Xuan Bao Hao Corp

		印刷電路板
		醫療應用
		磁芯上的應用
		橡膠上的應用
		微電子/微馬達

聚對二甲苯的真空氣相沉積工藝不僅和微電子積體電路製作工藝相似,而且,所製備的聚對二甲苯塗層介電常數也低,還能用微電子加工工藝進行刻蝕製圖、進行再金屬化。因此,在積體電路微電子領域中不僅可用作防護材料,而且也能作為結構層中的介電材料和製作時的掩模材料使用。經聚對二甲苯塗敷過的積體電路晶片,其25μm 細直徑金連接線,連接強度可提高5～10 倍。近十年來,國外在多層積體電路和超大規摸積體電路(ULIC) 中不斷報導在使用該材料,SCS還開發了一種耐溫更高、介電常數更低的氟代聚對二甲苯為其配套,利用真空氣相化學沉積的工藝方法,對原材料進行改性,就是在對二甲苯環二體上引入氟元素,利用該成膜方法,合成具有優異的超薄防護性能和高頻介電性能。可使防護的微波電路的頻率提高到20 GHz 左右。。另外,由於聚對二甲苯低溫性能特別好, I. B.M 公司還用聚對二甲苯開發了一種能在液氮下工作的積體電路。

MEMS 作為超小型電子機械,要求使用的材料必須具有如下特性: (a) 能進行微米級微細製作和加工; (b) 在微細結構中仍具有優良的電性能和物理機械性能; (c) 與其他微細結構材料有很好的相容性;(d) 對微電子機械系統的使用環境有很好的相容性和防護性。聚對二甲苯能在0. 2μm 厚時就完全沒有針孔,5μm 厚就能耐1 000 V 以上直流擊穿電壓,又是摩擦係數很低的一種自潤滑材料,化學惰性和阻隔性能也好。因此,在微電子機械系統中,聚對二甲苯除了作電介質材料外,還用作微型傳動機構和微型閥門的結構材料和防護材料。國外在這方面發展較快,經常有研究論文發表。

聚對二甲苯在感測器領域中的應用,除了作絕緣介質外,更多是用作防護材料。聚對二甲苯能耐酸、堿和有機溶劑,對水汽和鹽霧等惡劣環境有極好的阻隔防護能力。用極薄的聚對二甲苯作防護塗層,可以在幾乎不影響感測器功能的情況下,為傳感器提供良好的防護。這一特性引起了感測器領域的極大興趣,至今國外已有四千萬以上各種感測器用聚對二甲苯防護,其中有汽車感測器、腐蝕環境用傳感器、生物醫學用感測器、聲學感測器等等。

MEMS (Microelectromechanical System), (also called Nanotechnology) represents the highest level of micro-integration yet devised. MEMS integrate Motion, light, sound, molecular detection, radio waves, and computation. All converge on an unusual chip array, many times smaller than a grain of sand.

Developments in the MEMS arena show that MEMS can be used as a DNA detector; that can sense if a DNA strand is defective. Some devices are so small that they could be injected into the human body. The day may come when micro-robots, or "Nanobots", travel through the body to clear arteries and make repairs, borrowing a scene from the classic 1960's science fiction movie Fantastic Journey. MEMS could also find military uses suggested by science fiction writers like Dean Smith who tells of battles between earth Nanobots and alien micro-machines in The Tenth Planet.

Current MEMS Products

There are only a handful of MEMS products on the market but we will see a large variety come to commercial fruition during the upcoming decade.

Accelerometers (Used with virtually all modern automotive airbags)
Micro-Mirrors (MOEMS) (Used in some digital projectors)

Parylene with MEMS

Friction and Stiction. A common problem with the development of MEMS and MOEMS is the problem of Friction or Stiction. Friction is common to all mechanical products, however in MEMS, traditional lubricants are not practical. Stiction is a surface effect problem that is somewhat unique to micromechanical devices. The tiny MEMS elements, once they make contact with one another, are held together by surface tension and atomic-level forces (Similar to static electricity).

Parylene as a Friction, Stiction Solution

Many experts agree that a solution to the friction/stiction problem lies in an organic coating with low surface energy and, perhaps, hydrophobic properties. The coating would need to be very thin and this is the realm for vacuum coating technology.

Given these parameters, a logical solution is Parylene. First, it is important to say that only a limited amount of study has been done in this cutting edge area of technology, but SCS is working with the industry to test several Parylenes including a newer non-stick fluorinated product. (Right: "Digital Light Processing for High-Brightness, High-Resolution Applications", Larry J. Hornbeck).

Parylene (poly-para-xylylene) is a high temperature polymer film applied to substrates in a vacuum chamber by means of a gas phase polymerization that provides unusual electrical and environmental performance. This class of polymer has been used for decades on a variety of applications, especially those involving the protection of electronic devices and circuitry. CVD is used to form an insulating thermoplastic coating with a high degree of chemical inertness, absence of pinholes and perfect conformity to the topography of the surface applied. Coefficients of friction range from 0.25 to 0.33 so that the lubricity is close to that of Teflon. The table below summarizes the attributes of value to MEMS/MOEMS.

Attribute	MEMS	MOEMS
Stress-free coatings	Yes	Yes
Thin contiguous film without pinholes	Yes	Yes
Inert	Yes	Yes
Even coating of sides and edges	Yes	Yes
Hydrophobic	Yes	Yes
Low surface energy (especially fluorinated Nova HT)	Yes	Yes
High temp. capability up to 500° C	Yes	Yes
Low k down to 2.28	Yes
Optically clear, UV resistant		Yes

In deposition, the Parylene gas polymerizes spontaneously on the surface of coated objects that are at ambient temperature with no stresses induced initially or subsequently. There are no cure-related hydraulic or liquid surface tension forces in the process. The mean free path is only about 0.1 cm so that sides and small openings are coated. A typical rate of 0.2m or less provides precise thickness control. Polymerization occurs in crevices, under devices, and on exposed surfaces at about the same rate to give a very uniform film. Parylene coating thickness can be as low as 100 Angstroms.

Parylene Issues

There could be some issues with Parylene according to the few researchers who have experimented with the organic coatings on MEMS. Thin coatings gave good anti-stiction results before packaging but control may be difficult. Anti-stiction performance was apparently good using standard Parylene but sealing the hermetic package can cause degradation. Two recommendations were given for Parylene on MEMS devices:

A well-controlled deposition process for very thin coatings.
Higher temperature stability to withstand ceramic packaging processes.

References

Mignardi, M., "From ICs to DMDs", TI Technical Journal, pp. 56 - 63, July - Sept. 1998 (http://www.TI.com).
Miller, W. M., "MEMS Reliability and Testing", IMAPS Packaging of MEMS Microsystems Workshop, Chicago, Oct. 23 - 24, 1999.
Howe, R., et al., "Silicon Micromechanics: Sensors And Actuators On A Chip," I.E.E.E. Spectrum, Vol. 27, No. 7, pp. 30-35, July 1990.
Sherman, S, et al, "Monolithic Accelerometer", US Patent 5,345,824, September 13, 1994. Martin, J. and Zhao, Y., "Micromachined Devices Packaged to Reduce Stiction", US Patent 5,694,740, Dec. 9, 1997.