Patent Application
20100024840
1) Field
Embodiments of the present invention are in the field of Semiconductor Processing and, in particular, semiconductor processing equipment cleaning schemes.
2) Description of Related Art
For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory or logic devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. Tolerances in variations of the critical dimension from one device to another have become very constrained. Thus, any imperfections in a process step used to fabricate devices may unacceptably compromise the performance of the devices.
The stringent requirements for low process variations has placed a substantial burden on equipment manufacturers. In addition to addressing requirements of high throughput, process tools must also exhibit high intra-wafer uniformity as well as run-to-run consistency for a batch of production wafers. Equipment manufacturers therefore usually require customers to perform very detailed and time consuming preventative maintenance (PM) schemes to ensure wafer-to-wafer and run-to-run uniformity and consistency. However, such PM schemes can substantially impact the throughput of the process tool if long periods of tool idle time are required. This may lead to unacceptable delays in a semiconductor fabrication production line.
Embodiments of the present invention include methods for plasma-cleaning a chamber in a process tool. In one embodiment, a substrate (e.g., a wafer) is placed on a chuck in a process chamber having a set of contaminants therein. A plasma process is then executed in the process chamber to transfer the set of contaminants to the top surface of the substrate. The substrate, having the set of contaminants thereon, is removed from the process chamber. In a specific embodiment, the set of contaminants includes particles such as, but not limited to, metal particles and dielectric particles. In another specific embodiment, the plasma process is a low-pressure plasma process carried out at a pressure approximately in the range of 5-50 mTorr.
In another embodiment, a substrate is placed to cover a top surface of a chuck in a process chamber having a set of contaminants therein. A first plasma process is executed in the process chamber to transfer the set of contaminants to the top surface of the substrate. The substrate, having the set of contaminants thereon, is then removed from the process chamber. While the substrate is situated in the process chamber, a second plasma process is executed in the process chamber to season the process chamber. A third plasma process is executed in the process chamber while the top surface of the chuck is exposed.
Another embodiment includes a method for operating an etch process tool. A first substrate is provided on a chuck in a process chamber. The first substrate is etched with a first plasma process in the process chamber. The etching provides a set of contaminants in the process chamber. The first substrate is then removed from the process chamber. A second substrate is then placed to cover a top surface of the chuck in the process chamber. A second plasma process is executed in the process chamber to transfer the set of contaminants to the top surface of the second substrate. The second substrate, having the set of contaminants thereon, is then removed from the process chamber. A third plasma process is executed in the process chamber while the top surface of the chuck is exposed.
A method for plasma-cleaning a chamber in a process tool is described. In the following description, numerous specific details are set forth, such as plasma conditions and material regimes, in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known features, such as semiconductor substrate fabrication techniques, are not described in detail in order to not unnecessarily obscure the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.
Disclosed herein is a method for plasma-cleaning a chamber in a process tool. The method may include placing a substrate, such as a wafer, on a chuck in a process chamber having a set of contaminants therein. In one embodiment, a plasma process is then executed in the process chamber to transfer the set of contaminants to the top surface of the substrate. Then, the substrate, having the set of contaminants thereon, may be removed from the process chamber. In a specific embodiment, the set of contaminants includes particles such as, but not limited to, metal particles and dielectric particles. In another specific embodiment, the plasma process is a low-pressure plasma process carried out at a pressure approximately in the range of 5-50 mTorr.
Performing a chamber plasma-cleaning process while a substrate is situated on the top surface of a chuck may enable a reduction in critical dimension (CD) variation throughout the run lifetime of the chamber. For example, in accordance with an embodiment of the present invention, a plasma-cleaning process is carried out in a process chamber while a substrate rests on, and effectively blocks, the top surface of the chuck in the process chamber. In the absence of a substrate covering the chuck, contaminants adhering to the chamber walls or showerhead might otherwise land on the top surface of the chuck during the plasma-cleaning process. As product substrates are subsequently processed, e.g. etched, in the chamber the presence of such contaminants on the chuck can lead to hot spots in the product substrate as it rests on the chuck. These hot spots can affect the etching characteristics and can result in undesirable CD variations etched into the product substrate. Instead, in one embodiment, a dummy or seasoning substrate is used to cover the chuck during the plasma-cleaning process. In that embodiment, during the plasma-cleaning process, contaminants located in the process chamber are transferred to the dummy or seasoning substrate instead of to the top of the chuck. Accordingly, in an embodiment, the contaminants are removed from the process chamber upon removal of the dummy or seasoning substrate from the process chamber.
