Patent Application
20050218000
Metallization of small sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. In integrated circuit devices, such as very large scale integration (VLSI)-type and ultra large scale integration (ULSI)-type devices, e.g., 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 interconnect features, e.g., aspect ratio of greater than about 4:1, with a conductive material. 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. Accordingly, plating techniques, e.g., electrochemical plating (ECP) and electroless plating, have emerged as promising processes for void free filling of micron sized high aspect ratio interconnect features.
In an ECP process, for example, small sized, high aspect ratio features may be efficiently filled with a conductive metal material, such as copper. An interconnect process generally involves initially depositing a diffusion barrier layer over features on the surface of a substrate. A seed layer is then deposited over the diffusion barrier layer and then the surface of the substrate is exposed to an electrolyte solution while an electrical bias is applied between the substrate and an anode positioned within the electrolyte solution. The electrolyte solution generally contains a source of metal ions that are to be plated onto the surface of the substrate and the application of the electrical bias causes the metal ions to be plated onto the biased substrate, thus depositing a conductive metal layer onto the substrate surface and filling the features.
The conductive metal layer can then be planarized, such as by a chemical mechanical polishing (CMP) process. Metal film electroplating is accomplished by establishing a voltage/current level between the substrate and an anode. This voltage/current level is commonly established by use of a contact ring that contains contacts, leads, or contact pins to electrically contact the substrate, such as a silicon wafer. The contacts, leads, or contact pins are generally made from inert or electrically conductive materials.
However, the decreasing size of features being filled by ECP processes in semiconductor processing requires that the plating process generate minimal defects in order to produce viable devices. Research has shown that a primary cause of plating defects is metal buildup on the contacts. This occurs during plating as metals tend to deposit on these contacts as well as the substrate itself. Effective removal of the metal deposited onto these contacts and other residues and contaminants between successive substrate processing is necessary to ensure proper placement of the substrates and provide proper electrical contact to the substrates. It is also important to prevent contamination of the electrolyte solution, due to the presence of metal residues left on these contacts from processing of the previous substrate which could interfere with the processing of subsequent substrates.
Removal of any metal residues from the contacts is typically accomplished by a deplating process. Deplating typically involves applying a constant anodic current or potential to the contacts for a specified amount of time. An anodic current or potential is a current or potential designed to electrochemically dissolve chemical species on the contact pins. Several problems are encountered in prior art deplating processes. First, the deplating rate obtained by applying a fixed anodic potential for a fixed duration is generally uncontrollable and can vary over the course of the deplating process. This can cause undesirable physical and chemical processes to occur when the deplating rate is either too high or too low, or the deplating is allowed to proceed too long. Such effects may include breakdown of certain chemical components in the electrolyte solution, generation of unwanted byproducts, or introduction of unwanted particles to the bath that lead to defects.
Additionally, deplating for a specified amount of time under controlled current or voltage provides no way to determine whether the metal residue has been entirely removed from the contacts. Insufficient deplating can lead to accumulation of residue from substrate to substrate and variations in plating performance. Excessive deplating (i.e., deplating after the metal residue has been removed) can lead to uncontrolled or excessive breakdown of certain chemical components in the plating bath and/or generation of unwanted byproducts including gases, organic byproducts, and ionic species. Using a pre-specified deplating duration is particularly problematic if there are statistical variations in the degree of residue left after each substrate is plated/processed, or if there are variations among substrates due to differences in substrate types, plating thickness, or plating recipes.
Therefore, there exists a need for an improved method for conditioning contact leads for metal plating systems.
