Describe the eight steps involved in manufacturing semiconductors

Describe the eight steps involved in manufacturing semiconductors

If you hear the word semiconductor, what does it mean to you? It sounds complicated and distant, but semiconductors have already infiltrated every aspect of our lives: from smartphones and laptops to credit cards and subways, they're used in a wide variety of products.

The manufacturing of semiconductor technology products in each country needs to go through hundreds of processes, and the entire manufacturing development process in China can be divided into the eight following steps: wafer processing - oxidation - lithography - etching - thin film deposition - interconnect - testing - packaging.

The first step

Processing of wafers

Basically, semiconductor technology all begins with a grain of sand! This is because silicon is the raw material needed to make wafers. A wafer is a round sheet cut from a silicon (Si) or gallium arsenide (GaAs) single crystal column. The primary raw material for fabricating wafers is silica sand, a material containing up to 95 percent silica. Wafer fabrication is the process of making and obtaining wafers.

Casting of one ingot

Initially, the sand is heated and the carbon monoxide and silicon are extracted and examined. This cycle is then repeated until the desired result of ultra-high purity electronic grade silicon (EG-Si) is achieved. The purified silicon is then melted and cooled into a solid single-crystal structure known as an "ingot". This crucial step serves as the foundation for producing semiconductor materials in China. The production of silicon ingots, also referred to as silicon columns, requires precision at the nanometer level and is commonly done using the pull method.

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Cutting of two ingots

Once the design of the previous important step has been finished, the diamond saw will be used to cut off both ends of the ingot. Following this, the resulting sheet will be cut to a specific thickness. The diameter of the ingot wafer determines its size and enables larger and thinner wafers to be divided into more units, ultimately reducing production and management costs for enterprises. To ensure national standard compliance in future research steps, a "flat area" or "dent" mark must be added on the silicon wafer after cutting.

Surface polishing of wafers

The thin sheet obtained through the above cutting process is called "bare chip", that is, the raw "raw wafer". The surface of the bare wafer is uneven, and circuit graphics cannot be printed directly on it. In order to obtain a finished wafer with a clean surface, surface defects must be removed through grinding and chemical etching processes, smooth surfaces must be formed by polishing, and residual contaminants must be removed by cleaning.

Step two

Inflammation

During the oxidation process, a protective film is formed on the wafer's surface. The wafer is protected from chemical impurities, leakage current is prevented, diffusion is prevented during ion implantation, and the wafer is prevented from sliding during etching.

The initial stage of oxidation involves eliminating impurities and contaminants, consisting of a four-step process that involves the removal of organic matter, metals, and residual water evaporation. After this cleaning process, the wafer is ready to undergo high temperatures ranging from 800 to 1,200 degrees Celsius. This heat exposure causes a reaction between oxygen or steam and the wafer's surface, resulting in the formation of a layer of silica, known as "oxide." As oxygen penetrates through this layer, it reacts with silicon to produce an oxide layer of varying thicknesses. The resulting thickness can then be measured post-oxidation.

Oxidation by dry and wet methods

The thermal oxidation process can be divided into dry oxidation and wet oxidation depending on the different oxidants that are used in the oxidation reaction. In the former, pure oxygen is used to produce a silica layer, which is slow, but the oxide layer is thin and dense, while in the latter, oxygen and water vapor are used with high solubility, causing rapid growth but a thin protective layer and low density.

Aside from the oxidant, various factors also influence the thickness of the silica layer. Among these are the wafer's structure analysis, presence of defects on its working surface, and different levels of internal doping. Furthermore, pressure and temperature play a significant role in the rate of oxide layer formation through oxidation technology equipment. During this process, false wafers are utilized to protect and minimize discrepancies in oxidation degree based on the wafers' placement in the unit.

Step three

Etching by photo

As a semiconductor manufacturing process, photolithography involves printing circuit patterns on wafers with light, which can be viewed as drawing plans on wafer surfaces. Advanced lithography technology must be used when the circuit pattern is more precise, as this will result in a higher degree of integration on the finished chip. There are three steps in lithography: photoresist coating, exposure, and development.

Photoresist-coated

When drawing a circuit on a wafer, the first step is to apply photoresist to the oxide layer. Photoresist changes the chemical properties of the wafer to turn it into "photo paper." In this step, you can use the "spin coating" method to apply a thin layer of photoresist to the wafer surface to achieve a more uniform coating and finer pattern.

Photoresists can be divided into two types depending on their light reactivity. The positive film decomposes after light and disappears, leaving a pattern of the unexposed area, while the negative film merges after light, forming an image of the exposed part.

Exposure 2

Circuit printing can be completed by controlling the light after the wafer is covered with a photoresist film. The process is called "exposure." Light can be selectively passed through the exposure device, and when the light passes through the mask plate containing the circuit pattern, the circuit is printed on a chip coated with a photoresist film.

In the exposure process, the finer the print pattern, the final chip can accommodate more components at the same time, helping enterprises improve the efficiency of social production management and reduce the cost of individual components. As a result of its new technology, EUV lithography has attracted worldwide attention in this professional field.

Development 3

In order to display the printed circuit pattern after exposure, a developer is sprayed on the wafer to remove the photoresist from the uncoated areas. In order to ensure that the circuit diagram is of high quality, various measuring instruments and optical microscopes need to be checked after the development process is complete.

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Etching is the fourth step

After the circuit diagram is photoetched onto the wafer, an etching process is used to remove any excess oxide film, leaving only the semiconductor circuit diagram. This can be accomplished using liquid, gas, or plasma.

Depending on the substance used, etching research can mainly be divided into two categories: wet etching, which uses a specific chemical solution to perform an analytical chemical reaction to remove the oxide film, and dry etching, which uses various gases or plasmas.