Patent Application
20240229282
Disclosed is a process for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of a substrate with a resistance member, the process comprising: providing an electrodeposition composition comprising: a metal electrolyte comprising a plurality of metal ions and a solvent; and a suppressor disposed in the solvent; and a hysteretic cyclic voltammogram; providing the substrate comprising: a field surface; and the recess disposed in the substrate, the recess comprising a distal position and a proximate position relative to the field surface of the substrate; exposing the recess to the electrodeposition composition; potentiostatically or potentiodynamically controlling an applied electric potential of the recess with a potential wave form; autonomously reducing, with the resistance member in presence of the electrodeposition composition with the hysteretic cyclic voltammogram, the deposition potential of the recess from that applied by the potential waveform; bifurcating the recess into an active metal deposition region and a passive region in response to the deposition potential and ohmic variations of the substrate; forming, in response to bifurcating the recess, a transition zone at an interface of the active metal deposition region and the passive region; progressively moving the transition zone closer to the field surface and away from the distal position through the metal deposition; and reducing the metal ions to form metal and depositing the metal in the active metal deposition region and not in the passive region; and forming a resistance enhanced superconformal filling in the recess of the substrate from the metal in the active metal deposition region, the resistance enhanced superconformal filling being: void-free, disposed in the recess in the active metal deposition region from the distal position to the transition zone, and absent in the passive region between the proximate position and the transition zone, such that forming the resistance enhanced superconformal filling occurs in consequence of autonomously reducing the deposition potential of the recess with the resistance member in a presence of the hysteretic cyclic voltammogram of the electrodeposition composition.
Disclosed is a system for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of a substrate with a resistance member, the system comprising: a cell; an electrodeposition composition disposed in the cell and comprising: a metal electrolyte comprising a plurality of metal ions and a solvent; and a suppressor disposed in the solvent; and a hysteretic cyclic voltammogram; the substrate disposed in the cell in fluid communication with the electrodeposition composition and comprising: a field surface; and the recess disposed in the substrate, the recess comprising a distal position and a proximate position relative to the field surface of the substrate, such that the recess is in contact with the electrodeposition composition, such that an applied electric potential of the recess is under potentiostatically or potentiodynamically control with a potential wave form; the resistance member in communication with the electrodeposition composition and the substrate, wherein the apparatus is arranged and configured such that the resistance member in presence of the electrodeposition composition with the hysteretic cyclic voltammogram: autonomously reduces the deposition potential of the recess from that applied by the potential waveform, such that the recess is bifurcated into an active metal deposition region and a passive region in response to the deposition potential and ohmic variations of the substrate; whereby, in response to bifurcating the recess, a transition zone is formed at an interface of the active metal deposition region and the passive region, such that the transition zone progressively moves closer to the field surface and away from the distal position through the metal deposition to reduce the metal ions and form metal to deposit the metal in the active metal deposition region and not in the passive region; thereby forming a resistance enhanced superconformal filling in the recess of the substrate from the metal in the active metal deposition region, wherein the resistance enhanced superconformal filling is void-free, disposed in the recess in the active metal deposition region from the distal position to the transition zone, and absent in the passive region between the proximate position and the transition zone, such that forming the resistance enhanced superconformal filling occurs in consequence of autonomously reducing the deposition potential of the recess with the resistance member in a presence of the hysteretic cyclic voltammogram of the electrodeposition composition.
The following description cannot be considered limiting in any way. Various objectives, features, and advantages of the disclosed subject matter can be more fully appreciated with reference to the following detailed description of the disclosed subject matter when considered in connection with the following drawings, in which like reference numerals identify like elements.
A detailed description of one or more embodiments is presented herein by way of exemplification and not limitation.
It has been discovered that addition of an appropriate electrical resistance along a current path from a potentiostat to a substrate and then to a reference electrode through an electrodeposition composition provides a process for forming a resistance enhanced superconformal filling in a recess of a substrate in which metal deposition fills a recess on the substrate from a distal position such that the superconformal filling is a void-free, seam-free metallic filling.
A resistance enhanced superconformal filling can fill multiple recesses including recesses of different sizes on the same substrate seam-free and void-free using a single potential or a potential waveform within a broad potential window. The recess or recesses can be a tall and narrow high aspect ratio features such as a through hole (e.g., a through hole on a printed circuit board or a pinhole in a tube) or a blind hole in the substrate (e.g., a through silicon via in a silicon computer chip or a metal tube in a steam boiler). The process includes a suppressor in an electrodeposition composition that yields an hysteretic S-shaped negative differential resistance (S-NDR) current response during a voltage cycle of an electrodeposition such that both an active deposition rate of the metal and a passive deposition rate of the metal occur over a range of potential at the substrate (substrate potential) that is related to a type and a bulk concentration of the suppressor in the electrodeposition composition.
Beneficially, during filling of a recess the concentration of suppressor decreases from the field surface toward the distal position. Further, at a deposition potential in the range of potentials exhibiting the hysteretic current response (hysteretic range) active deposition of metal begins only in the recess from the distal position of the recess to a transition zone where a concentration of the suppressor is less than a critical concentration (CC). The critical concentration CC of the suppressor increases toward the bulk concentration at more negative values of the deposition potential within the hysteretic range. Accordingly, for a selected deposition potential in the hysteretic range, the decrease of suppressor concentration in a recess away from a field surface of a substrate provides deposition of the metal that can progress from the distal position to the transition zone, and the transition zone can progress toward the field surface.
Unexpectedly and advantageously, use of an electrical resistance in series with the deposition current allows void-free and seam-free filling of different diameter as well as different depth recesses to occur sequentially, simultaneously, or a combination thereof under a fixed applied potential and over a broad potential window because the deposition potential is altered from the applied potential in a time-dependent and feature size dependent manner by a resistive drop due to a deposition current associated with metal deposition (deposition current) across the electrical resistance.
For some electrodeposition compositions, suppressors, or substrate potentials, active metal deposition continues until reaching a position where a local concentration of the suppressor equals CC. For this subset active deposition in the recess halts at this position, i.e., deposition self-passivates. A more negative deposition potential within the hysteretic potential range corresponds to a more proximal position to which the transition zone can progress within the recess that is closer to the field surface and farther from the distal position.
It is contemplated that electrodeposition for filling high aspect ratio features relies on a variety of additives that selectively suppress deposition towards the top of the feature while permitting growth at the bottom. For additive packages consisting of a suppressor, localization of deposition is dictated by selective breakdown of the suppressor adlayer. Breakdown is associated with positive feedback and S-NDR in the global i-V response with characteristic features and deposit pattern formation influenced by the resistance of the electrochemical cell and operation mode of the electrochemical cell (potentiostatic or galvanostatic).
An external resistor and potentiostatic control can produce a filling dynamic that blends features of galvanostatic and external resistor-free potentiostatic deposition. Complete filling of features at a single potential followed by spontaneous interface passivation can occur. The extent of which depends on the magnitude of external resistance added to the cell.
