Parylene deposition process

The process takes place in two stages that must be physically separate but temporally adjacent. Figure 1 presents a schematic of a typical parylene deposition process, also indicating the approximate operating conditions. 

The quantitative models developed enabled a thorough understanding of the parylene deposition process.Further, these models suggested several deposition parameters that could be varied to tailor the thin film deposition for various applications. They indicate that the rate of consumption of the monomer during propagation is much larger than that during initiation, and is determined primarily by the monomer partial pressure and the substrate temperature. Influence of these two parameters viz., pressure and substrate temperature will be discussed here. 

FIGURE 2.1.6 Reactions involved in parylene deposition process (top) sublimation of dimers at 100°C, splitting into monomers at 700°C, and polymerization at room temperature. Inexpensive system for parylene deposition (bottom) consists of a two-zone tube furnace and a 20-mm ID quartz tube containing parylene dimer powder and connected to a one-stage mechanical pump through a liquid nitrogen trap. A sample with prefabricated contacts and attached wire leads is placed in the tube at about 30 cm from the furnace. 

Fig. 4.8. A summary of the three steps of the parylene deposition process. Parylene-C is shown. First, the stable dimer is vaporized at approximately 170°C, and diffuses into the cracker, which is held around 700°C. The cracker breaks the dimer into two reactive monomer units which diffuse into the deposition chamber and condense into a fully reacted polymer at room temperature. Unreacted material is captured in a cold trap to protect the vacuum pump, and the deposition process occurs at approximately 10-50mtorr for parylene-C.

Paralene [para-xylene] Also called Gorham and also spelled parylene. A process for coating articles with poly-p-xylene. The vapor of di-p-xylylene is pyrolyzed at 550°C, yielding p-xylyl free radicals, -CHj-CgH CH, which deposit and polymerize on cooled surfaces. Developed by W. F. Gorham at Union Carbide Corporation. 

Chemical vapor deposition of polynapthalene differs from the parylene and polyimide systems in terms of the deposition process. As mentioned in earlier sections deposition of parylenes and polyimides occurs on cold surfaces, and the deposition rate decreases with increasing substrate temperature. In other words, deposition is done in a "hot wall" reactor. In contrast, CVD of polynapthalenes is performed in a "cold wall" reactor, meaning that the substrate is maintained at a high temperature ( 350°C) while the surrounding wall temperature is kept at near room temperature. A schematic of the CVD reactor setup employed by Lang et al. can be found in Ref. 28. 

Radio frequency argon plasma treatment of Parylene C surfaces is very attractive because two processes—Parylene deposition and plasma treatment—can be carried out in the same reactor, the Parylene reactor. It was found that radio frequency... 

The deposition process was then improved and commercialized by William Gorham at Union Carbide." Gorham used cyclophanes to increase the yield of polymers. In 1968 the licence was transferred to Para Tech Coating, Inc. which developed the process further. Meanwhile, Par-ylene is a trademark used by several companies. The history of Parylene is given in the internet. ... 

The surface of a porous poly(ether sutfone) membrane film can be modified by the deposition of a nanoporous parylene film [121], The addition of glycerin vapor during the deposition process of the parylene prevents the parylene from forming over the pores. So, parylene could be coated onto the poly(ether sutfone) membrane while keeping some pores open provided that the amount of dimer is properly controlled. 

Deposition techniques fall into two broad categories, depending on whether the process is primarily chemical or physical [130]. Chemical deposition processes include for instance chemical vapor deposition (CVD), Parylene-coating deposition and plasma-enhanced chemical vapor deposition (PECVD) or plasma polymerization. Physical deposition processes include mainly physical vapor deposition (PVD). 

Figure 20.24 Illustration of the Parylene vacuum deposition process. (Reproduced with permission from Para Tech...

Parylene process A polymer film deposition process where a monomer is passed through a heated zone where it is polymerized and the resulting polymer (Example polyparaxylyene) is then condensed onto a surface under very benign conditions. 

The linear polymer of PX, poly(p-xylylene) (PPX) (2), is formed as a VDP coating in the parylene process. The energetics of the polymerization set it apart from all other known polymerizations and enable it to proceed as a vapor deposition polymerization. 

The parylcne process has certain similarities with vacuum metallizing. The principal distinction is that truly conformal parylene coatings are deposited even on complex, three-dimensional substrates, such as on sharp points and in hidden or recessed areas. Vacuum metallizing, on the other hand, is a line-of-sight coating technology. 

Polymer Properties. The single most important feature of the parylenes, that feature which dominates the decision for their use in any specific situation, is the vapor deposition polymerization (VDP) process by which they are applied. VDP provides the room temperature coating process and produces the films of uniform thickness, having excellent thickness control, conformality, and purity. The engineering properties of commercial parylenes once they have been formed are given in Table 2. 

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