Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
1999-09-29
2002-08-20
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S754000, C438S745000
Reexamination Certificate
active
06436723
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an etching method and an etching apparatus for etching inorganic materials, such as metal, metal oxide, and the like, a manufacturing method for manufacturing a semiconductor device, and a semiconductor device.
Etching techniques together with lithography techniques support micro-processing techniques in the process for manufacturing semiconductors. Conventionally, there has been no other ways than physical removal based on polishing, with respect to substances on which a determination has not yet been made as to etching removal with use of a solution. For example, metal oxide (SrRuO
x
) which is an oxide of strontium (Sr) and Ruthenium (Ru) is one of materials used for FRAM, DRAM, or the like. Since no method for etching has been proposed as to this kind of metal oxide, only the physical removal has been carried out.
Meanwhile, H
2
O
2
is known as a solution for conventional cleaning. To remove particles and organic materials, NH
4
OH/H
2
O
2
is mainly used and a cleaning solution containing this material is alkaline. To remove metal impurities, HCl/H
2
O
2
is mainly used and a cleaning solution containing this material is acid. These cleaning solutions are widely used before and after a step in which impurities are involved in the semiconductor process, and the cleaning using them is generally called RCA cleaning. Also, two kinds of cleaning solutions described above are used most generally and are called SC
1
and SC
2
, respectively.
For example, as described above, cleaning with water containing ammonium hydrogen peroxide has been used in particle cleaning. In the system for removing particles, it is considered that particles are lifted off during etching of a silicon substrate using alkaline solution, and the particles and the surface of the silicon substrate are set to an equal potential, thereby inducing mutual repulsion which hinders re-sticking.
Also, in case of removing organic substances by the RCA cleaning, cleaning with H
2
SO
4
is carried out. However, there are problems concerning scattering of sulfuric acid ion into a clean room and recycling of waste liquids. Hence, ozone-added ultrapure water technique has been proposed. This cleaning method is used as a strong oxidation agent for subjecting an ozone gas to oxidation decomposition. This method is advantageous in that organic substances can be effectively removed by a slight amount of ozone gas and that a waste liquid needs not be recycled since an ozone gas changes into oxygen due to autolysis. If ozone water is thus used for cleaning, the ozone water has a concentration of about 5 to 20 ppm at the room temperature, in general.
Further, HCl/H
2
O
2
cleaning and HF/H
2
O cleaning has been carried out as a method of cleaning metal impurities. By the HCl/H
2
O
2
cleaning, impurities in the native oxide film cannot be removed although metal impurities sticking to the surface of the silicon substrate and metal impurities sticking to the surface of the native oxide film can be removed. Therefore, a step of removing a native oxide film with use of HF/H
2
O
2
is carried out additionally. In the method of removing the metal impurities, cleaning with use of ozone water has been proposed lik in the above case of removing organic materials.
As has been explained, ozone water is used for cleaning of organic impurities on the wafer surface with utilization of an oxidation force of ozone, and cleaning and sterilization of organic impurities in pure water. With respect to solution of organic materials, the ozone water is used only from the viewpoint of cleaning.
In contrast, it has been recently attempted to use ozone water for etching of organic films such as a resist and the like. In case of etching of an organic film, the concentration of ozone in ozone water must be set to about 100 ppm in order to ensure an effective etching rate.
However, even in this case, ozone water is used for the purpose of etching an organic film but is not used for etching and removing inorganic materials such as metal and metal oxide films.
Meanwhile, a CMP (Chemical Mechanical Polishing) method has been widely used as a method of polishing and flattening the surface of a semiconductor substrate. This CMP method is a method of flattening the substrate surface with use of both the chemical operation and the physical operation. By using (NO
3
)
2
CeNH
4
as an oxidation agent to be added to slurry, it is possible to flatten the surface of an SrRuO
x
film, which is a metal oxide. However, in case where this material is not used for CMP but is used for chemical etching, (NO
3
)
2
CeNH
4
requires a concentration of several % order in order to ensure an effective etching rate (10 to 100 nm/min). However,. (NO
3
)
2
CeNH
4
is an oxidation agent which causes autolysis and is therefore unstable, so that it is very difficult to maintain a high concentration as a liquid for slurry. Also, since acid-alkaline waste liquid processing is required, this oxidation agent is difficult to treat as an etching solution.
As described above, it is difficult for a conventional etching technique to etch metal oxide materials such as an SrRuO
x
and the like used for FRAM, DRAM, and the like. Consequently, there is no other way than carrying out physical removal based on polishing. Even in case of carrying out polishing, since the several % order cannot be stably maintained for (NO
3
)
2
CeNH
4
, (NO
3
)
2
CeNH
4
must be dissolved as an additive agent immediately before etching, and thus a liquid for slurry must be prepared. It is thus very difficult to use this method for a semiconductor manufacture process. In addition, la discussion has been made as to use of ozone water for cleaning and etching of an organic film which are carried out before or after the step in which particles and metal impurities of dry etching or the like are generated. However, no consideration has been made as to application to metal and metal oxide films such as an SrRuO
x
film and the like.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide an etching method, an etching apparatus, and a method of manufacturing a semiconductor device, which are capable of easily removing a film made of an inorganic substance which cannot conventionally be etched without physical removal and without polluting the environment.
To achieve the above object, according to a first aspect of the present invention, an etching method comprises the steps of: preparing a substrate having a surface on which a film made of an inorganic substance is formed; and wet-etching the film on the substrate by oxidation-reduction reaction involving oxygen, with use of an etching solution containing an oxidation agent which has an oxidation-reduction potential of 2V or more measured at 25° C., 1 atm.
The oxidation agent captures and releases electrons and generates oxygen, in the oxidation-reduction reaction.
It is desirable that the inorganic substance is difficult to dissolve in water and the oxidation-reduction reaction generates an easily water-soluble or volatile substance from the inorganic substance.
It is also desirable that the inorganic substance is a metal or a metal compound and the inorganic substance is strontium ruthenium compound which is decomposed into an easily water-soluble compound and a ruthenium compound by the oxidation-reduction reaction.
The etching solution is desirably ozone water having a concentration of 5 ppm or more when the etching solution reaches the film.
Desirably, in the step of wet-etching the film, the substrate having the film made, of strontium ruthenium compound is rotated at a speed of 100 rpm or more and the ozone water is directly injected onto the substrate.
Also desirably, in the step of wet-etching the film, the substrate having the film made of strontium ruthenium compound is rotated at a speed of 1000 rpm or more and the ozone water is directly injected onto the substrate.
The etching solution is desirably ozone water having a concentration of 100 ppm or less when the etching solutio
Nadahara Soichi
Tomita Hiroshi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jr. Carl Whitehead
Kabushiki Kaisha Toshiba
Vockrodt Jeff
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