In an embodiment, a process for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of a substrate with a resistance member, the process includes: providing an electrodeposition composition including: a metal electrolyte comprising a plurality of metal ions and a solvent; and a suppressor disposed in the solvent; and a hysteretic cyclic voltammogram; providing the substrate including: a field surface; and the recess disposed in the substrate, the recess comprising a distal position and a proximate position relative to the field surface of the substrate; exposing the recess to the electrodeposition composition; potentiostatically or potentiodynamically controlling an applied electric potential of the recess with a potential wave form; autonomously reducing, with the resistance member in presence of the electrodeposition composition with the hysteretic cyclic voltammogram, the deposition potential of the recess from that applied by the potential waveform; bifurcating the recess into an active metal deposition region and a passive region in response to the deposition potential and ohmic variations of the substrate; forming, in response to bifurcating the recess, a transition zone at an interface of the active metal deposition region and the passive region; progressively moving the transition zone closer to the field surface and away from the distal position through the metal deposition; and reducing the metal ions to form metal and depositing the metal in the active metal deposition region and not in the passive region; and forming a resistance enhanced superconformal filling in the recess of the substrate from the metal in the active metal deposition region, the resistance enhanced superconformal filling being: void-free, disposed in the recess in the active metal deposition region from the distal position to the transition zone, and absent in the passive region between the proximate position and the transition zone, such that forming the resistance enhanced superconformal filling occurs in consequence of autonomously reducing the deposition potential of the recess with the resistance member in a presence of the hysteretic cyclic voltammogram of the electrodeposition composition.
In an embodiment, the resistance member consists essentially of a lumped resistor, a baffle, and a selected interelectrode separation distance between the substrate and a reference electrode in electrical communication with the electrodeposition composition. In some embodiments, the resistance member is the lumped resistor, and the lumped resistor includes a resistor in electrical communication with and electrically interposed between the substrate and a counter electrode in electrical communication with the electrodeposition composition. In an embodiment, the resistance member is the baffle, and the baffle is in fluid communication with and fluidically interposed between the substrate and the reference electrode. According to an embodiment, the resistance member is the selected interelectrode separation distance between the substrate and a reference electrode in electrical communication with the electrodeposition composition, and the process further comprises adjusting the interelectrode separation.
The electrical resistance provided by lumped resistor 400 is in series between potentiostat 100 and substrate 2 and is summed with electrical resistance between reference electrode 500 and substrate 2. When present, for the latter, this includes baffle 450 and electrical resistance of the electrodeposition composition 300 between substrate 2 and reference electrode 500. The current distribution that defines the electrolyte resistance can be influenced by the overall distribution of current flowing from substrate 2 to counter electrode 700.
The process can include terminating the depositing the metal before completely filling the recess to the field surface or terminating depositing the metal after completely filling the recess to the field surface.
In an embodiment, the hysteretic cyclic voltammogram comprises an S-shaped negative differential resistance.
In an embodiment, with reference to
According to an embodiment, with reference to panel B of
In an embodiment, as shown in panel C of
In an embodiment, with reference to
With reference to panel D of
With reference to panel D of
Metal can be deposited in various conventional ways that completely cover exposed surfaces of a material. Thin-film metallic microstructures have been produced by through-mask electroplating (also known as the LIGA). Through-mask deposition has been applied to a wide variety of metallic materials, including applications in both passive and active devices. LIGA combines template production (e.g., lithography) with electrodeposition whereby metal deposition proceeds on exposed surfaces of an underlying conductive seed layer. Additionally, damascene processes include metallizing a patterned dielectric with a thin seed layer across the entire surface followed by metal electrodeposition across the entire surface.
In this regard, with reference to
Panel C of
Panel E of
It should be appreciated that, as described herein, a combination of the resistance member and hysteretic behavior of the cyclic voltammogram of the electrodeposition composition provide conditions for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of the substrate to form the resistance enhanced superconformal filling, e.g., with the system including a cell to hold the electrodeposition composition in communication with various electrodes and the substrate having recessed features.
The deposition potential existing on the substrate can be offset from the applied potential provided by the potentiostat by the resistive potential losses associated with the electrical current that is, itself, coupled with the metal deposition flowing through the resistive components of an electrodeposition system. The system resistance includes terms from the electrodeposition composition between the reference and substrate, an external resistance placed in electrical series between the potentiostat and the substrate, a resistive permeable or semipermeable baffle or membrane placed in the electrodeposition composition between the substrate and reference electrode, or a combination. If the system resistance is large enough the measured hysteretic current response to substrate potential is stretched to more negative applied potentials in plots versus applied potentials and the applied potential range of the S-NDR of the suppression breakdown in the plots is reduced. For large enough resistance the S-NDR current response can be hidden entirely in plots versus applied potential. That said, the hysteretic potential range associated with suppressor breakdown and the interface reaction on the substrate still remain in either case.
Coupling of suppression breakdown in the electrodeposition composition (also referred to herein as additive-containing electrolytes) that exhibit S-NDR in plots versus deposition potential and surface topography in filling of recessed features including through silicon via (TSV) can provide controlled superconformal or bottom-up filling.
For filling of a recess in this case, including a recessed through silicon via (TSV) geometry, the decrease of suppressor concentration moving from the field surface to the distal surface of a recess introduces a position-dependent shift of the critical potential associated with the bulk suppressor concentration in the electrodeposition composition toward more positive values compared to that of the free-surface. This accounts for passivation breakdown being localized within the feature where the height of the passive-to-active transition zone is determined by the transport constrained suppressor flux. The deposit in the actively plating region of the TSV reflects the active state of the bifurcated system.
The applied potential in this case thus determines the location where the electrode (or a surface of a recess) bifurcates into passive areas and regions of active metal deposition as well as how close active deposition may approach the surface field before self-passivation at a particular applied potential. Absent sufficient electrical resistance, a potentiodynamic stepped potential wave form or ramped potential waveform is required in many systems to progressively move the passive-active transition zone during metal deposition to both avoid void formation that occurs at more negative applied potentials and also enable filling sufficiently close to the field surface than is possible at more positive applied potentials. Higher suppressor concentrations, characterized by larger voltammetric hysteresis, provide a wider potential range that facilitates the use of such potentiodynamic control for superfilling recessed surface feature. Higher concentrations also enable use of the higher deposition rates at more negative potentials, permitting faster filling.
Processes using such stepped potentials to achieve void-free filling of recessed features can yield seam-free and void-free superconformal filling. However, they require significant experimental exploration to fix the significant number of free parameter in each process that include initial potential, final potential, potential step size and step durations in addition to electrodeposition composition and transport related parameters for each geometry of substrate and recessed feature.
Use of an appropriate system resistance permits the use of constant, or simplified potentiodynamic, applied potential that avoids both the pitfalls of filling only near the distal region that occurs at more positive applied potentials as well as voided filling that occurs at more negative applied potentials. The impact of system resistance can be inferred from deposition as applied potentials approach the positive end of the hysteretic range.
The process for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of a substrate with a resistance member can be performed in various environments such as system 1000. In an embodiment, with reference to
In an embodiment, with reference to
Elements of system 1000 can be various sizes. It is contemplated that elements can be selected based on desired operating parameters. Such elements can be made of a material that is physically or chemically resilient in an environment in which system 1000 is operated. Exemplary materials include a metal, ceramic, thermoplastic, glass, semiconductor, and the like. Certain elements of system 1000 can be made of the same or different material and can be monolithic in a single physical body or can be separate members that are physically joined.