Embodiments of the invention generally provide a method for conditioning contacts and monitoring the contacts to ensure that the contacts are ready for metal plating on a substrate. In one embodiment, a method for conditioning one or more contacts in an electrochemical plating system includes immersing the contacts in the electrolyte solution of the electrochemical plating system, applying an electrical voltage or supplying an electrical current to the contacts, wherein the direction of the voltage or current is reversed from the direction of the voltage or current used for electrochemical plating, monitoring the electrical state of the system to obtain an indication of the progress of the conditioning process, using the indication of the electrical state of the system to determine the endpoint of the conditioning process, and removing the supply of electrical energy to the contacts. Once the endpoint has been achieved, the applied current or voltage may be stopped or it may be followed by additional conditioning steps, including additional deplating and plating steps, applied to the contacts in order to achieve a desired state of the contacts before the next substrate is processed.
In one aspect, a method for conditioning contacts of an electrochemical plating system having an electrolyte solution therein includes applying an electrical input to the contacts in the absence of a substrate thereon. The method further includes monitoring real-time electrical measurements to obtain an indication thereof and using the indication of the real-time electrical measurements to determine the endpoint of the deplating process.
In another aspect, a method for conditioning contacts of an electrochemical plating system having an electrolyte solution therein includes immersing the contacts in the electrolyte solution, applying an anodically controlled electrical input to the contacts, and monitoring real-time electrical measurements from the plating apparatus until a signal indicating the contacts are conditioned.
In still another aspect, a method for plating a metal material onto a substrate in an electrochemical plating system and conditioning contacts of the electrochemical plating system having an electrolyte solution and the substrate therein is provided. The method includes plating the metal material onto the substrate by applying a cathodic electrical input onto the contacts, removing the substrate from the electrochemical plating system, applying an anodically controlled electrical input to the contacts to remove the metal material left on the contacts, and monitoring real-time electrical measurements from the plating apparatus until a signal indicating the contacts are conditioned.
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. The drawings also show apparatus for practicing the method of the invention. 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 for conditioning contacts present in an electroplating apparatus which is adapted to electrochemically deposit a thin metal seed layer and/or a bulk metal layer onto a substrate. The metal material suitable for the bulk metal layer can be any metal materials that can be plated on a substrate surface, such as copper, nickel, etc. For example, the invention provides a deplating process performed on one or more contacts, contact leads, or contact pins of a plating cell such that the contacts can be ready for plating of a copper material on the surface of a substrate having a barrier material or a copper seed layer thereon during a direct or indirect copper plating process to fill submicron features for semiconductor interconnect formation.
In one embodiment, the one or more contacts can be conditioned by using electrical inputs, such as a controlled current or a controlled voltage, etc., to deplate the contacts and the deplating process is monitored by detecting an increase in deplating voltage level or a decrease in deplating current level, or monitored until a predetermined current or voltage values are reached. The electrical inputs can be any electrical inputs by using a power supply connected to the plating system to generate a current flowing though various parts of the plating system or a voltage, such as a total voltage of the plating system or a voltage of the contacts relative to an additional electrode placed inside the plating system, among others. For example, the electrical inputs may include, without limitation, a controlled current or controlled voltage, a constant current, a constant voltage, stepwise controlled currents, stepwise controlled voltages, smoothly varying current, smoothly varying voltage, oscillating current, oscillating voltage, current pulses, voltage pulses, pauses, or combinations thereof.
In another embodiment, the invention provides a method and control scheme for deplating one or more contacts in an electrochemical plating system using real-time electrical measurements of the electrochemical plating system to signal the endpoint of the deplating process. The electrical measurements are monitored by electrical instruments in real time. The electrical instrument for the electrical measurements may be adapted to generate one or more computer readable outputs.
For example, a method and apparatus of the invention may include applying a constant electrical current to one or more contacts or a contact assembly of a plating system to remove metallic residues electrochemically and deplate residues and/or contaminants from the one or more contacts. During the deplating process, the resulting voltage variation of the plating system is monitored electronically in real-time. When an endpoint in the deplating process is indicated, the deplating current is removed.
