Method for manufacturing capacitor element

The method of this invention provides a method for manufacturing a capacitor element composed of films. The films have a precise etched shape without a residue that may be generated as a reaction product in a dry-etching process. In this invention, washing in a non-oxidizing atmosphere, inclining a side of a mask for etching or heating a substrate prevents the reaction product from remaining on the film as a residue. The reaction product can be washed away with water, acid or organic solvent in inert gas. The reaction product can be removed from the side of the mask by sputter-etching with ions for dry-etching. The reaction product can be exhausted without adhering to the mask by heating the substrate at a temperature between 100.degree. C. and 400.degree. C.

FIELD OF THE INVENTION 
The present invention relates to a semiconductor device. More particularly, 
the present invention relates to a method for manufacturing a capacitor 
element having a capacitor dielectric layer of a capacitor dielectric film 
with high dielectric constant or a ferroelectric film. 
BACKGROUND OF THE INVENTION 
Consumer electronic equipment has been further advanced in the recent trend 
toward high-speed and low power consumption for microcomputers etc., and 
semiconductor elements for semiconductor devices used in such computers 
are also miniaturized rapidly. Accordingly, undesirable radiation, that 
is, electromagnetic wave noise generated from electronic equipment, has 
been a serious problem. As a method to decrease such undesirable 
radiation, a technique to integrate capacitor elements with a large 
capacity in semiconductor integrated circuit devices and the like has 
attracted attention. Such capacitor elements have capacitor dielectric 
layers of dielectric with high dielectric constant (hereinafter, high 
dielectric). With the trend toward high integration of dynamic RAM, a 
technique to use high dielectric materials for a capacitor dielectric 
layer instead of conventional silicon oxides or nitrides is widely 
researched. Moreover, research and development concerning ferroelectric 
films having a spontaneous polarization characteristics have been 
attracted much attention in order to practically apply a non-volatile RAM 
that enables writing and reading with lower operating voltage and higher 
speed compared to conventional devices. 
A method for manufacturing a conventional semiconductor device is explained 
below referring to FIGS. 6A to 6C. FIGS. 6A-6C are cross-sectional views 
showing the process of manufacturing conventional capacitor elements. 
As shown in FIG. 6A, a film 12 for an electrode or a capacitor dielectric 
layer is formed on a substrate 11 composed of a semiconductor or the like 
by sputtering or a metal organic decomposition method, followed by forming 
a mask 13 for patterning the film 12. Next, as shown in FIG. 6B, the film 
12 for the electrode or the capacitor dielectric layer is patterned by 
dry-etching. Subsequently, as shown in FIG. 6C, the mask 13 is removed. 
In the semiconductor device manufactured in the conventional method, 
however, as shown in FIG. 6B, the dry-etching is accompanied by generating 
a reaction product 14 that adheres to sides of the mask 13. As the product 
14 remains after removing the mask 13, a thin film formed to cover the 
capacitor element may suffer from inferior coverage, which prevents the 
capacitor element from operating normally. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind, it is the object of the present 
invention to provide a method for manufacturing a capacitor element to 
prevent a reaction product from remaining adhered to the film for the 
electrode or the capacitor dielectric layer as a residue. 
In order to achieve the above-described object, a method for manufacturing 
a capacitor element of the present invention comprises the steps of: 
forming a film for an electrode or a capacitor dielectric layer of the 
capacitor element, forming a pattered mask on the film, patterning the 
film by dry-etching utilizing the mask, removing from the mask reaction 
products generated by the dry-etching, and removing the mask from the 
film. 
A first embodiment of the method comprises the steps of: forming a film for 
an electrode or a capacitor dielectric layer of the capacitor element, 
forming a pattered mask on the film, patterning the film by dry-etching 
utilizing the mask, washing the patterned film in a non-oxidizing 
atmosphere, and removing the mask from the film. 
Thus, this embodiment can provide a capacitor element that can operate 
normally, because a reaction product generated in dry-etching is washed 
away before turning to a stable oxide so that a desirable etched shape of 
the film can be obtained. 
A second embodiment of the method comprises the steps of: forming a film 
for the electrode or the capacitor dielectric layer of the capacitor 
element, forming a mask on a surface of the film, pattering the mask so 
that the mask has a side inclining from 5 degrees to 80 degrees away from 
the surface of the film, patterning the film by dry-etching utilizing the 
patterned mask, and removing the mask from the film. 
Thus, this embodiment can provide a capacitor element that can operate 
normally, because a reaction product generated on the sides of the mask is 
removed physically by collision with ions for dry-etching so that a 
desirable etched shape of the film can be obtained. 
