RF powered plasma enhanced chemical vapor deposition reactor and methods

[0002] This is a Continuation of U.S. patent application Ser. No. 09/026,566, filed Feb. 19, 1998, now U.S. Pat. No. 6,112,697 and titled “RF Powered Plasma Enhanced Chemical Vapor Deposition Reactor and Methods.”

[0003] This invention relates to RF powered plasma enhanced chemical vapor deposition reactors and methods of effecting plasma enhanced chemical vapor deposition.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] Another problem associated with PECVD reactors stems from the use of the high frequency RF power which is utilized to develop the desired plasma environment. Such high frequency RF power typically develops a high frequency power loop which tends to interfere in an undesirable way with the operation of other reactor components. For example, often times a thermocouple link is established with one or more of the electrodes to monitor the subject electrode temperature during processing operations. The high frequency loop can and often does render the readings taken by the thermocouple link inaccurate. Thus, it is desirable to improve upon the manner in which high frequency RF power is utilized in PECVD reactors.

[0009] 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.

[0010] Plasma enhanced chemical vapor deposition (PECVD) reactors and methods of effecting the same are described. In a preferred implementation, a PECVD reactor includes a processing chamber having a first electrode therewithin. A second electrode is disposed within the chamber and is configured for supporting at least one semiconductor workpiece for processing. A first RF power source delivers RF power of a first frequency to the first electrode. A second RF power source delivers RF power of a second frequency to the second electrode. Preferably the first and second frequencies are different from one another, and even more preferably, the first frequency is greater than the second frequency. The preferred reactor includes a thermocouple which provides temperature information relative to one of the electrodes. According to a preferred implementation, the power loop developed by the first RF power source is grounded interiorly of the chamber in a manner which reduces if not eliminates interference with other reactor components, including the thermocouple.

[0011] Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

[0012] FIG. 1 is a view of a plasma enhanced chemical vapor deposition reactor constructed according to a preferred embodiment of the present invention.

[0013] FIG. 2 is a fragmentary portion of the FIG. 1 reactor which illustrates an alternate grounding configuration.

[0014] FIG. 3 is a flow chart illustrating a preferred processing method used in connection with the FIG. 1 embodiment.

[0015] 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).

[0016] Referring to FIG. 1, a plasma enhanced chemical vapor deposition (PECVD) reactor is shown generally at 10. Reactor 10 includes a reactor chamber 12 having an interior surface 14 which defines a processing chamber in which processing takes place in accordance with the invention. In accordance with a preferred aspect of the invention, at least a portion of interior surface 14 is grounded. Chamber 12 includes a first electrode 16 and a second electrode 18. Preferably, reactor 10 is a parallel plate reactor in which both the first and second electrodes are located or disposed within chamber 12. In the illustrated and preferred embodiment, first electrode 16 comprises a shower head electrode which is configured to provide gaseous reactants into the processing chamber and second electrode 18 is configured for supporting at least one semiconductor workpiece, such as wafer W. The term “supporting” as such is used in this document and in connection with the second electrode 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 reactor and methods can find use in systems which are not necessarily limited to only two electrodes.

[0017] A gas source unit 20 is operably connected with reactor 10 and includes a plurality of gas sources 22 for providing gaseous reactants to electrode 16 and into the interior of reactor chamber 12. A power/temperature control unit is shown generally at 24. The components of unit 24 may be separate units or may be contained within a single control unit. Accordingly, such components include a first RF power source 26, a thermocouple or temperature sensor 28, and a second RF power source 32. First RF power source 26 is operably associated with chamber 12 and connected with the first electrode 16 via a first conductive line 27 to deliver RF power of a first frequency thereto. Preferably, the first frequency is a high frequency in the range of between 2-50 MHz. Power source 26 develops, during operation, a first or high frequency power loop a portion of which extends or passes through the reactor chamber and is responsible for developing the plasma environment in which the preferred processing takes place. More specifically, power source 26 develops a high frequency power loop which flows from line 27, through electrode 16, across the gap between electrodes 16 and 18, and through electrode 18. Typically, in the past, the high frequency loop has been grounded through a line which exits an opening, such as opening 13 which is shared with other component connective lines. Although such other lines are typically insulated, the high frequency line has still created undesirable interference and crosstalk conditions.

[0018] Thermocouple 28 is operably connected with second electrode 18 via a thermocouple line or temperature sensor line 30 which extends through opening or conduit 13 in reaction chamber 12. The thermocouple or temperature sensor is configured to provide temperature information relative to the second electrode. Such enables the temperature of electrode 18 to be monitored and conventionally controlled by means not shown during semiconductor processing. Opening or conduit 13 defines a path from inside the reactor to outside the reactor.

[0019] Power/temperature control unit 24 also includes a second RF power source 32. Such is associated with chamber 12 and operatively connected with second electrode 18 to deliver RF power of a second frequency, which is preferably lower than the frequency delivered by first power source 26. Preferably, the frequency range of power source 32 is 100-1000 kHz. Accordingly, the frequency or frequencies of delivered or developed RF power from first RF power source 26 is (are) characterized as preferably higher than the frequency or frequencies delivered or developed by second or low frequency power source 32. In the illustrated and preferred embodiment, low frequency power source 32 is connected with second electrode 18 by an RF power line, low frequency power line or second conductive line 34 which extends through opening or conduit 13 and connects with second electrode 18.

