Patent Publication Number: US-6705246-B2

Title: RF powered plasma enhanced chemical vapor deposition reactor and methods of effecting plasma enhanced chemical vapor deposition

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This patent application is a Divisional Application of U.S. patent application Ser. No. 09/026,042, filed Feb. 19, 1998, now U.S. Pat. No. 6,395,128 B2, issued May 28, 2002. entitled “RF Powered Plasma Enhanced Chemical Vapor Deposition Reactor and Methods of Effecting Plasma Enhanced Chemical Vapor Deposition,” naming Sujit Sharan, Gurtej S. Sandhu, Paul Smith and Mei Chang as inventors, the disclosure of which is incorporated by reference. This application is related to U.S. Pat. No. 6,159,867, filed Aug. 19, 1999, which is a divisional application of U.S. Pat. No. 6,112,697, filed Feb. 19, 1998. 
    
    
     TECHNICAL FIELD 
     This invention relates to RF powered plasma enhanced chemical vapor deposition reactors and methods of effecting plasma enhanced chemical vapor deposition. 
     BACKGROUND OF THE INVENTION 
     Semiconductor processing often involves the deposition of films or layers over or on a semiconductor substrate surface which may or may not have other layers already formed thereon. One manner of effecting the deposition of such films or layers is through chemical vapor deposition (CVD). CVD involves a chemical reaction of vapor phase chemicals or reactants that contain the desired constituents to be deposited on the substrate or substrate surface. Reactant gases are introduced into a reaction chamber or reactor and are decomposed and reacted at a heated surface to form the desired film or layer. 
     There are three major CVD processes which exist and which may be utilized to form the desired films or layers. These are: atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), and plasma enhanced CVD (PECVD). The former two processes (APCVD and LPCVD) are characterized by their pressure regimes and typically use thermal energy as the energy input to effect desired chemical reactions. The latter process (PECVD) is characterized by its pressure regime and the method of energy input. 
     In PECVD systems, rather than relying on thermal energy to initiate and sustain chemical reactions, RF-induced glow discharge is used to transfer energy to the reactant gases. Such allows the substrate to remain at a lower temperature than the APCVD and LPCVD systems. Lower substrate temperatures are desirable in some instances because some substrates do not have the thermal stability to accept coating by the other methods. Other desirable characteristics include that deposition rates can be enhanced and films or layers with unique compositions and properties can be produced. Furthermore, PECVD processes and systems provide other advantages such as good adhesion, low pinhole density, good step coverage, adequate electrical properties, and compatibility with fine-line pattern transfer processes. 
     One problem, however, associated with deposition processing including PECVD processing stems from non-uniform film or layer coverage which can result especially in high aspect ratio topographies. For example, a problem known as “bread-loafing” or cusping can typically occur in deposition processing. Such normally involves undesirable non-uniform build-up of deposited material forming what appear as key hole spaces between features on a substrate. One prior art solution has been to conduct multiple depositions of very thin layers with intervening plasma etching treatments. The intervening plasma etching serves to remove or cut away the cusps to form a more uniformly applied layer. Thereafter, repeated depositions and etchings are conducted until the desired coverage is achieved. It is desirable to improve upon the quality of film or layer deposition in PECVD processes and reactors. 
     This invention grew out of concerns associated with improving PECVD processing systems and methods. This invention also grew out of concerns associated with improving the advantages and characteristics associated with PECVD systems, including those advantages and characteristics mentioned above. 
     SUMMARY OF THE INVENTION 
     Plasma enhanced chemical vapor deposition (PECVD) reactors and methods of effecting the same are described. In accordance with a preferred implementation, a reaction chamber includes first and second electrodes operably associated therewith. A single RF power generator is connected to an RF power splitter which splits the RF power and applies the split power to both the first and second electrodes. Preferably, power which is applied to both electrodes is in accordance with a power ratio as between electrodes which is other than a 1:1ratio. In accordance with one preferred aspect, the reaction chamber comprises part of a parallel plate PECVD system. In accordance with another preferred aspect, the reaction chamber comprises part of an inductive coil PECVD system. The power ratio is preferably adjustable and can be varied. One manner of effecting a power ratio adjustment is to vary respective electrode surface areas. Another manner of effecting the adjustment is to provide a power splitter which enables the output power thereof to be varied. PECVD processing methods are described as well. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
     FIG. 1 is a block diagram of a plasma enhanced chemical vapor deposition (PECVD) reactor system in accordance with preferred embodiments of the present invention. 
     FIG. 2 shows one implementation of one preferred PECVD reactor for use in the FIG. 1 system. 
