Plasma Processing Tools Dual-Source Plasma Etchers, Dual-Source Plasma Etching Methods, and Methods of Forming Planar Coil Dual-Source Plasma Etchers

The invention pertains to plasma processing tools, dual-source plasma etchers, dual-source plasma etching methods, and methods of forming planar coil dual-source plasma etchers.

Semiconductor processing typically involves depositing one or more layers of material and subsequently etching such layers to form a substrate feature. It is highly desirable to form uniform features over the entire surface of a semiconductor wafer. Yet, non-uniformities can arise based on the location of the feature relative to the wafer. For example, one type of semiconductor feature is a contact opening. Contact openings are typically etched through a dielectric material such as borophosphosilicate glass (BPSG). It has been observed that contact openings formed at or near the center of a wafer can have a different profile from contact openings formed away from the center of a wafer, e.g. at or near the wafer's periphery. Such non-uniformities are undesirable as they impart a degree of unpredictability in the finished integrated circuit.

This invention arose out of concerns associated with improving the uniformity with which substrate features, and in particular contact openings, are formed over a wafer. In particular, this invention arose out of concerns associated with improving dual-source plasma etchers and methods of using the same.

Plasma processing tools, dual-source plasma etchers, and etching methods are described. In one embodiment, a processing chamber is provided having an interior base and an interior sidewall joined with the base. A generally planar inductive source is mounted proximate the chamber. A dielectric liner is disposed within the chamber over the interior sidewall with the liner being received over less than an entirety of the interior sidewall. In a preferred embodiment, the interior sidewall has a groundable portion and the dielectric liner has a passageway positioned to expose the groundable interior sidewall portion. Subsequently, a plasma developed within the chamber is disposed along a grounding path which extends to the exposed interior sidewall. In another preferred embodiment, the dielectric liner is removably mounted within the processing chamber.

Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

FIG. 1 is a schematic view of a plasma processing tool in the form of a dual-source plasma etcher in accordance with the prior art.

FIG. 2 is a side sectional view of a portion of a sidewall of a dual-source plasma etcher in accordance with one embodiment of the invention.

FIG. 3 is a view of the FIG. 2 sidewall at a processing step which is different from that which is shown in FIG. 2.

FIG. 4 is a perspective view of a portion of a dual-source plasma etcher in accordance with one embodiment of the invention, with a portion broken away for clarity.

FIG. 5 is a schematic view of a portion of the FIG. 4 etcher.

FIG. 6 is a perspective view of a dielectric liner suitable for use in the FIG. 4 etcher.

FIG. 7 is a view of the FIG. 6 dielectric liner having been processed in accordance with one aspect of the invention.

FIG. 8 is a view of a dielectric liner in accordance with an alternate embodiment of the present invention.

FIG. 9 is a view of a dielectric liner in accordance with an alternate embodiment of the present invention.

FIG. 10 is a view of the FIG. 5 etcher, and depicts a plasma which is developed therein, in accordance with one embodiment of the invention.

FIG. 11 is a view of a pair of etched features which are spaced apart over a semiconductor wafer in accordance with prior art methods.

FIG. 12 is a view of a pair of etched features which are spaced apart over a semiconductor wafer in accordance with one aspect of the invention.

FIG. 13 is a view of another pair of etched features which are spaced apart over a semiconductor wafer in accordance with one aspect of the invention.

FIG. 14 is a side sectional view of a portion of a sidewall of a dual-source plasma etcher in accordance with one embodiment of the invention.

FIG. 15 is a side sectional view of a portion of a sidewall of a dual-source plasma etcher in accordance with another embodiment of the invention.

This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws "to promote the progress of science and useful arts" (Article 1, Section 8).

