Nowadays, with the continuous improvement of chip manufacturing processes, there can be more than 10 billion transistors in a chip. How are so many transistors installed?

This is a Top-down View SEM photo. You can clearly see the layered structure inside the CPU. The line width becomes narrower as you go down, closer to the device layer.

This is a cross-sectional view of the CPU. You can clearly see the layered CPU structure. The chip uses a hierarchical arrangement. This CPU has about 10 layers. The lowest layer is the device layer, which is the MOSFET transistor.

When the Mos transistor is enlarged in the chip, you can see a three-dimensional structure like a "podium". Transistors do not have inductors and resistors that easily generate heat. The top layer is a low-resistance electrode, separated from the platform below by an insulator. It generally uses P-type or N-type polysilicon as the raw material of the gate electrode. The insulator below is silicon dioxide.

Impurities are added to both sides of the platform to form the source and drain. Their positions can be interchanged. The distance between the two is the channel. It is this distance that determines the characteristics of the chip.

Of course, the transistors in the chip are not only Mos transistors, but also tri-gate transistors. The transistors are not installed, but engraved during the chip manufacturing.

When designing a chip, the chip designer will use EDA tools to layout and plan the chip, and then route and route the chips.

If we enlarge the designed gate circuit, the white dots are the substrate, and some green borders are the doping layers. The wafer foundry manufactures according to the physical layout designed by the chip designer.

There are two trends in chip manufacturing. One is that wafers are getting larger and larger, so that more chips can be cut and efficiency is saved. The other is the chip manufacturing process. The concept of process is actually the size of the gate, which can also be called is the gate length. In the transistor structure, the current flows from the Source to the Drain. The Gate is equivalent to the gate, which is mainly responsible for controlling the on and off of the source and drain stages at both ends.

Current will be lost, and the width of the gate determines the loss when the current passes through, which is manifested in the common heat and power consumption of mobile phones. The narrower the width, the lower the power consumption. The minimum width of the gate (gate length) is the process.

The purpose of shrinking the nanometer process is to pack more transistors into smaller chips so that the chips will not become larger due to technological improvements. 

But if we make the gate smaller, the current flowing between the source and drain will be faster, and the process will be more difficult.

The chip manufacturing process is divided into seven major production areas, namely diffusion, photolithography, etching, ion implantation, film growth, polishing, and metallization. Photolithography and etching are the two most core steps. 

Transistors are carved through photolithography and etching. Photolithography is to create the circuits and functional areas required for chip production.

The light emitted by the photolithography machine is used to expose the sheet coated with photoresist through a photomask with patterns. The properties of the photoresist change after exposure to light, so that the graphics on the photomask are copied to the sheet, thereby making the sheet have electronic circuits. The role of graphics.

This is what photolithography does, similar to taking pictures with a camera. The photos taken by the camera are printed on the negative, but what is engraved by photolithography is not the photo, but the circuit diagram and other electronic components.

Etching is the process of selectively removing unwanted material from the surface of a silicon wafer using chemical or physical methods. In the usual wafer processing flow, the etching process is located after the photolithography process. The patterned photoresist layer will not be significantly eroded by the corrosion source during the etching, thereby completing the pattern transfer process step. The etching step is a key step in replicating the mask pattern.

Among them, the material also involved is photoresist. We must know that the circuit design is first written on the photomask using a laser, and then the light source is irradiated through the mask onto the surface of the silicon wafer with photoresist, causing the exposed area to The photoresist undergoes a chemical effect, and then the exposed or unexposed areas are dissolved and removed through development technology, so that the circuit pattern on the mask is transferred to the photoresist, and finally etching technology is used to transfer the pattern to the silicon wafer.

Photolithography is divided into two basic processes: positive photolithography and negative photolithography based on the difference between positive and negative photolithography used. In positive photolithography, the structure of the exposed part of the positive resist is destroyed and washed away by the solvent, making the pattern on the photoresist the same as the pattern on the mask.

On the contrary, in negative photolithography, the exposed part of the negative resist will become insoluble due to hardening, and the mask part will be washed away by the solvent, making the pattern on the photoresist opposite to the pattern on the mask.

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