Patent Application
20080149490
1. Field of the Invention
This invention relates to structures and methods for electroplating on seed layers. More specifically, the invention relates to structures and methods for electroplating on ultra-thin seed layers.
2. Description of the Related Art
The use of seed layers to electroplate conductive interconnect lines and magnetic shield structures is widely practiced in the art of integrated circuit and micro-circuit fabrication. Typically, a thin, electrically conductive (seed) layer is vapor deposited on the circuit structure, which subsequently acts as a starting cathode for the electrochemical deposition of a much thicker plated layer. This technique is useful for depositing thicker metal layers used for interconnect, which would take very long times if deposited from the vapor by CVD or sputtering, or for depositing copper which is easily and economically electroplated.
A serious problem experienced by practitioners electroplating on seed layers results from the relatively low conductivity of thin seed layers as the wafer size increases and seed layer thickness decreases, resulting in significant voltage drops across the wafer during the electroplating process. Typically, electrical contact with the wafer in the plating tools occurs near the outer edge (or perimeter) of the wafer, and electrical current needed for the deposition of plated metal in the center of the wafer must travel across the radius. As wafer sizes continue to increase, and seed layers continue to decrease in thickness, this problem is exacerbated to the point where poor plating uniformity results. In some cases, there may even be a lack of plated conductor in the center portions of the wafer.
One solution to this problem is disclosed in
One disadvantage is that the seed layer 202 still must be reasonably thick, typically 250 to 1000 angstroms or greater. Otherwise electroplating of the conduction layer 306 will be non-uniform, with large variations in plated thickness occurring from center to edge. Voids may also be formed in the galleys, causing some die areas to be isolated in subsequent device structure plating processes. The use of ultra-thin seed layers, for example seed layers under 250 angstroms, may be unsuitable for this process.
Another disadvantage is that this prior art process uses a single seed layer of uniform composition. In current and future device technology, multiple seed layers of different chemical compositions, layer structures, and thickness may be required within the device die at varying locations. This functionality is required because seed layers have additional functional properties that are customized to match particular device structures. For example, seed layers may be required to have anti-reflective properties to aid in photo resist exposure. They must also have good adhesion to both underlying materials and photo resists that will be deposited on their surface, as well as the plated materials that will be deposited on them. They need to be compatible with the plating bath chemistry, and not oxidize, corrode, or dissolve in the bath. They need to be compatible with the plated device design, if they are part of critically dimensioned structure like a perpendicular write head, for example. A single seed layer cannot meet all these requirements. Thicker seed layers suitable for the prior art process, may not be compatible with device structures such as perpendicular write heads, where the seed layer is an integral part of the structure separating the plated shield from other structures within the head. Furthermore, due to the wide variety of seed materials needed, some compositions may not be chemically stable when exposed to copper plating bath chemistries, particularly at thickness ranges below 250 angstroms.
What is needed is a better process for electroplating on ultra-thin seed layers of varying composition and thickness, while maintaining good device structure plating uniformity across the full diameter of the wafer.
A summary of the relevant prior art is provided below.
An article entitled “Network Plating on Seed Layer to Improve Plating Uniformity”, by Fu et al., published in the IBM Technical Disclosure Bulletin, May 1992, discloses a method to improve plating uniformity throughout the active device area of a substrate based on pre-plating the inactive area of a substrate to enhance electrical conductivity and current distribution across the substrate.
United States Patent Application Publication 2001/0022704 discloses a method and system for a write head. The method and system include the steps of providing a first pole and providing a bottom antireflective coating (BARC) layer. The BARC layer is conductive, nonmagnetic, and an antireflective coating. A portion of the BARC layer is disposed above the first pole. The method and system also include providing a photoresist structure having a trench therein. The method and system also include providing a second pole. A portion of the second pole is disposed above the portion of the BARC layer and within the trench. Thus, the width of the pole may be better controlled.
