Integration Issues for Diamond Like Carbon in a Copper Damascene Process Flow

Abstract

Hydrogenated “diamondlike” carbon (DLC) is a potential candidate as a low k material for the back end interconnect (BEOL) dielectric for VLSI chips. The DLC material is an attractive dielectric due to its isotropic properties and the ability to deposit the films by CVD techniques, such as PECVD or HDP systems. Under suitable preparation conditions such materials can reach dielectric constant values below 2.8, even as low as 2.4. While the as-deposited films are not stable to exposure to subsequent processing temperatures of about 400 C, it appears that they can be stabilized, in terms of dimensional stability and material loss, by an initial anneal.The integration of DLC films in the BEOL structure further requires good adhesion with the materials in contact with the DLC dielectric, such as silicon nitride or silicon oxide, and liner metallurgy. As the potential application of the DLC films will be in Cu based damascene structures the behavior of the films under CMP conditions is also important.The talk will discuss the evaluation of DLC films and of integration issues such as adhesion under processing conditions, patterning, CMP behavior. Blanket and patterned structures built with DLC films will be presented.

Low and Ultralow Dielectric Constant Films Prepared by Plasma‐enhanced Chemical Vapor Deposition

“…As-deposited DLC fi lms of lower dielectric constants and lower stresses are not stable at this thermal exposure [26]. Nevertheless, it has been found that DLC fi lms having dielectric constants as low as 2.7 can be stabilized by annealing them fi rst in a nonoxidizing ambience at the highest temperature dictated by the integration processes [12,33]. Subsequent anneals at the same temperature did not modify the fi lms any more.…”

“…In order to introduce a new dielectric as the insulator of the BEOL, the material has to satisfy a large number of criteria imposed by its functionality in the structure and by the integration processing. Some of these criteria are listed next [3,11,12 The requirements listed above were fulfi lled by the classic dielectric SiO 2 , however most materials with lower k considered for replacing the oxide did fail many of these criteria and were removed from considerations. Even the low-k dielectrics that have fi nally been integrated in ULSI chips may not fulfi ll all the requirements listed above and the integration processes had to be modifi ed to accommodate for the lack of those.…”

“…Furthermore, the stresses in the DLC fi lms decreased after annealing from the as-deposited compressive stress of about 500 MPa and, for fi lms with k = 2.7, the stress became slightly tensile. Figure 1.4 [12] shows the leakage current through a DLC fi lm having a dielectric constant k = 2.8 after deposition of Cu dots on the stabilized fi lm and after annealing the Si/DLC/Cu structure at 400°C for 4 h in He. The leakage current is relatively high at 10 −7 A/cm 2 at a fi eld of 0.5 MV/cm, but it has been deemed to be suffi ciently low to make the material usable as the interconnect dielectric.…”

“…The leakage current is relatively high at 10 −7 A/cm 2 at a fi eld of 0.5 MV/cm, but it has been deemed to be suffi ciently low to make the material usable as the interconnect dielectric. An average acceptable leakage of only 3 × 10 −10 A was [12] with permission from The Electrochemical Society, Inc.) measured at 1.8 V in an integrated a Cu serpentine 3.8 m long, separated from an adjacent comb structure by 0.34 µm of DLC [34]. The repeated annealing at 400°C of the stabilized fi lms induced only a small increase in the leakage current trough the DLC fi lm.…”

“…The apparently stabilized FDLC fi lms had dielectric constant in the range of 2.4-2.6 and appeared to be promising candidates for the low-k dielectric of the interconnect structure [11,25]. Figure 1.7 [12] shows the leakage current trough a FDLC fi lm after the deposition of Cu dots and after annealing the entire structure at 400°C for 4 h in nitrogen. It can be seen that the leakage current of 2 × 10 −8 A/cm 2 at an operating fi eld of 0.5 MV/cm through the FDLC fi lm was lower than that of DLC (see Figure 1.4) and appeared to be suffi ciently low to enable the potential use of this material as the interconnect dielectric.…”