金属氧化物中有机污染物的影响

Adverse infuences of organic contaminants on electronic devices have been studied and the results are reported. Contamination ofsilicon wafers by organic compounds during their manufacturing processes has been clearly demonstrated by a few surfaceanalytical techniques. Silicon wafers were intentionally contaminated by one of the major contaminants, bis(2-ethylhexyl) phthaate: its incorporation into the silicon oxide layer during the thermal oxidation of silicon and its influences on device performanceshave been evaluated in detail by monitoring the breakdown voltages. During thermal oxidation of the contaminated silicon surfacethe atomized carbon species produced from the pyrolysis of organic contaminants help grow the oxide thicker, expand the silicoroxide latice, and degrade the silicon oxide, which was shown by transmission electron microscopy and secondary ion massspectroscopy, and finally exert adverse influences on the device performance.

As the device size decreases, metallic impurities,as well asorganic contaminants, on silicon wafer surfaces have been found toexert increasingly harmful influences on the performances of varioussemiconductor devices.Organic contaminants are particularlymore difficult to classify or control than the others, such as metaimpurities or particulate matters, because of their ubiquitous con-tamination from all sources of manufacturing facilities.8.9 They arisefrom outgassing operations of clean room facilities (filters, sealantswalls, floor tiles, etc.), the manufacturing processes (polishing residues, cleaning solutions, etc.), human operators (garments, glovescosmetics, etc.), and the wafer package materials (plastic packages.polyethylene bags, tapes, silica gel, etc.).When silicon wafers are exposed to the various environmentssemivolatile organic compounds are adsorbed onto their surface.These organic compounds have boiling points of 250-400°C withmolecular weights ranging from 200 to 500. Especially, bis(2ethylhexyl) phthalate (this compound is a derivative of diocthyl phthalates and is generally abbreviated as DOP: see Fig. 1) and dibutylphthalate (DBP) used as plasticizers are shown to be the indicatorsof organic contamination because of their non- or low volatility and.10,11 Figure 1 depicts thestrong adsorption onto the silicon wafer.molecular structures of these two organic contaminants, DBP andDOP!2 They have many oxygen atoms and planar aromatic ringsand, thus, induce strong hydrogen bonding with hydroxyl groups orsilicon hydrides on the wafer surface, along with additional van derWaals interactions with silicon atoms.Thus far, studies of a few organic contaminants on silicon wafershave been carried out by identifying contaminants by thermaldesorption-gaschromatography/massspectroscopy(TD-GCMS),13,14 time-of-flight secondary ion mass spectroscopy (SIMS),1X-ray photoelectron spectroscopy,’ and Fourier transform-infrared'The phenomenon has been explained by postulatedspectroscopy.degradation mechanisms but the causes of the device failure due tothe organic contamination have not been experimentally studied.

In this study, we focus on how the organic contaminants inducethe device failure. We first describe the results of surface analysis ofthe wafers contaminated by the TD-GC/MS method as well as byimaging contaminated surfaces using scanning electron microscopyenergy-dispersive spectroscopy (SEM/EDS) and atomic force mi-croscopy (AFM). We then show the influences of the organic con-taminants incorporated into the oxide layer during metal-oxidesemiconductor (MOS) processing on device performances by measuring breakdown voltages (BVs). Finally, we present the originand mechanism of the device failure obtained by transmission electron microscopy (TEM) and SIMS.

Experimental

Sample preparation.- The p-type Si(100) wafers (8 in. diam-eter) having a 10 12 cm resistivity were used for all experiments inthis study. Prior to each experiment, the wafers were cleaned using anormal cleaning procedure successively with cleaning solutions.SC-1 (NHOH:HO,:HO,1:2:20 v/v ratio) and SC-2 (HCI:H,O:H,O, 1:2:20 v/v ratio).18 The cleaned wafers were then dried andstored in a plastic storage box (Entegris).Analysis of organic compounds. A thermal desorption systemand a cryogenic unit (both GL Science) were used to desorb, collect.and concentrate organic compounds adsorbed on the silicon waferby the outgassing procedure, and GC/MS (Agilent) was used for thequantification of the organic compounds thus collected.Organic contamination by exposure in a clean room.- The clean-ed and dried wafers were left in the clean room (Clean class 100) for30 days so that their surface would be contaminated by variousorganic compounds. The size distribution of organic contaminantparticles was measured by a laser scattering topography detector(Mitsui Mining and Smelting), and their shapes and geometric con-figurations were confirmed by SEM (Seiko) and EDS (Thermoelec-tric). Their morphologies were examined by AFM (Seiko).