Patent Application
20110143553
The present invention relates generally to semiconductor substrate processing, and more particularly, to the handling of a substrate through an integrated electroless deposition process during fabrication.
In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of fabrication operations are performed to define multilevel features on semiconductor substrates (“substrates”). Features having multiple levels are becoming more prevalent as device dimensions fall to the sub-micron levels and there is constant demand to increase the density of devices in order to provide greater computational capacity.
The series of fabrication operations involve selectively removing (etching) or depositing different materials on the surface of the substrate. The fabrication operations start at a substrate level where transistor or capacitor devices with diffusion regions are formed. A first layer of dielectric (insulating) material is deposited on top of the formed transistors. In subsequent levels, interconnect metallization lines are patterned on top of the base layer as multiple thin-film layers through a series of manufacturing process steps. The interconnect metallization lines electrically connect to the underlying transistor or capacitor devices by way of contacts to thereby define a desired circuit. The patterned conductive layers are insulated from each other by layers of dielectric materials.
Copper is becoming a conductor of choice for most device interconnects due to its lower resistivity and lower susceptibility to electro-migration as compared to aluminum. Electro-migration is the transportation of material caused by the gradual movement of ions in a conductor due to momentum transfer between conducting electrons and diffusing metal atoms. Electro-migration decreases the reliability of integrated circuits (ICs). In the worst case, electro-migration leads to eventual loss of one or more connections resulting in intermittent failure of the entire circuit.
One commonly used method of patterning copper is called Copper Damascene Process, in which a substrate with patterned trenches undergoes an interconnect deposition (plating) process of copper after a barrier layer. During the deposition process, a copper seed layer is deposited on the top, along bottom and on the side walls of the patterned trenches. The top surface of copper will be polished with a subsequent chemical-mechanical polishing (CMP). Such steps leave copper lines or pads well defined with copper metal exposed on the top surface, but well isolated between dielectrics across the surface of the substrate.
A great effort has been made to alter or to modify copper surface property so as to drastically improve electro-migration properties of interconnect copper lines and to improve the interface property of copper with subsequent material deposited over the copper. Among them, capping of the top copper surface with cobalt alloys through electroless deposition (ELD) is proved the most effective technology to deliver required integrated performance of advanced nano-devices. ELD allows a selective and self-catalytic deposition of another metal over Cu lines, with essential absence of deposition over the dielectric layer. This selective process permits to preserve the electrical insulation between the interconnect lines, whilst providing the necessary capping to copper interconnect so as to enhance interface adhesion strength, and minimize the rate of electro-migration.
In the copper damascene process, the copper line is encapsulated on the sides and bottom by barrier metal, and on top by barrier/etch stop dielectric. The copper/dielectric interface has weaker adhesion than the copper/barrier metal interface, so copper precipitation occurs predominantly at the top surface. Under high current densities, copper electro-migration (EM) would cause atoms to move in the direction of the electron flow ultimately causing the device to fail. Attempts to improve copper/dielectric adhesion by inserting a barrier layer on top would not only require additional expensive patterning and etching procedures but also greatly increase the line resistivity. A better alternative to inserting a barrier layer is to add a cobalt tungsten phosphide (CoWP) cap to the copper using a selective ELD process after CMP. It has been demonstrated, in some cases, that using a CoWP cap has resulted in EM lifetime improvements of one to two orders of magnitude, compared with structures using the conventional dielectric layer alone. However, adding CoWP cap to the copper has its own problems. For instance, the un-capped copper and by-products of previous process steps can diffuse into the surrounding dielectric layer. The diffusion may cause migration of electrically conducting metal species into the porous dielectric layer potentially leading to high electric leakage.
After the capping operation, the substrate is then dried before moving the substrate out of the plating module to a subsequent processing module, such as a brush scrub module, a chemical module and/or a combined brush-rinse-and-dry module, for further processing. The substrate, of course, must be dried up in the rinse-and-dry module before the next manufacturing procedure of dielectric deposition. However, premature drying of the substrate between the ELD module and the final rinse-and-dry module would cause a serious issue. No matter how extensive the post-deposition rinse is in the ELD module, a low level of the metal ions exist in the liquid on top of the substrate. The metal ions could be cobalt ions resulting from constant dissolution of the metal in the aqueous solution on the substrate surface. The subsequent substrate drying in the ELD module could be a spin-dry process. The spin-dry process always leaves a very thin layer of liquid on some area of the substrate surface, that, of course, contains a higher concentration of the metal ions since it is the closest to the metal surface. The metal ions, once dissolved, are not localized only above the metal lines or pads, but will diffuse horizontally within the liquid layer.
Upon the final evaporation of the last bit of liquid solvent, the concentration of the metal ions can easily exceed the critical concentration and will thus be forced to precipitate out as conductive residues or contaminants covering metal lines, pads and the dielectric surface alike.
Worse, since the ELD module is not designed (optimized) for spin-dry, numerous liquid drops originally released from the substrate surface may unavoidably splash back onto the almost-dried substrate surface. Such small and fine drops would not be spun off. Instead, these fine drops would dry up to leave additional thicker residues or contaminants on the substrate surface, metal top and the dielectric top alike. These residues or contaminants, if not cleaned up, would seriously affect the time dependent dielectric breakdown (TDDB). If these residues/contaminants are to be cleaned up by the way of wet-etching, however, the integrity of the CoWP capping on top of the copper would be destroyed exposing copper at the copper-barrier interface, since there is no CoWP deposition on the barrier material.
