论文标题:GaAs MESFET击穿特性研究
Study of the Breakdown Characteristics in GaAs MESFET"s
论文作者 刘立浩
论文导师 杨瑞霞；赵正平,论文学位 硕士,论文专业 微电子学与固体电子学
论文单位 河北工业大学,点击次数 134,论文页数 61页File Size3565k
2003-02-01论文网 http://www.lw23.com/lunwen_27894467/ 砷化镓;金属半导体场效应晶体管;击穿电压;(NH_4)_2S_x处理;负电荷表面态
GaAs,metal-semiconductor field effect transistor,breakdown voltage,(NH_4)_2S_X treatment,negatively charged surface states
砷化镓(GaAs)晶体是一种电学性能优越的Ⅲ-Ⅴ族化合物半导体材料，以其为衬底制作的半导体器件及其集成电路由于具有信息处理速度快、超高频、低功耗、低噪声等突出的优点而得到广泛应用。GaAs器件及其集成电路在微波通信和军事领域显示出它的重要性。MESFET是GaAs电路中最常用，也是最成熟的一种器件。目前国产MESFET存在钝化后栅—漏反向击穿电压大幅度降低而且不稳定的问题，严重影响了器件的输出功率、效率、抗烧毁能力及长期可靠性。国内对于GaAs MESFET的击穿特性研究依然处于初期阶段，所以解决GaAs MESFET的击穿问题已经成为一个非常重要的问题。为了满足民用和国防工程需要，必须解决国产器件钝化后栅—漏反向击穿电压大幅降低的问题。本论文对GaAs MESFET的击穿特性进行了较为系统的研究。对使用不同方法处理过的GaAs外延片表面进行了XPS谱测试。对各外延片的Ga_(3d)谱和AS_(3d)谱进行了对比，并比较了各外延片表面的镓砷比。结果表明：氨水和(NH_4)_2S_X(溶液都有较强的去除GaAs自体氧化层能力；紫外臭氧和氨水处理过的表面镓砷比接近1∶1，(NH_4)_2S_X，溶液处理过的GaAs表面镓砷比约为1.5∶1，富镓。我们在13所3英寸GaAs生产线上制作了GaAs MESFET，并研究了其动态和直流击穿特性。在动态击穿特性测试中，我们发现，GaAs MESFET的击穿电压随栅极与漏极上所加脉冲电压宽度的增大而增大。我们认为击穿电压与脉冲宽度的关系，主要是因为表面态的原因。在直流特性测试中，分别使用(NH_4)_2S_X溶液、酸碱液和等离子体对GaAs MESFET进行了处理。发现使用(NH_4)_2S_X溶液对GaAs MESFET进行处理，器件击穿电压有了大幅度的提高。我们认为硫钝化减小了GaAs表面的N_d／N_a值(N_d为施主型缺陷浓度，N_a为受主型缺陷浓度)。表面受主态的增多使表面负电荷密度增大，表面聚集的负电荷可以分散漏侧栅边缘的电力线密度，所以随着表面负电荷密度的增大，漏侧栅边缘的电场强度将减小，因此器件的击穿电压就会提高。对于GaAs MESFET在真空中200℃下退火引起的击穿电压的减小，我们提出是由于As—S键很不稳定，在较高温度下分解，As—S键引入的受主缺陷就会减少，则GaAs表面负电荷密度减小，导致器件击穿电压降低。使用酸碱液处理和等离子体预处理法都未观察到击穿电压的明显提高。 ＊田AS MM＊SP【T击穿特性研究 通过实验，我们认为影响GaAS MESFET击穿特性的最重要因素是受主缺陷引入的表面负电荷密度。随着表面负电荷密度的增大，漏侧栅边缘的电场强度将减弱，因此器件的的击穿电压就会提高。
GaAs crystal is a kind of III-V compound semiconductor material with excellent electrical performance. GaAs semiconductor devices and integrated circuits are widely used because of their high speed of information processing, super-high frequency, low power consumption and low noise. GaAs devices and integrated circuits show their importance in microwave communication and military application. MESFET is the most universal and mature device in GaAs circuits. At present there exists a problem in domestic MESFET that gate-drain breakdown voltage decreases obviously and isn"t stable after passivation. It affects the output power, efficiency, the ability to anti-burnout and long-term reliability in GaAs MESFET"s. The study for the breakdown characteristics in GaAs MESFET"s is at initial stage in our country, so it becomes very important to solve the problem of breakdown in GaAs MESFET"s. In order to satisfy the need of civil use and national defence, we must solve the problem that gate-drain breakdown voltage decreases obviously after passivation.This paper has studied systematically the breakdown characteristics of GaAs MESFET"s. We performed a XPS spectrum test to the surface of a few GaAs epitaxial samples after treated with several kinds of methods. The Ga3d and As3d spectrums were compared for these samples. We also contrast the number ratio of Ga to As atoms in the surface of the samples. The result shows that ammonia solution and (NH4)2SX solution are effective in removing GaAs native oxides. The number ratio of Ga to As atoms is approximately 1:1 in the GaAs surface after treated with UV ozone or ammonia solution. The number ratio of Ga to As atoms is approximately 1.5:1 in the surface after treated with (NH4)2SX solution, that is to say, there are excess Ga atoms in thesurface.We fabricated GaAs MESFETs in the 3 inch production line of the 13th electronic research institute, and we investigated their dynamic and direct current breakdown characteristics. During the test for dynamic breakdown characteristics, we found that breakdown voltage increases as the lengths of the pulses applied to the gate and drain electrodes increase. We think that the relation between breakdown voltage and pulses lengths could be mainly due to the influence ofsurface states.During the test for DC characteristics, we treated GaAs MESFETs using (NH4)2SX solution, acid solution, alkali solution and plasma. We found that the breakdown voltage in GaAs MESFET"s increase obviously after treated with (NH4)2SX solution. We think that the sulfur passivation reduces the ratio N/M, in the surface of GaAs, where Nd is the concentration of donor-type defects and Na is the concentration of acceptor-type defects. The increasement of acceptor states in the surface increases the density of negative charge. The negative charge in the surface can reduce the density of electric field lines at the drain-side edge of the gate electrode,the electric field at the drain-side edge of the gate decreases with the increasing of negative charge density in the surface, so the breakdown voltage will increase in GaAs MESFET"s. For the decrease of the breakdown voltage in GaAs MESFET"s after annealed under vacuum, we think that As-S bonds are unstable and decompose under high temperature, then the concentration of acceptor-type defects induced by As-S bonds decrease and the negative charge density in the surface decreases, so the breakdown voltage in GaAs MESFET"s decreases. We didn"t find that the breakdown voltage changes obviously in the GaAs MESFET"s after treated with acid solution, alkali solution and plasma.On the basis of the experimental results, we think the most important factor affecting the breakdown characteristics in GaAs MESFET"s is the density of negative charge induced by acceptor-type defects in the surface. The electron field strength at the drain-side edge of the gate will be weakened as the density of negative charge increases in the surface, so the breakdown voltage in GaAs MESFET"s will increase.
|
