Dislocation nucleation triggered by thermal stress during Ge/Si wafer bonding process at low annealing temperature

Further cost reduction and miniaturization of electronic systems requires new concepts for highly efficient packaging of MEMS components like RF resonators or switches, quartz crystals, bolometers, BAWs etc. This paper describes suitable base technologies for the miniaturized, low-cost wafer level chip-scale packaging of such MEMS. The approaches are based on temporary handling and permanent bonding of cap structures using adhesives or solder onto passive or active silicon wafers which are populated with MEMS components or the MEMS wafer themselves. Firstly, an overview of the possible packaging configurations based on different types of MEMS is discussed where TSV based and non-TSV based packaging solutions are distinguished in general. The cap structure for the TSV based solution can have the same size as the MEMS carrying substrate, since the electrical contacts for the MEMS can be routed either thought the cap or base substrate. Thus, full format cap wafers can be used in a regular wafer to wafer bonding process to create the wafer level cavity packages. However, if no TSVs are present in the cap or base substrate, the cap structure needs to be smaller than the base chip, so that electrical contacts outside the cap area can be accessed after the caps were bonded. Such a wafer level capping with caps smaller than the corresponding base chips can be obtained in two ways. The first approach is based on fabrication and singulation of the caps followed by their temporary face up assembly in the desired pattern on a help wafer. In a subsequent wafer to wafer bonding sequence all caps are transferred onto the base wafer. Finally the help wafer is removed from the back side of the bonded caps. This approach of reconfigured wafer bonding is especially used for uniform cap patterns or, if MEMS have an own bond frame structure. In that case no additional cap is required, since the MEMS can act as their own cap. The second approach is based on cap structure fabrication using a compound wafer stack consisting of two temporary bonded wafers. One wafer acts as carrier wafer whereas the other wafer is processed to form cap structures. Processes like thinning, silicon dry etching, deposition and structuring of polymer or metal bonding frames are performed to generate free-standing and face-up directed cap structures. The so created “cap donor wafer” is used in a wafer to wafer bonding process to bond all caps permanently to the corresponding MEMS base wafer. Finally, the temporary bonded carrier wafer is removed from the backside of the transferred caps. With that approach a fully custom specific and selective wafer level capping is possible featuring irregular cap patterns and locations on the MEMS base wafer. Examples like the selective capping process for RF MEMS switches are presented and discussed in detail. All processes were performed at 200mm wafer level.

Download Full-text

TLP Bonding Technologies for Micro Joining and 3D Packaging

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/2010dpc-wa12 ◽

2010 ◽

Vol 2010 (DPC) ◽

pp. 001221-001252 ◽

Cited By ~ 1

Author(s):

Kei Murayama ◽

Mitsuhiro Aizawa ◽

Mitsutoshi Higashi

Keyword(s):

High Temperature ◽

Melting Point ◽

Low Temperature ◽

Wafer Bonding ◽

Bonding Process ◽

Tlp Bonding ◽

Hermetic Sealing ◽

Low Temperature Bonding ◽

Free Material ◽

Bonding Technique

The bonding technique for High density Flip Chip(F.C.) packages requires a low temperature and a low stress process to have high reliability of the micro joining ,especially that for sensor MEMS packages requires hermetic sealing so as to ensure their performance. The Transient Liquid Phase (TLP) bonding, that is a kind of diffusion bonding is a technique that connects the low melting point material such as Indium to the higher melting point metal such as Gold by the isothermal solidification and high-melting-point intermetallic compounds are formed. Therefore, it is a unique joining technique that can achieve not only the low temperature bonding and also the high temperature reliability. The Gold-Indium TLP bonding technique can join parts at 180 degree C and after bonding the melting point of the junction is shifted to more than 495 degree C, therefore itfs possible to apply the low temperature bonding lower than the general use as a lead free material such as a SAC and raise the melting point more than AuSn solder which is used for the high temperature reliability usage. Therefore, the heat stress caused by bonding process can be expected to be lowered. We examined wafer bonding and F.C bonding plus annealing technique by using electroplated Indium and Gold as a joint material. We confirmed that the shear strength obtained at the F.C. bonding plus anneal technique was equal with that of the wafer bonding process. Moreover, it was confirmed to ensure sufficient hermetic sealing in silicon cavity packages that had been bonded at 180 degree C. And the difference of the thermal stress that affect to the device by the bonding process was confirmed. In this paper, we report on various possible application of the TLP bonding.

