Performance Evaluation of Cleaning Solutions Enhanced with Tetraalkylammonium Hydroxide Substituents for Post-CMP Cleaning on Poly-Si Film

Abstract

The cleaning solutions augmented with tetraalkylammonium hydroxides ͑TAAHs͒ with various chain-lengths of hydrocarbon substituents were developed for post-poly-Si chemical mechanical polishing ͑CMP͒ cleaning. The cleaning performance with respect to particle, organic, and metal removal as well as surface roughness was evaluated for a series of 3% NH 4 OH solutions dosed with 0.26 M of a TAAH and 100 ppm of ethylenediaminetetraacetic acid ͑EDTA͒. The experimental results demonstrated that the cleaning solutions enhanced with these surfactants ͑TAAH͒ and a chelating agent ͑EDTA͒ achieved significantly better removal efficiencies of particle and metal impurities than the control solution containing 3% NH 4 OH only. A conceptual model involving surface adsorption and double-layer formation was used to postulate the aqueous-phase surface interactions between the tetraalkylammonium cations and the poly-Si surface, and to explain the removal mechanisms of particle and metal impurities from the surface. The improved electrical properties ͑current density-electric field and charge-to-breakdown characteristics͒ of the post-CMP capacitor after cleaning further demonstrated the reliability and feasibility of the proposed cleaning recipes.The increasing complexity and miniaturization of modern integrated circuits demand a high device yield, meaning that lower defect density in the active region of silicon devices is a necessity. 1,2 For instance, the reliability of nonvolatile memory devices such as EEPROM, EPROM ͑electrically erasable and erasable programmable read-only memory, respectively͒, and flash memory is strongly dependent on the polyoxide quality characterized by low leakage current and high breakdown electrical field to prolong their data retention capabilities. Inadequate control over the thickness uniformity and surface roughness of the poly-Si layer directly leads to defect formation on the poly-Si/polyoxide interface, thus severely degrading the electrical properties. In recent years, the chemical mechanical polishing ͑CMP͒ process has been widely accepted as the mainstream planarization technique in the fabrication of deep submicrometer integrated circuits 3 in light of its capability to reduce surface roughness. However, as the device's dimension continues to scale down, the requirement for post-CMP cleaning becomes increasingly more stringent to ensure high device yield.The brush-scrubbing technique in combination with dilute ammonium hydroxide solution has been employed for many years and was considered among the most effective methods for removing particles after the CMP process. 4 Numerous studies focusing on improving oxide layer CMP as well as the post-CMP cleaning efficiency have been reported. 5-9 Jolley 7 reported that the solution containing tetramethylammonium hydroxide ͑TMAH͒ showed enhancement of metal removal, and had little effect on the surface roughness for post tungsten-CMP cleaning as compared to ammonium hydroxide solution. Cady and Varadarajan 8 also proposed that the alkaline solution co...

Effect of Alkaline pH on Polishing and Etching of Single and Polycrystalline Silicon

“…20,22,23) The effect of various alkaline agents such as Tetramethylammonium hydroxide (TMAH), KOH and NaOH in colloidal silica slurry for poly silicon CMP was also reported. 21,24,25) Also, the effect of various chelating agents such as ethylenediaminetetraacetic acid (EDTA), citric acid, oxalic acid and TMAH was well reported in the literature. 26,27) However, the removal mechanism for poly-Si CMP in alkaline solutions is not discussed and well understood in detail yet.…”

Recent progress in low-temperature-process monolithic three dimension technology

“…However, defects are easily produced by CMP and hardly removed by general post-CMP cleaning owing to the high hydrophobicity of the poly-Si surface. 52) Multistep interfacial modification was performed to remove the defect layer and expose a low-defect-density poly-Si channel. In accordance with our AFM data and Raman spectroscopy results, surface roughness of the poly-Si channel markedly decreased from 38.5 to 7.8 Å and the crystallinity increased when the channel thickness decreased from 150 to 20 nm, as shown in Fig.…”

Angle‐resolved XPS study of thin oxides after wet cleaning on Si0.8 Ge0.2 substrates

“…The use of both surfactants and chelating agents is very challenging in the development of new wetcleaning methods. 3 A chelating agent allows to catch metallic contaminants, 4 and a surfactant prevents the re-adhesion of fine particles and accelerates particle removal. 5 We have chosen NH 4 OH-based solutions containing additives (surfactant <2 wt% and chelating agent <1 wt%), mixed potentially with H 2 O 2 , thereby forming SC1-like solutions.…”