Patent Application
20150371828
1. Technical Field
The disclosure relates to processing a workpiece, such as a semiconductor wafer, or cleaning a workpiece processing chamber.
2. Background Discussion
In etch and chemical vapor deposition (CVD) processes, reactive gases are supplied to the workpiece surface where reactions take place to etch an existing film (in etch processes) or form a desired film (in CVD processes) over the surface of the substrate being processed. In such processes, a plasma is formed using radio frequency (RF) energy or microwave energy to decompose and/or energize reactive species in reactant gases to produce the desired reactions.
One problem that arises during such plasma processes is that unwanted deposition of a residue occurs in the processing chamber and leads to potentially high maintenance costs. Undesired film or residue deposition can occur on any hot surface including the heater and/or various components of the process chamber, such as process kit parts for example. The undesired film grows during processing of successive workpieces, which degrades process performance, necessitating replacement of the various components of the process chamber, increasing the cost of operating the processing chamber.
A reactive plasma cleaning procedure is regularly performed in situ (in the processing chamber) to remove the unwanted deposition material from the chamber walls, heater, and other process kit parts of the processing chamber. Commonly performed between process steps for every wafer or a predetermined number of wafers, this in situ cleaning procedure is performed by dissociation of an etching (etchant precursor) gas through application of RF energy. However, where the residue to be removed contains a metal (e.g., a metal silicide), etching gases useful for etching the unwanted residue are often corrosive and attack the materials which make up the chamber, heater, and process kit parts of the processing chamber. Moreover, the in situ plasma cleaning procedure also causes ion bombardment of the metallic parts of the processing chamber. The ion bombardment makes it difficult to effectively clean the residue without damaging the heater and other chamber parts in the cleaning process, thus reducing the operational life of these components.
In order to overcome the problem of damaging chamber components during cleaning, one conventional approach employs a remote plasma source (RPS). The RPS provides radical species for cleaning the workpiece processing chamber. In a conventional RPS, the process pressure range is limited to relatively high pressures, leading to loss of radical species through recombination. This limits the concentration of radical species delivered to the processing chamber, thereby limiting throughput. With a conventional RPS cleaning system, the radicals generated in the RPS are delivered through a delivery tube into the volume above the gas shower head. Radicals recombine (are lost) within the RPS, the delivery tube and gas shower head, which limits the radical population delivered to the process.
A conventional RPS has limited performance in part due to the limited pressure range (e.g., 2-6 Torr) required for its efficient operation. This relatively high pressure range limits the density of the radical species delivered to the process, and promotes the recombination of radical species within the RPS, the delivery tube and the gas showerhead. Such recombination can reduce the radical species population delivered to the main chamber by a factor of a thousand, depending upon the type of radical species.
As an alternative to in situ plasma cleaning, some conventional plasma processing systems have their workpiece processing chamber connected through a delivery tube to a separate microwave RPS chamber having a microwave plasma source, which may be referred to as a microwave RPS. A microwave RPS is very expensive and therefore undesirable for many applications. The desired radical species are obtained as by-products from the plasma in the separate microwave RPS chamber. However, the microwave RPS suffers to a lesser degree some of the drawbacks of a conventional RPS plasma cleaning system. For example, as radical species flow from the separate microwave RPS chamber to the workpiece processing chamber, radical species recombine (are lost) within the RPS, the delivery tube and the gas shower head, which limits the radical population delivered to the process. Some of the radicals from the remote plasma may react with the components of the chamber. This may cause physical damage to the components of the chamber, including the chamber walls, substantially reducing their operational life. In addition, reactions between the chamber components and the radicals leaves a residue on the chamber components which may contaminate wafer surfaces during processing.
A plasma reactor having a microwave remote plasma source comprises chamber comprising a side wall and a ceiling, and a workpiece support stage within the chamber, an array of plural microwave sources mounted on an external side of the ceiling and an ion-blocking baffle between the ceiling and the workpiece support stage and defining: (a) an upper chamber portion between the ceiling and the ion-blocking baffle and (b) a lower chamber portion between the workpiece support stage and the ion-blocking baffle. The reactor further comprises a gas distributor comprising gas injection ports open to the upper chamber portion, and a process gas supply coupled to the gas distributor.
In one embodiment, each one of the microwave sources comprises a magnetron and a conical radiator antenna, each hollow conical radiator antenna having a cone apex facing the magnetron and a cone base facing the external surface of the ceiling.
The ceiling comprises a dielectric material. In one embodiment, the ceiling comprises a disk-shaped dielectric plate. In another embodiment, the ceiling comprises a metal plate, the metal plate comprising an array of plural openings extending through the metal plate in registration with respective ones of the plural microwave sources, and dielectric windows within the plural openings. In one implementation, each of the plural openings is circular with a diameter corresponding to a diameter of a respective conical base of the conical radiator antenna.
In one embodiment, the gas distributor is comprised within the ion-blocking baffle. In another embodiment, the gas distributor comprises gas injection ports in the side wall adjacent the upper chamber portion.
In one embodiment, each of the microwave sources occupies a zone of the ceiling that is sufficiently small that the array of microwave sources fits within a circumference of the ceiling.
In one embodiment, the plural microwave sources are spaced apart from one another at uniform intervals.