Substrate 2 can be electrically conductive, electrically semiconductive, or electrically insulating. It is contemplated that substrate 2 can have a gradient in electrical conductivity Exemplary electrically conductive substrates 2 include copper, gold, nickel, cobalt and the like. In an embodiment, substrate 2 is electrically conductive copper. Exemplary electrically semiconductive substrates 2 include silicon, germanium, gallium nitride, zinc oxide and the like. In an embodiment, substrate 2 is electrically semiconductive such as silicon. In certain configurations, e.g., a back contact geometry, the resistance of the semiconductor can be an external resistance. Exemplary electrically insulating substrates 2 include glass, quartz, and the like. In an embodiment, substrate 2 is electrically insulating such as glass. Substrate 2 can be any shape or size that does not interfere with formation of resistance enhanced superconformal filling 38 in recess. Moreover, substrate 2 can be an element of a larger structure such as a computer chip, interposer, circuit board, and the like. Substrate 2 can be a same or different material as the larger structure. Field surface 10 a substrate 2 can be planar, curved, irregular, corrugated, and the like, or a combination thereof.
Recess 4 (also referred to herein as recessed feature) is disposed on substrate 2 and receives electrodeposition composition 30 for formation of resistance enhanced superconformal filling 38 therein. Recess 4 can have a low aspect ratio or high aspect ratio. As used herein, “aspect ratio” refers to a ratio of length L to width W of recess 4. The aspect ratio can be from 0.5 to 200, specifically from 0.5 to 50, and more specifically from 0.5 to 10. It is contemplated that length L can be from 5 nanometers (nm) to 1000 micrometers (μm), specifically from 5 nm to 100 μm, and more specifically from 10 nm to 10 μm. Width W can be from 5 nanometers (nm) to 400 micrometers (μm), specifically from 5 nm to 100 μm, and more specifically from 10 nm to 10 μm. In an embodiment, recess 4 has a depth from the field surface to the distal position that is from 10 nm to 900 μm, and an aspect ratio from 1 to 70. It is contemplated that the recess can include a through hole, a blind hole, or a combination comprising at least one of the foregoing recesses.
A shape of recess 4 can be any shape and can include a dendritic arm that extends into substrate 2. Wall 6 and terminal wall that borders recess 4 independently can be curved, linear, irregular, or a combination thereof. Further, recess 4 can be a through hole or blind hole. Recess 4 includes a pinhole, aperture, capillary, fracture, seam, trench and the like.
It is contemplated that substrate 2 can include body member 16, electrically conductive layer 18 that is recessed with respect to field surface 10, and recess 4 bounded by wall 6 and terminal wall 8. Here, electrically conductive layer 18 provides an electrically conductive surface that can be subjected to a deposition potential for reducing metal ions in electrodeposition composition to form resistance enhanced superconformal filling 38 in recess 4. Exemplary materials for electrically conductive layer 18 include copper, gold, and the like. In an embodiment, electrically conductive layer 18 includes copper. Electrically conductive layer 18 can have a thickness selected to support electrodeposition of the metal and can be from 5 nanometers (nm) to 10 micrometers (μm), specifically from 5 nm to 10 μm, and more specifically from 5 nm to 1 μm.
To form resistance enhanced superconformal filling 38 in recess 4, metal ions in electrodeposition composition 30 are reduced at wall 6, terminal wall 8, or combination thereof. Electrodeposition composition 30 can be a fluid such as a gas or liquid. In an embodiment, electrodeposition composition 30 is the liquid and includes metal ions and a suppressor disposed in the solvent.
Electrodeposition composition 30 also can include additional additives such as an accelerator, leveler, source of halide ions, grain refiner, defoaming agent, alloying metal and the like. Exemplary levelers include an amine, a polyethyleneimine, a phenolphthalein, or alkylammonium cations, or a combination comprising at least one of the foregoing levelers.
The metal ions include ions of nickel (Ni2+), ions of cobalt (Co2+), gold (Au+ and Au3+), copper (Cu2+ or Cu+), iron (Fe2+ or Fe3+), platinum (Pt4 or Pt2+) and iridium (Ir3+ or Ir4+), rhodium Rh3+, palladium Pd2+, cobalt Co2+, zinc Zn2+, bismuth Bi3+, lead Pb2+, rhenium Re7+, silver Ag+, tin Sn2+, tungsten W6+, molybdenum Mo6+ or a combination thereof. The source of metal ions can be a metal salt such as a nickel salt, cobalt salt, gold salt, and the like. The metal salt that is soluble in electrodeposition composition 30 can be used.
In an embodiment, the metal ions include Fe2+, Fe3+, Pt2+, Pt4+, Ir3+, Ir4+, Rh3+, Pd2+, Co2+, Ni2+, Au3+, Zn2+, Bi3+, Pb2+, Re7+, Au+, Ag+, Sn2+, W6+, Mo6+, Cu2+, Cu+, or a combination comprising at least one of the foregoing metal ions, and the metal includes cobalt, gold, nickel, iron, silver, platinum, iridium, copper or a combination comprising at least one of the foregoing metals.
A copper salt can be used as a source of copper ions. Exemplary copper salts include copper sulfate, copper sulfonate, copper acetate, copper gluconate, copper fluoroborate, copper halides, copper nitrate, copper alkanesulfonates, copper arylsulfonates, copper complexes of citrate, tartrate ethylenediamine, ethylenediaminetetraacetic acid and the like. Suitable copper alkanesulfonates include copper methane sulfonate, copper ethanesulfonate, and copper propanesulfonate. Suitable copper arylsulfonates include copper benzenesulfonate, copper toluenesulfonate, and copper phenolsulfonate. The copper salt can be present in electrodeposition composition 30 in an amount sufficient to provide an amount of copper ion from 0.1 grams per liter (g/L) to 180 g/L, specifically from 1 g/L to 50 g/L, and more specifically from 1 g/L to 10 g/L.
A nickel salt can be used as a source of nickel ions. Exemplary nickel salts include nickel sulfate, nickel sulfonate, nickel acetate, nickel gluconate, nickel fluoroborate, nickel halides, nickel nitrate, nickel alkanesulfonates, nickel arylsulfonates, complexes of citrate, tartrate ethylenediamine (en), ethylenediaminetetraacetic acid (edta) and the like. Suitable nickel alkanesulfonates include nickel methane sulfonate, nickel ethanesulfonate, and nickel propanesulfonate. Suitable nickel arylsulfonates include nickel benzenesulfonate, nickel toluenesulfonate, and nickel phenolsulfonate. The nickel salt can be present in electrodeposition composition 30 in an amount sufficient to provide an amount of nickel ion from 0.1 grams per liter (g/L) to 180 g/L, specifically from 1 g/L to 50 g/L, and more specifically from 1 g/L to 10 g/L.
A cobalt salt can be used as a source of cobalt ions. Exemplary cobalt salts include cobalt sulfate, cobalt sulfonate, cobalt acetate, cobalt gluconate, cobalt fluoroborate, cobalt halides, cobalt nitrate, cobalt alkanesulfonates, cobalt arylsulfonates, complexes of citrate, tartrate ethylenediamine, ethylenediaminetetraacetic acid and the like. Suitable cobalt alkanesulfonates include cobalt methane sulfonate, cobalt ethanesulfonate, and cobalt propanesulfonate. Suitable cobalt arylsulfonates include cobalt benzenesulfonate, cobalt toluenesulfonate, and cobalt phenolsulfonate. The cobalt salt can be present in electrodeposition composition 30 in an amount sufficient to provide an amount of cobalt ion from 0.1 grams per liter (g/L) to 180 g/L, specifically from 1 g/L to 50 g/L, and more specifically from 1 g/L to 10 g/L.
