Patent Application
20070049020
1. Field of the Invention
Embodiments of the invention generally relate to a system for annealing semiconductor substrates.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio, i.e., greater than about 4:1, interconnect features with a conductive material, such as copper. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as the interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. Therefore, plating techniques, i.e., electrochemical plating (ECP) and electroless plating, have emerged as promising processes for void free filling of sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate (or a layer deposited thereon) may be efficiently filled with a conductive material. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate (generally through PVD, CVD, or other deposition process in a separate tool), and then the surface features of the substrate are exposed to an electrolyte solution (in the ECP tool), while an electrical bias is applied between the seed layer and a copper anode positioned within the electrolyte solution. The electrolyte solution generally contains ions to be plated onto the surface of the substrate, and therefore, the application of the electrical bias causes these ions to be plated onto the biased seed layer, thus depositing a layer of the ions on the substrate surface that may fill the features.
Once the plating process is completed, the substrate is generally transferred to at least one of a substrate rinsing cell or a bevel edge clean cell. Bevel edge clean cells are generally configured to dispense an etchant onto the perimeter or bevel of the substrate to remove unwanted metal plated thereon. The substrate rinse cells, often called spin rinse dry cells, generally operate to rinse the surface of the substrate (both front and back) with a rinsing solution to remove any contaminants therefrom. Further, the rinse cells are often configured to spin the substrate at a high rate of speed in order to spin off any remaining fluid droplets adhering to the substrate surface. Once the remaining fluid droplets are spun off, the substrate is generally clean and dry, and therefore, ready for transfer from the ECP tool.
To overcome problems associated with void formation as well as variation in copper oxidation, heat treatment of a film after deposition is generally performed. One effective technique for heat treating the film is annealing. Annealing is the process of subjecting a material to heat for a specific period of time. Annealing may also provide a thermodynamic driving force for the metal layers to form a predictable microstructure. A metal layer can, for example, be annealed in a particular atmosphere in order to provide a specific and predictable set of electrical properties (e.g. electrical resistivity).
Since copper has a relatively low melting temperature compared to other metals typically deposited in semiconductor manufacturing, copper is a promising candidate for annealing. New developments in semiconductor manufacturing that have focused on depositing copper, especially by ECP techniques, have sparked new interest in developing improved copper annealing processes. Additionally, copper deposited by ECP undergoes the physical phenomena of self-annealing. In self-annealing, copper undergoes microstructural changes after plating at room temperature. High temperature annealing can modify this self-annealing process.
In conventional annealing processes, substrates may be typically heated to temperatures from about 250° C. to 450° C. for about 45 seconds to about 30 minutes. However, due to the recrystallization or densification of the ECP deposited layer during the annealing process and perhaps, thermal expansion mismatch between the substrate and the ECP deposited layer, the ECP deposited layer often experiences a tensile stress after the annealing process. Depending on the extent of the stress, tensile stress often reduces the quality of the deposited layer.
Some have tried to reduce the extent of the tensile stress by varying plating bath compositions. However, varying the plating bath compositions often leads to a change in layer resistivity.
Accordingly, a need exists in the art for a new method and apparatus for reducing or compensating for the tensile stress experienced by the deposited layer during annealing.
Various embodiments of the invention are directed to a method for compensating for tensile stress on a layer deposited on a substrate. The method includes disposing the substrate between a bladder and a contact ring, and applying pressure against a back side of the substrate toward the contact ring to bend a center region of the substrate until the substrate assumes a convex shape relative to an upward flow of a plating solution.
Various embodiments of the invention are also directed to a method for compensating for tensile stress on a film deposited on a substrate. The method includes providing a thrust plate having a bottom surface defining a first circular recess for containing a first o-ring and a second circular recess for containing a second o-ring. The diameter of the first o-ring is substantially larger than the diameter of the second o-ring and the diameter of the first o-ring substantially coincides with the diameter of the substrate. The method further includes disposing the substrate between the thrust plate and a contact ring and applying pressure against a back side of the substrate toward the contact ring to bend a center region of the substrate.
