Patent Application
20060102208
The present invention relates to the field of substrate processing. More particularly, the present invention relates to removal of residue from a micro-feature on a substrate using supercritical carbon dioxide processing.
Plasma processing systems are used in the manufacture and processing of semiconductors, integrated circuits, micro-electro mechanical systems (MEMS), displays, and other devices or materials to both remove material from and deposit materials on a substrate. Plasma processing of semiconductor substrates to transfer a pattern of an integrated circuit from a photolithographic mask to the substrate, or to deposit dielectric or conductive films on the substrate, has become a standard method in the industry. Furthermore, the drive to reduce the minimum feature sizes of microelectronic devices to meet the demand for faster, lower power microprocessors and digital circuits has introduced new materials and processes into device manufacturing. These new materials include low dielectric constant (low-k) materials, ultra-low-k (ULK) materials, and porous dielectric materials, which tend to be less chemically robust than more traditional oxide and nitride dielectric layers.
In semiconductor processing, where various types of films are etched, integration challenges and trade-offs still remain. Conventionally, a dielectric layer is patterned with openings for depositing conductive materials to form vertical contacts. During the patterning process, an etch resistant photoresist layer and/or a hard mask layer is deposited over the dielectric layer, exposed to a selected pattern and developed. The layered structure is then etched in a plasma environment where the patterned photoresist layer defines openings in the dielectric layer. An ion implantation process is another example of a process that utilizes a photoresist to mask areas of a semiconductor substrate.
Halocarbon gases are commonly used in the plasma etching of dielectric materials. These gases are known to generate fluorocarbon polymer etch residues during the dielectric etch process. Following the etch process, photoresist remnants and etch residues, both of which are referred to herein as post-etch residues, are frequently observed on the micro-features and chamber surfaces. In the case of carbon-containing dielectric layers, the etch residues can contain a crust with very high carbon content.
A plasma ashing process to remove post-etch residues is commonly followed by wet processing using cleaning chemicals to further clean the residues from the micro-features. Wet processing usually includes the use of water as a carrier of the cleaning chemicals to the micro-features. In the case of carbon-containing low-k dielectric materials, an oxygen ashing process can reduce the carbon content and increase the dielectric constant of the materials. In addition, wet processing of porous dielectric layers can leave moisture and cleaning materials in the pores, which in turn can increase the dielectric constant of the layers.
There has been a significant amount of activity in developing alternative methods and systems for cleaning substrates and removing processing residues, especially post-etch residues. One technology that shows a great potential towards achieving this goal is supercritical fluid technology. Methods and systems for cleaning post-etch residues from substrates using supercritical processing have been described in U.S. Pat. Nos. 6,500,605 and 6,509,141, both of which are hereby incorporated by reference. While supercritical processing provides a promising alternative to ashing and wet processing for removing post-etch residues from wafer substrates, there is still a need to develop improved supercritical fluid processing systems and methods that can be used to reduce the time and/or steps required to clean the substrates and to address the requirements of new materials used for patterning the substrates.
The present invention is directed to a film removal system for removing a residue from a micro-feature on a substrate. By way of example, the residue can be a post-etch residue, including polymer etch residue, photoresist remnants, anti-reflective coatings and other materials used for patterning a substrate. To this end, the film removal system includes a supercritical fluid processing system that includes a process chamber and a carbon dioxide supply system. The processing system is configured for generating a supercritical carbon dioxide cleaning solution, for treating the substrate with the supercritical carbon dioxide cleaning solution to remove the residue from the micro-feature, and for maintaining the supercritical carbon dioxide cleaning solution at a temperature between about 35° C. and about 80° C. The film removal system further includes an ozone generator configured for providing an ozone processing environment for treating the substrate, and a controller configured for controlling the ozone generator and the supercritical fluid processing system.
According to one embodiment of the invention, the film removal system includes an ozone processing system that is operatively coupled to the supercritical fluid processing system and that comprises an ozone process chamber and the ozone generator for pre-treating the substrate prior to treating the substrate in the supercritical fluid processing system. In a further embodiment, a substrate transfer system couples the ozone process chamber to the process chamber of the supercritical fluid processing system for transferring the substrate therebetween.
According to another embodiment of the invention, the ozone generator is coupled to the process chamber in the supercritical fluid processing system and is configured to provide the ozone processing environment to the process chamber either to pre-treat the substrate prior to the treating step with the supercritical carbon dioxide cleaning solution or to concurrently treat the substrate.
