Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1998-10-15
2003-10-21
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C369S286000
Reexamination Certificate
active
06635896
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns an optical disk stamper examination machine for examining optical disk stampers, an optical disk stamper examination method, and an optical disk stamper.
2. Description of the Related Art
The process of producing optical disks ordinarily is dividable into two main processes, namely the process of making the stamper that is called mastering, and the process of making the disks by molding and film formation using the stamper so made. When any kind of trouble arises in the mastering process, using that stamper to manufacture disks and then examining the finished products result in losses, which losses are greater the larger the scale of disk production. Thus it is desirable to examine the stamper with a stamper examination machine prior to disk manufacture and to use that stamper in the disk production process only after verifying that it meets specifications. For this reason the examination of stampers plays a very important role. The method of examining stampers using a conventional optical disk stamper examination machine, wherein such playback characteristics as tracking error signals and HF signals from the pits formed in the optical disk stamper are examined, is now described with reference to FIG.
6
.
The optical disk stamper
600
being examined is attached to a revolving table
601
, a laser beam is aimed at the optical disk stamper by an optical head
610
while the optical disk stamper
600
is being rotated by a spindle motor
602
, and the amount of light reflected thereby is detected. In the optical head
610
, diffused light is emitted by a semiconductor laser
603
, and that light is converted to a parallel beam by a collimating lens
604
. After this beam passes through a beam splitter
605
, it is condensed by an objective lens
606
, passes through a plane parallel plate
607
, and strikes the signal face of the optical disk stamper
600
. The laser spot striking the signal face of the optical disk stamper
600
is reflected as it is modulated by the shapes of the pits and grooves in the signal face, and passes back through the plane parallel plate
607
and objective lens
606
to be reflected by the beam splitter
605
so that the quantity of light can be detected by a photodiode
608
. The plane of incidence in the photodiode
608
is divided into two areas, each of which performs current-voltage conversions and amplification, forming two channels. HF signals are obtained by adding the output signals of the respective channels while preserving the high band. Tracking error signals are obtained by subtracting the output signals of these two channels, one from the other.
The objective lens
606
used here is usually an objective lens having the same design specifications as those mounted in optical disk drives. These objective lenses that are used in optical disk drives are designed so that diffraction-limited focal points are formed in the reflection layer, through the optical disk substrate. For this reason, in optical disk examination machines also, a plane parallel plate
607
that is effective in correcting wave aberration, just as the aforesaid substrate, is typically provided between the objective lens
606
and the optical disk stamper
600
. With this configuration, diffraction-limited focal points having the same size as when performing disk examinations can be formed on the signal face of the optical disk stamper
600
.
In addition to methods wherein a plane parallel plate
607
or the like is fixed to an optical head, as in the example described above, an examination method has been devised wherein, instead of the plane parallel plate
607
, a transparent substrate is simply superimposed on the stamper and secured to the revolving table together with the stamper.
When optical disk stampers are examined using the methods described above, the playback characteristics are considerably different than the playback characteristics measured from actual optical disk stampers by the disk examination machine. The underlying principle here is explained with reference to
FIGS. 4 and 5
, taking the HF signal modulation factor that is one examination category of playback-only optical disks as an example. The playback-only optical disks discussed here are those of a type wherein concave and convex marks of differing lengths are continuously cut into the disk in a spiral form.
The case of examining an optical disk with a disk examination machine is first described. The laser beam emitted from the optical head of the disk examination machine strikes the substrate surface
405
a
of the optical disk, passes through the interior of the substrate, and arrives at a mark
406
a
on the head unit. When an examination is being conducted, measurements are made using a focusing servo so that the incident beams form a focal point in a reflection layer
400
a.
A beam waist is therefore formed in the reflection layer
400
a.
Looking at this portion microscopically, we can think of it schematically as a parallel beam. Here the beam component
401
a
prior to arrival at the mark
406
a
and the beam component
402
a
prior to arrival in space that is another portion are in phase with each other. After this, when each of the beam components is reflected, differences in light path arise in the round-trip portion of the height of the mark
406
a,
whereupon phase modulation is imposed. The beam components
401
a
and
402
a
are converted by reflection into beam components
403
a
and
404
a,
respectively, that are mutually out of phase.
When actually recorded marks are played back, tracking is effected on the continuous marks in a state wherein the focusing servo is applied to the reflection layer
400
a.
An example of an HF signal waveform is diagrammed in
FIG. 5A
at
501
a.
At the moment that the beam passes the mark
406
a,
due to the phase shift between the two beam components
403
a
and
404
a,
an action occurs whereby the components cancel each other out, the quantity of light incident on the photodiode is reduced, and a minimum
503
a
is formed in the waveform
501
a.
It is usually desirable that the height of the mark
406
a
be designed such that the phase difference between the beam components
403
a
and
404
a
becomes as close as possible to &pgr; in order to realize a large modulation factor in the HF signal having the waveform
501
a.
We here take the HF signal modulation factor to be the 14T mark modulation factor (where T is the channel pit period), and define that as
I
14
/I
14H
.
This phase difference is dependent on the wavelength of the beam in the interior of the substrate, wherefore it is necessary to take the wavelength in the substrate into consideration when setting the height of the mark
406
a.
If we designate the beam wavelength in a vacuum as &lgr;
0
and the refractive index of the substrate as n
s
, then the wavelength &lgr;
s
inside the substrate may be expressed as
&lgr;
s
=&lgr;
0
s
.
Then, when the phase difference is &pgr;, for example, the height h of the mark
406
a
becomes
h=&lgr;
0
/4
n
s
.
A case is described next wherein a stamper is examined directly with a stamper examination machine. The laser beam emitted from the optical head of the stamper examination machine passes through a plane parallel plate to correct for wave aberration and arrives at a stamper
400
b.
When an examination is being performed, the focus servo is operated to direct the beam onto the signal face of the stamper
400
b.
Here the beam component
401
b
prior to arrival at the mark
404
b
and the beam component
402
b
prior to arrival in space that is another portion are in phase with each other. After this, when each of the beam components is reflected, differences in light path arise in the round-trip portion of the height of the mark
406
a,
whereupon phase modulation is equivalently imposed. The beam components
401
b
and
402
b
will then be converted by reflection into beam components
403
b
and
404
b,
respectively, that are mutually out
Furuya Noboru
Hirono Kimio
Kurosawa Hirofumi
Lee John R.
Oliff & Berridg,e PLC
Pyo Kevin
Seiko Epson Corporation
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