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Apr 3 2018

​From Sand to Chip - Chip Formation Process

Warm hints: The word in this article is about 4500 words and reading time is about 25 minutes

Summary

This paper mainly explain the process of chip formation.How did sand become a chip? Before beginning to introduce a series of basic concepts of electricity and a variety of tedious formulas, I would like to solve the doubts that most of us have all along. However, this problem is still difficult to answer in a few words, we must use at least more than a dozen sections to complete all the knowledge contained in this. So in this section, I will focus on answering the most interesting and important part: How does sand become a transistor?

Article CoreExplanation of Chip Formation ProcessPurposeHow does sand become IC chips?
English NameChip Formation ProcessCategoryIC chips
ApplicationsComputer,biology,etc.KeywordsChip,transistor,MOSFET



Catalogs


Catalogs
I. From Sand to Chips--Process of Chip Formation
II. What Semiconductors Are
III. PN Junctions and Diodes
IV. Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
V. N+ type semiconductor
Chip formation PDF




Introduction

I. From Sand to Chips--Process of Chip Formation

PN junction is a structure widely existing in semiconductor devices. It is actually not a very accurate structure. A PN junction is actually a phenomenon referring to the resulting depletion that occurs near the contact portion of a P-type semiconductor and an N-type semiconductor. 

There are a lot of terms here, if I pull a little bit here and there from the various encyclopedias, the combined things are almost like this. At the beginning, why does the diode have unidirectional conductivity, and why the triode could amplify the current? The question of why the JFET could limit the current was bothering me one after another. The problem with teaching materials in major colleges and universities was that it never spoke detailed principles, even if it was told Can not understand, leading to more and more problems, formulas, theories are also difficult to remember. It was not until long ago that I finally understood their principles. In order to facilitate your understanding of the following series of theories, the first section will be very detailed and lay a solid foundation for subsequent learning.



Detail

II. What Semiconductors Are

Let's talk about what semiconductors are. Semiconductors are materials with conductive properties between the conductive properties of the conductor and the insulator. We know that the difference between a conductor and an insulator is that there is a large amount of free electrons in the conductor, and there is almost no free electron in the insulator. So, can the pure silicon crystal conduct electricity?

Pure silicon crystal

Pure silicon crystal

In the figure above, the blue solid sphere is a silicon atom, and the blue hollow sphere is an electron. Silicon atoms are positive tetravalent, so there are four electrons around an atom (8-4=4). Each silicon atom shares four electrons with the surrounding silicon atoms to form a stable structure of eight electrons. In this case, there is almost no free electrons in pure silicon crystals—electrons are firmly bound by covalent bonds, so pure silicon crystals are insulators.

So how do we enhance the conductivity of silicon crystals? The first method is to increase free electrons. After adding free electrons, because the electrons are negatively charged, we call the silicon crystals with free electrons as N-shaped semiconductors, where "N" is the abbreviation for "negative." The operation of adding free electrons is professionally called doping. Smart students can start with this term and think about how free electrons are added to crystals.

We need to replace silicon atoms with atoms that have higher valence than silicon, so that there will be 9 electrons around this atom. This extra electron will become free electrons and enhance the conductivity of the crystal. Doping this step is generally accomplished by bombarding the silicon crystal in a vacuum using an ion beam. The ions will strike a portion of the silicon atoms and will also inject the required atoms into the ion implementing.

negative semiconductor

negative semiconductor

What atom's valence is higher than silicon? Phosphorus,as an impurity, has a very low content and can approximate these phosphorus atoms as part of the crystal. In normal conditions, the extra electrons of phosphorus stay in the vicinity of donor atoms. However, once we apply voltage on both sides of the semiconductor material, since the stability of eight electrons is higher than nine electrons, both Si and P atoms will “discard” the electrons, and it will become free electrons, from the negative electrode of the battery. Run to the battery's positive pole. Directionally moving free electrons generate electricity.

Directional movement of free electrons

Directional movement of free electrons

Since we know that "N" stands for "negative", then naturally, "P" stands for "positive". Before explaining what a P-type semiconductor is, I have to ask a few questions:

  • (1) how to make silicon crystal reduce electrons?

