Prebake Process Research Articles

Synthesis of poly (amic ester) with controlled molecular weight for photosensitive polyimide in advanced package

Photosensitive polyimide (PSPI) with excellent lithography patterning and superior comprehensive properties have emerged as a very promising material for the advanced electronic package in IC field. Thereinto, poly (amic ester) (PAE) with highly sensitive groups and suitable molecular weight becomes the most important component in PSPI. Herein, a series of PAEs are synthesized by 4,4-oxydiphthalic anhydride, 4,4′-oxydianiline, and 2-hydroxyethyl methacrylate. The molecular weight of PAE was carefully controlled by using phthalic anhydride as the end-capping agent ranging from 9 000–20 000 g/mol. With the cooperation of photoinitiator and crosslinker, high-performance PSPIs were obtained. The results showed that the PAE with a molecular weight of 15 000 g/mol showed the best performance of lithography with resolution of 10 µm. The further increase of the molecular weight resulted the residues after developing, while lower molecular weight exhibited partially imidization during the pre-baking process, leading to a decrease in the solubility of PAE, as well. Additionally, as-prepared PSPIs also performed excellent thermal, mechanical, and dielectric properties, showing tensile strength of 120 MPa, elongation at break of 8%, glass transition temperature and the temperature of 5% weight loss of 260 °C and 430 °C, respectively. All these results exhibit a great application potential for high performance advanced packaging.

High‐Performance Self‐Assembled ZnO Nanowrinkle Network Structured Photodetectors

Herein, the effect of prebake temperature on the surface structure of zinc oxide (ZnO) nanowrinkle structures formed in a sol–gel growth process for UV photodetection is demonstrated. The sol–gel solutions are spin‐coated on glass and c‐plane sapphire substrates, and the resulting ZnO films are subjected to prebake and crystallization processes at 800 °C for an hour. In the sol–gel process, the prebake process is crucial in forming the nanowrinkle structure on the surface of the ZnO film. The maximum nanowrinkle structure of ZnO film is achieved at the prebake temperature of 150 °C. In addition to the formation of the optimized nanowrinkle structure, the UV response of the photodetector is further enhanced through the prebake temperature control. The nanowrinkle network structure significantly improves the optical absorbance and photoluminescence characteristics of the ZnO film, leading to high photocurrent, photoresponsivity, and external quantum efficiency for UV light. The results demonstrate the potential of sol–gel‐derived ZnO photodetectors with nanowrinkle network structures for UV sensing applications.

Improvement of sublimation in color film pre-baking process by optimizing the photoresist composition

Improvement of sublimation in color film pre-baking process by optimizing the photoresist composition

Adhesion–delamination phenomena at the interfaces of the dielectric layer

Fan-out wafer-level packaging (FOWLP) has been developed as an enhancement of standard wafer-level packaging solutions and is being intensively researched nowadays. However, issues of delamination remain unsolved. This study focuses on the interfacial characteristics between polyimide (PI) and redistribution layers (RDL) of the FOWLP to decrease the concerns in delamination. The problems of delamination were addressed through simulation and experimentation. In the simulation, the FOWLP package model was established by using the finite element analysis ANSYS software. The results showed various ways to reduce the residual stress, such as by adding a pre-baking process before reflow or by changing the thickness of each PI layer. These ways can effectively reduce the maximum residual stress of the FOWLP and improve the issue of delamination. Moreover, through plasma treatment with the different levels of powers and gases, the adhesion between PI and RDL can improve the overall strengthening of the FOWLP structure. While, in the experimental process, Taguchi design of experiment was utilized to determine the optimal process parameters and key factors. The physical and chemical properties were analyzed, such as the surface roughness via Atomic Force Microscope (AFM) and the surface material compounds by X-ray Photoelectron Spectroscopy (XPS). The relationship between the roughness and delamination was examined.

Characterization of Lift Off Resist during Thermal Compression Wafer Bonding Based on Polydimethylglutarimide (PMGI)

