Oral Sessions


S4:Advanced Packaging Ⅰ

Oct. 26, 2022 13:10 PM - 15:10 PM

Room: R503
Session chair: Chih Hang Tung, Deputy Director, TSMC/Tz-Cheng Chiu,Professor, NCKU

Additive Manufacturing Technologies for Custom-made Electronic Packaging
發表編號:S4-1時間:13:10 - 13:40

Invited Speaker

Ricky Shi-Wei Lee, Chair Professor, HKUST

Photolithography has been the main stream technology for microelectronics fabrication for decades. Although it offers high throughput for mass production, sophisticated facilities such as lithography systems, photo masks, and etching benches are required. For prototyping and small/medium production, photolithography may not be the ideal choice in terms of cost and lead time. With the advancement of printing technologies in recent years, additive manufacturing (AM) has become a competitive option for prototyping and small/medium production. This presentation will introduce the development of AM and its advantages for microelectronics fabrication. Examples of applications in chip level re-distribution layer and bumping will be given. Potential opportunities for future printed electronics will be discussed.

A Laser Release Temporary Bonding Tape for Hybrid Bonding Having High Thermal Resistance and Excellent Thickness Uniformity
發表編號:S4-2時間:13:40 - 13:55

Izumi Daido, Ryoichi Watanabe, Toshio Takahashi, Masateru Fukuoka

There has been strong demand to increase I/O bandwidth for higher performance of semiconductor packages. Hybrid bonding is a very important interconnect technology to increase the I/O bandwidth as a next generation HPC technology and 3D interconnection. Hybrid bonding process doesn’t have bumps on the interconnect interface, so it can fabricate very fine pitch interconnects such as under 5 micrometers, also it has very low interconnect resistance because of Cu-Cu direct bonding.
However, hybrid bonding needs very high temperature, so a lot of studies have been done by many researchers but it still needs 250-300 degC or more for Cu diffusion to perform robust joint. Therefore, not only process equipments but also process materials are required to have thermal resistance during the bonding process.
In response to such requests, a Temporary Bonding De-Bonding (TBDB) tape for hybrid bonding having superior thermal resistance is introduced in this paper. TBDB tape can support a wafer through an overall process. In TBDB process for hybrid bonding, a carrier substrate with a TBDB tape is bonded to a wafer. The backside of the laminated wafer is grinded so that the thickness of the wafer reaches a target value. Then, chemical treatments (CVD, CMP) and thermal treatments (hybrid bonding) are performed. Finally, the completed wafer is removed from TBDB tape and the carrier. The performance requirements of TBDB tape for hybrid bonding are mainly high thermal resistance, easy removal from a wafer and thickness uniformity (Total thickness variation, TTV).
TBDB tape with high thermal resistance for hybrid bonding can support a wafer on the carrier substrate without delamination at the high temperature. However, conventional tapes are delaminated during thermal process. To improve thermal resistance, the adhesive in this TBDB tape is composed of a resin having higher thermal resistance than conventional resins. Generally, thermal resistant resins are so rigid that it strongly adheres. Such characteristic might make it difficult to remove a tape from a wafer after the thermal process. However, this TBDB tape has both thermal resistance and flexibility because the adhesive is composed of soft and hard segments. Therefore, it can be removed easily.
For further easy removal of TBDB tape from a wafer, the adhesion strength of the tape is controlled by UV crosslinking of adhesive and addition of low polarity components. The adhesion strength is decreased by UV crosslinking and localization of low polarity components on the tape surfaces. These effects make it possible to suppress the increase of the adhesion strength during thermal process and be easily peeled off from the wafer.
TTV is important for high reliability of hybrid bonding. Flatness of grinded die or wafer surface is key for reliable D2W (Die to Wafer) interconnect. The flatness of each dies has dependency by not only grinding tool but TBDB thickness uniformity. This TBDB tape has superior thickness uniformity comparing with conventional TBDB tape.
This TBDB tape has high thermal resistance that is applicable to hybrid bonding process. It enables many thermal processes to fabricate high performance semiconductor packages.

Nano-Artifact Metrics Chip Mounting Technology for Edge AI Device Security
發表編號:S4-3時間:13:55 - 14:10

Hitoshi Masago

We studied the effect of surface treatment on the bonding strength for establishing the technology of the quad flat package (QFP)/Quartz glass bonding method. This bonding technique is neccessary to prevent physical attacks such as counterfeiting and modification of edge AI devices with Nano-artifact Metrics (NAM) chips. We investigated the relationship between surface roughness and tensile strength by applying surface treatments for QFP such as VUV and Ar/O2 plasma.

