基于片内热管理应用的碳化硅深孔刻蚀研究

针对传统SiC衬底GaN器件高功率密度工作时的热积累问题,开展基于芯片内部嵌入高热导率材料的GaN器件芯片级热管理技术研究。在实现工艺兼容性的基础上,采用反应离子刻蚀技术对GaN器件有源区下端的SiC衬底进行深孔刻蚀工艺研究,系统地分析了刻蚀气体、射频功率及腔室压强等工艺参数对刻蚀速率的影响,并结合能谱对刻蚀表面的质量和损伤进行分析。实验发现射频功率仅能影响刻蚀速率,而刻蚀气体和压强不仅影响其刻蚀速率,还影响其刻蚀表面质量。最终提出了一种基于反应离子刻蚀技术的SiC深孔刻蚀方法,对器件热管理和SiC深孔刻蚀技术具有重要的指导意义。     

ICP刻蚀GaN侧壁倾角以及刻蚀速率的控制

深入研究了Cl2基气体电感耦合等离子体(ICP)刻蚀系统对于GaN材料侧壁倾角的控制以及刻蚀速率的影响。通过调整ICP离子源功率、射频功率、气体流量、腔室压力等参数,经实验验证,实现了从23°～83°侧壁倾角的大范围工艺控制,为GaN基器件工艺提供了有益指导。     

栅槽刻蚀工艺对增强型GaN HEMT器件性能的影响

基于凹槽栅增强型氮化镓高电子迁移率晶体管(GaN HEMT)研究了不同的栅槽刻蚀工艺对GaN器件性能的影响。在栅槽刻蚀方面,采用了一种感应耦合等离子体(ICP)干法刻蚀技术与高温热氧化湿法刻蚀技术相结合的两步法刻蚀技术,将AlGaN势垒层全部刻蚀掉,制备出了阈值电压超过3 V的增强型Al_2O_3/AlGaN/GaN MIS-HEMT器件。相比于传统的ICP干法刻蚀技术,两步法是一种低损伤的自停止刻蚀技术,易于控制且具有高度可重复性,能够获得更高质量的刻蚀界面,所制备的器件增强型GaN MIS-HEMT器件具有阈值电压回滞小、电流开关比(I_ON/I_OFF)高、栅极泄漏电流小、击穿电压高等特性。     

基于电感耦合氧等离子体金刚石膜表面修饰的功率优化

采用电感耦合等离子体（ICP）氧等离子体刻蚀金刚石膜,探寻金刚石膜表面处理的方法。通过分析不同ICP射频源功率和不同偏压源功率下的刻蚀速率,研究了金刚石膜刻蚀的机理作用;通过拉曼光谱进行表征,分析刻蚀前后sp2与sp3的含量。结果表明,在ICP氧等离子体刻蚀的过程中,sp3键部分转化为sp2键;刻蚀后表面粗糙度降低;当...     

SiC材料的ICP-RIE浅槽刻蚀工艺

介绍了用于SiC器件浅槽制作的ICP-RIE刻蚀原理,选用Cl2/Ar混合气体对SiC材料进行浅槽刻蚀,研究了ICP功率和RIE功率对刻蚀速率、刻蚀后表面粗糙度及刻蚀倾角的影响,得到了刻蚀速率、刻蚀后表面粗糙度及刻蚀倾角随刻蚀功率的变化规律。最终得到了用于SiC器件浅槽刻蚀的最优刻蚀条件。实验结果表明,RIE功率和ICP最优功率配比分别为12和500 W。该刻蚀条件应用于SiC MESFET制备中,进行了多凹槽栅结构的浅槽刻蚀,实现了多凹槽栅结构。不同深度栅凹槽的片内均匀性均达到了4%以内,片间均匀性也达到了5%,工艺稳定性及均匀性均达到了批量生产要求。     

