US 20060266655 A1
Embodiments of the invention generally include a method and intermediate plating solution for plating metal onto a substrate surface. The method generally includes filling the features and/or growing a film layer on the field areas by plating a metal from a first solution on a seed layer under an applied first current, wherein the first solution includes an acid in an amount sufficient to provide a first solution pH of about 6 or less, copper ions, and at least one suppressor. The method may further include substantially filling features by plating metal ions from a second solution onto the substrate under an applied second current to form a metal layer, wherein the second solution includes an acid in an amount sufficient to provide a second solution pH of from about 0.6 to about 3, copper ions, at least one suppressor and at least one accelerator and growing a film layer on the field areas by contacting the metal layer with a third solution under an applied third current, wherein the third solution includes an acid, copper ions, at least one suppressor, at least one accelerator and at least one leveling agent. The intermediate plating solution generally includes copper sulfate in a concentration of from about 5 g/L to about 50 g/L, sulfuric acid in a concentration sufficient to provide a pH of less than about 6 and suppressors having a molecular weight of 600 or greater.
1. A method for plating metal onto a substrate, comprising:
forming a metal layer in features by plating metal ions from a first solution in the features formed into the substrate, wherein the first solution consists essentially of an acid concentration between 0.1 g/L and 5 g/L, a first solution pH between 3 and 6, copper ions, and at least one suppressor; and
substantially filling the features by plating metal ions from a second solution in the features, wherein the second solution comprises an acid, a second solution pH between 0.6 and 3, copper ions, at least one suppressor, and at least one accelerator.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. The method of
10. The method of
11. The method of
12. The method of
13. A method for depositing a metal on a substrate having features, comprising:
forming a metal layer in the features by plating metal ions from a first solution in the features, wherein the first plating solution has a resistance that is higher than a seed layer resistance upon which the metal layer is formed; and
substantially filling the features by plating metal ions from a second plating solution, wherein the second plating solution comprises an acid, copper ions, at least one suppressor, at least one accelerator, and at least one leveling agent, and wherein said first and second solutions are different.
14. The method of
15. The method of
16. The method of
17. The method of
controlling the plating from the first solution by increasing the first solution resistance to compensate for edge high deposition.
18. The method of
19. The method of
20. The method of
This application is a continuation of U.S. patent application Ser. No. 10/746,126 (APPM/007810), filed Dec. 24, 2003, which claims benefit of U.S. Provisional Patent Application Ser. No. 60/436,180 (APPM/007810L), filed Dec. 24, 2002, and U.S. Provisional Patent Application Ser. No. 60/510,190 (APPM/008039L), filed Oct. 10, 2003. All of the above applications are hereby incorporated by reference in their entireties.
1. Field of the Invention
Embodiments of the invention generally relate to a multiple chemistry electrochemical plating method.
2. Description of the Related Art
Metallization for sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. In devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), for example, have been used to fill these interconnect features. However, as interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as viable processes for filling sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate may be efficiently filled with a conductive material, such as copper. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate (this process may be performed in a separate system), and then the surface features of the substrate are exposed to an electrolyte solution while an electrical bias is simultaneously applied between the substrate and an anode positioned within the electrolyte solution. The electrolyte solution is generally rich in ions to be plated onto the surface of the substrate. Therefore, the application of the electrical bias causes these ions to be urged out of the electrolyte solution and to be plated onto the seed layer.