U.S. Pat. No. 5,744,019 discloses multiple-layer thin film devices deposited by electroplating on an otherwise substantially clean substrate wafer. The composition of the electroplated alloy layers is maintained substantially uniform using a cathode assembly on which the substrate wafer is mounted. The cathode assembly includes an inner cathode ring electrically connected to the wafer, a thief ring external to the cathode ring and an insulating ring connected between and electrically insulating the cathode and thief rings. The cathode ring and the thief ring are powered by separate power sources.
U.S. Pat. No. 5,805,392 discloses pole pieces of a thin film head formed by two thin film layers of the magnetic metal NiFe, each NiFe layer being about 20,000 angstroms thick. These two NiFe layers are separated by an electrically insulating layer of alumina (Al2O3), ceramic or NiFe oxide that is about 100 angstroms thick. In one embodiment, a hard-baked photoresist layer is formed only around the edges of the first NiFe layer, the electrically insulating layer is deposited over the top surface of the first NiFe layer and over the hard-baked photoresist layer, and the second NiFe layer is then deposited, thus providing a three-layer metal/insulator/metal pole piece wherein the hard baked photoresist blocks edge short circuiting between the two thin film NiFe layers. In another embodiment, edge short circuiting is minimized by allowing a small filament(s) of a high electrical resistance plating seed layer of NiFe to extend between the two NiFe thin film layers, the high resistance of these long and thin NiFe filaments being much greater than the resistance of the two NiFe thin film layers.
U.S. Pat. No. 5,901,432 discloses a method for making a merged thin film read/write head, where the first pole piece includes a pedestal or pole tip portion that extends up from the first pole piece layer, using electroplating to form the gap so that the gap layer does not have to be removed later. After the first pole piece is deposited, the coil insulation structure is built over the first pole piece. Afterwards an electrically conductive seed layer of the same ferromagnetic material as the first pole piece is formed over the wafer to provide an electrically conductive path for subsequent electroplating. After the seed layer deposition, a photoresist pattern is then formed to define the shape of the second pole piece. Nonmagnetic nickel-phosphorous is then electroplated onto the seed layer in the region not covered by the photoresist pattern to form the gap layer. The second ferromagnetic layer is then electroplated onto the gap layer to define the shape of the second pole piece. The thickness of the second pole piece layer is deliberately made thicker than the desired final thickness because the second pole piece layer is used as a mask for subsequent ion beam milling to form the notched pole tip element of the first pole piece. The photoresist is removed and ion beam milling performed to remove the seed layer and a portion of the first pole piece layer to define the pedestal pole tip element of the first pole piece. The ion beam milling does not have to remove the gap layer because the electroplated gap has been defined by the photoresist pattern to have the desired trackwidth.
U.S. Pat. No. 6,140,234 discloses selectively plating recesses in a semiconductor structure, by providing electrical insulating layer over the semiconductor substrate and in the recesses, followed by forming a conductive barrier over the insulating layer; providing a plating seed layer over the barrier layer; depositing and patterning a photoresist layer over the plating seed layer; planarizing the insulated horizontal portions by removing the horizontal portions of the seed layer between the recesses; removing the photoresist remaining in the recesses; and then electroplating the patterned seed layer with a conductive metal using the barrier layer to carry the current during the electroplating to thereby only plate on the seed layer. In an alternative process, a barrier film is deposited over recesses in an insulator. Then, relatively thick resists are lithographically defined on the field regions, on top of the barrier film over the recesses. A plating base or seed layer is deposited, so as to be continuous on the horizontal regions of the recesses in the insulator, but discontinuous on their surround wall. The recesses are then plated using the barrier film without seed layers at the periphery of the substrate wafers for electrical contact. After electroplating, the resist is removed by lift-off process and exposed barrier film is etched by RIE method or by CMP. Also provided is a semiconductor structure obtained by the above processes.
U.S. Pat. No. 6,514,393 discloses an electrochemical reactor used to electrofill damascene architecture for integrated circuits or for electropolishing magnetic disks. An inflatable bladder is used to screen the applied field during electroplating operations to compensate for potential drop along the radius of a wafer. The bladder establishes an inverse potential drop in the electrolytic fluid to overcome the resistance of a thin film seed layer of copper on the wafer.