Cl_2/BCl_3ICP刻蚀GaN基LED的规律研究

研究了用Cl2/BCl3刻蚀GaN基LED中,工艺参数对GaN刻蚀速率、刻蚀侧壁和GaN与SiO2刻蚀选择比的影响。研究结果表明,刻蚀速率随着ICP功率和压强的增大先增大继而减小,随RF功率的增大单调增大;刻蚀选择比随ICP功率增大单调减小,随压强增大而增大。还研究了刻蚀速率和选择比与气体比例变化的关系。刻蚀SEM图表明,压强和RF功率增大会使刻蚀垂直度增大。     

ICP技术在化合物半导体器件制备中的应用

介绍了ICP刻蚀工艺技术原理和在化合物半导体器件制备中的应用,包括ICP刻蚀技术中的低温等离子体的形成机理、等离子体与固体表面的相互作用等,并对影响ICP刻蚀结果的因素进行了分析.研究了不同的工艺气体配比、腔体工作压力、ICP源功率和射频源功率对刻蚀的影响,并初步得到了一种稳定、刻蚀表面清洁光滑、图形轮廓良好、均匀性较好和刻蚀速率较高的干法刻蚀工艺.     

ICP刻蚀对光刻胶掩模及刻蚀图形侧壁的影响

采用AZ1500光刻胶作为掩模对GaAs和InP进行ICP刻蚀,研究了刻蚀参数对光刻胶掩模及刻蚀图形侧壁的影响。结果表明,光刻胶的碳化变性与等离子体的轰击相关,压强、ICP功率和RF功率的增加以及Cl2比例的减小都会加速光刻胶的碳化变性,Cl2/Ar比Cl2/BCl3更易使光刻胶发生变性。对于GaAs样品刻蚀,刻蚀气体中Cl2含量越高,刻蚀图形侧壁的横向刻蚀越严重。Cl2/BCl3对GaAs的刻蚀速率比Cl2/Ar慢,但刻蚀后样品的表面粗糙度比Cl2/Ar小。刻蚀InP时的刻蚀速率比GaAs样品慢,且存在图形侧壁倾斜现象。该工作有助于推动在器件制备工艺中以光刻胶作为掩模进行ICP刻蚀,从而提高器件制备效率。     

GaN电感耦合等离子体刻蚀的优化和损伤分析

通过分别改变电感耦合等离子体(ICP)刻蚀过程中的ICP功率和DC偏压,对ICP刻蚀GaN材料的工艺条件和损伤情况进行了系统的研究。刻蚀后表面的损伤和形貌通过扫描电子显微镜(SEM)、原子力显微镜(AFM)、电子能谱(EDS)、荧光光谱(PL)等技术进行表征和分析。实验结果表明,刻蚀速率随ICP功率和DC偏压的增加而增加;刻蚀损伤与DC偏压成正比,而与ICP功率的关系较为复杂。实验中观测到刻蚀后GaN样品的荧光光谱带边发射峰和黄带发射峰的强度均有明显下降,这意味着刻蚀产生的缺陷中存在非辐射复合中心,并且该非辐射复合中心的密度与DC偏压成正比。为了兼顾高刻蚀速率和低刻蚀损伤,建议使用高ICP功率(450 W)和低DC偏压(300 V)进行ICP刻蚀。     

6H-SiC体材料在SF_6/O_2混合气体中的ICP刻蚀

采用SF6/O2作为刻蚀气体,对单晶6H-SiC材料的感应耦合等离子体(ICP)刻蚀工艺进行了研究。分析了ICP功率、偏置电压、气体混合比等工艺参数对刻蚀速率和刻蚀质量的影响。结果表明,刻蚀速率随着ICP功率及偏置电压的增大而提高,刻蚀表面质量随偏置电压及O2的含量的增大而降低,而ICP功率的变化对刻蚀质量影响不大。混合气体中O2含量为20%时刻蚀速率达到最大值,同时加入氧气后形成易于充电的SiFxOy中间层,从而促进了微沟槽的形成。     