As another example, a constant voltage can be applied to the plating system or to the contacts relative to an electrode and variation in the current level during the deplating process can be monitored in real-time. In addition, the deplating process of the invention may include multiple deplating steps using a combination of the constant current controlled method and the constant voltage controlled method to better achieve enhanced conditioning of the contacts and indicate the endpoint of the deplating process without excessive deplating or removing portions of the materials of the contacts. Additional deplating or plating steps may be performed after the endpoint is reached.
Plating Apparatus
The invention disclosed herein may be practice using any suitable electroplating apparatuses and systems, including but not limited to, an ECP Slim CeI™ processing system, commercially available from Applied Materials Inc., of Santa Clara, Calif.
The annealing station 135 generally includes a two position annealing chamber, wherein a cooling plate 136 and a heating plate 137 are positioned adjacently with a transfer robot 140 positioned proximate thereto, e.g., between the cooling plate 136 and heating plate 137. The transfer robot 140 is generally configured to move substrates between the respective heating plate 137 and cooling plate 136. Further, although the annealing station 135 illustrated as being positioned such that it is accessed from the link tunnel 115, embodiments of the invention are not limited to any particular configuration or placement. As such, the annealing station 135 may be positioned in communication with the mainframe 113.
The mainframe 113 may include a substrate transfer robot 120 centrally positioned thereon. The substrate transfer robot 120 generally includes one or more arms/blades 122, 124 configured to support and transfer substrates thereon. Additionally, the substrate transfer robot 120 and the blades 122, 124 are generally configured to extend, rotate, and vertically move so that the substrate transfer robot 120 may insert and remove substrates to and from the processing cells 102, 104, 106, 108, 110, 112, 114, 116 positioned on the mainframe 113. Similarly, the 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.
Generally, the processing cells 102, 104, 106, 108, 110, 112, 114, 116 may be any number of processing cells utilized in an electrochemical plating platform. More particularly, the processing cells may be configured as electrochemical plating cells, rinsing cells, bevel clean cells, spin rinse dry cells, substrate surface cleaning 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 ECP system 100 and appropriately control the operation of the ECP system 100 in accordance with the inputs.
One embodiment of the invention provides one or more metrology stations coupled to one or more processing cells for monitoring a deplating process inside the one or more processing cells. The metrology stations are adapted to monitor one or more substrates or contacts inside the one or more processing cells. The deplating process of the invention effectively removes any of the excess conductive materials, residues, and contaminants from one or more contacts in the one or more plating cells.
In the exemplary plating system illustrated in
Additional configurations and implementations of an electrochemical processing system are illustrated in commonly assigned U.S. patent application Ser. No. 10/616,284, which was filed on Jul. 8, 2003 under the title “Multi-Chemistry Plating System,” claiming priority to U.S. Provisional Patent Application Ser. No. 60/398,345, filed Jul. 24, 2002; U.S. Provisional Patent Application Ser. No. 60/435,121, filed Dec. 19, 2002; U.S. Provisional Patent Application Ser. No. 60/448,575, filed Feb. 18, 2003; U.S. Provisional Patent Application Ser. No. 60/463,956, filed Apr. 18, 2003; U.S. Provisional Patent Application Ser. No. 60/463,862, filed Apr. 18, 2003; U.S. Provisional Patent Application Ser. No. 60/463,860, filed Apr. 18, 2003; and U.S. Provisional Patent Application Ser. No. 60/463,970, filed Apr. 18, 2003, which are each incorporated herein by reference in their entireties to the extent not inconstant herewith.
The plating cell 200 is generally positioned at a tilt angle, e.g., a frame member 203 of plating cell 200 is generally elevated on one side such that the components of plating cell 200 are tilted between about 3° and about 30°, or generally between about 4° and about 10° for optimal results. The frame member 203 of plating cell 200 supports an annular base member 204 on an upper portion thereof. Since the frame member 203 is elevated on one side, the upper surface of the annular base member 204 is generally tilted from the horizontal at an angle that corresponds to the angle of the frame member 203 relative to a horizontal position. The annular base member 204 may include a plurality of fluid inlets/drains 209 extending from a lower surface thereof. Each of the fluid inlets/drains 209 are generally configured to individually supply or drain a fluid to or from either an anode compartment or a cathode compartment of the plating cell 200.
