Abstract:
A method for processing a substrate in a plasma processing system is provided. The method includes disposing a first confinement ring set in a first position. The method also includes depositing a first coating on a first portion of the plasma processing system using a first plasma in a first area defined by the first confinement ring set in the first position. The method further includes depositing a second coating on a second portion of the plasma processing system using a second plasma in a second area between the first confinement ring set in the first position and a second confinement ring set. The method yet also includes processing the substrate using a third plasma with the first confinement ring set disposed in a second position.

Description:
PRIORITY CLAIM 
     This divisional application claims priority under 37 CFR 1.53(b) of and claims the benefit under 35 U.S.C. §120 to a commonly assigned patent application entitled “Methods and Apparatus for Selective Pre-Coating of a Plasma Processing Chamber,” by Andreas Fischer, application Ser. No. 11/367,290 filed on Mar. 3, 2006, now U.S. Pat. No. 7,578,258 all of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to substrate manufacturing technologies and in particular to methods and apparatus for selective pre-coating of a plasma processing chamber. 
     In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate in a plasma chamber for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon. 
     In order to optimize the plasma process, many surfaces within the plasma chamber are further configured with plasma resistant materials (e.g., silicon, silicon carbide, silicon nitride, quartz, etc.) that help to minimize surface wear without substantially increasing contaminants that may, in turn, affect the substrate. However, continued exposure to the plasma sheath tends to etch away and eventually remove the protective material, often resulting in surface particle contamination and hence lower substrate yields. 
     Generally, the plasma sheath tends to accelerate charged particles (e.g., ions, etc.) from the plasma edge to strike surfaces in the plasma chamber. Eventually, the processing chamber surfaces may erode and thus need to be replaced in order to assure long-term stability to the plasma process. Consequently, substantial operational costs and downtime may be added to the substrate manufacturing process, depending on the chemistry, the process pressure, and the amount of power to be used to generate said plasma. 
     In view of the foregoing, there are desired methods and apparatus for selective pre-coating of a plasma processing chamber. 
     SUMMARY OF THE INVENTION 
     The invention relates, in an embodiment, to a method for processing a substrate in a plasma processing system. The method includes disposing a first confinement ring set in a first position. The method also includes depositing a first coating on a first portion of the plasma processing system using a first plasma in a first area defined by the first confinement ring set in the first position. The method further includes depositing a second coating on a second portion of the plasma processing system using a second plasma in a second area between the first confinement ring set in the first position and a second confinement ring set. The method yet also includes processing the substrate using a third plasma with the first confinement ring set disposed in a second position. 
     These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  shows a simplified diagram of a differential plasma processing chamber with a dual confinement ring set, according to an embodiment of the invention; 
         FIG. 2  shows the simplified diagram of a differential plasma processing chamber, in which an area underneath an ICP coil is pre-coated with a set of hydrocarbons, according to an embodiment of the invention; 
         FIG. 3  shows the simplified diagram of a differential plasma processing chamber of  FIG. 2 , in which a showerhead is pre-coated with a material comprising silicon, according to an embodiment of the invention; 
         FIG. 4  shows the simplified diagram of a differential plasma processing chamber of  FIG. 3 , in which a substrate is being etched, according to an embodiment of the invention; and 
         FIG. 5  shows a simplified set of steps for selectively pre-coating a plasma processing chamber, including a chamber wall, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. While not wishing to be bound by theory, it is believed by the inventors herein that plasma surface damage, as well as contamination within the plasma chamber, may be reduced by first substantially isolating, and then selectively pre-coating, a set of surfaces with an optimized pre-coat material. In general, optimum pre-coat materials include those that typically become volatile when exposed to a plasma (e.g., silicon, amorphous silicon, silicon nitride, silicon dioxide, silicon carbide, hydrocarbon gas, C 4 F 6 , C 4 F 8 , CH 3 F, etc.) 
     In an embodiment, a pre-coat may be added between the plasma processing of successive substrates. In an embodiment, the thickness of a pre-deposited layer in each region or zone should be thick enough to withstand the subsequent etching of at least one substrate. In an embodiment, the thickness of a pre-deposited layer in each region or zone should be thick enough to withstand the subsequent etching of several substrates, such as when processing a substrate cassette. In an embodiment, multiple pre-deposited layers are deposited in each region or zone. In an embodiment, after completion of an etch cycle, all pre-coated layers may be removed in a dry clean step such that pre-coating may commence again. 
