FIELD OF THE INVENTION
- BACKGROUND OF THE INVENTION
The present invention relates to the electrolytic deposition of conductive materials other than copper, such as gold into recessed features.
Gold is used in the microelectronics industry as a conductive material to fill recessed features. Examples of recessed features include trenches and vias. Trenches filled with gold serve as conductive lines and vias filled with gold serve as interlayer interconnects. Decreasing the sizes of conductive features and thus the recessed features which are used to form such conductive features places rigorous demands on existing electroplating chemistry to completely fill the recessed features. The expense of gold places additional pressure on manufacturers to consistently achieve void-free fill of recessed features in order to achieve high yields.
- SUMMARY OF THE INVENTION
In certain situations, conventional baths are unable to form conductive features in recessed structures without voids that render the conductive features unsatisfactory for most applications. The presence of voids within the deposited conductive material is particularly evident when the recessed features are reentrant, i.e., the opening at the top of the recessed feature is smaller than the dimension of the recessed feature at the bottom. The performance of conventional baths can be improved by conducting electrolytic deposition at optimum conditions such as low deposition rate, high agitation, or pulse plating. While low deposition rate, high agitation or pulse plating may improve the ability of conventional baths to fill reentrant features, even using such optimum conditions, there continue to be applications where conventional baths yield features which are not completely filled. Furthermore, manufacturers prefer not to use low deposition rates as they contribute to the cost of production.
The present invention provides bath compositions, methods and tools for achieving superconformal filling of recessed features with a conductive material other than copper, for example gold and silver. The baths and methods employ a superconformal deposition promoter selected from sulfonate terminated alkanethiols, sulfonic acid terminated alkanethiols, carboxylate terminated alkanethiols, carboxylic acid terminated alkanethiols, and sulfonate terminated alkanedisulfide compounds. The present inventors have observed that complete fill of recessed features and the demanding reentrant features can be achieved without other organic additives such as polyethylene glycol. In accordance with the present invention, complete fill is achieved at process conditions that device manufacturers find attractive.
Electrolytic plating baths of the present invention include ions of the conductive material to be deposited, a complexing agent, and a superconformal deposition promoter described above. In more specific embodiments, the baths are free of polyethylene glycol.
Processes carried out in accordance with the present invention for the superconformal deposition of a conductive material other than copper provide a substrate having recessed features containing a conductive feature, such as a seed layer, which are to be filled with the conductive material. The conductive feature within the recessed features is contacted with an electrolytic plating bath of the type described above. Thereafter, electroplating power is applied and the conductive material is deposited onto the conductive features to fill the recessed feature and provide inlaid features. In more specific embodiments, the recessed features are reentrant features.
Tools formed in accordance with the present invention for the superconformal electrolytic deposition of a conductive material other than copper include a reactor for receiving the substrate and contacting conductive features within recessed features with an electrolytic deposition bath. The electrolytic deposition bath includes a superconformal deposition promoter described above.
BRIEF DESCRIPTION OF THE DRAWINGS
Through the use of the compositions, methods and tools of the present invention, conductive materials can be deposited superconformally into small, e.g., submicron, recessed features at rates that microelectronic device manufacturers will find desirable. Device manufacturers will benefit from the increased productivity and yields achieved by the compositions, methods, and tools of the present invention.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
FIGS. 1A-1J are cross-sectional views illustrating one embodiment of a process for the superconformal deposition of a conductive material other than copper into recessed features in accordance with the present invention;
FIG. 2 is a process flowchart of the steps for superconformal deposition of a conductive material other than copper into a recessed feature in accordance with the embodiment illustrated in FIGS. 1A-1J;
FIGS. 3A-3E are cross-sectional views illustrating another embodiment of a process for the superconformal deposition of a conductive material other than copper into a recessed feature in accordance with the present invention;
FIG. 4 is a process flowchart of the steps for the superconformal deposition of a conductive material into a recessed feature in accordance with the embodiment illustrated in FIGS. 3A-3E;
FIG. 5 is a schematic top plan view of a tool formed in accordance with the present invention for carrying out processes of the present invention;
FIG. 6 is a schematic top plan view of a different tool formed in accordance with the present invention for carrying out processes of the present invention; and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 7 is a cross-sectional scanning electron microscope image of conductive features formed in accordance with the present invention.