基于平板热管的大功率LED散热系统模拟及优化

为解决大功率LED的散热问题,设计了平板热管散热器来实现LED芯片的高效散热。通过Flotherm模拟软件,对大功率LED在自然对流条件下的散热情况进行了三维数值模拟。通过平板热管与常规铜、铝散热基板对比,发现平板热管有效降低了大功率功率LED的结温和热阻,使得LED温度分布更为均匀。此外,还研究了平板热管LED散热系统在不同芯片功率下的热性能,并对四种不同排布方式的LED平板热管散热系统进行了优化,发现阵列分布其温度分布最为均匀,结温最低,是较优的排布方式。     

Prediction of gap in QFP with unattached heat spreader

Due to cost and process considerations, sometimes the heat spreader of a quad flat package (QFP) is not attached to the die pad. Consequently, due to mismatch of thermal expansions of the components, gapping is inevitable on the unattached interface during temperature change. Presence of the gap would potentially decrease the reliability and thermal performance of QFP. In this paper, contact methodologies were incorporated into finite element models to calculate the distribution of gap on the unattached interface. Both plane two-dimensional and general three-dimensional models were built up and compared for a multi-chip module QFP with a drop-in heat spreader.     

4 W single-transverse mode VECSEL utilising intra-cavity diamond heat spreader

An optically pumped semiconductor vertical external cavity surface emitting laser, with high output power and excellent beam quality operating at a wavelength near 1.05 /spl mu/m, is reported. A transparent diamond heat spreader was used for thermal management of the laser. The gain structure grown by molecular beam epitaxy includes 13 compressively strained InGaAs quantum wells. Maximum output power of 4 W with diffraction-limited beam (M/sup 2//spl les/1.15) was achieved using a 2% output coupler and incident pump power of 20 W. It is shown that power scalability is feasible with the presented laser geometry.     

Performance characterization of a novel flat plate micro heat pipe spreader

A combined numerical and experimental investigation was conducted on a novel flat plate micro heat pipe spreader, to better understand the effect of primary operating parameters governing the performance of such devices. A numerical thermal model was developed to predict the temperature response with variation in the leading geometrical, material and boundary parameters of the spreader, viz. wall thickness, thermal conductivity, power input and heat source size. The results showed that, unlike conventional heat pipes, wall thermal conductivity is a major factor in such thin, flat spreaders. The spreader performance also degrades with decrease in heat source size. Visualization experiments have been conducted to qualitatively understand the heat transfer phenomena taking place on these devices. These confirmed that the primary limitation to heat transfer from these devices was due to the capillary limitation of the wick structures.     

High-power optically pumped 1550-nm VECSEL with a bonded silicon heat spreader

We present an optically pumped 1550-nm vertical-external-cavity surface-emitting laser with improved output power and operating temperature using a bonded heat spreader. The laser comprises an InGaAsP-based gain element, with a resonant periodic gain structure on top of a distributed Bragg reflector, and a high reflectivity spherical mirror as the external reflector. Heat transport is enhanced by a Si heat spreader bonded to the InGaAsP surface by liquid capillary bonding. Optical pumping is achieved using a 1250-nm fiber Raman laser. A maximum continuous output power of 250 mW was obtained under multitransverse mode operation at 240 K. Under operation in the fundamental near-Gaussian mode, we obtained a maximum power of 230 mW with a beam quality factor (M/sup 2/) of 1.22. At room temperature, the output power was limited to 12 mW.     

