CVD Co and its application to Cu damascene interconnections

A colloidal silica-based slurry (3-10 wt%) containing H 2 O 2 (1 wt%) and citric acid (50 mM) was found to polish chemical vapordeposited (CVD) cobalt (Co) films with removal rates (RRs) of ∼180-500 nm/min and a dissolution rate (DR) of ∼0 nm/min at pH 8 along with an RMS roughness of ∼0.5 nm and a corrosion current of ∼50 μA/cm 2 . Our results suggest that, in the presence of H 2 O 2 , the Co film surface was covered with a passive film of CoO in acidic conditions and Co 3 O 4 in alkaline conditions. However, in the presence of H 2 O 2 and citric acid in acidic conditions, formation of the soluble complex [Co(C 6 H 5 O 7 ) 2 ] 3− from abraded Co enhanced the RRs significantly. The roles of H 2 O 2 , citric acid, and silica abrasives as well as the pH on the Co material removal process are discussed and a removal mechanism is proposed. Two inhibitors namely, 1, 2, 4-Triazole (TAZ) and Benzotriazole (BTA), were tested in the presence of 50 mM citric acid at pH 8 but were found to be ineffective even at concentrations of 100 mM in reducing the E corr of Co-Ti couple to minimize galvanic corrosion that is essential when the Co/Ti structure is polished after the removal of bulk of Co and requires further study. Sub-10 nm devices face several challenges with copper as an interconnect material for back-end-of-the-line (BEOL) processes during the manufacture of integrated circuits. These include increasing resistivity with decreasing thickness, 1 non-conformal deposition at narrow trench widths ∼20 nm or less, 2 and scaling limitations of the diffusion barrier/liner.3 This led to the investigation of new trench filling materials. Cobalt is a promising alternative to meet the challenges of interconnect lines at these lower nodes for the first two metal layers M1 and M2, due to its lower resistivity at smaller dimensions (∼10 nm) compared to copper. [4][5][6] Kamineni et al. 7 proposed the use of chemical vapor deposited (CVD) cobalt to replace the widely used tungsten for local interconnects for 10 nm and smaller nodes. They emphasized two main advantages of CVD Co metallization which are a) CVD Co precursors do not damage the Ti liner enabling barrier scaling and b) it achieves void free fill in high aspect ratio features without defects, something that is difficult to achieve with a conventional physical vapor deposited (PVD) Co process. 8,9 Hence, CVD-based Co metallization is an attractive option for the technology nodes below 10 nm.CVD-based cobalt has also gained prominence in the advanced copper interconnects below 22 nm as liner [10][11][12][13][14][15][16][17] to improve adhesion between the barrier (TaN, TiN) and Cu seed layer where the Co film thickness is only ∼2 nm. Several authors 18-26 have investigated cobalt polishing for such applications where RR requirements are typically <20 nm/min and Co loss due to corrosion has to be as close to zero as possible, since even a minute loss of Co material can degrade the device reliability significantly. Hence, since the potential gap between Co and Cu is a large ∼0...

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confidence: 99%

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confidence: 99%

Citric Acid as a Complexing Agent in Chemical Mechanical Polishing Slurries for Cobalt Films for Interconnect Applications

Popuri

Sagi

Alety

et al. 2017

“…Good adhesion with Cu is particularly important because, with current ULSI Cu interconnects, reliability is an important issue, and the adhesion of Cu with the underlayer is currently an area for further improvement. Such screening has already been carried out, resulting in the following candidate materials: Ru, [29][30][31][32][33] Co, [19][20][21][22][23][24] and Ta. [16][17][18] Among these elements, the underlayer material that is most favorable in terms of Cu nucleation should be selected based on solution (I); i.e., it should provide a small γ int and a small θ.…”

Section: Strategymentioning

confidence: 99%

“…Kim et al succeeded in forming ultra-thin (< 9-nm-thick) continuous Cu films, employing oxynitiride during CVD growth of Cu to lower the surface energy of the films, together with a subsequent reduction step. 15 However, this approach is not compatible with Ta [16][17][18] -and Co [19][20][21][22][23][24] -based underlayers due to oxidation during CuON deposition, which leads to poor adhesion between the Cu layer and the underlayers, as TaO x and CoO x were not reduced during the process. Au et al succeeded in filling narrow trenches (∼17 nm-wide) with Cu, employing iodine-catalyzed CVD of Cu onto Mn 4 N underlayer.…”

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confidence: 99%

Comparative Study on Cu-CVD Nucleation Using β-diketonato and Amidinato Precursors for Sub-10-nm-Thick Continuous Film Growth