In an aspect of the invention, a process chamber (e.g. an etch chamber) in a process tool may become contaminated during the processing of production substrates in the process chamber.
Referring to
During the etching of a product substrate with plasma 106, contaminants may be generated from the production substrate and may adhere to showerhead 104 and even to chamber walls 108 of process chamber 100. The accumulation of contaminants formed as a batch of production substrates is cycled through the process chamber for etching may impact the quality and repeatability of the etch process over time. For example, in one embodiment, the accumulation of contaminants on showerhead 104 leads to a variation in etch rate from one region of a production substrate to another region of the same production substrate, or from one production substrate to the next. The variation may be a result of portions of showerhead 104 becoming blocked by contaminants, hindering the flow of process gases through showerhead 104. In another embodiment, the accumulation of contaminants on chamber walls 108 can ultimately lead to the undesirable flaking of chunks of the contaminants onto a production substrate. A wet clean of the process chamber can be carried out to remove the contaminants, but it may be inefficient to perform such a wet clean more frequently than every few days in a production line.
Accordingly, it may be desirable to carry out a substrate-less chamber plasma-cleaning process after a certain number of production substrates has been etched in process chamber 100. Typical substrate-less plasma-cleaning processes involve the use of a high-pressure plasma process carried out in chamber 100 in the absence of a substrate on chuck 104. Such substrate-less plasma-cleaning processes may be carried out more frequently than a wet clean of clamber 100, such as between the etching of every product substrate, without impacting the timing of the production line. However, in accordance with an embodiment of the present invention, such a substrate-less plasma cleaning process can transfer contaminants from showerhead 104 or chamber walls 108 onto top surface 103 of chuck 102. Furthermore, in a specific embodiment, a high pressure substrate-less plasma cleaning process may not completely remove contaminants from showerhead 104 or chamber walls 108.
The transfer of contaminants onto top surface 103 of chuck 102 during a substrate-less chamber plasma-cleaning process may detrimentally impact etch processes applied to production substrates subsequent to carrying out the chamber plasma-cleaning process. For example, in one embodiment, the accumulation of contaminants onto top surface 103 of chuck 102 leads to a variation in CD from one production substrate to the next.
Referring to
Accordingly, an aspect of the present invention includes a method for plasma-cleaning a chamber in a process tool.
Referring to operation 302 of Flowchart 300, a substrate (e.g., a wafer) is placed on a chuck in a process chamber having a set of contaminants therein. In one embodiment, the substrate is a dummy wafer or a seasoning wafer such as, but not limited to, a bare silicon wafer or a wafer coated with thermally grown oxide. In a specific embodiment, the wafer is a 300 mm wafer and the process chamber is housed in a tool suitable for processing 300 mm wafers. In an embodiment, the set of contaminants includes particles such as, but not limited to, metal particles or dielectric particles.
Referring to operation 304 of Flowchart 300, a plasma process is then executed in the process chamber to transfer the set of contaminants to the top surface of the substrate. In accordance with an embodiment of the present invention, the plasma process is a low-pressure plasma process carried out at a pressure approximately in the range of 5-50 mTorr. In a specific embodiment, the plasma process is carried out at a pressure of approximately 10 mTorr. The use of a low-pressure plasma process at this operation may enable a more thorough cleaning of the parts of the process chamber, such as the showerhead and the chamber walls, than does a high pressure plasma process. For example, in one embodiment, the cleaning pattern starts at the center of the ceiling of the process chamber and migrates thoroughly to the walls of the process chamber.