The present invention is now described more fully with reference to the accompanying drawings, in which specific embodiments of the invention are shown. The present invention, however, will be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, the embodiments illustrated in the drawings noted above and described below are provided so that the description will be thorough and complete and will convey the scope of the present invention to those skilled in the art. For example, while the present invention is described below with respect to particular arrangements of conductive materials and recessed features, the present invention is not limited to any one specific arrangement and the present invention may be embodied in many different arrangements of various conductive layers and recessed features such as trenches and vias. In the figures, the thicknesses of the various layers and regions have been exaggerated for clarity and are not relative in scope. It should be understood that when an element, such as a layer, surface, or substrate is referred to as being over another element, it can be directly on the other element or there may be intervening elements which may also be present whether illustrated or not.
As used throughout the specification, the term “plating” refers to electrolytic deposition, i.e., electroplating, unless the context clearly indicates otherwise. The term “feature” refers to a structure on a substrate.
As used herein, the term “microelectronic workpiece” or “workpiece” is not limited to semiconductor wafers, but rather, refers to workpieces having generally parallel planar first and second surfaces that are relatively thin, including semiconductor wafers, ceramic workpieces, and other workpieces upon which microelectronic circuits or components, including submicron features, data storage elements or layers, and/or micromechanical elements are formed.
As used herein, the term “patterned features” refers to features that have been formed out of dielectric materials, including photoresists, which when filled with a conductive material form inlaid features such as trenches or vias and the like or construction elements or features.
As used herein, the term “reentrant features” refers to patterned features wherein the dimensions, e.g., the width of the trench, at the top is less than the dimension at the bottom of the patterned feature, e.g., the width at the bottom of the trench.
As used herein, the term “conformal” refers to the deposition of a material into a patterned feature such as a via or trench wherein the deposition of the material proceeds at all surfaces of the trench or via at a substantially similar rate.
As used herein, the term “superconformal” refers to the deposition of a material into a patterned feature such as a trench or via wherein a bottom up filling of the feature is achieved as a result of the deposition occurring at a faster rate at the bottom of the feature as compared to other surfaces of the feature.
As used herein, the term “superconformal deposition promoter” refers to sulfur-containing organic compounds such as: sulfonate terminated alkanethiols, sulfonic acid terminated alkanethiols, carboxylate terminated alkanethiols, carboxylic acid terminated alkanethiols, and sulfonate terminated alkanedisulfide compounds.
As discussed above, the present invention relates to compositions, processes, and tools for the superconformal deposition of a conductive material other than copper. One example of an overall plating process to which the aspects of the present invention can be applied is a blanket plating process described with reference to FIGS. 1A-1J and FIG. 2. Referring to these figures, a substrate 20, comprising a dielectric material embedded with microelectronic structures or a semiconductor material such as a semiconductor wafer is provided. Substrate 20 may include electrical contacts for making electrical contact with the conductive features that are deposited as described below in more detail. Such electric contacts are not illustrated in FIG. 1A. A dielectric layer 22 is deposited over substrate 20. Dielectric material making up layer 22 is deposited by conventional techniques such as chemical vapor deposition and the like. Dielectric layer 22 can be formed using conventional formation techniques that are well known to one skilled in the art, and therefore further description of such techniques are not provided herein.
Referring to FIG. 1C, a photoresist layer 24 is deposited over dielectric layer 22. Photoresist layer 24 can be formed using conventional techniques that are well known to one skilled in the art, and therefore further description of such techniques is not provided herein. Deposited photoresist layer 24 is then photolithographically patterned to provide patterned photoresist 26. Patterning of photoresist layer 24 is carried out using conventional techniques known to one skilled in the art, and therefore further description of such techniques is not provided herein. The patterned photoresist 26 exposes portions of underlying dielectric layer 22 as illustrated in FIG. 1D.