Although problems with the conventional process have been explained in great detail with reference to copper (due to preferred conductive metal of choice), it should be noted such problems are prevalent with other conductive metals that are used for defining device interconnects.
It is in this context embodiments of the invention arise.
Broadly speaking, the embodiments fill the need by providing improved apparatus, systems and methods to keep substrate surface wet while handling the substrate through an integrated electroless deposition process before a final dry operation. Accordingly, the surface of the substrate is processed in an electroless deposition (ELD) module to deposit a layer over conductive features of the substrate using a deposition fluid. After successfully depositing the layer, the surface of the substrate can be rinsed with a post-deposition rinsing fluid such as DIW in the ELD module to largely rinse off the deposition solution from the surface of the substrate. In one embodiment, with or without the DIW rinse, the substrate is rinsed with a rinsing fluid in the electroless deposition module. The rinsing is controlled to prevent de-wetting of the surface of the substrate. The rinsing enables, the rinsing fluid to be coated over the surface of the substrate. The rinsing fluid acts as a transfer film that prevents the surface of the substrate from drying and from being exposed to ambient air while ensuring that the surface of the substrate is kept wet during removal from the electroless deposition module. The substrate is removed out of the electroless deposition module with the transfer film over the surface of the substrate. The substrate is moved into a subsequent post-deposition module while maintaining the transfer film over the surface of the substrate till the start of the next process step.
The current embodiments address the drawbacks faced by conventional deposition process which involve pre-mature drying of the substrate between the ELD process and the final rinse-and-dry process. Specifically, the current embodiments address the issue of premature drying by ensuring that a post-deposition fluid film (which can be a chemical used for treating the surface of the substrate) uniformly covers the substrate surface keeping the substrate wet upon conclusion of the deposition process before subsequent cleaning process. In one embodiment, the substrate is kept wet while the substrate is transported out of the electroless deposition module into a subsequent processing module prior to rinse-and-dry module. The presence of the transfer film on the surface of the substrate defined by the post-deposition rinsing fluid ensures that damage due to precipitation and diffusion of processing chemistry or damage due to precipitation of contaminants and other impurities from the ambient environment are avoided.
With respect to issues associated with precipitation and diffusion, the conventional deposition process allows the substrate to be spin-dried to remove the deposition fluid from the surface of the substrate before moving the substrate out of the deposition module. However, because of the high moisture content within the deposition module, one or more droplets of the deposition fluid may precipitate on the surface of the substrate while the substrate is being moved out of the deposition module, resulting in damage to the active features formed on the substrate. Such damage is clearly avoided in the embodiments of the present invention by maintaining a layer of post-deposition fluid film on the surface of the substrate. As a layer of the post-deposition fluid film is already present on the surface of the substrate, an additional drop or two of the rinsing fluid settling on the surface of the substrate in the highly moist electroless deposition module will not adversely affect the active features formed on the surface of the substrate. In one embodiment, the post-deposition fluid film is a treating chemical film that acts as a barrier preventing the metal formed on the surface of the substrate and the interlayer dielectric (ILD) from getting exposed to the ambient air thereby reducing metal oxidation, chemical reaction and transformation of the materials on the surface of the substrate. In one embodiment, it is important to insulate the ILD from the ambient air as exposure to ambient air may result in metallic or ionic precipitations on the porous ILD surface resulting in increased “talk” between interconnection lines. The increased talk would result in increased leakage current thereby worsening electro-migration.
Further, the wet-dry cycles of the conventional deposition process enhance the level of contaminants on the ILD, which directly result in increased leakage current. The increased leakage current would cause increased total current density, and thus worsen electro-migration and eventually worsen time dependent dielectric breakdown (TDDB). By removing existing contaminants and preventing other contaminants to agglomerate on the surface of and inside the treated surface, the insulating properties of the ILD between metal lines and layers are maintained thereby ensuring that the TDDB is not affected. Further, in the convention process, the diffusion of electrically active species, such as copper, derivatives of copper and other metal derivatives, result in electric leakage or shorts between copper metal lines leading to the malfunction of the device formed therein. The current embodiments avoid the wet-dry cycles reducing the diffusion of metals' derivatives into the porous dielectric surface thereby avoiding the ensuing current leakage in the devices formed therein significantly increasing the electrical yield of the devices.
It should be appreciated that the present invention can be implemented in numerous ways, including methods, an apparatus, and a system. Several inventive embodiments of the present invention are described below.
In one embodiment a method for handling a substrate through processes including an integrated electroless deposition process is disclosed. The method includes processing a surface of the substrate in an electroless deposition module to deposit a layer over conductive features of the substrate using a deposition fluid. The surface of the substrate is then rinsed in the electroless deposition module with a rinsing fluid. The rinsing is controlled to prevent de-wetting of the surface so that a transfer film defined from the rinsing fluid remains coated over the surface of the substrate. The substrate is removed from the electroless deposition module while maintaining the transfer film over the surface of the substrate. The transfer film over the surface of the substrate prevents drying of the surface of the substrate so that the removing is wet. The substrate, once removed from the electroless deposition module, is moved into a post-deposition module while maintaining the transfer film over the surface of the substrate.
