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体硅Double RESURF器件表面电场解析模型及优化设计

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第27卷 第7期 半导体学报 VO1.27 No.7 2006年7月 CHINESE JOURNAL OF SEMICONDUCTORS July,2006 An Analytical Model for the Surface Electrical Field Distribution and Optimization of Bulk—Silicon Double RESURF Devices Li Q Li Zhaoji,and Zhang Bo (1C Design Center,University of Electronic Science and Technology of China,Chengdu 610054,China) Abstract:A new 2D analytical model for the surface electrical field distribution and optimization of bulk—silicon double RESURF devices is presented.Based on the solution to the 2D Poisson’s equation,the model gives the in— fluence on the surface electrical field of the drain bias and structure parameters such as the doping concentration, the depth and the position of the P.top region,the thickness and the doping concentration of the drift region,and the substrate doping concentration.The dependence of breakdown voltage on the length and doping concentration of the drift region is also calculated.Further more,an effective way to gain the optimum high—voltage is also pro— posed.All analytical results are verified by simulation results obtained by MEDICI and previous experimental data, showing the validity of the model presented here. Key words:bulk—silicon; double RESURF;surface electrical field;optimization EEACC:2560B;2560P CLC number:TN432 Document code:A Article ID:0253—4177(2006)07・1177—06 solution for the surface electrical field of double 1 Introduction RESURF structure so far. The purpose of this work iS to develop a 2D In recent years,(reduced surface field RE— analytical model for the surface electrical field SURF)technology has been widely used in power and potential distributions of bulk—silicon double integrated circuits deviceL ’ .Double RESURF is RESURF devices using the Poisson solution.The one of the most widely used methods to design analytical results of the presented models show a high voltage devices with low on—resistance.Much good agreement with the numerical simulation re・ research by numerical simulation and experiment suits obtained bv MEDICI and previous experi— shows that high breakdown voltage can be main— mental data.The dependence of the surface elec— tained while the drift region doping concentration trical field on the bias and structure parameters is increased to twice as much as that in single RE. has been discussed in detail.The proposed models SURF devicesc。~ ,and a good trade.off between will be helpful for designers to provide accurate breakdown voltage and on.resistance is realized. first—order design schemes and afford an effective Several analytical models have previously been in— way to improve the performance of high voltage troducedE ~ ]but are all for particular structures, bulk.silicon double RESURF devices. providing little information about breakdown phenomena of bulk.silicon double RESURF de. 2 Analytical model vices.A simple method for determining the opti— mal charge balance and processing window of A schematic cross.section of the bulk..silicon double RESURF lateral devices is presented by double RESURF device is shown in Fig.1,where solving the 1D Poisson equation,because of the x measures the horizontal position relative to the 2D nature of the charge distribution in the drift left edge of the double—diffused P n iunction and region,which cannot provide any detailed physi— v measures the vertical position relative to the cal insight into the RESURF principles and device surface.The drift region length is defined as the characteristicsL‘ .To the best of our knowledge, n—type region length,L 3一L 0 L 3,between the there has not been any 2D bulk—silicon analytical n drain and P wel1.The drift region thickness is 十Corresponding author.Email:lqphoenix@sina.corn Received 22 December 2005 ⑥2006 Chinese Institute of Electronics 维普资讯 http://www.cqvip.com