One challenge associated with conventional ECP processes is that the supporting hardware, i.e., the electrochemical plating systems, are limited to a single chemistry for use in the electrochemical plating process. The availability of a single chemistry presents challenges to plating processes, as the single chemistry must be used to accomplish several very different plating processes. For example, the single chemistry may be used to deposit a seed layer over a barrier layer, to deposit a feature filling layer, to deposit a bulk fill layer, to deposit a metal alloy layer, to deposit an adhesion layer, or any other layer known in the electrochemical plating art. The challenge with using a single chemistry for more than one plating process is that the single chemistry is generally not able to provide the best characteristics for each plating process. For example, a chemistry configured to deposit a feature fill layer would have different characteristics and chemical compositions than a chemistry configured to deposit a bulk fill layer. The feature fill layer is generally plated much slower than a bulk fill layer and a primary concern with the feature fill layer is not prematurely closing off the openings of high aspect ratio features being filled, wherein the bulk fill deposition is a much faster deposition process that is not concerned with the throat closure. Thus, conducting both steps from a single chemistry requires balancing of several parameters, which inherently sacrifices some of the advantageous characteristics of the respective processes.
Another example of a plating process where a multiple chemistry system would have advantageous over a single chemistry system is a direct plating on barrier layer (rubidium, cobalt, tantalum nitride, or other metal known to be an acceptable electrochemical plating barrier layer) plating processes. In this configuration a first chemistry could be configured to plate a layer directly on the barrier layer with adequate adhesion to support a subsequent layer plated thereon with a second chemistry configured to optimize the subsequent layer. Yet another example of an advantage provided by a multiple chemistry plating method is a plating process where a first plating chemistry may be configured to be highly resistive (more resistive than a thin seed layer), so that the chemistry can effectively plate on the thin seed layer without having edge high plating problems. Then a second chemistry that is less resistive may be used to continue plating at a much higher deposition rate than the resistive chemistry. Yet another example of an advantage provided by a multiple chemistry plating method is a process where multiple chemistries are used to plate a combination of alloy and generally pure metal layers, such as a copper alloy followed by a generally pure copper layer or a generally pure layer followed by a copper alloy layer.
Although a multi-chemistry plating process is desirable, system manufacturers have not been able to develop a multi-chemistry system. This is generally a result of the challenges (plumbing, isolation, space requirements, etc.) associated with providing multiple chemistries to a single electrochemical plating system. Space requirements are a primary factor limiting implementation of an ECP system having multiple chemistries, as conventional plating systems generally include a large (over 200 liters) tank that supplies electrolyte to one or more plating cells on the plating system. Thus, for each additional chemistry provided, an additional 200 liter tank would also have to be provided. Further, each tank of electrolyte is dosed with additives configured to control plating parameters, and these additives would also have to be dosed into the second tank, which again increases the hardware, space, and consumption requirements. Further still, plating solutions are known to deplete additives during the plating process, and although the solutions can be periodically dosed to increase the concentrations of the depleted additives, the solutions nevertheless accumulate additive breakdown products. As a result thereof, the entire solution must be periodically discarded and replaced with a new solution void of breakdown products, which is costly in view of the large volume to be replaced.
Therefore, in view of the challenges and limitations of single chemistry plating processes, there is a need for a method for plating metals onto a semiconductor substrate, wherein the method is capable of utilizing multiple chemistries in a single plating system.
In one embodiment of the invention a plating method generally includes plating metal ions from a first plating solution onto a substrate having features and field areas under a first applied current, wherein the first plating solution includes an acid in an amount sufficient to provide a first solution pH of about 7 or less, copper ions, and at least one suppressor. Generally, pH in the range of about 0.5 to about 3 corresponds to solutions containing primarily simple Cu ions, whereas a pH in the range of about 3 to about 7 corresponds to solutions generally containing complexed Cu ions where the complexing action is provided by complexing agents, such as citric acid or tartaric acid, for example. The process includes plating metal ions from a second plating solution onto the substrate under a second applied current to substantially fill the features, wherein the second plating solution includes an acid in an amount sufficient to provide a second solution pH of from about 0.6 to about 3, copper ions, at least one suppressor, and at least one accelerator. The process may further include plating metal ions from a third plating solution onto the substrate under a third applied current to ensure a substantially uniform fill of the features, wherein the third plating solution includes an acid, copper ions, at least one suppressor, at least one accelerator and at least one leveling agent.