     FIG. 3 shows another implementation of another preferred PECVD reactor for use in the FIG. 1 system. 
     FIG. 4 shows one implementation of one preferred power splitter for use in the FIG. 1 system. 
     FIG. 5 shows another implementation of another preferred power splitter for use in the FIG. 1 system. 
     FIG. 6 is a flow chart illustrating preferred processing methods for use in connection with the preferred embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 plasma enhanced chemical vapor deposition (PECVD) reactor system is shown in block diagram form generally at  10 . System  10  includes a gas supply unit  12 , a chemical vapor deposition reactor  14 , an RF power splitter  16  and an RF power generator  18 . 
     Gas supply unit  12  can supply one or more gaseous reactants into reactor  14  for processing in accordance with the invention. Typically, such systems use an RF-induced glow discharge to transfer energy into the reactant gases. Subsequently, free electrons are created within the discharge region which gain energy so that when they collide with gas molecules, gas-phase dissociation and ionization of the reactant gases occurs. Accordingly, energetic species are then absorbed on a workpiece or substrate. 
     PECVD reactor  14  defines a processing chamber or volume interiorly of which processing takes place in accordance with the invention. In a first preferred implementation, reactor  14  comprises a parallel plate reactor. Such parallel plate reactor can be configured to process only one semiconductor workpiece or wafer. Alternately, such reactor can be configured to process more than one semiconductor workpiece or wafer. In a second preferred implementation, reactor  14  comprises an inductive coil PECVD reactor. Both preferred implementations are discussed below in more detail in connection with FIGS. 2 and 3. 
     Referring still to FIG. 1, RF power splitter  16  in the illustrated and preferred embodiments splits or otherwise divides RF input power which is provided by RF power generator  18  into RF power components which are thereafter used to power separate reactor electrodes. In a preferred implementation, such power is split or divided in accordance with a selected power ratio which can be manipulated by an operator of the system. Preferably, such ratio is one which is other than a direct 1:1 ratio. Such split or divided power is subsequently applied via lines or terminals  15 ,  17  to individual electrodes comprising a part of reactor  14 , as will be described below. 
     Referring to FIG. 2, a PECVD reactor according to a first preferred implementation is set forth generally at  20 . Reactor  20  preferably comprises a capacitive parallel plate reactor which may or may not be configured to process more than one workpiece or wafer. Preferably, reactor  20  defines a processing chamber  21  which includes a first electrode  22  disposed internally thereof. Electrode  22  is configured for supporting at least one semiconductor workpiece in the form of semiconductor wafer W. The term “supporting” as such is used in this document and in connection with the first electrode in each of the embodiments is intended to mean holding or positioning one or more semiconductor workpieces in a desired orientation so that chemical vapor deposition can take place. Accordingly, semiconductor workpieces can be supported, held or otherwise positioned in orientations other than the shown horizontal position. Moreover, although the invention is discussed in the context of a system which includes only two electrodes, it is to be understood that the invented reactors and methods can find use in systems which are not necessarily limited to only two electrodes. First electrode  22  includes a first electrode surface area  24  upon which wafer W rests for processing in accordance with the invention. First electrode  22 , in the illustrated and preferred embodiment, is a susceptor which supports the workpiece. Processing chamber  21  includes a second electrode  26  which is disposed internally thereof. A gap exists between the electrodes such that the electrodes are suitably spaced from one another. In the illustrated and preferred embodiment, second electrode  26  constitutes a shower head electrode which is positioned operably adjacent the susceptor and configured to provide gaseous reactants into the chamber from gas supply unit  12  (FIG.  1 ). Gaseous reactants can, however, be introduced into the reactor in other ways. Preferably, second electrode  26  defines a second electrode surface area  28  which is different from and preferably smaller than first electrode surface area  24 . That is, first electrode surface area  24  is larger than the second electrode surface area  28 . Such surface area differential between the first and second electrodes enables an RF power differential to be developed as between the electrodes using only a single RF power source. Such will become apparent from the discussion below. 
     Referring still to FIG. 2, lines  15  and  17  are respectively operably connected to first and second electrodes  22 ,  26 . Such lines connect RF power generator  18  (FIG. 1) to the respective electrodes through RF power splitter  16  which, for the purpose of the ongoing discussion, is operatively interposed between the RF power generator and both the susceptor and the shower head electrodes. Preferably, RF power generator  18  comprises a single generator power source which is operatively associated with the processing chamber and configured to provide RF power to the RF power splitter which, in turn, provides RF power to both the susceptor and the shower head according to a selected power ratio which is discussed below in more detail. Such represents a novel departure from prior PECVD reactors wherein only the shower head electrode was powered by an RF power source with the susceptor electrode being grounded. The illustrated single RF power generator is preferably configured to provide RF power to the electrodes which is effective to both develop a plasma processing environment within the processing chamber and provide a desired bias relative to the semiconductor workpiece. For example, maintaining the electrodes at the preferred power differential facilitates acceleration of ions or ionic species toward the subject workpiece or wafer which enhances conformal coverage, particularly in high aspect ratio topographies. Furthermore, greater uniformity in film or layer composition, as well as greater film or layer purity levels are possible. 
