of manufacturing electronic components using such meters.
BACKGROUND OF THE INVENTION
A four probe technique is one of conventionally known techniques to measure the electrical resistance of a metal or alloy thin film formed by sputtering, vapor deposition, or another thin film formation technique.
The four probe technique is based on principles explained below in reference to FIG.
23
. Four acicular electrodes, which constitute testing probes
52
,
53
,
54
, and
55
, are positioned on the surface of a metal film
51
formed on a substrate
50
so that their ends directly contact the surface. Here, the testing probes
52
,
53
,
54
, and
55
are arranged in a straight line and separated from each other by some distance. A potential difference V is measured which develops between the inner testing probes
53
and
54
when an electric current I is passed through the outer testing probes
52
and
55
. The resistance R (=V/I) of the metal film
51
is calculated from the measurement. Then, the resistivity &rgr; is calculated as the resistance R multiplied by the thickness t of the metal film
51
and further by a correction factor F that is a dimensionless value determined from the shape and dimensions of the metal film
51
and the positions of the testing probes
52
,
53
,
54
,
55
.
Shortcomings, however, arise from the mechanism of the four probe technique whereby the acicular testing probes
52
,
53
,
54
, and
55
are pressed against the metal film
51
to make direct contact with it: the metal film
51
may be damaged, which leads to production of dust particles. Also, the testing probes
52
,
53
,
54
, and
55
per se are prone to wear due to abrasion and have to be replaced regularly.
Another problem develops with the four probe technique in the presence of vibration or shake, which obstructs the essential direct contact of the testing probes
52
,
53
,
54
, and
55
with the metal film
51
and makes it impossible to perform measurement. A further problem with the four probe technique is related to nothing but the size of a device to execute the method. The device grows too large for various reasons, such as the inclusion of a dedicated clamp stage for measuring, to be readily accommodated in a limited installation space, especially, along with other devices in existing manufacturing lines.
To address these shortcomings, non-contact measurement is available as an alternative to the four probe technique whereby testing probes are brought into direct contact with the target object to measure the resistivity of the semiconductor material.
The technique is known as the double-sided eddy current scheme, which will be detailed here. A metal thin film is formed on a glass substrate, wafer, or other substrate for semiconductor, and the substrate is placed in a magnetic field developed by a coil to which a high frequency power is supplied. Thus, eddy currents are induced in the metal thin film due to electromagnetic effects of the magnetic field. The induced eddy currents will dissipate as Joule heat. The consumption of high frequency electric power by the metal thin film formed on the substrate has a positive correlation with the conductivity of the metal thin film. This fact provides the basis of the double-sided eddy current scheme to calculate the conductivity (the reciprocal of resistivity) of the metal thin film without contacting the thin film.
The double-sided eddy current scheme is unique over the four probe technique in that the resistivity of the metal thin film is can be calculated and evaluated without direct contact. Therefore, with the double-sided eddy current scheme, it is ensured that the metal thin film on the substrate is not damaged by direct contact, pollutants, or exertion of force in the finishing process of ICs, liquid crystal panels, and other semiconductor products.
Now, the double-sided eddy current scheme will be described by way of an example. First, as shown in
FIG. 24
, a high frequency electric power is supplied to a coil
62
b
wound around a C-shaped ferrite core
62
. The ferrite core
62
has two end parts
62
a
which are positioned opposite to each other and separated by a 1- to 4-mm gap
61
.
When a wafer
63
is inserted in the gap
61
, eddy currents are induced in the metal thin film on the wafer
63
due to the high frequencies. Since the induced eddy currents dissipate as Joule heat, the supplied high frequency electric power is partly consumed by the metal thin film on the wafer
63
. The consumption has a positive correlation with the conductivity of the metal thin film on the wafer
63
. In the double-sided eddy current scheme, the resistivity of the metal thin film on the wafer
63
is measured without contacting the metal thin film based on the ratio of the consumed power.
The double-sided eddy current scheme has been applied in recent development of resistance meters which are intended for use in small sheet resistance monitors to control quality of semiconductors in their manufacturing process. For example, Japanese Laid-Open Patent Application No. 6-69310/1994 (Tokukaihei 6-69310; published on Mar. 11, 1994) discloses a wafer probing system whereby a resistance meter is disposed in the loader section and positioned parallel to the direction in which a transport robot moves so that the resistivity of the wafer can be measured using the resistance meter while the wafer is being transported. The laid-open patent application does not explicitly describe that the resistance meter is based on the double-sided eddy current scheme whereby the resistivity is measured without direct contact. It is inferred from the attached drawings, however, that the invention may be reduced to practice using either a contact-type resistance meter based on, for example, the four probe technique or one based on the double-sided eddy current scheme.
In this measuring system, there is provided an operation flow where either the robot is temporarily halted to measure resistivity or the wafer is inserted into, or transported through, the resistance meter, to measure the resistivity while the wafer is moving.
However, in this prior art system, the resistance meter is lacking in adequate sensitivity to be installed in an existing semiconductor manufacturing process and needs a transporter with one or more axes, for example, which makes it difficult to ensure a suitable installation space. The resistance meter is therefore difficult to install in an existing semiconductor manufacturing process.
Japanese Laid-Open Patent Application No. 5-21382/1993 (Tokukaihei 5-21382; published on Jan. 29, 1993) discloses a similar sheet resistance meter of an eddy current detection type and its usage whereby eddy currents are induced in a metal thin film deposited by sputtering, and lines of a magnetic force produced by the eddy currents are detected without contacting the metal thin film to calculate the sheet resistance.
This laid-open patent application discloses a system installed in the sputtering device that is capable of controlling the sheet resistance of a metal thin film deposited on a wafer or another type of substrate by sputtering. The system includes a load lock chamber interconnected with a gate valve of the sputtering device, a transporter which transports a substrate into the load lock chamber, and a resistance meter which measures the sheet resistance of the metal thin film on the substrate transported by the transporter.
However, in the laid-open patent application, the substrate becomes very hot after the thin film is deposited. The sheet resistance meter of an eddy current detection type is critically affected by the heat through resultant expansion of the coil, temperature dependence of the sheet resistance, etc., and gives inconsistent readings. In
Edwards & Angell LLP
Strecker Gerard R.
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