Various embodiments of the invention are also directed to thrust plate for retaining a substrate. The thrust plate includes a first o-ring for biasing a back side of the substrate against a contact ring. The first o-ring has a diameter substantially the same as the diameter of the substrate and a second o-ring for bending a center region of the substrate. The second o-ring has a diameter less than the first o-ring.
Various embodiments of the invention are also directed a method for annealing a substrate. The method includes positioning the substrate on a heating plate for a first predetermined period of time. The heating plate comprises a curved substrate support surface and the heating plate is maintained at a temperature of between about 200° C. and 400° C. The method further includes pressing the substrate against the curved substrate support surface.
Various embodiments of the invention are also directed an annealing chamber, which includes a heating plate having a first curved substrate support surface, a cooling plate having a second curved substrate support surface and a substrate transfer mechanism configured to transfer one or more substrates between the heating plate and the cooling plate.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical 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 invention provide a method and apparatus that can be used to reduce the tensile stress developed in a layer of film deposited by electrochemical plating (ECP). The method and apparatus generally provide ways to bend or bow a substrate during one of the ECP deposition processing steps (e.g., ECP deposition, anneal process) to compensate for the tensile stress induced in the ECP deposited film after the annealing process. Although the various to bend or bow the substrate are described with reference to an ECP process, other embodiments contemplate the various ways of bending the substrate in an electroless deposition processing system.
The term “substrate” as used herein may refer to any monolithic or multi-layer structure upon which a film forming process may be performed. Materials commonly used in the semiconductor industry to form substrates may include monocrystalline silicon (e.g., Si<100>, Si<111>), polycrystalline silicon, amorphous silicon, strained silicon, silicon on insulator (SOI), doped silicon, silicon germanium, germanium, gallium arsenide, glass, sapphire, silicon oxide, silicon carbon nitride, silicon nitride, silicon oxynitride and/or carbon doped silicon oxides, such as SiOxCy, for example, BLACK DIAMOND™ low-k dielectric, available from Applied Materials, Inc., located in Santa Clara, Calif. Substrates may have various dimensions, such as 200 mm or 300 mm diameter wafers, as well as rectangular or square panes. Substrates on which embodiments of the invention may be useful include, but are not limited to semiconductor wafers, such as monocrystalline silicon, silicon oxide, strained silicon, silicon germanium, doped or undoped polysilicon, doped or undoped silicon wafers, and patterned or non-patterned wafers. Substrates made of glass or plastic, which are commonly used to fabricate flat panel displays and other similar devices, may also be included.
The anneal station 135, which will be discussed further herein, may include a two position annealing chamber, in which a cooling plate/position 136 and a heating plate/position 137 are positioned adjacently with a substrate transfer robot 140 positioned proximate between the two stations. The robot 140 is generally configured to move substrates between the respective heating 137 and cooling plates 136. It should be noted that number of processing positions and the orientation of the anneal chamber as shown herein are not intended to limit the scope of the invention.
As mentioned above, ECP system 100 also includes a processing mainframe 113 having a substrate transfer robot 120 centrally positioned thereon. Robot 120 generally includes one or more arms/blades 122, 124 configured to support and transfer substrates thereon. Additionally, robot 120 and the accompanying blades 122, 124 are generally configured to extend, rotate, and vertically move so that robot 120 may insert and remove substrates to and from a plurality of processing locations 102, 104, 106, 108, 110, 112, 114, 116 positioned on the mainframe 113. Similarly, factory interface robot 132 also includes the ability to rotate, extend, and vertically move its substrate support blade, while also allowing for linear travel along the robot track that extends from the factory interface 130 to the mainframe 113.