Referring to FIG. 1, a known processing chamber is shown generally at 20 and comprises a plasma processing tool which, in one embodiment can function as a dual-source plasma etcher, and in another embodiment can function as a deposition tool under RF bias conditions. Chamber 20 includes an interior base 22, a sidewall 24 joined with interior base 22, and a top 26. A wafer support 28 is provided and is configured to support a semiconductor wafer during processing within the chamber. An inductive source 30 is provided, generally in the form of a planar inductive coil which is mounted proximate or over chamber 20. Typically, top 26 will include a dielectric window proximate coil 30 to facilitate inductive coupling with a plasma developed within the chamber. Inductive source 30 is typically powered by an RF power source, and wafer support 28 is typically powered by another power source such as a DC, AC or RF power source. Accordingly, processing chamber 20 is configured into a dual-source, plasma etching configuration. During operation, a portion of an interior surface of the chamber can be grounded. Dual-source plasma etchers and the operation thereof are described in a text entitled Principles of Plasma Discharges and Materials Processing, authored by Lieberman and Lichtenberg.

One problem which has arisen with chambers such as the FIG. 1 chamber, concerns non-uniformity in etching as described in the "Background of the Invention" section above. One source of the problem is believed to be associated with different voltages which can be present within a plasma during etching. Specifically, when a plasma is developed within chamber 20, the plasma can be, at different locations within the chamber, subjected to different voltages. These different voltages are believed to cause non-uniformity in etching across the surface of a wafer because of the impact the voltages have on plasma constituents. Further, in some etch processing, it is desired to ground a portion of wafer support 28. Thus, grounding lines which are established between a wafer supported by wafer support 28 and the ground have different lengths. For example, grounding lines originating from the periphery of the wafer are generally shorter than grounding lines which originate at or near the center of the wafer. The grounding line length is believed to have an adverse impact on etch uniformity across the wafer.

Another problem associated with chambers such as the FIG. 1 chamber are that internal chamber components can be undesirably etched during wafer etching. Specifically, some chambers can include components such as chamber wall heaters and the like. As a result of the undesirable etching, component lifetimes can be reduced thereby requiring more frequent replacement and increasing the cost of maintaining the processing chamber.

Referring to FIG. 2, a portion of a processing chamber sidewall in accordance with one embodiment of the invention is shown generally at 24a. Like numerals from the above-described embodiment have been utilized where appropriate, with differences being indicated by the suffix "a".

A dielectric liner 32 is provided within chamber 20 and covers at least a portion of interior sidewall 24a. Sidewall 24a is preferably configured to be grounded during plasma etching operations as will become apparent below. In a preferred embodiment, dielectric liner 32 comprises an anodized layer of material, formed through conventional anodization techniques. An exemplary dielectric material is Al.sub.2 O.sub.3. Preferably, anodized layer 32 is formed to have a thickness t of no less than about 5 mils, and is received over less than an entirety of interior sidewall 24a. Such is more apparent in FIG. 3 where passageways 34 are shown to expose a portion of interior sidewall 24a. The passageways are preferably positioned to expose one or more groundable portions of sidewall 24a. During operation, passageways 34 provide a grounding path to the grounded sidewall portions for plasma which is generated within the chamber.

Layer 32 can be provided or formed over sidewall 24a in any suitable way. In one aspect, layer 32 is first formed over the interior sidewall to define a dielectric liner body. Thereafter, portions of the dielectric liner body are removed sufficiently to provide a plurality of passageways 34. In a most preferred embodiment, passageways 34 are provided or formed to extend through and be surrounded or enclosed by material of the dielectric liner body. Accordingly, such passageways form a plurality of holes or openings received by the dielectric liner proximate the groundable portion of the interior sidewall. In another preferred embodiment, passageways or openings 34 are provided such that the dielectric liner or liner body is disposed over greater than about 10% of the surface area of interior sidewall 24a.

In another preferred embodiment, grounding paths are determined and appropriate grounding points are selected. Material is then selected for the groundable portion of the interior sidewall. Selection of the material for the groundable interior sidewall portion can be tailored to reduce formation of non-volatile byproducts. In this manner, openings in the dielectric liner or cover can outwardly expose the material comprising the groundable sidewall portion(s). Exemplary materials of choice for the groundable sidewall portion are silicon carbide or silicon to reduce formation of undesirable byproducts. Materials can also be selected to react with the various etch chemistries to form volatile products.