A third embodiment of the method comprises the steps of: forming a film for 
an electrode or a capacitor dielectric layer of the capacitor element on a 
substrate, forming a patterned mask on the film, patterning the film by 
dry-etching utilizing the patterned mask while the substrate is maintained 
between 100.degree. C. and 400.degree. C., and removing the mask from the 
film. 
Thus, this embodiment can provide a capacitor element that can operate 
normally, because a reaction product is kept to be evaporative enough to 
be easily exhausted in dry-etching so that a desirable etched shape of the 
film can be obtained. 
These and other advantages of the present invention will become apparent 
those skilled in the art upon reading and understanding the following 
detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the method of the present invention, a film for constituting the 
electrode preferably includes at least one material selected from 
platinum, palladium, ruthenium, ruthenium oxide, iridium, iridium oxide, 
titanium, titanium oxide and titanium nitride. 
In the method of the present invention, a film for constituting the 
capacitor dielectric layer preferably includes at least one material 
selected from a high dielectric and a ferroelectric. The high electric 
preferably has a high dielectric constant of 50 or more. As a high 
dielectric, strontium titanate (SrTiO.sub.3), barium strontium titanate 
(Ba.sub.x S.sub.1-x TiO.sub.3 ; 0&lt;x&lt;1), tantalum oxide (Ta.sub.2 O.sub.5) 
and the like can be used. As a ferroelectric, lead zirconium titanate 
(Pb.sub.x Zr.sub.1-x TiO.sub.3 ; 0&lt;x&lt;1), strontium bismuth tantalate 
(SrBi.sub.2 Ta.sub.2 O.sub.9) and the like can be used. 
In the method of the invention, the mask preferably includes at least one 
material selected from photoresist, silicon oxide, titanium, titanium 
oxide, titanium nitride, tantalum and tungsten. 
In the method of the invention, the non-oxidizing atmosphere includes at 
least one gas selected from nitrogen, argon and helium. 
In the method of the invention, the patterned film is washed with at least 
one liquid selected from water, hydrochloric acid, sulfuric acid, nitric 
acid, hydrofluoric acid and an organic solvent. 
First Embodiment 
FIGS. 1A-1D are cross-sectional views to show the steps of manufacturing a 
capacitor element in this embodiment. As shown in FIG. 1A, a film 2 for an 
electrode or a capacitor dielectric layer of a capacitor element is formed 
on a substrate 1 by sputtering or a metal organic decomposition method or 
the like. A semiconductor substrate composed of silicon, compound 
semiconductor such as GaAs or the like, and a glass substrate can be used 
for the substrate 1. On the film, a mask 3 is formed to give the film a 
predetermined pattern, followed by etching the film 2 by dry-etching as 
shown in FIG. 1B. While etching the film, a reaction product 4 adheres to 
the sides of the mask 3. The product 4 may turn into a stable compound by 
oxidation. Therefore, as shown in FIG. 1C, the substrate 1 is washed by a 
solution in a non-oxidizing atmosphere such as nitrogen so that the 
reaction product 4 is removed from the sides of the mask 3. 
Thus, the reaction product that has adhered to the sides of the mask for 
etching can be easily removed by washing the mask and the etched film 
before exposing the product to the air. 
For example, when using platinum as a material for the electrode of the 
capacitor element, some platinum reacts with chlorine gas contained as a 
main component of dry-etching gas to produce platinum dichloride or 
platinum tetrachloride, some of which adheres to the sides of mask. 
Platinum dichloride is soluble in hydrochloric acid, while platinum 
tetrachloride is soluble in water, ethanol or acetone. Therefore, any 
adhering of platinum compound can be washed away with the mixture of 
hydrochloric acid with water (diluted hydrochloric acid). Washing without 
exposing the compound to the air is necessary, because platinum dichloride 
or platinum tetrachloride may react with oxygen to produce platinum 
chloride oxide having a high chemical stability. 
When SrBi.sub.2 Ta.sub.2 O.sub.9 is used as a material for the capacitor 
dielectric layer of the capacitor element, some SrBi.sub.2 Ta.sub.2 
O.sub.9 reacts with chlorine gas or fluorine gas contained as a main 
component of dry-etching gas to produce a metal chloride or fluoride such 
as BiCl.sub.x, SrCl.sub.x, TaCl.sub.x, BiF.sub.x, SrF.sub.x and TaF.sub.x, 
some of which adheres to the sides of mask. Washing with the mixture of 
hydrofluoric acid with nitric acid can remove the adhesion, because these 
compound are soluble in the mixture of the acids. 