In the accompanying drawings:
The term micro-feature, as used herein, refers to a feature formed in a substrate and/or in a layer or layers formed on a substrate that has a dimension on the micrometer scale, and typically the sub-micron scale, i.e., less than 1 μm. The micro-feature can, for example, contain high-aspect ratio trenches and/or vias with lateral dimensions in the sub-micron or deep sub-micron regime and vertical dimensions up to several microns.
The micro-feature 1 in
Embodiments of the present invention are well suited for removing post-etch polymers and/or polymeric ARC layers from micro-features containing porous and/or low-k silicon oxide-based layers. Low-k silicon oxide-based layers include low-k layers formed of materials exhibiting low dielectric constants of between 3.5-2.5. Silicon oxide-based materials include a number of low-k materials that contain silicon oxide and hydrocarbon components. These carbon-containing dielectric materials include SiCOH materials. Embodiments of the present invention can also be applied to removing residues from a substrate doped through a photoresist mask using techniques such as ion implantation, where inorganic contaminants can become embedded in the photoresist mask, thereby changing the physical characteristics and the composition of the photoresist mask and making removal of the photo-resist mask more difficult.
While the present invention is described in relation to applications for removing post-etch residues typically used in wafer patterning processes, it will be clear to one skilled in the art that the present invention can be used to remove any number of different residues (including polymers and oils) from any number of different materials (including silicon nitrides) and structures, including micro-mechanical, micro-optical, micro-electrical structures, and combinations thereof.
According to an embodiment of the invention, a film removal system is provided for cleaning a substrate containing a micro-feature having a residue thereon. The film removal system includes a supercritical fluid processing system configured for treating the substrate witha supercritical carbon dioxide cleaning solution to remove the residue from the micro-feature, and for maintaining the supercritical carbon dioxide cleaning solution at a temperature between about 35° C. and about 80° C., an ozone generator configured for providing an ozone processing environment for treating the substrate, and a controller configured for controlling the supercritical fluid processing system and the ozone generator.
According to another embodiment of the invention, the film removal system can be configured to perform the treating step in a process chamber of the supercritical fluid processing system and a pre-treating step with the ozone processing environment in an ozone processing system that contains the ozone generator and that is operatively coupled to the supercritical fluid processing system.
According to yet another embodiment of the invention, the film removal system can be configured to perform both the ozone treating step and the supercritical cleaning solution treating step in a supercritical fluid processing system.
In one embodiment of the invention, the substrate 105 can be a silicon substrate containing etched micro-features with post-etch residues thereon, as explained above. In general, the substrate can include a semiconductor material, a metallic material, a dielectric material, a ceramic material, or a polymer material, or a combination of two or more thereof. The semiconductor material can, for example, include Si, Ge, Si/Ge, or GaAs. The metallic material can, for example, include Cu, Al, Ni, Ru, Ti, or Ta. The dielectric material can, for example, include SiO2, SiON, SiCOH, Ta2O5, TiO2, ZrO2, Al2O3, Y2O3, HfSiOx, HfO2, ZrSiOx, TaSiOx, SrOx, SrSiOx, LaOx, LaSiOx, YOx, or YSiOx. The ceramic material can, for example, include AlN, SiC, BeO, or LaB6. The substrate 40 can be of any size, for example a 200 mm substrate, a 300 mm substrate, or an even larger substrate. As would be appreciated by those skilled in the art, other semiconductor materials, metallic materials, dielectric materials, and ceramic materials may be employed without departing from the scope of the invention.
The ozone process chamber 20 is also equipped with a stage or chuck 35 for supporting and holding the substrate 105 while the substrate 105 is pre-treated by exposing it to the ozone processing environment 30. The stage or chuck 35 can also be configured to heat or cool the substrate 105 before, during and/or after exposing the substrate 105 to the ozone processing environment 30. In one embodiment of the invention, the substrate temperature can be between about 20° C. and about 400° C., during exposure to the ozone processing environment 30. In another embodiment of the invention, the substrate temperature can be between about 60° C. and about 200° C. Generally, the rate of reaction between a residue and an ozone processing environment increases with substrate temperature. However, care must be taken when pre-treating substrates with the ozone processing environment 30, since many dielectric materials, in particular low dielectric constant (k) or porous dielectric materials, can be damaged if the substrate temperature is too high during the ozone pre-treating process. In one embodiment of the invention, the substrate can be pre-treated for a time period between about 10 sec and about 1200 sec. In another embodiment of the invention, the substrate can be pre-treated for a time period between about 30 sec and about 300 sec.