Embodiments of the invention may further provide an intermediate plating solution for plating a metal on a metal seed layer. The intermediate plating solution generally includes copper sulfate in a concentration of from about 5 g/L to about 50 g/L, sulfuric acid in a concentration sufficient to provide a pH of less than about 6 and suppressors having a molecular weight of 600 or greater.
So that the manner in which the above-recited features of the present invention are obtained may be understood in detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof, which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of the invention, and are therefore, not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
ECP system 100 further includes a factory interface (FI) 130. FI 130 generally includes at least one FI robot 132 positioned adjacent a side of the FI that is adjacent the processing base 113. This position of robot 132 allows the robot to access substrate cassettes 134 to retrieve a substrate 126 therefrom and then deliver the substrate 126 to one of processing cells 114, 116 to initiate a processing sequence. Similarly, robot 132 may be used to retrieve substrates from one of the processing cells 114, 116 after a substrate processing sequence is complete. In this situation robot 132 may deliver the substrate 126 back to one of the cassettes 134 for removal from the system 100. Additionally, robot 132 is also configured to access an anneal chamber 135 positioned in communication with FI 130. The anneal chamber 135 generally includes a two position annealing chamber, wherein a cooling plate or position 136 and a heating plate or position 137 are positioned adjacently with a substrate transfer robot 140 positioned proximate thereto, e.g., between the two stations. The robot 140 is generally configured to move substrates between the respective heating 137 and cooling plates 136.
In another embodiment of the invention, a first plating solution and a separate and different second plating solution can be provided sequentially to a single plating cell. Typically, providing two separate chemistries to a single plating cell requires the plating cell to be drained and/or purged between the respective chemistries, however, in many cases a mixed ratio of less than about 10 percent first plating solution to the second plating solution is not detrimental to film properties.
The plating solution delivery system 111 typically includes a plurality of additive sources 302 and at least one electrolyte source 304 that are fluidly coupled to each of the processing cells of system 100 via a manifold 332. Typically, the additive sources 302 include an accelerator source 306, a leveler source 308, and a suppressor source 310. The accelerator source 306 is adapted to provide an accelerator material that typically adsorbs on the surface of the substrate and locally accelerates the electrical current at a given voltage where they adsorb. Examples of accelerators include sulfide-based molecules. The leveler source 308 is adapted to provide a leveler material that operates to facilitate planar plating. Examples of levelers are nitrogen containing long chain polymers. The suppressor source 310 is adapted to provide suppressor materials that tend to reduce electrical current at the sites where they adsorb (typically the upper edges/corners of high aspect ratio features). Therefore, suppressors slow the plating process at those locations, thereby reducing premature closure of the feature before the feature is completely filled and minimizing detrimental void formation. Examples of suppressors include polymers of polyethylene glycol, mixtures of ethylene oxides and propylene oxides, or copolymers of ethylene oxides and propylene oxides.
To minimize the amount of additives consumed/wasted in plating processes, and more particularly, to prevent situations where an additive source runs out and the system is not being supplied with a particular additive, each of the additive sources 302 generally includes a bulk or larger storage container coupled to a smaller shot-type container 316. The shot container 316 is generally filled from the bulk storage container 314, and therefore, the bulk container may be removed for replacement without affecting the operation of the fluid delivery system, as the associated shot container may supply the particular additive to the system while the bulk container is being replaced.
In the embodiment depicted in
In another embodiment of the invention the fluid delivery system may be configured to provide a second completely different plating solution and associated additives. For example, in this embodiment a different base electrolyte solution (similar to the solution contained in container 304) may be implemented to provide the processing system 100 with the ability, for example, to use plating solutions from two separate manufacturers. Further, an additional set of additive containers may also be implemented to correspond with the second base plating solution. Therefore, this embodiment of the invention allows for a first chemistry (a chemistry provided by a first manufacturer) to be provided to one or more plating cells of system 100, while a second chemistry (a chemistry provided by a second manufacturer) is provided to one or more plating cells of system 100. Each of the respective chemistries will generally have their own associated additives, however, cross dosing of the chemistries from a single additive source or sources is not beyond the scope of the invention.
