Sputter trap having multimodal particle size distribution

A sputter trap formed on at least a portion of a sputtering chamber component has a plurality of particles and a particle size distribution plot with at least two different distributions. A method of forming a sputter trap having a particle size distribution plot with at least two different distributions is also provided.

TECHNICAL FIELD

The instant disclosure relates to sputter or particle traps for use on sputtering chamber components and methods of making the same. More particularly, the instant disclosure relates to a sputter trap having a multimodal particle distribution.

BACKGROUND

Physical vapor deposition (“PVD”) methods can used to form a film or layer of material on a substrate surface. PVD methods can be used in, for example, semiconductor fabrication processes to form metallized layers in the fabrication of integrated circuitry structures and devices. Sputter deposition is a PVD method in which a glow plasma discharge bombards a sputtering target which releases atoms that are subsequently deposited onto a substrate.

A diagrammatic view of a portion of an exemplary sputter deposition apparatus8is shown inFIG. 1. In one configuration, a sputtering target assembly10comprises a backing plate12having a target14bonded thereto. A substrate18such as a semiconductive material wafer is within the sputter deposition apparatus8and provided to be spaced from the target14. As shown, the target14is disposed above the substrate18and is positioned such that a sputtering surface16faces substrate18.

In operation, sputtered material22is displaced from the surface16of target14and forms a thin film20on substrate18. In some embodiments, suitable substrates18include wafers used in semiconductor fabrication. For example, the target14is bombarded with energy until atoms from the surface16are released into the surrounding atmosphere and subsequently deposited on substrate18. In some embodiments, plasma sputtering is used to deposit a thin metal film onto chips or wafers for use in electronics.

Problems can occur in the deposition process if particles are formed, as these particles may fall into or onto a deposited film and disrupt desired properties of the thin film. A sputter or particle trap can be included on a sputtering target to capture particles formed during a deposition process. Additionally, there remains a risk that captured particles may flake off of the sputtering target and disrupt the thin film. For example, loosely held particles may flake from a sputter trap during cyclic thermal stress. Accordingly, it is desired to develop a sputter or particle trap that can be applied to a sputtering component, such as a sputtering target, which captures and retains particles formed during a deposition process. Capture and retention of such particles reduces the probability that a particles falls onto the deposited film during the deposition process.

SUMMARY

In some embodiments, a sputtering target assembly includes a front surface, a back surface opposite the front surface, a sputtering surface on at least a portion of the front surface, a flange extending radially from the sputtering surface, and a sputter trap formed on at least a portion of a front surface of the flange. The sputtering trap includes a plurality of particles and has a particle size distribution plot with at least two different distributions.

In some embodiments, a method of forming a sputter trap on a sputtering target assembly includes adhering particles to at least a portion the sputtering target assembly by a cold spray technique or a thermal spray technique. The particle size distribution plot of the particles adhered has at least two different distributions.

In some embodiments, a sputter trap is formed on at least a portion of a sputtering chamber component. The sputter trap includes a plurality of particles having a particle size distribution plot with at least two different distributions.

DETAILED DESCRIPTION

The instant disclosure relates to a sputter or particle trap for use on a PVD apparatus component and methods of making the same. In some embodiments, the PVD apparatus component is a sputtering target for use in a PVD sputtering chamber. However, one skilled in the art will recognize that the sputter trap may be formed on any component of a physical vapor deposition apparatus in which particles are a concern.

FIG. 2is a top view of a sputtering target assembly30andFIG. 3is a cross-sectional view of sputtering target assembly30taken along line3-3ofFIG. 2. Sputtering target assembly30includes a sputtering target31and a backing plate34. In some embodiments, sputtering target31and backing plate34having circular or substantially circular cross-sectional shape in the top view. In use, backing plate34is connected to the sputter deposition apparatus, for example, by bolts or clamps.

