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FIELD OF THE INVENTION AND RELATED ART
This invention relates to a method and apparatus for inspecting and/or
repairing a mask or reticle (hereinafter simply "mask") usable in the
manufacture of semiconductor microcircuits, for example, and having a
pattern to be transferred onto a workpiece such as a semiconductor wafer,
for example.
In addition to an increase in the degree of density and capacity of
integrated microcircuits, it is an important factor to improve the quality
of a used mask. Thus, among various mask preparing processes, the
importance of the inspection and repair of a mask pattern is increasing.
Many proposals have been made to such mask inspection and repair. As for
the mask inspection, a method is proposed in "The Transactions of The
Institute of Electronics and Communication Engineers of Japan" 80/12, Vol.
J63-C, No. 12, p. 817, according to which an X-ray mask having a
submicron-linewidth pattern is examined by using an electron beam having
high resolution.
An example of a conventional type mask inspecting apparatus is illustrated
in FIG. 2. Denoted in this Figure at 1 is a mask frame; at 2, is a mask
substrate; at 3 is a mask pattern; at 4 is an X-ray mask; at 6 is an
electron beam (a beam of charged particles); and at 7 is a secondary
electron detector for detecting secondary electrons emitted from a pattern
being examined (hereinafter "subject pattern"), as a result of irradiation
of the same with the electron beam 6. Denoted at 8 is an electron gun; at
9 is an electron lens; at 12 is a secondary electron signal processing
circuit for transforming those signals as obtained at the secondary
electron detector 7 into a subject pattern data for comparison
examination; at 15 is a subject pattern data storing circuit for holding
the subject pattern data; at 13 is a reference pattern data holding
circuit for holding a reference pattern data which may be prepared in
accordance with a design data concerning the pattern to be inspected; at
14 is a pattern defect detecting circuit for detecting any defect of a
pattern, on the basis of comparison of a subject pattern data with a
reference pattern data; and at 16 is a computer for controlling the system
as a whole.
In operation, electrons emitted from the electron gun 8 are concentrated
into a beam by the lens 9 (hereinafter, the beam of concentrated electrons
will be referred to as an "electron beam"), the electron beam then
irradiates a pattern to be inspected. As a result of irradiation of the
pattern with the electron beam, secondary electrons are produced which are
then detected by the secondary electron detector 7, whereby corresponding
signals are produced. Those detected signals are transformed by the
secondary electron signal processing circuit 12 into pattern data related
to the pattern being inspected (subject pattern), which data is held by
the subject pattern data storing circuit 15. Then, in the pattern defect
detecting circuit 14, the pattern data is compared with a reference
pattern data held by the reference pattern data storing circuit 13,
whereby any defect of the pattern (mask pattern) being inspected is
detected.
As a mask repair system, on the other hand, a proposal has been made in
"Electron-Beam, X-ray and Ion-Beam Techniques for Submicrometer
Lithographies", SPIE, Vol. 471,127; 111 (1984), according to which a laser
beam or a convergent ion beam is used.
However, those conventional mask inspection and repair systems involve the
following inconveniences.
That is, conventional mask inspecting systems do not include any specific
means for executing mask repair. Therefore, for mask repair, it is
necessary to transmit the data obtained during the mask inspection to a
separate mask repair system to allow the same to execute repair of any
detected defect. This results in the following disadvantages:
(1) In addition to a mask inspecting apparatus, use of a mask repairing
apparatus is necessary and, for this reason, the arrangement as a whole
for mask inspection and mask repair becomes bulky and expensive; and
(2) In a mask repairing apparatus, it is necessary to detect again the
defect by using the data transmitted thereto. This leads to a prolonged
time for the repair.
As for the mask repair itself, on the other hand, there are the following
problems:
(i) The mask repair using a laser beam or an ion beam has a large
possibility of damaging a mask untolerably, resulting in distortion of the
mask. This creates additional defects;
(ii) Further, the repair using a laser beam is only able to remove an
unwanted pattern and, additionally, the type of pattern that can be
repaired is limited; and
(iii) In the mask repair using an ion beam, due to the property of the ion
beam, it is not possible to converge the ion beam to a sufficiently small
beam diameter and, for this reason, the use of an ion beam is not very
suitable to repair of a mask having a pattern of submicron linewidth, such
as an X-ray mask.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a mask
inspection and repair method and apparatus by which, with a simple
structure the mask repair can be made efficiently and with reduced cost.