Referring to FIG. 1E, the portions of dielectric layer 22 that are not covered by the patterned photoresist 26 are removed using conventional etching techniques. Referring to FIG. 1F, after the portions of dielectric 22 that are not covered by patterned photoresist 26 are etched away. The remaining patterned photoresist 26 is removed using conventional solvents.
Referring to FIG. 1G, a barrier layer 28 is deposited over the patterned dielectric elements 30 and the exposed portions of the underlying substrate 20. Barrier layer 28 inhibits diffusion of conductive materials deposited subsequently, such as seed layer 32, described below in more detail, into underlying dielectric 30 and substrate 20. Barrier layer 28 can be formed from known materials, such as titanium, tantalum, tungsten and their alloys. Barrier layer 28 can be formed using conventional techniques, such as sputtering or any other well known techniques, accordingly, further description of the formation of barrier layer 28 is not necessary herein.
Referring to FIG. 1H, a conductive seed layer 32 is deposited over barrier layer 28 by conventional techniques such as electrolytic or electroless deposition. Referring to FIG. 1I, after formation of seed layer 32 is complete, the structure is placed in contact with a composition for the superconformal filling of the patterned features 34. The bath composition which is described below in more detail includes a superconformal deposition promoter that promotes the superconformal filling of the patterned features 34 and produces deposited features that are substantially free of seam voids. After the conductive material 35 is deposited to fill patterned features 34, planarization is carried out to produce the inlaid features 36 as illustrated in FIG. 1J. Planarization can be achieved using conventional techniques such as chemimechanical planarization.
The bath compositions, methods, and tools of the present invention are equally useful in pattern or through-mask plating processes such as the one described below with reference to FIGS. 3A-3E and FIG. 4. In pattern plating embodiments, referring to FIG. 3A, a substrate 38 similar to substrate 20 described above is provided with a blanket barrier layer 40 similar to barrier layer 28 described above and a blanket seed layer 42 similar to the seed layer 32 described above. Over seed layer 42 is deposited a blanket photoresist layer 44 similar to photoresist 24 described above with respect to FIG. 1C. Photoresist 44 is patterned to provide the patterned features 46 illustrated in FIG. 3B. Patterning of photoresist 44 exposes portions 48 of seed layer 42. These exposed portions 48 are contacted with the compositions of the present invention. Electroplating power is applied and the voids 50 between patterned features 46 are superconformally filled with a conductive material in accordance with the present invention to provide inlaid features 52. After inlaid features 52 are formed, the patterned photoresist features 46 are removed to expose those portions of seed layer 42 that are not covered by the deposited conductive material. Referring to FIG. 3E, the portions of seed layer 42 and barrier layer 40, not covered by feature 52 can then be etched by conventional techniques to electrically isolate once inlaid features 52 to provide isolated conductive structures 54.
In accordance with the present invention, bath compositions for achieving superconformal deposition of a conductive material are sulfite or cyanide-based baths that include a source of ions of the conductive material to be deposited, other than copper, complexing agent, e.g., sulfite or cyanide, a superconformal deposition promoter, an optional grain refiner and an optional pH buffer.
The source of ions of conductive material will depend upon the particular conductive material to be deposited. In accordance with the present invention, the conductive material is a metal other than copper. Examples of conductive materials other than copper include gold and silver. The foregoing conductive metals can be provided in the bath from sources such as sulfite or cyanide salts, such as sodium gold (I) sulfite, potassium gold (I) cyanide, silver nitrate, silver sulfate, silver acetate, and silver tetrafluoroborate.
Complexing agents are employed in the compositions of the present invention in order to stabilize ions of the conductive materials in solution. Examples of suitable complexing agents include alkali metal sulfites or cyanides such as sodium sulfite, potassium sulfite, sodium cyanide, or potassium cyanide.
