Vapor Deposition Of Anti-Stiction Films And The Equipment Used For That Purpose.

1. Vapor Deposition Of Anti-Stiction Films And The Equipment Used For That Purpose. hightechservices.com

2. High Tech Services, Inc. (HTS) was founded in 1983 for the purpose of providing engineering services to the semiconductor industry. During the late 1980's we began moving more into the design and manufacturing of specialized equipment that we built for specific process applications. Primarily our focus has been on vacuum equipment that is used in semiconductor manufacturing. hightechservices.com

3. In the early 1990's we engaged with various companies involved in the manufacturing of MEMS devices. It became apparent early on that one of the handicaps of MEMS manufacturing is a phenomenon called Stiction, defined as "sticking friction". This is where two micro surfaces come in contact with each other, they stick together and cannot be unstuck. This is a common problem with MEMS components that have a high ratio of the contact area to the mass of the part.

4. One type of MEMS device that is particularly vulnerable to stiction is the micro mirror. It has a very high ratio of surface area to mass.

5. The industry accepted practice to prevent failures due to stiction, is to apply an anti-stiction coating to the device. This coating is applied after manufacture but before packaging. The most widely used, and industry standard, of these anti stiction coatings is Perflourodecanoic acid also known as PFDA. CF3(CF2)8COOH

6. PFDA is associated with the group of chemicals called perflourocarbons (PFC’s are long CF2 chains) and is a pefluorocarbon derivative because it has additional molecules to the CF2 chain much like PFOA . On one end of the PFDA molecule is the Reactive molecule (COOH) and the other end is the non reactive molecule (CF3). In between is the long chain of non reactive CF2 Molecules.

7. When PFDA is deposited, the reactive end of the molecule (COOH) is attracted to and will attach to the aluminum substrate by chemisorptions where strong mechanical bonds are formed . The Fluorine (F3C) at the functional end will not stick to the surface and the molecule will stand up. All of the molecules will continue to form in this manner. This type of film formation is called Self Assembled Monolayer's or SAMS. With the functional F3C molecule becoming the new surface. Because it is resistant to interfacial forces such as capillary and van der Wals forces, this coating will have become an anti-stiction surface. Substrate

8. The key to making these coatings work is to deposit a single layer of molecules, no more, no less. This is called a MONOLAYER. CF3 “Functional” (8)CF2 “Tail” COOH “Head”

9. When you begin deposition, the molecules are attracted to the surface and attach themselves individually through chemical bonding. CF3 COOH

10. If the deposition is too slow or incomplete, voids will be left in the film. Over time these voids can grow large enough that impact points will contact each other and stick, causing premature device failures.

11. If the deposition is too fast, or too thick, the PFDA will tend to pile up in spots and have a sticking effect much like jelly would.

12. If done correctly a perfect monolayer of PFDA will form. These molecules will also be attracted to all surfaces to form a conformal coating. The HTS systems provides the precise process control that allows depositions of one monolayer films with exacting repeatability.

13. With two substrate surfaces coated, the long chains of the attached molecules prevent stiction forces between the surfaces.

14. It has been shown that PFDA monolayers deposited with this technique exhibit surface films with a coefficient of friction (CoF) of .026 and it is well documented that perfluorocarbon chains have a CoF of .04.

15. HOW THIS IS ACCOMPLISHED. The fluorine chemicals come in the form of a powder and look similar to table salt. In order to apply them to the MEMS surfaces you first need to melt them at elevated temperatures, turn them into a vapor, and expose the substrate to the vapor.

16. In 1997 we began working on the vapor deposition process and in 1999 we produced our first anti-stiction deposition system; the model 8100. This design accepts single wafers up to 200 mm in three separate chambers. Patented Since 1999 we have delivered a total of 17 of the Model 8100 systems to the world’s largest MEMS manufacturer.

17. In 2003 we began development of our model 9100 deposition system and delivered the first production system in 2004. It is designed to accept a cassette of up to 24 – 200mm wafers. Patented Since 2004 we have delivered a total of 15 of the Model 9100 systems to the world’s largest MEMS manufacturer .

18. This shows a simplified schematic of our deposition systems with the basic components.

19. Before depositions begin the vapor source is filled with the precursor and heated under vacuum until the predetermined temperature and vacuum level is reached. This is called charging the source. One charge of material should last for 700 to 800 runs in the 8100 system and up to 200 runs in the 9100.

20. To begin the process, the wafers are loaded into the chamber and the operator would press the start button. At this time the computer controls the process. The program will open the exhaust valve and pump down the chamber to a user selectable vacuum level. Next the exhaust valve is closed and the delivery valve is opened. The PFDA vapor enters into the chamber and film formation begins. This continues until a predetermined pressure level is reached, then the delivery is stopped. After a user selectable soak time the chamber is pumped and purged quickly to stop film formation and to purge out any remaining PFDA vapor. At this time the chamber is vented and the substrate is unloaded.

21. By controlling the pressures, temperatures, and flows precisely a single monolayer can be produced with exacting repeatability.

22. HTS 8100 Anti-Stiction Vapor Deposition System patented

23. Model 8100 Dual Sources and Delivery Manifolds

24. Chamber Manifolds

25. Process Chamber

26. Sophisticated Computer Process Interface

27. Typical cleanroom installation

28. HTS 9100 Anti-Stiction Vapor Deposition System Patented

29. 9100 Vapor Source

30. Delivery Manifolds

31. Process Chamber

32. Vapor Recycling Trap. For recovery and recycling of up to 99% of the PFDA without waste.

33. Sophisticated Computer Process Interface

34. On April 11, 2011 – The United States Patent and Trademark Office (USPTO) awarded High Tech Services the patent No. 79274423 for the method of VAPOR DEPOSITION OF ANTI-STICTION LAYERS FOR MICROMECHANICAL DEVICES. With more than 30 production systems being shipped into MEMS manufacturing facilities over the past 10 years and with over 50 million MEMS devices processed in our systems it is clear that High Tech Services, Inc. is the industry leader for the deposition of anti-stiction coatings.

35. For more information Contact Ken Abbott High Tech Services, Inc. 999 E. Arapaho Richardson, Texas 75081 Phone 972-690-0901 hts@applink.net

36. Benefits of the HTS 8100 and 9100 Vapor Deposition Monolayer Process • Conformal coating of every surface in the device. • Uniformity across all surfaces. • Repeatability from run to run. • Negligible PFDA loss to environment or scrubber systems with Vapor Recovery Trap. • Real production capability. • More controlled and simplistic with fewer particulate issues than liquid processes. • Application is at lower temperatures (108c) than Diamond Like Coatings (400c), or AlMg Coatings (1000c)