Introduction to Microelectronic Fabrication by Richard C Jaeger

Introduction to Microelectronic Fabrication by Richard C. Jaeger Distinguished University Professor ECE Department Auburn University Chapter 7 Interconnections and Contacts © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Copyright Notice • © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. • For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1. © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections and Contacts MOS Logic Circuit • 3 Basic Interconnection Levels – n+ diffusion – Polysilicon – Aluminum Metallization • Contacts – Al-n+ – Al-Polysilicon – Al-p • Substrate Contact Not Shown Figure 7. 1 Portion of MOS integrated circuit (a) Top view (b) Cross section © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Resistivity of Metals Commonly Used Metals Aluminum Titanium Tungsten Copper Less Frequently Utilized Nickel Platinum Paladium © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Ohmic Contact Formation (a) (b) (c) Ideal Ohmic Contact Rectifying Contact (similar to diode) Practical Nonlinear “Ohmic” Contact © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Ohmic Contact Formation Figure 7. 2 Figure 7. 3 • Aluminum to p-type silicon forms an ohmic contact similar to Fig. 7. 2(a) [Remember Al is p-type dopant] • Aluminum to n-type silicon can form a rectifying contact (Schottky barrier diode) similar to Fig. 7. 3(b) • Aluminum to n+ silicon yields a contact similar to Fig. 7. 3 c © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Aluminum-Silicon Phase Diagram Aluminum-Silicon Eutectic Point 577 o C © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Aluminum Spiking and Junction Penetration • Silicon absorption into the aluminum results in aluminum spikes • Spikes can short junctions or cause excess leakage • Barrier metal deposited prior to metallization • Sputter deposition of Al - 1% Si © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Alloying of Contacts © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Contact Resistance © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Electromigration High current density causes voids to form in interconnections “Electron wind” causes movement of metal atoms (a) © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. (b) For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Electromigration • Copper added to aluminum to improve lifetime (Al, 4% Cu, 1% Si) • Heavier metals (e. g. Cu) have lower activation energy © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Diffused Interconnections Figure 7. 9 Lumped RC model for a small section of an n+ diffusion © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. • n- and p-type diffusions can be used for local interconnections • pn-junction diode must be kept in its reverse-biased (nonconducting) state • All interconnections have a series resistance R and shunt capacitance C per unit length • The RC time constant limits operating frequency • n+ and polysilicon lines RS ≥ 30 W/square For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Diffused Interconnection • Diffused interconnection in NMOS OR gate. • Merged source and drain regions used to interconnect devices • Multiple contacts used to reduce overall contact resistance Figure 7. 10 © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Buried and Butted Contacts Techniques for interconnecting polysilicon and n+ diffusion Figure 7. 11 © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. (a) Standard metal level link (b) Buried contact with polysilicon in contact with diffusion (requires additional mask step to place n+ under polysilicon (c) Butted contact with aluminum overlap For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Silicides/Polycides/Salicides Figure 7. 12 • Silicides of noble and refractory metals can be used to reduce sheet resistance of polisilicon and diffused interconnections • Provide shunting layer in parallel with original inteconnection © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Properties of Various Silicides © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Salicide • Self-Aligned Silicide on silicon and polysilicon • Often termed “Salicide” © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Contacts Silicide Contacts in Devices © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Liftoff Process (a) Subtractive etching process (b) Additive metal liftoff process Figure 7. 15 © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Multilevel Metallization Figure 7. 16 © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. • Two level metal processes • Silicon dioxide, polyimide or silicon nitride dielectrics • Vias formed to connect between metal levels • Vias can be filled (b)to improve planarization For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Multilevel Metallization Al Figure 7. 17 Multilevel aluminum metallization with tungsten plugs. Copyright 1998 IEEE. Reprinted with permission from Ref. [7]. © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. • Example of multilevel aluminum metallization with tungsten via plugs • Planarity achieved through Chemical Mechanical Polishing (CMP) For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Plated Copper • Copper deposited using “standard” plating processes adapted to microelectronics • Seed layer deposited • Mask layer deposited and patterned • Copper plated up • Mask layer removed • Seed layer etched away © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Copper Damascene Process • Damascene process used to obtain highly planar surfaces • Dielectric layer (insulator) deposited and patterned • Seed layer deposited • Copper plated • Surface polished mechanical & chemical © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Dual Damascene Process © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections Dual Damascene Process (cont. ) © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Multilevel Metallization Examples (b) (a) © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. Figure 7. 20 (a) Dual Damascene copper combined with aluminumcopper and tungsten plugs on the lower levels. Copyright 1997 IEEE. Reprinted with permission from Ref. [6]. (b) Dual Damsascene Copper. Courtesy of Motorola Inc. (b)Note planarity of both structures. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

Interconnections and Contacts References © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.

End of Chapter 7 © 2002 Pearson Education, Inc. , Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher. For the exclusive use of adopters of the book Introduction to Microelectronic Fabrication, Second Edition by Richard C. Jaeger. ISBN 0 -201 -44494 -1.