Semiconductor device manufacturing: process – Chemical etching
Reexamination Certificate
2000-07-21
2001-12-04
Hiteshew, Felisa (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
C438S714000
Reexamination Certificate
active
06326308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor storage element utilizing a ferroelectric material.
2. Description of the Related Art
A ferroelectric material has the property of spontaneous polarization and is characterized by reversing a direction of its spontaneous polarization in accordance with an applied electric field. There are two types of semiconductor storage elements in which spontaneous polarization of the ferroelectric material is utilized. One is of a so-called one-transistor type, and another is of a so-called one-transistor/one-capacitor type. There has recently been expected realization of the one-transistor type due to reasons that high-speed operation is possible, nondestructive readout of data can be effected, and high integration can be expected.
An example of the one-transistor type semiconductor storage element is disclosed in “Technical Report of IEICE SDM93-136, pp. 53-59”. According to Metal/ Ferroelectric/ Metal/Insulator/Semiconductor (MFMIS) structure disclosed herein, an insulating film, a lower electrode, a ferroelectric film, and an upper electrode are formed in layers on a semiconductor substrate in that order. This structure is provided for the reason that the ferroelectric film does not satisfactorily grow on a semiconductor or an insulator. In the MFMIS structure, it suffices that the ferroelectric film (for example, a film of lead titanate-zirconate, or a film of bismuth strontium tantalate) may be formed on a conductor film (for example, a platinum (Pt) film), and therefore, film formation is facilitated.
Further, when voltage is applied to the ferroelectric film, charge is accumulated in the ferroelectric film itself due to residual polarization of the ferroelectric film. Specifically, when positive voltage is applied to the ferroelectric film, positive charge is accumulated therein. On the other hand, when negative voltage is applied to the ferroelectric film, negative charge is accumulated therein. In a semiconductor storage element having the MFMIS structure, the accumulated charge excites charge on the surface of a semiconductor substrate. Accordingly, even if applied voltage is 0 volt, a switching operation of a transistor, namely, on state or off state is selectively maintained. As a result, data is written in the ferroelectric film. Further, current flowing between a source electrode and a drain electrode varies in accordance with the switching state of a transistor, and therefore, readout of data is made possible by detecting the variation of current.
However, processing of the above-described ferroelectric film and conductor film cannot easily be carried out by reactive ion etching (RIE) normally used in a semiconductor process, and therefore, it is necessary to effect processing by milling using argon gas. In this method, however, selectivity with a gate oxide film cannot be obtained, and therefore, there is a possibility that a semiconductor (silicon substrate) be damaged, thereby interfering with an operation of a finished product.
SUMMARY OF THE INVENTION
Accordingly, there has conventionally been required the advent of a method for manufacturing a semiconductor storage element, in which a gate structure including a ferroelectric film and a conductor film can be easily processed without causing damage thereto.
In accordance with a first aspect of the present invention, there is provided a method for manufacturing a semiconductor storage element, which comprises the steps of: (a) depositing a first conductor layer on a substrate; (b) applying, onto the first conductor layer, a light-sensitive solution with a ferroelectric material dissolved therein to form a ferroelectric film, the light-sensitive solution making a difference in solubility at the time of development between an exposed portion and an unexposed portion thereof; (c) depositing a second conductor layer on the ferroelectric layer; (d) forming, on the second conductor layer, a shading film and an etching mask of predetermined patterns; (e) transferring the pattern of the shading film to the ferroelectric layer by effecting exposure; (f) processing the exposed ferroelectric layer by effecting development; and (g) processing the first conductor layer and the second conductor layer using the etching mask.
As described above, the ferroelectric layer can easily be processed by exposure and development processes and other portions are not damaged. Further, the first and second conductor layers are processed by etching, and therefore, selectivity with other portions can easily be obtained and no damage is caused to other portions.
Further, in the method for manufacturing a semiconductor storage element of the present invention, according to a second aspect of the present invention, the first conductor layer and the second conductor layer are each comprised of iridium dioxide (IrO
2
).
The iridium dioxide (IrO
2
) layer is excellent in processability, and therefore, the first and second conductor layers can easily be processed.
In accordance with a third aspect of the present invention, the first conductor layer and the second conductor layer are each comprised of platinum (Pt).
In accordance with a fourth aspect of the present invention, the first conductor layer and the second conductor layer are each comprised of gold (Au).
In accordance with a fifth aspect of the present invention, the first conductor layer and the second conductor layer are each comprised of ruthenium dioxide (RuO
2
).
In accordance with a sixth aspect of the present invention, the ferroelectric material is bismuth strontium tantalate (SrBi
2
Ta
3
O
9
).
In accordance with a seventh aspect of the present invention, the light-sensitive solution is a light-sensitive sol-gel solution.
In accordance with an eighth aspect of the present invention, there is provided a method for manufacturing a semiconductor storage element, which comprises the steps of: (a) forming a silicon dioxide (SiO
2
) region, as an element isolation region, on an n-type Si substrate; (b) forming an SiO
2
film, as a gate oxide film, on the n-type Si substrate; (c) depositing a first conductor layer; (d) forming a ferroelectric film on the first conductor layer; (e) depositing a second conductor layer on the ferroelectric film; (f) forming, on the second conductor layer, a shading film and an etching mask of predetermined patterns; (g) etching the second conductor layer by a reactive ion etching process using the etching mask to form an upper electrode; (h) effecting exposure with irradiation of ultraviolet rays; (i) removing an exposed portion of the ferroelectric film by effecting development; (j) etching the first conductor layer by a reactive ion etching process using the etching mask to form a lower electrode; (k) removing the etching mask and the shading film by wet etching using hydrofluoric acid and ammonia hyperhydration, respectively; and (l) forming a source/drain region and a wiring structure.
In accordance with a ninth aspect of the present invention, in the above-described method of the eighth aspect, the first conductor layer and the second conductor layer are each comprised of IrO
2
.
In accordance with a tenth aspect of the present invention, in the above-described method of the eighth aspect, the first conductor layer and the second conductor layer are each comprised of Pt.
In accordance with an eleventh aspect of the present invention, in the above-described method of the eighth aspect, the first conductor layer and the second conductor layer are each comprised of Au.
In accordance with a twelfth aspect of the present invention, in the above-described method of the eighth aspect, the first conductor layer and the second conductor layer are each comprised of RuO
2
.
In accordance with a thirteenth aspect of the present invention, in the above-described method of the eighth aspect, the ferroelectric film is formed by applying a light-sensitive sol-gel solution containing a ferroelectric material dissolved therein using a spin coating p
Burdett James R.
Hiteshew Felisa
Oki Electric Industry Co. Ltd.
Venable
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