In one embodiment, the ceiling is planar and the plural microwave sources are attached to the ceiling and are arrayed in a plane.
In one embodiment, each hollow conical radiator antenna has an axis of symmetry parallel with an axis of symmetry of the ceiling.
In an embodiment, the ion-blocking baffle comprises an array of slots extending from the upper chamber portion to the lower chamber portion, each of the slots being sufficiently narrow to limit or prevent propagation of plasma ions through the slots. The slots are sufficiently wide to permit diffusion of neutral radical species through the ion-blocking baffle. In one embodiment, the ion-blocking baffle comprises metal.
A vacuum pump is coupled to the lower chamber portion. The process gas supply contains gas comprising a precursor of a desired radical species.
In accordance with another aspect, a method is provided of treating with radical species either a surface of a workpiece in a process chamber or an internal surface of the process chamber. The method comprises forming a ceiling of the process chamber of a material comprising a dielectric material, dividing the process chamber into an upper portion and a lower portion, mounting an array of plural microwave sources on an external side of the ceiling, injecting a process gas into the upper portion, and generating a plasma in the upper portion by radiating microwave power from the array of plural microwave sources into the upper portion of the process chamber, while preventing plasma ions from passing into the lower portion, and while allowing radical species to flow from the upper portion into the lower portion.
The microwave power may be of a frequency of about 2.45 GHz. The chamber may be maintained at pressure of less than 2 Torr.
So that the manner in which the exemplary embodiments of the present invention are attained can be understood in detail, a more particular description of the invention summarized above is given by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In the below-described embodiments, a new RPS that delivers a much higher concentration of desired radical species is used as a radical species source for either processing a workpiece in a process chamber or for cleaning the chamber itself. Processes may include etch processing or chemical vapor deposition processing, for example. The new RPS consists of an array of low cost microwave magnetron heads coupled to conical, horn or other microwave emitter antennas above the gas shower head. A plasma is formed in a plasma generation zone between the microwave emitter antennas and the gas shower head. Radical species in the plasma diffuse through the shower head into a zone of the chamber containing the workpiece support stage. Ions in general do not diffuse through the gas shower head. The array of microwave magnetron heads delivers microwave power through localized dielectric windows to generate a plasma in the plasma generation zone, the plasma having a high concentration of radical species, in an extremely wide range of chamber pressures including an extremely low minimum pressure. The radical generation efficiency is increased significantly by reducing recombination losses, which increases productivity. These recombination losses are reduced because the radical species are produced in the processing chamber, not in a separate chamber. These recombination losses are further reduced because the minimum chamber pressure is far below minimum pressures required in conventional RPS systems.
Referring to
An array 120 of microwave sources 122 (microwave emitters) is supported on the ceiling 104. Referring to
The chamber 100 has a plasma generation zone 100a defined between the ceiling 104 and the gas shower head 110. The chamber 100 further has workpiece process zone 100b defined between the workpiece support stage 106 and the gas shower head 110. The gas showerhead 110 delivers process gases from the gas supply 112 into the plasma generation zone 100a. Power from the array 120 of microwave sources 122 excites the process gas to produce a plasma in the plasma generation zone 100a. This plasma contains the desired radical species. The direction of flow of raw or unexcited process gas from the gas shower head 110 into the plasma generation zone 100a is in the upward direction in the view of
An advantage is that the plasma generation zone 100a and the workpiece process zone 100b are both within the same chamber (the chamber 100). This minimizes or nearly eliminates losses of radical species through recombination inherent in a conventional reactor chamber connected to a separate RPS chamber via a delivery tube.
In one embodiment, the gas shower head 110 may be implemented in the manner depicted in
In another embodiment depicted in
In one embodiment, an optional RF bias power generator 133 is coupled to the workpiece support stage 106 through an optional impedance match 135.
As shown in
In an alternative embodiment depicted in
A conventional reactor employing a remote plasma source (RPS) typically has a main chamber for processing a workpiece and a separate RPS chamber in which a remote plasma is generated. Radical species are drawn from the remote plasma and travel through a delivery tube from the separate RPS chamber to the main chamber. Significant losses of radical species occur due to recombination during transit along the length of the delivery tube. In the embodiments of
Another advantage is that the microwave source can produce a high plasma ion density across an extremely wide range of chamber pressures (e.g., 0.5 Torr to 10 Torr). One of the reasons for this is the high frequency of a microwave source (e.g., 2.45 GHz). In contrast, RPS chambers employing inexpensive plasma sources (e.g., inductively coupled plasma sources, or capacitively coupled plasma sources, for example) are confined to a relatively high range of chamber pressures (e.g., 2 Torr to 6 Torr). (A microwave RPS is not practical in many cases because of its high cost, e.g., on the order of tens of thousands of dollars.) The high chamber pressures (required by non-microwave sources) increase recombination losses of radical species and limit the ion density of the plasma in the RPS chamber. In the described embodiments, the cost of a microwave plasma source is radically reduced by employing an overhead array of extremely low cost microwave emitters, as depicted in
The reduction of recombination losses of radical species together with the higher plasma density achieved with a microwave source results in a yield of radical species of as much as four or more times that of conventional RPS systems. The above-described embodiments are useful in performing various plasma processes on a workpiece, including etch processes and chemical vapor deposition processes, in addition to chamber cleaning processes.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