In order to implement the fluid delivery system capable of providing two separate chemistries from separate base electrolytes, a duplicate of the fluid delivery system illustrated in
The manifold 332 is typically configured to interface with a bank of valves 334. Each valve of the valve bank 334 may be selectively opened or closed to direct fluid from the manifold 332 to the first process cell 102 and/or the second process cell 104. The manifold 332 and valve bank 334 may optionally be configured to support selective fluid delivery to an additional number of process cells. In the embodiment depicted in
In some embodiments, it may be desirable to purge the dosing pump 312, output line 340 and/or manifold 332. To facilitate such purging, the plating solution delivery system 111 is configured to supply at least one of a cleaning and/or purging fluid. In the embodiment depicted in
A second gas delivery line 352 is teed between the first gas delivery line 350 and the dosing pump 312. A purge fluid includes at least one of the electrolyte, deionized water or non-reactive gas from their respective sources 304, 342, 344 may be diverted from the first delivery line 350 through the second gas delivery line 352 to the dosing pump 312. The purge fluid is driven through the dosing pump 312 and out the output line 340 to the manifold 332. The valve bank 334 typically directs the purge fluid out a drain port 338 to the reclaimation system 232. The various other valves, regulators and other flow control devises for not been described and/or shown for the sake of brevity.
In one embodiment of the invention, a first chemistry may be provided to the manifold 332 that promotes feature filling of copper on a semiconductor substrate. The first chemistry may include between about 2 and about 20 g/l of copper, between about 20 and about 100 ppm of chlorine, and between about 0.1 and about 5 g/l of acid. As the first chemistry generally does not completely fill the feature and has an inherently slow deposition rate, the first chemistry may be optimized to enhance the defect ratio of the deposited layer. In another embodiment, the first chemistry generally includes between about 30 and about 65 g/l of copper, between about 15 and about 100 ppm of chlorine, between about 5 and about 50 g/l of acid, between about 4 and about 100 ppm (or milligram per liter) of accelerator, between about 50 and 1000 ppm of suppressor, and no leveler. The first chemistry is delivered from the manifold 332 to a first plating cell 102 to enable features disposed on the substrate to be substantially filled with metal. A second chemistry may be provided to another plating cell on system 100 via manifold 332, wherein the second chemistry is configured to promote planar bulk deposition of copper on a substrate. The second chemistry may include between about 20 and about 70 g/l of copper, between about 15 and about 100 ppm of chlorine and between about 10 and about 100 g/l of acid, for example. In a specific embodiment, the second chemistry may include between about 30 and about 60 g/l of copper, between about 20 and about 80 ppm of chlorine, between about 10 and about 50 g/l of acid, between about 4 and about 100 ppm of accelerator, between about 50 and about 1000 ppm of suppressor, and between about 6 and about 10 ml/L (or the equivalent ppm) of leveler. The second chemistry is delivered from the manifold 332 to the second process cell to enable an efficient bulk metal deposition process to be performed over the metal deposited during the feature fill deposition step to fill the remaining portion of the feature. Since the second chemistry generally fills the upper portion of the features, the second chemistry may be optimized to enhance the planarization of the deposited material without substantially impacting substrate throughput. Thus, the two step different chemistry deposition process allows for both rapid deposition and good planarity of deposited films to be realized.
When utilized with a process cell requiring anolyte solutions, the plating solution delivery system 111 may generally include an anolyte fluid circuit 380 that is coupled to the inlet 209 of the plating cell 200. The anolyte fluid circuit 380 may include a plurality of additive sources 382 coupled by a dosing pump 384 to a manifold 386 that directs additives (typically not utilized) selectively metered from one or more of the sources 382 and combined with an anolyte in the manifold 386 to those process cells (such as the cell 200) requiring anolyte solution during the plating process. The anolyte may be provided by an anolyte source 388.