The bath may optionally contain a grain refiner such as thallium. An appropriate source of a grain refiner such as thallium is thallium sulfate.
Another optional component is a pH buffer. Suitable pH buffers include phosphoric acid or phosphates and pyrophosphates or pyrophosphoric acid.
The superconformal deposition promoters of the present invention have been briefly described above. They include sulfonate terminated alkanethiols, sulfonic acid terminated alkanethiols, carboxylate terminated alkanethiols, carboxylic acid terminated alkanethiols and sulfonate terminated alkanedisulfide compounds.
The sulfonate terminated alkanethiols and the sulfonic acid terminated alkanethiols can be represented by the general formula:
wherein R is an alkyl backbone which can be linear, branched and/or perfluorinated. The length of the alkyl chain can vary from two to ten carbon atoms. X is either hydrogen or an alkali metal ion such as sodium or potassium ion. Particular examples of sulfonate terminated alkanethiols or sulfonic acid terminated alkanethiols include mercaptopropanesulfonic acid, sodium 3-mercapto-1-propane-sulfonate, potassium 3-mercapto-1-propane-sulfonate, sodium mercaptoethanesulfonate, potassium mercaptoethanesulfonate, and sodium 10-mercaptodecane-1-sulfonate. The foregoing are examples of sulfonate terminated and sulfonic acid terminated alkane thiols. It should be understood that the use of a suitable sulfonic acid in combination with sodium hydroxide or potassium hydroxide is equivalent to the use of a sodium or potassium salt of the particular sulfonic acid.
Carboxylate terminated alkanethiols or carboxylic acid terminated alkanethiols can be represented by the general formula:
wherein R is an alkyl group containing 2 to 16 carbon atoms which can be linear, branched, and/or perfluorinated. X represents hydrogen or an alkali metal ion such as sodium or potassium ion. Specific examples of this type of superconformal deposition promoter includes mercaptoacetic acid, 3-mercapto-1-propionic acid, 11-mercapto-1-undecanoic acid, 16-mercapto-1-hexadecanoic acid, and their alkali metal salts thereof. As with the sulfonate terminated alkanethiols, the use of a carboxylic acid terminated alkanethiol and sodium hydroxide or potassium hydroxide is equivalent to the use of the salt of the corresponding carboxylate terminated alkanethiol.
Sulfonate terminated alkanedisulfide compounds are characterized by terminal sulfate groups and a disulfide linkage. Such compounds can generally be represented by the formula:
wherein X is an alkali metal ion such as sodium or potassium ion, R is an alkyl having 2 to 10 carbon atoms which may be linear, branched, and/or perfluorinated. A particular example of a sulfonate terminated alkane disulfide compound is bis-(sodium sulfopropyl)disulfide. The acid form of this sulfonate terminated alkane disulfide compound can also be used in accordance with the present invention by combining it with a base such as sodium hydroxide or potassium hydroxide.
The solubility of the respective superconformal deposition promoter in aqueous solution must be considered in practicing the present invention. The solubility of the superconformal deposition promoters in water decreases with the increase in carbon-chain length. In addition, the solubility of superconformal deposition promoters terminated with carboxylate or carboxylic acid is generally lower than the corresponding promoters terminated with sulfonate or sulfonic acid, especially at lower pHs, because the sulfonate terminated agents readily deprotonate at low pH as compared to the tendency of the carboxylate terminated agents to deprotonate. Accordingly, superconformal deposition promoters having a short chain length are preferred over those having longer chain lengths, and sulfonate terminated superconformal deposition promoters are preferred over those terminated with carboxylate or carboxylic acid.
In addition to their low solubility, the longer chain superconformal deposition promoters, particularly the linear ones, will have a stronger resistance to heterogeneous electron transfer taking place on the surface of the substrate during electrolytic deposition processes. In other words, superconformal deposition promoters having a longer chain length will function as a stronger suppressor compared to superconformal deposition promoters that have a shorter chain length when used as an additive for the deposition of a conductive material in accordance with the present invention.
