Semiconductor device manufacturing: process – Making passive device – Stacked capacitor
Reexamination Certificate
1998-05-05
2001-06-26
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making passive device
Stacked capacitor
C438S239000, C438S216000, C438S006000
Reexamination Certificate
active
06251743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to micro-structures which are typically found in semiconductor devices and other minute devices such as resonant sensors or micromachines. More particularly, the invention relates to a method of liquid treatment of micro-structures comprising structural members liable to be bent during the process of the liquid treatment, and to micro-structures having structural members able to withstand a permanent bend through the liquid treatment thereof. By way of example, such a micro-structure is often found in a capacitor of a semiconductor device called a DRAM, in which the micro-structure is made up of structural members in the form of, e.g., thin sheet, one end of which is fixed and the other end is free.
2. Description of Related Art
In capacitors of DRAM semiconductor devices referred to above, since the capacitors are required to have a certain capacity in very small, limited regions, a means to secure the required capacitor areas is found by incorporating a three-dimensional construction such as a finned structure. Other minute devices, which are exemplified by resonant sensors and micromachines and are made by applying utilizing processes used in the production of fine semiconductor devices, may employ micro-structures having members liable to be bent, such as fine beams or sheets, supported at one end or both ends thereof.
By way of example, a three-dimensional capacitor of a DRAM semiconductor device is illustrated in FIG.
1
. In this drawing,
1
represents a semiconductor substrate,
2
and
3
are capacitor electrodes, and
4
is an insulating film. This capacitor is produced by the following procedure:
First, as shown in
FIG. 2A
, a first insulator film
11
, a conductor film
12
for forming a horizontal electrode of the capacitor, and a second insulator film
11
′ are sequentially laminated on a semiconductor substrate
10
. The insulator films
11
and
11
′ are formed by, e.g., chemical vapor deposition (CVD) of SiO
2
, and the conductor film
12
is made by, e.g., CVD of polysilicon. Subsequently, holes are made in the laminated films so as to expose the surface of the substrate
10
at the bottoms of the holes, and a film of conductor
13
(polysilicon in this explanation) is then deposited, as shown in FIG.
2
B. Inside the holes, the deposited polysilicon is connected to the former polysilicon film
12
, and will form a support for supporting a horizontal electrode later formed from the film
12
. The laminated films are then etched so as to leave separate, respective portions around the holes on the substrate, to thereby provide separate capacitor portions, as shown in FIG.
2
C. Thereafter, the remaining insulator films
11
and
11
′ are etched and removed, while micro-structures
14
are left which form one of the capacitor electrodes, one end of which is fixed at the central support and the other is free. A thin film of silicon nitride is then formed by CVD to provide an insulator film
15
for the capacitor, as shown in FIG.
2
D. Finally, a polysilicon film is formed to provide opposite electrodes, to thereby complete a capacitor of three-dimensional structure as shown in FIG.
1
.
During the sequential manufacturing processes described above, liquids, such as an enchant solution and water, are used for the etching of the insulator films
11
and
11
′ and the pretreatment (i.e., washing) for the subsequent formation of silicon nitride film
15
. Conventionally, in these treatments using liquids, the substrate bearing materials for the production of the capacitor are immersed in the liquid, and then removed therefrom at atmospheric pressure. To the inventors' knowledge, it is not known in the art to use an environment of a pressure less than atmospheric pressure to which a substrate is removed from a treating liquid, as in the present invention.
When the micro-structure of one of the electrodes for a capacitor as indicated by
14
in
FIG. 2D
is investigated after the etching of the laminated films for the formation of the separate capacitor portions (FIG.
2
C), followed by the removal of the insulator film, a phenomenon may be observed in which the free end of a fin-like electrode
22
projecting from the support
21
is bent, and is in contact with the free end of another electrode
22
or the substrate
20
, as shown in FIG.
3
. The phenomenon will become more common as finer capacitors are made and the space between the fins and the thickness of the fins are accordingly reduced. In most cases, such a fin-like member brought into contact with another member or the substrate, will not be separated from the opposite member or substrate, that is, such a member will remain deformed. The bend and contact of the fin-like member with another member or substrate leads to the a decrease in the capacitor area, and should therefore be eliminated.
Also, in resonant sensors such as those described in Goran Stemme, J. Micromech. Microeng., 1(1991) 113-125, a micro-structure having a beam-, bridge-, or diaphragm-like member of thin, flexural material is employed. Such a micro-structure, in a resonant sensor, is made by applying the production techniques used in the manufacture of semiconductor devices, such as photolithography and etching. Thus, the flexural members may suffer from permanent deformation through the bend and contact thereof with another component of the sensor during the production process of the member, which leads to a failure of the intended sensor, as in the production of capacitors of semiconductor devices described above.
Furthermore, similar micro-structures having a beam-, bridge-, or diaphragm-like member may also be used in various devices called micromachines, and can cause the same problem as in the above-mentioned micro-structures of DRAM semiconductor devices and resonant sensors.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of liquid treatment of micro-structures comprising at least a structural member liable to be bent, which can prevent the permanent deformation of the member through the treatment.
It is another object of the invention to provide a micro-structure comprising at least a member supported at one end thereof and liable to be bent, which is capable of avoiding permanent deformation of the member resulting from a liquid treatment.
According to an aspect of the invention, there is provided a method of liquid treatment of a micro-structure comprising at least a structural member liable to be bent, the member being formed so as to leave a space between the same and another member liable to be bent and/or other such rigid component, the method comprising placing the micro-structure in a treating liquid and subsequently removing the micro-structure therefrom, wherein the micro-structure is removed from the liquid to an environment having a pressure less than atmospheric pressure.
In a variation of the method of the invention, the micro-structure in the treating liquid is then displaced therefrom to another treating liquid having a smaller surface tension than that of the former treating liquid, and is subsequently removed from the latter treating liquid. In other words, the micro-structure is placed in a first treating liquid and then in a second treating liquid having a smaller surface tension than that of the first liquid, and subsequently removed from the second liquid.
Alternatively, the method of the present invention may comprise drying the micro-structure removed from the treating liquid by exposing the micro-structure to vapor of a liquid having a smaller surface tension than that of the treating liquid.
According to another aspect of the invention, the micro-structure is removed from the treating liquid to the atmosphere, and is then dried using laser light, infrared radiation, an electron beam, microwaves, or ultrasonic waves.
As is used herein, the term “micro-structure” refers to a structure or construction comprising a member or members having e.g., minute dimensions of, e.g.,
Ikeda Toshimi
Inoue Fumihiko
Ishikawa Junichi
Katayama Masaya
Kuwamura Masahiro
Fujitsu Limited
Mulpuri Savitri
Staas & Halsey , LLP
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