l178 半导体学报 9l(L ,0)=92(L ,0), ! 第27卷 t ,with a uniform doping concentration of N , whereas Pt。p and t t。p are the doping concentration { :  ly:0 !! { ax  ly:0 (7) (8) and depth of the P・top region.respectively.A neg— ax 92(L 2,0):93(L 2,0), 丝 ! f : ! f Fig.1 Cross—section of the double RESURF device ative concentration denotes P—type doping,and a positive concentration is n・type doping.The whole drift region is divided into four regions along the edges of the P・top region,and their boundary po— sitions are given by x 0,L1,L 2,L 3 and Y 0, t t。p,t .The substrate depletion layer thickness is f蚍b,with doping concentration P b.The dielectric constant of bulk—silicon is£。i.The device is biased in the off—state configuration;substrate,source, and gate are grounded while the drain is biased to a positive voltage Vd.The potential function ( ,y)in the silicon film must satisfy the 2D Poisson’s equation given by 尝 +d 1 , ‘  dY 1 9 :一 £si ,  ’ …V1'2’3, 4 (1) Assuming that the drift region is completely de— pleted and the potential functions f( ,Y)can be approximated by the second order Taylor expan— sions (x,y)= ,(x,0)+ y+ y , f:1.2,3 (2) 9a( ,Y) (x,ttop)+ (y 0p)+ 2O 2 (y一 , ∞p )z(3) the boundary conditions for the potential func. tions are then 竺 ! ay =0, f=1,2,3 (4) v:0 : a v l… , 1.3,4 t sub (5) 2( ,ttop)= 4( ,ttop), : !. a v l… aY ax  ly:0 a  lv:0 1(0,0)一0, 仇(L 3,0)=Vd (9) where N1=N3=N4=N ,N2=Pt。。.Equation(4) assumes that the electric field at the surface can be minimizedE .Equation(5)is obtained from a linear field variation along the vertical direction within the substrate depletion thickness t su0.Equa・ tions(6)~(8)are the continuity of the potential and electrical field along the boundary of regions 1-2,2-3,and 2-4,respectively,and Equation(9)is the voltage condition applied to the device.Substi— tuting Eqs.(2)and(3)into Eq.(1)under bound・ ary conditions Eqs.(4)~(6)leads to a general differential equation for the potential distribution function along the surface: + :一 qN',i:1,2,3 dX t一 £ (】0) HereⅣ ff=Ⅳ:ff=N。,t= ,\/——广_b  andⅣ ff= ——Pt。 c c r。——rt。 r c r ——rt。 We assume that t b is a constant in the first— order approximation,and with the general formu— la for the double—sided junction may be taken as t sub ×c 蕊 Solving Eq.(10)with the boundary condi— tions 91(L1,0) V1, 2(L2,O) V2 and (L3,0) V3 gives the surface potential ( ,O)and elec— trical field E ( ,0)as × t si! nh((Lf—L L二 ! !)/t)  , LH≤x<L 维普资讯 http://www.cqvip.com

u > I】,p 【J :)u1第7期 Li Qi etⅡ1.: An Analytical Model for the Surface Electrical Field Distribution and Optimizati0n 0f… 1 1 79 一Lwhere i=1,2,and 3 are applied,V1 and V?are the surface potential of two boundaries between the p。top and drift regions,respectively.The sur. face potential (x,0)and surface electrical field E (x,0)are now obtained from Eqs.(11)and (12),respectively,by finding V1 and V2 for given V0 0 and V3=Vd using the continuity condition Eqs.(8)and(9)。Using P c =N in Eq.(12),the surface electric field of a single RESURF device can be obtained by E(x,0)=(Vd— qN t )× ! + tsinh(L 3/t) e × s inh( )亩L/ t ,o≤ <L。 ’ 、  3 Results and discussion 一Lu0\> IjIn order to verify the proposed model。a 2D device simulation is performed using MEDICI for the same structure.In the following figures,the curves denote the analytical results and the points represent the numerical results. Figure 2 shows the surface potential and elec. trical field distributions of single RESURF and double RESURF devices.A fair accordance be. tween the analytical and numerical results may generally be found.The discrepancies between them are due to the penetration of the space charge region between two regions with different doping concentrations in x=0,L1,L 2 and L 3. However,this kind of discrepancy has little effect Fig.2 Surface potential and electrical field distribu.. tions of single RESURF and double RESURF devices on the breakdown voltage analysis.One can see that a new electric field peak appears at x=L 2 in the double RESU RF device as compared to the single RESU RF structure.Because of the incorpo— ration of the P-top region inside the drift region, the peaks of the electric field of the double RE. SU RF is decreased at x=0 and increased a little at x=L 3.The potential of the double RESURF is distributed linearly in most of the drift region,but the potential distribution of the single RESURF shows a large curvature in the whole drift region, which leads to a non.uniform surface field profile that may cause the degradation of the breakdown voltage. Figure 3 illustrates the surface electrical dis. tributions for different doping concentrations, >\ 【1c l0口 thicknesses,and positions of the p-top region.It is ,p c 0【J100 00 Jn∽ 一Lu0\>r0【】,p 【J i0【J100石00匹Jn∽ 一Lu0\> 一0 0 Fig.3 Surface electrical distributions of the double RESURF device along the drift region(a)Different PI。p;(b)Different t10口;(c)Different L1 u100维普资讯 http://www.cqvip.com