Process locations 102, 104, 106, 108, 110, 112, 114, 116 may be any number of processing cells utilized in an electrochemical plating platform. More particularly, the process locations may be configured as electrochemical plating cells, rinsing cells, bevel clean cells, spin rinse dry cells, substrate surface cleaning cells (which collectively includes cleaning, rinsing, and etching cells), electroless plating cells, metrology inspection stations, and/or other processing cells that may be beneficially used in conjunction with a plating platform. Each of the respective processing cells and robots are generally in communication with a process controller 111, which may be a microprocessor-based control system configured to receive inputs from both a user and/or various sensors positioned on the system 100 and appropriately control the operation of system 100 in accordance with the inputs.
In the exemplary plating system illustrated in
Each of the fluid inlets/drains 209 are generally configured to individually supply or drain a fluid to or from either the anode compartment or the cathode compartment of plating cell 200. Anode member 205 generally includes a plurality of slots 207 formed therethrough, wherein the slots 207 are generally positioned in parallel orientation with each other across the surface of the anode 205. The parallel orientation allows for dense fluids generated at the anode surface to flow downwardly across the anode surface and into one of the slots 207.
Plating cell 200 further includes a membrane support assembly 206. Membrane support assembly 206 may be secured at an outer periphery thereof to base member 204, and may include an interior region configured to allow fluids to pass therethrough. A membrane 208 is stretched across the support assembly 206 and operates to fluidly separate a catholyte chamber and anolyte chamber portions of the plating cell. The membrane support assembly 206 may include an o-ring type seal positioned near a perimeter of the membrane, wherein the seal is configured to prevent fluids from traveling from one side of the membrane secured on the membrane support to the other side of the membrane. A diffusion plate 210 is generally positioned in the cell between membrane 208 and the substrate being plated. The diffusion plate 210 may be a porous ceramic disk member configured to generate a substantially laminar flow or even flow of fluid in the direction of the substrate being plated. The exemplary plating cell 200 may be further described in commonly assigned U.S. patent application Ser. No. 10/268,284, which was filed on Oct. 9, 2002 under the title “Electrochemical Processing Cell”, which is incorporated herein by reference in its entirety.
Because of its flexibility, the bladder 336 deforms to accommodate the asperities of the substrate backside and contacts of the cathode contact ring 319, thereby mitigating misalignment with the conducting cathode contact ring 319. The compliant bladder 336 prevents the electrolyte from contaminating the backside of the substrate 321 by establishing a fluid tight seal at a perimeter portion of a backside of the substrate 321. Once inflated, a uniform pressure is delivered downward toward the cathode contact ring 319 to achieve substantially equal force at all points where the substrate 321 and cathode contact ring 319 interface. The force may be varied as a function of the pressure supplied by the fluid source 338.
In one embodiment, the bladder 336 may continued to be inflated until a center region of the substrate 321 is bent or bowed. For a 200 mm substrate, a backside pressure up to 5 psi may be used to bow the substrate, while for a 300 mm substrate, a backside pressure up to 10 psi may be used. Because substrates typically exhibit some measure of pliability, a backside pressure causes the substrate 321 to bow or assume a convex shape relative to the upward flow of the electrolyte. The degree of bowing may be varied according to the pressure supplied by the pumping system 359. In one embodiment, for a 300 mm substrate, the center region of the substrate may be bowed to a distance from about 2 mm to about 5 mm above a horizontal line connecting the periphery of the substrate. Other details of the inflatable bladder assembly 370 may be described in commonly assigned U.S. patent application Ser. No. 10/690,033 filed Oct. 20, 2003 under the title “Electro-chemical Deposition System”, which is incorporated herein by reference in its entirety.