In another embodiment, a method for handling a substrate through processes including an integrated electroless deposition process is disclosed. The method includes processing a surface of the substrate in an electroless deposition module to deposit a layer over conductive features of the substrate using a deposition fluid The surface of the substrate is then rinsed with a rinsing fluid in the electroless deposition module. A treating fluid is applied in the electroless deposition fluid. The treating fluid defines a transfer film. The application of the treating fluid is controlled to prevent de-wetting of the surface and to chemically treat the surface while the transfer film remains coated over the surface of the substrate. The substrate is removed out of the electroless deposition module while the transfer film is maintained over the surface of the substrate. The transfer film prevents drying of the surface of the substrate so that the substrate is removed wet. The substrate, once removed from the electroless deposition module, is moved into a post-deposition module while maintaining the transfer film over the surface of the substrate.
In yet another embodiment, a system for handling a substrate through processes including an integrated electroless deposition process is disclosed. The system includes an electroless deposition module that is configured to process a surface of a substrate by depositing a layer of deposition fluid on conductive features formed on the substrate and to control the application of a fluid that prevents de-wetting and applies a coating of the fluid over the surface of the substrate. The system also includes a wet robot that is configured to remove the substrate out of the electroless deposition module while maintaining the coating of the fluid over the surface of the substrate and to move the substrate into a post-deposition module while maintaining the coating of the fluid over the surface of the substrate.
In another embodiment, a system for handling a substrate through processes including an integrated electroless deposition process is disclosed. The system includes an electroless deposition module that is configured to supply a deposition fluid, wherein the deposition fluid is used to deposit a layer over conductive features formed on a surface of the substrate; apply a rinsing fluid to rinse the surface of the substrate, after depositing the layer; and to apply a treating fluid to the surface of the substrate, wherein the treating fluid defines a transfer film. The electroless deposition module includes control to control the application of the treating fluid to prevent de-wetting of the surface and to chemically treat the surface while the transfer film is maintained over the surface of the substrate. The system also includes a wet robot that is configured to remove the substrate out of the electroless deposition module while maintaining the transfer film over the substrate, wherein the transfer film prevents drying of the substrate so that the substrate is removed wet from the electroless deposition module; and to move the substrate into a post-deposition module while maintaining the transfer film over the substrate.
The integrated electroless deposition process provides selective deposition of deposition fluid to cap the conductive features on the surface of the substrate while preventing oxidation, other chemical reactions and transformations of materials formed on the surface of the substrate. The post-deposition fluid film prevents any contaminants, residues of chemistries from damaging the ILD and metal features on the surface of the substrate resulting in high electrical yield of devices defined on the surface of the substrate.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
The invention will be readily understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings should not be taken to limit the invention to the preferred embodiments, but are for explanation and understanding only. Like reference numerals designate like structural elements.
Several embodiments for handling a substrate efficiently through processes including an integrated electroless deposition (ELD) process will now be described. The various embodiments describe an ELD process wherein the substrate undergoes a deposition in an electroless deposition module to cap conductive features formed on the surface of the substrate and then a transfer film is applied to wet the surface of the substrate. A transfer film, as used in this application, is a chemical, such as de-ionized water (DIW), with or without a surfactant that acts to provide a barrier so as to protect the underlying features/components from getting exposed to the ambient air. The substrate with the transfer film wetting the surface is transferred from the ELD module or a post-deposition module to a subsequent post-deposition module within the system for further processing.
It should be noted, that exemplary embodiments have been described to provide an understanding of the invention. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.
The transfer film on the surface of the substrate acts as a barrier to reduce oxidation, other chemical reactions and/or transformation of the materials on the surface of the substrate. Transformation, as used in this application, defines a change in chemical properties of a material due to chemical reaction such that the resulting material includes chemical properties that are substantially different from the material. The chemical transformation of the material may result in device malfunctions due to the difference in the properties of the transformed material. The transfer film also prevents contaminants and other residues from precipitating on the surface of the substrate and compromising the characteristics of the dielectric as well as the conducting material. Further, the transfer film on the substrate surface prevents defects from being formed due to premature drying of the surface of the substrate both during process and during transfer between modules.
Conventional ELD system enabled selective deposition to be performed on the surface of the substrate within an ELD module. Upon successful deposition, the surface of the substrate was rinsed to remove any chemicals and residues left behind on the surface of the substrate from the deposition process and dried before transporting the substrate out of the ELD module to a post-deposition module where additional processing was performed. The wet-dry cycle of the conventional ELD system caused pre-mature drying of the substrate surface and resulted in moisture breaks, oxide removal and re-oxidations. The re-oxidation causes undesirable metal line corrosion thereby weakening interconnection of metal lines of a device. The pre-mature drying leaves defects and contaminants on the substrate surface that results in device malfunctions leading to substantial yield loss. The frequent moisture breaks also enable contaminants released from the surface of the substrate into the ambient air to precipitate on the surface of the substrate causing further damage to the devices. Thus, using the conventional ELD deposition process, the desirable capping property on the copper surface cannot be delivered, significantly compromising the key electric properties of advanced nano-devices due to time dependent dielectric breakdown (TDDB) and electro-migration. This results in electrical yield loss and degradation in device reliability.
