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Carbon Contamination

Material Name: Carbon
Record No.: 123
Primary Chemical Element in Material: C
Sample Type: Wafer
Uses: Contamination
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: Organic (H and C containing materials) contaminants arrive at wafer surfaces from diverse sources: (1) photo resist out gassing products as vapors and as de laminated particles from organic accumulation on beam line surfaces, (2) residue from "clea ning" products used in periodic maintenance of end station chambers, (3) out gassing and abrasion wear products from O rings and other seals, (4) elements from "vacuum lubricants" used on moving machine parts and (5) contact transfers from wafer "heat sink s" (which often contain metals and organic materials to enhance elastomer adhesion to wafer backsides and thermal conductivity).
In the example shown in Fig.1, a Teflon O ring seal on a gas cooled wafer fixture was over heated by the incident ion bea m and out gassed onto the wafer surface area. The ion beam then cross linked the organic residue onto the wafer surface.
Lubricants for moving parts throughout the implanter vacuum system can be an uncontrolled source of diverse elements, including many that are usually "bann ed" from use in IC fabrication. A survey of elemental composition in a variety of "vendor certified" lubricants ( Fig.12 4.10) shows many examples of high metal (Al, Zn) and alkali (Na, Ca, Li) elements. An additional complication is that lubricants that are approved for use for atmospheric conditions can be accidentally used as vacuum lubricants leading to excessive vapor pressures in vacuum and the presence of diverse and potentially harmful (to semiconductor devices) elements.

Reference: Michael I. Current, Heiner Ryssel, Chapter 12, Ion Beam Purity and Wafer Contamination, ResearchGate, 2018, https://www.researchgate.net/publication/330357088, p. 27.


Figure 1: Organic flow path (left) for an over heated Teflon O ring seal for a gas cooled wafer fixture and photo (r ight) of C residues cross linked by the incident ion beam on the wafer front surface

Table 1: Elemental analysis of a variety of "vendor certified" lubricants for ion implantation systems.