The important position of lithography technology in the semiconductor industry (2)

    ●Analysis of semiconductor chip production process

   To understand the production process of the chip, we need to know how the chip is made. Let us learn the production process of the chip in several steps.

    1. Silicon purification

   The material for the production of chips and other chips is semiconductors. At this stage, the main material is silicon, which is a non-metallic element. From a chemical point of view, it is located at the junction of the metal element area and the non-metal element area in the periodic table of elements. Because it has the properties of a semiconductor, it is suitable for the manufacture of various tiny transistors, and is currently one of the most suitable materials for the manufacture of modern large-scale integrated circuits.

   In the process of silicon purification, the raw material silicon will be melted and put into a huge quartz furnace. At this time, a seed crystal is put into the furnace so that silicon crystals grow around the seed crystal until a nearly perfect single crystal silicon is formed. In the past, the diameter of silicon ingots was mostly 200 mm, and chip manufacturers are increasing the production of 300 mm wafers.

Monocrystalline silicon ingot

   2. Cutting the wafer

   The silicon ingot is created and shaped into a perfect cylinder, which will then be cut into slices, called wafers. Wafers are actually used for chip manufacturing. The so-called "cut wafer" is to use a machine to cut a piece of silicon wafer with a predetermined specification from a single crystal silicon rod, and divide it into multiple small areas, each of which will become the core of a chip (Die ). Generally speaking, the thinner the wafer is cut, the more finished chips can be manufactured with the same amount of silicon material.

ORION single wafer cleaning system

   3. Photolithography

   A photoresist material is coated on the silicon oxide layer obtained by heat treatment. The ultraviolet light irradiates the silicon substrate through the template printed with the complex circuit structure pattern of the chip, and the photoresist material is dissolved in the place irradiated by the ultraviolet light. In order to prevent areas that do not need to be exposed to light interference, masks must be made to cover these areas. This is a very complicated process, and the complexity of each mask has to be described by dozens of gigabytes of data.

   4. Etching

   This is an important operation in the chip production process, and it is also an important technology in the chip industry. Etching technology pushes the application of light to the limit. The etching uses ultraviolet light with a short wavelength and a large lens . Short-wavelength light shines through the holes of these quartz masks on the photoresist film to expose it. Next, stop the light and remove the mask, and use a specific chemical solution to clean the exposed photoresist film and a layer of silicon next to the resist film.

 Photolithography area of AMD GlobalFoundries plant in Dresden, Germany (Picture of Drive House)

   Then, the exposed silicon will be bombarded by atoms, so that the exposed silicon substrate is partially doped, thereby changing the conductive state of these areas to create an N-well or P-well. Combined with the substrate manufactured above, the gate circuit of the chip is completed. Up.

   5. Duplication, layering

   In order to process a new layer of circuits, silicon oxide is grown again, and then a layer of polysilicon is deposited, photoresist material is applied, and the process of photocopying and etching is repeated to obtain a trench structure containing polysilicon and silicon oxide. Repeat it many times to form a 3D structure, which is the core of the final chip. Fill in the middle of every few layers with metal as a conductor. The number of layers is determined by the transistor layout and transistor scale of the chip during the design, as well as the amount of current passed.

    6. Package

   At this time, the chip is a piece of wafer, it can not be used directly by the user, it must be enclosed in a ceramic or plastic package, so that it can be easily mounted on a circuit board. The package structure is different, but the more advanced the chip package is, the more complex it is. The new package can often improve the electrical performance and stability of the chip, and indirectly provide a solid and reliable foundation for the improvement of the main frequency.

   7, multiple tests

   Testing is an important part of chip manufacturing and a necessary test before a chip leaves the factory. This step will test the electrical performance of the wafer to check if there are any errors and at which step these errors occur (if possible). Next, each chip core on the wafer will be tested separately.

The chip is passing test after test

   Due to the complex structure and high density of SRAM (static random access memory, the basic composition of the cache in the chip), the cache is a problem-prone part of the chip, and the test of the cache is also an important part of the chip test.

   Each chip will be fully tested to verify all its functions. Some chips can run at a higher frequency, so they are marked with a higher frequency; and some chips are marked with a lower frequency because of various reasons. Finally, individual chips may have some functional defects. If the problem lies in the cache, the manufacturer can still block some of its cache, which means that the chip can still be sold, but it may be a low-end product such as Celeron. .

   Before the chip is put into the packaging box, a final test is usually performed to ensure that the previous work is accurate. According to the previously determined maximum operating frequency and different caches, they are put in different packages and sold all over the world.