118O 半导体学报 第27卷 evident that there are three surface electric field peaks,which appear at x=0,L 2 and L 3,respec- tively,and strongly depend on the parameters of the p-top region.In Fig.3(a)and(b),Pt。p and ttop have the same effect on the surface electric field distribution.With an increase in Pt。p or t t0p,the e- lectric field peaks decrease at x=0 and increase at x=L 2,L 3,and there exists an electric field value that is fixed between x=L】and L 2.This means that the highest electric field may move from x= L 3 to x=0 with a decrease in P or tt。p,which is responsible for the change of the potential distri— bution.Therefore the breakdown point moves from x L 3 to x=0 as Ptop or tt0p decreases below a critical value。at which the two electric field peaks(x=0,L 3)are equa1.In Fig.3(c),the posi— tion of the electric field peaks at x=L 2 moves with the change of the P-top region position, while the positions of other electric field peaks do 2一gu\>c 2 0【】/p一∞【J一8暑u∞一∞∞uBJJn∞ 0 一gu\>c0【】not change.Because the p-top region’s charge can restrain the peaks at x 0.but enhance those at other places,one can find that with the increase Of L1,the values of the electric field at x 0,L,, and L3 increase,but the value of the electric field decreases at x L 1.Therefore,in order to obtain the ideal electric field distributiOn at which the maximum breakdown is realized,a smaller L is required. Figure 4 demonstrates the surface electric field distributions for different drift region do— ping cOncentratiOns,thicknesses,and substrate do. ping concentrations.In Figs.4(a)and(b),with the increase of N。or t ,the magnitude of the e— lectric field increases at x=0,L 1,and decreases at x=L3,but is fixed at x=L 2,so the maximum peak field point may translate from =L3 to = 0.The maximum breakdown point will change with a change of the position of the highest elec— tric field peak value.When the three electric field peaks(x=0,L 2,L 3)have a uniform value,which must be less than the critical value。the maximum breakdown voltage will appear.In contrast,the substrate doping concentration of the substrate causes the magnitude of the peak field to decrease at x 0 and increase at x L 3 with the increase in the substrate doping concentration.In the optimi. zation of the devices,the substrate doping concen— tration is a very important parameter,which to a large extent determines the position and ampli— tude of the maximum peak electric field ∞IJ—B。【J1u∞一∞∞uBJJn∞ 一gu\>c0【j/p一∞ —B。Eu∞一∞∞uBJJn∞ 2.5 (c) 口尸 b=-4×10 cm。 A P ̄ub=-2X10 cm‘ 2.0 ’ oJD b=一1×1O L 5cm。 D i 1.5 te=6 m =1.5x10”cm。 1.0 /top=1 m尸l。P一1.5xl01 5cm。 140V o 0 5 10 15 20 25 30 35 /LLm Fig.4 Surface electrical distributions of double RE— SURF device along the drift region(a)For different drift region doping concentrations:(b)For different drift region thicknesses;(c)For different substrate doping concentrations The breakdown voltage of a double RESURF device is determined by the minimum of the later. al breakdown voltage BVl t,and the vertical breakdown voltage BV 。 .BVl t due to the surface electric field E i(x,0)can be calculated from the avalanche breakdown condition of the critical e. 1ectric field concept.The maximum surface elec. tric field reaches the critical value E。l t,which can be given as /p一维普资讯 http://www.cqvip.com