It is another object of the present invention to provide a mask repair
method and apparatus by which, without damaging a mask, both removal of an
unwanted pattern (or pattern portion) and re-formation (complementation)
of a missing pattern (or pattern portion) can be made efficiently and with
certainty.
In accordance with one aspect of the present invention, to achieve at least
one of these objects, a single apparatus is provided with both a mask
inspecting function and a mask repairing function and, for the mask
inspection and repair, an electron beam is used in a specific way.
These and other objects, features and advantages of the present invention
will become more apparent upon a consideration of the following
description of the preferred embodiments of the present invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic and diagrammatic view showing a general arrangement
of a first embodiment of the present invention.
FIG. 2 is a schematic and diagrammatic view showing a general arrangement
of a conventional type mask inspecting apparatus.
FIG. 3(a)-(f) is a schematic view, for explaining a second embodiment of
the present invention.
FIG. 4(a)-(f) is a schematic view, for explaining a third embodiment of the
present invention.
FIG. 5(a)-(h) is a schematic view, for explaining a fourth embodiment of
the present invention.
FIG. 6 is a graph showing the relationship between the quantity of
irradiated electron beam and the developing speed.
FIG. 7(a)-(i) is a schematic view, for explaining a fifth embodiment of the
present invention.
FIG. 8(a)-(i) is a schematic view, for explaining a sixth embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a general arrangement of a first embodiment of the present
invention, wherein like numerals as those of FIG. 2 are assigned to
corresponding or similar elements.
In FIG. 1, denoted at 1 is a mask frame; at 2 is a mask substrate; at 3 is
a mask pattern; at 4 is a mask; at 5 is a photosensitive or
radiation-sensitive layer applied to the mask pattern 3 and the mask
substrate 2; at 6 is an electron beam; at 7 is a secondary electron
detector; at 8 is an electron gun; at 9 is an electron lens; at 10 is a
control circuit for controlling the magnitude or rate of current of an
electron beam; at 11 is a deflection controlling circuit; at 12 is a
secondary electron signal processing circuit; at 13 is a reference pattern
data holding circuit; at 14 is a pattern defect detecting circuit; at 15
is a subject pattern data storing circuit; at 16 is a computer; at 17 is a
condenser lens; at 18 is a deflecting electrode; at 19 is a holding means;
at 22 is an X-Y stage which is moved by a driving means, not shown; at 20
is an X-Y stage drive controlling circuit; and at 21 is a chamber.
Mask 4 which is going to be subjected to the inspection is coated, on its
side having a mask pattern 3, with a photosensitive or radiation-sensitive
layer. Electrons emitted from the electron gun 8 are concentrated by the
electron lens 9 into a convergent beam (which hereinafter will be referred
to as an "electron beam") and, after being deflected by the deflection
controlling circuit 11, it is projected upon the mask 4. At this time, by
means of the control circuit 10, the magnitude of the current of the
electron beam is adjusted, taking into account the scan speed, the
acceleration voltage and the like, so as to prevent substantial reduction
in film thickness of the photosensitive layer 5 when in a later stage it
is developed. This adjustment can be made by changing the lens power of
the condenser lens 17. Secondary electrons as can be created as a result
of the irradiation of the mask 4 with the electron beam 6 are detected by
the secondary electron detector 7. The thus detected signals can be
processed by the secondary electron signal processing circuit 12 in a
known manner, like that of the data processing in a measuring apparatus
such as an SEM (Scanning Electron Microscope). The data obtained by the
signal processing is compared within the pattern defect detecting circuit
14 with data (reference pattern data) held by the reference pattern data
holding circuit 13, whereby any defect of the pattern can be detected.
Subsequently, on the basis of the data related to any detected defect of
the pattern, the deflection control circuit 11 operates to controllably
deflect the electron beam 6 to expose the portion of the photosensitive
layer 5 corresponding to the detected defect portion to the electron beam,
for repair of the defect. At this time, by means of the control circuit
10, the magnitude of the current of electron beam is controlled, while
taking into account the scan speed, the acceleration voltage and the like,
so that a larger current flows than that at the time of detection of the
defect of the pattern. In other words, the current is controlled to such
magnitude that the film thickness of the photosensitive layer 5 is reduced
when the same is developed in a later stage. Details of this will be
described later.
The mask 4 having been exposed in the described manner is then subjected to
the development of the photosensitive layer 5 and, thereafter, pattern
correction or repair is made by means of an etching or plating process, a
lift-off process and the like.