A gold salt can be used as a source of gold ions. Exemplary gold salts include gold sulfate, gold sulfonate, gold acetate, gold gluconate, gold fluoroborate, gold halides, gold sulfite, gold nitrate, gold alkanesulfonates, gold arylsulfonates, and the like. Suitable gold alkanesulfonates include gold methane sulfonate, gold ethanesulfonate, and gold propanesulfonate. Suitable gold arylsulfonates include gold benzenesulfonate, gold toluenesulfonate, and gold phenolsulfonate. The gold salt can be present in electrodeposition composition 30 in an amount sufficient to provide an amount of gold ion from 0.1 grams per liter (g/L) to 180 g/L, specifically from 1 g/L to 50 g/L, and more specifically from 1 g/L to 10 g/L.
The electrodeposition composition can include anions for the metal ions. Exemplary anions include sulfate, chloride, sulfite, perchlorate, bromide, citrate, tartrate, ethylenediamine, ethylenediaminetetracetic acid, or a combination comprising at least one of the foregoing anions. It is contemplated that the electrodeposition composition can include chloride, bromide, or iodide.
The metal electrolyte can be alkaline or acidic. An acid that is compatible with the source of metal ions can be present in electrodeposition composition 30. Exemplary acids include sulfuric acid; acetic acid; fluoroboric acid; nitric acid; sulfamic acid; phosphoric acid; hydrogen halide acids such as hydrochloric acid; alkanesulfonic acids and arylsulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, toluenesulfonic acid, phenolsulfonic acid and benzenesulfonic acid; halogenated acids such as trifluoromethylsulfonic acid and haloacetic acids such as trifluoroacetic acid: and the like; or combination thereof. The metal electrolyte is present in an amount sufficient to provide electrical conductivity to electrodeposition composition 30. A pH of the acidic electrolyte can have a value of less than 7, and specifically less than 2. Exemplary alkaline electrodeposition compositions can use pyrophosphate, en, EDTA, or carboxylic acids in the metal electrolyte although other electrolytes can be present. It should be appreciated that the pH of the metal electrolyte can be adjusted. The acid or alkaline additive species can be present in electrodeposition composition 30 in an amount from 0 to 200 g/L, specifically from 5 to 200 g/L. and more specifically from 0 to 120 g/L.
Exemplary solvents for electrodeposition composition 30 include water, an alcohol, polar organic solvent, and the like, deep eutectic solvents based on choline chloride, room temperature ionic liquids or a combination thereof. The solvent can be present in a wide range of amounts.
As used herein, “suppressor” refers to an additive that suppresses a rate of electrodeposition of the metal as resistance enhanced superconformal filling 38. In electrodeposition composition 30, the suppressor decreases the rate of electrodeposition of the metal. Exemplary suppressors include a polyethylene oxide; a polyethylene glycol, alkylammonium cations, polyethers, poloxamers, polyoxamines, optionally in conjunction with halides, polyethyleneimine, nitrogen bearing polymers, PVP, polypyrrole, pyridine, and alkylammonium salts, benzotriazole, benzimidazole, mercapto-benzimidazole, and other N- and/or S-bearing aromatics, or a combination thereof. The polyethyleneimine can have a repeating unit formula (1).
The polyethyleneimine compound can include from 1 to _2, 4 or more, or 6 or more, of the repeating unit of formula 1. The polyethyleneimine can include nitrogen atoms that are present as a primary amine, secondary amine, or tertiary amine and can include a terminal hydroxyl group, e.g., as a polyhydroxylamine. The polyhydroxylamine can have a structure of formula (2): R″HN—(CH2—CH2—NR)a—R′, wherein R is a group including the repeating units of formula (1); R′ and R″ independently are each a hydrogen atom or hydroxyl group, and a is an integer of 4 or greater.
The polyethyleneimine can have a linear structure in which the repeating units of formula (1) are linearly linked or a molecule in which such repeating units are linked in a branched structure. Examples of polyethyleneimine compounds that exhibit linear or branched structures are provided as formulas (3) and (4).
wherein R′ and R″ are as described above, and a and b are integers of 4 or greater, specifically 6 or greater. In formula (4), linkage groups of the nitrogen atom are not shown, but the linkage groups can be selected from repeating units of formula (1), hydrogen atoms and hydroxyl groups. In formula (4), repeating units having branches and repeating units not having branches can be linked randomly as desired.
When the polyethyleneimine compounds have a branched structure, branching chains (represented by R in formula (2)) having any length and branching form are bonded to the nitrogen atom in any number of repeating units and at any position from the termini of the side chains in the polyethyleneimine to which multiple units of the aforementioned repeating unit (1) are linked. With regard to bonding format in the branched regions, the bondable carbon atoms in repeating units (1) (carbon atoms that are not bonded to nitrogen atoms in the above repeating units) are bonded to the nitrogen atoms of other repeating units (nitrogen atoms to which R is bonded in formula (2)). Branching chains in the polyethyleneimine (represented by R in formula (2)) also can be chains that have the repeating units of formula (1), or can be chains formed by the linkage of any number of repeating units, where the linkage mode can manifest a branching or linear structure.
In formula (2), R′ and R″ are each independently hydrogen atoms or hydroxyl groups such that the terminals of the polyethyleneimine will be amino groups or hydroxyamino groups. In addition, the aforementioned branched chains in the polyethyleneimine can be amino groups or hydroxyamino groups.
A molecular weight of the polyethyleneimine can be, e.g., 300-100,000, with 1000-20,000 being preferred. The polyethyleneimine can be present in electrodeposition composition 30 in an amount from 0.01 g/L to 100 g/L, specifically from 0.01 g/L to 100 g/L, and more specifically from 0.01 g/L to 100 g/L.
Similarly, polyethers or block co-polymers such PEO-PPG-PEO or PPO-PEO-PPO, poloxamers, or poloxamines can be used. Exemplary amount of each independently can be from 0.1 μmol/L to 500 μmol/L.
Accordingly, the resistance member in presence of the electrodeposition composition in contact with substrate 2 can make the resistance enhanced superconformal filling due to autonomously reducing the deposition potential of the recess. The potential wave form used in the process for filling the recessed features of the substrate can include a single fixed applied potential. It is contemplated that deposition can be controlled by an applied potential imposed in a two or three electrode configuration (e.g., as shown in
It should be appreciated that various resistance members can be used, including the lumped resistor in an electrical circuit electrically interposed between and in electrical communication with the reference electrode and the substrate and can be an input to the potentiostat that provides the applied potential. Reducing the deposition potential of the recess from that applied by the potential waveform due to ohmic resistance can occur with current flow through a permeable or semipermeable baffle disposed in the electrodeposition composition and interposed between the reference electrode and the substrate. Optionally, the interelectrode separation can be changed between the working electrode substrate and the reference electrode. A magnitude of resistance provided by the resistance member can be from 1 times to 1000 times greater than the system resistance from closely disposing the reference electrode to the substrate, such as a separation of about 1 mm to 10 mm, e.g., 2.5 mm. It is contemplated that an uncompensated ohmic drop for conductivity of the electrodeposition composition and a geometric configuration of the cell, with the working and counter electrode positioned at opposite end of circular tube of radius Rc, has ohmic losses due to current flow in the electrodeposition composition given by
For a given substrate, area is the cross sections of the cell (e.g., πRc2) so that changes in Ωs are accomplished by adjusting the position of the RE/CE, L, or through the solution conductivity, κ.
In an embodiment, substrate 2 includes recess 4 Recess 4 can be formed in substrate 2 by lithographic patterning, etching, laser drilling, cutting, scratching, mechanical deformation, thermal cycling and the like, or a combination thereof.
