Plasma etching apparatus (sometimes referred to as dry etchers) are typically used to support etching operations as part of a semiconductor device production process. One known type of plasma etching apparatus is a flat plate-type plasma etching apparatus. A flat plate-type plasma etching apparatus typically includes a lower electrode and an upper electrode. The lower electrode is typically positioned within the chamber of the plasma etching apparatus and an object, such as a semiconductor wafer, to be etched is placed on the lower electrode in the plasma etching chamber. The upper electrode is typically placed opposite the lower electrode. In a flat plate-type plasma etching apparatus, the upper electrode generally further acts to provide an upper wall of the plasma etching chamber.
Plasma etching operations may then be carried out on the semiconductor wafer located on the lower electrode in the chamber using the plasma etching apparatus. In order to create an appropriate plasma between the upper electrode and the lower electrode, a high-frequency power signal, such as a radio frequency (RF) signal, is generally applied to the upper or the lower electrode. The applied high-frequency power signal acts on the etching gas injected into the chamber to generate active free radicals or other ionized species to form the plasma. The surface of the semiconductor wafer placed on the lower electrode may then be etched by the plasma.
As semiconductor device technology continues to evolve, critical dimensions for features, such as contacts, continue to be reduced. For example, dimensions for such features may be less then 250 nm. One approach to providing semiconductor device features supporting these critical dimensions includes the use of plasma etching apparatuses which include an upper electrode which itself includes a gas distribution plate through which the gas used in the etching process is injected into the chamber. The gas distribution plate, in turn, is connected to an external gas supply source. Examples of this type of flat plate-type plasma etching apparatus include the Centura5200-MXP device available from the Applied Materials (AMT) and the Unity II 855Dd device of the Tokyo Electron Limited Etch Systems (TEL) department of Samsung Electronics Company.
In plasma etching apparatus such as the MxP and the DRM, the upper electrode is typically a separate member from the components generally defining the plasma etching chamber and is configured to be connected to the remaining chamber wall components so as to close the chamber and position the upper electrode relative to the lower electrode. When the upper electrode is connected to the sidewall portion of the chamber housing member, the plasma etching chamber may be sealed up to allow a vacuum to be generated in the chamber during etching operations. It is, accordingly, desirable to provide a connection between the upper electrode and the remaining walls of the chamber which provides for sealing of the chamber and further provides the ability to electrically connect the upper electrode to the sidewalls of the chamber. In such devices, the upper electrode is typically made with a contact portion which connects with the sidewalls of the chamber and which is made of the same material as the remainder of the upper electrode.
The upper electrode in a flat plate-type plasma etching apparatus is typically made of an aluminum (Al) material. Generally, commercially used Al materials contain some amount of impurity elements which may provide for improved mechanical or chemical characteristics in, the Al material. Likewise, the sidewall and bottom wall portions defining the chamber of the plasma etching apparatus may similarly be made from the same Al material as the upper electrode. As the plasma etching is performed by applying a high-frequency signal to the Al material defining the upper electrode and other walls of the chamber, which Al material may contain such impurities, particles of the impurity atoms or of Al may themselves be etched from the electrode or walls of the chamber and be distributed into the chamber itself. Such released particles or impurity atoms may subsequently be mixed with a feature, such as a thin film, which is being formed on a semiconductor wafer or other object being etched. This, in turn, may result in what is sometimes referred to as heavy metal contamination or other defects in the etched wafer.
In order to reduce the problem caused by impurity atoms or other particles being introduced during the etching process, it is known to anodize the surface of the Al material (i.e., anodic oxidation is applied to a surface of the Al material which is exposed to the chamber). The exposed surface of the Al material is thereby coated with an alumina coating film (typically Al.sub.2 O.sub.3). The alumina coating film is generally higher than Al in hardness and has improved anti-corrosive properties. Accordingly, during the plasma etching operations, the alumina coating film on the Al material surface may reduce the potential for particles of Al or impurity ions from being introduced into the chamber and subsequently being deposited on the semiconductor material being etched.
The inner surface of a flat plate-type upper electrode typically has an anodized portion with a non-planar or stepped feature on the inner surface of the electrode in the region where the upper electrode is connected to a upper surface of the sidewalls of the chamber when assembled. Such an irregular, stepped feature may be provided because of the thickness introduced by the alumina coating film on the underlying plate electrode as a portion of the inner surface in the contact region between the upper plate electrode and the sidewalls of the chamber is typically left non-anodized to provide a common material contact area between the upper electrode and the sidewalls of the chamber. This surface discontinuity may interfere with the effectiveness of the seal between the upper electrode and the remaining walls of the chamber. Accordingly, the vacuum rate or concentration of processing gas may vary within the chamber. As such, these known systems may have difficulty in maintaining processing conditions for etching the surface of the semiconductor wafer being etched. For example, impurity particles may be allowed to enter into the chamber between the upper electrode and the sidewalls of the chamber. Furthermore, component parts forming the chamber of the plasma etching apparatus may be exposed to environmental contaminants which may, in turn, shorten the operative life cycle of various exposed parts.
A further problem which may occur in these prior approaches to plasma etching apparatus results from the use of a non-anodized region (provided for allowing an improved electrical connection between the upper electrode and the sidewalls of the chamber) which region may be damaged during operation. As imperfect seal may occur between the anodized and non-anodized regions of the upper electrode resulting from the imperfect sealing between the parts forming the plasma etching chamber. For example, when an imperfect seal is provided, arcing into the chamber may be generated at the non-anodized portions when high-frequency power is applied during the plasma etching operation. Surface damage resulting from such arcing originating at the non-anodized region may result in further vacuum leakage and generate additional particle impurity introduction into the chamber.