The film for the electrode or the capacitor dielectric layer formed as 
described above can have a thickness of 0.2 .mu.m to 0.4 .mu.m. 
When platinum used as a material of the electrode is substituted with 
palladium, ruthenium, ruthenium oxide, iridium, iridium oxide, titanium, 
titanium oxide, titanium nitride or the like, the same effect can be 
obtained by washing the reaction product away with an appropriate 
detergent. Such a detergent can be selected according to the material of 
the film. For example, water at temperature of 80.degree. C. or more and 
some organic solvents are effective in many cases as well as the acids as 
described above. The reaction product can be washed away in an inert gas 
such as argon and helium as well as nitrogen. 
Second Embodiment 
FIGS. 2A-2C are cross-sectional views to show the steps of manufacturing a 
capacitor element in this embodiment. As shown in FIG. 2A, a film 2 for an 
electrode or a capacitor dielectric layer of a capacitor element is formed 
on a substrate 1 by the same method as described in the first embodiment. 
On the film 2, a mask 3 of photoresist is formed to give the film a 
predetermined pattern. The mask 3 formed in a predetermined pattern is 
baked to cause it to contract according to the baking temperature so that 
the mask has an inclined side. The angle of .theta. between the side of 
the mask 3 and the surface of the film 2 can be adjusted by a baking 
temperature. One example of a preferred angles is 75 degrees. The film 2 
etched by dry-etching has an inclined side due to the inclined side of the 
mask 3. During the dry-etching, the reaction product 4 that has adhered to 
the sides of the mask 3 is removed by sputter-etching with ions 5 for the 
dry-etching, as shown in FIG. 2B. As shown in FIG. 2C, the mask 3 is 
removed from the film. 
Thus, the reaction product that has adhered to the sides of the mask is 
exposed to the ions during dry-etching because of the inclination of the 
sides so that the reaction product does not remain on the film as a 
residue. 
In order to examine the relationship between the effect of the angle of 
.theta. and the rate of occurrence of adhesion by a reaction product, some 
masks having various kinds of the angle of .theta. were utilized for 
etching the film. Four masks were used per angle. The rate of occurrence 
was determined by observing with a scanning electron microscope (SEM). As 
a result, the angle of 80 degrees or less was found to make it possible to 
realize a desirable etched shape of the film without the residue as shown 
in FIG. 3. The angle of 5 degrees or less may make it difficult that the 
mask works effectively especially in the edge portion of the mask. 
Therefore, the angle of .theta. is preferably between 5 and 80 degrees. 
When photoresist used as a material of the mask is substituted with silicon 
oxide, titanium, titanium oxide, titanium nitride, tantalum, tungsten or 
the like, the same effect can be obtained. 
Third Embodiment 
FIGS. 4A-4C are cross-sectional views to show the steps of manufacturing a 
capacitor element in this embodiment. As shown in FIG. 4A, a film 2 for an 
electrode or a capacitor dielectric layer of a capacitor element is formed 
on a substrate 1 by the same method as described in the first embodiment. 
On the film 2, a mask 3 is formed to give the film a predetermined 
pattern. As shown in FIG. 4B, the film 2 is etched by dry-etching while 
heating the substrate 1. One example of the preferred temperatures of the 
substrate is 120.degree. C. During the dry-etching, the reaction product 4 
is kept in an evaporative state so that the product can be exhausted 
without adhering to the sides of the mask 3. As shown in FIG. 4C, the mask 
3 is finally removed from the film. 
Thus, the reaction product that may adhere to the sides of the mask in room 
temperature is sufficiently evaporated by heating so as not to remain on 
the film as a residue. 
In order to examine the relationship between the substrate temperature and 
the rate of occurrence of adhesion by a reaction product, some films were 
etched by dry-etching while the substrate was kept at various 
temperatures. Four masks were used per temperature. The occurrence rate is 
determined by observing with a SEM. As a result, the substrate temperature 
of 100.degree. C. or more was found to make it possible to realize a 
desirable etched shape of the film without the residue as shown in FIG. 5. 
The temperature of more than 400.degree. C. tends to deteriorate the 
capacitor element itself. Therefore, the temperature of the substrate 
during the dry-etching is preferably between 100.degree. C. and 
400.degree. C. 
As explained in the above embodiments, the invention provides a reliable 
capacitor element having a precise etched shape, because the reaction 
product accompanied by etching the film does not remain adhered to the 
film. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The embodiments 
disclosed in this application are to be considered in all respects as 
illustrative and not restrictive, the scope of the invention being 
indicated by the appended claims rather than by the foregoing description, 
all changes that come within the meaning and range of equivalency of the 
claims are intended to be embraced therein.