It is contemplated that substrate 2 can be exposed to electrodeposition composition 30, e.g., by immersing, coating, spraying, and the like substrate 2 with electrodeposition composition 30. Electrodeposition composition 30 can be prepared by dissolving salts in solvent sequentially or in combination or mixing in pre-dissolved salts. Exposing recess 4 to electrodeposition composition 30 can be accomplished by partial immersion or total immersion of a substrate within a container already containing electrodeposition composition or addition of electrodeposition composition to a container already containing the substrate or the like.
Potentiostatically or potentiodynamically controlling the deposition potential of the recess with a potential wave form can be performed by a potentiostat connected through a resistor to the substrate or with a resistive baffle or membrane placed in the electrodeposition composition between the substrate and reference potential or by controlling the resistivity of the electrodeposition composition and the distance between the reference electrode and the substrate or a combination thereof. A potential waveform can include a single potential, potential step waveform, potential ramp, or a combination thereof.
Formation of potential controlled superconformal filling 38 from transition zone 32 to distal position 14 in active metal deposition region 36 while formation of potential controlled superconformal filling 38 is absent in passive region 34 occurs due to electrodeposition composition 30 in combination with time-dependent potential drop across a resistance between the potentiostat supplying power and the substrate that reduces the deposition potential at wall 6 of recess 4 from the potential supplied by the potentiostat. In an embodiment, electrodeposition composition 30 provides an S-NDR cyclic voltammogram, e.g., as shown in panel A of
The process for forming resistance enhanced superconformal filling 38 has numerous beneficial uses, including simplified control and a wider potential range for void-free and defect-free metal deposition in recesses that can include different feature shapes, feature widths and feature depths on a single substrate. In an embodiment, resistance enhanced superconformal filling 38 can be used to copper fill through vias with different dimensions on a glass interposer. In another embodiment, resistance enhanced superconformal filling 38 can be used to copper fill through silicon vias with different dimensions.
Advantageously, the resistance member enables the beneficial behavior of S-NDR for the electrodeposition composition under a fixed applied potential to be attenuated for uniform and complete filling for an array of features with spontaneous self-termination upon completion of the filling process by formation of the resistance enhanced superconformal filling. Moreover, the process for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of a substrate with a resistance member overcomes limitations and disadvantages of conventional processes that typically involve galvanostatic control, optimization, and monitoring of the charge during deposition. The process for performing hysteretic current-voltage mediated void-free superconformal and bottom-up filling of recessed features of a substrate with a resistance member provides more complete void-free feature filling followed by self-termination upon making the resistance enhanced superconformal filling compared with conventional processes.
The articles and processes herein are illustrated further by the following Example, which is non-limiting.
Void-free Cu electrodeposition in high aspect ratio features relies on preferential growth proceeding from the most recessed surfaces where sustained breakdown of the co-adsorbed polyether-halide suppressor layer occurs. Localization is the result of positive feedback between inhibitor breakdown and metal deposition subject to transport limitations on the suppressor precursor(s). This gives rise to a negative differential resistance (S-NDR) that, convolved with ohmic resistance of the system that has not been compensated for by software or hardware (uncompensated), results in electrode bifurcation into active and passive zones. The interplay between the additive derived S-NDR behavior, uncompensated system resistance, and potentiostatic regulation is explored in comparison to galvanostatic feature filling. Uncompensated resistance arises from the working electrode contact and electrolyte between the working and reference electrode. For a CuSO4—H2SO4 electrolyte containing 80 μmol/L Cl− and 40 μmol/L polyether, simulations of potentiostatic deposition with minimal uncompensated resistance reveal a narrow window between fully passive and voided feature filling; bottom-up filling even terminates prematurely under the most favorable conditions. In contrast, optimized galvanostatic operation enables void-free feature filling with termination dictated by the operator. Increasing the uncompensated resistance along with application of accordingly more negative applied potentials produces filling dynamics that blends the positive attributes of galvanostatic and potentiostatic deposition to enable complete, void-free feature filling with spontaneous passivation near the feature opening. Importantly, these beneficial filling effects are also evident for via and trench arrays with variable widths or heights.
Electrochemical deposition is widely used to fabricate microscale structures ranging from nanometer sized on-chip interconnects to larger scale wiring in printed circuit boards and packaging for microelectromechanical devices. Central to these applications is the need to fill high-aspect ratio recessed surface features. Multicomponent additive packages are involved for void-free filling of sub-micrometer trenches and vias. In the case of Cu electrodeposition, three components are often used that include a polyether-based suppressor, sulfonate-terminated thiol or disulfide accelerator, and some N-bearing leveler molecules, all of which have distinctive effects on the rate of metal deposition. Superconformal feature filling results from competitive adsorption between these species that, in the case of sub-micrometer features, includes the effect of rapid area change on the coverage of the respective species. For larger scale features constraints on mass and charge transport become increasingly important to the filling process. Herein the filling of larger features, such as through silicon vias (TSV) whose depth approaches the thickness of the adjacent hydrodynamic mass transport boundary layer, are examined. For these conditions a more extreme form of preferential bottom-up feature filling is possible based on selective breakdown of passivating additives that otherwise serve to block access of the metal cations to the electrode surface.
In the case of Ni, Co, and Au, a single suppressing additive is used to induce localized deposition while suppression of Cu deposition involves co-adsorption of a polyether and halide. Polarization to sufficiently negative potentials disrupts the adlayer, permitting Cu2+ access to the electrode for electrodeposition. In addition to applied potential, suppressor breakdown depends on the concentrations of its precursor components and hydrodynamics. Activation involves suppressor desorption and/or incorporation of some components into the growing deposit. It is also possible that the desorption process itself may be further stimulated by metal deposition. In either case, the positive feedback associated with potential-driven activation results in a sharp increase in deposition current and thereby significant hysteresis in cyclic voltammetry and galvanodynamic measurements. Operating at applied potentials within the hysteretic region leads to bifurcation of the electrode surface into active and passive reaction zones that give rise to Turing patterns on planar electrodes and bottom-up filling of recessed electrode geometries such as through-holes and TSVs. The two phenomena are closely connected, resulting from differing time-scales between the ‘fast’ electronic response and ‘slow’ evolution of chemical gradients. The topography of the TSV substrate is coupled with local mass transport conditions that serve to guide the electrode bifurcation, where the planar field is passive due to a higher suppressor flux and active metal deposition occurs on the most recessed surfaces. A contribution to the phase separation process is the longer range global coupling associated with the electrical response that is much faster than the development of suppressor and metal cation gradients driven by diffusion, electromigration, and sometimes convection. Dynamic coupling between these two effects underlies patterning associated with S-NDR systems. The strength of global coupling is a function of both the magnitude and geometry of the uncompensated resistance in the system. In a related fashion, the interaction between critical bistable systems and different regulation modes, controlled potential versus current, have been examined with particular attention to the important role of uncompensated resistance.
Uncompensated resistance includes ohmic losses associated with current flow in the electrolyte as well as external losses associated with the working electrode substrate contacts that in combination cause the overpotential at the working electrode to deviate from the applied potential. These respective resistances are design parameters that include variation of the reference electrode position in 3-electrode systems, introduction of a porous, resistive baffle into the electrolyte between the reference and working electrode, and the insertion of an external resistor between the working electrode and the sensing point in the potentiostatic circuit.