In order to best take advantage of ELD capping and to improve advanced nano-devices reliability with enhanced electrical yield and minimized device malfunctions, novel systems, apparatuses and methods are disclosed that use an integrated electroless deposition module to perform a deposition process to cap (e.g. with cobalt, CoWP) conductive features (e.g. copper) after a fabrication operation, such as chemical-mechanical polishing (CMP), and to apply a film of post-deposition fluid after the deposition process to coat the surface of the substrate so as to prevent de-wetting. The post-deposition fluid defines a transfer film on the surface of the substrate. The substrate is transported wet with the transfer film covering the surface of the substrate from the ELD module to a post-deposition module for further processing. A wet robot is used to assist in the transportation of the wet substrate from one module into another for further processing of the substrate. After substantial processing, the substrate is transported wet with such a transfer film covering the surface of the substrate to a clean module where the substrate is rinsed and dried. The rinsed and dried substrate is transported out of the ELD system using a dry robot. By removing contaminants and not allowing other contaminants to agglomerate on the treated surface of the substrate, the insulating properties of the ILD between metal layers is maintained and the electrical enhancements provided by the capping layer, such as CoWP capping layer, is realized, thereby resulting in optimization of the time dependent dielectric breakdown (TDDB). The resulting substrate is substantially clean, devoid of defects caused due to oxidation, other chemical reaction or transformation of the materials and has a substantial electrical yield due to minimal wet-dry cycles.
In order to better understand the various advantages of the ELD system, various embodiments will now be described with reference to the attached drawings.
After successful planarization, the surface of the substrate is cleaned to remove residues and contaminants left behind by the planarization operation (e.g. cu-based particles on the dielectric) and subsequent oxidation. Following the planarization process, the substrate is treated to an Electroless Deposition (ELD) process wherein the exposed conductive features, such as copper interconnects, are capped. A typical capping process uses a chemical with cobalt based alloy. The cobalt capping reduces electro-migration of copper over the course of the lifetime of the device, which would otherwise concentrate in certain regions and create a void or open in other regions (resulting in device failure, aka EM). Further, cobalt capping may assist in preventing copper from diffusing into dielectric material surrounding the area where copper is deposited on the surface of the substrate. Due to the porosity of the dielectric material, the precipitation of the copper and cobalt derivatives left on the surface or in pores of the dielectric material can compromise the characteristics of the low-k dielectric material resulting in device malfunctions. The benefits of CoWP capping are realized so long as the electrical integrity of the existing ILD can be preserved.
Referring back to
Typically with the device dimensions reaching the sub-micron levels, the width of the conductive features, such as copper metal lines, that provide interconnects to the underlying devices, are in the sub-100 nanometer range with some having a width below 50 nanometers. In such cases, the capping normally is less than about 10 nanometers. The typical capping process of applying a cobalt-rich chemical as shown in step B of
As a result, an enhanced ELD process is disclosed that provides contaminant-free and residue-free dielectric surface after the ELD process. The various embodiments described hereunder provide an effective way of preserving the characteristics of the dielectric material using an integrated wet process. The integrated wet process described herein prevents and reduces such contamination due to precipitation and migration by keeping the surface of the substrate wet and by passivating the cobalt deposition after the ELD capping process. The surface is kept wet by maintaining a thin layer of transfer film on the porous dielectric surface of the substrate. The transfer film is defined in part by the deposition fluid used during the deposition process in the ELD module. For instance, based on the composition of the deposition fluid, the composition and application parameters, such as concentration, flow-rate, etc., of a post-deposition fluid defining a transfer film may be determined so as to effectuate passivation of the cobalt deposition. The thin layer of transfer film on the dielectric material surrounding the conductive features largely prevents contaminants from the capping process, such as metal containing species, organic and inorganic material, from being trapped in the pores of the dielectric material by providing an effective barrier so as to prevent anchoring of the metal containing species on the surface of the substrate. Thus, after the ELD capping process, the surface of the substrate is maintained wet by subjecting the substrate to a rinse cycle using either an inhibitor chemical that defines a transfer film, as illustrated in step D1 of
The ELD module 200 is used to prepare a top surface of the substrate for deposition and is configured to pre-clean, perform the ELD process to cap the conductive features formed on the surface of the substrate, rinse the surface of the substrate and coat a post-deposition fluid film so as to prevent de-wetting of the surface of the substrate. Towards this end, the ELD module 200 includes a mechanism to receive, hold and spin the substrate along an axis of rotation. The electroless deposition module is configured to isolate the substrate from ambient air and to modulate the oxygen level within to a desired concentration. In one embodiment, the mechanism to receive the substrate is a chuck 130 that is used within the ELD module to receive, hold and spin the substrate along the axis of rotation. The chuck mechanism is described in U.S. Pat. No. 6,935,638, issued on Aug. 30, 2005 and entitled, “UNIVERSAL SUBSTRATE HOLDER FOR TREATING OBJECTS IN FLUIDS,” which is incorporated herein by reference. The embodiments are not restricted to a chuck mechanism for receiving, holding and spinning the substrate but can include other forms of substrate receiving mechanism so long as the mechanism is able to receive, hold and spin the substrate along the axis of rotation within the ELD module. The chuck 130 includes a plurality of chuck pins 132 that extend and retract to receive and release the substrate, respectively. The chuck pins 132 are an exemplary form of receiving, holding and releasing the substrate. The embodiments are not restricted to the chuck pins 132 but can engage other types of mechanism to receive, hold and release the substrate. As illustrated in
The ELD module includes an arm, such as a first arm 110, to supply a rinsing chemistry to pre-clean the substrate before the deposition process. In one embodiment, the first arm 110 is configured as a moveable arm that moves along a radial path from a periphery to the center of the ELD module, as shown by arrow 112 in
The ELD module includes a lid 120 to tightly seal the ELD module during the deposition process, as illustrated in
A second arm (not shown) disposed in the ELD module is used to supply a deposition fluid to the surface of the substrate. In one embodiment, the second arm is disposed on the underside of the lid 120 of the ELD module so that when the lid 120 is engaged, the second arm is configured to supply the deposition fluid to the surface of the substrate in the ELD module and when the lid is disengaged, the supply of the deposition fluid ceases. In one embodiment, the second arm is stationary.
