Process for production of semiconductor device

Details Process for production of semiconductor device Process for production of semiconductor device

2000-01-28

2001-06-12

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Forming schottky junction

Using platinum group metal

C438S003000

Reexamination Certificate

active

06245650

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for production of a semiconductor device, particularly to a process for production of a semiconductor device having a capacitor part comprising electrodes made of a platinum group metal (e.g. platinum or iridium), which process comprises steps of removing the contaminants derived from the platinum group metal.
2. Description of the Related Art
Memory cells such as DRAM have become increasingly fine in recent years, but it is difficult to allow them to have a sufficient capacity when a conventional nitride or oxide film is used as the dielectric film, because the film has a dielectric constant of only about 2 to 3. In order to solve this problem, there has come to be used a ferroelectric film having an ionic bond type perovskite structure composed of barium titanate, strontium titanate, barium strontium titanate or the like. Also, logic LSI's mounting a ferroelectric random access memory (FeRAM) thereon have come to be widely used in IC cards or general-purpose microcomputers, and ferroelectric films such as PZT (Pb(ZrTi)O
3
) and SBT (SrBi
2
Ta
2
O
9
) are in use as the capacitive insulating film of the FeRAM. These ferroelectric films, when in direct contact with the substrate of FeRAM, give rise to oxidation of the substrate and consequent deterioration of FeRAM capacity. Therefore, in using such a ferroelectric film composed of the above material, there has come to be used an upper or lower capacitor electrode composed of a platinum group metal (e.g. platinum or iridium) which is non-reactive to the material of ferroelectric film. FIG.
4
(
a
) to FIG.
4
(
i
) are sectional views showing the steps employed in production of a semiconductor memory device which has, in combination, a MOS transistor and a capacitor part comprising platinum group metal electrodes and a ferroelectric film and which can conduct data storage by charge accumulation. Referring to these figures, an example of use of platinum group metal in production of a semiconductor memory device is described specifically.
First, a MOS type transistor is formed on a silicon substrate
1
according to a known method, as shown in FIG.
4
(
a
). That is, there is formed a field oxide
2
as an element-isolating region, by a known method such as LOCOS (Local Oxidation of Silicon); subsequently, there is formed a silicon oxide film as a gate-insulating film
3
in a thickness of about 50 to 100 nm, by thermal oxidation. Then, a P-doped polysilicon film and a WSi film are formed in this order; after which they are subjected to patterning to form a gate electrode
4
. Thereafter, ion implantation is conducted to form an impurity-diffused layer
5
, whereby a MOSFET is completed.
Next, as shown in FIG.
4
(
b
), there is formed, by CVD, a boron-containing silicon oxide film (BPSG) as a first inter-layer insulating film
6
; then, etching is conducted to form a contact hole; in the hole are formed a Ti film and a W film in this order to form a vertical interconnect
7
.
Subsequently, as shown in FIG.
4
(
c
), there is formed a platinum thin film which becomes a lower electrode layer
8
of capacitor part; then, there are formed a ferroelectric film
9
(e.g. PZT) and a platinum thin film which becomes an upper electrode layer
10
of capacitor part, in this order.
Next, as shown in FIG.
4
(
d
), a masking layer
11
consisting of a silicon oxide film is formed in order to protect the above-formed capacitor part at a time when other element part is formed.
After the other element part has been formed, a photoresist pattern
12
is formed on the masking layer
11
, as shown in FIG.
4
(
e
). Using this resist pattern as a mask, the masking layer
11
, the upper electrode layer
10
, the ferroelectric film
9
and the lower electrode layer
8
are dry-etched to form a desired capacitor part
14
and leave thereon the masking layer
11
, as shown in FIG.
4
(
f
).
Next, the masking layer
11
is removed, as shown in FIG.
4
(
g
). Then, a second inter-layer insulating film
15
is formed so as to cover the capacitor part
14
and the first inter-layer insulating film
6
, as shown in FIG.
4
(
h
); thereafter, there is formed, in the film
15
, an opening
16
for connecting an upper wiring (to be formed later) to the upper electrode layer
10
, as shown in FIG.
4
(
i
).
Lastly, a metal film is formed so as to fill the opening
16
and further cover the whole surface of the material obtained in the step of FIG.
4
(
i
); the metal film is subjected to patterning to form a desired upper wiring
17
; thereon is formed a third inter-layer insulating film
18
(e.g. a silicon nitride film), whereby is formed a semiconductor memory device such as shown in the sectional view of FIG.
3
.
In the steps of
FIG. 4
, in conducting etching to form a capacitor part
14
having a masking layer thereon, there was a fear that the etching residue adhered to the side wall of the capacitor part
14
, resulting in the reduced property of the device produced. To remove the etching residue, a cleaning operation has been carried out. For example, JP-A-10-12836 discloses a method for removing the etching residue by using, as a cleaning solution, hydrochloric acid, nitric acid, hydrofluoric acid, a mixture thereof, water of 80° C. or higher temperature, or an organic solvent.
In production of a semiconductor memory device, when there is formed, as mentioned above, for example, a silicon oxide film as a protective mask
11
for formation of other element part, or a second inter-layer insulating film
15
so as to cover a capacitor part
14
, platinum atoms or particles
13
are generated from the upper platinum thin film
10
of the capacitor part
14
and deposit on the protective mask
11
or the second inter-layer insulating film
15
; when there is formed a contact hole communicating with the upper electrode, there adhere, onto the second inter-layer insulating film
15
, the platinum atoms or particles vaporized from the upper platinum thin film, a reaction product thereof with chlorine gas (a dry-etching gas), i.e. platinum chloride, and an oxide thereof; further, they adhere even onto the back surface of a silicon substrate
1
. Since the platinum atoms, in particular, easily cause thermal diffusion in the silicon substrate, the platinum atoms adhering onto the back surface of the substrate may move to the transistor element region of semiconductor device; this affects a serious problem on the property of the element. A similar problem arises also when, in forming an insulating film on other silicon substrate for production of a semiconductor device by using the apparatus used for formation of the above-mentioned protective mask or second inter-layer insulating film, the platinum atoms or particles remaining in the apparatus adhere onto the insulating film formed on the other silicon substrate or onto the back surface of the other silicon substrate. It is known that the above remaining of platinum contaminants, even if the amount is as small as about 1×10
10
atoms/cm
2
, adversely affects the life time or electrical property of the semiconductor device produced.
Such contaminants include (1) a metal ion adsorbed by or bonded with the surface of a semiconductor substrate, the surface of an insulating film (e.g. a silicon oxide film) formed thereon, and the back surface of the substrate, and (2) metal particles adhering thereon.
It is necessary, therefore, to remove such contamination by platinum group metal. However, there has been developed almost no effective methods for removing the contamination.
In practical production of a semiconductor device, there is a case that one cleaning tank is used for a plurality of cleaning steps, depending upon the kind of the target substance to be removed. In such a case, if one cleaning tank used for cleaning of a substrate contaminated with a platinum group metal is used for cleaning of other substrate, secondary contamination may take place. Therefore, the contamination of the former substrate b

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