The plasma used for the plasma-cleaning process of operation 304 may be based on a gas suitable to bombard contaminants located on various parts of the process chamber and to transfer the contaminants to the top surface of the substrate which can be a dummy or seasoning wafer, as previously mentioned. For example, in an embodiment, the plasma for the plasma-cleaning process is based on a gas such as, but not limited to, oxygen or argon gas. In one embodiment, the plasma process is based on oxygen gas having a flow rate approximately in the range of 500-2000 standard cubic centimeters per minute (sccm) and is carried out for a duration approximately in the range of 60-200 seconds. In a specific embodiment, the plasma process is based on oxygen gas having a flow rate of approximately 1500 sccm and is carried out for a duration of approximately 180 seconds. In an embodiment, the process chamber has a top electrode and a bottom electrode, and the top electrode has a source power approximately in the range of 500-2000 Watts while the bottom electrode has a source power of approximately 0 Watts (no bias) during the plasma process. In a specific embodiment, the top electrode has a source power of approximately 1000 Watts while the bottom electrode has a source power of approximately 0 Watts during the plasma process.
Referring to operation 306 of Flowchart 300, the substrate, having the set of contaminants thereon, is then removed from the process chamber. Thus, the set of contaminants is removed from the process chamber without becoming situated on the surface of the chuck. For example in accordance with an embodiment of the present invention, prior to executing the plasma-cleaning process, the set of contaminants is situated on a showerhead housed in the process chamber. Using a low-pressure plasma-cleaning process, the set of contaminants is removed from the tool because the set of contaminants is transferred to the surface of the substrate instead of to the top surface of the chuck.
In an additional aspect of the invention, a second plasma-cleaning process operation may be carried out following the plasma-cleaning process described in association with operations 302, 304 and 306 from Flowchart 300. Referring to operation 308 of Flowchart 300, a second plasma process may be executed in the process chamber while the top surface of the chuck is exposed.
The second plasma process may be used to remove other contaminants or impurities that are not readily transferred out of the process chamber according to the low-pressure plasma-cleaning process scheme from operations 302, 304 and 306. For example, in one embodiment, the second plasma process consumes organic contaminants situated in the process chamber. In accordance with an embodiment of the present invention, the second plasma-cleaning process relies on a high pressure plasma to convert contaminants or impurities (such as organic contaminants or impurities) to volatile species that can be pumped out of the process chamber. Thus, a substrate (e.g., a wafer) need not be used to cover the chuck at this operation because the second plasma volatilizes, as opposed to bombards and transfers, the remaining contaminants or impurities. It may even be preferable to have the top of the chuck exposed so that the top surface of the chuck may be cleaned by the second plasma process.
The plasma used for the second plasma-cleaning process of operation 308 may be based on a gas suitable to volatilize contaminants located on various parts of the process chamber. For example, in accordance with an embodiment of the present invention, the second plasma-cleaning process is carried out at a substantially higher pressure than the first plasma-cleaning process. In an embodiment, the first plasma-cleaning process is a low-pressure plasma process carried out at a pressure approximately in the range of 5-50 mtorr, and the second plasma-cleaning process is a high-pressure plasma process carried out at a pressure approximately in the range of 200-600 mTorr. In a specific embodiment, the first plasma-cleaning process is a low-pressure plasma process carried out at a pressure of approximately 10 mTorr, and the second plasma-cleaning process is a high-pressure plasma process carried out at a pressure of approximately 300 mTorr. In one embodiment, the second plasma process is based on oxygen gas having a flow rate approximately in the range of 500-4000 sccm and is carried out for a duration approximately in the range of 10-60 seconds. In a specific embodiment, the second plasma process is carried out for a duration of approximately 30 seconds. In an embodiment, the process chamber has a top electrode and a bottom electrode, and the top electrode has a source power approximately in the range of 0-100 Watts while the bottom electrode has a source power of approximately 0 Watts (no bias) during the second plasma process.
In an aspect of the present invention, a chamber plasma-cleaning process is performed following the contamination of a process chamber with a set of contaminants.
In an aspect of the invention, a chamber plasma-cleaning process scheme may be incorporated into a production line integration scheme. For example,
Referring to operation 502 of Flowchart 500, a seasoning substrate is placed on a chuck in a process chamber having a set of contaminants therein. The seasoning substrate and the set of contaminants may be a seasoning wafer and a set of contaminants described in association with operation 302 from Flowchart 300. In accordance with an embodiment of the present invention, a seasoning substrate is a wafer to which a production etch recipe is applied in the process chamber prior to running the production etch recipe on an actual production wafer.
