Realization of an ultraclean Si wafer surface is essential for achieving the advanced process in the ultralarge scale integrated production such as low-temperature process and high selectivity. An ultraclean wafer surface is defined as a surface completely free from particles, organic impurities, metallic impurities, native oxide, surface microroughness, and adsorbed impurities. Since metallic impurities, one of the above contaminants, cause fatal damage to device characteristics, metallic impurities on the wafer surface need to be suppressed at least below 10 l~ atom/cm 2 which is the level of the detection limit of total reflection x-ray fluorescence. The current dry processes such as ion implantation and reactive ion etching cause metallic contamination of 1012 to 1013 atom/cm 2. In order to remove the metallic contamination, the wet cleaning process plays an increasingly important role. When organic impurities remain on the wafer surface, native oxide and metallic impurities on the wafer cannot be completely removed. In order to establish an ultraclean wafer surface, therefore, it is crucial to remove organic impurities first of all. The wet cleaning process is the only possible method at present to remove trace organic contaminants on the wafer surface. We have studied the segregation and removal of metallic impurities on the solid/liquid interface between chemicals and various Si wafer surfaces (p, n, p+, n+). We tested several chemicals employed in the process to remove oxide on the Si surface. Metals featuring high electronegativity (such as Cu) are directly adsorbed on the bare Si surface while taking electrons away from the Si surface. It has been found that these metals are hard to remove. We used Cu as being representative of metals to be directly adsorbed on the bare Si surface and studied its segregation and removal on the solid/liquid interface between Si wafer and chemicals to keep the Si surface bare such as DHF, DHF-H~O2, and BHF. It has been found that Cu ion in DHF adheres on every Si wafer surface that we used in our study (p, n, p § n § especially on the n+-Si surface. The DHF-H202 solution is found to be effective in removing metals featuring high electronegativity such as Cu from the p-St and n-St wafers. Even when the DHF-H202 solution has Cu ions at the concentration of 1 ppm, this solution is found effective in cleaning the wafer. In the case of the n*-Si and p+-Si wafers, however, their surfaces get contaminated with Cu when Cu ion of 10 ppb remains in the DHF-H203 solution. When BHF is used, Cu in BHF is more likely to contaminate the p-St, n-St, and p+-Si wafers but is less likely to contaminate the n*-Si wafer. It is also revealed that the surfactant added to BHF to improve its wettability onto the Si wafer is effective in preventing Cu precipitation onto the p-St, n-St, and p*-Si wafers. This effect of the surfactant, however, is not observed on the n+-Si wafer. It is found also that the surface microroughness on the n § wafer is increased when it is immersed in the DHF-H202 soluti...

The adhesion of fine particles onto bubbles in flotation was studied on the basis of surface charge measurement3 of the bubbles and particles.The surface charges of the bubbles were measured by the use of a micro-electropheresis apparatus devised in our previous study and the mechanism of the bubble charging was studied under various experimental conditions. In distilled water, the bubbles were negatively charged and the iso-electric point appeared at pH = 2.5. The surface charges of the bubbles in the surfactant solution were determined by the surfactant molecules adsorbed at the surface and depend strongly on the values of pH.The flotation efficiency of latex particles (0.923 pin) was found to be strongly influenced by the surface charges of both the particles and the bubbles. The force between the particle and the bubble was estimated from the observation of the particle attachment to the bubble surface, and a simple equation including the effects of the hydrodynamic and surface charge interactions was proposed to determine the floatability limit.L'adhCsion de particules fines dans des bulles en tlottation a Ct C etudiee sur la base de mesures de charge de surface des bulles et des particules.Les charges de surface des bulles ont kte mesurees au nroyen d'un appareillage de micro-dectrophorese c o n y danr nos etudes anterieures, et on a Ctudit le mecanisme de chargement des bulles dans des conditions experimentales variees. Dans de I'eau distillte, les bulles ont CtC chargees negativement et le point iso-blectrique est apparu au pH de 2.5. Les charges de surface de bulles dans la solution de surfactant ont ttC dkterminees par les molkcules de surfactant adsorbkes B la surface et elles dCpendent fortement des valeurs du pH. On a trouve que I'effcacitC de flottaison des particules de latex (0,923 pm) Ctaient fortenient influencee par les charges de surface a la fois des particules et des bulles. La force entre les particules et les bulles a cte estimee 2 partir de I'observation de la liaison des particules a la surface des bulles, et on propose une equation simple incluant les effets des interactions des charges de surface et de I'hydrodynamique pour determiner la limite de flottabilitk.

To manufacture ULSI devices with high performance and reliability in large volume, further integration and miniatur: ization are being promoted. The key issue in realizing what we call "Noise-Free Manufacturing" is to keep the wafer surface ultraclean all the time. To realize the ultraclean wafer, organic impurities adsorbed on the wafer surface must be removed first before other wafer cleaning procedures. This is because native oxide and metallic impurities on the wafer

The trajectory of a small particle moving to a bubble surface was analyzed by taking into account the effects of surface charges of the bubble and particle and the short range hydrodynamic interaction near the bubble surface, in a flotation process. The particle trajectories obtained theoretically were in good agreement with those obtained by direct observation. Even if the signs of the surface charges of the bubble and particle were the same, the particle adhered to the bubble surface when the net surface force, that is, the sum of the electrostatic force and the van der Waals force, was attractive. Particle capture efficiency, vs, per bubble was estimated by trajectory analysis and the flotation efficiency, qT, was calculated. The values of q calculated by the particle trajectory analysis were in reasonable agreement with those obtained experimentally. The dependence of particle diameter on q T was also examined by the particle trajectory analysis.~~ ~~~~ ~. . . ~~ ~~~~ On a analyse la trajectoire d'une petite particule se dtplaFant vers la surface d'une bulle en tenant compte des effets des charges de surface de la bulle et de la particule ainsi que de I'interaction hydrodynamique h courte distance pres de la surface de la bulle, dans un processus de flottaison. Les trajectoires de particules obtenues de maniere thdorique montrent un bon accord avec celles obtenues par observation directe. M&me si les signes des charges de surface de la bulle et de la particule sont identiques, la particule adhere B la surface de la bulle lorsque la force de surface nette, a savoir la somrne de la force Clectrostatique et la force de van der Waals, est attractive. L'efficacitt de capture des particules, q5, par bulle, a CtC estimCe par l'analyse de la trajectoire et I'efticacite de la tlottaison, v T , a CtC calculee.Les valeurs de q r , calculee par I'analyse de la trajectoire des particules, concordent raisonnablement avec celles obtenues expkrimentalement. La dipendance du diametre de particule sur q a Cgalement Ctt examinCe par l'analyse de la trajectoire des particules.

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