Patent Application
20080008842
So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Embodiments of the present invention include methods for plasma processing. The method may be employed to reduce plasma instability and/or improve substrate processing. The plasma process may be part of a deposition process, etch process, annealing process, surface treatment process or other suitable plasma process. In one embodiment, the method provided herein advantageously improves plasma stability in a plasma processing chamber by optimizing the ramp-up rate of RF power applied during processing. Substrates having a patterned structure with an antenna ratio over 50,000 may be used for amplifying and/or enhancing a discharge effect which may occur during the plasma process. A data acquisition system is used to collect DC bias information during processing, which is utilized to optimize the RF power ramp-up rate. The RF power ramp-up rate is optimized to obtain a DC bias variation during ramp-up that is less than a determined value. The optimizing RF power ramp-up rate allows the plasma generated in the processing chamber to be distributed uniformly across the substrate in the chamber, substantially eliminating the discharge effect and arcing damage, and thus providing a robust product yield while extending the life of chamber components.
The chamber 100 has a body 102 that defines separate processing regions 118, 120. Each processing region 118, 120 has a pedestal 128 adapted to support a substrate (not shown) within the chamber 100. The pedestal 128 may include a heating element (not shown). The pedestal 128 is coupled by a stem 126 to a drive system 103 that controls the elevation of the pedestal 128 in each processing region 118, 120. Internal movable lift pins (not shown) may be provided in the pedestal 128 to facilitate the movement of the substrate disposed on the pedestal 128. The lift pins are adapted to lower or to raise the substrate off the pedestal 128 as needed.
A lid 104 is coupled to the top portion of the chamber body 102. The lid 104 includes a gas distribution assembly 108 comprising a manifold 148, a blocker plate 146 and a showerhead 142. A gas inlet passage 140 is included in the gas distribution assembly 108 and is coupled to a gas panel 119 to facilitate the flow of process gases into processing regions 118, 120 through the showerhead 142. The showerhead 142 is located above the pedestal 128 and disperses a process gas mixture into the process regions 118, 120. The showerhead 142 may also comprise different zones, such that various gases may be released into the chamber 100 at various flow rates and/or at various volumetric distributions.
An RF (radio frequency) source 125 is used to provide a bias potential to the showerhead 142 to facilitate plasma generation between the showerhead 142 and the pedestal 128. The showerhead 142 and the pedestal 128 form a pair of spaced apart electrodes to facilitate plasma generation in the presence of process gas mixture in the processing regions 120, 118. The source 125 generally comprises an RF generator (not shown) and a matching network (not shown). The RF source 125 may provide a single or mixed-frequency RF signal frequency to the showerhead 142. In one embodiment, the source 125 generally is capable of producing up to 5000 W of continuous or pulsed power at an RF signal frequency ranging from about 50 kHz to 60 MHz. Alternatively, the RF source 125 may be coupled to the pedestal 128 or to both the showerhead 142 and pedestal 128.
In one embodiment, the pedestal 128 may serve as a cathode for generating RF bias within the chamber body 102 in a plasma-enhanced chemical vapor deposition process. The cathode is electrically coupled to an electrode power supply (not shown) to generate a capacitive electric field in the deposition chamber 100. Power applied to the pedestal 128 creates a substrate bias in the form of a negative voltage on the upper surface of the substrate. This negative voltage is used to attract ions from the plasma formed in the chamber 100 to the upper surface of the substrate. The capacitive electric field forms a bias which accelerates inductively formed plasma species toward the substrate to provide a more vertically oriented anisotropic filming of the substrate during deposition and etching of the substrate during cleaning.
The data acquisition system 162 is coupled to at least one of the showerhead 142 or pedestal 128 and is utilized to collect the bias voltage of at least one of the electrodes generating the plasma within the chamber 100. The data acquisition system 162 may be configured to collect data samples over a predetermined time period. In one embodiment, the data acquisition system 162 may collect up to 10 million data samples per second from a voltage probe 160 coupled to the showerhead 142.
During processing, process gases are distributed radially across the substrate surface. The plasma is formed from one or more process gases by applying RF energy from the RF power supply 125 to the showerhead 142. As the RF power is applied to the showerhead 142, the data acquisition system 162 is operated to collect the bias generated in the showerhead 142.