Embodiments of the invention generally provide a method for plating metal onto a substrate. Various embodiments of the method are described in detail below. The embodiments of the invention generally include a multiple chemistry or solution plating process. For example, the embodiments described herein generally include plating a metal from a first solution onto the substrate and plating a metal from a second solution, having a different chemistry than the first solution, onto the substrate. As used herein, the terms chemistry and solution (which are used interchangeably) are intended to generally represent a fluid solution and the accompanying additives used to conduct an electrochemical plating process.
The process is described herein in terms of copper, but it will be known to those skilled in the art that any metals and metal alloys used for semiconductor processing, such as tungsten, nickel, cobalt, silver, ruthenium, titanium, titanium nitride, and other similar metals can be used in embodiments of the invention. The process generally includes depositing a barrier layer, such as tantalum nitride, tungsten nitride, cobalt, and/or ruthenium over a patterned dielectric material, such as silicon dioxide, deposited on the surface of the substrate. The barrier layer generally prevents the migration of copper (or other overlying materials) into the dielectric material. Many techniques known to one skilled in the art, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), or electroless plating, for example, can be used to deposit the barrier layer. Generally, the barrier layer has a thickness of between about 100 Å and about 300 Å.
The first and second plating chemistries or solutions generally include copper sulfate and other copper salts, such as copper fluoborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, or copper cyanide. Additionally, the first and second solutions generally include an acid in an amount sufficient to adjust the pH of the solution to a desired level for the particular plating process. Acids typically used in electrochemical plating chemistries generally include sulfuric acid, phosphoric acid, and/or derivatives thereof. Additionally, the first and second solutions may include halide ions, such as chlorine and/or bromine, for example.
The first and second solutions can further include plating solution additives, generally organics, which aid in controlling the plating characteristics of the copper ions onto the substrate and into the features. For example, the additives can include suppressors, which adsorb on the surface of the substrate to slow down copper deposition in the adsorbed area. The suppressors may include any organic substance that will slow down metal deposition on the substrate or reduce corrosion of the deposited metal under otherwise identical conditions. The suppressors are generally organic oxides or glycol ethers having a molecular weight of greater than about 500. Preferably, the suppressors have a molecular weight of between about 1000 and about 10000. For example, the suppressor may include copolymers of ethylene oxide and propylene oxide, polyethylene glycol, polypropylene glycol, and glycol ethers. The suppressors are commercially available from many suppliers, such as chemicals supplied by BASF Chemicals of Mt. Olive, N.J. under the trade names Pluronic and Tetronic. The additives may further include accelerators, which generally compete with suppressors for adsorption sites on the substrate surface, accelerating the copper deposition in adsorbed areas. Accelerators generally include sulfides or disulfides, such as mercapto-propyl-sulphide (MPS) and bis(3-sulfopropyl) disulfide. Preferably, the accelerator includes sulfopropyl disulfides (SPS). The additives may further include leveling agents configured to minimize localized heavy deposits of metal, e.g., metal over the narrow features. Additionally, the leveling agent is configured to reduce copper growth at the edge of features, thereby providing a smoother metal finish. Levelers generally behave like suppressors, but tend to be more electrochemically active (i.e., levelers are generally more easily electrochemically transformed) than suppressors typically being consumed during electroplating. Levelers also tend to accelerate plating on depressed regions of the surface undergoing plating, thus, tending to level the plated surface. Commonly used levelers generally include nitrogen-containing compounds, such as derivatives of amines and imidazoles. Other levelers include 2,4-imidazolidine-diol, thiohydantoin, polyethers, polysulfides, and various dyes. The additives may further include surface wetting agents, anti-foaming agents or other oxygen-reduction agents.