The annular base member 204 may further include an annular or disk shaped recess formed into a central portion thereof, the annular recess being configured to receive an anode member 205, which may be a disk shaped anode member. The 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 member 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. The plating cell 200 may further include a membrane support assembly 206. The membrane support assembly 206 is generally secured at an outer periphery thereof to the annular base member 204, and includes an interior region configured to allow fluids to pass therethrough.
A membrane 208 is stretched across the membrane support 206 and operates to fluidly separate the catholyte compartment and the anolyte compartment portions of the plating cell 200. The membrane support assembly 206 may include an o-ring type seal positioned near a perimeter of the membrane 208, wherein the seal is configured to prevent fluids from traveling from one side of the membrane 208 secured on the membrane support assembly 206 to the other side of the membrane 208.
A diffusion plate 210, which 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, is positioned in the plating cell 200 between the membrane 208 and the substrate being plated. The exemplary plating cell is further illustrated 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”, claiming priority to U.S. Provisional Application Ser. No. 60/398,345, which was filed on Jul. 24, 2002, both of which are incorporated herein by reference in their entireties to the extent not inconstant herewith.
The mounting member 312 may be attached to a contact ring 350 via one or more attachment members 316. The attachment members 316 may be spaced sufficiently to allow insertion of the substrate (e.g., a spacing of the attachment members 316 may be greater than a diameter of the substrate). The mounting member 312 may be used to attach or connect the contact ring 350 to a head assembly (not shown) that is configured to vertically actuate, rotate, and tilt the contact ring 350.
The mounting member 312, the contact ring 350, and the attachment members 316 may optionally be coated with a plating-resistant material, such as a PTFE material (e.g., Aflon® or Tefzel®) or any other suitable plating-resistant coating material. The contact ring 350 generally includes a substrate seating surface 352 that is adapted to receive the substrate with the plating surface of the substrate facing the plating cell, which is generally positioned below the contact ring 350.
The thrust plate assembly 340 may include a thrust plate 344 and a seal plate 342 that is adapted to be vertically actuated (toward the contact ring 350) so that a securing force may be exerted on the backside of the substrate such that the substrate plating surface is pushed against the substrate seating surface 352 of the contact ring 350 for processing. The securing force applied by the thrust plate 344 may be sufficient to ensure adequate sealing between an annular sealing member 348 disposed on the seal plate 342 and the non-plating surface (backside) of the substrate. The annular sealing member 348, which may be an o-ring type seal, for example, may be adapted to contact the non-plating surface (backside) of the substrate at a substantially equal location radially inward from edges of the substrate as the contacts 354 engage the plating surface of the substrate.
The securing force exerted by the thrust plate 344 may also be sufficient to ensure adequate electrical contact between the plating surface (generally having an electrically conductive seed or barrier layer on the plating surface) of the substrate and the contacts 354 extending from the substrate seating surface 352 of the contact ring 350. The contacts 354 are generally adapted to electrically contact the plating surface of the substrate in order to supply an electrical plating bias to the plating surface during the plating process.
The contacts 354 may be made of any suitable conductive material, such as copper (Cu), platinum (Pt), tantalum (Ta), titanium (Ti), gold (Au), silver (Ag), stainless steel, an alloy thereof, or any other suitable conducting material. While the contacts 354 are herein depicted as contact pins on a contact ring, this description is solely for illustrative purposes. It should be understood that the contacts contemplated by the present invention may comprise any means of contactively supplying an electrical plating bias to the plating surface during the plating process.