A system controller 134 comprises a central processing unit (CPU) 164, a memory 138, and a support circuit 166 coupled to the chamber 100 utilized to control process sequence and regulate the gas flows from the gas panel 119. The CPU 164 may be of any form of a general purpose computer processor that can be used in an industrial setting. The software routines can be stored in the memory 138, such as random access memory, read only memory, floppy or hard disk drive, or other form of digital storage. The support circuit 166 is conventionally coupled to the CPU 164 and may comprise cache, clock circuits, input/output subsystems, power supplies, and the like. The software routines, when executed by the CPU 164, transform the CPU into a specific purpose computer (controller) 134 that controls the process chamber 100 such that the processes are performed in accordance with the present invention. The software routines may also be stored and/or executed by a second controller (not shown) that is located remotely from the chamber 100.
The method 200 begins at step 202 by providing a substrate in the chamber 100. The substrate may have patterned structures with a relatively large antenna ratio disposed thereon to amplify the potential arcing, or discharge non-uniformity across the substrate when exposed to plasma. In one embodiment, the substrate may have patterned structures having an antenna ratio larger than about 50,000 disposed thereon. In another embodiment, the substrate may have patterned structures having an antenna ratio larger than about 700,000. In yet another embodiment, the substrate may have patterned structures similar as the structures disposed on a production wafer. In still another embodiment, the substrate may be a production wafer or other workpiece.
At step 204, one or more gases are flowed into the chamber. The gas or gas mixture supplied to the chamber may be utilized to perform or simulate one or more of the processes performed in the chamber. For example, the gases may be thermally decomposed to deposit a dielectric layer, such as an amorphous carbon film, on the substrate. It is contemplated that other plasma processes may be performed, including deposition, etching, annealing or thermal treatment, or an etching process. In one embodiment, the gas mixture contains a hydrocarbon compound and an inert gas, such as argon (Ar) and/or helium (He). The hydrocarbon compound has a general formula CxHy, where x has a range between 1 and 6 and y has a range between 2 and 14. For example, propylene (C3H6), propyne (C3H4), propane (C3H8), butane (C4H10), butylenes (C4H8), butadience (C4H6), or acetelyne (C2H2) as well as combinations thereof, may be used as the hydrocarbon compound. Similarly, a variety of gases, such as hydrogen (H2), nitrogen (N2), ammonia (NH3), or combination thereof, may be added to the gas mixture. As the exemplary embodiment, the gas mixture includes C3H6, He and Ar.
Process parameters are regulated at step 204 while the gas mixture is supplied into the chamber 100. In one embodiment, a pressure of the gas mixture disposed in the chamber is regulated between about 1 Torr and about 30 Torr, for example, between about 4 Torr and about 10 Torr. The substrate temperature is maintained between about 75 degrees Celsius and about 600 degrees Celsius, for example, about 200 degrees Celsius and about 550 degrees Celsius. The spacing between the showerhead 142 and the substrate pedestal 128 is set to between about 50 mils and about 2000 mils, for example, about 200 mils and about 400 mils. The gas flow of hydrocarbon compound, such as C3H6, is provided to the chamber at a flow rate between about 200 sccm to about 4000 sccm, for example, about 600 sccm to about 1800 sccm. The gas flow of inert gas, such as Ar, is flowed into the chamber at a rate between about 0 sccm to about 10000 sccm, for example, about 0 sccm to about 4000 sccm. In an embodiment where the inert gas is He, the gas flow of He is provided to the chamber at a flow rate between about 0 sccm to about 2000 sccm, for example, about 200 sccm to about 1000 sccm.
At step 206, an RF power is applied to the showerhead 142 of the chamber 100 to generate a plasma from the gas mixture within the chamber 100. Variations in the DC bias of the showerhead 142 are monitored during the RF power application. To obtain an optimized parameter for RF power application, the plasma process is performed using different RF power application parameters so that multiple DC bias data sets may be collected. The application parameters may have different power application rates, different time periods over which the power is ramped-up and/or other parameter change which may be analyzed to determine an optimal operation set-point. For example, the RF ramp-up may be sampled over rates having power applications of between about 20 Watt/seconds and 5000 Watts/seconds, for example, between about 50 Watt/seconds and 1000 Watts/seconds to generate a data set suitable for optimizing the RF power application. The period of the ramp-up time for the RF power into the predetermined range is set between 0.1 seconds to 100 seconds.