Sputtering target31has a front or sputtering surface32, a back surface29opposite the sputtering surface32, and a sidewall35extending between the sputtering surface32and the back surface about the circumference of sputtering target31. In some embodiments, the sputtering surface32may be generally flat or planar. For example, the sputtering surface32may be parallel to a horizontal first plane. In other embodiments, the sputtering surface32may have one or more convex or concave portions or features. Additionally or alternatively, the back surface of the sputtering target31may be substantially planar. Alternatively, the back surface may have protrusions or indentations. For example, the back surface may receive or be received within a portion of backing plate34, a design which is known as an embedded backing plate.

Sputtering target31may be formed from any metal suitable for PVD deposition processes. For example, sputtering target31may include aluminum (Al), vanadium (V), niobium (Nb), copper (Cu), titanium (Ti), tantalum (Ta), tungsten (W), ruthenium (Ru), germanium (Ge), selenium (Se), zirconium (Zr), molybdenum (Mo), hafnium (Hf), and alloys thereof such as an Al alloy, a V alloy, a Nb alloy, a Cu alloy, a Ti alloy, a Ta alloy, a W alloy, a Ru alloy, a Ge alloy, a Se alloy, a Zr alloy, a Mo alloy, and a Hf alloy. Suitable alloys include but are not limited to copper-manganese (CuMn) alloys, aluminum-copper (AlCu) alloys, titanium-tungsten (TiW) alloys, tantalum-aluminum (TaAl) alloys, and ruthenium (Ru) alloys.

Backing plate34has front surface37, back surface39opposite front surface37, and sidewall41extending from front surface37to back surface39about the outer circumference of backing plate34. The back surface of sputtering target31is adjacent and bonded to front surface37of backing plate34. The radius of backing plate34is larger than that of sputtering target31such that at least a portion of the backing plate34, referred to as flange44, extends radially outward from the outer diameter or radial edge of the sputtering target31. In some embodiments, backing plate34may be formed from the same material as the sputtering target31. For example, backing plate34and sputtering target31may be part of an integral or monolithic sputtering target assembly30. In other embodiments, backing plate34and sputtering target31may be separate pieces which are bonded together. In such embodiments, the backing plate34may be formed of the same or different material than the sputtering target31.

Flange44, which extends radially outward from sputtering target31, may be substantially flat or planar. In some embodiments, the exposed portion of front surface37may be parallel or substantially parallel to the horizontal plane. In other embodiments, the exposed portion of front surface37may be in a plane at an angle to the first plane. Flange44can include one or more counter bore holes or/and through-holes45for connecting or bolting backing plate34to the sputter deposition source or apparatus.

Backing plate34may be formed from any suitable metal. For example, backing plate34may include aluminum (Al), vanadium (V), niobium (Nb), copper (Cu), titanium (Ti), tantalum (Ta), tungsten (W), ruthenium (Ru), germanium (Ge), selenium (Se), zirconium (Zr), molybdenum (Mo), hafnium (Hf), and alloys and combinations thereof. For example, alloys include an Al alloy, a V alloy, a Nb alloy, a Cu alloy, a Ti alloy, a Ta alloy, a W alloy, a Ru alloy, a Ge alloy, a Se alloy, a Zr alloy, a Mo alloy, and a Hf alloy. Suitable alloys include but are not limited to copper-manganese (CuMn) alloys, aluminum-copper (AlCu) alloys, titanium-tungsten (TiW) alloys, tantalum-aluminum (TaAl) alloys, and ruthenium (Ru) alloys. In some embodiments, backing plate34and sputtering target31may be formed of the same material. In other embodiments, backing plate34and sputtering target31may be formed of different materials.

Backing plate34also includes sputter trap46formed on the front surface37of flange44. In some embodiments, the sputter trap46can extend from where the sidewall of sputtering target31meets front surface37of backing plate34. For example, the sputter trap46can extend radially about the circumference of sputtering target31. In some embodiments, the back surface of target31can have an outer radius of r1and sputter trap46can have an inner radius r1and an outer radius r2. For example, sputter trap46can be formed immediately adjacent where target31joins to backing plate34. Additionally or alternatively, the sputter trap may be formed on the sidewall35of sputtering target31.

