Semiconductor lithography equipment is used to perform exposure, part of the semiconductor chip manufacturing process. Semiconductor chips are created by performing exposure of microscopic circuit patterns on semiconductor substrates called "wafers." Semiconductor lithography equipment exposes wafers by using projection lenses to reduce the circuit pattern of an original plate, called a "reticle." This equipment consists of three mechanisms: a reticle stage, a projection optical system comprising multiple lens groups, and a wafer stage.
The reticle on which the electronic circuit pattern has been drawn is placed on the reticle stage. Ultraviolet (UV) light is then shined down through it from above. The UV light that passes through the reticle is relayed through the projection optical system, forming an image of the reticle's electronic circuit pattern on the semiconductor substrate placed on the wafer stage. A resin, called "resist," has been applied to the surface of the wafer in advance. This resist undergoes changes when it is exposed to UV light, so the electronic circuit pattern on the reticle is transferred to the areas on which the UV light shines.

Overview of semiconductor lithography equipment

Semiconductor Chip Applications

The Semiconductor Chip Manufacturing Process

The semiconductor chip manufacturing process can be broadly divided into three processes.
1. The design process, in which the wiring circuits are designed
2. The front-end process, in which electronic circuit patterns such as transistors and wiring are transferred to a semiconductor wafer through exposure
3. The back-end process, in which wafers with electronic circuits formed on them are divided into individual chips and assembled

• [Front-end process]
  
  Creating the reticle (original plate)

  Once the electronic circuits that determine the functionality and performance of the semiconductor chip are designed, glass plates called "reticles" are created for transferring these circuit patterns to semiconductors.

• 
  Preparing the wafer

  The wafer that will serve as the base of the semiconductor chip is prepared. The wafer is heated to a high temperature to create an oxide film on its surface. A uniform layer of resist (photosensitive material), which changes when exposed to UV light, is applied over the entire surface of the wafer.

(1)Transferring the circuit pattern to the wafer

The reticle is exposed to light to transfer the circuit pattern to the wafer. Lenses are used to shrink the circuit pattern, making it possible to transfer even finer circuit patterns. The narrower the circuit widths, the more semiconductor elements can fit on a single semiconductor chip. This produces semiconductor chips that provide higher performance and functionality.

The narrower the circuit widths, the more semiconductor elements can fit on a single semiconductor chip. This produces semiconductor chips that provide higher performance and functionality.

How exposure works

The resist that is exposed to light undergoes change, and then developer is used to dissolve and remove this changed resist.

(2)Removing unnecessary sections

A fluorine-based gas is used to remove the oxide film from areas that are not covered by resist. This process leverages the chemical reaction (vaporization) between the gas and the oxide film.

(3)Forming semiconductor elements

After the excess resist is removed, dopants that increase transistor efficiency are injected into the exposed areas of the wafer which are not covered by oxide film to create semiconductor elements.

(4)Covering the wafer with insulating film and flattening its surface

After the oxide film is removed, the entire wafer is covered with insulating film. The surface is flattened to prepare the wafer for the creation of the next layer. Resist is then applied in preparation for the exposure of the next layer of circuit pattern.

• [Back-end process]
  
  Cutting out the chips

  The semiconductor chips are then cut out of the wafer.

• 
  Assembly and completion

  A die bonder is used to affix each chip to a frame and bond it with wires. The product then undergoes inspection, completing the manufacturing process.

The Three Main Performance Characteristics of Semiconductor Lithography Equipment

The following three performance characteristics have the greatest impact on the performance of semiconductor lithography equipment.

1. Resolution
Resolution is a measure of how fine the circuit patterns that are transferred (via exposure) to the wafer can be. Generally speaking, the finer the circuit pattern, the more compact the resulting semiconductor chip and the greater its performance. This helps make the products containing the semiconductor chips more compact.

2. Overlay accuracy
Each wafer is exposed multiple times to create numerous circuit patterns. Overlay accuracy indicates how precisely wafers and reticle circuit patterns can be overlaid. This characteristic is directly linked to semiconductor chip yield rates.

3. Throughput
This refers to the speed with which wafers can be processed, and is an indicator of production efficiency. It is an important indicator for mass production intended to manufacture as many semiconductor chips as possible within a given amount of time.

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Extraordinary Aberration Control for Achieving Theoretical Resolution Limits

Semiconductor chips are manufactured via reduced image exposure, projecting circuit patterns drawn on plates (reticles) onto wafers. The greater the resolution of the projection lenses, the more delicate the patterns can be, increasing the circuit density.
Lithography equipment incorporates ultraviolet (UV) light sources such as mercury lamps, whose wavelengths include i-line wavelengths (365 nm*), and excimer laser, whose wavelengths include KrF wavelengths (248 nm), alongside high numerical aperture projection lenses. Canon uses advanced optical design technology, lens-polishing technology with nm-level precision, and design, assembly, and adjustment technologies for ultra-high-precision optical system mechanisms to manufacture projection lenses that reach the theoretical limit of resolution. Furthermore, Canon's lithography equipment incorporates a high-precision lens driving mechanism to correct for aberration caused by minor environmental changes during exposure, including atmospheric pressure and temperature changes, thereby producing a high level of resolution.
(*) nm = nanometer, or 1/1,000,000,000 of a meter

Achieving High Resolution and Productivity through the World's Finest Acceleration*¹ and Precision Control Technologies

In addition to circuit pattern miniaturization technologies, Canon's semiconductor lithography systems also rely on key technologies including stage acceleration and synchronization control technologies. Moving the stage at high speed and accurately positioning it helps improve productivity and yield rates, making it possible to mass produce high-performance semiconductor products.
In semiconductor lithography equipment that uses the step-and-scan method*², the wafer stage and reticle stage are continuously moved in sync during wafer exposure. Canon has developed extremely precise synchronization control technology with a sub-nanometer level of positioning precision. The use of technologies such as a special linear motor and a lightweight, high-rigidity stage enables repeated acceleration and deceleration of the reticle stage at accelerations of 12 G or more (1/4 that for the wafer stage), contributing to increased productivity.

*¹ One of the world's highest levels of acceleration
As of August 2018, according to research by Canon.

*² Step-and-scan method
The "step-and-scan method" refers to the use of scan-and-repeat projection by lithography equipment. It is capable of achieving higher resolutions than stepper projection, in which the reticle is secured in place and exposure is performed repeatedly.

An AI System that Pushes Lithography Equipment Performance to the Limit

For semiconductor lithography equipment to achieve high productivity and exposure accuracy, it is important to maximize and maintain the performance of its hardware.
To ensure that the diagnosis system used in Canon's semiconductor lithography equipment can accurately detect various events and changes in the status of the equipment, Canon uses high-speed data transfer technology that complies with EDA standards* as well as big data analysis technology that utilizes deep learning and other machine learning algorithms. By quickly collecting and analyzing operation data from lithography equipment, wafer measurement equipment and peripheral equipment, this system can identify changes in equipment status that would be difficult for humans to observe, as well as detect abnormalities and perform prediction and maintenance to achieve the level of operational stability demanded by the equipment industry.

*EDA: Equipment Data Acquisition. EDA standards dictate semiconductor manufacturing equipment standards (SEMI standards) related to data collection.