As illustrated in
For some embodiments, the contact ring 350, the attachment members 316, and the mounting member 312 may all be made of any of suitable electrically conductive materials. For example, the contacts 354, the contact ring 350, the attachment members 316, and mounting member 312 may be made of stainless steel. Accordingly, the attachment members 316 may electrically couple the mounting member 312 and the contact ring 350. Therefore, electrical power may be supplied to the contacts 354 by one or more electrical connections between the mounting member 312 and a power supply.
Further, for some embodiments, the mounting member 312 may be physically and electrically coupled with a thrust plate mounting member 346, which may also be made of an electrically conductive material and may be attached to a power supply. The mounting member 312 or the thrust plate mounting member 346 may be connected to one or more power supplies via any suitable attachment means adapted to provide electrical power to the contacts 354 as the substrate securing assembly 310 is moved (i.e., raised, lowered and rotated) by the head assembly, which will be further discussed herein.
As previously described, the seal plate 342 may be attached to the thrust plate 344. The thrust plate 344 may be adapted to move (i.e., up and down) independently of the contact ring 350 to exert a securing force with the annular sealing member 348 on the non-plating surface of a substrate to secure the substrate to the substrate seating surface 352 of the contact ring 350. The sealing member 348 may be designed to provide a uniform contact force between the contacts 354 and the plating surface of the substrate.
For example, the sealing member 348 may be made of a pliable material designed to decrease an effective spring constant of the annular sealing member 348. In other words, the annular sealing member 348 may compress to adapt to slight non-uniformities in the non-plating surface of the substrate (or slight non-uniformities in the annular sealing member 348). As the annular sealing member 348 compresses, less force may be needed to seal against the highest point of the non-plating surface before sealing against the lowest point. With less force difference between the highest and lowest points, the local force on the non-plating surface of the substrate, and therefore on the contacts 354 in contact with the plating surface of the substrate, may be more uniform. A more uniform force on the contacts 354 may lead to uniform contact resistance and improved plating uniformity.
The plurality of the downwardly extending scallops 356 may be formed on a bottom surface of the contact ring 350 below the plurality of contacts 354. The size and shape of the downwardly extending scallops 356 are not limited and may vary according to different application. For example, as illustrated in
The head assembly 400 is generally configured to impart motion to the contact ring and thrust plate assembly 310. More particularly, the head assembly 400 is configured to rotate the contact ring and thrust plate assembly 310, vertically actuate the contact ring and thrust plate assembly 310, and pivot the contact ring and thrust plate assembly 310 about a pivot point 402 that is generally near the vertical axis of the head assembly 400. This pivotal movement allows the contact ring 350 (and the substrate positioned thereon) to be tilted such that the substrate surface is not horizontal.
The head assembly 400 is configured to rotate, pivot, and vertically actuate the contact ring and thrust plate assembly 310 all at the same time, or alternatively, the head assembly 400 may conduct rotation, vertical actuation, and/or tilting motions in any combination, or alone if desired. A more extensive description of the electroplating apparatus disclosed herein may be found in commonly assigned U.S. Provisional Patent Application Ser. No. 60/463,972, filed on Apr. 18, 2003, which is incorporated by reference herein in its entirety to the extent not inconstant herewith.
The exposed surfaces of the contact ring, except the surfaces of the contact pads that come in contact with the substrate, are preferably treated to provide hydrophilic surfaces or coated with a material that exhibits hydrophilic properties. Hydrophilic materials and hydrophilic surface treatments are known in the art. One company providing a hydrophilic surface treatment is Millipore Corporation, located in Bedford, Mass. The hydrophilic surface significantly reduces beading of the electrolyte on the surfaces of the contact ring and promotes smooth dripping of the electrolyte from the contact ring after the contact ring is removed from the electroplating bath or electrolyte. By providing hydrophilic surfaces on the contact ring that facilitate run-off of the electrolyte, plating defects caused by residual electrolyte on the contact ring are significantly reduced. The hydrophilic treatment or coating can also be applied to other embodiments of the contact rings to reduce residual electrolyte beading on the contact ring and the plating defects on a subsequently processed substrate that may result therefrom.
