Manganese Steel Sputtering Target: Composition, Manufacturing, And Applications In Semiconductor And Optical Recording Industries

Chemical Composition And Alloy Design Principles For Manganese Steel Sputtering Targets

Manganese steel sputtering targets encompass a diverse range of compositions tailored to specific deposition requirements. Pure manganese targets demand total gas impurity content (O, C, N, H, F, S) ≤200 ppm to minimize particle generation and ensure high film quality 4,13. For manganese alloy targets, the composition typically comprises 10–98 at% Mn with the balance consisting of at least one element selected from Ni, Pd, Pt, Rh, Ir, Au, Ru, Os, Cr, and Re 5,11,12. Oxygen content must be controlled to ≤1000 ppm and sulfur to ≤200 ppm to suppress oxide particle formation and nodule generation during sputtering 2,5,8,11,12.

Copper-manganese alloy targets represent a distinct category, with Mn content ranging from 0.05–20 wt% 3 or 2–20 wt% 15,16 in a copper matrix. For semiconductor interconnect applications, carbon content is restricted to ≤2 wt ppm to limit particle generation (≤30 particles ≥0.20 μm diameter per wafer) 3. Advanced formulations incorporate trace additions of P (0.001–0.06 wt ppm), S (0.005–5 wt ppm), Ca, and Si (total 0.01–20 wt ppm) to enhance machinability and surface smoothness while maintaining low particle counts 6.

Complex oxide targets such as Mn-Zn-W-O and Mn-Nb-W-Cu-O systems are designed for optical recording media. The Mn-Zn-W-O target exhibits a metal molar ratio Mn/W ≥1.0 and contains crystalline phases of W, MnWO₄, and MnO, with W phase content >16 mol% relative to total W + MnWO₄ to suppress abnormal discharge during DC sputtering 10. The X-ray diffraction peak intensity ratio P_MnO/P_W (manganese oxide to tungsten) must be ≤0.027 to achieve excellent crack resistance 7,17. Mn-Nb-W-Cu-O targets incorporate a MnNb₂O₃.₆₇ crystal phase and achieve relative density ≥90% 1.

The selection of alloying elements and impurity thresholds directly influences target mechanical integrity, sputtering stability, and deposited film properties. For instance, the addition of 2–20 wt% Mn to copper increases target strength, enabling use in high-power sputtering for 300 mm and 450 mm wafer processes 15,16. Conversely, excessive oxygen or sulfur promotes brittle oxide phases (grain diameter ≥5 μm), increasing crack susceptibility and particle generation 5,11,12.

Microstructural Characteristics And Mechanical Property Requirements Of Manganese Steel Sputtering Targets

Microstructural control is paramount for manganese steel sputtering targets to withstand thermal and mechanical stresses during sputtering. Forged manganese alloy targets must exhibit a single-phase equiaxed grain structure with crystal grain diameter ≤500 μm 5,8,11,12. This refined microstructure, combined with oxygen ≤1000 ppm and sulfur ≤200 ppm, ensures high transverse rupture strength and minimizes crack initiation sites 2,5,11,12. The number of oxide particles with diameter ≥5 μm should be ≤1 per 100 μm × 100 μm area to prevent nodule formation and irregular film deposition 5,11,12.

Copper-manganese alloy targets benefit from substantially refined secondary phases, with mean diameter at least 1.5 times smaller than conventional thermo-mechanical processing achieves 16. This refinement enhances thermal stability and mechanical strength, critical for high-power sputtering applications. The forged texture imparted by controlled deformation improves isotropy and reduces preferential grain orientation, which can cause non-uniform erosion and sputtering rate variations 2,5,11,12.

For oxide targets, relative density ≥90% is essential to minimize porosity-induced arcing and ensure consistent sputtering behavior 1. Sintered manganese oxide targets (MnO) with ≤50 wt% metallic Mn powder and purity ≥99.9%, sintered at ≥1000°C for ≥3 hours via hot-press or hot isostatic pressing, achieve crack-free structures suitable for stable deposition 14.

Mechanical property benchmarks include:

• Transverse rupture strength: Forged Mn alloy targets must exceed strength thresholds to prevent cracking during handling and sputtering; specific values depend on alloy composition but are significantly higher than cast or powder metallurgy targets 11,12.
• Crack resistance: Oxide targets with P_MnO/P_W ≤0.027 demonstrate excellent crack resistance, enabling mass production without target failure 7,17.
• Thermal stability: Copper-manganese targets with refined microstructures maintain dimensional stability under high sputtering power, reducing deflection and warping risks in large-format targets (300–450 mm) 15,16.

