2. Semiconductor - 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 semiconductor manufacturing process to ensure that a certain yield can be confirmed and maintained.

Metrology and Inspection

What is metrology?

The followings are the examples of metrology in the semiconductor wafer manufacturing process.

Metrology 1：

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

(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

Metrology 2：

Measurement of the thickness of the thin films on the surface of a semiconductor wafer (ellipsometer, etc.)

(Example) D=100nm

Metrology 3：

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

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

Overlay marking and metrology for errors

Metrology generally means a method of measuring numbers and volumes, mainly by using metrology 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 metrology 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 manufacturers or devices.
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 metrology 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 ?

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