Referring to FIG. 4, another processing chamber embodiment is set forth. There, a portion of a dual-source plasma etcher includes a processing chamber 20b. Like numerals from the above-described embodiment have been utilized where appropriate, with differences being indicated by the suffix "b". The illustrated etcher is the TCP 9100 high-density oxide etch system, which is available through Lam Research Corporation of Fremont, Calif. A portion of chamber 20b has been broken away to show a dielectric liner or cover 32b which is disposed over the entirety of interior sidewall 24b. Such configuration has led to some of the above-described etch non-uniformities which are addressed and improved upon by certain aspects of the invention.

Referring to FIG. 5, a plurality of passageways or openings 34b are formed or otherwise provided within dielectric liner body 32b. Such openings are positioned to preferably expose a gas plasma developed therewithin to groundable portions of interior sidewall 24b. Doing so has been observed to improve etch uniformity across a wafer. Such is illustrated in FIG. 10 where a portion of a gas plasma, indicated by the stippled shading, is seen to electrically contact a grounded portion of sidewall 24b.

Referring to FIG. 6, and in accordance with one aspect of the invention, dielectric liner body 32b is removably mountable within chamber 20b and comprises a generally frustum-shaped interior surface 36. The liner body is preferably formed, in this example, away from chamber 20 and separately provided with passageways 34b as shown in FIG. 7. To form the passageways, portions of liner body 32b are removed. In this example, passageways 34b comprise a plurality of holes which extend through liner body 32b and have a generally elongated shape in a direction generally parallel with interior surface 36. Passageways or holes 34b can, however, have any desired shape, number, and/or orientation.

Referring to FIGS. 8 and 9, two different dielectric liner bodies, in accordance with alternate embodiments of the invention, are shown generally at 32c and 32d respectively. Like numerals from the above-described embodiment have been utilized where appropriate with differences being indicated by the suffixes "c" and "d", respectively.

Dielectric liner body 32c (FIG. 8) is configured to be mounted over at least a bottommost portion of interior sidewall 24b (FIG. 4). Accordingly, a grounding path would be provided by a passageway which is disposed over or above dielectric liner body 32c when mounted in processing chamber 20b (FIG. 4). In this example, the passageway defining the grounding path is neither surrounded by nor enclosed by dielectric liner material.

Dielectric liner body 32d (FIG. 9) is configured to be mounted over at least an uppermost portion of interior sidewall 24b (FIG. 4). Accordingly, a grounding path would be provided by a passageway which is disposed below or under dielectric liner body 32d when mounted in processing chamber 20b (FIG. 4). In this example, the passageway defining the grounding path is neither surrounded by nor enclosed by dielectric liner material.

Referring to FIGS. 14 and 15, two alternate exemplary embodiments are shown. These embodiments can provide plasma processing tools having chambers which can be specifically engineered to achieve desired grounding paths for the plasma as described above, and which are formed from material which can be selected to reduce, or eliminate undesirable formation of non-volatile by-products. In addition, the various described tool embodiments can be less expensive to build and maintain than currently available tools.

Preliminarily, by determining the location or locations of the grounding paths or points, one can take measures to ensure that grounding takes place through these paths or points. Materials can then be selected for the grounding surfaces which are selected to reduce formation of non-volatile by-products.

FIGS. 14 and 15 show portions of an interior groundable chamber surface at 38, 38a respectively. Surfaces 38, 38a are configured for grounding during operation of the processing tool of which they are a part. Each surface generally has a surface area. In one embodiment, at least one grounding electrode 40, 40a respectively, is disposed over and in operative contact with surface 38, 38a respectively. More preferably, a plurality of grounding electrodes are provided and discretely positioned over surfaces 38, 38a respectively. Preferably, during operation of the processing tool, a grounding path is established through one or more of the electrodes. The illustrated and preferred grounding electrodes cover less than an entirety of the surface area of surfaces 38, 38a. For example, each illustrated grounding electrode 40, 40a has a small gap between it and a next adjacent grounding electrode. Each gap potentially leaves a portion surface 38, 38a, e.g. surface portions 42, 42a respectively, exposed. A dielectric covering 44, 44a is provided and disposed over the remaining portions of surface 38, 38a, i.e. portions 42, 42a. Preferably, a plurality of dielectric coverings are provided and discretely positioned over the surface area. The dielectric covering ensures that the risk of exposure of surfaces 38, 38a to the processing environment inside of the chamber is reduced, thereby avoiding corrosion and the like.