Download Full-text

Low Temperature Wafer Level Bonding Using Benzocyclobutene Adhesive Polymers

Additional Conferences (Device Packaging HiTEC HiTEN & CICMT) ◽

10.4071/2012dpc-wp13 ◽

2012 ◽

Vol 2012 (DPC) ◽

pp. 1-24

Author(s):

Michael Gallagher ◽

Jong-Uk Kim ◽

Eric Huenger ◽

Kai Zoschke ◽

Christina Lopper ◽

...

Keyword(s):

Low Temperature ◽

Wafer Bonding ◽

Flip Chip ◽

Bonding Temperature ◽

Bonding Process ◽

Curing Temperature ◽

Wafer Level ◽

Mechanical Adhesion ◽

3D Stacking ◽

Dry Etch

3D stacking, one of the 3D integration technologies using through silicon vias (TSVs), is considered as a desirable 3D solution due to its cost effectiveness and matured technical background. For successful 3D stacking, precisely controlled bonding of the two substrates is necessary, so that various methods and materials have been developed over the last decade. Wafer bonding using polymeric adhesives has advantages. Surface roughness, which is critical in direct bonding and metal-to-metal bonding, is not a significant issue, as the organic adhesive can smooth out the unevenness during bonding process. Moreover, bonding of good quality can be obtained using relatively low bonding pressure and low bonding temperature. Benzocyclobutene (BCB) polymers have been commonly used as bonding adhesives due to their relatively low curing temperature (~250 °C), very low water uptake (<0.2%), excellent planarizing capability, and good affinity to Cu metal lines. In this study, we present wafer bonding with BCB at various conditions. In particular, bonding experiments are performed at low temperature range (180 °C ~ 210 °C), which results in partially cured state. In order to examine the effectiveness of the low temperature process, the mechanical (adhesion) strength and dimensional changes are measured after bonding, and compared with the values of the fully cured state. Two different BCB polymers, dry-etch type and photo type, are examined. Dry etch BCB is proper for full-area bonding, as it has low degree of cure and therefore less viscosity. Photo-BCB has advantages when a pattern (frame or via open) is to be structured on the film, since it is photoimageable (negative tone), and its moderate viscosity enables the film to sustain the patterns during the wafer bonding process. The effect of edge beads at the wafer rim area and the soft cure (before bonding) conditions on the bonding quality are also studied. Alan/Rey ok move from Flip Chip and Wafer Level Packaging 1-6-12.

Download Full-text

Thermal Analysis of Heating System in Thermosonic Bonding Process

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.300-301.794 ◽

2013 ◽

Vol 300-301 ◽

pp. 794-801

Author(s):

Lu Fan Zhang ◽

Xue Li Li ◽

Ji Wen Fang ◽

Jian Dong Cai ◽

Long Sheng Nian ◽

...

Keyword(s):

Finite Element Method ◽

Thermal Analysis ◽

Thermal Stress ◽

Thermal Model ◽

Reference Value ◽

Heating System ◽

Bonding Process ◽

Thermal Displacement ◽

Process Heating ◽

Thermal Stress Distribution

A constant temperature range of the heating system plays an important role in the thermosonic bonding process. Heating block will provide enough heat for the heating system. In the paper, the thermal model of heating block and heating system were calculated by finite element method, and then some important conclusions were obtained. The change of temperature and thermal stress of block with the reference value of x and y was obtained. And an optimal structure of block for right temperature was built. The temperature distribution, thermal displacement and thermal stress distribution of the heating block and heating system were disclosed. The relevant change trends of temperature and thermal stress under the different load of temperature were investigated. These results can help improve the reliability of the heating system used in the thermosonic bonding process.

Download Full-text