As discussed herein, particle formation during the sputtering process is a concern because such particles, if deposited on the substrate, will affect the uniformity of the film formed. Even if a particle is trapped or captured in a sputter trap, there is a potential that the particle may flake off during a sputtering deposition. Sputter trap46is configured to capture and prevent deposition particles formed during a sputtering deposition process onto the film formed. Additionally, sputter trap46is configured to retain the trapped particles. As described herein, sputter trap46can be formed by spraying and adhering particles onto backing plate34and/or along the circumference of sputtering target31. Suitable particles for forming sputter trap46include metals and metal alloys, ceramics, carbides, and metalloids. Suitable metal and metal alloy particles include titanium and titanium alloys.

For example, particles can be adhered to flange44to form sputter trap46by a thermal or cold spray process. Such process may form particles from a wire or powder source. For example, particles may be formed from a wire source by a twin wire arc spray process or may be formed from a powder using a plasma spray or cold spray process. The particles formed on the flange44have a particle size distribution. A particle distribution plot is formed by plotting particle size against the frequency (i.e., percent of particles). In a powder having a symmetric distribution, the particle distribution plot has a single distribution in the shape of a downward open parabola. The particle distribution plot has a single vertex or peak which is equal to the mean particle size. For a symmetric distribution, the mean, median and mode are equal. The width or breadth of the distribution can be described by the standard deviation or the coefficient of variation of the particles.

The particle size of spherical particles can be described by a diameter. Non-spherical particles are typically described by an equivalent spherical diameter. An equivalent spherical diameter is determined by measuring a physical characteristic, such as scattered light, and determining the size of sphere that would produce the measurement.

The particle size of the particles of sputter trap46can be determined using, for example, a scanning electron microscope (SEM), laser diffraction particle analyzer, or energy dispersive X-ray spectropcopy (EDS). Sputter trap46has a particle distribution plot having at least two distinct normal distributions, and each distribution has a mean. For example, the particle distribution plot for the particles of sputter trap46may resemble two partially overlapping parabolas. An illustrative plot is shown inFIG. 4, which has a first mean M1of a first distribution D1and a second mean M2of a second distribution D2. In some embodiments, the particle size distribution plot is from a representative sample area of the sputter trap46. For example, the particle size distribution plot may be created from four equally sized samples taken at four locations equally spaced about sputter trap46.

The mean surface roughness (Ra) of sputter trap46may be at least 5 μm (200 microinches), at least 10 μm (400 microinches), at least 25 μm (1000 microinches), or greater than or equal to 38 μm (1500 microinches). In some embodiments, the Ra of sputter trap46may be about 15 μm (600 microinches) to about 50 μm (2000 microinches). The surface roughness may be determined using a surface roughness tester. Suitable surface roughness testers include the Surftest SJ-410 series and the Surftest SJ-201P series, which are both available from Mitutoyo of Aurora, Ill.

Sputter trap46may be formed by adhering particles, such as powder particles, to the textured surface. In some embodiments, a texture may be formed on sputter trap46before adhesion of the particles. For example, the textured surface may be formed by a saw, knurling device, computer numerically controlled (CNC) device, manual lathe or other suitable machining tool to form a random or repeating pattern. In some embodiments, a saw can be used to cut into a surface and leave the pattern. Alternatively or additionally, a knurling device can be used to press into the surface of the material and leave the desired pattern.

In some embodiments, the textured surface may have a height difference as measured from a maximum height to a minimum height from about 14 μm (550 microinches) to about 30 μm (1150 microinches), from about 19 μm (750 microinches) to about 29 μm (1125 microinches), or from about 23 μm (900 microinches) to about 28 μm (1100 microinches). For example, the textured surface may have height differential from about 13 μm (500 microinches) to about 18 μm (700 microinches), from about 13.5 μm (525 microinches) to about 17 μm (675 microinches), or from about 14 μm (550 microinches) to about 16.5 μm (650 microinches). In other embodiments, the textured surface may have a height differential from about 24 μm (950 microinches) to about 29 μm (1150 microinches), from about 25 μm (975 microinches) to about 28.5 μm (1125 microinches), or from about 25.5 μm (1000 microinches) to about 28 μm (1100 microinches).