In one embodiment, the deposition fluid is heated outside of the ELD module in a separate microwave/RF unit and discharged into the ELD module at a prescribed temperature. In another embodiment, the ELD module is equipped with a heating element to heat one or more chemistries that is delivered to the ELD module. In this embodiment, a substrate supporting mechanism, such as a chuck, in the ELD module could be equipped with heating elements and thermocouples or other means of heating to heat the deposition fluid and or substrate to a deposition temperature. In this embodiment with heating elements, the heating elements would heat the chuck, which in turn heats the substrate and deposition fluid received thereon. When the heated deposition fluid is at or reaches the deposition temperature, a deposition reaction is triggered causing deposition of a layer of deposition fluid over conductive features on the substrate.
Upon completion of the deposition process the substrate is rinsed by applying a rinsing fluid in the ELD module. The application of the rinsing fluid is controlled to substantially rinse the substrate to remove left-over deposition fluid from the areas of the surface of the substrate that were not intended to receive the deposition fluid, protect metal surface with proper passivation, and, prevent de-wetting of the surface. The rinsing fluid acts as a transfer film over the surface of the substrate keeping the surface of the substrate wet. It should be noted that, the thin layer of the transfer film remains on the surface of the substrate as the substrate is moved out of the electroless deposition. The controlled application of the post-deposition rinsing fluid after the electroless deposition process enables replacing the layer of deposition fluid with the thin layer of post-deposition rinsing fluid on the surface of the substrate. In one embodiment, the first arm may be engaged to apply the post-deposition rinsing fluid so as to define a transfer film coat over the surface of the substrate. The thin layer of the transfer film prevents the surface of the substrate from getting exposed to the ambient air. As mentioned earlier, exposure to the ambient air might cause residues to precipitate on the substrate surface. The transfer film prevents precipitation and agglomeration of the metal alloys on and inside the porous ILD, thereby preserving the insulating properties of the ILD between metal lines and in the layers, resulting in the optimizing of the TDDB. Referring back to
The substrate is removed from the ELD module with the layer of transfer film maintained on the surface of the substrate. The transfer film keeps the substrate surface wet while the substrate is moved to a post-deposition module for further processing. The transportation of the wet substrate to the post-deposition module is performed in the controlled environment of the ELD system.
An electroless deposition system will now be described with reference to
Referring to
The ELD module 350 is used in the deposition process. Aside from the ELD module 350, the ELD system includes a plurality of modules to perform post-deposition process of the substrate. In addition to the dry robot, the ELD system includes a wet robot 340 to transfer the substrate wet from one module to another within the ELD system. To begin with, the wet robot 340 retrieves the substrate from the transfer shelf 330 or directly from the ATM module 320 and transports the substrate to the ELD module 350, as illustrated by path “B” in
As the substrate is typically received at the ELD module 350 after a chemical-mechanical polishing (CMP) operation, the substrate surface is cleaned to remove any residues from the CMP operation prior to starting the deposition. As a result, a pre-deposition rinsing fluid is provided at the ELD module 350 to clean the substrate. Typical pre-deposition rinsing fluids that are used in the cleaning operation prior to the deposition process have been described in the following co-pending U.S patent applications: U.S. patent application Ser. No. 11/760,722, filed on Jun. 8, 2007, entitled “SEMICONDUCTOR SYSTEM WITH SURFACE MODIFICATION”, U.S. patent application Ser. No. 12/205,894, filed on Sep. 7, 2008, entitled “CLEANING SOLUTION FORMULATIONS FOR SUBSTRATES”, Ser. No. 12/334,462, filed on Dec. 13, 2008, entitled “POST-DEPOSITION CLEANING METHODS AND FORMULATIONS FOR SUBSTRATES WITH CAP LAYERS”, Ser. No. 12/334,460, filed on Dec. 13, 2008, entitled “ACTIVATION SOLUTION FOR ELECTROLESS PLATING ON DIELECTRIC LAYERS,” which are incorporated herein by reference. After cleaning the surface of the substrate to remove the residues from the CMP operation, the pre-deposition rinsing fluid is removed from the ELD module 350 through the outlet valves 150, as illustrated in
Following the cleaning operation to remove the residues from the CMP operation, the surface of the substrate is subjected to a deposition process within the ELD module 350. In the deposition process, a layer of deposition fluid is deposited over conductive features formed on the surface of the substrate. The formulation of the deposition fluid is such that it creates a cap over the conductive features during selective deposition and to the extent possible, acts as a barrier preventing copper and other metals that are used in forming the conductive features from migrating to the surrounding dielectric layer. In one embodiment, the deposition fluid is cobalt rich to enable forming a cobalt cap over the conductive features on the surface of the substrate. The deposition fluid is carefully selected so as to inhibit oxidation reactions. Towards this end, the deposition fluid includes an inhibitor and chemistry that includes a rich source of active control cobalt ions. Example deposition