The Effect of Material and Process Interactions on BEOL Integration

Abstract

In agreement with the ITRS roadmap, there have been several publications supporting the reduction in critical dimensions and the introduction of new materials to semiconductor processing (1,2,3). This paper highlights the observations and solutions to some of the critical material and process interactions encountered during the integration of the back end of line interconnect.

Impact of VUV photons on SiO2 and organosilicate low-k dielectrics: General behavior, practical applications, and atomic models

“…Specifically, Goto et al, 393 and Liu et al, 394 have both observed UV cure induced hydrogen loss and more dramatic compressiveto-tensile (-250 MPa to 100 MPa) stress changes in PECVD SiCNH Cu cap materials. Even more dramatic -500 MPa to 750 MPa stress swings have been reported by Spooner et al 9 Liu also observed using FTIR that significant UV-induced structural modifications occurred for SiCNH Cu cap materials with higher nitrogen and hydrogen content. 394 Interestingly though, small (< 1-2%) changes in dielectric constant and film thickness for SiCNH and SiOCH Cu cap materials with UV curing were observed relative to pSiOCH materials.…”

“…7 One significant impact of this incidental exposure is UV-induced stress changes in the Cu cap layer, typically SiNH or SiCN, on which the pSiCOH film is deposited. 8,9 Since interconnects are composed of up to a dozen wiring layers, 6 the stress of each layer is additive and can subject the interconnect wiring levels to substantial stresses. In some cases, the tensile stress can become high enough to induce cracking in the pSiCOH film, especially when the wafer is subjected to additional stresses during the chip packaging process.…”

“…One method demonstrated by Spooner involves simply tuning the PECVD process to produce films with increasingly higher levels of compressive stress such that the films remain compressive after the UV cure. 9 As shown by Nguyen et al, this can be achieved by increasing the H2 dilution flow during PECVD using trimethylsilane (Si(CH3)3H) and ammonia (NH3). 7 Other methods for mitigating the ILD UV-cure impact on the Cu capping layer stress involve employing a SiCNH/SiNH bilayer or SiCNH/SiNH/SiNH tri-layer film stack to mitigate the  impact of using a higher compressive stress / higher  material to compensate for the increased tensile stress component induced by the UV irradiation.…”

“…One consequence was a UV-induced change in stress from compressive to tensile in SiCNH films used to passivate the top Cu surface. 7,8,9 Films with modestly compressive or neutral stress are desired because tensile films can induce cracking during the chip packaging process. Thus, there was a need to understand how UV light affects all the films used to fabricate BEOL interconnects.…”

Chemical Treatment of Low-k Dielectric Surfaces for Patterning of Thin Solid Films in Microelectronic Applications

“…In particular, it has been determined that the dielectric constant of SiO 2 can be reduced by using doping with carbon-containing organics. ,, The resulting SiCOH materials have dielectric constants in the range from 2.7 to 3.0, and even lower values are possible by adding porosity. On the flip side, these new materials exhibit limited chemical stability, requiring special care during microelectronics manufacturing. ,− One of most difficult challenges when patterning the SiCOH dielectric is to minimize damage during the photoresist stripping processes, which typically relies on the use of plasmas with ions and radicals that can remove methyl groups from the surface of the SiCOH. , Because of this, the surface becomes hydrophilic, facilitating water absorption and leading to an increase in the dielectric constant of the material. ,, Several processes have been developed to minimize these problems, but those are multistep and introduce additional complications. ,− …”