Setting different magnitudes of current of electron beam at the time of
inspection and at the time of repair, while taking into account the scan
speed, the acceleration voltage and the like, is to prevent substantial
sensitization of a photosensitive material applied to the mask surface,
during the inspection, and, on the other hand, to assure sensitization of
the photosensitive material in the repair process to cause reduction in
film thickness by the development. Namely, it is made to variably define
an appropriate quantity of irradiated electron beam (dose per unit area of
the resist surface) for the inspection and for the repairing. The dose
adjustment may, of course, be made by changing the scan speed of the
electron beam, by changing the times of scan with the laser beam or by
changing the acceleration voltage.
While, in the described example, secondary electron signals from a mask
surface are detected for detection of any defect of a mask pattern, the
signals to be detected are not limited to the secondary electrons. For
example, signals of electrons transmitted through a mask, reflected
electrons, Auger electrons or fluorescent X-rays may be detected.
Next, description will be made of the manner of mask repair according to a
second embodiment of the present invention, which uses the mask inspecting
and repairing apparatus having been described with reference to the first
embodiment. In the second embodiment to be described below, a positive
resist is used as the material of a photosensitive or radiationsensitive
layer.
In FIG. 3, parts (a)-(f) schematically illustrate the steps to be made in
sequence in accordance with the mask repair method of the second
embodiment.
Denoted in FIG. 3 at 31 is a mask substrate; at 32 is a plating substrate
layer; and at 33 is a mask pattern. The mask substrate 31, the plating
substrate layer 32 and the mask pattern 33 in combination provide a mask
34. The mask 34 is supported by a frame, not shown. Denoted at 35 is a
photosensitive or radiationsensitive layer which covers the surface of the
mask 34 on one side thereof on which the mask pattern is formed. Denoted
at 36 is an electron beam which is deflected by a deflecting means 18 to
thereby scan the mask surface. Denoted at 7 is a secondary electron
(reflected electron) detector for detecting secondary electrons or
reflected electrons as emitted from the mask surface when it is scanned by
the electron beam. Reference character A denotes a defect (which is called
a "transparent defect") in which a pattern that should normally exist is
missing.
The process to be made in accordance with this embodiment will be
explained, in a sequence of (a)-(f) of FIG. 3.
Step (a)
First, a photosensitive material is applied to a mask 34 to form a
photosensitive layer 35 thereupon.
Step (b)
Second, the mask 34 is scanned with an electron beam 36, and secondary
electrons which are generated as a result of the irradiation of a mask
pattern 33 by the electron beam 36 are detected by the secondary electron
detector 7 (FIG. 3, part (b)). At this time, the magnitude of the current
of electron beam 36 is adjusted, while taking into account the scan speed,
the acceleration voltage and the like, to such a level by which
substantially no change appears in the photosensitive layer 35 when the
same is developed (i.e. it is not substantially sensitized). The signals
detected by the secondary electron detector 7 are then processed by the
secondary electron signal processing circuit 12, and the thus obtained
data is compared in the pattern defect detecting circuit 14 with a
reference pattern data, whereby any defect of the pattern is detected. In
this particular example, the lack of the pattern portion as denoted by
reference character A is detected.
Step (c)
Subsequently, on the basis of a detection signal corresponding to the
detected defect, an electron beam is applied to the portion A (FIG. 3,
part (c)). At this time, the quantity of irradiated electron beam (i.e.
dose D1) is adjusted to an amount substantially equal to that to be
provided in usual electron beam exposure (printing). Namely, the magnitude
of the current of electron beam is set to such level by which the
photosensitive or radiationsensitive layer 35 is sufficiently sensitized.
Step (d)
Next, the mask 34 is subjected to a developing process, whereby the
material of the photosensitive layer 35 is removed (FIG. 3, part (d)).
Step (e)
Subsequently, a mask pattern 33a of a predetermined thickness is formed at
the portion A (the region the photosensitive material of which has been
removed), this being made by plating or otherwise (FIG. 3, part (e)). In
this particular example, where a plating process is to be used, an
electroplating or an electroless plating may preferably be used. This is
also with the case of other embodiments which will be described in a later
part of this Specification.
Step (f)
Finally, the photosensitive layer 35 and the plating substrate layer 32 are
removed as required, whereby the mask repair is accomplished (FIG. 3, part
(f)).
FIG. 4, parts (a)-(f), illustrate the steps of a process to be made in
accordance with a third embodiment of the present invention. This
embodiment is an example wherein an unwanted or unnecessary pattern (which
is called a "non-transparent defect") is removed.
Step (a)
The content of this step is substantially the same as that in the second
embodiment described above.
