A hardmask is a material used in

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

processing as an etch mask instead of a polymer or other organic "soft"

resist A resist, used in many areas of manufacturing and art, is something that is added to parts of an object to create a pattern by protecting these parts from being affected by a subsequent stage in the process. Often the resist is then removed. For ...

material. Hardmasks are necessary when the material being etched is itself an

organic polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

. Anything used to etch this material will also etch the

photoresist A photoresist (also known simply as a resist) is a light-sensitive material used in several processes, such as photolithography and photoengraving, to form a patterned coating on a surface. This process is crucial in the electronic industry. T ...

being used to define its patterning since that is also an organic polymer. This arises, for instance, in the patterning of

low-κ dielectric In semiconductor manufacturing, a low-κ is a material with a small relative dielectric constant (κ, kappa) relative to silicon dioxide. Low-κ dielectric material implementation is one of several strategies used to allow continued scaling of micr ...

insulation layers used in

VLSI Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) c ...

fabrication. Polymers tend to be etched easily by

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

and other reactive gases used in

plasma etching Plasma etching is a form of plasma processing used to fabricate integrated circuits. It involves a high-speed stream of glow discharge (plasma) of an appropriate gas mixture being shot (in pulses) at a sample. The plasma source, known as etch speci ...

. Use of a hardmask involves an additional deposition process, and hence additional cost. First, the hardmask material is deposited and etched into the required pattern using a standard photoresist process. Following that the underlying material can be etched through the hardmask. Finally the hardmask is removed with a further etching process. Hardmask materials can be metal or dielectric. Silicon based masks such as

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...

are usually used for etching low-κ dielectrics. However, SiOCH ( carbon doped hydrogenated silicon oxide), a material used to insulate copper interconnects, requires an etchant that attacks silicon compounds. For this material, metal or

amorphous carbon Amorphous carbon is free, reactive carbon that has no crystalline structure. Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. As with other amorphous solids, some short-range order can be observed. Amor ...

hardmasks are used. The most common metal for hardmasks is

titanium nitride Titanium nitride (TiN; sometimes known as Tinite) is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface prope ...

, but

tantalum nitride Tantalum nitride (TaN) is a chemical compound, a nitride of tantalum. There are multiple phases of compounds, stoichimetrically from Ta2N to Ta3N5, including TaN. As a thin film TaN find use as a diffusion barrier and insulating layer between cop ...

has also been used.Shi ''et al.'', p. 87

References

Bibliography

* Shi, Hualing; Shamiryan, Denis; de Marneffe, Jean-François; Huang, Huai; Ho, Paul S.; Baklanov, Mikhail R., "Plasma processing of low-κ dielectrics", ch. 3 in, Baklanov, Mikhail; Ho, Paul S.; Zschech, Ehrenfried (eds), ''Advanced Interconnects for ULSI Technology'', John Wiley & Sons, 2012 . * Wong, T.; Ligatchev, V.; Rusli, R., "Structural properties and defect characterisation of plasma deposited carbon doped silicon oxide low-k dielectric films", pp. 133–141 in, Mathad, G.S. (ed); Baker, B.C.; Reidesma-Simpson, C.; Rathore, H.S.; Ritzdorf, T.L. (asst. eds), ''Copper Interconnects, New Contact Metallurgies, Structures, and Low-k Interlevel Dielectrics: Proceedings of the International Symposium'', The Electrochemical Society, 2003 Semiconductor device fabrication {{materials-sci-stub