Photolithography

 

Description: Overview of the photolithography: resolution and alignment, the basic photoresist properties, mask and etch. Final discussion includes both the basic steps and a detailed view of the process.

Length of Time: 9 hours

Prerequisites:

Module: Oxidation

Topics:

1. Photolithography

Purpose

Resolution

Alignment - Overlay accuracy

2. Basic photoresist properties

Positive

Negative

Chemistry

Physical properties

3. The mask

Light (clear) field

Dark field

4. Etch

5. Basic "photolith" process flow

Steps

Purposes

Cross-sections

6. Detailed view of process steps

Methods

Materials

Equipment

Measurements

Tests

Safety

The environment

 

Student objectives:

Student will be able to:

1. Define "photolithography" in the context of semiconductor manufacturing process. Explain why photolithography is necessary.

2. Compare and contrast negative and positive photoresists. Include a brief discussion of some chemical and light-sensitive properties particularly with reference to polymerization.

3. Give some key properties of photoresists with bearing on physical, optical, storage, shelf life, and cleanliness factors.

4. Explain the difference between light field and dark field mask-reticles. Explain when each type would be used.

5. Explain, briefly and generally, what is meant by "etch."

6. Using approximately 10 steps, construct a flow diagram that represents a photolithographic (photomasking) process. Give reasons for each step, and show a cross-section of 7. materialson the wafer at each step.

7. For each step of the photolithographic (photomasking) process discuss details pertaining to specific methods, materials, and equipment. Include, as appropriate, a description of tests and measurements. Also include safety and environmental concerns.

8. Discuss various errors and problems associated with photolithography.

9. Explain the differences between mask and reticles.

10. Compare and contrast alignment and overlay.