With the emergence of various 3-D integration techniques, wafer bonding technology has experienced renewed interest. Decades of relentless device scaling leading to today’s state-of-the-art nanotechnology have ultimately focused on the third dimension for stacking of device layers. Temporary bonding is also of interest for the integration of dissimilar materials in device structures, which cannot be achieved by epitaxial growth techniques alone when the lattice mismatch between the dissimilar materials is too large. Recently lift-off resists (LOR) based on polydimethylglutarimide (PMGI) have been found to be especially suitable for film exfoliation and layer transfer of 2D materials by temporary bonding [1]. For the experimental preparation the 2-inch diameter Si wafers were cleaned with Standard Clean 1 (H2O:NH4OH:H2O2=5:1:1) before spin coating the Si wafers with polydimethylglutarimide LOR resist at an optimized spin speed of 2000 rpm. This was followed by a pre-bake process at 160ºC for 5 min in order to evaporate the cyclopentanone solvent with a boiling point of 131ºC. In the last process step two LOR coated Si wafers were bonded face to face via the LOR resist in an EVG®501 Wafer Bonding Systemin a vacuum of 10-3 Pa and at a temperature of 250ºC. The EVG®501 Wafer Bonding Systemis capable of thermo-compression bonding with up to 10 kN force. In this study we report on Thermal Gravimetric Analysis (TGA) which is widely applied on thermoplastic polymeric materials in order to elucidate chemical phenomena such as decomposition and mass loss, which also occur during thermal compression bonding of Silicon wafer pairs coated with spin-on LOR resist. From TGA data (Figure 1), the LOR precursor solution lost 93% of its original mass starting at 100˚C because of solvent vaporization. The LOR resist exhibits a glass transition point (Tg) of 180-190 ºC, which aids the wafer bonding process at 250ºC by rendering the resist softer and initiating viscous flow for surface planarization. The final 7% of resist mass was lost started at around 281˚C due to thermal decomposition of PMGI. The functional groups of polydimethylglutarimide based Lift Off Resist (LOR) layers were studied before wafer bonding and after wafer compression bonding by attenuated total reflection infrared (ATR-IR) spectroscopy (Figure 2). All functional groups before and after bonding via the LOR layers at 250 ºC were identical, except for the disappearance of the two bands at 3188 and 3088 cm-1after thermal compression bonding. The disappearance of these two bands, which are associated with the N–H group, is interpreted as a result of cross linking of polymers. This cross linking of polymer chains is the chemical process that enables the actual wafer bonding across the two joined polydimethylglutarimide resist interfaces.

The effect of temporary bonding on post processing in TSV interposer manufacturing

Thermo-gravimetric analysis (TGA) was used to assess the thermal stability of a temporary adhesive. High temperature is one important factor leading to the voids formation in bonded wafers, which can degrade bonding force and cause chipping. Some heat treatment experiments were devised to investigate the influence of high temperature on the bonding quality. The prebake process before temporary bonding plays a very important role in preventing voids from forming between bonded wafers, which can be confirmed by the TGA results. A short loop evaluation was performed to assess the temporary bonding quality with different prebake and heat treatment temperatures. The results were used to optimize prebake conditions. Application to 2.5D through silicon vias temporary bonding and backside processing is demonstrated.

Ultrafine Particle (UFP) Exposures in an Aluminium Smelter: Soderberg vs. Prebake Potrooms

The objectives of this work were to evaluate ultrafine particle (UFP) exposures during aluminium smelting in Soderberg and prebake potrooms. Particle concentrations were monitored using the P-Trak 8525 and aerosol particle size distributions were monitored with the electrical low pressure impactor (ELPI). UFP samples were analyzed for chemical composition by transmission electron microscopy (TEM). Workers who accomplished tasks in the Soderberg cell environment were more exposed to UFP than those who worked in the prebake; however, the specific task of anode shift in the prebake process was an important source of UFPs. More than 92 % and 98 % of particles had aerodynamic diameters less than 98 nm in the Soderberg and prebake processes, respectively. TEM/EDS analysis suggests that workers are exposed to short fibrous aluminium particles with a nanometric aerodynamic diameter. Overall, this study suggests that occupational hygiene practices aimed at evaluating UFP exposures should include monitoring of the particle number concentration, monitoring of the particle size distribution, and characterization of the nanoscale fraction of the aerosol.

Solution-processed zinc–tin oxide thin-film transistors with low interfacial trap density and improved performance

Solution-processed amorphous oxide semiconductors are attractive channel materials in thin-film transistors (TFTs) for low-cost electronics. We demonstrate improved performance and uniformity of solution-processed zinc–tin oxide (ZTO) TFTs by optimizing the prebake process for the ZTO precursor film. ZTO prebake process prearranges the dielectric/semiconductor interface and minimizes the performance variation caused by the uneven thermal distribution during annealing process. Prearranging the interface also reduces interfacial trap density and results in improved performance. A mobility of 27.3 cm2/V s, an on/off ratio of ∼107, and a subthreshold swing of 122 mV/decade have been obtained. Significant improvement in operational stability has also been observed.