Step (b)
Then, as in the second embodiment, a mask 34 surface is scanned with an
electron beam 36 and, on the basis of detection by the secondary electron
detector 7, any defect of the mask pattern is detected (FIG. 4, part (b)).
By this, in this particular example, a non-transparent defect (unnecessary
pattern 37) as depicted by reference character B is detected.
Step (c)
Subsequently, on the basis of a detected signal related to the detected
defect B, the portion of a photosensitive layer 35 corresponding to the
portion B is exposed to an electron beam (FIG. 3, part (c)).
Step (d)
Next, the mask 34 is subjected to a developing process, whereby the exposed
portion of the photosensitive layer 35 is removed (FIG. 4, part (d)).
Step (e)
Subsequently, by means of dry etching or wet etching or otherwise, the
unnecessary pattern 37 of the portion B is removed (FIG. 4, part (e)).
Step (f)
Finally, the photosensitive layer 35 and the plating substrate layer 32 are
removed as required, whereby the mask repair is accomplished (FIG. 4, part
(f)).
FIG. 5, parts (a)-(h), illustrate the steps of a process to be made in
accordance with a fourth embodiment of the present invention. This
embodiment corresponds to an example wherein a transparent defect and a
non-transparent defect, both of which are present on the same mask, can be
corrected or repaired uninterruptedly.
Step (a)
The content of this step is substantially the same as those in the second
and third embodiments described above.
Step (b)
Then, a mask 34 surface is scanned with an electron beam 36, and a
transparent defect at portion A as well as a non-transparent defect at
portion B are detected (FIG. 5, part (b)).
Step (c)
Thereafter, on the basis of the detection, the portions A and B are
irradiated with an electron beam (FIG. 5, part(c)). At this time, the
quantity D.sub.A of beam irradiation at the portion A is set smaller than
the quantity D.sub.B of beam irradiation at the portion B (i.e. D.sub.A
<D.sub.B).
Step (d)
Subsequently, the mask 34 is subjected to a developing process. At this
time, the developing time is set so that the photosensitive material
covering the portion A remains, but the photosensitive material covering
the portion B is removed (FIG. 5, part (d)). As an example, such
developing time is determined on the basis of a graph such as shown in
FIG. 6. Here, the graph of FIG. 6 represents the relationship of the
developing speed (the axis of ordinate) to the quantity of irradiation
(the axis of abscissa). In this particular example, a PMMA resist was used
and an acceleration voltage of 20 Kv and a developing liquid of isoamyl
acetate were used. The developing speed to the quantity of irradiation
under these conditions is such as illustrated. It is seen that the
relationship of the developing speed to the quantity of irradiation is
changeable, depending on a used resist material, a used acceleration
voltage for an electron beam and a used developing agent. Therefore, upon
determination of the developing time, it is necessary to fully take these
factors into consideration.
The term "developing speed" means the amount (rate) of reduction in film
thickness of a photosensitive layer in the direction of its thickness, per
unit time, when the photosensitive layer is dipped in a developing liquid.
In this example, the developing time t.sub.d is determined to satisfy the
following relationship:
T.sub.0 /R.sub.A >t.sub.d >T.sub.0 /R.sub.B (1)
where T.sub.0 is the initial film thickness of the photosensitive layer,
and R.sub.A and R.sub.B are the developing speeds at the portions A and B,
respectively.
When the height of a pattern on a mask is denoted by P and if the
developing time t.sub.d is selected to satisfy the following relationship:
(T.sub.0 -P)/R.sub.A >t.sub.d >T.sub.0 /R.sub.B (T.sub.0 >P) (2)
it is possible to prevent damage of an adjacent pattern portion, juxtaposed
to the portion A, during the etching process to be made in the next step
(e). To assure this relationship, a relationship such as follows is
satisfied:
(T.sub.0 -P)/R.sub.A >T.sub.0 /R.sub.B (3)
Also, to ensure the relationship (3), the developing speeds D.sub.A and
D.sub.B are predetermined so as to satisfy the following relationship:
(T.sub.0 -P)/T.sub.0 >D.sub.A /D.sub.B (4)
Further, when the quantity of electron beam irradiation at the time of
pattern inspection is denoted by D.sub.S and if the developing speed
corresponding to such D.sub.S is denoted by R.sub.S, then it is necessary
to determine the value D.sub.S so that a relationship R.sub.S <R.sub.A is
satisfied.
Step (e)
Next, the unnecessary pattern at the portion B is removed by an etching
process or otherwise (FIG. 5, part (e)). On that occasion, also the
plating substrate layer 32 at the portion B is removed.