In one embodiment of the invention, the first solution is generally configured to deposit a barrier coverage layer from the first solution onto a barrier layer. Direct plating on barrier layers, such as cobalt, for example, presents several challenges. However, plating on a barrier layer is desirable, as this process eliminates the requirement for depositing a seed layer on the substrate, and thus, reduces the cost per substrate. With regard to the challenges associated with plating on barrier layers, in direct plating on a barrier layer the electrolyte and applied current density combination must be carefully configured such that the substrate metal or barrier layer is well protected during the electrodeposition process. Additionally, the electrolyte and current density combination should be configured to promote adequate adhesion between the substrate metal and the deposited layer. Further, in direct plating on barrier layer applications a very thin 3rd metal layer maybe needed between the substrate and the deposition layer of interest in order to further facilitate adhesion. Once the layer is plated on the barrier layer, a second plating solution is generally configured to deposit a layer over the barrier coverage layer and to fill the features formed on the substrate or into a layer formed on the substrate. The second solution generally includes copper sulfate at a concentration of between about 20 g/L and about 50 g/L, and halide ions (such as chlorine ions) at a concentration of between about 10 ppm and about 100 ppm. The second solution further includes one or more suppressors. Preferably, the second solution includes suppressors in a concentration greater than the saturation suppression limit, e.g., the concentration where the metal deposition would not be further suppressed with additional suppressors. The suppressor concentration in the second solution generally depends upon the individual system requirements and the suppressor used, but is generally between about 10 ppm and about 20,000 ppm. Additionally, the second solution generally includes an acid at a concentration of between about 5 g/L and about 100 g/L, or more specifically, between about 5 and about 10 g/L, resulting in a second solution pH of between about 0.6 and about 3.
In another embodiment of the invention, a copper seed layer is deposited on the barrier layer using conventional methods, such as PVD, CVD, or ALD, to improve adhesion between a subsequently deposited metal layer and the substrate/barrier layer. The seed layer generally has a thickness of between about 50 Å and about 1500 Å, depending on the aspect ratio of the features. In many embodiments the seed layer may be between about 50 and about 500 Å thick. One advantage of the current invention is that the thin seed layer need not have uniform coverage over the barrier layer in order to support uniform plating thereover in subsequent plating processes. To enable the use of very thin seed layers, or seed layers having such non-uniformity, the substrate is plated to form a thin film layer thereon, with the features thereof are filled in a continuous, multiple chemistry deposition process.
When the seed layer is continuous, but very thin, the resistance of the seed layer is generally higher than the resistance of a thicker seed layer, e.g., a seed layer having a thickness of greater than about 500 Å. As a result, the resistance of a thin seed layer can be higher than the resistance of traditional plating solutions, thereby causing a flux differentiation in the plating process that generally results in an edge high layer, i.e., a layer that is thicker near the perimeter of a circular substrate. Accordingly, in one embodiment of the invention, the first plating solution includes a low Cu and low acid concentration, e.g., between about 2 and about 20 g/L Cu, and between about 0.1 and about 5 g/l acid, which results in a first solution resistance of between about 40 ohm cm and about 200 ohm cm (e.g., a resistance that is generally higher than the seed layer resistance). Accordingly, in one embodiment of the invention, the first plating solution includes a low chlorine concentration that is configured to increase the bath resistance in order to compensate for the edge high deposition that inherently results when thin seed layers are used. The bath electrical resistivity of acidic CuSO4 bath is generally determined by the acid concentration of the bath, followed by the CuSO4 concentration. Lowering the acidity from between about 30 and about 50 g/l to about 0.1 to about 1 g/l, and lowering the CuSO4 concentration from about 30 to about 70 g/l to about 2 to about 20 g/l will greatly increase the bath resistivity, and therefore, facilitate plating on a very thin seed layer. As an example, the resistivity for 50 g/l Cu (as CuSO4)+30 g/l H2SO4 is about 10 ohm cm, while the resistivity for 5 g/l Cu+0.2 g/l H2SO4 is increased to about 130 ohm cm, which is greater than a 10 times increase in resistivity of the bath. As a result of the increased resistance, the metal ions plate from the solution onto the very thin seed layer very slowly, resulting in improved control over the plating process and the ability to plate on a very thin, possibly discontinuous, seed layer.
