Plasma etch residue formation and its removal from silicon nitride (SiN) films deposited at 200ºC, 480ºC and 700ºC is explored. X-Ray Photoelectron Spectroscopy (XPS) measurements showed that SiN contains more nitrogen (N) and less oxygen (O) with increasing deposition temperature. SiN films were etched in an Inductively Coupled Plasma (ICP) reactor in a halogen/hydrofluorocarbon (H:HFC) gas mixture; the carbon (C) containing species in the resulting residue films were studied as a function of the H:HFC ratio in the plasma. Post-plasma etch cleaning methods of the SiN surface were compared, these included: wet treatment with diluted hydrofluoric acid (dHF), sputtering with argon (Ar) plasma, and combined dHF and Ar plasma. After etch, Secondary Ion Mass Spectroscopy (SIMS) and XPS data showed formation of fluorocarbon (FC) films on SiN. FC film thickness after etch was estimated from XPS to reach up to 2 nm. Ultimately the SiN etch rate was shown to drop with increasing deposited C thickness while the lower nitrogen content in the SiN film (i.e. 200ºC) led to higher etch rate, which is in good agreement with literature. Ar plasma sputter turned out to be the most effective way of cleaning C residues: C surface content after Ar sputter was reduced to or below the reference data (unetched sample). In terms of wet treatment, an optimized chemistry was identified (AltChem) and post-RIE cleaning was more efficient than dHF in reducing C surface concentrations.

A plasmaless, photochemical etch process using ultraviolet (UV) light in the presence of NH3 or O2 etched porous organosilicate glass films, also called pSiCOH films, in a two-step process. First, a UV/NH3 or UV/O2 treatment removed carbon (mostly methyl groups bonded to silicon) from a pSiCOH film by demethylation to a depth determined by the treatment exposure time. Second, aqueous HF was used to selectively remove the demethylated layer of the pSiCOH film leaving the methylated layer below. UV in the presence of inert gas or H2 did not demethylate the pSiCOH film. The depth of UV/NH3 demethylation followed diffusion limited kinetics and possible mechanisms of demethylation are presented. Unlike reactive plasma processes, which contain ions that can damage surrounding structures during nanofabrication, the photochemical etch contains no damaging ions. Feasibility of the photochemical etching was shown by comparing it to a plasma-based process to remove the pSiCOH dielectric from between Cu interconnect lines, which is a critical step during air gap fabrication. The findings also expand our understanding of UV photon interactions in pSiCOH films that may contribute to plasma-induced damage to pSiCOH films.

In this work, ultra-dilute HF systems with the addition of functional hydrocarbon as an additive at elevated temperatures were evaluated to remove the post reactive ion etching (RIE) residues in a controlled chamber with ambient O2 concentration <30ppb. Controlling the HF and additive concentration was critical to achieve minimum dielectric loss (<2Å) and to suppress the formation of copper oxides while effectively removing post etch residues (PER). Cu 2p XPS peaks confirmed the removal of residues from the Cu and ULK sidewalls. An oxide free Ta/TaN liner and Cu surface was achieved and confirmed using time of flight secondary ion mass spectroscopy (TOF-SIMS). In addition, the impact of HF solution was electrically evaluated by measuring via resistance and yield. A clear trend in via resistance reduction and yield improvement (40%) was observed with applying the optimized cleaning conditions when compared to the control samples.

