Novel phosphate-functionalized silica-based dispersions for selectively polishing silicon nitride over silicon dioxide and polysilicon films

ECS J. Solid State Sci. Technol.

2015

Electrical isolation of the billion or so active components in each integrated device is achieved using shallow trench isolation (STI) which requires chemical mechanical planarization (CMP) involving silicon dioxide removal at a high rate and stopping on an underlying silicon nitride film. Several colloidal slurries with various additives can yield the desired high rate selectivity between the oxide and nitride films during CMP while maintaining an acceptably low nitride rate. Here, many of such high selectivity STI CMP slurries described in the literature are reviewed along with the characteristics of the colloidal dispersions like the abrasives, additives, the interactions between them and with the films being planarized and the associated pH range in which the high selectivity is observed. The mechanisms proposed to explain the high reactivity of ceria with oxide, the role of additives in suppressing the nitride removal rate and resulting high selectivity are discussed. Reduction of a multitude of defects in post-CMP processed STI structures still remains an important challenge, especially as the feature sizes continue to shrink. Chemical mechanical planarization (CMP) is one of the important enabling processes in facilitating multilevel metallization (in some cases reaching up to 14 levels) and incorporation of novel gate and channel materials at the component level in modern semiconductor device manufacturing where its use has become widespread and ubiquitous.1-6 Here, we review recent advances and remaining challenges in one specific application of CMP, the shallow trench isolation (STI) process. STI is a method of electrically isolating active areas using trenches created in the Si substrate around the active elements and filling it with an insulating dielectric, such as silicon dioxide or silicon oxy-nitride or silicon carbonitride.7-11 Process details of the STI structures are available in numerous publications. There are a multitude of techniques available for oxide deposition and even though the resulting oxides have very different properties, for simplicity we do not distinguish between them in this review. For completeness and ease of reference, a schematic representation of the STI process is given in Figure 1. While the trenches are being filled, silicon dioxide also deposits over unwanted areas on the entire wafer (since selective deposition in trenches only is not possible) creating an uneven topography. The excess and unwanted oxide has to be completely removed and CMP has proven to be the only viable and robust global and local planarization capable process technology.Here, as shown in Figure 1, presence of a very thin silicon nitride stop layer (deposited on another thin pad oxide layer to control film stress) is an essential and integral part of the process. This nitride stop layer prevents any damage during planarization to the all-important epitaxially grown surface underneath and is itself removed by a wet etch process subsequent to the overburden oxide removal. Since the integrity of the...

“…Silica Surface 67 oxide RR ( Figure 5). XRD analyses of the abrasives suggest that the crystallite size is positively correlated to the calcination temperature.…”

Section: Ecs Journal Of Solid State Science and Technology 4 (11) P5mentioning

confidence: 99%

Shallow Trench Isolation Chemical Mechanical Planarization: A Review

Ramanathan

Dandu

ECS J. Solid State Sci. Technol.

2015

“…Interestingly, the addition of ceria abrasives had no effect on these RRs, while the poly-Si RRs are slightly higher with silica abrasives. In contrast, several researchers reported that silica- and ceria-based slurries can suppress poly-Si RRs with varying oxide and nitride RRs. − …”

Section: Introductionmentioning

confidence: 95%

“…This can be achieved using an oxide and nitride polishing slurry that also provides very low poly-Si RRs (<5 nm/min). In view of the importance of these processes, considerable work has been done to develop slurries that can provide these two different options. − …”

Section: Introductionmentioning

confidence: 99%

Charge Density and pH Effects on Polycation Adsorption on Poly-Si, SiO₂, and Si₃N₄ Films and Impact on Removal During Chemical Mechanical Polishing

Penta

Veera

ACS Appl. Mater. Interfaces

2011

Self Cite

The pH-dependent interactions of five aqueous abrasive-free polycationic solutions, all at a concentration of 250 ppm, with poly-Si, SiO(2), and Si(3)N(4) films and IC1000 polishing pads used in chemical mechanical polishing have been investigated and compared with the interaction of poly(diallyldimethyl ammonium chloride) (PDADMAC) that was investigated recently. Three of the polycationic solutions, poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), poly(allylamine), and poly(ethylene imine) (PEI) enhance poly-Si removal rates (RRs) to the range of about 500 to 600 nm/min at pH 10. In contrast, poly(acrylamide) (PAA) suppressed poly-Si RRs to about 50 nm/min, whereas with a copolymer of PAA and PDADMAC, the RRs were lower than those obtained with PDADMAC but higher than those obtained with PAA. For all the polycationic solutions, the RRs of both SiO(2), and Si(3)N(4) films were ~0 nm/min. These solutions offer a low-defect option for the processing of emerging FinFET devices. The variation in the RR magnitude and dependence on pH among the different polycations is related to the relative charge density of the polycations as well as the films being polished, consistent with ζ potential data. Based on the ζ potential data and earlier published reports, it is suggested that the strong polycation-mediated bridging interactions between the polarized and weakened Si-Si bonds of the poly-Si surface and the polyurethane IC 1000 pad are responsible for the high poly-Si RRs.