Plating and Deplating Process
As noted above, the process of plating a conductive material, such as copper, among others, onto a substrate via a plating process generally includes electrically contacting the plating surface of the substrate. For example, a plating process may include plating a metal material onto a substrate in an electrochemical plating system by applying a cathodic electrical input onto the contacts. The electrochemical plating system includes a plating solution into which the substrate is immersed for plating.
Contacts suitable for the invention are not limiting and generally referred to any of contacting members which support and contact a substrate during plating, such as contact leads, contact pins, contact elements, etc., e.g., the contacts 354. The materials of theses contacts can be any of the inert material or conductive material, for example, platinum, among others.
During plating, the contacts may be fully or partly exposed to the plating solution. As such, plated metal materials may deposit/plate onto these contacts as well as the substrate itself. These metal materials, other residues, and contaminants on the contacts of the plating apparatus are known to cause variations in a plating process and to increase defect ratios, and as such, it is desirable to remove them from the contacts via a deplating process.
Contacts of the electrochemical plating system are conditioned in the absence of the substrate, such as by re-immersing the contacts without the substrate sitting thereon into the same plating solution in the same electrochemical plating system after removing the substrate from the contacts. The deplating solution/electrolyte can be the same solution for a previous plating process having all the chemical components required, including, for example, copper ions, chloride ions, organic additives, inorganic additives, activators, suppressors, levelers, enhancers, etc. Alternatively, the deplating solution can be a replenished solution such that the level of residues, chemical breakdown, unwanted contaminants, byproducts, etc., is minimized. In another embodiment, the deplating solution can be a different solution from the previous plating process located in the same or different plating cell. For example, the contacts to be conditioned can be immersed into a different plating/deplating solution in a different electrochemical cell. This may be desirable if the conditioning process requires a specific chemical makeup for optimal conditioning or if the conditioning process has severe undesirable side effects if performed in the plating solution. Such side effects may include excessive breakdown of chemical components, introduction of byproducts, or introduction of defects. In another embodiment, the conditioning bath may be a previously used plating solution that is no longer suitable for plating onto substrates but is adequate for the purpose of conditioning the contacts and provides cost savings.
At step 620, the contacts are conditioned by providing an anodically controlled electrical input to the contacts and metal residues can be deplated from the contacts. The anodically controlled electrical input can be, for example, a constant anodic current (one example is shown in
Embodiments of the invention also includes one or more, or combination of these exemplary anodically controlled electrical inputs that can be applied to the contacts or plating cell of the invention. For example, the anodically controlled electrical input can be a controlled cell current, a controlled cell voltage, stepwise controlled currents, stepwise controlled voltages, smoothly varying current, smoothly varying voltage, oscillating current, oscillating voltage, a sequence of a controlled cell current and a controlled cell voltage steps, current pulses, voltage pulses, pauses, or combinations thereof. Further, a zero-current or zero-voltage step may be included as part of the combinations of electrical inputs. The controlled electrical inputs of the invention are selected to achieve rapid and effective removal of metal residue from the contacts with no or minimal undesired side effects such as defect generation, breakdown of chemical components in the bath, or generation of byproducts. In addition, this invention provides a method to detect the endpoint of the conditioning process once the contacts have been sufficiently conditioned, thereby preventing undesired side-effects associated with excessive deplating.
The anodically controlled electrical input applied to condition the contacts can be a current supplied to the contacts of a contact ring, a voltage applied to the entire plating cell, a voltage applied to the contacts relative to a reference electrode, or a voltage applied to the contacts relative to a counterelectrode present in the plating bath. The reference electrode can be any suitable reference electrode generally known in the art, such as a silver-silver chloride reference electrode. Examples of a counterelectrode include the anode 205 or an auxilliary electrode placed inside the plating cell. One example of an auxilliary electrode that can be placed inside the plating system is described in co-pending U.S. patent application, entitled “Plating of a Thin Metal Seed Layer” (AMAT/9313), which is hereby incorporated by reference to the extent not inconsistent with the disclosure herein.