Referring to operation 504 of Flowchart 500, a plasma-cleaning process is performed by executing a plasma process in the process chamber while the seasoning substrate, or the seasoning wafer, is situated on the chuck. This operation is carried out in order to transfer the set of contaminants from, e.g., the process chamber walls or the process chamber showerhead to the top surface of the seasoning substrate. In one embodiment, the plasma-cleaning process is a low-pressure plasma process such as the low-pressure plasma process described in association with operation 304 from Flowchart 300.
Referring to operation 506 of Flowchart 500, a seasoning recipe is executed in the process chamber to season the process chamber, while the seasoning substrate is present on the chuck in the process chamber. In accordance with an embodiment of the present invention, the seasoning recipe is the same etch recipe that will be used to subsequently etch a production substrate in the process chamber. In an additional embodiment, an ash recipe is performed following the seasoning recipe, while the seasoning substrate is still situated on the chuck in the process chamber. In one embodiment, the ash recipe used is similar or the same as an ash recipe performed on a subsequently processed production substrate. Such seasoning (i.e. etch) and ash recipes may involve the use of several plasma gases and a variety of process conditions, as are known in the art.
Referring to operation 508 of Flowchart 500, the seasoning substrate, having the set of contaminants thereon, is removed from the process chamber. Then, referring to operation 510 of Flowchart 500, a substrate-less or wafer-less plasma-cleaning recipe is carried out in the process chamber. In one embodiment, the substrate-less plasma-cleaning process is a high-pressure plasma process, such as the high-pressure plasma process described in association with operation 308 from Flowchart 300.
At this point, the process chamber plasma-cleaning and seasoning operations may be complete and a production substrate, or a batch of production substrates, may be processed in the process chamber. Referring to operation 512 of Flowchart 500, a production substrate is inserted into the process chamber and a production recipe is executed on the production substrate. For example, in accordance with an embodiment of the present invention, the production substrate is etched with a recipe that is the same or similar to the seasoning recipe described in association with operation 506. An ash recipe may also be performed on the production substrate following execution of the etch recipe, mirroring the process sequence described in association with operation 506.
Referring to operation 514 of Flowchart 500, the production substrate, or production wafer, is removed from the process chamber and a substrate-less or wafer-less plasma clean recipe is performed in the process chamber. In one embodiment, the substrate-less plasma-cleaning process is a high-pressure plasma process, such as the high-pressure plasma process described in association with operation 308 from Flowchart 300 or operation 508 above. Depending on the requirements of the production line, operations 512 and 514 may be cycled through multiple times, as depicted by cycle arrow 516. For example, in one embodiment, operations 512 and 514 are cycled through 25 times to accommodate a single batch of 25 production substrates.
Referring to cycle arrow 518, once a desired number of operation 512/514 cycles is completed, the plasma-cleaning operations 502 through 510 may be performed prior to processing another batch of production substrates or production wafers. Then, the two cycles 516 and 518 may be repeated until a preventative maintenance (PM) process, such as a wet clean, need be performed on the process chamber. In accordance with an embodiment of the present invention, by incorporating a low-pressure plasma-cleaning process in to the production sequencing of a process chamber, the number of production substrates that can be processed prior to a PM process is required is approximately three times the number of production substrates that can be processed if a low-pressure plasma-cleaning process is not used. In one embodiment, by incorporating a low-pressure plasma-cleaning process into the production sequencing of a process chamber, a process chamber can be used for approximately 1000 process hours between PM processes.
Chamber plasma-cleaning process schemes, such as those described above, may be employed in a variety of etch or reaction chambers. For example, in one embodiment, a chamber plasma-cleaning process is carried out in a plasma etch chamber capable of energizing an etchant gas mixture with multiple RF frequencies, such as the Enabler™ etch chamber manufactured by Applied Materials of CA, USA. In another embodiment, a chamber plasma-cleaning process is performed in a magnetically enhanced reactive ion etcher (MERIE) etch chamber, such as the MxP®, MxP+™, Super-E™ or E-MAX®chamber, also manufactured by Applied Materials of CA, USA. A chamber plasma-cleaning process may also be performed in other types of high performance etch chambers known in the art, for example, chambers in which a plasma is formed using inductive techniques.