     For example, an upper grounded electrode of a capacitively coupled source may be already configured with a protective layer of silicon that shields the underlying grounded surface (e.g., single-crystal silicon or aluminum, etc.) from the plasma process. Consequently, pre-coating the grounded electrode with a material that is compatible the silicon protective layer (e.g., silicon, amorphous silicon, silicon carbide, silicon nitride, etc.), prior to etching the substrate, would substantially reduce contamination as well as extend the operational life of the upper grounded electrode. 
     In another example, a lower grounded electrode of an inductively coupled source may be already configured with a protective cover of quartz that shields the underlying grounded surface (e.g., aluminum, etc.) from the plasma process. Consequently, pre-coating the quartz cover with a material that is compatible with quartz (e.g., hydrocarbons, etc.), prior to etching the substrate would substantially reduce contamination as well as extend the operational life of the quartz cover. 
     In an embodiment, the plasma chamber comprises a plurality of concentric confinement ring sets, each with a different diameter. By raising and lowering a particular confinement ring set, an appropriate pre-coat plasma may be isolated to a particular area of the plasma chamber. 
     In an embodiment, the plasma used to etch the substrate is a differential plasma. That is, a plasma that is sustained with a plurality of energy sources. For example, in a dielectric etch system, a capacitively coupled plasma source which principally controls ion energy, and an inductively coupled plasma source, which principally controls plasma density, may be combined in order to etch a substrate with substantial radial plasma uniformity and radial etch uniformity. 
     In general, the capacitively coupled plasma source may be configured with a set of electrode plates (e.g., powered electrode, grounded electrode, etc.) positioned above and below the center of the substrate. Typically, the powered electrode is configured also as an electrostatic chuck (chuck), upon which the substrate is placed during the plasma process. Likewise, the grounded electrode is typically configured as a showerhead. 
     An inductively coupled plasma source may be configured with a set of induction coils and a grounded ring positioned above and below the perimeter of the substrate. In an embodiment, an inner confinement ring set is positioned between the capacitively coupled plasma and the inductively coupled plasma source, and an outer confinement ring may be positioned between the inductively coupled plasma source and a plasma chamber wall. 
     Referring now to  FIG. 1 , a simplified diagram of a differential plasma processing chamber with a dual confinement ring set is shown, according to an embodiment of the invention. In general, in order to sustain the differential plasma, a capacitively coupled plasma (CCP) source is configured to control ion energy, and an inductively coupled plasma (ICP) source is configured to control plasma density. 
     A typical CCP source configuration commonly consists of two metal electrodes separated by a small distance, and operates in a manner similar in principle to a capacitor in an electric circuit. A first powered electrode  102  is typically configured as a chuck. Additionally, a second grounded electrode  108  is typically configured as part of a showerhead assembly  106 , which commonly also includes a protective layer of perforated silicon that allow plasma gases to pass through into the plasma chamber from a gas distribution system [not shown]. Furthermore, a substrate  104  is commonly positioned with edge ring  120  on chuck/grounded electrode  102 . 
     Likewise, a typical ICP source configuration commonly consists of a set of induction coils  112  and a grounded ring  116 . The set of induction coils  112  is typically configured to radiate radio frequency energy into the plasma gas through a quartz window  113 , which may provide a protective shield from a generated plasma [not shown]. Likewise, grounded ring  116  is also configured with a protective quartz layer, and is typically positioned below the perimeter of substrate  102 . Quartz is essentially transparent to the generated RF waves. In addition, typically coupled to both the CCP source and the ICP source is a matching network [not shown] that attempts to match the impedances of each RF generator to that of the load which is, in part, formed by the plasma. 
     In addition, an inner confinement ring set  118  may be positioned between the CCP source and the ICP source, and may further be raised and lowered as required to isolate and/or channel the plasma to specific areas of the plasma chamber. For example, when inner confinement ring set  118  is positioned in an up position, and the CCP source and/or the ICP source is energizing a set of plasma gases, the resulting plasma may extend across substrate  104  toward outer confinement ring set  114 . 