The annealing system 400 may also include an electrical system controller 406 positioned on an upper portion of the frame member 401. The electrical system controller 406 generally operates to control the electrical power provided to the respective components of the annealing system 400, and in particular, the electrical system controller 406 operates to control the electrical power delivered to a heating element of the annealing chamber 402 so that the temperature of the annealing chamber may be controlled. The annealing system 400 may further include fluid and gas supply assembly 404 positioned on the frame member 401, generally below the annealing chambers 402. The fluid and gas supply assembly 404 may be configured to supply an annealing processing gas, such as nitrogen, argon, helium, hydrogen, or other inert gases that are amenable to semiconductor processing annealing, to the respective annealing chambers 402. Fluid and gas supply assembly 404 is also configured to supply and regulate fluids delivered to the annealing chamber 402, such as a cooling fluid used to cool the chamber body and/or annealed substrates after the heating portion of the annealing process is completed. The cooling fluid, for example, may be a chilled or cooled water supply. Supply assembly 404 may further include a vacuum system (not shown) that is individually in communication with the respective annealing chambers 402. The vacuum system may operate to remove ambient gases from the annealing chambers 402 prior to beginning the annealing process and may be used to support a reduced pressure annealing process. Therefore, the vacuum system allows for reduced pressure annealing processes to be conducted in the respective annealing chambers 402, and further, varying reduced pressures may be simultaneously used in the respective annealing chambers 402 without interfering with the adjoining chamber 402 in the stack.
The cooling plate 504 may include a substantially planar substrate support surface. In one embodiment, the cooling plate includes a curved substrate support surface. The substrate support surface includes a plurality of vacuum apertures 522, which are selectively in fluid communication with a vacuum source (not shown). The vacuum apertures 522 may be used to generate a reduced pressure at the substrate support surface to secure or vacuum chuck a substrate to the substrate support surface. The interior portion of the cooling plate 504 may include a plurality of fluid conduits formed therein, wherein the fluid conduits are in fluid communication with the cooling fluid source used to cool the chamber body 501. When the fluid conduits are implemented into the cooling plate 504, the cooling plate 504 may be used to rapidly cool a substrate positioned thereon. Alternatively, the cooling plate 504 may be manufactured without the cooling passages formed therein, and as such, the cooling plate 504 may be used to cool a substrate at a slower rate than the embodiment where the cooling plate 504 is essentially chilled by the cooling conduits formed therein. Further, as noted above, the cooling plate 504 includes a plurality of notches 516 formed into the perimeter of the plate 504, wherein the notches 516 are spaced to receive the tabs 510 of the substrate support blade 508 when the blade is lowered into a processing position.
The heating plate 502, in similar fashion to the cooling plate 504, may also include a substantially planar substrate support surface. In one embodiment, the heating plate 502 includes a curved substrate support surface. The substrate support surface includes a plurality a vacuum apertures 522 formed therein, each of the vacuum apertures 522 being selectively in fluid communication with a vacuum source (not shown). As such, the vacuum apertures 522 may be used to vacuum chuck or secure a substrate to the heating plate 502 for processing. The interior of the heating plate 502 includes a heating element (not shown), wherein the heating element is configured to heat the substrate support surface of the heating plate 502 to a temperature of between about 100° C. to about 500° C. The heating element may include, for example, an electrically driven resistive element or a hot fluid conduit formed into the heating plate 502. Alternatively, the annealing chambers may utilize an external heating device, such as lamps, inductive heaters, or resistive elements, positioned above or below the heating plate 502. Further, as noted above, the heating plate 502 includes a plurality of notches 516 formed into the perimeter of the plate 502, wherein the notches 516 are spaced to receive the tabs 510 of the substrate support blade 508 when the blade is lowered into a processing position. Additionally, one or more of the vacuum apertures 522 may also be in fluid communication with a heated gas supply, and as such, one or more of the apertures may be used to dispense a heated gas onto the backside of the substrate during processing. The heated gas, which may be heated to a temperature of between about 100° C. and 400° C., may be supplied from a plurality of apertures in fluid communication with the heated gas source, and then pumped from the backside of the substrate by other ones of the apertures 522 that are in fluid communication with the vacuum source noted above.
