Semiconductor Room What are semiconductors? Semiconductor manufacture

2. Metrology and inspection

Metrology and inspection are important for the management of the semiconductor manufacturing process. There are 400 to 600 steps in the overall manufacturing process of semiconductor wafers, which are undertaken in the course of one to two months. If any defects occur early on in the process, all the work undertaken in the subsequent time-consuming steps will be wasted. Metrology and inspection processes are therefore established at critical points of the manufacturing process to ensure that a certain yield can be confirmed and maintained.

Metrology

What is metrology in the processing steps of semiconductor wafers?

It is the measurement of the line width and hole diameter of a circuit pattern at
  a specified location of a wafer (CD-SEM).

Individual patterns

(Example) L=28nm, Φ=30nm

1nm: 1 nanometer or 1/1,000,000,000m

The measurements below are provided for reference purposes.
Human hair: 60 - 100μm (60,000 - 100,000 nm)
Bacteria: 1μm (1,000nm)
Cigarette smoke: 100nm

 

Measurement of the thickness of thin films on the surface of
  wafers (ellipsometer, etc.)

(Example) D=100nm

 

Metrology system to check the accuracy of the
  overlay(overlay metrology tool)

Measurement is performed to check the accuracy of the shot overlay of the first and second layer patterns transferred onto a wafer.

 

Metrology generally means a method of measuring numbers and volumes, mainly by using equipment.
Metrology, though often considered synonymous with measurement, is a more comprehensive concept that refers not only to an act of measurement itself but to measurement performed by factoring in errors and accuracy, as well as the performance and mechanisms of equipment. If pattern measurements are not within a given specification range, a manufactured device does not operate as designed, in which case the exposure transfer of the circuit patterns may be reworked.
The number of measurement points varies by semiconductor device manufacturer or device.
Metrology is undertaken according to the following sampling method:
-10 to 100 points for one die*
- 5 to 20 dies taken from one wafer
- 1 to 2 wafers taken from one lot (25 wafers).
Newly designed devices may go through several thousand metrological processes for one wafer during the start-up period of manufacture.

*

Die:
A die is one unit of an electronic circuit aligned on a semiconductor wafer. A large number of dies containing the same electronic circuit are created and laid out on a wafer in a grid-like pattern. A die can be likened to a stamp on a stamp sheet. Eventually, they are all cut into separate semiconductor chips (dicing), which are then packaged to create the final semiconductor product.

Wafer inspection

What is inspection in the semiconductor wafer manufacturing process?

It involves the use of inspection equipment to check for compliance or non-compliance, as well as abnormality or unsuitability, in terms of specific criteria. It is a process for detecting any particles or defects in a wafer. Specifically, it is aimed at finding the position coordinates of defects (X, Y). One of the causes of defects is the adhesion of dust or particles. It is therefore not possible to predict where defects will occur. If numerous defects occur on the surface of a wafer, the circuit patterns are not created correctly, causing patterns to be missing. If there are numerous defects, they prevent the electronic circuit from operating correctly, thereby making the wafer a lot-out* product as a defective product. Detecting defects and specifying their locations (position coordination) are the primary role of inspection equipment.

 

*

Lot out:
A situation in which manufactured products are found to be defective and cannot be shipped due to the observation of defects in the inspection stage, such as failure to meet the required specifications. lot rejection、rejected lot