Process and design analysis for ultrafine-pitched wiresweep elimination in advanced copper heat spreader BGA package

The semiconductor device trend for increasing functionalities and performances yet with smaller overall feature sizes presents escalating obstacles to the decreasing form factor along with demanding thermal carrying capability required at the package level. To confront this compounding issue, ultrafine-pitch wirebond interconnect coupled with thermally enhanced copper heat spreader attached to the package are introduced. However, the additional copper heat spreader thickness introduced within the package challenges the design of the package's wire, its loop height, and the molding process control to prevent wire sweeping occurrences. This study investigates the impact of different ultrafine pitched wire types, wire loop designs, copper heat spreader structures, and mold material types on eliminating device short from occurring due to the wire sweeping phenomena. A full factorial experiment is performed using an active silicon device packaged in a thermally enhanced ball grid array (BGA) test vehicle. In addition, test characterization is carried out using x-ray and multiinsertions hot/cold continuity tests. Then, a detailed failure analysis is performed by package decapsulation and scanning electron microscopy/energy-dispersive x-ray (SEM/EDX) to confirm the experimental findings. In conclusion, the study finds that for an ultrafine-pitched thermally enhanced BGA package, wire type is insignificant to reduce wire shorting occurrences. However, mold material and copper heat spreader structure using an optimized wire loop design are significant factors in eliminating wiresweep shorting phenomena. This study concludes with a wirebond interconnect and heat slug design recommended along with an improved process parameters and assembly material sets found from the experiment.     

Thermal characteristics evaluation for board-level high performance flip-chip package equipped with vapor chamber as heat spreader

Thermal analysis was performed in this work to compare the thermal performance of a board-level high performance flip-chip ball grid array package equipped with solid Cu or vapor chamber (VC) as the heat spreader and Al-filler gel or In solder as the thermal interface material (TIM). The effect of different heat source sizes was also examined. Numerical results indicate that for the particular test vehicle under a power dissipation of 160 W, the thermal performance is remarkably enhanced by switching TIM from Al-filler gel to In solder while the enhancement by using VC instead of solid Cu heat spreader is only observable when In solder is incorporated. Moreover, the performance of VC gradually enhances then retards as the heat source size decreases. The retardation can be attributed to the more dominant role of die in heat dissipation when the heat source size gradually shrinks.     

Effect of a diamond heat spreader on the characteristics of gallium nitride-based transistors

A problem, which concerns the effect of the diamond heat-spreading layer on the temperature and voltage-current characteristics of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) is solved for the first time in a hydrodynamic model (which includes the continuity equation, Poisson equation, and equations for electron and lattice temperatures). The mechanism of the occurrence of peak electron and lattice temperatures (hot spots) is analyzed. It is shown that introducing a heat spreader considerably reduces the maximum temperature (by 263 K for a sapphire substrate and by 163 K for a silicon carbide substrate) and improves the voltage-current characteristics. The effectiveness of the heat spreader is evaluated depending on its thickness, gate size, and substrate material to find the optimum design.     

Effect of surface roughness of silicon die and copper heat spreader on thermal performance of HFCBGA

From the available mass production devices of HFCBGAs, there can be a range of surface roughness with different surface finished of silicon dies and heat spreader. An aluminum filled gel is used to examine the surfaces clamping with both identical substrates at both sides whether compatible to the thermal conduction. Their thermal contact resistances are measured by laser flash technology and therefore modeling HFCBGAs with those measured roughnesses and resistances for characterizing thermal performances.     

空间无源沾染技术的撒布装置优化

空间无源对抗被认为是避免严重国际纠纷的典型软对抗手段,其作战载荷可分为直接在空间平台上进行撒布作战的星载撒布器和天基干扰弹。以星载撒布器为研究对象,以无源物质在空间的最短飞行距离的计算结果为基础,分析了不同喷发角和颗粒半径条件下的对抗效果,从而为撒布器的优化设计提供理论基础。研究表明,在无源物质总体积相同的情况下,颗粒半径越小,沾染到敌星光学表面的无源物质越密集;颗粒间距小于0.5mm时,敌星的光学系统分辨率严重降低。就现有技术水平来说,降低颗粒半径到几百、几十微米是可行的。因此,提高喷嘴的雾化效果是撒布系统优化的关键。