Low-Temperature Silicon Wafer-Scale Thermocompression Bonding Using Electroplated Gold Layers in Hermetic Packaging

Park, Gil Soo; Kim, Yong Kook; Paek, Kyeong Kap; Kim, Jin Sang; Lee, Jong Heun; Ju, Byeong Kwon

doi:10.1149/1.2077077

Cited by 31 publications

(18 citation statements)

References 10 publications

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“…In summary, buckling and rupture of the TiW barrier, the changes in the gold film and a eutectic Si-Au reaction seem to have caused areas without gold, both outside the bonding area and in the bonding frame (figures [10][11][12]. This effect can prevent hermetic sealing if channels without gold are formed across the entire bond frame.…”

Section: Discussionmentioning

confidence: 99%

“…Pressure and heat are applied simultaneously to bring two metal surfaces into close contact. The atoms can then migrate from lattice site to lattice site joining the interface together [9,10]. To enable metal-to-metal contact, the bonding mechanism must deform the two surfaces in contact in order to disrupt any intervening surface films [11].…”

Section: Introductionmentioning

confidence: 99%

“…The helium leak rate of Au-Au thermocompression bonds was measured to be 2.74×10 -11 Pa m 3 /s by Pa m 3 /s by Xu et al, indicating that high quality hermetic packaging can be realized using this technology [10,20]. As diffusion barrier and adhesion layer Cr, Ti, W, TiW and NiCr have been used [10,12,16,17,19,20].The relatively large discrepancy in the reported bonding parameters for Au-Au thermocompression bonding indicates that the process is still not fully understood and described. This paper presents an investigation of Au-Au bonding in the temperature range 350 -450 °C.…”

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confidence: 98%

“…However, in order to activate a getter material during the bonding process, a bonding temperature of 400 -450 °C can be demanded [18]. According to Park et al and Taklo et al, increased bonding temperature improves the bond quality [10,19], while Kurotaki et al did not find any relationship between bonding temperature and bond strength [16]. Several authors report that an increased bonding pressure increases bond quality [10,17,19], while the bonding time has been found to be of low importance for the final bond strength [10,17].…”

mentioning

confidence: 99%

“…Several authors report that an increased bonding pressure increases bond quality [10,17,19], while the bonding time has been found to be of low importance for the final bond strength [10,17]. The helium leak rate of Au-Au thermocompression bonds was measured to be 2.74×10 -11 Pa m 3 /s by Pa m 3 /s by Xu et al, indicating that high quality hermetic packaging can be realized using this technology [10,20]. As diffusion barrier and adhesion layer Cr, Ti, W, TiW and NiCr have been used [10,12,16,17,19,20].The relatively large discrepancy in the reported bonding parameters for Au-Au thermocompression bonding indicates that the process is still not fully understood and described.…”

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confidence: 99%

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Wafer-level Au–Au bonding in the 350–450 °C temperature range