The textured surface may additionally or alternatively be formed by bead blasting. When bead blasting is used, abrasive particles may be sprayed onto the surface, such as along the front surface of backing plate34and/or along the circumference of sputtering target31. Suitable abrasive particles for texturing sputter trap46include metals powders, ceramics, carbides, hardened alloys, glass bead, aluminum oxides, zirconia aluminum oxide, silicon carbide, steel grit, steel shot, and ceramic beads. In general, the particles of the bead blasting technique impact the surface creating a texture and are removed from the surface. The particles do not bond or adhere to the surface. Similarly, a knurling process presses a pattern into the surface to create a texture, and machining cuts a pattern (i.e., removes material) into the surface to create a texture. Knurling and machining are not intended to bond or adhere particles to the surface of sputter trap46.

Sputter trap46may also be subjected to grit blasting prior to adhering particles to the surface of sputter trap46. For example, sputter trap46having a textured surface may then be subjected grit blasting followed by adhesion of particles to the surface of sputter trap46. Suitable media for grit blasting include, for example, metals powders, ceramics, carbides, hardened alloys, glass bead, aluminum oxides, zirconia, aluminum oxide, silicon carbide, steel grit, steel shot, and ceramic beads. In some embodiments, the sputter trap46may be grit blasted to an Ra of about 2.5 μm (100 microinches) to about 15 μm (600 microinches). In some embodiments, the grit blasting process may increase adhesion of the particles applied in a subsequent process.

Sputter trap46is formed by adhering or coating particles, such as powder particles or particles from a wire, onto the surface. As discussed herein, the sputter trap46may be textured and/or subjected to grit blasting prior to adhering or coating particles to the surface of sputter trap46. In some embodiments, sputter trap46may be subjected to a thermal spray technique, such as plasma spray, high velocity oxygen fuel (HVOF) coating. Additional suitable methods for adhering particles to sputter trap46include a flame spray coating technique or twin wire arc spray coating technique using wire. In some embodiments, sputter trap46may be formed on the target assembly or backing plate by a cold spray technique in which the coating material, such as powder particles, are accelerated to high velocities by a supersonic compressed gas at temperature below the melting point of the coating material. The resulting coating is sputter trap46which is formed by the accumulation of numerous sprayed particles.

The powder particles used to form sputter trap46have a particle distribution plot having at least two peaks. For example, the powder mixture fed to the cold spray apparatus may be formed by mixing two powder compositions having different mesh sizes. Mesh size is the mesh number (a U.S. measurement standard) and its relationship to the size of the openings in the mesh and thus the size of the particles that can pass through these openings. For example, a first powder having a mesh size of 20 μm (635 mesh), 25 μm (500 mesh), 37 μm (400 mesh) or 44 μm (325 mesh) may be combined with a second powder having a mesh size of 210 μm (70 mesh), 74 μm (200 mesh), 88 μm (170 mesh) or 105 μm (140 mesh) to form a powder mixture which applied to the sputtering target assembly by a cold spray technique, in which the mesh size of the first powder is larger (corresponding to a smaller opening size) than the mesh size of the second powder (corresponding to a larger opening size) and the mesh sizes of the first and second powders are different. The powders may be combined in equal amounts by volume. Alternatively, the powder mixture may contain a greater amount by volume of the larger mesh size powder or a greater amount by volume of the smaller mesh size powder. For example, the powder mixture may be formed by mixing 45% by volume of the first powder and 55% by volume of the second powder. The mesh size and volume of each powder may be selected to achieve a desired surface roughness of the sputter trap. Suitable mesh sizes and volume content of a first powder and second powder for the powder mixture are provided in Table 1.

The powders may be of the same material or different materials. For example, the first and second powders may be titanium powders. It is also contemplated that the powder mixture is formed by combining three or more powders corresponding to different mesh sizes in equal or non-equal amounts by volume. In some embodiments, the powders may be the same type of material as sputtering target31. For example, the powders and the sputtering target31may be nickel alloy materials.

