Semiconductor Device Structures and Metallization Techniques

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What is the primary purpose of the epitaxial layer in a bipolar circuit?

To provide isolation between devices

To control the doping concentration in the device (correct)

To serve as the base region of the transistor

To act as a conducting layer for the circuit

What is the main purpose of the intermetal dielectric (IMD) layers in a device structure?

To enhance the thermal conductivity of the device

To control the stress in the device structure

To act as a conducting path between metal layers

To provide electrical insulation between metal layers (correct)

Which of the following is NOT a common technique for layer deposition in semiconductor device fabrication?

Sputtering

Physical vapor deposition

Chemical vapor deposition

Spin coating (correct)

What is the primary purpose of the final passivation layer in a semiconductor device?

To act as a barrier against environmental contaminants Signup and view all the answers

What is the main advantage of using the dual-damascene process for metal deposition?

It reduces the number of processing steps required Signup and view all the answers

Which of the following is NOT a general criterion that all films must meet for semiconductor use?

Electrical conductivity Signup and view all the answers

What was the main performance barrier that aluminum metallization ran into as circuits reached 100MHz speeds?

Signals could not move fast enough through the metal system to prevent processing delays. Signup and view all the answers

What is the main advantage of using copper over aluminum as a conducting metal?

Copper is more resistant to electromigration than aluminum. Signup and view all the answers

What are some of the drawbacks of using copper as a conducting metal?

Copper requires the use of barrier metals to keep it out of the silicon. Signup and view all the answers

What are some of the deposition methods that can be used for copper?

CVD, sputtering, electroless plating, and electrolytic plating. Signup and view all the answers

What was the resistance value of aluminum compared to copper?

Aluminum had a resistance of 3.1 μΩ-cm, while copper had a resistance of 1.7 μΩ-cm. Signup and view all the answers

What companies were the first to announce the availability of production copper-based devices?

IBM and Motorola. Signup and view all the answers

What is a key advantage of LPCVD systems?

Good step coverage and uniformity Signup and view all the answers

How is the pressure range typically reduced in an LPCVD system?

By connecting the tube to a vacuum pump Signup and view all the answers

What is a disadvantage of using a hot-wall LPCVD system?

Formation of particles on the inside wall surface Signup and view all the answers

Why do some systems in LPCVD have injectors positioned directly over the wafers?

To improve gas mixing and deposition uniformity Signup and view all the answers

What additional component needs to be added to an LPCVD system to reduce pressure in the chamber?

A vacuum pump Signup and view all the answers

What is one advantage of the horizontal LPCVD system design discussed in the text?

Lower exposure to particles Signup and view all the answers

What is the main advantage of an epitaxial film in terms of doping?

Epitaxial films can be grown with a wider range of dopant concentrations compared to silicon wafers. Signup and view all the answers

How is doping achieved in an epitaxial film?

By adding a dopant gas stream to the deposition reactants in the CVD chamber. Signup and view all the answers

What is the classic epitaxial film used in bipolar technology?

An N-type epitaxial film on a P-type wafer. Signup and view all the answers

What is the purpose of the lower temperature used in epitaxial film growth?

To improve the uniformity of the crystal structure in the film. Signup and view all the answers

What is the upper limit of dopant concentration that can be achieved in an epitaxial film?

10^19 atoms/cm^3 Signup and view all the answers

Which statement about in situ CVD doping is true?

It has the lowest dopant carrier mobility due to grain-boundary trapping. Signup and view all the answers

What advantage does doped polysilicon have?

It has a good ohmic contact with the wafer silicon and can be oxidized to form an insulating layer. Signup and view all the answers

Why are polysilicon oxides considered to be of lower quality than thermal oxides grown on single-crystal silicon?

Because of the nonuniformity of the oxide grown on the rougher polysilicon surface. Signup and view all the answers

What is the solution to the problem of polysilicon having a high resistance to metal materials used for conductive leads?

Using a polycide structure with a multimetal stack of polysilicon and a silicide. Signup and view all the answers

Which of the following is an advantage of LPCVD (Low-Pressure Chemical Vapor Deposition) for metal depositions?

It offers good conformal step coverage and high production rates. Signup and view all the answers

What is the key challenge in filling via holes with metal for effective multimetal systems?

The dielectric layer is relatively thick, and the via holes have a high aspect ratio. Signup and view all the answers