Etching a substrate: processes – Gas phase etching of substrate – Etching inorganic substrate
Reexamination Certificate
1999-07-26
2003-12-02
Kunemund, Robert (Department: 1765)
Etching a substrate: processes
Gas phase etching of substrate
Etching inorganic substrate
C216S074000, C134S001300, C134S002000, C134S026000, C438S905000
Reexamination Certificate
active
06656376
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention is in the area of semiconductor technology and relates to a process for cleaning CVD units.
In process reactors for the deposition of oxide ceramics on semiconductor substrates, the interior walls of the reactor, in addition to the substrates to be processed, are also coated with oxide ceramics. As a consequence of the deposition processes, the interior walls of the reactor have an amorphous coating of metal oxides or alkaline earth metal oxides, hydroxides, carbonates and organic precursor residues (residues of precursor compounds). Such deposits must be regularly removed in order to prevent substrate contamination.
One way of cleaning process units is by wet-chemical or mechanical cleaning. In this case, however, the reactor space must be opened to the clean room, which can contaminate the latter. In addition, these cleaning processes are generally carried out manually in a very time-consuming manner.
A second possibility includes using back-sputtering methods, for example argon sputtering. In this process, however, shadowing results in that not all areas of the interior walls of the reactor are cleaned. In addition, the back-sputtering results in attacks on the interior walls of the reactor, which usually are formed stainless steel.
The use of dry etchants opens up a further way of cleaning the interior walls of reactors. A suitable process is revealed, for example, by a paper by Jain et al. in “Thin Solid Films”, Vol. 269, pgs. 51-56, from 1995. The paper deals with the use of b-diketones for removing copper residues. Further processes using b-diketones are disclosed in Published, European Patent Application EP 0 701 274 A1, U.S. Pat. No. 5,094,701 and U.S. Pat. No. 5,782,986. However, it has been found that the processes proposed therein are only of limited suitability for cleaning the interior walls of CVD unit reactors coated with residues containing alkaline earth metals.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a process for cleaning CVD units which overcome the above-mentioned disadvantages of the prior art methods of this general type, which enables simple cleaning of CVD units.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for cleaning chemical vapor deposition (CVD) units used for depositing oxide ceramics, the CVD units have surfaces facing a process space being coated with residues containing at least one of alkaline earth metals and metals, which includes:
carrying out a cleaning process using an etching medium containing diketones including free diketones coming into contact with process residues, the free diketones reacting with process residues to form at least one of alkaline earth metal complexes and metal complexes; and
forming the etching medium with at least one compound selected from the group consisting of ammonia, amines, polyether additives, polyamine additives and tetraglyme for preventing oligomerization of the alkaline earth metal complexes and the metal complexes.
The object is achieved according to the invention by a process for cleaning CVD units used for depositing oxide ceramics. During the depositing process, surfaces of the CVD units facing the process space are coated with process residues containing alkaline earth metals and/or metals. The cleaning of the CVD units is carried out using an etching medium containing free diketones which comes into contact with the process residues. The diketones react with the process residues to form alkaline earth metal and/or metal complexes, and the etching medium contains, in order to prevent oligomerization of the alkaline earth metal and/or metal complexes, at least one compound from the group consisting of ammonia, amines, polyether additives, polyamine additives and tetraglyme.
The process residues containing metals and in particular alkaline earth metals are attacked by the diketones, which are present in adequate concentration and are generally in unbound form, and form therewith volatile alkaline earth metal or metal complexes. In order to support these reactions, the gaseous etching medium is introduced into the reactor space at, for example, an elevated temperature and at greatly reduced pressure. The amount of diketones fed in and the feed rate thereof depend on the size of the reactor space and on the amount of process residues to be removed. The introduction of the etching medium into the reactor space preferably takes place via the feed systems already present in the CVD units. These include, for example, pipelines for media supply and devices for dispersing or evaporating liquids. The diketones are preferably fed in at the elevated temperature, so that they are in gaseous form. Even if they are introduced in liquid form, the diketones are thus already in gaseous form when they come into contact with the process residues. The etching medium preferably comes into contact with the process residues under a greatly reduced pressure and at an elevated temperature compared with standard normal conditions. Under these conditions, the complexes formed at the elevated temperature from the free diketones and the alkaline earth metals or metals are likewise gaseous and can sublime rapidly from the interior walls of the reactor and can thus easily be removed from the interior of the reactor. Under the selected conditions (pressure and temperature), the volatility of the resultant complexes is promoted. Standard normal conditions correspond to a pressure of about 105 Pa and a temperature of about 20° C.
The cleaning process according to invention is advantageously suitable for in-situ cleaning of CVD units, achieving rapid cleaning and reduced environmental pollution. Furthermore, use of the feed systems already present in the CVD units for the etching medium produces the same spatial concentration distribution in the process space as also occurs during deposition of the substances to be deposited. If some areas in the process space are afflicted with greater deposits owing to non-uniform distribution of the substances to be deposited, the concentration of the etchant in these areas is also increased. This results, advantageously, in a higher etching rate in areas with greater deposits. By contrast, significant overetching in less afflicted areas can be substantially excluded.
The interior walls of the reactor to be cleaned usually consist of stainless steel or other inert metal surfaces. The cleaning process according to the invention advantageously allows metal-containing or alkaline earth metal-containing oxides, hydroxides, carbonates and precursor residues of oxide ceramics deposits to be removed.
An advantageous embodiment of the invention is characterized in that sterically hindered and/or fluorine-containing diketones are used.
Sterically hindered and fluorine-containing diketones have proven particularly advantageous. Fluorine-containing diketones have high etching rates, for example owing to their high volatility, whereas sterically hindered diketones, owing to their molecular structure, prevent the bonded metals from forming complexes with other ligands owing to steric screening. The sterically hindered diketones in particular prevent multiple complex formation, which results in oligomerization and thus in the formation of low-volatility complexes.
A further advantageous embodiment of the invention is characterized in that the greatly reduced pressure is below 2000 Pa, preferably below 200 Pa.
A further advantageous embodiment of the invention is characterized in that the elevated temperature is between 200° C. and 300° C., in particular between 230° C. and 250° C.
Very good cleaning results can be achieved at a pressure of about 200 Pa or below. For a further improvement in cleaning, a temperature of between 230° C. and 250° C. is used. This temperature is on the one hand sufficient for the formation of volatile metal complexes, while on the other hand the chamber walls and sealants for sealing the reactor space are only aff
Dehm Christine
Fritsch Elke
Weinrich Volker
Wendt Hermann
Ahmed Shamim
Greenberg Laurence A.
Kunemund Robert
Mayback Gregory L.
Siemens Aktiengesellschaft
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