Continuous shrinking of the interconnect dimensions with each technology node requires reduction in RC (resistance-capacitance) delays. Reduction in capacitance requirement at 45nm node was met by introducing a k 2.4 inter-layer dielectric (ILD) at 2X metallization level [1]. However, the material was not readily extendable to next technology node because of the need for even higher modulus at the advanced nodes. Thus, there was a need to develop a new pSiCOH k 2.4 ILD with improved mechanical properties and damage susceptibility for back end of the line (BEOL) capacitance reduction. IBM/Alliance team has developed a number of pSiCOH films using a variety of precursors. Generally, the porous ultra-low k films are prepared by using a subtractive approach [2] in which the film is deposited using a mixture of skeleton and porogen precursor and then cured to remove the labile organic fraction [2]. An alternative to the above approach is to use a single precursor molecule consisting of skeleton with embedded porogen [3]. Developing a robust pSiCOH film with k < 2.55 has always been a challenge with this approach. This paper reports the development of a pSiCOH k 2.4 film deposited using a single precursor showing superior time dependent dielectric breakdown (TDDB) performance with lower integrated k (lower capacitance) as compared to the k 2.55 ILD pSiCOH film at 80 nm, 56 nm and 48 nm pitch. Octamethylcyclotetrasiloxane (OMCTS) precursor used for fabricating dense SiCOH dielectrics (k= 3.0-2.7) was used to form low k=2.4 film. The modified PECVD deposition conditions along with optimized UV cure resulted in k 2.4 ILD film deposited using a single precursor henceforth referred to as OMCTS Ex k 2.4. The new OMCTS Ex k 2.4 film has only slightly lower modulus as compared to the k 2.7 film deposited using OMCTS and O2 while showing comparable plasma induced damage (PID). PID was measured by thickness change after HF wet etch removed the damaged layer caused by standard plasma. In general, good TDDB performance is obtained by lowering porosity, increasing %C and reducing PID [4]. Each of these properties has been carefully optimized for new OMCTS Ex k 2.4 film by tuning the deposition and the UV cure conditions. Fig. 1 compares the RC performance for ULK k 2.55, ULK A k 2.4 (another PECVD k2.4 ILD) and OMCTS Ex k 2.4 film at 10 nm node. ULK A k 2.4 shows higher PID as compared to k 2.55 resulting in higher capacitance. In contrast, the OMCTS Ex k 2.4 retains the capacitance benefit because of the lower PID for this film. Table 1 compares the extracted k value for k 2.55 and the k 2.4 ILD’s at 80, 56 and 48 nm pitch. OMCTS Ex continues to show lower extracted k number with no significant increase in value with technology node scaling. Fig. 2 shows the TDDB performance of these ILD’s at 10 nm node. The higher carbon content with low plasma induced damage resulted in dramatically better TDDB for OMCTS Ex than other films. Important to note that the TDDB performance of this film is almost 15X better than the TDDB performance of k 2.55 and ULK A k 2.4 ILD. Conclusion A new advanced single precursor OMCTS Ex k 2.4 pSiCOH ILD film has been developed to meet the integration scaling and reliability requirements. The new OMCTS Ex k 2.4 film shows better film properties than the reference k 2.55 and other 2.4 films and retains capacitance benefit by demonstrating an overall lower integrated k value as compared to the k 2.55 ILD. Acknowledgement This work was performed by the Research and Development Alliance Teams at various IBM Research and Development Facilities. References [1] S. Sankaran, et al , “A 45 nm CMOS node Cu/low-k/ultra low-k PECVD SiCOH (k=2.4) BEOL technology”, Electron Devices Meeting, IEDM International , 2006 [2] A. Grill and C. Patel, “Ultralow dielectric constant pSiCOH films prepared with tetramethylcyclotetrasiloxane as skeleton precursor,” J. Appl. Phys., vol. 104, pp. 024113-9, 2008 [3] S. Nguyen, S. Gates, D. Neumayer, and A. Grill, US patent 7,491,658, 2009 [4] E.G. Liniger, et al , “TDDB extendibility of ULK materials to 14nm BEOL and beyond,” Adv. Metal Conf. 2012 Figure 1

Effects of clean chemical pH on PR/FM and HM defects for W-CMP are examined. Oxalic acid, DIW, and a QAC-based basic chemicals are evaluated for their PR/FM cleaning performance and hollow metal generation. Basic clean chemistry is demonstrated to be more efficient for PR/FM removal but more prone to HM defects. AFM and XPS surface analyses conducted on post W-CMP wafers help discern the cleaning mechanism for W-CMP.

A multilayer SiN barrier film with high breakdown field and low leakage current is developed for Cu low-k interconnects and is compared with the SiCNH barrier film used in previous technology nodes. Ultrathin SiN barrier cap films also provide high conformality and fill recessions in Cu lines as observed after CMP. The conformal ultrathin (8-14 nm) multilayer SiN cap is robust with higher breakdown field, lower leakage and forms a good oxidation barrier. The electromigration activation energy for a SiN cap layer of 10-12 nm dielectric thickness is about 0.9 eV.

A "hybrid" post-Cu CMP cleaning process that combines acidic and basic cleans in sequence is developed and implemented. The new process demonstrates the advantages of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic brush clean process. It also eliminates the circular ring defects that occur intermittently during roller brush clean. TXRF scans confirm the reduction of AlOx defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. Both short and open yields can be improved by using the new clean process. The underlying mechanism of the huge defect reduction benefits is discussed.

The authors have addressed the application of advanced ion beam-based analytical techniques to various physical characterization aspects in sub-32-nm semiconductor front-end-of-line materials and processes. We have presented the application of O-18-isotope labeling in combination with SIMS depth profiling to follow O-migration in high-k/metal gate stacks. We have also demonstrated the application of complementary low-energy ion scattering and time-of-flight SIMS surface analysis to determine high-k thin film closure and growth mode for different deposition techniques. We have also proposed alternative Dynamic Secondary Ion Mass Spectrometry (DSIMS) protocols for the quantitative analysis of phosphorous ultra-shallow junctions, resulting in more accurate near-surface P-profile and in situ B-doped Si1-xGex epitaxial films with explicit correction of sputter and ionization yield variations as function of [Ge]. We have demonstrated the feasibility of backside SIMS on appropriate III-V high-mobility channel stacks, resulting in unprecedented depth resolution at the source/drain metal-contact/III-V interface. Copyright (C) 2012 John Wiley & Sons, Ltd.

