Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2001-10-26
2003-04-08
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S692000
Reexamination Certificate
active
06544897
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for forming a through-hole on a mask, especially a stencil mask of an electron beam stepper, used for forming a desired pattern by projection on a semiconductor wafer or the like.
Conventionally, as a method for forming a through-hole on a stencil mask such as a silicon thin film, sputtering etching or gas assisted etching using a focused ion beam device as shown in
FIG. 5
is carried out. Specifically ions are drawn out from an ion source
10
such as liquid gallium, accelerated by focusing into a beam through an ion optical system
11
, and irradiated while scanning a sample on a sample stage
15
by deflecting so that etch processing is carried out. However, a through-hole in this method becomes a cone-shaped hole due to etching through a wide area on the surface of the side where a focused ion beam
12
is irradiated. If a square region is set to be scanned by beam irradiation, the hole is formed in an inverted pyramid shape as shown in
FIG. 4B
, which shows a view from the side where an ion is irradiated and
FIG. 4A
shows a cross-section thereof. Even if the scanning region shown in the drawing is set and an etching process is carried out a through-hole H then corresponds to the scanning region at the back surface, and the opening at the side where an ion is irradiated becomes a sloping S shape. This is because if ions focused into a beam by an optical system
11
are irradiated, in reality, it is a Gaussian distribution, so the periphery of the beam is also influenced by weak ion irradiation and this causes a side irradiated with a focused ion beam to be exposed to the irradiation for a long time resulting up to beyond the set region. Theoretically speaking, it is difficult to excavate a deep hole with a sputtering process using a focused ion beam
12
involving re-attachment. That is, there is a limit to irradiating a focused ion beam
12
into the deep inner part of a small hole and eliminating sputtered material from outside of the hole without re-attachment. The limit is such that a 0.3 &mgr;m through-hole (aspect ratio:5) is formed in a thin film having a thickness of 1.5 &mgr;m.
It is difficult to process a hole of much higher aspect ratio even if a gas assisted etching technique where an assisted ion beam
12
is irradiated while gas is sprayed from a gas gun
14
is employed to process in order to avoid re-attachment. Further, the slope of the opening surface has nonuniformity of a sample thin film thickness which cause a problem that, when using an electron beam stepper or the like as a stencil mask, electron diffusion becomes non-uniform and this is not suitable for a stencil.
The object of the present invention is to provide a processing method capable of forming a vertical edge through-hole on a thin film of a stencil mask such as an electron beam stepper, the hole having a small diameter with respect to the thickness of the thin film, and this kind of stencil mask.
SUMMARY OF THE INVENTION
In this invention, a method for forming a vertical edge submicron through-hole comprising the steps of; forming a large hole, in a thin film sample, with a diameter larger than a design size of a through-hole, with a bottom having thickness close to the design size remaining, by etching using a focused ion beam device; forming a through-hole having the design size in the bottom section by focused ion beam etching; and backfilling the large hole to the design size by deposition using a focused ion beam device, and another forming method is further adopted comprising the step of finishing the inner surface of the through-hole by gas assisted etching using a focused ion beam device.
REFERENCES:
patent: 5166556 (1992-11-01), Hsu et al.
patent: 5504340 (1996-04-01), Mizumura et al.
patent: 5741557 (1998-04-01), Corbin et al.
patent: 5962341 (1999-10-01), Ito
patent: 5973295 (1999-10-01), Corbin et al.
patent: 6263292 (2001-07-01), Fiekowsky
patent: 6303014 (2001-10-01), Taylor et al.
patent: 6305072 (2001-10-01), Yoda et al.
patent: 6397165 (2002-05-01), Fiekowsky
Adams & Wilks
Luk Olivia
Niebling John F.
Seiko Instruments Inc.
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