The heating plate 602 may include a heating plate base member 608 that has a resistive heating element 600 positioned thereon. The resistive heating element 600 may be encased in the interior portion 610 of the heating plate 602. A top plate 612 is positioned above the interior portion 610. The top, interior, and base members are generally manufactured from a metal having desirable thermal conductivity properties, such as aluminum, for example. Additionally, the three sections of the plate 602 may be brazed together to form a unitary heat transferring plate 602. The lower portion of the plate 602, i.e., the bottom of the base member 608, may include a stem 606 that supports the plate 602. The stem is generally of a substantially smaller diameter than the plate member 602, which minimizes thermal transfer to the chamber base or walls. More particularly, the stem member generally has a diameter of less than about 20% of the diameter of the heating plate 602. Additionally, the lower portion of the stem 606 includes a thermocouple 614 for measuring the temperature of the heating plate 602 and a power connection 616 to conduct electrical power to the heating element 600.
Referring back to
The annealing chamber 500 may further include a pump down aperture 524 positioned in fluid communication with the processing volume 550. The pump down aperture 524 is selectively in fluid communication with a vacuum source (not shown) and is generally configured to evacuate gases from the processing volume 550. Additionally, the annealing chamber generally includes at least one gas dispensing port 526 or gas dispensing showerhead positioned proximate the heating plate 502. The gas dispensing port is selectively in fluid communication with a processing gas source, i.e., supply source, and is therefore configured to dispense a processing gas into the processing volume 550. The gas dispensing port 526 may also be a gas showerhead assembly positioned in the interior of the annealing chamber. The pump down aperture 524 and the gas dispensing nozzle may be utilized cooperatively or separately to minimize ambient gas content in the annealing chamber, i.e., both of the components or one or the other of the components may be used.
The annealing chamber 500 may further include a substrate transfer mechanism actuator assembly 518 in communication with the substrate transfer mechanism 506. The actuator 518 is generally configured to control both pivotal movement of the blade 508, as well as the height or Z position of the blade relative to the heating or cooling member. An access door 514, which may be a slit valve-type door, for example, is generally positioned in an outer wall of the chamber body 501. The access door 514 is generally configured to open and allow access into the processing volume 550 of the annealing chamber 500. As such, access door 514 may be opened and a robot 512 (which may be robot 132 from the exemplary FI or the exemplary mainframe substrate transfer robot 120 illustrated in
More particularly, the process of inserting a substrate into the annealing chamber may include positioning the blade 508 over the cooling plate 504 in a loading position, i.e., a position where the tabs 510 are vertically positioned at a location above the upper surface of the cooling plate 504. The blade 508 and tabs 510 may be positioned relative to each other such that there is a vertical space between the upper surface of the tabs 510 and the lower surface of the blade 508. This vertical space is configured to allow a robot blade 512 having a substrate supported thereon to be inserted into the vertical space and then lowered such that the substrate is transferred from the blade 512 to the substrate support tabs 510. Once the substrate is supported by the tabs 510, the external robot blade 512 may be retracted from the processing volume 550 and the access door 514 may be closed to isolate the processing volume 550 from the ambient atmosphere.
Once the door 514 is closed, a vacuum source in communication with the pump down aperture 524 may be activated and caused to pump a portion of the gases from the processing volume 550. During the pumping process, or shortly thereafter, the gas dispensing port(s) 526 may be opened to allow the processing gas to flood the processing volume 550. The process gas is generally an inert gas that is known not to react under the annealing processing conditions. This configuration, i.e., the pump down and inert gas flooding process, is generally configured to remove as much of the oxygen from the annealing chamber/processing volume as possible, as the oxygen is known to cause oxidation to the substrate surface during the annealing process. The vacuum source may be terminated and the gas flow stopped when the chamber reaches a predetermined pressure and gas concentration, or alternatively, the vacuum source may remain activated during the annealing process and the gas delivery nozzle may continue to flow the processing gas into the processing volume.
Once the substrate is positioned on the support blade 508, the substrate may be lowered onto the cooling plate 504 or heating plate 502. The process of lowering the substrate onto either the heating plate 502 or the cooling plate 504 generally includes positioning the support blade 508 above the respective plate such that the substrate support tabs 510 are positioned above the notches 516 formed into the perimeter of the plates. The support blade 508 may then be lowered such that the tabs 510 are received in the notches 516. As the substrate support tabs 510 are received in the notches 516, the substrate supported on the tabs 510 is transferred to the upper surface of the respective heating or cooling plate.