The bath compositions can be formed as aqueous mixtures. One way of forming the compositions of the present invention is to modify a conventional gold plating bath to contain a superconformal deposition promoter of the present invention. Formation of a bath of the present invention is described below in the context of a bath useful for the superconformal deposition of gold. It should be understood that the foregoing description is equally applicable to the formation of baths useful for the superconformal deposition of other conductive materials.
The bath compositions of the present invention are formed by adding a superconformal deposition promoter such as sodium mercaptopropanesulfonate to an electrolytic gold plating bath. Baths for the electrolytic deposition of gold are available from numerous commercial sources such as Enthone-OMI, Inc., under the designation of Neutronex® 3091 and Neutronex® 309. Useful gold plating baths can be alkaline or neutral and can be cyanide or sulfite based. Such baths include 5 to 20 grams per liter gold, 5 to 40 grams per liter of a complexing agent such as sodium sulfite and 10-80 grams per liter potassium pyrophosphate or potassium phosphate as a buffer. The baths have a pH ranging from about 6 to 10. The superconformal deposition promoter such as sodium mercaptopropanesulfonate can be added to the bath so as to provide a concentration in the bath ranging from about 0.05-0.3 millimoles.
When the bath composition is a sulfite-based bath for plating gold, the bath must be maintained so as to keep the free gold ion concentration below the threshold concentration when out plating occurs. Outplating refers to the spontaneous decomposition of the bath. Maintaining a sufficiently high concentration of free sulfite ion minimizes the free gold ion concentration and minimizes out plating. With higher pHs, the sulfite ion concentration increases and thus, out plating is reduced. The pH of the sulfite-based gold plating bath can be controlled by a pH buffer such as potassium pyrophosphoric or pyrophosphoric acid.
Operating conditions such as the temperature of the bath, the degree of agitation, and the waveform employed can be varied in order to achieve the desired deposition rate and the desired void-free fill. The temperature of the bath can vary over a wide range. With increasing temperature, the likelihood of plate out increases. The temperature of the bath can range from 35° C.-55° C. Generally, the higher the temperature, the better the mass transfer; however, this must be balanced against the stability of the bath.
The bath may be agitated or the substrate may be rotated in order to impart agitation. Agitation can vary over a wide range.
Once the substrate is contacted with the bath, an electroplating power is applied. The current density can vary over a wide range. The waveform can include pulse plating or non-pulse plating. Desirably, the electroplating power provides plating rates on the order of 0.05-0.2 micrometers per minute. By using the bath compositions and methods of the present invention, superconformal void-free filling of patterned features is achieved.
The superconformal filling of patterned features in accordance with the present invention may be implemented in a wide range of tools. Integrated processing tools that incorporate one or more reactors capable of electrolytic deposition of conductive materials are particularly suitable for implementing the processes of the present invention and are available from numerous sources, including Semitool, Inc., of Kalispell, Mont. Such tools are sold by Semitool, Inc. under the trademarks Equinox® and Paragon®. Advantageously, the reactors employed in these tools rotate a workpiece during the electrolytic deposition process thereby enhancing the uniformity of the deposited material. To further enhance the quality of the resulting deposited features, the reactors of these tools may be fitted with an ultrasonic generator that provides ultrasonic energy to the electroplating solution during the electrolytic deposition process to enhance the desired characteristics of the deposited feature.
In addition to the electrolytic deposition reactors, such tools frequently include other ancillary processing chambers, such as, for example, pre-wetting chambers, rinsing chambers, etc., that are used to perform other processes associated with electrolytic deposition. Semiconductor wafers, as well as other microelectronic workpieces, are transferred between the various processing reactors, as well as between the processing reactors and input/output stations, by a robotic transfer mechanism. The robotic transfer mechanism, the electroplating reactors, and the plating recipes used, as well as other components of the tool, may all be under the control of one or more programmable processing units.
