Effect of Hydroxyethyl Cellulose Concentration on Surface Qualities of Silicon Wafer after Touch Polishing Process

Abstract

We investigated the effect of hydroxyethyl cellulose ͑HEC͒ concentration in the alkaline slurry on the surface qualities of polished silicon wafers after touch polishing, such as the number of remaining particles and the haze level. They significantly decreased and saturated over the addition of a 0.2 wt % HEC. We attributed these surface quality enhancements to a formation of nanometersized passivation layers onto the silicon wafer and colloidal silica surfaces during touch polishing. The formation of passivation layers were shown by the results of investigations with an average particle size, the zeta potential of abrasives, the contact angle, and X-ray photoelectron spectroscopy measurements.Chemical mechanical polishing ͑CMP͒ using the alkaline slurry added with nanoscale colloidal silica abrasives is a key silicon wafer manufacturing process to planarize the surface topography on silicon wafers, i.e., stock polishing and touch polishing. The aim of stock polishing is to planarize the silicon wafer surface topography in the wavelength of approximately several tens of millimeters, while that of touch polishing is to planarize the silicon wafer surface topography in the wavelength between several micrometers and millimeters. 1-3 In general, touch polishing is done after stock removal. As the design rule of memory devices has decreased, the degree of surface roughness and the number of remaining particles on the silicon wafer need to be controlled more tightly. 4 To satisfy this restriction, the touch polishing of the silicon wafer has become increasingly important during the silicon manufacturing process because it is the final process that determines the surface qualities of the silicon wafer, such as surface roughness and remaining particles.Although many experiments on silicon wafer polishing have been done on electrochemical behavior, the removal rate, and the reduction in surface roughness, 1-3,5-7 there have been few reports on how to reduce the remaining particles on the silicon wafer. In our experiments, first of all, we developed the alkaline slurry added with colloidal silica abrasives, hydroxyethyl cellulose ͑HEC͒, and tetramethylammonium hydroxide ͑TMAH͒ for touch polishing. We selected HEC as a nonionic organic additive in the alkaline slurry because it reduces the silicon wafer surface topography via producing a nanoscale passivation on the silicon wafer surface during touch polishing. 2 Then, we investigated the effect of the HEC concentration in the alkaline slurries on the number of remaining particles and surface roughness of the polished silicon wafers after touch polishing.We used nanometer-sized colloidal silica ͑PL-3, Fuso Chemical Inc., Japan͒. The solid content of colloidal silica in each of the alkaline slurries was 10 wt %, and pH adjustment was carried out by adding TMAH. We then added HEC ͑Mw = 1,000,000͒ to each of the alkaline slurries from none to 0.4 wt %. The HEC chemical structure is shown in Fig. 1a. To estimate the slurry characteristics such as pH, conductivity, viscosity, c...

Effects of Hydroxyethyl Cellulose and Colloidal Silica Abrasive on the Hydrophilicity of Polished Si Wafer Surfaces

“…It has been shown that wafer surface protection using a polymer is effective for reducing defects and adsorption of particles. 3 The slurry creates a protective layer on the wafer surface and has been widely used in the final polishing step. Typical final polishing slurries contain watersoluble polymers that make a protective layer on the wafer surface and introduce hydrophilicity to the surface to avoid the adsorption of dried particles, which may originate from many substances, such as silica abrasives, silicon debris, and foreign contamination from environment.…”

“…Hydroxyethyl cellulose (HEC) is usually preferred as a hydrophilizing agent and many studies exploring the effect of HEC on wafer properties have been reported. [3][4][5][6][7][8] However, the hydrophilic properties imparted on the wafer by HEC during the polishing process have not been well documented.…”

Insight on Surface Changes Post Chemical Mechanical Polishing (CMP) of the Silicon Substrate by Adding Polyoxyethylene Ether

“…This result coincided with data from earlier reports. [10][11][12] We sought to further understand the different polishing performances obtained with slurries containing various surfactants. The slurries were characterized and the adsorption properties were evaluated using large particle count, contact angle measurement, XPS, FTIR, and SEM techniques.…”

Effect and Mechanism of Dual-Official Group of Ethanolamines on the Chemical Mechanical Polishing of Monocrystalline Silicon

“…26 During touch polishing, the formation of the passivation layer on the Si wafer surface is a key factor in improving the surface roughness. 27 Furthermore, there is an electrostatic repulsive force between the negatively charged colloidal silica abrasives and Si substrate in an alkaline region. We believe these combinational effects protect against the readsorption of colloidal silica abrasives and polished debris during touch polishing.…”