When the seed layer includes non-uniformities, the first solution generally includes copper sulfate at a concentration of between about 2 g/L and about 50 g/L. Preferably, the first solution includes copper sulfate at a concentration of less than about 20 g/L. Additionally, the first solution may include sulfuric acid at a concentration of between about 0.1 g/L and about 1 g/L, resulting in a first solution pH of between about 1 and about 4. More preferably, the first solution pH is between about 2 and about 3. Additionally, the first solution also includes halide ions, such as chlorine, at a concentration of between about 20 ppm and about 100 ppm. Additionally, the first solution may include oxygen reducing agents to limit copper corrosion rate.
The first solution further includes one or more suppressors in a concentration greater than the saturation suppression limit, e.g., the concentration where the metal deposition would not be further suppressed with additional suppressors. The suppressor concentration in the first solution generally depends upon the individual system requirements and the suppressor used, but is generally between about 100 ppm and about 10,000 ppm. The seed layer is exposed to the first solution under an applied first current, generally having a current density applied to the surface of the substrate of less than about 5 mA/cm2, or the current density may be less than about 3 mA/cm2, however, embodiments of the invention are not limited to current densities lower than 5 mA/cm2. The substrate is then subjected to further copper deposition, whereby the copper deposition is essentially continuous, but the plating solution is modified, e.g., a second solution provides the metal ions to the substrate. As used herein, “continuous” can include a minimal plating stoppage, e.g., a pause in plating while either the plating solution is being replaced or while the substrate is being transferred to another plating cell. Generally, a current density of less than about 10 mA/cm2 is applied to the second solution to urge the metal ions out of the second solution and into the features. Preferably, the current density is less than about 5 mA/cm2. The second solution generally includes the same components as the first solution, plus an accelerator. Therefore, the second solution can be used in conjunction with the first solution without significant variations in the design of the plating cell and plating conditions. The accelerator generally competes with the suppressors for adsorption sites, accelerating the copper deposition in adsorbed areas. The accelerator generally includes sulfides or disulfides, such as mercapto-propyl sulphide (MPS) and bis(3-sulfopropyl) disulfide. Preferably the accelerator includes sulfopropyl disulfides (SPS). The first solution, which is acidic, is generally configured to plate a metal, generally copper, onto a thin and sometimes noncontiguous seed layer. Thus, the first solution is generally configured to plate with minimal defects at a relatively slow plating rate so that the layer generated by the first solution adequately covers the underlying seed layer and does not contain any discontinuities.
The second solution generally includes an acid at a concentration of between about 5 g/L and about 10 g/L, resulting in a pH of between about 0.6 and about 3. The second solution may also contain various concentrations of the above noted additives (levelers, suppressors, accelerators, and copper corrosion inhibitors, such as benzotriazole and other amine, amino derivatives, etc). The second solution may generally be configured to plate either a feature fill layer over a layer plated on a thin seed layer or a bulk fill layer over a layer plated over a normal thickness seed layer. In the instance where the second solution is plated over a layer that is plated on a thin seed layer, the second solution is generally configured to provide good feature fill, minimal defects, and relatively fast plating rates from the acidic bath.
In another embodiment of the invention, the plating process includes plating a metal alloy on the substrate. The alloy may be plated onto the surface of the substrate in order to reduce stress migration, improve electromigration characteristics, and/or increase adhesion between an overlying fill layer and the underlying layer, which may be a seed layer or other layer. For example, the first solution can include copper sulfate, as described above, while the second solution includes a copper alloy solution rather than copper sulfate. Alternatively, the first solution can include the copper alloy solution and the second solution can include copper sulfate, or both the first and second solution can include copper alloys. Generally, the alloy included in the solution is the same metal as either the seed layer or the barrier layer material upon which the first solution is contacting, which facilitates adhesion between the respective layers. Regardless of the order of the particular chemistries, the process is generally configured to plate an alloy and/or a metal from a first chemistry, and then plate an alloy or a metal from a second bath.