Tofteberg

Schjølberg-Henriksen

Fasting

et al. 2014

J. Micromech. Microeng.

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Abstract:Metal thermocompression bonding is a hermetic wafer-level packaging technology that facilitates vertical integration and shrinks the area used for device sealing. In this paper, Au-Au bonding at 350, 400 and 450 °C has been investigated, bonding wafers with 1 µm Au on top of 200 nm TiW. Test Si laminates with device sealing frames of width 100, 200, and 400 µm were realized. Bond strengths measured by pull tests ranged from 8-102 MPa and showed that the bond strength increased with higher bonding temperatures and decreased with increasing frame width. Effects of eutectic reactions, grain growth in the Au film and stress relaxation causing buckles in the TiW film were most pronounced at 450 °C and negligible at 350 °C. Bond temperature below the Au-Si eutectic temperature 363 °C is recommended. CONFIDENTIAL -FOR REVIEW ONLY JMM-100282.R2Wafer-level Au-Au bonding in the 350-450 °C temperature range Abstract. Metal thermocompression bonding is a hermetic wafer-level packaging technology that facilitates vertical integration and shrinks the area used for device sealing. In this paper, Au-Au bonding at 350, 400 and 450 °C has been investigated, bonding wafers with 1 µm Au on top of 200 nm TiW. Test Si laminates with device sealing frames of width 100, 200, and 400 µm were realized. Bond strengths measured by pull tests ranged from 8-102 MPa and showed that the bond strength increased with higher bonding temperatures and decreased with increasing frame width. Effects of eutectic reactions, grain growth in the Au film and stress relaxation causing buckles in the TiW film were most pronounced at 450 °C and negligible at 350 °C. Bond temperature below the Au-Si eutectic temperature 363 °C is recommended. Submitted to: Journal of Micromechanics and Microengineering IntroductionMicroelectromechanical system (MEMS) technology enables sensitive and reliable devices to be produced at low cost due to the advantages of batch processing. However, packaging of the individual devices can account for more than 70% of the device cost [1]. Wafer-level bonding lowers these costs substantially. Several bonding technologies are used in packaging of commercial MEMS devices. Glass-frit bonding [2-4], anodic bonding [5,6] and fusion bonding [7,8] are well known and widely used techniques for wafer-level packaging and sealing of MEMS devices.Recently, metal thermocompression bonding has found its application as a hermetic waferlevel packaging technology that facilitates vertical integration. Thermocompression bonding, also referred to as diffusion bonding, is a form of solid-state welding. Pressure and heat are applied simultaneously to bring two metal surfaces into close contact. The atoms can then migrate from lattice site to lattice site joining the interface together [9,10]. To enable metal-to-metal contact, the bonding mechanism must deform the two surfaces in contact in order to disrupt any intervening surface films [11].Cu, Al, and Au are the three most commonly applied metals for thermocompression bonding. The lowest proces...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 98%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Wafer-level Au–Au bonding in the 350–450 °C temperature range

Tofteberg

Schjølberg-Henriksen

Fasting

et al. 2014

J. Micromech. Microeng.

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Electrodeposition of Gold

Kohl¹

2010

Modern Electroplating

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While all that glitters may not be gold, it is the most beautiful of all the elements in their pure form. The name gold comes from the Old English Anglo-Saxon word for geolo meaning "yellow" while the symbol, Au, comes from the Latin word aurum, meaning "glowing dawn." Historically gold was one of the first metals known. Gold has been valuable throughout the ages chiefly because of its physical properties of softness, ductility, corrosion resistance, density, and scarcity. The first gold coin dates back to about 560 BC. Gold cups and jewelry predating 3500 BC have been found in Iraq. The ancient Egyptians knew how to hammer gold into leaf as thin as 66 nm. The importance of gold as a form of currency was at a high point in the 1900s when most countries were on the gold standard. The bullion price of gold over the past 21 years is shown in Figure 4.1.There have been about 160 metric kilotons of gold mined since it was first discovered, and it occupies about 0.005 ppm of the earth's crust. The world demand for gold in 2007 was approximately 80,000,000 troy ounces. Figure 4.2 shows the breakdown of the gold usage by industry. Jewelry comprises the largest fraction of the usage; however, much of that is not electroplated. For jewelry applications, gold is commonly alloyed with group IB or IIB metals, particularly copper, silver, platinum, and palladium, principally to improve its strength and wear resistance.The electrodeposition of gold is a relatively new process; it has been traced to the early work of Brugnatelli in 1805 [1]. The motives behind the use of electroplated gold changed dramatically in the mid-twentieth century when the emerging electronics industry required special-purpose electrical connections. The electronics industry consumed 5,330,000 troy ounces in 1994. Figure 4.3 shows the growth in the use of gold in the electronics industry by year. The use of electroplated gold in a variety of different functions in the electronics industry has led to (1) many advances in our fundamental understanding of the electrodeposition process and (2) new electroplating technologies over the past 25 years.Electrochemically deposited gold has satisfied many of the demands of the electronics industry. Gold has the third best electrical and thermal conductivity of all metals at room temperature. Also it has high ductility and excellent wear resistance, which are important for electrical contacts. The inertness of gold prevents the formation of insulating surface oxides (as compared to metals like aluminum). Group IIB metals (e.g., gold) are not good catalysts for other reactions, thus avoiding certain problems. For example, group IB metals (particularly platinum and palladium) can catalyze the polymerization of organic molecules forming insulating layers. In addition, gold is an excellent metal for wire bonding integrated circuits (ICs). Gold wires can be bonded to pure, soft gold pads by thermocompression bonding (300-400 C at high pressure to form a weld) or thermosonic bonding (150-200 C with ultrasonic energy to fo...

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