Radiant energy – Inspection of solids or liquids by charged particles – Methods
Reexamination Certificate
2001-05-30
2003-08-05
Berman, Jack (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Methods
C250S311000, C250S492220, C250S492230, C430S296000
Reexamination Certificate
active
06603120
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a test method of a mask for electron-beam exposure and a method of electron-beam exposure.
2. Description of the Related Art
An electron-beam exposure method of segmented projection type has been recently proposed as a novel method of electron-beam exposure to replace the cell projection method and the variable-shaped beam exposure method. This electron-beam exposure method of segmented projection type is a method wherein a prescribed primary pattern for projection is segmented into a plurality of divisions and every said division is subjected to exposure one by one till the whole of this prescribed primary pattern is transferred. Although the prescribed primary pattern is segmented into a plurality of divisions, this electron-beam exposure method of segmented projection type uses a mask or a pair of masks onto which the whole segmented portions of the prescribed pattern of one chip are formed in all. In this respect, the electron-beam exposure method of segmented projection type is altogether different from the variable-shaped beam exposure method wherein a pattern that is to be transferred is not actually formed onto the mask but processed as soft data or the cell projection method which employs a mask onto which only repeated parts of a prescribed pattern is formed. In consequence, this electron-beam exposure method of segmented projection type can markedly improve the throughput, compared with these conventional exposure methods.
This electron-beam exposure method of segmented projection type is explained well in the section of the prior art in Japanese Patent Application Laid-open No. 176720/1999 with reference to
FIG. 2
in the publication. On the basis of this description, one example of the electron-beam exposure method of segmented projection type is described below.
FIG. 7
is a schematic view in explaining the electron-beam exposure method of segmented projection type. In
FIG. 7
, referential numeral
100
indicates a mask;
100
a
, a division on the mask
100
;
100
b
, a demarcation region between divisions
100
a
;
110
, a substrate, such as a wafer coated with a resist;
110
a
, a region for one die (one chip) on the substrate
110
;
110
b
, a region for projection on the substrate
110
, each corresponding to a division
100
a
; AX, an optical axis of an optical system of charged particle beam; EB, a charged particle beam and CO, a crossover point of the optical system of charged particle beam.
On the mask
100
, being separated by a demarcation region
100
b
without a pattern, there are present numerous divisions
100
a
each of which is provided, on a membrane, a pattern to be transferred onto the substrate
110
. Further, a support structure in the form of a grid is set over the demarcation region
100
b
, protecting the membrane thermally and mechanically. The mask
100
herein is a scattering membrane mask wherein, on a membrane, for example, a silicon nitride film with a thickness of 100 nm or so, there are formed electron-beam scatterer patterns made of, for example, tungsten with a thickness of 50 nm or so. This scattering membrane mask is the mask used mainly for the electron-beam exposure method of scattering-angle limiting type (referred to as “SAL type” hereinafter) and the exposure method herein is assumed to be the SAL type.
Every division
100
a
is provided with one of segmented patterns which the pattern that is to be transferred onto a region
110
a
for one die on the substrate
110
is segmented into, and every segmented pattern is transferred onto the substrate
110
, one by one. The external appearance of the substrate
110
is as shown in FIG.
7
(
b
). A section (the Va section of FIG.
7
(
b
)) of the substrate
110
is shown in FIG.
7
(
a
) on an enlarged scale.
In
FIG. 7
, the z-axis is taken parallel to the optical axis AX of the optical system of charged particle beam, and the x-axis and y-axis are taken parallel to the directions of the array of divisions
100
a
, respectively. While the mask
100
and the substrate
110
are moved continuously in opposite directions along the x-axis as arrows Fm and Fw indicate, respectively, patterns of divisions
100
a
in one line are transferred in succession through step-by-step scanning of the charged particle beam in the direction of the y-axis. After completing projection of the patterns in one line, divisions
100
a
in the next of that line in the direction of the x-axis receive scanning of the charged particle beam. Thereafter, in the same manner, projection (segmented projection) of divisions
100
a
is successively performed one by one so as to transfer the whole pattern for one die (chip).
The scanning order over the divisions
100
a
and the transcribing order onto the substrate
110
are presented by lines with arrowheads, Am and Aw, respectively. Hereat, the directions of movements for the mask
100
and the substrate
110
are opposite to each other, because the x-axis and y-axis for the mask
100
and the substrate
110
are reversed by a pair of projection lenses, respectively.
When the projection (segmented projection) is carried out in this manner, if patterns of divisions
100
a
in one line lying in the direction of the y-axis are projected on the substrate
110
by a pair of projection lenses as they are, gaps corresponding to the demarcation region
100
b
develop between regions for projection
110
b
on the substrate
110
, each region for projection corresponding to a division
100
a
, respectively. To overcome this problem, the charged particle beam EB having passed through each division
100
a
is made deflected as much as the width Ly of the demarcation region
100
b
in the direction of the y-axis, whereby correction for the pattern projection position is made.
For the direction of the x-axis, besides moving the transmittable scattering mask
100
and the substrate
110
at respective specific speeds, in proportion to the ratio of pattern reduction, similar care is also taken. That is, when completing projection of divisions
100
a
in one line and turning to projection of divisions
100
a
in the next line, the charged particle beam EB is made deflected as much as the width Lx of the demarcation region
100
b
in the direction of the x-axis, whereby correction for the pattern projection position is made so as not to create a gap in the direction of the x-axis between regions for projection
110
b.
Although, in the mask in the above description of the segmented projection type method, the demarcation region to partition prescribed patterns is in the form of a grid, it can be stripe-shaped. In the case that such a mask is utilized, the projection of each division is carried out, while scanning electrically the inside of one zonal division partitioned by the stripe-shaped demarcation region, with the electron beam, in the direction of the length.
As described above, in the segmented projection type method, a mask or a pair of masks onto which the whole segmented portions of the prescribed pattern of one chip are formed in all are used so that the throughput thereof can be greatly improved as compared with the conventional cell projection method and the variable-shaped beam exposure method. Hereat, in the case that a plurality of masks onto which the whole segmented portions of the prescribed pattern of one chip are formed in all are utilized, the number of masks required is equivalent to the number of segmentation.
Further, in the segmented projection type method, since a support structure in the form of a grid can be set over the demarcation region
100
b
which is formed between respective divisions
100
a
, bending and thermal distortion of the mask substrate which may result from irradiation of the charged particle beam can be suppressed well and projection can be performed with high accuracy.
For the electron-beam exposure of segmented projection type described above, a mask (referred to as a “scattering membrane mask”, hereinafter) in which a pattern made of an elect
Berman Jack
Katten Muchin Zavis & Rosenman
NEC Electronics Corporation
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