U.S. Pat. No. 6,540,928 discloses a method and apparatus for fabricating an electroplating mask for the formation of a miniature magnetic pole tip structure. The method incorporates a silylation process to silylate photo-resist after creating a photo-resist cavity or trench in the electroplating mask. The silylation process is performed after a dry etch of the photo-resist. Alternatively, silylation is performed after a lithographic patterning of the trench. As a result of chemical biasing, the vertical side walls of the photoresist layer shift inward creating a narrower trench. The resulting structure formed after electroplating has a width of less than 0.3 micrometers. This structure can be used as a magnetic pole of a thin film head (“TFH”) for a data storage device.
U.S. Pat. No. 6,589,816 discloses a method of forming metal connection elements in integrated circuits formed on adjacent areas of a wafer, including forming a conductive seed layer on a substrate of the wafer. A first mask covers the integrated circuits and leaves exposed areas of the seed layer overlying predetermined scribe lines used for separation of the integrated circuits. Using the seed layer as a cathode, a metal is deposited by an electrochemical process on exposed areas of the seed layer. The first mask is removed and a second mask is formed, leaving predetermined areas of the seed layer exposed. Using the seed layer as a cathode a metal is deposited on the exposed predetermined areas by an electrochemical process. The second mask is then removed. Connection elements of uniform thickness throughout the substrate are produced with the use of a very thin seed layer.
U.S. Pat. No. 6,774,039 discloses copper bus bars formed between adjacent die on a wafer during the process flow. The bus bars are between 50 and 100 microns wide and between 2 and 5 microns deep. A barrier layer is formed between the bus bars and the die to prevent copper diffusion. A dielectric layer is deposited over the bus bars and die and etched with contacts and features, such as vias. A seed layer is subsequently deposited over the wafer, which allows electrical conductance between the bus bars and the die during a subsequent electroplating process to fill the features and contacts. The bus bars carry electroplating current from the die edge to the die center. As a result, current does not need to be carried by a low sheet resistivity seed layer from the wafer edge to the center. This allows the seed layer to be thinner and of materials other than copper. Further, thinner seed layers allow thicker barrier layer for more reliability.
U.S. Pat. No. 6,807,027 discloses a perpendicular write head including a main pole, a return pole, and conductive coils. The main pole includes a seed layer and a magnetic layer that is plated upon the seed layer. The seed layer is nonmagnetic, electrically conductive, and corrosion-resistant. The return pole is separated from the main pole by a gap at an air bearing surface of the write head and is coupled to the main pole opposite the air bearing surface. The conductive coils are positioned at least in part between the main pole and the return pole.
U.S. Pat. No. 6,811,670 discloses a method for forming electroplating cathode contacts around the periphery of a semiconductor wafer, including forming an insulating layer over a conductive layer extending at least around the periphery of a semiconductor wafer substrate; etching a plurality of openings around a peripheral portion of the semiconductor wafer substrate through the insulating layer to extend through a thickness of the insulating layer in closed communication with the conductive layer said conductive area in electrical communication with a central portion of the semiconductor wafer substrate; filling the plurality of openings with metal to form electrically conductive pathways; planarizing the electrically conductive pathway surfaces; and, forming a metal layer over the electrically conductive pathway surfaces to form a plurality of contact pads for contacting a cathode for carrying out an electroplating process.
U.S. Pat. No. 6,861,355 discloses a seed film and methods incorporating the seed film in semiconductor applications. The seed film includes one or more noble metal layers, where each layer of the one or more noble metal layers is no greater than a mono-layer. The seed film also includes either one or more conductive metal oxide layers or one or more silicon oxide layers, where either layer is no greater than a mono-layer. The seed film can be used in plating, including electroplating, conductive layers, over at least a portion of the seed film. Conductive layers formed with the seed film can be used in fabricating an integrated circuit, including fabricating capacitor structures in the integrated circuit.