In a preferred embodiment, one of the grounding electrode and the dielectric covering overlaps the other of the grounding electrode and the dielectric covering. For example, in FIG. 14, portions of dielectric coverings 44 overlap with their associated grounding electrodes 40. Here, the grounding electrodes are simply mounted on or over surface 38, with dielectric coverings 44 being mounted on or over electrodes 40. In FIG. 15, portions of grounding electrodes 40a overlap with their associated dielectric coverings. Here, portions of surface 38a can be removed to form slots within which dielectric material can be deposited.

Exemplary materials for grounding electrodes 40, 40a include silicon carbide or silicon. Other materials can be utilized, and can be specifically selected to reduce the possibilities of undesirable reactions with chamber reactants during processing. One advantage provided by these embodiments are that certain materials of choice for the grounding electrodes are much less expensive, and are more easily produced when they are produced in smaller pieces. In this way, and in some applications, a grounding electrode "mosaic" can be assembled from the individual discrete grounding electrodes.

Alternately considered, a grounding node is provided and disposed over and in operative contact with surfaces 38, 38a respectively. Respective plasma grounding paths can be established during operation through the grounding nodes. Exemplary grounding node portions are respectively provided by electrodes 40, 40a in FIGS. 14 and 15. The illustrated grounding nodes each have at least one, and more likely a plurality of openings over a portion of the surface area of surfaces 38, 38a respectively. Exemplary surface area portions are shown at 42, 42a respectively. Preferably, at least one dielectric covering, and more likely a plurality of dielectric coverings are disposed over surface area portions 42, 42a. The dielectric coverings are preferably discretely positioned over surfaces 38, 38a. In one embodiment (FIG. 14), a portion of at least one grounding node is disposed intermediate the dielectric covering and groundable surface 38. In this example, a region of overlap is defined between each dielectric covering 44 and its associated intermediately-disposed grounding node portion. In another embodiment (FIG. 15), dielectric coverings 44a are received within the interior conductive groundable surface 38a. In another embodiment (FIG. 15), the grounding node comprises grounding node portions which are received over both the groundable surface 38a and the dielectric covering 44a.

The percentage of surface area coverage of the dielectric covering can be quite small as compared with the overall surface area available, or, the surface area covered by electrodes 40, 40a respectively. For example, surface area percentages as small as 0.01% can be covered by the dielectric material.

Referring to FIG. 11, two portions of a semiconductive wafer 100 are shown generally at 102, 104 and constitute portions of the same wafer which are spaced apart over the wafer body in accordance with the prior art. For example, portion 102 constitutes a portion at or near the edge of a wafer, while portion 104 constitutes a portion at or near the center of the wafer. Utilizing the above-described TCP 9100 high-density oxide etch system with an unmodified dielectric liner body, i.e. one that covers an entirety of the chamber's sidewall, a pair of substrate features 106, 108 were etched through an oxide layer 110. As can be observed, such features are non-uniform in taper, appearance, and configuration. Such is undesirable for all of the reasons mentioned above.

Referring to FIGS. 12 and 13, a pair of similarly spaced-apart substrate features 106a, 108a, and 106b, 108b, respectively, are shown. Such constitute features which were etched using the above-described TCP 9100 high-density oxide etch system with a modified dielectric liner body, i.e. one that covers less than an entirety of the chamber's sidewall. Features were etched near the edge of a wafer (106a, 106b), and near the center of the wafer (108a, 108b). Such features are generally uniform in taper, appearance, and configuration. By providing a grounding path for a gas plasma along one or more passageways as described above, etch non-uniformities can be reduced, if not eliminated, thereby increasing the quality of resultant semiconductor devices. In addition, advantages are gained in that internal chamber components can be protected by a dielectric liner or cover, while rendering desirable etch uniformities. And, while the invention has been described in the context of providing enhanced etch uniformities, uniformities in depositions can also be attained utilizing the inventive plasma processing tools and methods described above. More specifically, depositions conducted under RF bias conditions can have increased uniformities.

In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.