fluid and application parameters used are described in U.S. Pat. No. 6,911,067, issued on Jun. 28, 2005, and entitled “Solution composition and method for electroless deposition of coatings free of alkali metals” and U.S. Pat. No. 6,902,605, issued on Jun. 7, 2005, and entitled “Activation-free electroless solution for deposition of cobalt and method for deposition of cobalt capping/passivation layer on copper”, and methods for its use have been discussed in U.S. Pat. No. 6,794,288, issued on Sep. 21, 2004, and entitled “Method for electroless deposition of phosphorus-containing metal films onto copper with palladium-free activation” and in co-pending U.S. patent application Ser. Nos. 11/199,620, filed on Aug. 9, 2005, entitled “Methods for forming a barrier layer with periodic concentrations of elements and structures resulting therefrom” and 11/760,722, filed on Jun. 8, 2007, and entitled “Semiconductor System with Surface Modification,” all of which are herein incorporated by reference in their entirety. As mentioned earlier, the deposition fluid is applied to the surface of the substrate through a second arm that acts as a distribution device, in one embodiment of the invention. As mentioned earlier, the second arm can be a spray, a nozzle or any other suitable mechanism so long as it can apply the deposition fluid in a controlled manner over the conductive features formed on the surface of the substrate. In an alternative embodiment, all fluids could be distributed to the substrate from a single arm or distribution device, so long as the fluid is distributed in a controlled fashion over the surface of the substrate.
In one embodiment, the deposition fluid is heated to a reactive temperature prior to being introduced into the ELD module 350 where the deposition reaction takes place on the substrate. The reactive temperature of the deposition fluid varies based on the type of the deposition fluid and the application conditions used. In one embodiment, the deposition temperature is about 70°C. to about 90° C. or as described in U.S. Pat. No. 6,913,651, typically in the range of about 0% to about 25% below the boiling point of the deposition fluid solution.
In one embodiment, the deposition fluid is supplied to the ELD module at mostly a non-reactive temperature. In the ELD module, the deposition fluid is then heated using a heating element to a reactive temperature. As the deposition fluid heats up and approaches the reactive temperature, the humidity within the ELD module increases. In one embodiment, the humidity within the ELD module reaches to about 80%. In another embodiment, the humidity within the ELD module is at about 95%.
As the temperature within the ELD module reaches reactive temperature or when the deposition fluid is introduced into the ELD module preheated to a reactive temperature, a deposition reaction is triggered. The deposition reaction deposits a layer of deposition fluid on the conductive features on the surface of the substrate. After the deposition process, the surface of the substrate is rinsed using a rinsing fluid, such as a post-deposition rinsing fluid. The post-deposition rinsing fluid is defined from the deposition fluid and is applied in a controlled manner onto the surface of the substrate. The post-deposition rinsing fluid rinses the surface and prevents de-wetting of the surface of the substrate by defining and maintaining a transfer film, on the surface of the substrate. The controlled application of the post-deposition rinsing fluid enables replacing the deposition fluid layer from the surface of the substrate with the transfer film. After the application of the post-deposition rinsing fluid, the substrate is removed from the ELD module 350 by a wet robot 340 while maintaining the transfer film on the surface of the substrate. The wet robot 340 moves the substrate wet with the transfer film to a post-deposition module within the ELD system. Thus, as the substrate is kept constantly wet during the integrated ELD process, any residues present in the ELD module, including a droplet of the deposition fluid or any other chemistry/residue that precipitates on the substrate will not damage the substrate or materials thereon during the integrated deposition process.
To efficiently wet the surface of the substrate and to prevent de-wetting of the surface of the substrate, one or more surfactants may be added to the post-deposition rinsing fluid. The surfactants help in uniformly wetting the surface of the substrate by reducing the surface tension of the rinsing fluid. The concentration of the one or more surfactants that have shown effective result range between about 50 parts/million (ppm) to about 2000 ppm. Some of the surfactants that are used herein are described in U.S. patent application Ser. Nos. 12/334,462 and 12/334,460, which are incorporated herein by reference in its entirety. Some sample surfactants may include Linear AlkylBenzene Sulphonate, TRITON™ QS-44, Perfluoro Anionic and nonionic surfactants like Zonyl™ from DuPont and Masurf™ by Mason. In addition to one or more surfactants, one or more chelating agents may be added to the post-deposition rinsing fluid so as to bond with metal containing residues to form complexes. The chelating agents are chosen such that the complexes formed with the metal containing residues are soluble in an aqueous portion/component of the post-deposition rinsing fluid. Some of the chelating agents include Tetra-Methyl Ammonium Hydroxide (TMAH) or MethylAmine (MA) containing metal-chelating agents such as Hydroxyethyl Ethylenediamine Triacetic Acid (HEDTA) and/or Lactic Acid. In one embodiment, the concentration of the chelating agent(s) within the post-deposition rinsing fluid may range between about 100 ppm to about 5000 ppm.