In the case of a 2-electrode cell operating under constant applied potential, i.e. with the reference and counter electrode shunted, an external in-line resistor can be introduced. However, knowledge of the counter electrode reaction characteristics is required for analysis of the working electrode overpotential. With the development of a suitable counter electrode it is interesting to contemplate the use of a 2-electrode cell run under constant applied potential as a useful variant to conventional galvanostatic operation. If the shunted counter/reference electrode reaction is non-polarizable and the symmetry of the cell and workpiece are uniform, so that the lumped resistor approximations for the electrolyte can be used, then modeling of the 2- and 3-electrode configurations are analogous to one another. That said in moving beyond 1-D models, the location of the reference electrode, i.e., Haber-Luggin capillary, with respect to a multidimensional working electrode can be destabilizing to a uniform electrode state and the effect is accentuated as the reference point is brought closer to the working electrode.
In 2-D simulations this concern is mitigated by sampling the reference potential at a plane within an idealized parallel plate cell where the potential is expected to be uniform based on the primary current distribution and the periodic nature and scale of the workpiece patterns.
Post-measurement correction for the uncompensated ohmic losses in conventional voltammetry reveals an inversion, or bi-stable S-shaped negative differential resistance (i.e., a decrease in driving force associated with an increase in reaction rate) that underlies the behavior of the suppressor based critical system. In the absence of ohmic losses, potentiostatic control within the S-NDR region is not viable as the system is unstable and jumps to either the active or passive branch. Rather, the presence of a significant uncompensated resistance enables operation within the hidden S-NDR region by providing a single valued applied potential for stable global potentiostatic operation while the bifurcation, with it dynamic variations in overpotential and dissipative ohmic losses, evolve freely leading to pattern development. In contrast, galvanodynamic measurements enable the potential inversion associated with S-NDR critical systems to be revealed more directly by virtue of the single valued control points within the S-NDR region that enable a fixed deposition rate to be easily specified and maintained.
Non-linear effects arise from coupling resistive electrolyte losses with transport constrained suppressor adsorption and its subsequent disruption by metal deposition and occur in extreme bottom-up filling of TSVs. However, engineering the uncompensated resistance to optimize feature filling has largely remained unexplored.
Simulations of copper deposition in TSVs and trenches compare feature filling dynamics between galvanostatic and potentiostatic control modes with an adjustable uncompensated resistance. The computations are built upon a suppressor co-adsorption S-NDR model that has been previously shown to capture feature filling dynamics and the relevant critical behavior. The base case is potentiostatic deposition with a minimum uncompensated resistance, comparable to prior experimental systems, that results in a narrow window for bottom-up filling that is subject to self-termination, preventing complete filling of the TSVs and trenches examined. Systematic stepping of the applied potential to more negative values (i.e., potentiodynamic control) can be used to adjust the termination point to achieve the desired level of filling. Conventionally, optimized galvanostatic deposition enables stable filling of high-aspect ratio features for a limited range of applied currents with growth termination determined by coulometry. However, designing the system to have a larger uncompensated resistance, coupled with the associated increases in the applied potential, enables significant expansion of the operational window and void-free feature filling by a potentiostatic control mode. Morphological evolution during filling under these conditions is nominally akin to that seen for galvanostatic deposition and, with optimization, the height of self-termination can be adjusted to match the feature opening. Another attribute associated with optimized use of the uncompensated resistance is an improvement in the ability to fill both simple and complex trench arrays under a fixed applied potential. Interestingly, iterative filling of individual recessed features may occur within the array when applied potentials/currents are at the less reducing end of the hysteretic window. For galvanostatic control this has an interesting analogy to the bifurcation reactions on microelectrode arrays where the individual microelectrodes not only sequentially switch from the passive to active state as the applied current density is increased but can also exhibit oscillatory behavior.
Finite element method (FEM) computations are used to simulate copper electrodeposition in 2D axisymmetric annular and cylindrical through-silicon vias and 2D trench arrays. The dimensions of the annular TSV (Ri=4 μm, Ro=9.5 μm, and H=56 μm) match those of prior experimental systems. Simpler cylindrical TSV were also examined having radii of Rcyl=5 μm and heights, Hcyl, ranging from 50 μm to 200 μm corresponding to aspect ratios from 5 to 20. Trench array were simulated in a 4×1 configuration with dimensions of trench width Wt=10 μm, trench height Ht=50 μm, and pitch Pt=20 μm between trench edges. More complex trench arrays having a 3×1 configuration with varying trench width from 10 μm to 30 μm and trench height from 50 μm to 100 μm were also examined. For all workpiece geometries, the reference and counter electrode were combined in a common plane opposite the working electrode at a distance L, and the electric potential is fixed at zero. For the base case, L was taken to be 0.25 cm, thereby specifying the uncompensated resistance between the working and reference electrode. The hydrodynamic boundary layer thickness δ is set to 25 μm in all simulations and the concentration of each species (Cu2+, Cl−, and polymer) is set equal to that of the bulk solution (Ci0) at these boundaries. The solution conductivity κ for the 1.0 mol/L CuSO4—0.5 mol/L H2SO4 equals 15.26 S/m. Each simulation begins with a 2 min incubation period that emulates an experimental setup where patterned electrode fragments are pretreated with an ethanol wetting solution prior to insertion into the plating solution. Computationally, this is approximated with an applied potential of −0.40 V (or current equal to 1% of the set value) for 2 min before stepping to the set value. Initial concentrations are 0.01Cib in the electrolyte domain below the hydrodynamic boundary layer to emulate electrolyte exchange with the ethanol filled features.
Variation in the uncompensated resistance between the reference and working electrodes was examined using three different schemes: (a) alteration of the distance between the reference and working electrodes, (b) insertion of a baffle into the electrolyte phase with fine scale porosity that effectively increases the resistance between the working and reference electrodes, and (c) insertion of an external resistor between the sensing point on the working electrode and the actual metal/electrolyte interface. All three approaches have been used by experimentalists for various ends. The first provides a simple method to evaluate the effect of the electrochemical cell time constant (t˜RC) while a baffle has been used in commercial electroplating cells to counter the terminal effect that otherwise leads to non-uniform deposition on resistive seed layers. The last approach, namely the introduction of the external resistor in series with a 2-electrode cell, has been used to examine the effects of variation in the experimental control mode, from potentiostatic to galvanostatic, and its impact on pattern formation in bistable systems.
