Optics: measuring and testing – Dimension – Cavities
Reexamination Certificate
2001-01-19
2003-11-11
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Dimension
Cavities
C356S241100
Reexamination Certificate
active
06646751
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an apparatus for measuring a trench depth and, more particularly, to an apparatus for measuring the depth of a trench, groove or hole (collectively referred to as “trench” in this text) formed on a semiconductor wafer etc. The present invention also relates to a method for measuring the depth of such a trench.
(b) Description of the Related Art
Along with development of higher integration of semiconductor devices, a three-dimensional structure is now employed for arranging semiconductor elements, in addition to the conventional two-dimensional structure. In the three-dimensional structure, as well as a two-dimensional structure, a trench is generally formed for electrically isolating adjacent semiconductor elements. Since the depth of the trench significantly affects the device characteristics of the semiconductor elements, it is desired to measure the depth of the trench thus formed or examine whether or not the trench has a design depth.
A technique using an optical interference or optical diffraction has been generally used for measuring the depth of a fine trench in a semiconductor device. However, a measuring apparatus using such a technique has a complicated structure and thus is expensive. In addition, such a measuring apparatus is not suited for measuring the depth at a high speed
FIG. 1
shows a conventional apparatus for measuring the depth of a trench, described in Patent Publication JP-A-61-099806. Laser beam
111
emitted from a laser source
11
is focused by a lens
12
to be incident onto an end of an optical fiber
13
. The laser transmitted by the optical fiber
13
is received by an optical head
14
, which collimates the laser beam to form a parallel ray
112
. The parallel ray
112
is incident onto the sample
17
having a subject trench
10
to be measured for the depth thereof.
The optical head
14
then receives the laser reflect from the sample
17
, and reflects the received laser by a semi-transparent mirror prism in the optical head
14
to be incident onto an optical sensor
18
. The optical sensor
18
converts the laser to an electric signal, witch is measured by a volt meter
19
to detect the intensity of the reflected laser. A power supply source
20
supplies power to the optical sensor
18
.
A slider
21
attached onto the optical head
14
is moved along an arched arm
22
having a scale thereon for changing the incidence angle of the laser
112
while observing the indication of the volt meter
19
. The depth of the trench
10
can be measured from the incidence angle &thgr;
R
at which the reading of the volt meter
19
assumes a minimum. The depth (d) is obtained from the following equation:
&thgr;
r
=tan−1(
a/d
)
wherein “a” is the width of the trench.
In the technique as described above, it also takes a long time to measure the depth of the trench and not suited for measuring the depth of a subject trench at a high speed.
SUMMARY OF THE INVENTION
In view of the above problems in the conventional techniques, it is an object of the present invention to provide an apparatus and a method for measuring the depth of a subject trench at a higher speed with a simple structure of the apparatus.
The method of the present invention for measuring the depth of a subject trench, in one embodiment thereof, includes the steps of forming, on a substrate, a plurality of measurement trenches having different widths a
i
(a
i
<a
i+1
, i=1, 2, . . . , n) and a depth equal to the depth d
0
of the subject trench, irradiating the measurement trenches with a parallel ray at an incidence angle of &thgr; with respect to the surface of the substrate at the location of the trenches and detecting the reflected ray from tie substrate, separating the measurement into a first group of trenches providing dark images and a second group of trenches providing bright images, and calculating the range for the depth d
0
by using the largest width a
k
of the trenches in the first group and the smallest width a
k+1
of the trenches in the second group based on the following relationship:
(
a
k
/2)tan &thgr;<
d
0
≦(
a
k+1
/2)tan &thgr;.
By setting the incidence angle &thgr; of the parallel ray with respect to the substrate surface at 45 degrees in the above method, calculation can be simplified due to the fact that tan &thgr;=1. This further reduces the time length for the measurement. In addition, by determining the term {(a
i+1
−a
i
)/2}tan &thgr; below an allowable error for the depth, the accuracy of measurement based on the above relationship can be improved
The method of the present invention, in another embodiment thereof, includes the steps of preparing a plurality (M) of reference image patterns each formed from a plurality (N) of reference trenches having different widths of a
j
(a
j
<a
j+1
, j=1, 2, . . . N) and a common depth selected from M different depths of d
h
(d
h
<d
h+1
, h=1, 2, . . . M, and M≠N or M=N) by using a parallel ray irradiated at an incidence angle of &thgr; with respect to the surface of a reference substrate having the reference trenches, forming, on a measurement substrate, a plurality of measurement trenches having different widths a
i
, (a
i
<a
i+1
, i=1, 2, . . . , n) and a depth equal to the depth d
0
of the subject trench, irradiating a parallel ray at an incidence angel of &thgr; with respect to the surface of the measurement substrate and detecting the reflected ray from the measurement substrate, detected a boundary width (or critical width) between the widths of a first group of trenches providing dark images and the width of a second group of trenches providing bright images, and selecting, for the depth d
0
, the depth of the plurality of reference trenches which provide one of the reference image patterns having a boundary width corresponding to the boundary width detected from the measurement trenches. The depths d
h
of the reference trenches are measured beforehand by using a known technique.
The apparatus of the present invention for measuring the depth of a subject trench, in one embodiment thereof, includes a device for forming on a substrate a plurality of measurement trenches having a depth equal to the depth of the subject trench, a light source for irradiating light to the substrate at an incidence angle of &thgr; with respect to the substrate surface, a CCD camera for detecting the images of the trenches in the reflected light from the substrate to output a image signal, and a processing unit for calculating the depth d
0
of the subject trench based on the image signal from the CCD camera, by separating the measurement trenches into a first group of trenches providing dark images and a second group of trenches providing bright images, and calculating the range for the depth d
0
by using largest width a
k
of the trenches in the first group and the smallest width a
k+1
of the trenches in the second group based on the follow relationship:
(
a
k
/2)tan &thgr;<d
0
≦(
a
k+1
/2)tan &thgr;.
The apparatus of the present invention for measuring the depth of a subject trench, in another embodiment of includes a storage device for storing a plurality (M) of reference images patterns each formed from a plurality (N) of reference trenches having different widths of a
j
(a
j
<a
j+1
,j=1, 2, . . . N) and a common depth selected from M different depths of d
h
(d
h
<d
h+1
,h=1, 2, . . . M, and M≠N or M=N), a device for forming on a substrate a plurality of measurement trenches having a depth equal to the depth of the subject trench a light source for irradiating light to the substrate at an incidence angel of &thgr; with respect to the substrate surface, a CCD camera for detecting the images of the trenches the reflected light from the substrate to output an image signal, and a processing unit for calculating the depth do of the subject trench based on the ima
Katten Muchin Zavis & Rosenman
NEC Electronics Corporation
Rosenberger Richard A.
LandOfFree
Apparatus and method for measuring trench depth does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for measuring trench depth, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for measuring trench depth will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3146036