     Referring to FIG. 3, and in accordance with another preferred implementation of the invention, a different type of PECVD reactor  30  is set forth. Such reactor comprises an inductive coil PECVD reactor. Reactor  30  comprises a processing chamber  31  interiorly of which chemical vapor deposition processing can take place in accordance with the invention. A first electrode  32  is disposed internally of the reactor and is configured for supporting at least one semiconductor workpiece, such as wafer W thereon. First electrode  32  is powered by the preferred single RF power generator  18  (FIG.  1 ). It is possible for more than one wafer to be processed in accordance with the invention. A second electrode  34  is provided externally of processing chamber  31  and comprises a plurality of coils which are powered by the same preferred single RF power generator. 
     Referring to both FIGS. 2 and 3, such comprise PECVD reactors which include respective electrodes both of which are powered by a single RF power generator or supply. According to a first implementation, both electrodes are disposed internally of the processing chamber (FIG.  2 ). According to second preferred implementation, at least one of the electrodes is disposed externally of the processing chamber (FIG.  3 ). Both electrodes in both preferred implementations are powered from and by a single RF powered generator, such as generator  18  in FIG.  1 . As mentioned above, this represents a novel departure from previous PECVD reactors where both electrodes were not powered with RF power from a common, single RF power source. 
     Referring to FIG. 4, a preferred RF power splitter is set forth generally at  36 . Power splitter  36  in the illustrated and preferred embodiment comprises a transformer  38  which includes an input side or primary windings  40  and an output side or secondary windings  42 . Input side  40  is operatively coupled or connected to RF power generator  18  (FIG. 1) via a coaxial cable  44  and receives power generated thereby. Output side  42  includes at least two output terminals  15 ,  17  which are operatively coupled or connected to respective first and second electrodes  22 ,  26  (in the FIG. 2 PECVD reactor) or first and second electrodes  32 ,  34  (in the FIG. 3 PECVD reactor). In a preferred implementation, the output side has no more than two terminals, and the first and second electrodes constitute the only processing chamber electrodes which are powered thereby. Power splitter  36  splits input power provided by power generator  18  into first and second power components which are thereafter provided to the respective electrodes. The output side of the preferred transformer provides power to each of the first and second electrodes in accordance with a selected power ratio which is discussed below. A suitable matching network  46  is provided for impedance matching purposes. Such networks typically include various capacitative and inductive components which are configured for impedance matching. Such are represented in block diagram form in box  46 . 
     In accordance with a preferred aspect of the invention, RF power splitter  36  comprises a center tapped transformer in which the output power provided to the respective first and second electrodes is substantially equal in magnitude. Such is desirable when power splitter  36  is used in connection with the PECVD reactor of FIG.  2 . In such circumstances, it has been found that the ratio of power which is applied to the electrodes is related to surface areas  24 ,  28  of electrodes  22 ,  26 . Hence, by changing or manipulating the subject surface areas, one can manipulate or select the power ratio and affect the magnitudes of the first and second power components which are “seen” by the respective electrodes to which such power components are applied. In the illustrated and preferred embodiment, such surface areas are different from one another, with the susceptor surface area being larger than the shower head surface area. Such enables a power differential to be developed according to a definable relationship. Such relationship consists of a predefined relative magnitude which is directly proportional to the inverse ratio of the 4th power of the areas of the electrodes. Put another way, by varying the relative surface area ratios as between the susceptor and shower head, a variation in power applied thereto can be effectuated. In the illustrated and preferred embodiment, second electrode or shower head  26  has a surface area which is less than or smaller than the surface area of the first electrode or susceptor  22 . Such results in a higher magnitude of power being applied to the shower head than is applied to the susceptor. This advantageously allows deposition of reactants introduced into chamber  21  in a preferred manner by causing highly energetic species to be drawn toward and in the direction of the electrode supporting the workpiece. 
