Evaluation apparatus and fabrication system for semiconductor

Details Evaluation apparatus and fabrication system for semiconductor Evaluation apparatus and fabrication system for semiconductor

1998-07-30

2001-04-03

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

C324S754090, C250S306000

Reexamination Certificate

active

06211686

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique analyzing impurity distribution and surface shape of a semiconductor specimen.
2. Discussion of the Background
As one of methods analyzing impurity distribution, there is a SCM (Scanning Capacitance Microscopy) measurement that is disclosed to “J. of Elec. Mat. Vol25, No2, p301, 1996”.
FIG. 34
is a block diagram showing overall configuration of a conventional SCM measuring apparatus
1
. The SCM measuring apparatus
1
in
FIG. 34
comprises a stage
11
on which a specimen
16
is placed, XY scanning circuit
12
that scans the stage
11
in the XY direction, a control circuit
13
that controls XY scanning circuit
12
, data storing section
14
in which measuring data, control data and the like are stored, a probe
17
, a tip
15
of which is contacted on surface of the specimen
16
, a sensor
18
, and CV measuring apparatus
19
.
The signal detected by the probe tip
15
is inputted to the sensor
18
via a cantilever
20
, and then amplified. After that, the amplified signal is inputted to the CV measuring apparatus
19
via a UHF transfer line L
1
.
The SCM measuring apparatus
1
measures the capacitance by the same principle as that of a UHF resonance capacitance sensor. When the probe tip
15
is put on the specimen
16
, all of the probe tip
15
, the sensor
18
, the transfer line L
1
, and the specimen
16
constitute a part of the resonator. That is, the fluctuation of the capacitance C between the probe tip
15
and the specimen
16
is equivalent to the load, and due to the load, the resonance frequency changes. As a result, with a little change of the resonance frequency, the resonance amplitude changes considerably. By means of this resonator, the sensitivity of attofarads (10
−18
F) is obtained.
The SCM measuring apparatus
1
in
FIG. 34
gives the desired change of the capacitance in the specimen
16
adjacent to the probe tip
15
, by supplying the electric field (AC bias of kHz band-width) between the probe tip
15
and the specimen
16
.
Free carriers beneath the probe tip
15
is induced or repelled to the probe tip
15
in order to form depletion state or accumulation state. Such depletion state and accumulation state are equivalent to the case changing the distance between the capacitors.
The depth of the depletion layer, that is, the change of the distance between the plates of the capacitor is determined by three factor, that is, i) intensity of supplied electric field; ii) quality and thickness of a dielectric between the probe tip and the measuring object, iii) concentration of the free carriers.
It is assumed that the carrier shields and terminates the supplied electric field. The more intensive the electric field is, or the lower the concentration of the carrier is, the depletion layer is formed until the location deep from the surface. Conversely, the weaker the electric field is, or the higher the concentration of the carrier is, the depletion electric field ends nearby of the surface.
For the specimen that has both of the region with high carrier concentration and the region with low carrier concentration, in case of comparing by the supply voltage with the same level, the region with low carrier concentration has thicker depletion layer.
The SCM measuring apparatus
1
in
FIG. 34
measures the moving of the carriers. The lower the carrier concentration is, or the thinner the surface oxidation layer is, the signal with higher signal intensity is outputted. The signal obtained by the SCM measurement is a dC/dV, that is, the change of the capacitance of the depletion layer for the change of the supplied voltage. In the SCM measurement, because the alternating voltage is supplied on the surface of the specimen, the above-mentioned dV may be considered the peak-to-peak voltage. In other words, the above-mentioned dV may be considered a changing amount of all the depletion layer formed beneath the probe tip.
The SCM measuring apparatus
1
of
FIG. 34
outputs the relationship between the voltage V supplied on the surface of the specimen and the capacitance C by the form of C-V curve. More specifically, the SCM measuring apparatus
1
converts a modulated component dC of the capacitance in case of supplying a constant voltage amplitude dV to the specimen into a image. Further, the DC bias for the specimen is also capable of adjusting. By adjusting the DC bias, the standard voltage of AC bias changes.
FIG. 35
is a figure showing typical high-frequency CV property of n-type semiconductor. In case of p-type semiconductor, the polarity of the CV property is contrary to FIG.
35
. As shown in
FIG. 35
, when a positive bias voltage is applied to the gate terminal or the probe tip, inversion electrons are induced on the surface of the semiconductor. In the strong inversion state, the total capacitance of the capacitor is equal to that of the dielectric which is usually a oxidation layer.
On the other hands, in case of changing the voltage supplying to the probe tip in the negative direction, the depletion layer enlarges and the capacitance goes down. Further, as the lower the concentration of the carrier is, the more early the depletion layer enlarges, and the capacitance goes down quickly when the voltage changes. That is, the SCM measuring apparatus can regard as a gradient measuring apparatus of the CV property.
By the way, as one method analyzing the surface of the specimen, an AFM (Atomic Force Microscopy) is being known.
FIG. 36
is a block diagram showing overall configuration of an AFM measuring apparatus
5
. The AFM measuring apparatus
5
in
FIG. 36
comprises a probe
21
, a piezoelectric element (PZT)
23
on which the specimen
22
is placed, a XY scanning circuit
24
that scans the PZT
23
in the XY direction, a control circuit
25
that controls the XY scanning circuit
24
, a data storing apparatus
26
in which measuring data, control data and so on are stored, a servo circuit
27
that controls the PZT
23
, a photo-detector
28
, a mirror
29
, and laser diode
30
.
When the distance between the probe tip
31
and the specimen
22
changes within the range of 1 &mgr;m-100 Å, the following force works between the probe tip
31
and the specimen
22
. Within the distance close to the surface of the specimen, i.e. about 100 Å, an inter-atomic force works mainly. Within the distance of about 3-4 Å from the surface of the specimen, a repulsive force works mainly. Over more than the distance, an attractive force works mainly. On the other hands, at the far distance from the surface of the specimen, an static electricity force due to an electric dipole of the electric charge or the polarity material.
The AFM measuring apparatus
5
in
FIG. 36
changes asperity on the surface of the specimen into displaced amount of a cantilever
32
, and then detects the displacement amount by using a principle of the optical lever. More specifically, the laser diode
30
rays out the laser for the probe tip
31
, and the photodetector
28
detects the reflecting light from the probe tip
31
. The servo circuit
27
moves the specimen
22
put on the PZT
23
in up and down direction so that the reflective light aggregates to the center of the photo-detector
28
, and the signal moving the PZT
23
in up and down direction is changed into image showing the surface shape of the specimen.
The above-mentioned SCM measuring apparatus
1
in
FIG. 34
is capable of analyzing the impurity distribution inside the specimen. The above-mentioned AFM measuring apparatus
5
in
FIG. 36
is capable of analyzing the surface shape of the specimen. However, in case of performing the SCM measurement and AFM measurement by using the above-mentioned conventional apparatuses, there are the following problems.
Firstly, because the probe tip has width with about several hundred Å, it is virtually impossible to measure the width smaller than several hundred Å. That is, in case of performing the SCM measurement or the AFM measurement, t

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