At step 630, electrical measurements are monitored in real-time while the electrical input is applied. When the applied electrical input is a voltage, the monitored electrical measurement is the current flowing through the contacts. When the electrical input is a current, the monitored measurement is the cell voltage, the voltage of the contact ring relative to a reference electrode, or the voltage of the contact ring relative to a counterelectrode, such as the anode 205 or an auxiliary electrode placed inside the cell. The electrical input is maintained during step 630 until a signal indicating the endpoint of the deplating process is detected.
The endpoint signal is a predetermined value of voltage or current, a predetermined change in the voltage or current, a predetermined rate of variation of the current or voltage in time, or a predetermined change in the rate of variation of the voltage or current. The endpoint signal indicates that the contacts are essentially free of metal residues. Prior processes usually include deplating for a predetermined or specified time period according to processing of previous substrates and/or similar process regimes for various applications, and do not provide a way of monitoring the deplating process in real time or any indication of the completion of the removal of metal residues from the contacts, particularly when there are statistical variations in the degree of residues present from substrate to substrate. One key aspect of the invention is the use of real-time electrical measurements from the plating apparatus to signal the endpoint of deplating instead of a pre-specified deplating time.
The real-time electrical measurements are monitored continuously in real-time in order to feed back any information regarding the real time electrical measurements and collect and graph all the electrical measurements by suitable electrical instruments or software control systems connected to the plating system 100. The invention provides a built-in feedback loop whereby changes in electrical measurements allow the true endpoint of the contact conditioning process to be detected, regardless of how much residues have been left on the contacts after the previous substrate plating process and without affecting subsequent substrate plating process.
Once an endpoint signal has been detected, in one embodiment, the electrical input is stopped. In another embodiment, additional steps may be applied at this point to further condition the contacts. Such additional steps may be needed if the deplating rate is not exactly uniform at all points on the contact and a few points or a small fraction of the contacts deplate more slowly than the rest of the contact so that when the endpoint is reached, some residue is still present at the slow-deplating points. Alternatively, it may be desirable to remove most of the residue (for example, 80 or 90%) from the contacts with one type of electrical input and the rest of the residue using a different type of electrical input. In such cases, after the real-time electrical measurements have indicated the end-point of the deplating process, there can be one or more controlled electrical inputs applied. The electrical input may include any combination of one or more controlled current or voltage steps, including a constant current or voltage, a sequence of current or voltage steps, a smoothly varying current or voltage, a current or voltage pulse, current pulses in combination with one or more controlled currents or controlled voltages, voltage pulses in combination with one or more controlled currents or controlled voltages, an oscillating current or voltage, stepwise varying controlled currents, a stepwise varying controlled voltage, a step of zero-current or zero-voltage (pauses) in combination with one or more controlled currents or controlled voltages, and any combinations thereof. The one or more controlled electrical inputs applied in the additional conditioning steps can be scheduled for a predetermined time or be monitored in real time until a second endpoint fro the additional step is reached.
Another aspect of the invention provides that after the deplating process to condition the contacts of the plating system is performed, another step of plating a thin metal layer (a metallization step) onto the contacts of the plating system can be performed in the absence of a substrate in order to improve the electrical connection between the contacts and the subsequent substrate. For example, a metal coating of less than about 600 Å, such as from about 50 Å to about 500 Å, is plated on the contacts, contact pins or various contact elements/points of the plating system. In this case, the contacts are conditioned to be covered with a fresh layer of a metal material, which may be the same metal material to be plated on the next substrate, such that a good platable metal to platable metal interface can be provided from the contacts to the surface of the next substrate to be processed, instead of noble metal of the contacts to platable metal of the substrate surface. This metallization step can reduce the resistance of the electrical connection between the contact element and the substrate and make the electrical connection more repeatable from substrate to substrate.