유리섬유강화 복합재의 점탄성 특성 규명 및 인쇄회로기판 열변형해석에의 적용

초록: 전자기기부품에적용되는회로기판의패키지공정상에서가해지는온도변화에따른신뢰성평가시발생되는문제들은, 주로회로기판을구성하고있는기본재료들의열팽창계수차이및시간의존성물성에의해영향을받는다. 특히, 인쇄회로기판내부회로층사이에서절연역할을수행하는유리섬유강화복합재료와같은수지몰딩고분자재료는온도에따른물성변화뿐만아니라, 변형및하중이가해지는시간에대한물성변화도고려해야하는점탄성성질을나타낸다. 본논문에서는인쇄회로기판에사용되는주요고분자재료인유리섬유강화복합재의시간및온도에따른점탄성특성을규명하기위하여, 단축인장모드의응력완화시험과크리프시험을각각수행하였다. 또한, 고분자재료점탄성물성의영향성을파악하기위하여, 유한요소해석을이용한인쇄회로기판의예비가열공정상에서가해지는온도변화에따른열변형을평가하였다. 이러한해석결과를바탕으로, 인쇄회로기판과같이고분자재료를사용하는전자회로구조물의수치해석기반의열변형예측시점탄성물성의고려필요성을검증하였다.Abstract: The reliability problems of flip chip packages subjected to temperature change during the packaging processmainly occur due to mismatches in the coefficients of thermal expansion as well as features with time-dependentmaterial properties. Resin molding compounds like glass fiber reinforced epoxy composites used as the dielectric layer inprinted circuit boards (PCB) strongly exhibit viscoelastic behavior, which causes their Young’s moduli to not only betemperature-dependent but also time-dependent. In this study, the stress relaxation and creep tests were used tocharacterize the viscoelastic properties of the glass fiber reinforced epoxy composite. Using the viscoelastic properties,finite element analysis (FEA) was employed to simulate thermal loading in the pre-baking process and predict thermalwarpage. Furthermore, the effect of viscoelastic features for the major polymeric material on the dielectric layer in thePCB (the glass fiber reinforced epoxy composite) was investigated using FEA.

Improved Corona-Charging-Assisted Surface-Relief Amplification on Polymer Film for Low-Noise Holograms

The corona-charging-assisted technique for amplifying surface-relief holograms on a polymer film has been reported in recent years. However, it was found that light-scattering noise was undesirably superimposed on the reconstructed image of the amplified hologram. With a view to improving the technique for amplifying the surface relief, we explored the possible origins of the noise produced during the process. It was found that the noise originates from random submicron-scale surface structures produced during corona charging. In investigating the possibility of reducing this noise, we found that prebaking the polymer film at 150 °C for 10 min before inscribing the gratings was effective in inhibiting the generation of random surface structures. By inhibiting the generation of light-scattering noise, this prebaking process improved the optical quality of the amplified hologram. This tendency was also confirmed using a surface-relief-templated hologram recording to a glass substrate; that is, a nearly noiseless hologram was successfully transferred to the glass substrate.

Fabrication of very high quantum efficiency planar InGaAs PIN photodiodes through prebake process

The fabrication is reported of large-area (73 μm in diameter) front-illuminated planar InGaAs PIN photodiodes on S-doped InP substrates through the prebake process and investigations are made of various Zn diffusion times on a 2.9-μm thick absorption layer. As a result of the best tuning of the Zn diffusion time, the large-area planar InGaAs PIN photodiodes achieve a lowest capacitance of 0.43 pF, a lowest dark current of 39 pA, a highest responsivity of 0.99 A/W (79% quantum efficiency) at λ=1.55 μm, and a highest 3-dB bandwidth of 6.98 GHz for a bare chip and 4.53 GHz for the device packaged in a TO can, respectively. Furthermore, the developed PIN photodiodes possess high breakdown voltage (less than −25 V) and provide the P and N electrodes located at different sides of the photodiodes, thus improving the devices for easy bonding and packaging.

Reliability of vacuum packaged MEMS gyroscopes

The greatest challenge for the successful commercialization of MEMS (micro-electro-mechanical system) technology is proving its reliability. Of concern in particular are the reliability and long-term stability of wafer level vacuum packaged MEMS gyroscope sensors subjected to cyclic mechanical stresses at high frequencies. In this study, we carried out several reliability tests and investigated the failure mechanisms of the anodically bonded vacuum gyroscope sensors designed for commercial electronic products. Particularly we studied mechanical reliability issues such as fatigue, shock, and vibration. It was found that successful vacuum packaging could be achieved through the optimization of the bonding process by reducing leakage and the deposition of titanium coating for reducing out-gassing inside the cavity. The effects of the pre-baking process are also described in this study. The current design of the gyroscope structure is found to be safe from fatigue failure for the 1000 h of operation test. The MEMS gyroscope sensor survives the drop and vibration qualification tests for electronic products without any damage, indicating the robustness of the sensor. The reliability test results presented in this study demonstrate that the MEMS gyroscope sensor is very close to commercialization.