In order to maximize functionality of the chelating agent(s) and the surfactant(s), a pH value of the post-deposition rinsing fluid may be adjusted. The range of pH value that has shown promising results is between about 2.0 pH (acidic) to about 12 (base). In one embodiment, the pH value of the post-deposition rinsing fluid can be adjusted using a pH adjusting agent. The pH adjusting agent can be any one of the surfactants or chelating agents added to the post-deposition rinsing fluid or could be a distinct pH adjusting agent added to the post-deposition rinsing fluid.
In addition to the surfactants, chelating agents and pH adjusting agents, one or more oxygen consuming/reducing agents can also be added to the post-deposition rinsing fluid to effectuate post-deposition cleaning of the substrate. The oxygen reducing agents directly react with the dissolved oxygen molecules in the transfer film in order to reduce the oxygen concentration contained therein. An exemplary oxygen reducing agent that has shown promising results in reducing oxygen concentration in the transfer film on the substrate is dimethylaminobenzaldehyde (DMAB). In one embodiment, in addition to DMAB, a second or additional oxygen reducing agents may be included in the post-deposition rinsing fluid to help reduce oxygen concentration and to recover the first oxygen reducing agent. An exemplary second reducing agent that has shown promising results in reducing oxygen concentration while helping in the recovery of the first oxygen reducing agent is L-ascorbic acid. The concentration of the oxygen reducing agents that have shown promising results are in the range of about 100 ppm to about 5000 ppm.
In addition to the surfactants, chelating agent, oxygen reducing agent and pH adjusting agents, one or more etching inhibitors may be added to the post-deposition rinsing fluid to preserve the layer deposited over the conductive features on the surface of the substrate. In one embodiment, an exemplary etching inhibitor for CoWP capping is benzotriazol. The concentration of such etching inhibitor that has shown promising results is in the range from about 20 ppm to about 2000 ppm. A thickening agent may also be added to the post-deposition rinsing fluid to add thickness to the post-deposition rinsing fluid so that a film of the post-deposition rinsing fluid applied to the surface of the substrate can be maintained over an extended period of time. The thickening agent is selected such that it does not adversely react or otherwise affect the surface of the substrate when applied and maintained for extended period of time. The thickening agent also reduces evaporation rate of the solvent within the post-deposition rinsing fluid. An exemplary thickening agent that has shown promising results is poly-ethanol. The concentration of the thickening agent that has shown promising results range from about 50 ppm to about 5000 ppm.
In addition to the ELD module 350, the ELD system illustrated in
In another embodiment, the substrate may be moved from the chemical module wet with rinsing fluid into a second chemical module (chemical rinse module) so as to treat the surface of the substrate with a passivation fluid. The operation of the second chemical module is similar to the operation of the chemical module 370 that applied the acid containing fluid to the surface of the substrate. The passivation fluid is introduced to passivate metal lines and pads formed on the surface of the substrate. The passivation fluid is selected based on the substrate layer and metal pads/lines formed on the surface and is used to minimize metal corrosion. In this embodiment, the substrate is received into the chemical rinse module (a second chemical module) wet with the transfer film from the chemical module and the passivation fluid is applied to the surface of the substrate. The passivation fluid replaces the transfer film and passivates the substrate layer and metal pads. After treating the substrate with the passivation fluid, a transfer film, defined by the passivation fluid, is applied to the substrate to rinse the passivation fluid and to wet the surface of the substrate. The wet substrate is moved out of the chemical rinse module while maintaining the transfer film on the surface of the substrate.
The wet robot 340 helps in transferring the substrate wet with the transfer film to a subsequent post-deposition module within the ELD system, such as a brush scrub module 360 as illustrated by path D of
The wet robot 340 removes the substrate wet with the transfer film from the ELD module 350 and inserts the substrate into a brush scrub module 360 while continuing to maintain the transfer film on the substrate's surface. The only difference between the embodiments illustrated in
It should be noted that the above embodiments reflect only two different configurations of the various components and modules of the ELD system. It should be clear to one skilled in the art that there could be variations in the configurations including using more than one ELD module, chemical module, brush scrub module and/or clean module so long as the functionalities of each of the various modules are maintained. Further, there could be variations of the different modules for processing the surface of the substrate within the ELD system. For instance, in an alternate embodiment to the ELD system illustrated in
In order to increase the throughput in the ELD system, one or more stacks of modules may be employed.
Referring now to
Continuing to refer to
Some of the exemplary rinsing fluids that are used during the pre-deposition cleaning of the substrate include citric acid with one or more surfactants, oxalic acid with one or more surfactants, CP-72™, ESC-784™, ESC-90™ from ATMI, etc. The concentration ranges of surfactants are between about 0.1% to about 5% with preferred concentration of about 1%, and a flow rate between about 100 parts per million (ppm) to about 2000 ppm with a preferred flow rate of about 500 ppm. After the pre-deposition clean, the substrate is subjected to a deposition process (step 3) to cap the conductive features formed on the surface of the substrate by applying deposition fluid. During the deposition process, a humid environment is provided within each of the ELD modules by pre-heating and supplying the heated deposition fluid into the ELD modules or heating the deposition fluid within the ELD modules to a deposition temperature and triggering a deposition reaction. After the deposition process, the substrate is rinsed (step 4) in the corresponding ELD modules 350 within the ELD stack wherein the deposition fluid is replaced with a post-deposition rinsing fluid that defines a transfer film on the top surface of the substrate.