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Details of processing equipment that have multiple process chambers, including at least one supercritical fluid process chamber, are described in U.S. Pat. No. 6,748,966, the contents of which is hereby incorporated by reference.
In
In
The processing module 110 can include an upper assembly 112, a frame 114, and a lower assembly 116. The upper assembly 112 can comprise a heater (not shown) for heating the process chamber 108, the substrate 105, or the supercritical carbon dioxide fluid, or a combination of two or more thereof. Alternately, a heater is not required. The frame 114 can include means for flowing a supercritical carbon dioxide fluid through the process chamber 108. In one example, a circular flow pattern can be established in the process chamber 108; and in another example, a substantially linear flow pattern can be established in the process chamber 108. Alternately, the means for flowing a processing fluid in the process chamber 108 can be configured differently. The lower assembly 116 can comprise one or more lifters (not shown) for moving the chuck 118 and/or the substrate 105. Alternately, a lifter is not required.
In one embodiment, the processing module 110 includes a holder or chuck 118 for supporting and holding the substrate 105 while processing the substrate 105. The stage or chuck 118 can also be configured to heat or cool the substrate 105 before, during, and/or after processing the substrate 105. Alternately, the processing module 110 can include a platen (not shown) for supporting and holding the substrate 105 while processing the substrate 105. Like the ozone processing system 10, the process chamber 108 can process a substrate 105 of any size, for example a 200 mm substrate, a 300 mm substrate, or an even larger substrate.
The circulation system 120 can comprise one or more valves for regulating the flow of a supercritical processing solution through the circulation system 120 and through the processing module 110. The circulation system 120 can comprise any number of back-flow valves, filters, pumps, and/or heaters (not shown) for maintaining and flowing a supercritical carbon dioxide solution through the circulation system 120 and through the processing module 110. Carbon dioxide fluid is in a supercritical state when above the critical temperature Tc of about 31° C. and the critical pressure Pc of about 1,070 psig. Supercritical carbon dioxide fluid has virtually no viscosity or surface tension and has therefore no difficulty in penetrating all the way to the bottom of a micro-feature to remove a residue from the micro-feature. In one embodiment of the invention, the temperature of the supercritical carbon dioxide fluid in the process chamber 108 can be between about 35° C. and about 80° C. Alternately, the temperature of the carbon dioxide fluid in the process chamber 108 can be between about 60° C. and about 70° C.
The processing system 100 can contain a carbon dioxide supply system 140. As shown in
The carbon dioxide supply system 140 can contain a carbon dioxide source (not shown) and a plurality of flow control elements (not shown) for controlling delivery of carbon dioxide fluid to the process chamber 108. For example, the carbon dioxide source can include a carbon dioxide feed system, and the flow control elements can include supply lines, valves, filters, pumps, and heaters. The carbon dioxide supply system 140 can comprise an inlet valve (not shown) that is configured to open and close to allow or prevent the stream of carbon dioxide from flowing into the process chamber 108. For example, controller 180 can be used to determine fluid parameters including pressure, temperature, process time, and flow rate.
In the illustrated embodiment in
Further details of fluoride sources and methods of generating supercritical fluid processing solutions containing fluorine are described in U.S. patent application Ser. No. 10/442,557, filed May 20, 2003, and titled “TETRA-ORGANIC AMMONIUM FLUORIDE AND HF IN SUPERCRITICAL FLUID FOR PHOTORESIST AND RESIDUE REMOVAL”, and U.S. patent application Ser. No. 10/321,341, filed Dec. 16, 2002, and titled “FLUORIDE IN SUPERCRITICAL FLUID FOR PHOTORESIST POLYMER AND RESIDUE REMOVAL,” both of which are hereby incorporated by reference.
In addition, the cleaning chemical can include chelating agents, complexing agents and other oxidants, organic and inorganic acids that can be introduced into supercritical carbon dioxide with one or more carrier solvents, including N,N-dimethylacetamide (DMAC), gamma-butyrolacetone (BLO), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), N-methylpyrrolidone (NMP), dimethylpiperidone, propylene carbonate, or alcohols (e.g., methanol, ethanol, or 2-propanol), or a combination of two or more thereof. As may be appreciated by those skilled in the art, other solvents may be employed without departing from the scope of the invention.
The chemical supply system 130 can furthermore provide a rinsing chemical for generating supercritical carbon dioxide rinsing solutions within the process chamber 108. The rinsing chemical can include one or more organic solvents including, but not limited to, alcohols, ketones, or both. In one embodiment of the invention, the organic solvent can contain methanol, ethanol, n-propanol, isopropanol, benzyl alcohol, acetone, butylene carbonate, propylene carbonate, dimethylsulfoxide, γ-butyrolactone, dimethyl formamide, dimethyl acetamide, or ethyl lactate, or a combination of two or more thereof. As may be appreciated by those skilled in the art, other organic solvents may be employed without departing from the scope of the invention.