“…This removal rate selectivity requirement in this SiN cap CMP process is the reverse of that needed in the more conventional shallow trench isolation (STI) CMP and is often referred to as reverse STI selectivity. [2][3][4][5][6][7][8] Several authors [2][3][4][5][6][7][8] investigated reverse STI selectivity CMP processes using ceria and silica based dispersions with various additives. Recently Bae et al 2 achieved highly selective Si 3 N 4 to SiO 2 removal rate (RR) ratio of ∼ 95.0 at pH 1.5 using modified silica abrasives.…”

mentioning

confidence: 99%

“…While this selectivity is excellent, the presence of the chloride ions can be a major drawback. In another publication, Dandu et al 5 formulated phosphate functionalized silica particle based dispersions and reported nitride:oxide removal rate selectivity of >20:1. Several other authors 6,7 reported reverse STI selectivity using ceria dispersions and additives such as co-polymers of acryl amide, diallydiethyl ammonium chloride and polyethylene imine with a nitride:oxide RR selectivity of ∼ 4:1 and in some cases higher.…”

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confidence: 99%

Role of Ce³⁺Ions in Achieving High Silicon Nitride Polish Rates

Alety

Sagi

ECS J. Solid State Sci. Technol.

2017

We show that Ce 3+ ions when used as an additive to ceria dispersions enhance plasma-enhanced chemical-vapor-deposited silicon nitride polish or removal rates (RRs). Ceria slurries (0.1 wt% and 140 nm avg. size) containing 2.3 mM Ce(NO 3 ) 3 and no other additive gave nitride RRs of ∼300 nm/min at 4 psi and ∼350 nm/min at 5 psi, both at pH4. The nitride RRs measured in the presence of Ce(NO 3 ) 3 , Ce(CH 3 COO) 3 and KNO 3 suggest that the rate enhancement is solely due to the presence of Ce 3+ ions. We discuss the underlying mechanism causing high silicon nitride RRs in the presence of Ce 3+ ions based on XPS analysis of pre-and post-polished silicon nitride and oxynitride film surfaces, streaming potential data and high oxynitride RRs obtained using the same ceria particle-based slurries as above. It is suggested that the Ce 3+ ions convert the upper layers of the nitride film into an oxynitride that is polished by the abrasives at a high rate. In this process, the conversion of the nitride film seems to be the rate controlling step with the oxidation and polishing occurring in a repetitive manner. © The Author Semiconductor device scaling led to the shrinking of device structures and also created new challenges in the front end of line integration schemes that required several additional new chemical mechanical planarization (CMP) steps. One such new integration scheme in the replacement metal gate (RMG) process is the self-aligned contact (SAC) module where a silicon nitride CMP step is required as shown in Figure 1 (Redrawn from Ref. 1). Since the composition of this silicon nitride film and those used in our experiments is nonstoichiometric, we will refer to them by the generic symbol SiN. In this SAC module, one of the challenges is the misalignment of the contact metal and source/drain, leading to device failure. In order to provide a wider process margin in contact alignment, a SiN cap is deposited on top of the metal gate.1 In the process of depositing this SiN cap, there will always be some SiN overburden, as shown in Fig. 1, which needs to be removed using a highly selective nitride slurry that has a very low oxide removal rate to minimize loss of the underneath oxide. This removal rate selectivity requirement in this SiN cap CMP process is the reverse of that needed in the more conventional shallow trench isolation (STI) CMP and is often referred to as reverse STI selectivity. 2-8Several authors 2-8 investigated reverse STI selectivity CMP processes using ceria and silica based dispersions with various additives. Recently Bae et al.2 achieved highly selective Si 3 N 4 to SiO 2 removal rate (RR) ratio of ∼ 95.0 at pH 1.5 using modified silica abrasives. They modified the surface charge of the silica abrasives toward more negative values (−50 mV) since creating higher negative charge on silica abrasives enables stronger attractive forces between them Si 3 N 4 films and a stronger repulsive force toward silica films in a low pH environment, which can lead to high nitride to oxide removal rate selectiv...