Stealth Dicing Technical Information for MEMS

1 Technical Stealth DicingInformationfor MEMS23" Stealth Dicing features" that will completely rewrite conventional Dicing conceptsProcessing methodWater (cooling / cleaning)ChippingDebris generationT-shape and round shape dicingHigh-speed ultra-thin wafer dicingChip yieldProcessing speedThermal effect on deviceGrinding cutting and processRequiredOccursGeneratesNot possibleMight be possible in certain casesNot so goodNot so goodAffected (including residual stress)* HAZ: Heat Affective ZoneSurface absorption laser process(melting, evaporation)RequiredOccursGeneratesPossi ble in certain casesPossible in certain casesNot so goodNot so goodAffected (HAZ*)Internal absorption laser process(locally selective)Not requiredDoes not occurDoes not generatePossiblePossibleGoodGoodNot affectedStealth dicingLaser dicingWafer dicingLaser ablation dicingBlade dicing1.

2 Introduction2. Problems with Dicing in MEMS fabrication processes Grinding wheel type blade Dicing Making Dicing a completely dry process3. Stealth Dicing technology Basic principle of Stealth Dicing Internal-process laser Dicing versus surface-process laser processing Range of thermal effects on MEMS devices during internal laser process Checking thermal effects on device characteristics Limitations when using Stealth dicing4. Stealth Dicing boosts profits Benefits from a 10 m kerf width Benefits when Dicing irregular chip shapes5. Dicing materials other than silicon Glass wafers6.

3 How green-friendly Stealth Dicing improves our environment7. ConclusionTable of Contents4 Various different kinds of technologies such as mechanical engineering, quantum mechanics, electrical engineering, chemistry, and optics that were thought of as different fields until recently were merged on a semiconductor fabrication process as microma-chining technology. This new technology offers tremendous possibilities that are starting to gather much attention. This technol-ogy has gradually grown along with the spread of etching technol-ogy since it could freely form thin film structures, girders and hollow structures with fine accuracy to the micro level on wafers.

4 These capabilities appealed to the imaginations of MEMS (micro electro mechanical system) designers who are now starting to create totally new functional devices. Stealth Dicing is a completely new laser Dicing technology. Stealth Dicing offers amazing advantages since it is a "completely dry process" yet generates "no debris" and has "zero kerf loss". This technology was especially developed for the purpose of high-speed yet high-quality Dicing of ultra-thin semiconductor wafers and its features are equally effective in Dicing processes for MEMS devices.

5 Stealth Dicing is already being used for mass producing MEMS devices and is on its way to becoming an industry standard for MEMS device Technical material covers problems encountered in MEMS Dicing as well as principles and processes involved in Stealth Dicing technology. It also offers a brief look at trends in developing new types of Stealth Dicing for use on materials other than silicon. Grinding wheel type blade dicingMajor problems that must be avoided during Dicing of MEMS devices with fragile structures include contamination and stress loads on the functional elements.

6 The following are inevitable problems with the Dicing process used in typical blade Dicing with wet processes Fluid pressure applies stress loads on the structure due to use of cooling water and rinse water during Dicing . Functional elements are re-contaminated by foul cutting fluid Requires adding a protective film for protecting device structures from water and foul water as well as a process to remove that film 2 Problems with contact type processes Contact type cutting processes apply a vibrating load to the structureFigure 1 shows problems that occur when an MEMS device having a membrane structure is cut by blade Dicing .

7 Photo 1 shows damage to membrane structures due to fluid pressure during blade damageMembrane crackDiamond grinding wheelCooling / rinse waterDebris adhesionKerf lossDebrisgenerationChippingFigure 1: Problems with blade dicingPhoto 1: Membrane damage due to fluid pressure2. Problems with Dicing in MEMS fabrication processes1. Making Dicing a completely dry processWhen Dicing an MEMS device, Dicing technology is needed that applies minimal stress to the delicate structures inside the MEMS device. At the same time, some measures are also needed to prevent the device structures from particle recontamination.

8 These problems can be eliminated by switching to a Dicing process with the following features: 1 Fully dry processing: Prevents defects caused by wet process and reduces man-hours needed for production/inspection2 Non-contact Dicing process: Eliminates stress applied to the device structures due to vibration accompanying the cutting processStealth Dicing offers both these features 1 and 2 described above. In Dicing technology using lasers, the ablation method has long been studied as a laser process method 1) 2).

9 Laser ablation, however, produces debris contaminants during processing so pre-processing is needed to coat a protective film for protecting the device structures from these contaminants, and post-processing such as wet washing is also next section briefly describes how Stealth Dicing is performed in a completely dry Basic principle of Stealth dicingIn Stealth Dicing , a laser beam at a light wavelength semitranspar-ent to the material is focused on a point inside that material to form a cleaving start point (transformed area: hereafter called SD layer), and external pressure then applied to the wafer to separate it into multiple chips 3) 4).

10 This technology therefore includes two processes. One is a "laser process" to form a cleaving start point (SD layer) on the interior of the wafer for separating it into chips; and the other is a "separation process" to divide the wafer into small chips. Figure 2 above shows an overview of the laser 1 - Laser processA laser beam is focused on points inside the wafer to form an SD layer for cutting the wafer. Cracks are also formed on this SD layer in the interior of the wafer, which extend towards both surfaces of the wafer. These cracks are an indispensable element for dividing the wafer into chips and should not twist broadly around the chip or be prevented from developing towards both surfaces.