The RF power applied at step 206 may ramp-up the RF power to a final set-point value suitable for depositing an amorphous carbon or other film. In one embodiment, the final set-point value for an amorphous carbon deposition process may be set at between about 500 Watts and about 2000 Watts, while ramping up the RF power density at a rate between about 0.15 W/cm2/sec and about 0.75 W/cm2/sec in a 300 mm substrate processing chamber. In another embodiment, the final set-point value may be at a range between about 50 Watts and about 500 Watts, while ramping up the RF power density at a rate between about 0.01 W/cm2/sec and about 0.75 W/cm2/sec in a 300 mm substrate processing chamber.
At step 208, the data acquisition system 162 coupled to the showerhead 142 is operated to collect DC bias information obtained during the RF ramp-up. The data acquisition system 162 collects and receives the value of DC bias of the showerhead 142 from the voltage probe 160 over a predetermined time interval. In one embodiment, the data acquisition system 162 samples a metric of DC bias about every 0.1 milliseconds (ms) to about every 500 milliseconds (ms) until the RF power is stabilized or terminated. In another embodiment, the data acquisition system 162 samples a metric of DC bias about every 80 ms to about every 250 ms, such as 200 ms.
At step 210, the RF power is terminated after depositing the amorphous carbon or other film. At step 212, the gas mixture flow into the chamber is stopped and the chamber throttle valve is opened to allow the process gas mixture to be pumped out of the chamber after RF power termination. The substrate is subsequently removed from the process chamber.
Step 202 to step 212 may be performed repeatedly to obtain a plurality of DC bias data sets from substrates processed using different RF power application parameters, ramp-up rate settings and/or different power application periods, as indicated by the loop 218 depicted in
At step 214, the DC bias data set is analyzed by one of the data acquisition system 162, controller 134 or other processor. The processed substrates may also be inspected and evaluated by an inspection tool, such as Scanning Electron Microscopy (SEM), thickness measuring tool, optical measuring tool, conductance measuring tool or other tool suitable for evaluating substrate and/or device processing, performance and/or physical characteristic.
The DC bias trace 306 illustrates a more stable process as compared to the step RF power application trace 302, but not as stable as the trace 304. The DC bias trace 304 has a smooth transition from power application to a steady state processing condition. The smooth transition of DC bias is indicative of processes having stable plasma generation and uniform plasma distribution within the process region, which minimize charge accumulation and arcing. Additionally, the substrates processed in this manner have higher product yields in comparison with the substrates processed with processes having large DC fluctuation bias. The elimination of the localized charge due to non-uniform plasma distribution advantageously minimizes arcing and defect generation on the substrate and system components, and thereby promoting higher product yield and longer service of the processing chamber components.
At step 216, an optimized ramp-up rate of the RF power is determined by analyzing the DC bias information. Inspection results may also be considered to determine which ramp-up rates exhibit less contamination and/or process damage. In one embodiment, measured variation in the DC bias during RF ramp-up of less than 3 volts, such as 1 volt, enables good processing results. In another embodiment, inspection of processed substrate indicates that a variation in DC bias of less than 5 volts provides a relatively higher product yield and acceptable particle counts. To achieve the variation in DC bias of less than 3 volts, such as 1 volt, the optimized ramp-up rate is selected at a range between about 100 Watts/sec and 500 Watts/sec for the amorphous carbon deposition process described above. The selected range of optimized RF ramp-up rate provides an arcing-free process condition, thereby efficiently providing a longer service of the process components and robust product yield. Of course, other processes will have different optimized rates.
Thus, the present application provides methods for reducing plasma instability in a plasma processing chamber. The methods advantageously promote stability and uniformity of the plasma by optimizing an RF power ramp rate. The optimized process minimizes potential plasma damage to the substrate and processing system and, thus, promotes robust product yields and long service life of system components.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