The processing system 100 can also comprise a pressure control system 150. As shown in
Furthermore, the processing system 100 can comprise an exhaust system 160. As shown in
Controller 180 can be used to feed forward and/or feed back information. For example, feed-forward information can comprise pre-process data associated with an in-coming substrate. This pre-process data can include lot data, batch data, run data, composition data that includes type of photoresist used, type of substrate, type of layers overlying the substrate, and history data including, for example, type of process gases used in a prior etch process. The pre-process data can be used to establish an input state for a substrate. The controller 180 can use the difference between an input data item for an incoming substrate (input state) and a desired data item (desired state) to predict, select, or calculate a set of process parameters to achieve the desired result of changing the state of the substrate from the input state to the desired state. The desired state can, for example, indicate the level of substrate cleanliness following a cleaning process and/or a rinse process. For example, this predicted set of process parameters can be a first estimate of a recipe to use based on an input state and a desired state. In one embodiment, data such as the input state and/or the desired state data can be obtained from a host.
In one example, the controller 180 knows the input state and a model equation for the desired state for the substrate, and the controller determines a set of recipes that can be performed on the substrate to change the status of the substrate from the input state to a desired state. For example, the set of recipes can describe a multi-step process involving a set of process systems. For example, post-process metrology data can be obtained to evaluate the state of the substrate, i.e., if the residue has been sufficiently removed from the substrate. Post-process metrology data can be obtained after a time delay that can vary from minutes to days. Post-process metrology data can be used as a part of the feedback control.
The controller 180 can compute a predicted state for the wafer based on the input state, the process characteristics, and a process model. For example, a cleaning rate model can be used along with a contaminant level to compute a predicted cleaning time. Alternately, a rinse rate model can be used along with a contaminant level to compute a processing time for a rinse process. The controller 180 can comprise a database component (not shown) for storing input and output data. Process models can include linear models, quadratic models, full quadratic models, and higher order polynomial models. A process model can provide the relationship between one or more process recipe parameters or setpoints and one or more process results and can include multiple variables.
In a supercritical cleaning/rinsing process, the desired process result can be a process result that is measurable using an optical measuring device. For example, the desired process result can be an amount of contaminant (e.g., residue) on a micro-feature. After each cleaning process run, an actual process result can be measured and compared to a desired process result to determine process compliance. After each cleaning process run, the actual process results can be determined, and a system of equations can be created to solve for the coefficients in the model equation.
In general, process control can include updating a process module recipe using metrology information measured on the substrate prior to its arrival in the process module 110. For a cleaning process, the incoming substrates should all be the same, with the same pre-processing data. The controller can use the pre-processing data to verify that all of the substrates used in a group are the same. The process of creating the process models requires an understanding of the mechanics of experimental design, execution of an appropriate experiment and analysis of the resultant experimental data. This process can be highly automated and integrated into the film removal system 70 using the technique described herein.
In operation, the ozone generator 45 generates ozone that enters into the process chamber 108, where the substrate 105 is exposed to the ozone processing environment. In one embodiment of the invention, a continuous stream of ozone can be generated and used to pressurize the process chamber 108, or the ozone can flow through the process chamber 108 and exit the process chamber 108 through the exhaust system 160. After the ozone pre-treatment, the pre-treated residue can be removed from the substrate 105 using a supercritical carbon dioxide cleaning solution. After the pre-treated residue has been removed from the substrate 105, the substrate can be treated with one or more supercritical rinsing solutions in the process chamber 108.
In another embodiment of the invention, an ozone pre-treatment can be omitted from the process and the substrate treated with a supercritical carbon dioxide cleaning solution to remove a residue from the substrate.
In yet another embodiment of the invention, the process chamber 108 can be pressurized with ozone from the ozone generator 125, and a supercritical carbon dioxide cleaning solution containing ozone can be generated within the process chamber 108 to remove the residue from the substrate 105. An ozone pre-treatment may be included or omitted. After the residue has been removed from the substrate 105, the substrate 105 can be treated with one or more supercritical carbon dioxide rinsing solutions in the process chamber 108.