The impact of uncompensated resistance on via filling was examined using the three different configurations outlined above. Given the symmetry of the cell and workpiece, despite differences in the location of the uncompensated resistance within the cell, the net effect on feature filling is the same, provided that the baffle is located sufficiently far from the working electrode to not influence the development of chemical gradients. Increasing the uncompensated resistance relative to that for the default geometry is investigated. Considering the uncompensated ohmic drop in the context of the electrolyte conductivity and the geometric configuration of the cell, with the working and counter electrode positioned at opposite end of circular tube of radius Rc, allows the ohmic losses due to current flow in the electrolyte to be defined by
For a given workpiece, area is taken to define the cross sections of the cell (i.e., πRc2) so that changes in Ωs are accomplished by adjusting the position of the RE/CE, L, or through the solution conductivity, κ. A series of calculations were performed where Ωs is increased by a factor of 6×, 9×, 11×, 21×, 41×, 81×, 161×, or 401×. This can be realized by an increase in L from 0.25 cm to 1.5 cm, 2.25 cm, 2.75 cm, 5.25 cm, 10.25 cm, 20.25 cm, 40.25 cm, and 100.25 cm, respectively. Alternatively, the same effect can be obtained, perhaps more conveniently, by holding L at 0.25 cm and increasing the effect of K by insertion of a porous but insulating baffle whose net effect on ohmic losses is a composite of the respective materials properties. This is realized by making a slice of the electrolyte adjacent to the RE/CE plane having a thickness of 25 μm have a conductivity smaller, e.g. 500× to 20,000×, than that of the actual electrolyte conductivity, κ, effectively increasing the uncompensated resistance, e.g. by factor of 11× to 201×, greater than the default Ωs based on the homogenous κ solution resistance and L=0.25 cm. Going further, the same effects can be obtained, again perhaps more conveniently, by inputting an external resistor, that is some multiple of Ωs, between the WE and RE contacts (or CE/RE plane in the current construct). In fact, as long as the equivalent total cell resistance is the same, simulations produce identical results regardless of which method for adjusting resistance as outlined above is implemented. Nevertheless, of the three methods, adjusting the position of the RE/CE plane is the most computationally demanding as it requires additional meshing that leads to longer computational times. From an experimental standpoint, integrating uncompensated resistance as a variable control parameter into an existing 2- or 3-electrode system is most easily realized by the external resistor approach. As such, all simulations presented herein use an external resistor to adjust the overpotential to account for the potential drop associated with the deposition current flowing the external series resistor in order to model the impact of a modified global cell resistance.
The concentration Ci and flux Ni of each species in the electrolyte domain is described by the Nernst-Planck equation, capturing both diffusion and electromigration, such that the evolution of concentration is given by
given the species' charge zi, diffusion coefficient Di, Faraday's constant F, and mobility um,i calculated by the Einstein relationship
The simulated electrolyte assumes full dissociation of CuSO4 and NaCl, reasonable for the relevant concentrations Cu2+ and Cl−, ignoring hydronium, sulfate, bisulfate, and sodium species. The poloxamine suppressor (subscript P) is assumed to be neutral in charge (zp=0). Diffusion coefficients listed in
Due to the high concentration of CuSO4 and H2SO4 supporting electrolyte, potential in the electrolyte (ϕ) is well approximated by Laplace's equation
which neglects potential variation in solution arising from ionic gradients. The current density associated with the Cu2+ flux through the electrolyte is given by Ohm's law
where κ is the solution conductivity. A zero flux symmetry condition is imposed on the side of the cell (at r=Rc in axisymmetric simulations and x=0 and x=12 Wt in 2D simulations) for gradients of solution potential
and gradients of concentration
Accumulation of adsorbates on the electrode follows Langmuir adsorption kinetics with deactivation of suppression related to metal deposition involving a combination of desorption and/or incorporation into the growing deposit. Evolution of the fractional chloride coverage θCl, defined as the surface concentration divided by the saturation coverage, is described by
where kCl+ is the adsorption rate constant, CCl is the chloride concentration at the evolving metal/electrolyte interface, kCl− is the deactivation rate constant and u is the metal deposition rate. Evolution of the fractional poloxamine coverage θP, is described by the analogous
where the poloxamine is restricted to adsorption on top of the halide covered sites and thereby implicitly subject to the requirement that θP cannot exceed θCl through adsorption. The fractional chloride and poloxamine coverages are further limited to values between 0 and 1. Values for ki+ and ki− listed in
The metal deposition rate is assumed to be a function of the suppressor coverage θP (or equivalently, coverage of the polyether-chloride bi-layer), metal ion concentration CCu, and overpotential η at the interface, thus
The current densities on unsuppressed (jθ=0) and suppressed (jθ=1) surfaces for the two electron reduction of Cu2+ to its metallic form are translated into growth velocity, u, using Faraday's constant (F=96,485 C-mol−1), the ionic charge n, and the molar volume Ω of solid copper. This simple form captures suppression arising from the polyether coverage (as limited by chloride coverage). The current densities (jθ=0.1) are assumed to exhibit the conventional exponential dependence on overpotential q by
The applied potential Vapp is related to the working electrode through
where the potential ϕ within the electrolyte is evaluated at the electrolyte/deposit interface to capture the dissipative losses between the workpiece and the reference electrode associated with current flow through the electrolyte and external resistor layer. The overpotential driving electrodeposition is referenced to the reversible Nernst potential for the Cu2+/Cu reaction. The values of jθ=10 and αθ=1 for the fully suppressed surface are obtained by fitting the negative-going voltammetric scans up to the onset of suppression breakdown. Although the kinetics of metal deposition on polymer-free surfaces are known to be a function of halide coverage, for simplicity, the present work uses a single set of jθ=00 and αθ=0 values for deposition on the polymer-free surface.
The local current density at the electrode is equated to the Cu2+ flux from the electrolyte onto the electrode interface (outward surface normal {circumflex over (n)}) according to
Similarly, the normal fluxes of chloride and polyether from the electrolyte to the interface are equated to the rates of their adsorption yielding
with saturation coverages Γi estimated. As stated previously, the (θCl−θP) term captures the requirement that suppressor adsorption only occurs at chloride covered surface sites.
The full system of equations is solved numerically in 2D and 2D-axisymmetric geometries using a finite element method employed in the COMSOL Multiphysics version 5.5 software package with the default solver, implementing the following modules: tertiary current distribution, primary current distribution, separate coefficient form boundary partial differential equations for both chloride and suppressor, and deformed geometry. The 2D triangular mesh elements are more highly refined along the electrode interface, their dimensions initially equal to 20% of the feature radius or width on each side. The mesh scales up to a maximum of 2.5 μm within the boundary layer and 26 μm outside of the boundary layer. The mesh in the thin resistive layer is also refined, having a maximum size of 5.2 μm. Automatic remeshing is enabled, prompting re-mesh when the maximum mesh distortion parameter exceeded 1.56. A moving boundary smoothing parameter of 2, geometry shape order of 1, and Laplace mesh smoothing type are used in the deformed geometry module (see COMSOL documentation for detailed explanation on how these parameters impact moving boundary convergence). The system of equations was solved so that the overall charge imbalance (the fractional difference between the total integrated currents at the counter and working electrodes) was less than 0.02%. The numerical evaluation error, thus, is acceptably small for the present purposes. To give a sense of the computational expense, the smaller geometry simulations having 1800 domain and 400 boundary mesh elements take on the order of 5 minutes to compute. Larger simulations having 5000 domain and 800 boundary mesh elements takes on the order of 30 minutes to compute. All simulations used a Dell Precision 3630 desktop computer with an Intel Xeon E-2186G CPU @ 3.80 GHz and 64 GB RAM using a Windows 10 Enterprise 64-bit operating system.
