Kurt H. Junker

Effect of material properties on integration damage in organosilicate glass films

Most organosilicate glass1 (OSG), low dielectric constant (low-k) films contain Si–R groups, where R is an organic moiety such as –CH3. The organic component is susceptible to the chemically reactive plasmas used to deposit cap layers, etch patterns, and ash photoresist. This study compares a spin-on, mesoporous OSG film with a completely connected pore structure to both its nonmesoporous counterpart and to another low-density OSG film deposited by plasma-enhanced chemical vapor deposition. The results show that the film with connected pores was much more susceptible to integration damage than were the nonmesoporous OSG films. As integrated circuit device and interconnect dimensions continue to scale smaller, low dielectric constant (k) interlayer dielectric (ILD) materials will become necessary to mitigate RC (product of resistance and capacitance) propagation delay and reduce power consumption and crosstalk. Lowering the k-value of a material requires either altering the chemical bonding to reduce the bond polarizability or decreasing the number of bonds (density) in a material. To reduce the k-value below 2.2, most dielectric materials will require a density decrease by introducing free volume (micropores < 2 nm in diameter) or mesoporosity (2–50 nm diameter pores). Unfortunately, lowering the density also compromises the mechanical strength and other properties of the material. The material properties of mesoporous dielectric films, such as connected pores and low mechanical strength, create a host of integration problems including integration damage to the film. The Si–R groups make organosilicate glass (OSG) films hydrophobic and they lower the density by breaking up the tetrahedral Si–O bonding. However, the carbon component is susceptibleto degradation when exposed to the reactive plasmas used for capping, etching, and ashing processes, especially oxidizing plasmas that induce silanol formation. Such plasma-induced chemical modifications can cause film densification, dangling bonds and defects, and moisture uptake. Recently, International SEMATECH monitored several OSG films for change in k caused by integration damage (ID) while integrating the films into SEMATECH’s Cu/Damascene test chip using their standard processing flow (Table I). Mesoporous OSG films with connected pores exhibited a large increase in k due to ID during integration. In contrast, nonmesoporous OSG films showed much smaller changes in k. Thus, connected mesoporosity appears to facilitate film damage during processing by allowing reactive species to more easily penetrate the film. Various plasma pretreatments (PPT) have been reported to form densified and chemically modified interface layers on OSG films, and these skin layers can prevent film damage by photoresist ash processes. This study reports the effects of oxygen and nitrogenbased plasmas on one mesoporous and two nonmesoporous blanket films. To our knowledge, this is the first direct demonstration that a mesoporous film is more susceptible to ID than its nonmesoporous counterpart. OSG-1 is a proprietary spin-on mesoporous methylsilsesquioxane (MSQ)-based film where porosity is created by thermal decomposition of a porogen that is incorporated into the MSQ-based film. The mesoporosity of OSG-1 is about 58%. Positronium annihilation lifetime spectroscopy (PALS) determined that the average pore diameter is 2.5 nm and that the pores are 80–100% connected to the surface of the film. OSG-1 was deposited using a TEL Mark-8 spin-coater and oven-cured at 425 °C. OSG-2 is the nonmesoporous version of OSG-1 deposited with the same MSQ-based precursor but without the porogen. OSG-2 was spin-deposited and cured for less time at 450 °C by the supplier. The MSQ-based precursor for both OSG-1 and OSG-2 contains approximately 12% carbon. OSG-3 is a trimethylsilane-based, plasma-enhanced chemical vapor deposited (PECVD) Address all correspondence to this author. e-mail: r6758c@email.sps.mot.com

Integration damage in organosilicate glass films

This study compares integration damage (ID) to two non-mesoporous organosilicate glass (OSG) films and several mesoporous OSG films with completely connected pores. The results show that the mesoporous OSG films are more susceptible to integration damage than are the non-mesoporous films.

Integration Challenges of Inorganic Low-K (K≤2.5) Materials with Cu for Sub-0.25µm Multilevel Interconnects

The recent introduction of dual inlaid Cu and oxide based interconnects within sub-0.25μm CMOS technology has delivered higher performance and lower power devices. Further speed improvements and power reduction may be achieved by reducing the interconnect parasitic capacitance through integration of low-k interlevel dielectric (ILD) materials with Cu. This paper demonstrates successful multi-level dual inlaid Cu/low-k interconnects with ILD permittivities ranging from 2.0 to 2.5. Integration challenges specific to inorganic low-k and Cu based structures are discussed. Through advanced CMP process development, multi-level integration of porous oxide materials with moduli less than 0.5 GPa is demonstrated. Parametric data and isothermal annealing of these Cu/ low-k structures show results with yield comparable to Cu/oxide based interconnects.