1 / 23

Contact Resistance Measurement Techniques between Metal semi

Contact Resistance Measurement Techniques between Metal and Semiconductor Interface

Download Presentation

Contact Resistance Measurement Techniques between Metal semi

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Contact Resistance Measurement Techniques between Metal and Semiconductor Contacts- Part-A Ajaya Kumar Kavala Reg No:0921PH01 Department of Physics

  2. Content of My Seminar • Ohmic Contact: practical perspective • What is the Contact resistance? • Different types of measurement techniques • Conclusions

  3. Ohmic Contact :practical perspective • Ohmic Contact could have linear or quasi-linear current voltage characteristics but what is essential: it must be able to supply necessary device current and the voltage drop should be small, and • Contact should not degrade the device and should not inject minority carriers

  4. Contact resistance • The term contact resistance refers to the contribution to the total resistance of a material which comes from the two material contact (metal-semiconductor) and electrical leads, which is an inherent property, independent of the measurement method

  5. Various Geometry of Contact Vertical Horizontal(Lateral) • Vertical and horizontal (lateral) contacts can behave quite differently, because contact area may differ from true contact area.

  6. A Rough Method for Measuring Contact Resistance of a Semiconductor: Two probe lateral contact on a diffused semiconductor layer Total Contact Resistance RT = 2Rm + 2Rc + Rsemi Rm=Resistance of the metallic conductor Rc= Contact Resistance Rsemi=Semiconductor resistance

  7. How to characterize Contact resistance of different areas and geometry? Specific Interfacial Resistivity (Theoretical) It depends on barrier height and interfacial doping density. • For Practical purpose: • ρc=Specific Contact resistivity is for real contacts their measurements and measurements interpretations , ( m2) • It is independent of contact area and is convinent parameter when comparing contacts of various sizes A → 0

  8. Measurement techniques Contact resistance measurement techniques fall into four categories 1.Two -contact Two –Terminal 2.Multiple –Contact two –Terminal 3.Four-Terminal Contact resistance method 4.Six -Terminal Contact resistance method

  9. Two-Contact Two-Terminal Method • Contacts on the Top surface • RT =Rc+ Rsp+Rcb+Rp • Rc = Contact resistance of the top contact • Rsp= The spreading resistance in the Semiconductor • Rcb =The Contact Resistance of the bottom contact • Rp= The Probe Resistance • The Bottom contact usually has a large contact area with a small resistance

  10. Two-Contact Two-Terminal method • The spreading resistance can be defined in the following expression Rsp = ρ/2r×arctan(2t/r)  r = Circular top contact radius t = Thickness ρ = Surface of a Semiconductor resistivity • For 2t >> r Rsp= C × ρ/4r where C is Correction Factor that depends on the ρ, r, and on the current distribution .R.H. Cox and H. Strack, “Ohmic Contacts for GaAs Devices,” Solid-State Electron. 10, 1213–1218, Dec. 1967.

  11. Two-Contact Two-Terminal Method • The Current flowing vertically into the top contact for that contact resistance is(Correction factor C=1) Rc = ρc/Ac = ρc/r2 For very small Rcb. Rc=RT - Rsp The Two Terminal method works best when Rsp << Rc

  12. Lateral Two terminal contact geometry The Two terminal method is more commonly implemented with lateral structure. Shown below are side and top views. • Total ResistanceRT=Rshd/W+2Rc

  13. Multiple Contact Two terminal methods • To overcome the deficiencies of the two contact two terminal method • Three identical contacts are made to the semiconductor with contact spacing d1 and d2 • Total contact resistance RTi= Rshdi/ W+2Rc Where i=1 or 2 for Rc Rc= (RT2d1-RT1d2)/2(d1-d2)

  14. Multiple-contact Two-Terminal methods • Identical Contact resistance for all three contacts is some what questionable but is reasonable for not too large sample. • The determination of lengths d1 and d2 is source of inaccuracy (Negative contact resistance). • An early Two dimensional current flow analysis by Kennedy and Murley in diffused semiconductor resistors ,That revealed current crowding at the contacts

  15. Transfer Length Method • When current flows from the semiconductor to metal, it encounters the resistances ρc and Rsh • The Potential distribution under the contact  • The Transfer length is  H.H. Berger, “Models for Contacts to Planar Devices,” Solid-State Electron. 15, 145–158, Feb. 1972; H.H. Berger, “Contact Resistance and Contact Resistivity,” J. Electrochem. Soc. 119, 507–514, April 1972.

  16. Transfer Length: Physical Significance • 1/e distance of the voltage curve is defined as the transfer length • The transfer length can be thought of distance over which most of current transfer from semiconductor into metal and vice versa Potential under a contact versus x as a function of ρ , where x= 0 is the contact edge L=10 𝝁m,Z=50𝝁m and Rsh=10𝜴/square

  17. Transfer length method • Transfer length method can be divided into Two categories 1. Front contact resistance tests structure 2. Cross bridge Kelvin resistance Structure

  18. Front contact resistance tests structure • In This method W = Z has been assumed. • With V measured Contacts 1 and 2 at x = 0 The contact front resistance can be expressed as

  19. Circular transfer line structure W ≠ Z Can be avoided with circular test structures It consists a conducting circular inner region of radius L , a gap of width d and a conducting outer The total contact resistance between the internal and external contacts Where I and K denotes the modified Bessel functions of the first order For L >> 4LT I0/I1→1 and K0/K1→1 S.S. Cohen and G.Sh. Gildenblat, VLSI Electronics, 13, Metal-Semiconductor Contacts and Devices, Academic Press, Orlando, FL, 1986, p. 115; G.S. Marlow and M.B. Das, “The Effects of Contact Size and Non-Zero Metal Resistance on the Determination of Specific Contact Resistance,” Solid-State Electron. 25, 91–94, Feb. 1982; M. Ahmad and B.M. Arora, “Investigation of AuGeNi Contacts Using Rectangular and Circular Transmission Line Model,” Solid-State Electron. 35, 1441–1445, Oct. 1992

  20. Circular transfer line structure C is correction factor C=L/dln (1+d/L) For d/L <<1 Circular contact resistance test structure )

  21. Cross bridge Kelvin resistance Structure • The Voltage is measured at right angles to the current • In this method the voltage contact 3 is located at the side of contact • Voltage is the linear average of the Potential over the contact length L • The Contact resistance is Rc=V/I=ρc/LZ

  22. Conclusion 1.Ohmic contact and Contact resistance will be mainly concerned with metal-semiconductor contacts because they are most common. 2.From the Two Terminal-Two Contact we cannot overcome the crowding current 3.From Two terminal-multiple contact we can not avoid the high current density(Degradation the device)

  23. Thanks

More Related