Effect of Polysilicon Wettability on Polishing and Organic Defects during CMP

Abstract

This study investigated the wettability effect of polysilicon on the polishing performance and organic defect contamination during polysilicon chemical mechanical polishing ͑CMP͒. Contact angle measurement was utilized to understand the nature of polysilicon surfaces. An oxidizer, H 2 O 2 , was added to the silica slurry to modify a hydrophobic polysilicon surface to a hydrophilic surface during polishing. The adhesion force was measured between a polymeric pad particle and a poly-Si wafer surface in KOH solution ͑pH 11͒ as a function of H 2 O 2 concentration. The adhesion force of the polymeric pad particle on the polysilicon decreased from 14 to 8 nN as the peroxide concentration increased to 10 vol %, at which the surface became hydrophilic. The hydrophilization of the polysilicon surface during polishing drastically reduced the organic contamination on the polysilicon wafers after polishing. The removal rate, frictional force, and pad temperature during CMP, with and without oxidizing the surface, were measured. They all decreased with the increasing concentrations of the oxidizer. The decrease was attributed to the formation of the lubrication layer of the oxide surface due to the oxidation of polysilicon.Dynamic random access memory ͑DRAM͒ process technology has become a leading semiconductor technology, with the highest production volume among very large scale integration ͑VLSI͒ semiconductor products. The density of DRAM quadrupled approximately every three years by virtue of advances in DRAM technology. 1 Because of the decrease in device feature size, the chemical mechanical polishing ͑CMP͒ process has become a necessary processing step for planarizing the surfaces during the DRAM process. 2 Poly-Si CMP is implemented to reduce the step height of a gate poly-Si in the construction of a recess channel array transistor and Fin Field Effect Transistor ͑FinFET͒ three-dimensional structures. 3 Although the CMP process is performed effectually, there are several problems that need to be overcome, such as local dishing/erosion, scratches, and abrasive and organic particle contamination. 4 After the CMP process, the wafer surface might be contaminated by the abrasive particles and polymeric residues from the pad, the retainer ring, and other consumables. The removal of organic residues from the wafer surfaces is a great challenge for the next processing step. The surface of poly-Si is hydrophobic in nature. Hence, it attracts hydrophobic organic residues, mostly pad debris, during the CMP process. These organic defects are difficult to be removed by general post-CMP cleaning methods. 5-7 Because there is much concern about organic contamination on polished polysilicon surfaces after polishing, understanding the interaction between the organic residues and the polysilicon surface is required.Therefore, this study investigated the organic contamination mechanism of polymeric residues on polished polysilicon surfaces. H 2 O 2 , as an oxidizer, was added to the silica slurry to modify the wettability of the polysil...

Role of Poly(diallyldimethylammonium chloride) in Selective Polishing of Polysilicon over Silicon Dioxide and Silicon Nitride Films

“…These Zp values of poly-Si are similar to those reported by several authors. [16][17][18] In the absence of any additive, the IEP of poly-Si is ∼3.3. However, on adding 250 ppm PDADMAC, the zeta potentials of polysilicon increased dramatically to highly positive values (g40 mV) in the pH range 2-10, again suggesting Langmuir ARTICLE that PDADMAC binds to and modifies the poly-Si surface.…”

Generation of Pad Debris during Oxide CMP Process and Its Role in Scratch Formation

“…[25][26][27]30 Figures 8a and 8b show the presence of some of the larger particles in the gathered slurry during CMP with in situ conditioning, but no such large particles were observed in the gathered slurry during ex situ conditioning. 6,8,15 It is known that the parameters of the diamond conditioner also play a vital role in effecting the conditioning of the pad. As mentioned above in Fig.…”

“…[1][2][3] However, to optimize the CMP performance, several parameters have to be monitored such as pad, conditioner, and slurry. [8][9][10][11][12] Microscratches, in particular, may lead to device failure and yield reduction as well as potential reliability issues. [8][9][10][11][12] Microscratches, in particular, may lead to device failure and yield reduction as well as potential reliability issues.…”

“…5,6,25,[28][29][30] Achuthan et al conducted an extensive study on this aspect and showed the results of pad profiles as a function of conditioning down force, speed, diamond size, and shape. 6,8 Despite this importance, no studies have gathered pad debris directly from the polishing pad during the CMP process. 6 Tsai et al developed a new pad design to regenerate a stable pad surface texture.…”

Synthesis of Fe metal precipitated colloidal silica and its application to W chemical mechanical polishing (CMP) slurry

“…Fumed silica suffers from the high instability problem, which would cause the silica particles to get agglomerated and hence produces more defects, where as colloidal silica has been known to be stable and well suspended slurry [4,9]. Reduction of all types of surface defects, especially scratch formation, has become a critical element of the fabrication processes [20][21][22].…”