Metallic Impurities Segregation at the Interface Between Si Wafer and Liquid during Wet Cleaning

Abstract

It is crucial to make Si wafer surfaces ultraclcan in order to realize low-temperature processing and high-selectivity in ultralarge scale integrated production. The ultraclean wafer surface must be perfectly free from particles, organic materials, metallic impurities, native oxides, surface microroughness, and adsorbed molecular impurities. Metallic contamination, the major type of contaminants to be overcome, has a fatal effect on device characteristics and must be suppressed to at least below 10 ~~ atom/cm ~. The current dry' processes, such as reactive ion etching or ion implantation, cause metallic contamination as high as 10~-10 ~: atom/cm-. The wet process becomes increasingly important to remove these metallic impurities introduced during dry processing. Employing a new evaluation method, the metallic impurity segregation at the interface between the Si wafer and the liquid in the wet cleaning process was studied. It has been found that metals, such as Cu having higher electronegativity than Si, are directly adsorbed on the Si surface by taking an electron from the Si. On the other hand, metals, such as Fe and K having lower electroncgativity than Si, are not adsorbed on the Si surface. In the normal wet cleaning process when a native oxide is formed on the Si surface, metals such as Fe and K that are oxidized more easily than Si, are preferentially included into the native oxide. When the metals are in ultrapure water or chemicals with a concentration of 1 ppb, they are included into the Si surface, and native oxide with evaluation was 10~2-10 ~: atom/cm 2. Therefore, to decrease the metallic contamination level on the Si surface to levels less than 1 • i0 ~~ atom/cm 2, the metallic impurities must be suppressed to at least below the 1 ppt level in ultrapure water and high-purity HF, which are employed in the final step of the cleaning process. To prevent the metallic contamination on the wafer surface, it was found that it is important to maintain an inert atmosphere, such as N2 or Ar, to suppress native oxide growth and to reduce metallic impurities in the ultrapure water rinse. Moreover, it has been found that the diluted HF-H~O2 cleaning is effective in removing metals such as Cu, having high electronegativity, from the Si surface at room temperature and that it does not induce surface microroughness. This means the diluted HF cleaning, which has been employed in the final step of the conventional wet cleaning process to remove the native oxide, needs to be replaced with the diluted HF-H2Q cleaning, tt was also found that surfactants added to improve the wettability of chemicals on the Si surface were also able to prevent metallic impurity precipitation on the wafer surface.As the ultralargc scale integrated (ULSI) device featuring increasingly finer patterns is further integrated, it is becoming more critical to keep the Si wafer surface ultraclean in order to improve the device reliability and performance. The establishment of the advanced process technology requires the perfect control of the Si-g...

Surface reactivity of Si nanowires

“…The Si wafer can not reduce the metal ions in the solution except in the presence of HF in the solution. 25,26 However, interaction of SiNWs with metal ions in solution is a complex surface electrochemistry system. Although a plausible reaction mechanism can be deduced by the reaction products, the reaction mechanism needs to be confirmed by further studies.…”

Etching Kinetics of Silicon Dioxide in Aqueous Fluoride Solutions: A Surface Complexation Model

“…As already noted above, the available literature on anion adsorption on oxides45'5456'6° suggests that for silicon dioxide, log K,F 6. Figure 10 shows the fluoride-containing species with the silicon dioxide surface can be described as follows SiOH + HF = SiF + H20 [39] SiOH + HF = SiF + HF + 0H [40] SiOH + F = SiF + OW [41] According to Eq. Also, the bulk-aqueous-phase fluoride speciation is such that as pH is increased (at constant total fluoride concen-2 tration), the HF species is initially predominant, but then declines as the HF concentration increases.…”

“…First, it increased the bulk-aqueous-phase concentration of fluoride-containing species; this increased the surface concentration of adsorbed fluoride (Eq. [39][40][41]. Second, the increase in NH4F concentration increased the pH as a result of the partial protonation of the fluoride ion F+W=HF [43] This increase in pH and the corresponding increase in the OH-concentration would be expected to decrease fluoride adsorption, as discussed above (Eq.…”

In-Line Copper Contamination Monitoring Using Noncontact Q-VSPV Techniques

“…In the experiments with deliberately contaminated silicon, copper was adsorbed onto the silicon surface by exposure to diluted hydrofluoric acid ͑HF 4%͒ spiked with copper from a properly diluted AAS standard solution ͑concentration range 0-256 ppb, 10 min exposure at 21°C͒. 14,15 The amount of copper adsorbed on the silicon surface was determined by vapor phase decomposition droplet collection total reflection X-ray fluorescence ͑VPD/TXRF͒ measurements or direct TXRF. d Copper in-diffusion and surface passivation was accomplished by oxidation in a quartz furnace.…”