     In contrast, when inner confinement ring set  118  is positioned in a down position [not shown], and the CCP source is energizing a set of plasma gases, the plasma may be confined to the area defined by the diameter of the inner confinement ring set. 
     However, when inner and outer confinement ring sets  118  and  114  are positioned in a down position [not shown], and the ICP source is energizing a set of plasma gases, the plasma may be confined to the area (e.g., toroid, etc.) defined by both the inner confinement ring set  118  and the outer confinement ring set  114 . 
     Alternatively, when inner and outer confinement ring sets  118  and  114  are positioned in a down position [not shown], and both the CCP and the ICP source are energizing a set of plasma gases, a first plasma may be confined to the area defined by the diameter of the inner confinement ring set, and a second plasma may be confined to the area defined by both the inner confinement ring set  118  and the outer confinement ring set  114 . 
     Typically, each confinement ring set is configured as a series of quartz rings positioned around a horizontal perimeter of a substrate, and further positioned in varying distances above the substrate along the vertical axis, commonly by the use of a cam ring. In general, the thickness of each confinement ring, as well as the size of the gap between any two rings, is configured in order to optimize the particular plasma process and control the pressure within the plasma. In some configurations, the confinement rings are of differing diameter and thickness. For example, a confinement ring positioned closer to a substrate along the vertical axis, may be smaller in diameter to one farther away from the substrate. 
     Referring not to  FIG. 2 , the simplified diagram of a differential plasma processing chamber of  FIG. 1  is shown, in which an area underneath an ICP coil is pre-coated with either a set of hydrocarbons or with silicon dioxide, according to an embodiment of the invention. As previously stated, both the set of induction coils  112  and grounded ring  116  are typically shielded from a plasma by a set of quartz surfaces. In an advantageous manner, prior to processing a substrate, a substantial portion of these quartz surfaces may be pre-coated with a hydrocarbon layer or with a silicon dioxide layer, such that the hydrocarbon layer or the pre-deposited silicon dioxide layer, and not the underlying quartz surface, may be etched during plasma processing. In an embodiment, the thickness of the hydrocarbon pre-coat or silicon dioxide layer is about 1.5 μm. 
     A hydrocarbon is generally a Teflon-like material that may be chemically described by C x H y F z , where x is an integer greater than 0, and y and z are integers greater than or equal to zero (e.g, C 4 F 6 , C 4 F 8 , CH 3 F, etc.). Quartz is silicon oxide and is chemically described as SiO 2 . The Teflon-like or silicon dioxide pre-coat is physically bonded to the quartz surface via Van-der Waals forces; no chemical reaction between the coat and the quartz generally needs to occur. 
     In one method of pre-coating the quartz surfaces, both inner confinement ring set  118  and the outer confinement ring set  114  are lowered. A hydrocarbon gas is then fed into the differential plasma chamber through showerhead  106 , and consequently seeps into a channel defined by inner confinement ring set  118  and outer confinement ring set  114 . In an embodiment, the hydrocarbon is a fluorinated hydrocarbon gas. The set of induction coils  112  may then energized, causing a hydrocarbon pre-coat to be deposited on the quartz surfaces. Typically, a covering or dummy substrate  124  is placed on powered electrode  102  in order to shield it during the pre-coat process. 
     Referring now to  FIG. 3 , the simplified diagram of a differential plasma processing chamber of  FIG. 2  is shown, in which a showerhead is pre-coated with a material comprising silicon, according to an embodiment of the invention. As previously stated, showerhead assembly  106  shields grounded electrode  108  with a protective layer of perforated silicon that allow plasma gases to pass through into the plasma chamber from a gas distribution system [not shown]. In an embodiment, the thickness of the silicon pre-coat layer is about 4.0 μm. 
     In an advantageous manner, prior to processing a substrate, a substantial portion of the showerhead is pre-coated with a material comprising silicon (e.g., silicon, silicon nitride, silicon carbide, etc.). In an embodiment, the material comprising silicon is amorphous silicon. In general, amorphous silicon may be deposited from silane gas by using an electric discharge. Generally, the deposited amorphous silicon sticks well to the underlying single-crystalline silicon of the shower head because of a fairly close lattice match between the atoms of each layer. 
