Coating for parts used in semiconductor processing chambers

Improved semiconductor processing chamber parts are provided. An improved part is made of an underlying part having both an intermediate coating and a surface layer applied thereto. The intermediate coating includes a plurality of layers each having a CTE intermediate the CTE of the underlying part and the CTE of the surface layer. The intermediate coating reduces the stress between any two layers, allowing use of underlying parts and surface layers having dissimilar CTEs. The universe of acceptable materials for use within a semiconductor processing chamber is expanded, as fewer selection criteria exist for a given layer.

FIELD OF THE INVENTION
 The present invention relates to an improved coating for parts used within
 semiconductor processing chambers, and more specifically to an
 intermediate coating that effectively adheres to both an underlying part
 and to a surface layer, despite differing thermal expansion rates between
 the part and the surface layer.
 BACKGROUND OF THE INVENTION
 During fabrication, a semiconductor device undergoes a variety of
 processing steps such as physical vapor deposition, chemical vapor
 deposition, etching and the like. Many of these processes, particularly
 etching, are performed within corrosive processing chamber environments
 (e.g., NF.sub.3, F, and/or O.sub.3 at elevated temperatures). These
 corrosive environments may attack and corrode the various parts within the
 processing chamber, such as heaters, electrical coils, chamber walls,
 clamp rings, collimators, shields, etc. Therefore, processing chamber
 parts must be resistant to corrosive processing environments, so as not to
 degrade and possibly contaminate a semiconductor device being processed
 within the chamber.
 Further, a number of corrosive fabrication processes involve the deposition
 of material layers on a semiconductor substrate. As material is deposited
 on a semiconductor substrate, it also deposits on processing chamber
 parts, and in turn may flake therefrom, contaminating semiconductor
 substrates processed therewithin. To prevent such contamination, chamber
 parts are periodically etched to remove deposited material. Thus, many
 processing chamber parts must be resistant to the deposited material's
 etchant, such that selective etching may occur.
 Accordingly, when constructing a part for use within a semiconductor
 processing chamber, the selection of materials that exhibit not only
 favorable surface characteristics (e.g., corrosion resistance, or desired
 etch properties), but also exhibit favorable bulk characteristics (e.g.,
 inexpensive, easily manufactured, good thermal conductivity, desirable
 magnetic properties, strength, etc.) presents a significant challenge. To
 broaden the universe of materials that may be used for processing chamber
 parts, coated parts are often employed wherein an underlying part is
 formed of a material that exhibits desired bulk characteristics, and a
 material that exhibits desired surface characteristics is applied thereto.
 While such coated parts somewhat ease the material selection process,
 coated parts can present a significant source of contamination when
 processing at elevated temperatures. Specifically, as the processing
 chamber thermally cycles (e.g., between various processing, cleaning or
 maintenance steps) so do the processing chamber's coated parts. If an
 underlying part and its coating differ in thermal coefficient of
 expansion, during thermal cycling the underlying part and the coating will
 expand and contract at different rates, resulting in stress therebetween
 (i.e., thermal stress). Such thermal stress can cause the coating material
 to flake from the underlying part, leaving the underlying part exposed to
 corrosive processing gases, and, moreover, introducing potential
 contaminants to the processing atmosphere. Thus, because of the need to
 match thermal coefficients of expansion, the practice of coating parts
 introduces additional constraints to the material selection process.
 A need therefore exists for processing chamber parts which satisfy both the
 bulk characteristics and the surface characteristics required for a given
 processing environment, without introducing undesirable particles thereto.
 SUMMARY OF THE INVENTION
 The present invention significantly expands the universe of acceptable
 materials for semiconductor processing chamber parts by providing an
 intermediate coating between the underlying part and the surface layer.