Novel methods to incorporate deuterium in the MOS structures

The deuterium concentration as high as 2/spl times/10/sup 20/ cm/sup -3/ can be incorporated in rapid thermal oxide layers by a process of deuterium prebake and deuterium post oxidation anneal. The deuterium distributed not only at Si/oxide interface but also in the bulk oxide. The deuterium incorporation shows the improvement on soft breakdown characteristics and the interface state density at SiO/sub 2//Si after stress. The addition of very high vacuum prebake process yields a deuterium concentration of 9/spl times/ 10/sup 20/ cm/sup -3/, but also leads to the formation of rough oxide.

Dependence of the quality of thick resist structures on resist baking

Interest in thick photoresist applications is steadily growing. Specialised equipment has been developed to cope with the new challenges to process and pattern extremely thick photoresist layers. A decisive step in the preparation of resist layers is the prebaking. The impact of three different prebaking technologies on the resist performance has been investigated. Resist patterns obtained after oven, hotplate or IR prebaking exhibit equal high quality. Compared to oven and hotplate baking the process length and energy consumption is markedly reduced using IR radiation favouring this variant to be the optimum prebaking process for very thick photoresist layers.

Thermal Decomposition of Dissolution Inhibitor in Chemically Amplified Resist during Prebake Process

The equation which represents the decomposition mechanism for two dissolution inhibitors in a chemically amplified positive resist consisting of polyvinylphenol protected with p-t-butoxycarbonylmethyl (BCM-PVP) and p-t-butoxycarbonyl (BOC-PVP) groups was investigated by isothermal thermogravimetry (TG) analysis. The reaction orders of these polymers were different and this difference was caused by the difference in the thermal deprotection reaction of the protecting group. It was shown that the decomposition of BCM-PVP is promoted as decomposition proceeds, which is expressed by the equation. This result indicates that, when BCM-PVP is used as an inhibitor in chemically amplified resists, it is important to determine the baking temperature and duration in order to prevent its decomposition.

Non-silver paste method for making thermal contact to substrates for high T/sub c/ film growth

The authors describe a procedure for using thin layers of gold foil to make thermal contact between insulating substrates and Haynes alloy heater blocks. This method has several advantages over using silver paste compounds to improve the thermal contact. Samples are easily removed from the metal blocks after heating up to 850 degrees C, and no prebake process is required prior to sample loading into the deposition chamber since no organic binder is used. Because only a thin layer (1- mu m thick) of gold foil is required, the method is extremely economical. Thermal contact resistance measurements performed using MgO substrates demonstrate that this technique promotes thermal contact between the substrate and heater block comparable to silver paste. These measurements are presented along with a design for a fixture capable of holding wafers up to 0.75 in diameter. >

Application of polymer–bisazide composite system negative resists to electron beam lithography

Pattern profiles achieved in composite resists of a polymer and a bisazide compound tend to be rectangular, in spite of electron backscattering from substrates. This phenomenon is explained by the bisazide concentration dependence of the composite resist sensitivity to electron beam and the depth profile of bisazide distribution in a polymer film. An optimum amount of bisazide compound, needed to obtain the highest sensitization, exists. It does not depend on molecular weight, but on the kind of polymers used. An excessive amount of bisazide compound incorporation is found to reduce sensitivity. Bisazide compounds distribute to a great extent in the vicinity of a substrate during a prebaking process. These factors reduce the backscattering problem taking place in electron beam lithography to obtain resist patterns with vertical walls.

Crystalline film quality in reduced pressure silicon epitaxy at low temperature

The influence of deposition pressure on epitaxial crystalline film quality has been investigated with respect to vapor-phase silicon epitaxial growth (SiH2Cl2-H2 system). It is shown that the crystalline film quality has been improved by reducing the deposition pressure. In addition, a prebaking process at reduced pressure has been found to be effective for obtaining single-crystalline silicon films with atmospheric pressure deposition as well as reduced pressure deposition. The deposition temperature can be lowered down to 930 °C with perfect crystalline film by reducing the deposition pressure. The crystalline quality of epitaxial films grown at a low temperature of 930 °C using the reduced pressure technique has been verified to be excellent by fabricating bipolar transistors with an oxide isolation technique.