Additionally, the first solution may include an anti-foaming agent to reduce foam on the surface of the solution at the outset of plating, e.g., initial application of current. The foam that often results in plating solutions is generally the result of agitation of the plating solution by the plating processes, i.e., insertion, removal, an rotation of a substrate support or head assembly in the plating solution. Since the foam itself may contain contaminants or otherwise concentrate elements that are not favorable to plating processes, it is desirable to minimize or eliminate the foam that forms on top of the baths, as the contaminants and/or undesirable elements that form on the foam have been shown to increase plating defects. There are generally three types of surfactants that can be used as effective wetting agents in semiconductor processing applications. For example, anionic surfactants are generally sulfonic acids or thiols with long hydrocarbon chains of greater than 16 carbon atoms; cationic surfactants are in general amine or amino acids with long hydrocarbon chains; and non-ionic surfactants like alcohols and glycols with long enough hydrophobic hydrocarbon chains such as octanol and all the suppressors mentioned in the application. Additional exemplary antifoaming agents include hydrophobic oil, compounds with surfactants or surfactant mixtures that have limited solubility in aqueous mixtures, and ethanol solutions. The anti-foaming agent generally operates to reduce defects formed in the initial metal film. However, generally the foam that forms on the surface of electrochemical plating baths is most detrimental only to the initial plating process, i.e., the plating of the initial layer. As such, since antifoaming agents may have some adverse effect on other plating parameters, a first solution may include an antifoaming agent and a second solution may be configured to plate a layer over a layer formed in the first solution. This method allows for a first layer to be formed with minimal defects, as the foam is reduced, and then the substrate may be further plated in a second solution without the antifoaming solution.
Additionally, each of the plating processes described herein may further include as an intermediate step the plating process associated with the first solution and the plating process associated with the second solution, rinsing the substrate surface to remove any localized concentrations of additives, such as suppressors, on the surface of the substrate, as these concentrations may adversely affect the subsequent plating process in the next chemistry. Preferably, this rinsing is provided by passing a solution including pure deionized water, e.g., deionized water including less than about 1 ppm of chlorides and no organic compounds, over the substrate.
Another embodiment of the invention may be utilized to ensure that features are adequately filled in preceding plating processes. Inherently, the filling of each and every feature on a substrate may not occur simultaneously or in the same time frame. Therefore, embodiments of the invention may further include plating a substrate with a third solution to form an overburden layer and ensure that all of the features have been adequately filled. The overburden step generally includes contacting the deposited metal with a third solution under an applied current density of at least 10 mA/cm2, and generally the current density is greater than about 30 mA/cm2, which is permissible because, the lower or deeper regions of the features will already be filled and the higher current density at this stage will not cause closure of the openings of high aspect ratio features. The third solution generally includes the components of the second solution used in the plating process, as described above and, in addition, one or more leveling agents, which have been described above.
In operation, the individual plating solutions can be supplied to the plating cell by flushing or rinsing. For example, the first solution may be rinsed from the plating cell and the second plating solution may be flowed into the plating cell, preferably with deionized water, to provide continuous metal deposition to the substrate. In another embodiment, the above-described process generally is carried out in separate processing cells located on the same platform, e.g., each solution is used in a separate cell in communication with additional plating cells, although other plating platforms can be utilized. By utilizing separate processing cells, the individual solutions are tailored to meet the different needs required by each step, thereby improving the resultant metal layer. For example, the second solution generally provides bottom-up fill of the features, but results in mounding of the narrow features if used past the filling of the narrow features. Therefore, once the narrow features have been filled, a third solution is utilized to ensure a smooth finish and enabling subsequent processing steps. As a result of the individual solutions and solution requirements, solution supplies of less than about 15 mL are possible, thereby facilitating the complete disposal and replacement of the solutions when necessary.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention can be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.