     Referring to FIG. 5, an alternate preferred power splitter is set forth generally at  36   a . Such alternate preferred power splitter enables the desired power differential to be developed without regard to and independently of the surface area ratios between the subject electrodes, whether such electrodes be those associated with the FIG. 2 reactor or the FIG. 3 reactor. Like numbers from the first described power splitter are utilized where appropriate, with differences being indicated with the suffix “a” or with different numerals. Accordingly, power splitter  36   a  comprises an input side  40  which is operatively coupled with RF generator  18  (FIG. 1) and an output side  42   a  which is operatively coupled with one of the preferred reactors  20 ,  30 . Such enables, but does not require reactor  20  of FIG. 2 to have a susceptor electrode and a shower head electrode with respective surface areas which are more nearly equal. Power splitter  36   a  advantageously allows the selected power ratio to be adjusted in a manner which varies the power supplied to the electrodes. Accordingly, and in the illustrated and preferred embodiment, the RF power splitter comprises a transformer having a plurality of secondary windings  42   a . Such are desirably variably groundable as is indicated at  48 . 
     Referring still to FIG.  5  and for illustrative purposes only, output side  42   a  is shown as comprising nine windings. By selectively grounding different windings or coils, different ratios of power are provided to the shower head and susceptor electrodes. More specifically for example, if the number  2  coil or winding is grounded as shown, then the first electrode, either electrode  22  (FIG. 2) or  32  (FIG. 3) receives two ninths ({fraction (2/9)}) or 22.2% of the input power from the power generator. Accordingly, the second electrode, either electrode  26  (FIG. 2) or  34  (FIG. 3) receives seven ninths ({fraction (7/9)}) or 77.8% of the input power. Relatedly, if the number  7  coil or winding is grounded, the distribution in of power is reversed, i.e. the first electrode receives seven ninths ({fraction (7/9)}) of the input power and the second electrode receives two ninths ({fraction (2/9)}) of the input power. As such, the provision of power to the preferred electrodes can be varied to accommodate different processing regimes. In the illustrated and preferred FIG. 5 embodiment, power splitter  36   a  is able to be adjusted by an end user for varying the selected power ratio to accommodate different processing regimes. Such processing regimes preferably provide a greater quanta of power to the second electrode rather than the first electrode. Alternately, the power provided to the electrode which is closest in proximity to the semiconductor workpiece is less than the power provided to the electrode which is spaced apart from such workpiece. 
     Accordingly, two separate and preferred power splitters have been described. The first of which (FIG. 4) is advantageous for producing output power having magnitudes which are substantially the same. Such power splitter is suited for use in reactors, such as reactor  20  of FIG. 2 in which the ultimate magnitude of power supplied to the illustrated electrodes can be adjusted by varying the surface area ratios of the subject electrodes. Such power splitter may also be used in connection with reactor  30 . Alternately, and equally as preferred, a power splitter  36   a  (FIG. 5) allows for the output power to be variably adjusted to a selected power ratio which is suitable for use in reactors, such as reactor  20  of FIG. 2, in which electrodes do not have or are not required to have a meaningful variance between the electrode surface areas. Additionally, such power splitter can be and preferably is utilized in connection with reactor  30  of FIG.  3 . 
     Referring to FIG. 6, a representative flow chart of a preferred method of processing semiconductor workpieces in connection with the above described reactors is set forth generally at  100 . The preferred methodology involves first at step  110  placing a semiconductor workpiece in a selected one of the above-described PECVD reactors. According to a preferred implementation, a susceptor is provided for supporting the workpiece internally of the processing chamber. In accordance with the FIG. 2 embodiment, a shower head electrode  26  is provided operably adjacent the susceptor and is configured for providing gaseous reactants into chamber. According to the FIG. 3 embodiment, at least one of the reactor electrodes is disposed externally of the chamber. At step  112 , gaseous reactants are provided into the reactor chamber whereupon, at step  114 , RF power from the preferred single or common RF power source is provided. At step  116 , the provided RF power is split into first and second power components which are selectively provided to the respective electrodes discussed above. For example, a first power component at step  118  is applied to a first of the electrodes. At step  120 , a second of the power components is applied to a second of the electrodes. Preferably, the applied power components are different from one another with such difference stemming from either a variation in electrode surface areas (FIG. 2) or a variably selectable grounding of the secondary or output side  42   a  (FIG. 5) of power splitter  36   a . According to a preferred implementation, a transformer output coil, other than the center coil, can be selectively grounded for varying the relative magnitudes of the power components. Such is indicated as an optional step  122  wherein an individual user may select a desired power ratio as between reactor electrodes. At processing step  124 , and with the desired power ratio being applied to the selected electrodes, the semiconductor workpiece is processed to effect chemical vapor deposition thereupon. At step  126 , processing is complete and a next workpiece may be processed in accordance with the above description. 
     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.