Experimental copper deposition in through-silicon vias (TSV) in electrolytes having a single suppressing polyether additive for a range of chloride concentrations (2 μmol/L to 1000 μmol/L) and combinations of CuSO4 and H2SO4 concentrations were performed. In low chloride solutions (s 80 μmol/L), copper deposition initially occurs on the bottom of the via as well as the neighboring sidewalls up to a position marking a transition between active and passive plating regions. This transition point shifts upward in the via with lower chloride concentrations or more negative potentials. At fixed potential, deposition is eventually quenched at a position within the via determined by the balance between transport constrained adsorption of the suppressing additives and its disruption by the metal deposition reaction. Thus, for these low chloride electrolytes it is necessary to step or ramp the potential to more negative values in order to fully fill features. This approach requires tuning of the applied potential waveform to optimize filling. For stepped potentials, the discontinuous nature of the increase in available free energy might be expected to impact, or at least mark, the deposit microstructure. Galvanostatic deposition provides both operational simplicity and cost advantages in process control, congruent with its use in industrial electroplating practice. Deposition is sustained as long as the current is applied and with proper optimization void free filling is possible. If the applied current is too high void formation will occur while too low a value will result in uneven activation of deposition across the workpiece. Even with an appropriate value of applied current substantial under- or overfill will occur if the deposition time is not tuned appropriately for each substrate pattern. Alternatively, the spontaneous self-passivation associated with potential-controlled deposition offers an alternative path to feature filling that should be less sensitive to variations in pattern density on the work piece.
Simulations in annular TSV—
Current and potential transients in
In an embodiment
The current and overpotential transients associated with the filling simulations are shown in
Simulations of the impact of uncompensated resistance on the filling of the annular TSVs were expanded to explore the full range of applied potentials between passive and voided growth profiles and include an intermediate value for total uncompensated resistance of 21 Ωs.
Simulations in cylindrical TSV—The simulations of deposition in annular TSV in the preceding section offer prediction that can be validated against prior experimental work.20 This section explores the influence of uncompensated resistance on deposition in the more generic cylindrical TSV geometry depicted in
The interesting behaviors uncovered thus far motivated further exploration of the effect of uncompensated resistance on the filling of even higher aspect ratio features.
A sequence of simulations are presented for deeper cylindrical TSVs having aspect ratios of 10 and 20 (Rcyl=5 μm) in
Deposition in trench arrays—The influence of uncompensated resistance on Cu deposition in high aspect ratio features was further explored in trench arrays as depicted in the 2D geometric configuration of
In an embodiment with multiple features on a single substrate
Deposition at the lower applied current of −16 μA exhibits analogous behavior, although deviation of height among the trenches in the array begins at a lower height within the trench after ≈35 min. In this case, deposition dynamically passivates and re-activates within various trenches from 35 min to 95 min, at which point the profiles all merge again. Similar to the −30 μA condition, there is an a 10 μm difference in height between trenches 1 and 4 at t=67 min although in this simulation trench 1 is the last to reach the field (y=0). Deviation across the trench array occurs at even earlier times for a lower applied current of −8 μA, after only 3 minutes of deposition, and progresses in almost discrete steps, not unlike the sequential activation seen in the case of microelectrode arrays under controlled current where the total current is a globally conserved quantity. At 35 min the difference in height between trenches 1 and 4 is 34 μm. After 110 min the individual trenches have all reached roughly the same height, breaking the y=0 threshold at 124 min.
Inherent to the S-NDR system is competition between interface activation driven by disruption of the suppressor layer by metal deposition that is balanced against interface passivation driven by additive adsorption. In short, under galvanostatic control, higher applied currents for a given active area are associated with higher rates of deposition and increased suppressor disruption associated with halide incorporation at larger overpotentials. If the applied current is sufficiently high then transport limited passivation is insufficient to shut down deposition within the feature (suppressor flux being reduced deeper within a feature) and the deposition profiles across the array are uniform. However, the additive flux available to passivate active deposition in a feature increases as filling proceeds upward. At some point, variations in the geometry between the individual features, or its numerical simulation, occur such that a portion of the active interface can passivate and redistribute the current to other features. Subsequently the inverse can occur as well, where passive features reactivate and draw current from other sites. Such localized passivation and reactivation is the origin of the non-uniform profiles across the arrays in
As with the annular and cylindrical vias shown earlier, simulation of trench array filling under potentiostatic conditions in the presence of 1 Ws of uncompensated resistance has a narrow operating window between fully passive (−0.58 V) and voided deposition (−0.60 V). Deposition at −0.59 V (not shown) eventually passivates after 30 minutes at a height 13 μm below the field (y=0). An increase in the uncompensated resistance to of 11 Ωs allows for complete filling of the trench arrays similar to galvanostatic operation. The potentiostatic operating window is also much wider between full passivation (−0.64 V) and voided deposition (−1.02 V), examined in 20 mV increments.
Deposit profiles and interface contours for two potentiostatic conditions are shown in
The influence of the control mode on copper deposition behavior is further explored in trench arrays of varying widths as shown in
In an embodiment
Unlike galvanostatic deposition, or even potentiostatic deposition in a uniform array, simulations of potentiostatic deposition for the base case with 1 Ws results in either conformal deposition or voided filling in the varying width trench array in
Increasing the uncompensated cell resistance makes potentiostatic deposition behave more like galvanostatic deposition. With a 41 Ωs uncompensated resistance, the operating window between fully passive (−0.78 V) and voided fill (−2.38 V) is greatly widened. However, simulations within this range, in 100 mV increments, show intermediate potentials can produce voids similar to the galvanostatic conditions seen in
Copper deposition is further explored in an even more complex trench array of varying depths in
In another embodiment
Similar to deposition in the other trench arrays (
Bottom-up via and trench filling were shown for a variety of additive-derived S-NDR metal deposition systems. The simulations in the present work indicate that with appropriate optimization of the applied current, galvanostatic Cu deposition from a polyether—Cl− suppressed CuSO4—H2SO4 electrolyte can completely fill high-aspect ratio via and trench features for various dimensions. The same is true for potentiostatic conditions, however, filling under conditions where the uncompensated resistance is minimized often results in passivation before feature filling is complete. Different strategies have been explored to overcome this limitation that range from the use of potentiodynamic waveforms to increasing the uncompensated resistance of the electrochemical cell. The latter can be implemented in a number of ways, from judicious positioning of the reference electrode to insertion of a baffle that increases the effective resistivity of the electrolyte, to the addition of an external series resistor. The latter can be envisioned as a resistive contact on the working electrode in a 3-electrode system and, more generally, a series resistor located anywhere in a 2-electrode circuit. The current response to potentiostatic deposition in the S-NDR system with a significant uncompensated resistance begins to approach that for galvanostatic control. This not only helps establish conditions where complete feature filling is possible but also significantly broadens the processing window making the method more robust to variations in the workpiece geometry, from trench dimensions to patterning effects. Particularly interesting characteristics are captured for feature arrays of both uniform and variable dimensions where sequential filling of different sized features are predicted as well as oscillation between passivation and reactivation during filling under different conditions. Even more complex behavior can occur with discontinuities appearing in the processing window where periodic transitions between complete filling and void formation occur as the control parameter (potential or current) is increased linearly. All of the above reflect the strong path-dependent behavior expected for non-linear bifurcation reactions and further highlights the complex interactions in systems where a rapid electric response is globally coupled to slower, locally non-uniform, mass transport constrained, mixed control reactions such as evidenced in additive induced S-NDR systems.
The following are incorporated by reference herein in their entirety.
While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined.
Reference throughout this specification to “one embodiment,” “particular embodiment,” “certain embodiment,” “an embodiment,” or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of these phrases (e.g., “in one embodiment” or “in an embodiment”) throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). “Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.
As used herein, “a combination thereof” refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements.
All references are incorporated herein by reference.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and/or.” Further, the conjunction “or” is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances. It should further be noted that the terms “first,” “second,” “primary,” “secondary,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity).
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/187,509 (filed May 12, 2021), which is herein incorporated by reference in its entirety.
This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US22/28946 | 5/12/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63187509 | May 2021 | US |
