Makiko Tamaoki

The effect of airborne contaminants in the cleanroom for ULSI manufacturing process

In this paper we report on the effect of airborne organic contaminants in actual cleanrooms. We have developed methods for the analysis of contaminants adsorbed on wafer surfaces, including thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and thermal desorption-atmospheric pressure ionization mass spectrometry (TD-APIMS). From the results of analysis using TD-GC/MS, TD-APIMS, and ion chromatography (IC), we demonstrate that several specific organic compounds in cleanroom air tend to adsorb on silicon wafers. These include dioctyl-phthalate (DOP), other esters, and amines. We have also found that these organic contaminants adsorbed on the wafer surface cause a reduction in the breakdown field strength of an insulating SiO/sub 2/ layer. The origin of DOP and the other esters is the plasticizer added to many polymeric materials. DOP exists in the cleanroom inlet atmosphere, and there are additional outgassings from many polymeric materials in the cleanroom itself. The major source of amine contaminants is chemicals added to the steam which is used for humidity control in the cleanroom. We show that organic contaminants from the wafer carriers and boxes also cause a reduction in the breakdown field strength of a SiO/sub 2/ layer. We also succeed in decreasing organic contaminants by use of adopting charcoal air filtering.

Quantitative Secondary Ion Mass Spectrometry Analysis of Carbon and Fluorine Impurities on Silicon Wafers Stored in Polymer Carrier Cases

We have investigated the carbon and fluoride contaminants on silicon wafers during their storage in quartz-glass boxes equipped with carrier cases made of either polypropylene (PP), polybutylene-terephthalate (PBT), or perfluoroalkoxy polymer (PFA). The adsorbed organic contaminants on the wafer surfaces were identified by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). The concentrations of contaminants on the wafer surface have been measured as a function of wafer storage positions as well as carrier case storage time. For quantitative analyses, secondary-ion mass spectrometry (SIMS) combined with the encapsulation method was employed, and carbon (12C-) and fluorine (19F-) ions were detected. It has been found that the amount of adsorbed contaminants on the surface of silicon wafers depend on both the wafer storage conditions and the carrier case materials.

Novel model of haze generation on photomask

ArF lithography sometimes generates the haze defects on the photomask substrate, resulting in serious yield deterioration in ULSI production. In order to solve this problem, experimental and theoretical studies have been carried out on the generated haze defects. In characterizing the haze defects, the composition and chemical structure of the haze defects were analyzed by focusing on 1.0 x 0.3μm sizes defects using Raman, ToF-SIMS and AES spectroscopy with their highest spatial and mass resolution level. To confirm the experimental analyses, theoretical ab initio molecular orbital calculations were carried out on the model compounds of the generated haze defects. These experimental and theoretical studies indicate that the haze defects on quartz surface consist of (NH4)2SO4 and that those on half-tone (HT) film surface, on the other hand, consist of (MoO3)x(SO4)y(NH4)z complex including Mo from HT film material. In the latter case, NH4 ion was observed only in surface region of the haze defects. Based on these results, we have proposed a novel model of haze generation mechanism on quartz and HT film surfaces of photomask substrate.

Investigation into behavior of mobile ions in storage device using ToF-SIMS

Diffusion behavior of mobile ions in the memory device was successfully visualized as 3D mapping by using ToF-SIMS. In order to realize, we were mainly prepared two kinds of samples. One is a sample written a simple stripe pattern, the other is a sample written a stripe pattern with a density difference. By burning these samples, we were able to estimate the three-dimensional diffusion behavior of the mobile ions. In the temperature range used as usual devices, only Na should be careful because of the large diffusion coefficient and other elements are considered to have little electrical influence.

Carrier Profiling Technology in Ten Nanometers Devices

The advanced carrier concentration evaluation scheme was proposed with combined higher precise scanning spreading resistance microscopy (SSRM) measurement and technology-CAD (TCAD) analysis in this paper. The cyclic contact (CC) method was applied to variation reduction of SSRM resistance to more accurately characterize for the device. The CC method suppresses dust generation. The variation of resistance with the CC method decreased drastically less than 10%. SSRM resistances were corrected to obtain the potential drop in the probe and other resistance component in the measurement system using TCAD analyses. The effective contact probe tip radius was derived from TCAD analysis. The optimization of both sample and measurement conditions were obtained before the actual measurement. The electrical phenomenon in the device measurement can be known by the TCAD analysis. The SSRM measurement of advanced flash memory was successfully demonstrated with adapted these technologies. This result suggests strongly that 10 nm order size device can be measured by using SSRM with the CC method.

Development of DAF (Die Attach Film) with functional gettering agent for metal impurities

Gettering effect which is to trap metal ions on the dangling-bonds located far from the device area is widely known as an inhibition way of this problem. Extrinsic Gettering (EG) method that is formed during back side grinding in the wafer thinning process is one of the most significant technologies considering of reducing cost. However the chip strength has been decreased with increasing the roughness derived from crystal defect. Under these circumstances, we focused on the DAF (Die Attach Film) which is commonly used as an adhesive sheet to stack thin chips and attempted to add a functional gettering agent in this film. We selected Inorganic Ion-Exchange materials as a gettering agent and prepared some samples which have Oxidized Sb for gettering agent. From the result based on this study, the main factor determining gettering effect is an amount of substance of Ion-Exchange materials in the DAF. Its also estimated the quantity of Cu ion adsorption was about 33~50% in the whole of trapped Cu ions in the DAF. And we obtained 38 % Cu ions were adsorbed in the DAF with 10um thickness, which is about 68 % compared to the value from #2000.