While it is highly desirable for the contacts to be free of any residues prior to this metallization step, this metallization step can be performed independent of the type of prior deplating steps. For example, it is not necessary for the metallization step to follow the specific deplating methodology described elsewhere in this patent. Other conditioning process may also be used to prepare the contacts.
In one embodiment, the method of the invention may be implemented as appropriate control software and hardware for detecting the value of the electrical measurements or variations and rates of change of the electrical measurements in order to respond to a signal of endpoint and turn off the anodic deplating current. In another embodiment, the real-time electrical measurements are monitored by electrical instruments adapted to generate a computer readable output. A plurality of computer readable outputs can be generated to be analyzed by the control software. The control software may generally be configured to detect the endpoint signal for completion of the deplating process, while also being configured to ignore various electrical measurement fluctuations and noises that would falsely indicate completion of the deplating process.
It is observed that when the metallic residue has been removed from the contacts 354 after applying a constant cell current, the cell voltage exhibited a sharp change (increase) 710, which signals the endpoint of the deplating process and/or indicates that all of the metal residues have been removed from the contacts 354. Not wishing to be bound by theory, it is contemplated that the increase in voltage generally results from the removal of metal material from the contacts. For example, copper residues operate as a current carrier for the deplating circuit, and as such, when copper has been completely or almost completely removed from the contacts, the resistance in the deplating circuit increases. This increase in circuit resistance after a constant current applied inherently causes the cell voltage to increase when the current-carrying copper has been completely removed from the contacts 354. This endpoint may be detected as the point where the voltage reaches a predetermined value, changes by a predetermined amount, changes at a predetermined rate, or shows a predetermined change in its rate of variation. Once this endpoint has been reached, the deplating step may be deemed essentially complete and the contacts 354 are ready for a next substrate.
In one embodiment, once the endpoint has been reached, an additional conditioning step may be optionally applied to further condition the contacts once the endpoint has been reached and before the next substrate is processed. This step may be comprised of applying to the contacts a constant, step-wise varied, oscillating, or smoothly varied current or voltage or a combination thereof. It may also include a pulsed current or voltage or a pause (zero-current or zero-voltage) step. For example, in the example of
An additional embodiment of the invention includes a multi-stages deplating process where one or more additional deplating steps under current or voltage control may also be applied to remove any trace residue from the contacts 354 and to further condition the contacts. For example, a sequence of steps of controlled current or controlled voltage as electrical inputs can be applied to the plating apparatus.
In one embodiment of this invention, a deplating process may include applying a first controlled electrical input to the contacts and monitoring a first set of real-time electrical measurements until an endpoint of the deplating process is detected. The real-time electrical measurement information feeding back to the plating apparatus can be analyzed by a control software to determine the endpoint of the deplating process. In addition, an additional conditioning step can be applied to the contacts to further condition or overetch the contacts. This additional conditioning step can be performed by an anodically controlled current or voltage as described above or for a fixed duration. Further, additional plating/metallization step may be performed, such as by applying a cathodic current or voltage to the contacts or the plating system to plate a thin metal layer to the contacts in the absence of a substrate. This additional plating step helps to condition the contacts for the next substrate.
In another embodiment of this invention, the deplating process may be performed as a combination of the controlled current method or the controlled voltage method as described herein. For example, a sequence of controlled current method followed by the controlled voltage method or vice versa can be used in a deplating process. Accordingly, methods of the invention provides an electrochemical process to monitor a deplating process in real-time in order to achieve satisfactory conditioning of the contacts while minimizing undesired chemical and physical reactions.
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.
This application claims benefit of U.S. provisional patent application Ser. No. 60/560,226, filed on Apr. 6, 2004, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60560226 | Apr 2004 | US |