Referring to FIG. 5, a tool 100 formed in accordance with the present invention includes a plurality of workstations for carrying out pre-wetting, rinsing, electrolytic deposition of a conductive material and drying steps. The particular arrangement of the various workstations can vary; however, FIG. 5 illustrates an exemplary layout. In FIG. 5, workstations 102 and 104 are spin/rinse/dry chambers capable of applying a medium such as acid, base or any other kind of aqueous solution to the substrate to be processed. The spin/rinse/dry stations are also capable of applying water to the substrate. Pre-wetting of the substrate can be carried out in spin/rinse/dry chamber 102. From chamber 102, the workpiece is transferred by the robotic arm 106 between the various workstations. A workpiece after being pre-wetted in workstation 102 can be transferred to one of the other eight reactors 110, 112, 114, 116, 118, 120, 122, or 124 where electrolytic deposition of gold in accordance with the present invention is carried out. Subsequent to the electro-deposition of gold, the workpiece can be transferred to spin/rinse/dry chamber 104 where it is rinsed and dried and prepared for further processing.
Referring to FIG. 6, another tool 126 formed in accordance with the present invention includes a plurality of workstations for carrying out pre-wet, spin/rinse/dry, electrolytic deposition of a conductive material, and electrolytic etching of a conductive material. The particular arrangement of the various workstations can vary; however, FIG. 6 illustrates another exemplary layout. In FIG. 6, workstations 128, 130, 132, and 134 are spin/rinse dry chambers capable of applying an acid, base, or any other kind of aqueous solution to the substrate. In addition, the spin/rinse/dry chambers are capable of rinsing and drying the workpiece. Reactors 136 and 138 are reactors that are useful for electrolytically etching a conductive material from the workpiece. Workstations 140, 142, 144, and 146, are configured to electrolytically deposit a conductive material onto a workpiece in accordance with the present invention. In an exemplary processing sequence, a workpiece is pre-wetted at one of the four spin/rinse/dry chambers 128, 130, 132, or 134. The workpiece is then delivered to one of the reactors 140, 142, 144, or 146, where electrolytic deposition of the conductive material using the processes and compositions of the present invention is carried out. The workpiece is then delivered to a spin/rinse/dry chamber where it is rinsed and dried in preparation for other processes such as electrolytic etching of the conductive material in either of chambers 136 or 138. Following the electrolytic etching of the conductive material, the workpiece can be delivered to a spin/rinse/dry chamber for rinsing and drying.
Superconformal Electrolytic Deposition of Gold into Patterned Features
It should be understood that there are numerous configurations of various workstations that can be employed depending on the particular configuration of conductive and nonconductive layers to be formed on the substrate. The foregoing is provided as an example of tool configurations useful for carrying processes in accordance with the present invention.
In this example, a silicon wafer including patterned features having a feature depth of 3.8 μm and an aspect ratio of 4:1 was processed to deposit gold into the patterned features superconformally. The patterned features included a titanium-based barrier layer 500 Å thick and a gold seed layer 500 Å thick. The titanium-based barrier layer and gold seed layer were deposited by sputtering. The wafer was contacted with the electroplating bath in an Equinox® brand single wafer plating tool available from Semitool, Inc. of Kalispell, Mont. The plating tool included an inert platinum anode. The plating was carried out at 50° C. The chemical flow rate was 3.5 gpm and the wafer was rotated at 40 rpm. The electroplating power was pulsed with 2 ms on and 8 ms off. The peak current density was 8 mA/cm2 and an average current density was 1.6 mA/cm2. This resulted in a plating rate of about 0.1 μm per minute.
The wafers were 100 mm in diameter. The wafer included patterned features that were reentrant in that the width at the top of the feature is less than the width of the feature at the bottom.
The plating bath comprised Enthone Neutronex 3091 with about 0.15 millimoles or 26 ppm sodium mercaptopropanesulfonate. The plating bath included 50 ppm thallium.
A cross-sectional scanning electron microscope image is shown in FIG. 7.
This example illustrates how the compositions, processes, and tools of the present invention are able to completely fill reentrant features.
While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.