     In one method of pre-coating the showerhead, both inner confinement ring set  118  and the outer confinement ring set  114  are lowered. A silicon containing gas is then fed into the differential plasma chamber through showerhead  106  into the plasma chamber. Powered electrode  102  may then be energized, causing a silicon pre-coat to be deposited on the showerhead. Typically, a covering or dummy substrate  124  is placed on powered electrode  102  in order to shield it during the pre-coat process. 
     Referring now to  FIG. 4 , the simplified diagram of a differential plasma processing chamber of  FIG. 3 , in which a substrate is being etched, according to an embodiment of the invention. For example, in a Lam Research 2300 Exelan Flex plasma processing system, a common etching recipe may be 2000 W(27 MHz)/3000 W(2 MHz), 300 sccm Ar, 20 sccm C 4 F 8 , 20 sccm O 2 , 45 mTorr. As previously stated, a substantial portion of the showerhead  106 , quartz window  113 , and grounded ring  116  are pre-coated, such that these surfaces are protected during an etch process. In general, inner confinement ring set  118  may be in a raised position in order to allow differential plasma  124  to extend across substrate  104  toward outer confinement ring  114 . For example, a substrate may be etched as part of a dual damascene process in which, dielectric layers are electrically connected by a conductive plug filling a via hole. 
     Referring now to  FIG. 5 , a simplified set of steps is shown for selectively pre-coating a plasma processing chamber, including a chamber wall, according to an embodiment of the invention. Initially, at  502 , a first set of RF electrodes is configured to strike a first pre-coat plasma, the first set of RF electrodes defining a first plasma chamber zone. Next at  504 , a first set of confinement rings is configured around the first set of RF electrodes. Then at  506 , a second set of confinement rings is configured between the first set of confinement rings and the chamber wall. 
     In an embodiment, a second set of RF electrodes is also configured between the first set of confinement rings and the second set of confinement rings. In an embodiment, a the second set of RF electrodes is configured to strike a second pre-coat plasma, the second set of RF electrodes defining a second plasma chamber zone. 
     Finally at step  508 , a gas delivery system is configured to apply a first pre-coat layer to the first plasma zone when a first pre-coat gas is delivered and the first set of RF electrodes is energized. For example, the first pre-coat gas may include one of silicon, amorphous silicon, silicon nitride, and silicon carbide. In an embodiment, the gas delivery system is configured to apply a second pre-coat layer to the second plasma zone when a second pre-coat gas is delivered, and the second set of RF electrodes is energized. For example, the second pre-coat gas may include a hydrocarbon gas. 
     In an embodiment, the first set of RF electrodes is capacitively coupled, and the second set of RF electrodes is inductively coupled. In an embodiment, the first set of RF electrodes is inductively coupled, and the second set of RF electrodes is capacitively coupled. In an embodiment, both the first set of RF electrodes and the second set of RF electrodes are capacitively coupled. In an embodiment, both the first set of RF electrodes and the second set of RF electrodes are inductively coupled. In an embodiment, at least one of the first set of confinement rings and the second set of confinement rings is configured to be movable. 
     While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. For example, although the present invention has been described in connection with plasma processing systems from Lam Research Corp. (e.g., Exelan™, Exelan™ HP, Exelan™ HPT, 2300 Exelan Flex™, Versys™ Star, etc.), other plasma processing systems may be used. This invention may also be used with substrates of various diameters (e.g., 200 mm, 300 mm, etc.). Also, photoresist plasma etchants comprising gases other than oxygen may be used. It should also be noted that there are many alternative ways of implementing the methods of the present invention. 
     Advantages of the invention include methods and apparatus for selective pre-coating of a plasma processing chamber. Addition advantages include protecting surfaces within the plasma chamber, minimizing contamination, simplifying the manufacturing process, and improving substrate yield. 
     Having disclosed exemplary embodiments and the best mode, modifications and variations may be made to the disclosed embodiments while remaining within the subject and spirit of the invention as defined by the following claims.