The correlation between microstructure and performance underscores the necessity of advanced manufacturing techniques, particularly forging and controlled sintering, to achieve target specifications.

Manufacturing Methods And Process Optimization For Manganese Steel Sputtering Targets

Forging Processes For Manganese Alloy Targets

Forging is the preferred method for producing high-performance manganese alloy sputtering targets, overcoming the brittleness and low rupture strength inherent to manganese. The process begins with ingot preparation via induction melting, arc melting, or electron beam melting to achieve high purity 5,11,12. Forging is conducted at temperatures 0.75 T_m(K) ≤ T(K) ≤ 0.98 T_m(K), where T_m is the alloy melting point, with an optimal range of 0.80 T_m(K) ≤ T(K) ≤ 0.90 T_m(K) to balance ductility and grain refinement 5,11,12. The average actual strain rate is maintained at 1×10⁻² to 2×10⁻⁵ s⁻¹, and draft (reduction in thickness) ranges from 30% to 99% 5,11,12.

Forging is performed in vacuum or inert gas (e.g., argon) atmospheres to prevent oxidation and contamination 5,11,12. Upset forging or die forging techniques are employed to achieve the desired shape and microstructure 5,11. The resulting forged texture, characterized by elongated grains aligned with the deformation direction, enhances mechanical strength and reduces anisotropy 2,5,11,12.

Key process parameters and their effects:

• Temperature: Higher temperatures (approaching 0.98 T_m) increase ductility but may promote grain growth; lower temperatures (near 0.75 T_m) refine grains but risk cracking 5,11,12.
• Strain rate: Slower rates (2×10⁻⁵ s⁻¹) allow dynamic recrystallization, producing equiaxed grains ≤500 μm; faster rates may induce residual stress 5,11,12.
• Draft: Higher reductions (≥70%) are necessary to break up cast dendritic structures and achieve uniform grain size 5,11.

Post-forging, targets undergo machining to final dimensions, with surface roughness controlled to minimize particle generation during sputtering 6.

Sintering Techniques For Oxide And Composite Targets

Oxide-based manganese steel sputtering targets (e.g., Mn-Zn-W-O, Mn-Nb-W-Cu-O, MnO) are manufactured via powder metallurgy and sintering. The process involves:

1. Powder preparation: High-purity manganese oxide (MnO), tungsten oxide (WO₃), zinc oxide (ZnO), niobium oxide (Nb₂O₅), and copper oxide (CuO) powders are wet-mixed to ensure homogeneity 1,7,17.
2. Molding: The mixed powder is compacted into green bodies using uniaxial or isostatic pressing 1,14.
3. Sintering: Sintering is conducted at ≥700°C (for Mn-Zn-W-O) 7,17 or ≥1000°C for ≥3 hours (for MnO) 14 in air or controlled atmospheres. Hot-press or hot isostatic pressing (HIP) is employed to achieve relative density ≥90% and suppress porosity 1,14.
4. Phase control: Sintering conditions are optimized to form desired crystalline phases (e.g., MnNb₂O₃.₆₇ 1, WMnO₄ 7,17) while minimizing undesirable manganese oxide phases (P_MnO/P_W ≤0.027) 7,17.

For Mn-Zn-W-O targets, sintering at ≥700°C promotes the formation of WMnO₄ phase, which enhances crack resistance by reducing the volume fraction of brittle MnO 7,17. The metal molar ratio Mn/W ≥1.0 and W phase content >16 mol% are achieved by adjusting powder composition and sintering temperature 10.

Sintered targets are subsequently machined and bonded to backing plates (typically copper or aluminum alloys) using indium or elastomer bonding to ensure thermal and mechanical coupling during sputtering 1,7,17.

Advanced Processing For Copper-Manganese Alloy Targets

Copper-manganese alloy targets with 2–20 wt% Mn are produced via casting followed by thermo-mechanical processing or advanced techniques such as severe plastic deformation (SPD) to refine secondary phases 15,16. SPD methods (e.g., equal-channel angular pressing, high-pressure torsion) reduce the mean diameter of Mn-rich precipitates by at least 1.5 times compared to conventional rolling and annealing, enhancing thermal stability and strength 16.