Step (f)
Next, development of the photosensitive layer 35 is executed again. The
developing time on this occasion is set so that only the portion of the
photosensitive layer at the portion A is removed (FIG. 5, part (f)).
Step (g)
Subsequently, a supplementing pattern 33a is formed at the portion A, this
being made by plating, for example (FIG. 5, part (g)).
Step (h)
Finally, the plating substrate layer 32 and the photosensitive layer 35 are
removed as required, whereby the mask repair is accomplished (FIG. 5, part
(h)).
FIG. 7 illustrates a fifth embodiment of the present invention, which
corresponds to an example wherein, after repair of a non-transparent
defect such as at B in the fourth embodiment and during repair of a
transparent defect such as at A, an additional step is included to prevent
plating formation on a side wall surface of the pattern at the portion B.
Steps (a)-(e)
Those processes to be made up to the completion of the repair of a
non-transparent defect at portion B, are substantially the same as those
made in the fourth embodiment shown in FIG. 5 (FIG. 7, parts (a)-(e)). It
is to be noted here that, in this embodiment, it is not always necessary
to remove the plating substrate layer.
Step (f)
Subsequently, on a side wall surface of a pattern 31, uncovered by the
removal of the photosensitive material at the portion B, a protecting
layer 39 for preventing re-formation of any pattern on that surface is
provided (FIG. 7, part (f)). Such a protecting layer may be provided by
plating, for example, of Ni to about several hundred angstroms, for
example.
Steps (g)-(i)
Subsequently, as in the fourth embodiment, the photosensitive material
layer 35 at the portion A is removed (FIG. 7, part (g)); a pattern 36 is
formed at the portion A by plating, for example (FIG. 7, part (h)); and
finally the photosensitive layer 35 and the plating substrate layer 32 are
removed, whereby the mask repair is accomplished (FIG. 7, part (i)). In
this example, film is not easily formed by plating upon the protecting
layer 39, as compared with the film formation on the plating substrate
layer 32. Therefore, a pattern is formed only at the portion A, and no
pattern is formed at the portion B.
Referring now to FIG. 8, a sixth embodiment of the present invention will
be explained. This embodiment corresponds to an example wherein, when a
transparent defect and a non-transparent defect should be corrected or
repaired uninterruptedly, the transparent defect at a portion A is first
repaired as compared with the fourth embodiment.
Step (a)
The process to be made in this step is substantially the same as that in
the foregoing embodiment.
Step (b)
Then, by the electron beam scan, a transparent defect at portion A and a
non-transparent defect at portion B are detected (FIG. 8, part (b)).
Step (c)
Then, portions of a photosensitive layer 35 covering the portions A and B
are irradiated with an electron beam (FIG. 8, part (c)). At this time, the
quantity of irradiation at the portions A and B is preset to satisfy
D.sub.A >D.sub.B.
Step (d)
Subsequently, the photosensitive layer is developed. By this developing
process, the photosensitive material at the portion A is removed, but the
photosensitive material at the portion B partially remains (FIG. 8, part
(d)). Namely, a photosensitive layer 38 of a reduced thickness remains on
the unnecessary pattern 37.
Step (e)
Then, plating is made, whereby a film growing with plating is formed on the
plating substrate layer 32 at the portion A and, finally, a pattern 39 is
formed thereat (FIG. 8, part (e)).
Step (f)
Subsequently, an etching preventing or resistive layer 40 is formed upon
the thus repaired and re-formed pattern 33a at the portion A (FIG. 8, part
f)). This etching preventing layer 40 is provided to protect the pattern
33a against etching thereof during an etching process to be made later,
removing the unnecessary pattern at the portion B. When a pattern is made
of gold, such etching preventing layer 40 may be provided by plating the
pattern 33a with Ni, for example.
Step (g)
Next, the photosensitive material layer 38 on the unnecessary pattern 37 at
portion B is removed (FIG. 8, part (g)).
Step (h)
Then, the unnecessary pattern 37 at portion B is removed by etching, for
example (FIG. 8, part (h)). When a pattern is made of gold and if the
etching preventing layer 40 is formed of Ni, the unnecessary pattern
removing etching may be made by a dry etching process using Kr, for
example.
Step (i)
Finally, the plating substrate layer 32, the photosensitive layer 35 and
the etching preventing layer 40 are removed as required, whereby the mask
repair is accomplished (FIG. 8, part (i)).
While the invention has been described with reference to the structures
disclosed herein, it is not confined to the details set forth and this
application is intended to cover such modifications or changes as may come
within the purposes of the improvements or the scope of the following
claims.
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