A “hybrid” post Cu CMP cleaning process that combines acidic and basic clean in sequence is developed and implemented. The new process demonstrates the strengths of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic clean process. It also eliminates the circular ring defects that occur intermittently during roller brush cleans. TXRF scans confirm the reduction of AlOx defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. As revealed by XRD analysis, surface Cu oxide is dissolved into aqueous solution by the acidic clean chemical. The formation mechanism of circular ring defects and the key to their elimination is discussed.

Cu(Mn) alloy seed BEOL studies revealed fundamental insights into Mn segregation and EM enhancement. We found a metallic-state Mn-rich Cu layer under the MnOx layer at the Cu/SiCNH cap interface, and correlated this metallic layer with additional EM enhancement. A carbonyl-based CVD-Co liner film consumed Mn, reducing its segregation and EM benefit, suggesting O-free Co liner films are strategic for Cu-alloy seed extendibility.

Effects of Cu surface treatment (NH3 plasma irradiation) before the cap dielectric deposition on low-k surface damage and Cu surface cleaning were systematically investigated. From the blanket film surface damage evaluations of porous low-k film with high carbon content and the oxygen removal on blanket Cu film after chemical mechanical polishing (CMP), the optimized NH3 plasma condition such as high RF power and high pressure exhibited the high efficiency for oxygen removal from the Cu surface without increasing the k-value of low-k film. The low-k/Cu interconnect (line/space = 40/40 nm) for 22 nm-node with the high plasma resistant low-k film and the optimized Cu surface treatment showed longer electro-migration lifetime without large degradation of RC performance.

Robust ultrathin (20 nm) trilayer low k SiNx/SiNy/SiCNH dielectric Cu caps (k ~4.0-4.2) with post ultraviolet (UV) cure compressive stress were developed and integrated into 22nm CMOS Back End Of Line (BEOL) devices. The new cap reduces device's capacitance (~ 4 %) and enhances stress stability in Cu-Ultra low k structures

There is an ongoing need in the microelectronics industry to increase circuit density in multilevel back-end-of line (BEOL) interconnects to improve the operating speed and reduce power consumption. One way to maintain capacitance-resistance (RC) performance, without de grading yield or reliability is through introduction of porous ultra low-kappa materials (ULK) as interlevel dielectrics (ILD). This paper presents the ability to tune ULK films through simple processing optimization steps to meet the specific integration requirements. Balancing composition of the film to minimize damage needs to be coupled with improving mechanical integrity for packing compatibility.

A cost effective 28nm CMOS Interconnect technology is presented for 28nm node high performance and low power applications. Full entitlement of ultra low-k (ULK) inter-level dielectric is enabled. Copper wiring levels can be combined up to a total of 11 levels. The inter-level dielectric was optimized for low k-value and high strength. The feature profiles were optimized to enable defect-free metallization using conventional tools and processes. High yields and robust reliability were demonstrated.

Cu films were directly deposited on Ru to check the feasibility of this process for Cu back-end-of-the-line integration beyond 32-nm technology nodes. Feature-fill enhancement was observed from the direct electroplating process as compared to the conventional one with the Cu electroplating performed on a PVD Cu seeding layer. Reasonable parametric yields were demonstrated for the direct electroplating process. The electromigration (EM) resistance of the directly plated Cu lines was degraded relative to that observed on the conventionally plated Cu lines. The observed EM resistance degradation is attributed to a weak interface between Ru/Cu, which can be caused by impurities from the electroplating process.

A CVD-hybrid dielectric/metal liner has been demonstrated by simulation and actual structure. From line resistance (R) and line capacitance (C) simulation, the CVD-hybrid liner deposited on porous ULK (k=2.2) inter layer dielectrics (ILD) is shown that it is possible to improve RC performance. The CVD-hybrid liner with CVD-SiCN and CVD-Ru shows good liner conformality, Cu diffusion barrier property and oxidation barrier property. Integration process is investigated to achieve optimum CVD-hybrid liner structure with special RIE technique. 14.6% RC performance improvement can be achieved with triple-layered ULK(k=2.2)/Cu integrated interconnect structure. The CVD-hybrid liner is a strong candidate to achieve a better RC performance for future technology nodes.

A 32 nm BEOL with PVD CuMn seedlayer and conventional PVD-TaN/Ta liner was fully characterized by fundamental, integrated, and reliability methods. CuMn was confirmed to have fundamental advantages over CuAl, such as higher electromigration (EM) reliability for the same Cu line resistance (R). Both low R and high reliability (EM, SM, and TDDB) were achieved. Improved extendibility of CuMn relative to CuAl was also supported by studies of alloy interactions with advanced liner materials Ru and Co, and by enhancement of ultra-thin TaN barrier performance.