 Specifically, the intermediate coating of the present invention comprises
 a plurality of material layers each having a coefficient of thermal
 expansion (CTE) between that of the underlying part, and that of the
 surface layer. The part's overall CTE therefore gradually transitions from
 the CTE of the underlying part to the CTE of the surface layer, reducing
 thermally induced stress and contamination associated therewith. Each
 layer within the intermediate coating may reduce thermal stress by the
 same amount, or by a varying amount.
 The inventive intermediate coating enables an underlying part having both
 favorable bulk characteristics (e.g., inexpensive, easily manufactured,
 high thermal conductivity) and unfavorable surface characteristics (e.g.,
 poor etch properties, unsuitable corrosion resistance) to be employed
 within a corrosive fabrication process, and broadens the universe of
 acceptable surface layers that effectively adhere to the underlying part.
 The inventive intermediate coating particularly benefits heaters exposed
 to corrosive environments, and process kit parts exposed to deposition
 material etchants during cleaning. However, the inventive intermediate
 coating may be advantageously applied to any part that undergoes thermal
 cycling.
 Other objects, features and advantages of the present invention will become
 more fully apparent from the following detailed description of the
 preferred embodiments, the appended claims and the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1A is a side elevational view, generally representing a processing
 chamber part 11, configured in accordance with the present invention. The
 processing chamber part 11 comprises an underlying part 13 having a first
 CTE, an intermediate coating 15 having an intermediate CTE, and a surface
 layer 17 having a second CTE. The underlying part 13 exhibits one or more
 bulk characteristics which are favorable, and one or more surface
 characteristics which are unfavorable, and the surface layer 17 exhibits
 at least one surface characteristic which is favorable, and which is
 unfavorably possessed by the underlying layer 13 (e.g., the underlying
 part 13 is corrosive in the processing environment and the surface layer
 17 is not corrosive in the processing environment). The intermediate
 coating 15 is comprised of a plurality of intermediate layers 19a-e, as
 shown in FIG. 1A, each of which has an intermediate CTE. As used herein,
 an intermediate CTE refers to a CTE value that falls within the range
 between the CTE value of the underlying part 13 and the CTE value of the
 surface layer 17.
 Preferably the CTE of each intermediate layer 19a-e falls within the range
 defined by the CTE of the layers on either side thereof. The overall CTE
 of the processing chamber part 11, therefore gradually transitions between
 the first CTE and the second CTE, reducing the thermal stress that exists
 between any two adjacent layers, and reducing thermal stress induced
 particle generation.
 Preferably, each layer within the intermediate coating 15 exhibits a
 thermal stress of (1/n)(x), where n is the number of intermediate layers
 and x is the thermal stress that would occur if the underlying part 13 and
 the surface layer 17 were in direct contact, with no intermediate coating
 15 therebetween.
 FIG. 1B is a side elevational view representing the part of FIG. 1A at an
 elevated temperature. FIG. 1B is useful for understanding how the
 inventive processing chamber part 11 reduces the selection criteria for
 each material layer.
 For example, assume the underlying part 13 has a CTE of
 7.times.10.sup.-6/c, and the surface layer 17 has a CTE of
 1.times.10.sup.-6/c. The difference in CTE, in this example
 6.times.10.sup.-6/c, is proportional to the overall thermal stress that
 would exist between the underlying part 13 and the surface layer 17 if no
 intermediate coating 15 existed therebetween. Preferably, to gradually
 reduce the overall thermal stress, each intermediate layer 19a-e reduces
 the overall thermal stress by an equivalent amount, in this example by an
 amount proportional to 1.times.10.sup.-6/c. To achieve equal thermal
 stress reduction, intermediate layer 19a has a CTE of 6.times.10.sup.-6/c,
 intermediate layer 19b has a CTE of 5.times.10.sup.-6/c, intermediate
 layer 19c has a CTE of 4.times.10.sup.-6/c, intermediate layer 19d has a
 CTE of 3.times.10.sup.-6/c and intermediate layer 19e has a CTE of
 2.times.10.sup.-6/c. Accordingly, during thermal cycling, stress between
 any two adjacent layers is proportional to 1.times.10.sup.-6/c, 1/6 the
 stress that would exist in the absence of the intermediate coating 15.