U.S. Pat. No. 6,949,833 discloses a structure including a substrate with a top surface and a bottom surface, an etched dielectric layer having sidewalls and an upper surface, wherein the etched dielectric layer with a thickness of v, is positioned upon a first portion of the top surface of the substrate but not positioned upon a second portion of the top surface of the substrate having a width equal to x, an atomic layer deposited (ALD) film with a thickness of y, positioned upon the upper surface of the etched dielectric layer, the sidewalls of the etched dielectric layer, and the second portion of the top surface of the substrate, and a trench formed by the atomic layer with a width equal to x−2y. The patent also discloses a method of forming a structure with a trench that includes the steps of depositing a dielectric layer on a substrate, forming a patterned photoresist on the dielectric layer, forming a space having a width x, by etching the dielectric layer, removing the patterned photoresist to form a gap having sidewalls and a bottom, and depositing an atomic layer with a thickness of y on the etched dielectric layer, and the sidewalls and the bottom of the gap, wherein a trench is formed by the atomic layer deposited on the sidewalls and bottom of the gap.
U.S. Pat. No. 7,037,574 discloses an atomic layer deposition (ALD) process that deposits thin films for microelectronic structures, such as advanced gap and tunnel junction applications, by plasma annealing at varying film thicknesses to obtain desired intrinsic film stress and breakdown film strength. The primary advantage of the ALD process is the near 100% step coverage with properties that are uniform along sidewalls. The process provides smooth (Ra about 2 angstroms), pure (impurities <1 at.%), AlOx films with improved breakdown strength (9-10 MV/cm) with a commercially feasible throughput.
U.S. Pat. No. 7,052,922 discloses a method and apparatus for plating facilitating the plating of a small contact feature of a wafer die while providing a relatively stable plating bath. The method utilizes a supplemental plating structure that is larger than a die contact that is to be plated. The supplemental plating structure may be located on the wafer, and is conductively connected to the die contact. Conductive connection between the die contact and the supplemental plating structure facilitates the plating of the die contact. The supplemental plating structure also can be used to probe test the die prior to singulation.
It is an object of the present invention to provide a method for electroplating device structures, including vapor depositing a seed layer on a first portion of a wafer surface; vapor depositing a conduction layer on a second portion of the wafer surface, wherein the conduction layer is electrically coupled to the seed layer; and, electroplating a device structure on the seed layer by conducting electrical current through the conduction layer to the seed layer.
It is another object of the present invention to provide a method for electroplating device structures, including vapor depositing a first seed layer on a first portion of a wafer surface; vapor depositing a second seed layer on a second portion of the wafer surface; vapor depositing a conduction layer on a third portion of the wafer surface, wherein the conduction layer is electrically coupled to the first and second seed layers; electroplating a first device structure on the first seed layer by conducting electrical current through the conduction layer to the first seed layer; and, electroplating a second device structure on the second seed layer by conducting electrical current through the conduction layer to the second seed layer.
It is another object of the present invention to provide a method for electroplating device structures, including vapor depositing a seed layer on a wafer surface, vapor depositing a conduction layer on a first portion of the seed layer and, electroplating a device structure on a second portion of the seed layer by conducting electrical current through the conduction layer to the second portion of the seed layer.
It is yet another object of the present invention to provide a method for electroplating device structures, including vapor depositing a conduction layer on a first portion of a wafer surface, vapor depositing a seed layer on a second portion of the wafer surface, and on at least a portion of said conduction layer; and, electroplating a device structure on the seed layer covering the second portion of the wafer surface, by conducting electrical current through the conduction layer to at least a portion of the seed layer.