Trace element additions (P, S, Ca, Si) are introduced during melting to improve machinability and surface finish 6. Post-processing includes vacuum annealing to homogenize the microstructure and reduce residual stress, followed by precision machining to achieve surface roughness <0.5 μm Ra 6.

Impurity Control And Purity Specifications For High-Performance Manganese Steel Sputtering Targets

Impurity control is critical for manganese steel sputtering targets to minimize particle generation, arcing, and film contamination. For pure manganese targets, total gas impurity content (O, C, N, H, F, S) must be ≤200 ppm 4,13. This is achieved through:

• High-purity feedstock: Starting materials with purity ≥99.9% or higher 4,13,14.
• Vacuum melting: Induction melting, arc melting, or electron beam melting in vacuum (≤10⁻³ Pa) to prevent gas pickup 4,5,11,12,13.
• Degassing: Prolonged holding at elevated temperatures under vacuum to allow diffusion and removal of dissolved gases 4,13.

For manganese alloy targets, oxygen ≤1000 ppm and sulfur ≤200 ppm are mandatory 2,5,8,11,12. Oxygen primarily originates from oxide inclusions (e.g., MnO, Mn₃O₄) formed during melting or forging; sulfur is introduced via raw materials or atmospheric contamination. Control measures include:

• Oxide reduction: Forging in inert atmospheres and rapid cooling to minimize oxide formation 5,11,12.
• Sulfur scavenging: Addition of reactive elements (e.g., Ca, rare earths) that preferentially form stable sulfides, which are then removed during machining 6.
• Particle size control: Ensuring oxide particles ≥5 μm diameter are ≤1 per 100 μm × 100 μm area through optimized melting and forging 5,11,12.

Copper-manganese alloy targets require carbon ≤2 wt ppm to limit particle generation 3. Carbon is controlled by:

• Low-carbon copper feedstock: Using oxygen-free high-conductivity (OFHC) copper with <10 ppm C 3.
• Vacuum induction melting: Preventing carbon pickup from graphite crucibles or atmospheric CO₂ 3.
• Trace element optimization: Balancing P, S, Ca, and Si additions (total 0.01–20 wt ppm) to enhance machinability without increasing particle counts 6.

For oxide targets, purity ≥99.9% is standard, with particular attention to transition metal impurities (Fe, Ni, Co) that can alter magnetic or optical properties of deposited films 1,14. Analytical techniques such as inductively coupled plasma mass spectrometry (ICP-MS), glow discharge mass spectrometry (GDMS), and inert gas fusion are employed to verify impurity levels 4,13.

Performance Metrics And Quality Assurance For Manganese Steel Sputtering Targets In Deposition Processes

Performance evaluation of manganese steel sputtering targets encompasses mechanical, sputtering, and film quality metrics:

Mechanical Performance

• Transverse rupture strength: Forged Mn alloy targets exhibit significantly higher strength than cast or powder metallurgy targets, enabling handling and installation without cracking 11,12.
• Crack resistance: Oxide targets with P_MnO/P_W ≤0.027 demonstrate excellent resistance to thermal shock and mechanical stress during sputtering 7,17.
• Dimensional stability: Copper-manganese targets with refined microstructures maintain flatness and minimize warping under high sputtering power (≥10 kW) 15,16.

Sputtering Performance

• Particle generation: High-purity targets (O ≤1000 ppm, S ≤200 ppm, C ≤2 wt ppm) produce ≤30 particles ≥0.20 μm diameter per 300 mm wafer, meeting semiconductor industry standards 3,5,11,12.
• Nodule suppression: Forged texture and controlled oxide particle size (≤1 particle ≥5 μm per 100 μm × 100 μm) prevent nodule formation, ensuring uniform erosion and film thickness 2,5,11,12.
• Arcing resistance: Oxide targets with relative density ≥90% and optimized phase composition (W phase >16 mol%) suppress abnormal discharge during DC sputtering 1,10.
• Sputtering rate uniformity: Equiaxed grain structure (≤500 μm) and isotropic texture minimize preferential sputtering, achieving thickness uniformity <±2% across 300 mm wafers 5,8,11,12.

Film Quality

• Composition control: Targets with well-defined alloy or oxide phases enable precise stoichiometry transfer to deposited films, critical for GMR (giant magnetoresistive