A cross-sectional view of an exemplary multi-frequency etch system 600 in which a chamber plasma-cleaning process can be performed, such as the Enabler™ etch chamber, is shown in
When RF power is applied, a plasma is formed in the chamber processing region over substrate 610. Bias power RF generator 625 is coupled to cathode 620. Bias power RF generator 625 provides bias power to further energize the plasma. Bias power RF generator 625 typically has a low frequency between about 2 MHz to 60 MHz, and in a particular embodiment, is in the 13.56 MHz band. In certain embodiments, the plasma etch system 600 includes an additional bias power RF generator 626 at a frequency at about the 2 MHz band which is connected to the same RF match 627 as bias power RF generator 625. Source power RF generator 630 is coupled through a match (not depicted) to a showerhead 635 which may be anodic relative to cathode 620 to provide high frequency source power to energize the plasma. Source RF generator 630 typically has a higher frequency than the bias RF generator 625, such as between 100 and 180 MHz, and in a particular embodiment, is in the 162 MHz band. Bias power affects the bias voltage on substrate 610, controlling ion bombardment of substrate 610, while source power affects the plasma density relatively independently of the bias on substrate 610. It is noted that the etch performance of a given set of input gases from which the plasma is generated varies significantly with a plasma density and substrate bias, thus both the amount and frequency of power energizing the plasma are important. Because substrate diameters have progressed over time, from 150 mm, 200 mm, 300 mm, etc., it is common in the art to normalize the source and bias power of a plasma etch system to the substrate area.
In particular embodiments, the plasma etch chamber includes a CSTU for a controlling inner and out diameter magnetic field strength ratio to control the density of charged species in the plasma across the diameter of the substrate 610. One exemplary CSTU includes the magnetic coil 640 proximate a periphery of substrate 610 and the magnetic coil 641 proximate a center of substrate 610 to provide a magnetic field of between 0 G and about 25 G in either or both of an inner zone and outer zone of chamber 605.
In an embodiment of the present invention, system 600 is computer controlled by controller 670 to control the low frequency bias power, high frequency source power, CSTU inner to outer magnetic field ratio, etchant gas flows and NSTU inner to outer flow ratios, process pressure and cathode temperatures, as well as other process parameters. Controller 670 may be one of any form of general-purpose data processing system that can be used in an industrial setting for controlling the various subprocessors and subcontrollers. Generally, controller 670 includes a central processing unit (CPU) 672 in communication with memory 673 and input/output (I/O) circuitry 674, among other common components. Software commands executed by CPU 672 cause system 600 to, for example, load a substrate into chamber 605, introduce a plasma-cleaning process gas, such as O2, into chamber 605 and transfer contaminants to the top surface of the substrate. Other processes, such as etching an inorganic dielectric cap layer over a metal layer on a product substrate, in accordance with the present invention, may also be executed by controller 670. Aspects of the present invention may be provided as a computer program product, which may include a computer-readable medium having stored thereon instructions, which may be used to program a computer (or other electronic devices) to load a dummy or seasoning substrate into chamber 605 and introduce a plasma-cleaning gas, such as O2, into the chamber 605, in accordance with an embodiment of the present invention. The computer-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs (compact disk read-only memory), magneto-optical disks, ROMs (read-only memory), RAMs (random access memory), EPROMs (erasable programmable read-only memory), EEPROMs (electrically-erasable programmable read-only memory), magnet or optical cards, flash memory, or other commonly known type computer-readable storage media suitable for storing electronic instructions. Moreover, the present invention may also be downloaded as a program file containing a computer program product, wherein the program file may be transferred from a remote computer to a requesting computer.
Thus, a method for plasma-cleaning a chamber in a process tool has been disclosed. In accordance with an embodiment of the present invention, a substrate is placed on a chuck in a process chamber having a set of contaminants therein. A plasma process is then executed in the process chamber to transfer the set of contaminants to the top surface of the substrate. Then, the substrate, having the set of contaminants thereon, is removed from the process chamber. In one embodiment, the set of contaminants includes particles such as, but not limited to, metal particles and dielectric particles. In another embodiment, the plasma process is a low-pressure plasma process carried out at a pressure approximately in the range of 5-50 mTorr.