Alternatively, the particles may be applied to the backing plate with a thermal spray coating techniques such as ultra high velocity (UHV), high velocity oxygen fuel (HVOF), plasma flame spray, twin wire arc, fusion bonded and wire metallizing. In a thermal spraying technique, the coating material is melted or heated and sprayed onto the surface. The coating material may be fed to the thermal spray device in a powder or wire form. The thermal spray device heats the coating material to a molten or semi-molten sate and accelerates the material towards the flange in the form of micrometer-size particles. The resulting coating is sputter trap46which is formed by the accumulation of numerous sprayed particles, such as powder particles or melt materials.

In one embodiment, a sputter trap is formed by plasma spraying a powder mixture containing 44 μm (325 mesh) and 210 μm (70 mesh) titanium powder onto a flange of a sputtering target assembly. In some embodiments, the mixture may include about 50 vol % to about 45 vol % of 44 μm (325 mesh) titanium powder and about 50 vol % to about 55 vol % of the 210 μm (70 mesh) titanium powder.

When the coating material of the thermal spray coating process is a powder, the coating material may be formed by mixing two or more powder compositions having different mesh sizes as described herein with respect to cold spray techniques. When the coating material of the thermal spray coating process is a wire form, the thermal spray coating process is designed or controlled such that the material sprayed from the thermal spray device has particle size distribution having at least two peaks.

A sputter trap formed with one powder will have a particle distribution plot having a single peak (i.e., a mono-modal particle size distribution). The sputter trap disclosed herein is formed with a mixture of two or more powders having different mesh sizes and has a particle distribution plot having two or more different or independent distributions as illustrated by the particle distribution plot having two or more peaks (i.e., multi-modal particle size distribution). For example, a sputter trap formed with a mixture of two powders having different mesh sizes has a particle distribution plot having two separate distributions and having two peaks, and a sputter trap formed with a mixture of three powders having three different mesh sizes has a particle distribution plot having three distributions and having three peaks.

A sputter trap having a multi-modal particle size distribution as described herein may mitigate the potential flaking of prevalent planarized re-deposited film, which is a more stressed film as compared to a non-planarized re-deposited film per geometric effect or roughness effect, Ra of the sputter trap, along the sputter trap during a PVD sputtering process. The multi-modal particle size distribution forms a cluster type re-deposited film along the sputter trap during a PVD process and help reduce the fallen particles from the cyclic thermal stress. The multi-modal particle size distribution can also mitigate the potential flaking off of loosely held re-deposited particles during cyclic thermal stress. That is, the multi-modal particle size distribution of the sputter trap may result in particle reduction during the sputtering process.

The difference in mesh size of a multi-modal powder may also form a surface having an increased surface roughness as compared to a surface formed of only one of the particle sizes. For example, a sputter trap formed of a mixture of 210 μm (70 mesh) and 44 μm (325 mesh) powders may have a surface roughness greater than a sputter trap formed of 210 μm (70 mesh) powder only or 44 μm (325 mesh) powder only.

FIG. 5is an image of a witness sample sputter trap. The witness sample was subjected to grit blasting. Following grit blasting, Side B of the witness sample was subjected to a plasma spray process and bi-modal titanium powder particles were adhered to the surface of the sputter trap. A titanium powder was formed by mixing titanium powders having a first mesh size and a second mesh size and the titanium powder was plasma sprayed onto the sputter trap. Large particle sizes and small particle sizes are seen inFIG. 5. In summary, Side A of the witness sample was subjected to grit blasting. Side B of the witness sample was subjected to the grit blasting following by plasma spray of a bimodal titanium power.

FIG. 6is a scanning electron microscope (SEM) micrograph of the sputter trap after bead blasting but before adhesion of particles.FIG. 7is a SEM micrograph of a multimodal sputter trap after a plasma spray process in which a bi-modal titanium powder was adhered to the surface of the sputter trap. The bi-modal titanium powder was formed by mixing titanium powders having a first mesh size and a second mesh size.FIG. 8is a plot depicting the elemental analysis of the high purity bi-modal titanium powder ofFIG. 7using an energy dispersive X-ray spectroscopy (EDS).