Aside from the ELD module stack, the ELD system illustrated in
In the embodiment illustrated in
As shown in step 6 of
Following the brush clean, the substrate is transported wet to a clean module where the substrate is subjected to a final rinse cycle and dried, as illustrated in steps 7 and 8 of
Although the embodiments were discussed with reference to a single wet robot, it should be noted herein that the ELD system could include a plurality of wet robots to transfer the substrate from one module to another. The plurality of wet robots can improve the throughput by simultaneously transferring more than one substrate from one module to another. In one embodiment, the throughput using the ELD system defined with respect to
Thus, the various embodiments disclose ways to improve the electrical performance of the sub-micron devices formed on the substrate and throughput. The embodiments teach ways to make the substrate substantially defect free and corrosion free by providing a layer of transfer film on the surface of the substrate. The transfer film protects the substrate surface from corrosion by-products, metals and other residues/contaminants by trapping the contaminants and residues that precipitate on the substrate during the deposition/cleaning operations and also ensures that the substrate is not exposed to the ambient air that causes oxidation of the metal implants. Further, the transfer film reduces the wet-dry cycle thereby reducing the moisture breaks which resulted in substantial damage to the substrate due to precipitation of contaminants. The deposition of the cobalt cap on the conductive features and the maintenance of transfer film prevents precipitation and migration of the copper into the surrounding dielectric film layer and the electro-migration of the copper metal alloys thereby preserving the integrated circuit device.
The process, thus, defines an efficient way of preventing de-wetting, overcoming problems associated with premature drying and frequent moisture breaks during the integrated electroless deposition process. The resulting substrate is substantially defect-free resulting in substantial electrical yield of the resulting devices.
In one embodiment, the treating fluid may include an inhibitor to prevent corrosion of the conductive features and an acid containing fluid that acts as an active agent to enable chemical reaction with the substrate surface. It should be noted that during the integrated ELD process the substrate can be dry on the bottom surface but wet on the top surface or the substrate could be wet on both the bottom and top surfaces. At any rate, it is critical that after each process in the ELD system the substrate is kept sufficiently wet on at least the top surface during transfer of the substrate from one module to another module within the ELD system. After the sequence of processing operations at the different post-deposition modules, the substrate is rinsed and dried. The resulting substrate is substantially clean and defect/corrosion free.
The selection of the various post-deposition rinsing fluids and treating fluid are based on the amount of clean that is required, the nature and type of the pre-deposition fabrication operation, the fabrication chemistries used and the type of substrate. Similarly, the process parameters used to apply the cleaning chemistries varies based on the analysis of the type of fabrication layers that form the features.
For additional information with respect to the proximity head, reference can be made to an exemplary proximity head, as described in the U.S. Pat. No. 6,616,772, issued on Sep. 9, 2003 and entitled “METHODS FOR WAFER PROXIMITY CLEANING AND DRYING.” This U.S. patent, which is assigned to Lam Research Corporation, the assignee of the subject application, is incorporated herein by reference.
For additional information about menisci, reference can be made to U.S. Pat. No. 6,998,327, issued on Jan. 24, 2005 and entitled “METHODS AND SYSTEMS FOR PROCESSING A SUBSTRATE USING A DYNAMIC LIQUID MENISCUS,” and U.S. Pat. No. 6,998,326, issued on Jan. 24, 2005 and entitled “PHOBIC BARRIER MENISCUS SEPARATION AND CONTAINMENT.” These U.S. patents, which are assigned to the assignee of the subject application, are incorporated herein by reference in their entirety for all purposes.
For additional information about top and bottom menisci, reference can be made to the exemplary meniscus, as disclosed in U.S. patent application Ser. No. 10/330,843, filed on Dec. 24, 2002 and entitled “MENISCUS, VACUUM, IPA VAPOR, DRYING MANIFOLD.” This U.S. patent, which is assigned to Lam Research Corporation, the assignee of the subject application, is incorporated herein by reference.
While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. Therefore, it is intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention. In the claims, elements and/or steps do not imply any particular order of operation, unless explicitly stated in the claims.
This application claims the priority of U.S. Provisional Application No. 61/285,950, filed on Dec. 11, 2009, and titled “Integrated Tool Sets and Process to Keep Substrate Surface Wet During Plating and Clean in Fabrication of Advanced Nano-Electronic Devices.” This application is incorporated herein by reference in its entirety for all purposes. This application is related to U.S. patent application Ser. No. 11/760,722, filed on Jun. 8, 2007, and entitled “Semiconductor System with Surface Modification,” and to PCT Application No. PCT/US09/55943, filed on Sep. 3, 2009, and entitled “Cleaning Solution Formulations for Substrates.” The disclosure of these applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61285950 | Dec 2009 | US |