The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:
a (Prior Art) is a schematic plan view of a wafer having a plurality of device die;
b (Prior Art) is a cross sectional view through section A-A of
a (Prior Art) is a schematic plan view of the wafer of
b (Prior Art) is a cross section view through section B-B of
a (Prior Art) is a schematic plan view of the wafer of
b (Prior Art) is a cross sectional view through section C-C of
a is a schematic plan view of a wafer subsequent to the deposition of ultra-thin seed layer 406, in accordance with an embodiment of the present invention;
b is a cross sectional view through section D-D of
c is an expanded schematic plan view of die 404c of
a is a schematic plan view of a wafer subsequent to the vapor deposition of conduction layer 502, in accordance with an embodiment of the present invention;
b is a cross sectional view through section E-E of
c is an expanded schematic plan view of die 404c of
a is a schematic plan view of a wafer subsequent to the vapor deposition of conduction layer 602, in accordance with an embodiment of the present invention;
b is a cross sectional view through section F-F of
c is an expanded schematic plan view of die 404c of
a is a schematic plan view of a wafer subsequent to the vapor deposition of ultra-thin seed layer 702, in accordance with an embodiment of the present invention;
b is a cross sectional view through section G-G of
c is an expanded schematic plan view of die 404c of
a is a schematic plan view of a wafer subsequent to the vapor deposition of conduction layer 804, and the selective vapor deposition of a plurality of ultra-thin seed layers, in accordance with an embodiment of the present invention;
b is a cross sectional view through section H-H of
c is an expanded schematic plan view of die 404c of
a is a schematic block diagram of a first electroplating process, in accordance with an embodiment of the present invention;
b is a schematic block diagram of a second electroplating process, in accordance with an embodiment of the present invention;
c is a schematic block diagram of process step 902 of
d is a schematic block diagram of process step 904 of
a-3b have been discussed above in the Background section.
a is a schematic plan view 400 of a wafer subsequent to the deposition of ultra-thin seed layer 406, in accordance with an embodiment of the present invention.
c is an expanded schematic plan view of die 404c of
a is a schematic plan view 500 of a wafer subsequent to the vapor deposition of conduction layer 502, in accordance with an embodiment of the present invention.
Conduction layer 502 can be composed of any conductive material, preferably a metal or metal alloy, that can be deposited by a vapor deposition technique. All the materials and deposition techniques cited for the ultra-thin seed layer are acceptable, with the inclusion of low cost base metals such as copper and aluminum. Conduction layer 502 can comprise a single layer, or have multiple layers. For example, conduction layer 502 could be composed of a copper or aluminum base layer, covered with a thin gold protective layer, to reduce corrosion in the plating bath. Conduction layer 502 must be compatible with ultra-thin seed layer 406 with respect to adhesion, interfacial resistance, and galvanic corrosion. That is, the two layers (seed and conduction) must adhere to one another, there should be an acceptably low resistance at their interface, and the coupling of the two layers cannot promote corrosion in the aqueous plating bath when the device structures are plated. Conduction layer 502 can range from about 20 nm to 100 nm in thickness, depending on its conductivity, with the more conductive materials, such as copper and Rh, requiring thinner layers.
c is an expanded schematic plan view of die 404c of
a-7c disclose an alternate embodiments of the present invention, wherein the deposition order of the conduction layer and the ultra-thin seed layer(s) are reversed.
a is a schematic plan view 700 of a wafer subsequent to the vapor deposition of ultra-thin seed layer 702, in accordance with an embodiment of the present invention.
c is an expanded schematic plan view of die 404c of
a is a schematic plan view 800 of a wafer subsequent to the vapor deposition of conduction layer 804, and the selective vapor deposition of a plurality of ultra-thin seed layers, in accordance with an embodiment of the present invention.
c is an expanded schematic plan view of die 404c of
a is a schematic block diagram of a first electroplating process 900, in accordance with an embodiment of the present invention. In step 902, ultra-thin seed layers are vapor deposited in the wafer surface, in accordance with the processes and limitations previously disclosed. In step 904, the conduction layer is deposited, also in accordance with the processes and limitations previously disclosed. In step 906, a plating mask is deposited to limit the plating deposition to desired areas and structures within the device die, using processes well known to those skilled in the art. In step 908, the device structures are electroplated. In an optional step (not shown), the ultra-thin seed layers can be removed by etching without damage to remaining structures.
b is a schematic block diagram of a second electroplating process 901, in accordance with an embodiment of the present invention. In this process, steps 902 and 904 are reversed.
c is a schematic block diagram of process step 902 of
d is a schematic block diagram of process step 904 of
The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.