 It will be understood the CTE values provided above are merely exemplary;
 materials with these exact CTE values may not exist. Similarly, any
 materials may be employed that have CTE values that result in an
 acceptable thermal stress value between adjacent layers; the differences
 in CTE values of adjacent layers provide above are merely exemplary.
 As the processing chamber part 11 thermally cycles the part's various
 layers expand and contract between the positions represented in FIGS. 1A
 and 1B. At elevated temperatures the expansion of each layer increases
 from the underlying part 13 to the surface layer 17, as shown in FIG. 1B.
 Thus, thermal stress (represented in FIG. 1B by opposing arrows S1 and S2)
 between adjacent layers, and the particles generated thereby, is
 significantly reduced with use of the present invention.
 Moreover, material selection is facilitated, as both the materials of the
 underlying part, and of the surface layer may be selected for their
 respective bulk, and surface characteristics, without regard for CTE
 matching. Thus, the present invention greatly increases the universe of
 acceptable materials for underlying parts and for surface layers, allowing
 semiconductor processing chamber parts to be easily tailored to meet the
 requirements of a given process. Similarly, with use of the present
 invention, materials for the intermediate layers 19a-e may be freely
 selected without regard for surface characteristics--the primary
 consideration for selection of an intermediate layer 19a-e being the
 desired CTE.
 The processing chamber part 11 represents any number of processing chamber
 parts (e.g., process kit parts, heaters, chamber walls). For example, the
 underlying part 13 may be a heating layer (e.g., comprising aluminum or
 aluminum nitride), and the surface layer 17 may be magnesium fluoride,
 iridium, aluminum trifluoride, etc., each of which exhibits a favorable
 surface characteristic when employed as a heater coating within a
 semiconductor device processing chamber. It will be understood that in
 most instances, the thickness of the intermediate coating, and preferably
 the thickness of each of the intermediate layers therein, is minimal
 (i.e., only as thick as is needed to effectively reduce thermal stress).
 Intermediate coatings of minimal thickness reduce attenuation of the
 underlying part's favorable characteristics (e.g., heat transfer) and
 reduce material costs. The intermediate layers 19a-e may be formed by
 conventional methods (e.g., chemical vapor deposition, physical vapor
 deposition, plasma spray, diffusion bonding) as will be apparent to those
 of ordinary skill in the art.
 FIG. 2 is a diagrammatic side elevational view of a processing chamber 21
 used for chemical vapor deposition. The processing chamber 21 is
 operatively coupled to a source of a first gas 23, and to a source of a
 second gas 25. The processing chamber 21 contains a number of exemplary
 parts which may benefit from the present invention, such as a chamber
 liner 27, an L-insert 29, an isolator 31, a clamp ring 33, and a heater
 35. Other types of processing chambers, such as physical vapor deposition,
 chemical etch or degassing chambers may contain a number of parts which
 also benefit from the present invention (e.g., RF coils, collimators, gas
 distribution plates, shields, or shutters).
 The foregoing description discloses only the preferred embodiments of the
 invention, modifications of the above disclosed apparatus and method which
 fall within the scope of the invention will be readily apparent to those
 of ordinary skill in the art. For instance, while the intermediate layers
 nearest the underlying part and/or nearest the surface layer may contain
 the underlying or surface material, other intermediate layers may not
 include the underlying and/or surface materials (i.e., may be exclusive of
 the underlying and/or surface materials). In fact, all of the intermediate
 layers may be exclusive of the underlying material and/or the surface
 material. Further, intermediate layers may be graded (i.e., have
 compositions which gradually transition from one material to the next) to
 further facilitate gradual transitioning of CTE. Accordingly, while the
 present invention has been disclosed in connection with the preferred
 embodiments thereof, it should be understood that other embodiments may
 fall within the spirit and scope of the invention, as defined by the
 following claims.