[0020] The above represents a novel departure from conventional reactors and is one which enables PECVD to take place in a manner which can provide deposited films or layers with improved properties over those films or layers which are deposited using conventional reactors. 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. In a preferred implementation, the first and second electrodes constitute the only electrodes which are capable of being powered.

[0021] Referring still to FIG. 1, chamber interior 14 includes a side wall at least a portion of which is grounded as shown. Such desirably enables the high frequency RF power loop which is developed or produced by RF power source 26 to be grounded internally of the chamber. Such reduces interference between the high frequency energy generated thereby and either of the thermocouple connective line 30 or the low frequency power line 34. Alternately and with reference to FIG. 2, a fragmentary portion of reactor chamber 12 is shown. Such alternately enables the high frequency power loop to be grounded externally of the reactor chamber. Accordingly, a grounding path is provided which extends through the reactor side wall to a point externally thereof.

[0022] In the FIG. 1 embodiment, a grounding point for the high frequency power loop is provided which is remote from conductive line 34 and thermocouple connective line 30. Preferably the grounding point is inside the reactor chamber and comprises the grounded portion of the chamber interior. According to a preferred aspect of the invention, a grounding path is provided and leads to and defines in part the grounding point. Such is illustrated generally at 36. In the illustrated and preferred embodiment, grounding path 36 includes a portion of the low frequency power line which is disposed on the inside of the chamber. Accordingly, the grounding path grounds or provides a mechanism by which the high frequency power loop can be grounded through the low frequency line from a point taken within the reactor. According to a preferred implementation, grounding path 36 includes a bypass or bandpass filter 38 which is configured to pass only high frequencies, such as those generated or produced by high frequency power source 26. Accordingly, such provides a mechanism by which the high frequency loop can be grounded without affecting the operation of low frequency power source 32 or power produced thereby.

[0023] Alternately, as mentioned above, other manners of grounding the high frequency power loop can be utilized. For example, the high frequency power loop may be grounded to an interior portion of the reaction chamber through a suitable grounding wire which is connected directly with the grounded chamber interior portion. By grounding the high frequency RF power loop as just described, undesirable effects associated with interference between the RF frequency developed by power source 26 and the thermocouple line 30 are avoided. Furthermore, the high frequency loop can be grounded at a point or location which is remote from power source 26 and external to the reaction chamber, as shown in FIG. 2. Accordingly, thermocouple 28 provides more accurate temperature information relative to the second electrode or susceptor electrode 18 and crosstalk between the low and high frequency lines is desirably reduced if not eliminated.

[0024] In accordance with the preferred parallel plate PECVD reactor, and referring now to FIGS. 1-3, a preferred semiconductor processing method is set forth in a flow diagram indicated generally at 100 in FIG. 3. Accordingly, at step 110 a semiconductor workpiece such as wafer W (FIG. 1) is placed in reactor 10 and preferably upon second or susceptor electrode 18 as shown. The susceptor electrode supports the workpiece interiorly of the preferred reactor for subsequent processing. As pointed out above, other manners of supporting the workpiece or wafer are possible. Gaseous reactants are introduced into the reactor at step 112 preferably through the shower head electrode 16. At step 114, the reactants are exposed to at least two different RF power frequencies to a degree which is sufficient to effect deposition of a reactant product over the semiconductor workpiece. In accordance with a preferred aspect of the invention, RF power of a first frequency is applied to shower head electrode 16 from high frequency RF power source 26. Additionally, a second frequency of RF power is applied to susceptor electrode 18 which supports semiconductor workpiece W. In accordance with a preferred implementation and at step 116, a grounding path is provided which leads to and defines a grounding point for the high frequency power loop developed or produced by first RF power source 26. The grounding point is preferably located at a remote location from other component connective lines. Such may be in the chamber interior, such as on a portion of the chamber interior side wall which is maintained at ground. Alternately, such may be on the chamber exterior or at a point outside of the chamber.

[0025] In accordance with a preferred aspect of the invention, the grounding path includes a bypass or bandpass filter 38 which is preferably configured for passing only frequencies of the higher of the two frequencies i.e. those generated or produced by the high frequency power source 26. The filter is advantageously configured for grounding the high frequency power source internally or externally of the reactor which serves to reduce if not eliminate any interference with the thermocouple line 30 and RF power line 34 which extends through a common opening 13.

[0026] Among the advantages provided by the above described reactor design and PECVD processing methods are that interference which is generated from the high frequency power loop and which interferes with other of the system's components is reduced if not eliminated by grounding the associated high frequency power loop at a location which is remote from those components. Such provides a PECVD system which is less prone to failure. Additionally and independently of the interference advantage, better film and layer deposition is possible. Such is made possible, in the preferred embodiment, by developing a power or power frequency differential between reactor electrodes with the preferred power or power frequency differential being developed in a parallel plate PECVD reactor by powering the shower head electrode at a high frequency and the susceptor electrode at a low frequency. By doing so, advantages include better film adhesion, lower pinhole density, better step coverage especially in high aspect ratio topographies, and films or layers with better electrical properties. Additionally, in PECVD systems in which etching is performed, better compatibility with fine-line pattern transfer processes can be achieved. Other advantages will be evident to those of skill in the art.

[0027] 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.