Effects of Shielding Materials on EMI Performance for 5G Wi-Fi Applications
發表編號:S4-4時間:14:10 - 14:25

Shen-Yu Yang

Electronic communication devices used in many fields such as the internet, military, electronic industry, medical care, and electronic payment are growing rapidly. However, these demands lead to a new type of pollution called noise or radio frequency interference (RFI) or electromagnetic interference (EMI), which may interfere with equipment performance and cause equipment shutdown. As a result, there is a great need for electromagnetic waves shielding and other components in the module would not be disturbed by outer electromagnetic waves. The influence factors of EMI shielding include forming process, coating thickness and material. In this study, silver and copper are the metals adopted in EMI shielding due to their excellent properties of electrical conductivity and magnetic permeability. We focus on the effects of coating thickness and different processes including sputter, screen printing and spray. 2.4 GHz/5 GHz Wi-Fi module is utilized for EMI shielding test. The results of EMI block are measured by Keysight N9010B equipment to check electromagnetic waves shielding capability by dBm value at 4.8GHz (2nd harmonic), 7.2 GHz (3rd harmonic) and 6.43 GHz (noise). Besides measurement by using functional products, radiation simulation is used to simulate antenna efficiency under designed coating thickness of EMI shielding layer. The results of simulation and experiments show that coating thickness is the key factor to affect EMI shielding effectiveness. Moreover, processes of screen printing and spray are applicable and would be cost-effective alternates compared to sputtering.

Plasma-Activated Cu-Cu and Al-Al Direct Bonding for Electronics Packaging
發表編號:S4-5時間:14:25 - 14:40

Liangxing Hu, Simon Chun Kiat Goh, Yu Dian Lim, Peng Zhao, Michael Joo Zhong Lim, Weiyang Miao, Van Quy Dinh, and Chuan Seng Tan

In this paper, we report Ar/N2 plasma-activated Cu-Cu/Al-Al direct bonding conducted at room temperature in ambient environment. Surface characterizations are performed on the Cu and Al surfaces before and after plasma exposure, revealing that the plasma-activated surfaces remain in an “activated” state for up to 6 hours compared to the as-deposited Cu and Al surfaces. Subsequently, the plasma-activated dies are bonded. The bonded dies are examined for the bonding quality. The results show that a high-quality bonding is achieved. This reported bonding technology would be suitable for high-throughput CMOS-MEMS 3D integration and electronics packaging.

Metal-metal bonding is a promising semiconductor bonding technique, which has been widely developed to produce vertically electrical connections, provide mechanical support, and form hermetically sealed encapsulation [1]. Metal diffusion (thermo-compression) bonding, eutectic alloy bonding, and transient liquid phase diffusion bonding (TLPDB) are highly used in 3D integrated circuits (ICs) packaging [2]. The latter two bonding methods, which are based on solder materials, may be faced with inter-metallic compound (IMC) issue. On the contrary, metal diffusion bonding, such as Cu-Cu/Al-Al, is absent of IMC issue. However, Cu and Al are prone to rapid oxidation. To tackle this issue, Cu and Al surface treatments such as specialized chemical mechanical polishing (CMP), chemical treatment, surface assembled monolayer (SAM), and plasma activation, have been reported [3-7]. Among these methods, plasma activation is favorable as the process does not leave behind any residue [8-17]. In this paper, we report the plasma-activated Cu-Cu/Al-Al direct bonding conducted at room temperature in ambient environment.

Si wafers are patterned and deposited with 10 nm thickness of Ti as adhesion layer, followed with 100 or 200 nm thickness of Cu or Al via electron-beam evaporation, respectively. Afterwards, the wafers are diced into small dies with dimensions of 2 mm × 2 mm and 10 mm × 10 mm. Thereafter, the Cu or Al surface of the diced dies is exposed to Ar/N2 plasma. During the plasma process, Ar plasma are firstly applied to remove surface contaminants and native oxides, N2 plasma are subsequently applied on the Cu or Al surface to form an ultra-thin layer of nitride for passivating the Cu or Al surface and achieving low temperature bonding. Finally, the “activated” dies are pre-bonded in ambient environment in clean room (18ºC and 40% humidity) and are annealed at 300ºC to enhance the bonding strength.