Shima

Shimizu

Momose

et al. 2015

We demonstrate the growth of sub-10-nm-thick continuous Cu films using chemical vapor deposition (CVD) for next-generation Cu interconnects for ultra-large-scale integration (ULSI). The thickness of such films is equivalent to that of Cu during coalescence, and optimized operating conditions and substrate materials are required to form high-density nucleates. Ru was used as an underlayer, and the time evolution of nucleation and grain growth were studied with systematically varied conditions using two Cu precursors: conventional β-diketonato and newly developed amidinato precursor compounds. The revealed geometry of the initial nano-scale Cu grains prior to coalescence suggests the required nucleate density for 7-nm-thick continuous film growth, and which was 2.4 × 10 11 /cm 2 . The maximum nucleate density was achieved with the lowest deposition temperature and highest precursor concentration for both precursors; i.e., 6.9 × 10 11 /cm 2 for β-diketonato at 100 • C, and 4.6 × 10 11 /cm 2 for amidinato at 150 • C. A 10-nm-thick continuous Cu film was formed using amidinato under the optimized conditions. Furthermore, the framework used in this study to enable a high nucleate density suggests that it is possible to form thinner (4 nm∼) Cu films using amidinato. Because of the inherent good step coverage of CVD, this process is a promising candidate for next-generation ULSI Cu interconnects. Cu interconnects for ultra-large-scale integration (ULSI) are currently fabricated using the so-called 'damascene process,' which consists of: (i) the formation of three-dimensional features (i.e., trenches and via-holes) in the inter-layer dielectric using etching; (ii) sputtering of TaN x onto the inter-layer dielectric to form a Cu diffusion barrier; (iii) sputtering of Ta as an adhesion layer; (iv) sputtering of Cu as a seed layer for subsequent electro-plating; and (v) electro-plating of Cu to fill the remaining gaps. As the dimensions of complementary metal-oxide-semiconductor (CMOS) transistors in ULSI have reduced, the feature size of the Cu interconnects has also reduced. 1After 2016, the Cu line width will become smaller than 22 nm, so the Cu seed layer must be thinner than 7 nm.2 With such small dimensions, conventional physical vapor deposition (PVD) processes (including sputtering) face difficulties in forming conformal Cu films on narrow and high aspect-ratio (AR) features. Hence, it is essential to develop alternative deposition processes that are capable of highly conformal film growth. The current leading candidates are atomic layer deposition (ALD), 3,4 chemical vapor deposition (CVD), 5-9 and supercritical fluid deposition (SCFD).10 ALD-grown films exhibit the required properties for this purpose, but the growth rate of 0.1-1.9 Å/cycle 11 is too slow for mass production. SCFD is an emerging technology, but it requires a high-pressure environment, which is not compatible with current vacuum processes and now under investigation. 12,13 CVD is the most widely studied method, due to its fast growth rate of 2.0-14...

“…However, for future technologies scaling Co thickness is challenging due to the loss of Co Cu plating solutions and CMP, resulting in sidewall voids and poor reliability. [7][8][9][10] Ru is also a good wetting layer for Cu. Ru has better corrosion resistance in Cu plating solutions compared to Co and is a good substrate for PVD Cu reflow fill processes.…”

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confidence: 99%

CMP Development for Ru Liner Structures beyond 14nm

Patlolla

Motoyama

Peethala

et al. 2018

For better gap fill in beyond 56nm pitch Cu interconnect structures, Ru liner is one of the most promising solutions with better coverage and wettability. In this paper several new challenges in Ru CMP specific to ≤ 48nm pitch structures (also called 10nm technology) are presented. New CMP solutions were developed by optimizing the slurry, consumables, and process sequence to address the observed challenges such as Ru bending and Cu recess. The optimized solutions to address these challenges were further tested on integrated wafers and improvements in resistance and yield were demonstrated through electrical tests. Meeting the resistance target in back end of the line (BEOL) interconnects is increasingly challenging for sub-14nm technologies and there has been a continuous focus to find the right combination of barrier and Cu metallization.1-6 For better gap fill in these fine dimension structures, new liner materials and wetting layers are required. [7][8][9][10][11][12][13] Co is a known wetting layer for Cu that enables void free metallization. However, for future technologies scaling Co thickness is challenging due to the loss of Co Cu plating solutions and CMP, resulting in sidewall voids and poor reliability. [7][8][9][10] Ru is also a good wetting layer for Cu. Ru has better corrosion resistance in Cu plating solutions compared to Co and is a good substrate for PVD Cu reflow fill processes.11,12 With Ru, low line resistance and void free metallization has been achieved in sub 14 nm technologies. However, a major challenge to implementation of Ru in a semiconductor product is CMP. The industry does not yet have a CMP process that can planarize Ru liner and Cu without defects such as galvanic corrosion of Cu, dendrite formation, and interlayer dielectric damage. 14 Several researchers have studied Ru CMP.15-19 CMP of this material requires novel slurries with strong oxidizers such as ceric ammonium nitrate, NaIO 4 , KIO 4 , KMnO 4 , etc. As an example, the reaction below shows the mechanism for potassium periodate as the oxidizer for Ru CMP. PH values greater than 8 are preferred for Ru CMP due to the formation of toxic (RuO 4 ) formation in the acidic and neutral pH regions.Many CMP studies have been conducted showing high Ru removal rates (RRs) both with and without tunable RR selectivity on Cu and dielectrics. Galvanic corrosion of Cu in Ru slurries has been a focus and indicates the need for corrosion inhibitors to minimize the corrosion potential difference between Ru and Cu. 20,21 These studies have primarily focused on blanket Ru polishing and ways to mitigate corrosion based on electrochemical data. In this study, we evaluate commercially available slurries on 48nm pitch (10nm) integrated structures with Ru liner. Critical challenges in planarizing Ru CMP are identified. Using experimental data, the defect mechanism and a mitigation path are shown.Experimental 300mm diameter wafers with 10nm dual damascene test structures were used for all CMP experiments. The barrier/liner materials for the test st...