第7期 Li Qi et a1.:An Analytical Model for the Surface Electrical Field Distribution and Opti> mizatg一i0>Lon I≥0勺)of… l 2∞ 1 1 8 1 Max[-El(x,0)]:E l。 = where A兰3.1V/cm and B兰0.5 are related to the ionization rates[ .BV is determined solving the ionization integral with ionization rates for an abrupt two.sided p-n junction : (卜 ̄lt e N)2 BVv 5・238×l0】3ב —■■ l Ps—ub with丁 ≈[ ×( (1+ 汀吉 0s 』T eAnalytical results for the breakdown voltage are shown in Fig.5 with simulation results as a function of the drift region length for a set of de- vice parameters and compared with the experi— mental data obtained by ColakLi/s∞ II)l 三 I10 .I 0  .One can see that both show good accordance.For a given set of parameters.with the increase of the drift re- gion length,the breakdown voltage reaches a con’ stant value BV 。 that is limited by the vertical P-n junction breakdown. Length ofthe drift region/Ixm Fig.5 Breakdown voltage as a function of drift re‘ gion length Figure 6 gives the critical drift region thick— ness and breakdown voltage change as a function of drift region doping concentration.There exists an optical drift region doping concentration at which the maximum breakdown voltage Occurs for a double RESURF.which is similar to the results given by Souza ̄引.For a certain drift region thick. ness,a double RESURF device allows a significant increase in the drift region doping concentration responsible for the reduction of the on.resistance when compared with a single RESURF device, which improves the trade.off between the break. down voltage and on.resistance. 钢∞ O O O O O O O O O O 如 加 m gJ101 5cm。 Fig.6 Critical drift region thickness and breakdown voltage as a function of drift region doping concentra— tion 4 Conclusion The surface field distribution and optimal de- sign of double RESURF devices have been studied analytically.The dependence of the surface elec- tric field and potential distributions on the thick- ness and doping concentration of the drift region, depth,doping concentration,and position of the P-top region and substrate doping concentration and the influence of the drift region length and doping concentration on the breakdown voltage also have been discussed.All analytical results have been shown to be in agreement with the re- suits obtained by the MEDICI simulation.In order to enhance the breakdown characteristics of the devices while maintaining the low on.resistance, an ideal surface field distribution is much needed and the critical doping concentration of Pt∞and N is of considerable importance.Therefore,the analytical model proposed in this paper will be a good tool for a designer to optimize double RE- SURF devices. References [1]Appels J,Vaes H,Verhoeven J.High voltage thin layer de— vices(RESURF devices).IEDM Tech Digest,1979:238 [2] Baliga B J.An overview of smart power technology.IEEE Trans Electron Devices,1991,38(7):1568 r 3] Souza M M D,Narayanan E M S.Double RESURF technolo— gY for HVIC.Electron Lett,1996,32(12):1092 r 4]Hardikar S,de Souza M M,Xu Y Z,et a1.A novel double RESURF LDMoS for HVIC’s.J Microelectron,2004,35 (35):305 r 5]Parthasarathy V,Khemka V,Zhu R,et a1.SOA improve— ment by a double RESURF LDMOS technique in a power IC technology.IEDM,2000:75 r 6]Hossain Z,Imam M,Fulton J,et a1.Double—RESUF 720V n- channel LDMOS with best—in-class on.resistance.Proceed一 维普资讯 http://www.cqvip.com

ll82 ings of ISPSD,2002:137 半导体学报 (2):243 第27卷 :7] Imam M,Hossain Z,Quddus M,et a1.Design and optimiza— tion of double—RESURF high—voltage lateral devices for a manufacturable process.IEEE Trans Electron Devices.2003. [11_- Imam M,Quddus M,Adams J,et a1.Efficacy of charge sha- ring in reshaping the surface electric field in high-voltage lateral RESURF Devices.IEEE Trans Electron Devices. 2004,51:141 2O(7):1697 :8 Fang Jian.Yi Kun,Li Zhaoji.et aI_On—state breakdown model for high voltage RESURF LDMOS Chinese Journal of Semiconductors,2005,26(3):436 [12] Han S Y,Kim H W,Chung S K.Surface field distribution and breakdown voltage of RESURF LDMOSFETs.J Micro— electron,2000,31:685 Li Qi.Zhang Bo,Li Zhaoji.A breakdown model of thin drift region LDMOS with a step doping profile.Chinese Journal [13} [143 Sze S M.Physics of semiconductor devices.New York:Wi. 1ey.1981 Han S Y,Na J M,Choi Y I,et a1.An analytical model of the of Semiconductors,2005,26(11):120(in Chinese)[李琦,张 波,李肇基.阶梯掺杂薄漂移区RESURF LDMOS耐压模型 半导体学报,2005,26(11):12o3 breakdown voltage and minimum EPI layer length for RE- SURF pn dides.Soloid.State Electron,1996,39(8):1353 ak S.Effects of drift region parameters on the static [153 Colproperties of power LDMOST.IEEE Trans Electron De- lO3 Guo Yufeng,Zhang Bo,Mao Ping,et a1.Unified breakdown model of SOI RESURF device with uniform/step/linear do. ping profile.Chinese Journal of Semiconductors.2005.26 vices,1981,28(12):1455 体硅Double RESURF器件表面电场解析模型及优化设计 李 琦 李肇基 张 波 (电子科技大学Ic设计中心,成都 610054) 摘要:提出了体硅double RESURF器件的表面电场和电势的解析模型.基于分区求解二维Poisson方程,获得 double RESURF表面电场的解析表达式.借助此模型,研究了p-top区的结深,掺杂浓度和位置,漂移区的厚度和 掺杂浓度,及衬底浓度对表面电场的影响;计算了漂移区长度,掺杂浓度和击穿电压的关系.从理论上揭示了获得 最大击穿电压的条件.解析结果、验证结果和数值结果吻合良好. 关键词:体硅;double RESURF;表面电场; 优化设计 EEACC:2560B;2560P 中图分类号:TN432 文献标识码:A 文章编号:0253.4177(2006)07.1177.06 十通信作者.Email:lqphoenix@sina.corn 2005-12-22收到 ⑥2006中国电子学会 

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