When the pressure within the process chamber 108 reaches an operating pressure Pop at the start of time period T2, the supercritical carbon dioxide cleaning solution is circulated over and/or around the substrate 105 and through the process chamber 108 using the circulation system 120, such as described above. The operating pressure Pop can be any value as long as the pressure is sufficient to maintain supercritical fluid conditions and can, for example, be about 2,800 psig. The length of the time period T2 can be selected to remove the desired amount of the residue from the substrate 105.
Next, a push-through process can be carried out during time period T3, where a fresh stock of supercritical carbon dioxide fluid is fed into the process chamber 108 from the carbon dioxide supply system 140, thereby increasing the pressure in the process chamber 108. Furthermore, during the push-through process in period T3, the supercritical carbon dioxide cleaning solution, along with any process residue suspended or dissolved therein, is simultaneously displaced from the process chamber 108 using the exhaust system 160.
The push-through process reduces the amount of particulates and contaminants that can fall-out from the supercritical carbon dioxide cleaning solution when its composition is altered by adding the fresh stock of supercritical carbon dioxide fluid. A number of methods for reducing fall-out of particles and contaminants using push-through techniques and/or pressurization techniques are described in U.S. patent application Ser. No. 10/338,524, filed Jan. 7, 2003, titled “METHOD FOR REDUCING PARTICULATE CONTAMINATION IN SUPERCRITCIAL FLUID PROCESSING”, and U.S. patent application Ser. No. 10/394,802, filed Mar. 21, 2003, titled “REMOVAL OF CONTAMINANTS USING SUPERCRITICAL PROCESSING”, both of which are hereby incorporated by reference in their entirety.
When the push-through step is complete at the end of time period T3, a plurality of decompression and compression cycles can be performed in the process chamber 108 during time period T4 to further remove contaminants from the substrate 105 and the supercritical fluid processing system. The decompression and compression cycles can be performed using the exhaust system 160 to lower the process chamber pressure to below the operating pressure Pop and then injecting fresh supercritical carbon dioxide fluid to raise the process chamber pressure to above the operating pressure Pop. The decompression and compression cycles allow the cleaning chemicals and any removed residue to be removed from the system before the next processing step. The supercritical cleaning steps are repeated as needed with the same or different cleaning chemicals. After a pre-determined number of the decompression and compression cycles are completed (four cycles are shown in
The graph shown in
After the substrate is pre-treated with ozone, in step 504 carbon dioxide is added to the process chamber, which is then pressurized to generate supercritical carbon dioxide fluid, and a cleaning chemical is added to the supercritical carbon dioxide fluid to generate a supercritical carbon dioxide cleaning solution. After the supercritical carbon dioxide cleaning solution is generated in step 504, the substrate is maintained in the supercritical carbon dioxide cleaning solution in step 506 for a period of time sufficient to remove at least a portion of the residue from the substrate, where the supercritical carbon dioxide cleaning solution is maintained at a temperature between about 35° C. and about 80° C. During the step 506, the supercritical carbon dioxide cleaning solution can be circulated through the process chamber and/or otherwise agitated to move the supercritical carbon dioxide cleaning solution over surfaces of the substrate.
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It will be clear to one skilled in the art that any number of different treatment sequences are within the scope of the invention. For example, cleaning steps and rinsing steps can be combined in any number of different ways to facilitate the removal of residue from a micro-feature. Furthermore, it may be appreciated by those skilled in the art that each of the steps or stages in the flowchart of
A substrate containing photoresist and etch residues on etched dielectric micro-features was cleaned according to embodiments of the invention. The substrate was cleaned using an ozone processing system operatively coupled to a supercritical fluid processing system as schematically shown in
Scanning electron microscope (SEM) images of the substrate showed complete removal of the photoresist and etch residues from the micro-features. The SEM images further showed the presence of polymer residue on the sidewalls of the micro-features. The polymer residue was subsequently fully removed by performing an additional cleaning step using a supercritical carbon dioxide cleaning solution containing 15 ml of dimethyl acetamide and 80 μl (microliters) of pyridine-HF at 3,000 psig. Following the additional cleaning step, the substrate was exposed for 2 min to a supercritical carbon dioxide rinse solution containing 20 ml of methanol (CH3OH) at 3,000 psig.
While the present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the invention, such references herein to specific embodiments and details thereof are not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications may be made in the embodiments chosen for illustration without departing from the scope of the invention.
The present invention is related to U.S. patent application Ser. No. 10/______, entitled METHOD FOR REMOVING A RESIDUE FROM A SUBSTRATE USING SUPERCRITICAL CARBON DIOXIDE PROCESSING and filed on even date herewith, the entire content of which is herein incorporated by reference. The related application is not commonly owned.