The evolution of water contact angle (θ) with varying time for both the as-deposited and the Ar/N2 plasma-activated Cu or Al surface is performed. The results for Al are shown in Fig. 1. Compared to that of the as-deposited surface (~60º), the water contact angle of the Ar/N2 plasma-activated surface (~10º) is lower initially, revealing that the activated surface is more hydrophilic. Subsequently, the water contact angle of the Ar/N2 plasma-activated surface increases gradually until it is comparable to that of the as-deposited surface. The results show the metastability and degradation of nitride layer, revealing that the nitride layer remains in an “activated” state for up to 6 hours post plasma exposure. In addition, the bonded dies are assessed for the bonding quality and the bonding interfaces are shown in Fig. 2. The results show that a high-quality bonding is achieved.

In this paper, Ar/N2 plasma-activated Cu-Cu/Al-Al direct bonding conducted at room temperature in ambient environment is reported. Surface analysis reveals that the plasma induced metastable nitride surface is more hydrophilic than the as-deposited surface and the plasma-activated surface remains in an “activated” state for a duration of 6 hours post plasma exposure. In addition, the bonding interfaces of the bonded dies are examined, the results show that the dies are well bonded. This bonding technology would be suitable for high-throughput CMOS-MEMS 3D integration and electronics packaging.

Authors acknowledge funding support from A*STAR (A18A4b0055) under the “Nanosystems at the Edge” program.

Low Thermal Budget Cu/SiO2 Hybrid Bonding Using Highly <111>-oriented Nanotwinned Cu with Low Contact Resistivity and High Bonding Strength
發表編號:S4-6時間:14:40 - 14:55

Jia-Juen Ong

Fine-pitch hybrid bonding with dielectric layer (PECVD SiO2) and metal layer (nanotwinned Cu (nt-Cu)) was fabricated in both die and wafer level bonding process. The pitch and diameter of the nt-Cu microbumps were 20 m and 8 m, respectively. They were electrodeposited on a Tantalum (Ta) adhesion layer. Highly <111>-oriented nt-Cu was successfully electrodeposited in the trench which was etched using a damascene process. The dishing between the Cu and SiO2 layer could be precisely controlled within 3 nm. Prior to the bonding, the top and bottom dies were treated by a 20-W Ar plasma for 120 s to remove the native oxide layer on the Cu joints and to modify the SiO2 surface. Thus, their hydrophilicity could be increased. The relationship between surface contact angle and plasma power was also investigated. We found that the 20-W Ar-plasma was the optimized parameter to effectively remove the oxide layer and obtain the lowest hydrophilicity of the nt-Cu and SiO2.
After the pre-bonding at room temperature and ambient pressure by dripping DI water droplets at the bonding interface, thermal compression bonding (TCB) was conducted at 200 C for 1 h in vacuum with a compressive pressure of 3 MPa. Post-bonding annealing without external pressure was then carried out. The electrical properties of Kelvin structure and daisy chains with 2500 and 50 bumps were also studied using a 4-point probe method. Results showed that a contact resistivity of 10-9 -cm2 was obtained. This is the lowest value found in literature as bonded at a temperature below 300 C. Such a low contact resistivity achieved was mainly due to the lowest oxidation rate and highest surface diffusivity of the <111>-oriented Cu, as well as the twist-type grain boundaries at the bonding interfaces Die shear tests with a shear speed of 100 m/s and a shear height of 200 m were subsequently executed. Results showed that the bonding strength is exceed 30 MPa, which was greater compared to that in some recent studies. Additionally, three-dimensional (3D) X-ray was then used to characterize the bonding quality of the electrical structure. To observe the microstructure and bonding quality of the Cu joints, cross-sectional analysis was conducted using focused ion beam (FIB) and scanning electron microscope (SEM). High resolution transmission electron microscope (HR-TEM) was also employed to examine lattice arrangement of the bonding interface.

Large area Cu-to-Cu Bonding for Heat Pipe Applications
發表編號:S4-7時間:14:55 - 15:10

Guan-You Shen

As the performance requirement continues to increase, the power in the devices also continues to increase, resulting heat dissipation is a big issue for high performance devices, such as high performance computing devices. In this study, large area Cu-to-Cu bonding can be achieved by thermo-compression process at 250°C with high bonding strength exceed 30 MPa. Percentage of (111) orientation at the surface can be increased to 49% on regular Cu foils for electroplated nanotwinned Cu (nt-Cu) films. Due to the high surface diffusivity of (111) surfaces, high bonding strength of 30 MPa can be achieved at 250°C for 30 min for the bonded films with 4.5 cm2 bonding area. We provided a simple and efficient highly (111) diffusion bonding process for large area bonding especially for heat pipes, which needs high thermal conductivity materials to dissipate the heat away.


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