The transfer process generally includes activating the vacuum apertures 522 formed into the plate upper surfaces, so that a substrate is secured to the surface without movement when placed thereon. The heating plate is generally heated to a predetermined annealing temperature, such as between about 150° C. and about 400° C. or 450° C., before the substrate is positioned thereon. Alternative temperature ranges for the heating plate include between about 150° C. and about 250° C., between about 150° C. and about 325° C., and between about 200° C. and about 350° C., for example. The substrate is positioned on the heating plate 502 (generally vacuum chucked thereto) for a predetermined period of time and annealed, generally between about 15 seconds and about 120 seconds, for example, depending on the desired annealing temperature and the time required to generate the desired structure in the layer deposited on the substrate.
In high temperature annealing processes, i.e., annealing processes where the annealing temperature (the temperature of the heating plate 502) is high enough to thermally shock and possibly damage the substrate, a temperature ramping process may be implemented. As such, the heating plate 502 may be maintained at a first temperature and the substrate may be positioned on the heating plate 502. The first temperature is calculated to begin the annealing process without damaging or shocking the substrate. Once the substrate is positioned on the heating plate, the temperature of the plate may be increased to a second temperature, wherein the second temperature is greater than the first temperature. In this configuration, the substrate temperature increases from the first temperature to the second temperature at a rate that is calculated not to damage or shock the substrate.
The heating plate 502 may also be heated to the annealing temperature. However, the annealing process begins with the substrate being positioned immediately above the heating plate 502, e.g., an air space or gap is left between the substrate and the upper surface of the heating plate 502. During the time period while the substrate is positioned above the heating plate, i.e., hovered above the plate, heat is transferred from the plate 502 to the substrate, thus heating the substrate. Once the substrate temperature is increased to a temperature where thermal damage or shock may be prevented, then the substrate is lowered onto the heating plate 502, i.e., into direct contact with the heating plate. This configuration allows for temperature ramping of the substrate without having to control the heating mechanism of the heating plate 502.
Once the heating portion of the annealing process is completed, the substrate may be transferred to the cooling plate 504. The transfer process includes terminating the vacuum chucking operation and lifting the support blade 508 upward until the tabs 510 engage and support the substrate thereon, i.e., wherein the tabs 510 lift the substrate off of the heating plate surface. The support blade 508 may then be pivoted from the heating plate 502 to the cooling plate 504. Once above the cooling plate 504, blade 508 may be lowered to position the substrate onto the cooling plate 504. In similar fashion to the lowering process described below, the substrate may be lowered onto the cooling plate while the vacuum apertures 522 are simultaneously operating to secure the substrate to the upper surface of the cooling plate 504.
The cooling plate may generally be maintained at a reduced temperature, such as between about 15° C. and about 40° C., and therefore, the cooling plate operates to receive or sink heat from the substrate positioned thereon or proximate thereto. This process may be used to cool the substrate from the annealing temperature down to less than about 70° C., or more particularly, between about 50° C. and about 100° C. in less than 1 minute, or more particularly, in less than about 15 seconds. More particularly, the cooling plate may be used to rapidly cool the substrate to between about 50° C. and about 70° C. in less than about 12 seconds. Once the substrate is cooled to the desired temperature, the blade 508 may be used to raise the substrate off of the cooling plate 504. With the substrate raised, the door 514 may be opened and the outside robot blade 512 may be brought into the processing volume and used to remove the substrate from the support blade 508. Once the substrate is removed, another substrate may be positioned in the annealing chamber and the annealing process described above may be repeated.
The annealing chamber 500 and various processes used therein may be further described in commonly assigned U.S. patent application Ser. No. 10/823,849, filed Apr. 13, 2004 under the title “Two Position Anneal Chamber”, which is incorporated herein by reference in its entirety.
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.
