Backside Damage Research Articles

Plasma immersion ion implantation for ULSI processing

With a high ion-density plasma produced by electron cyclotron resonance (ECR) sources, the space charge region between the plasma and a negatively biased target can sustain a potential difference up to 50 kV, with an implantation flux as high as 10 16/cm 2 s. Other unique features of this plasma immersion ion implantation (PIII) technique include: no ion mass selection, no beam transport optics, and the ion energy and angular distributions controlled by the plasma gas pressure and the applied bias waveforms. By adding a sputtering electrode into the plasma which is powered by a separate voltage supply (i.e., a triode configuration) the implantation chamber can also be converted into an ion-assisted physical vapor deposition system. In this review paper, we outline the physical mechanisms and operation modes of PIII and discuss applications of PIII's unique features for ultra-large-scale integrated circuit fabrication. Recent successes of using PIII for conformal doping of nonplanar device structures, sub-100-nm p +/n junction formation, backside damage impurities gettering, and selective electroless plating of metal interconnects are presented.

Gettering mechanisms in silicon

Various procedures for heavy metal gettering in silicon p-n junctions have been compared in order to test the effectiveness of dopants and extended defects as getter sites; the role of silicon interstitials in the gettering process has also been studied. It has been found that only phosphorus and boron atoms are effective getter sites, while arsenic and antimony are not; such gettering effectiveness is independent of the presence of extended defects in the heavily doped regions. During a moderate temperature annealing (segregation annealing) dissolved metal impurities diffuse from the space-charge region of the devices and segregate at getter sites. Extended defects generated by oxygen precipitation and stacking fault backside damage have some ability to capture metal impurities, but electrical tests show that they do not provide a satisfactory gettering technique. The role of self-interstitials consists of increasing the dissolution rate of metal precipitates with subcritical radii, so that the segregation of metal impurities into getter sites is made easier; however, a complete gettering process requires three steps, that is: (1) the creation of effective getter sites; (2) the dissolution of metal precipitates; (3) the segregation of dissolved metal impurities at getter sites. Some of these steps may be activated simultaneously.

Comparison of Gettering Techniques by Means of Intentional Quantitative Cu Contamination

Gettering is a very important technique for the LSI process. The effects of gettering techniques such as intrinsic gettering (IG), backside damage (BD), and polysilicon gettering (PG) were investigated by the MOS c-t method after intentional quantitative Cu contamination. These three techniques showed different gettering behaviors in the heat treatments simulating a device heat process. IG and BD were not effective in the beginning of the heat process, but they began to show stronger gettering effects with heat treatments and gained sufficient abilities. The IG kept its effect until the end of the heat process, but BD's effect decreased with subsequent heat treatments. PG had a sufficient gettering effect from the beginning of the heat process, but PG also showed a decrease of gettering effect at the end of the heat process.

Laser induced backside damage gettering : G. E. J. Eggermont, R. J. Falster and S. K. Hahn. Solid St. Technol. 171 (November 1983)

Laser induced backside damage gettering : G. E. J. Eggermont, R. J. Falster and S. K. Hahn. Solid St. Technol. 171 (November 1983)

CW Backside Laser Gettering

ABSTRACTA variety of backside damage techniques are available for gettering heavy-metal contaminants in silicon wafers. These include mechanical damage, ion implantation, thin film deposition, and pulsed–laser surface melting. In each case, strain fields and microscopic defects induced by the processing trap impurities as they diffuse through the wafer during subsequent high–temperature processing steps. We examine the defect structures produced by CW laser gettering, describe the dependence of gettering efficiency on wafer oxygen content and processing conditions, and demonstrate that CW laser processing can be an effective gettering technique even when the number of laser scan lines is reduced to make wafer processing acceptably rapid.

Reduction of Defects in Ion Implanted Bipolar Transistors by Argon Back Side Damage

The effectiveness of argon backside implants on the reduction of defects in an implanted bipolar process has been investigated. Insertion of an argon backside implant at two places in the processing sequence has been found to be beneficial. A backside implant before initial oxidation of the wafers will minimize the density of epitaxial defects for both arsenic diffused or implanted buried layers. For diffused buried layers, the backside damage offers only minimum improvement in yield because of the gettering action of the diffused arsenic itself. For implanted buried layers, the backside damage allows for higher arsenic doses and shorter etch‐back prior to epi growth, resulting in lower sheet resistance while still maintaining acceptably low defect levels. Correlation of electrical parameters and crystal defects showed that small defects in the emitter, probably dislocations generated by the implanted emitter process are responsible for “piped” transistors, leaky base emitter junctions, and poor low current beta. An argon backside implant just prior to emitter processing will reduce the density of these small defects and improve device yield.

Characterization of Laser Induced Backside Damage for Gettering Purposes

ABSTRACTA characterization of Q-switched Nd-YAG laser induced backside damage in various stages of a bipolar process is presented. TEM-analysis shows the occurence of microcracks, low angle boundaries and dislocations in as-irradiated wafers, of which the microcracks anneal out during an initial oxidation at 1050°C. The other damage is very stable and remains even after a heat treatment at 1200°C. This is quite in contrast with mechanically or Ar implantation induced backside damage, which anneal out completely at such high temperatures. Side effects of laser induced backside damage such as surface roughness and influence on wafer strength are found to be of no consequence within a limited range of laser pulse energy densities where the gettering efficiency is found to be very promising.

(Invited) Wafer Bow and Warpage

Initial Si wafer bow origin, and the relation between initial wafer bow and heat cycled wafer warpage were studied systematically through looking at crystal growth, from wafering process to heat cycle conditions. Initial bow and heat cycled warpages were studied from the view point of their sign and type, and their state was characterized as being of a non-elastic, elastic or plastic wafer deformation nature. Several instruments were used including a newly developed one. Initial wafer bow is seen to originate from initial slicing blade rim bending. Heat cycled warpage a fixed wafer buckling form, caused by dislocation generation and multiplication. Wafer warpage is thus seen to be affected by residual backside damage, oxygen concentration, and oxygen precipitation.