硅片上亚微米颗粒的去除方法

In order to successfully clean particulate contamination from wafer surfaces, it isnecessary to understand the adhesion and deformation between the particles and the substratein contact, The adhesion and removal mechanisms of deformed submicron particles have notbeen addressed in many previous studies. Submicron Polystyrene Latex particles (0.1-0.5 um)were deposited on silicon wafers and removed by spin rinse and megasonic cleanings. Particlerolling is identified as the major removal mechanism for the deformed submicron particles fromsilicon wafers. Megasonics provides larger streaming velocity because of the extremely thinboundary layer resulting in a larger removal force that is capable of achieving complete removalof contaminated particles.

Introduction

The adhesion and detachment of submicron particles from surfaces are of greatsignificance in semiconductor industry. Over 50 percent of' yield losses in integrated circuitfabrication are due to micro contamination on device wafers. As feature sizes continue to shrinktechniques to avoid contamination and processes to maintain clean wafer surfaces have becomecritically important. Effects to bring low-k polymer into future generation semiconductor devicewafers gives rise to the need of removing polymer particles from semiconductor surfaces. Inorder to remove particles, it is necessary to understand the adhesion and deformation betweenthe particles and the substrate in contact.

The classical solution of nonadhesive spheres was given by Hertz in 1881.' Derjaguinwas the first to consider the effect of contact deformation on adhesion.2 In 1971, JohnsonKendall and Robert extended the theory to adhering materials in contact using the surfaceenergy approach.3 This model was referred to as JK R theory, which considered the adhesionbetween the contact materials a variation of surface energy, i.e, that the attractive forcebetween them was of infinitely short range. Derjaguin, Muller and Toporov (later referred to asDMT theory) treated the long range van der Waals force as a body force and found that thedeformation of the particle was caused by the repulsive components of the interaction forces.JKR and DMT theories predicted different removal forces (pull-off forces) for a particle adhering on the surface.

The particle adhesion and removal experiments were conducted in the Class 10cleanroom of the Microcontamination Research Laboratory at Clarkson University. ThePolystyrene Latex particle of 0.1-0.5 um in diameter (Duke Scientific Inc.) were immersed inIPA solution and then deposited on silicon wafer surfaces by spraying the contaminated IPAsolution onto the wafers using a nozzle. Wafers were immediately cleaned using a quartzMegasonics tank (made by PCT, Inc.) with a frequency of 760 kHz and a maximum inputpower of 640 Watts (intensity of 7.75 W/cm') and a spin rinser made by Headway ResearchInc. with maximum rotation speed of 7500 rpm. A laser surface scanner made by ParticleMeasuring Systems, Inc. was used to scan and determine surface particle counts in theexperiment. The scanner has a minimum resolution of 0.l ym and a size range of 0.l um to 10μm.Particle removal efficiencies were obtained by dividing the differences of post-cleaning and pre-cleaning particle count by pre-cleaning count. Additional experimental data for rotating rinse and megasonic cleaning were obtained from Ref. 28.

Results and Discussion

The Adhesion Forces

Solid surfaces in water become charged due to the adsorption of ions or dissociation ofsurface groups. Zeta potential of PSL particles is measured as negative from pH 3-12 rangeAt the pH of water, the silicon surface with a native oxide has a negative zeta potentialTherefore, the electrical double-layer force is repulsive in nature between a PSL particle andthe silicon wafer in water. The DLVO model (after Derjaguin, L andau, Verway, and Overbeek)combined electrical double-layer repulsion and van der Waals attraction to explain the colloidalinteraction. The van der Waals force is dominant in short separation distance (4 to 20A) whilethe electrical double-layer force controls the interaction at larger distances. Therefore, only vander Waals interaction will be considered in this study.