  • (2)Should the impurities we use be more lively or more stable?

  • (3)Do the nature of the impurities be closer to or farther from silicon?

  • (4) What kind of impurities are easier to add?

The answer is the fifth element boron. Boron has several excellent properties. First of all, it is the main element of the third group, so its outermost layer has three electrons, one less than silicon, so when doped in silicon crystals, the whole lacks free electrons. Second, boron is the only non-metallic element in the third main group that is similar to silicon, and has a strong similarity to silicon. Finally, boron is stable, light in weight, and easily implanted into silicon crystals.

Injecting boron into silicon crystals

Injecting boron into silicon crystals

Boron is a black powdered solid, so I replaced it here with a black ball. There is a dotted ball next to it. This is an electron hole, which means that an electron is missing in this position. So we can think of this hole. Positively charged.

We call electrons and holes charge carriers. They carry their own charge and can act as current generators. The concept of hole may be too abstract, but we can understand it like this: Imagine the hole as a bubble in a glass of water, the gravitational potential of the cup is low, so we think of it as the negative electrode of the battery, and the bottom of the cup is the positive electrode. And then we Think of water molecules as electrons. The water molecules above the bubbles will go to the bottom of the cup, then a new bubble will be created where the original water molecules are located, thus constituting an illusion that the bubbles move upwards. In the circuit, electrons are also affected by the voltage to fill this hole. Then the position of the original electron is replaced by the hole. It seems that the hole moves from the positive electrode to the negative electrode.

charge carrier

charge carrier

III. PN Junctions and Diodes

Now we can finally talk about the PN junction. As we said before, the PN junction is a phenomenon that exists between P-type semiconductors and N-type semiconductors. 

PN junction

PN junction

From now on, the color of the P-type semiconductor will be represented by the hole orange, and the color of the N-type semiconductor will be represented by the electronic blue.

Near the contact surface between the P-type semiconductor and the N-type semiconductor, the electrons of the N-type semiconductor are filled into the holes of the P-type semiconductor, resulting in the absence of carriers in the PN junction. The attraction of holes to electrons is still large. In the part of P-type semiconductors, holes are filled by electrons, but the impurities contained in P-type semiconductors are boron, and there are only three electrons outside boron. When the holes are filled, There are four electrons around boron, one more electron, so the whole is negatively charged. In the same way, in the part of the N-type semiconductor, electrons run into the holes of the P-type semiconductor, and there is one less electron around the phosphor, so the whole is positively charged. In this area, electrons fill all the holes [1], resulting in no free-moving carriers to carry the charge, so that the current does not pass through this area well. P-type semiconductors and N-type semiconductors can conduct electricity when they are alone, but when they are put together, they have unidirectional conductivity, and at this time they form a diode.

diode

diode

We refer to the P-shaped semiconductor portion of the diode as the anode and the N-shaped semiconductor portion as the cathode. This is easy to understand. Review previous knowledge: Empty flows from the positive electrode to the negative electrode, and electrons flow from the negative electrode to the positive electrode. The hollow of the P-shaped semiconductor and the electrons of the N-shaped semiconductor are squeezed toward the PN junction with the help of the forward voltage, so that carriers are regained on both sides of the PN junction and have the ability to conduct electricity. For silicon diodes, as long as the forward voltage exceeds 0.7V, the width of the PN junction shrinks short enough to allow current to pass through the diode.

I have replaced the above battery with the circuit symbol. Correspondingly, the diode also has its own circuit symbol, which is longer:

Diode circuit symbol

Diode circuit symbol

So what if we apply a reverse voltage to the diode? You may think about the direction of movement of electrons and holes. Think about whether the width of the PN junction will change. What effect will this change have on current?

Apply reverse voltage to the diode

Apply reverse voltage to the diode

Similarly, holes will flow to the negative electrode, electrons will flow to the positive electrode, carriers will be far away from the PN junction, and regions where carriers do not exist will become large, so the PN junction will become wider, resulting in no current flowing, and the reverse voltage applied. The larger the current is, the less current can pass through the diode. Therefore, the diode has unidirectional conductivity and can only allow current to flow from the anode to the cathode. [2]

current-voltage diagram

current-voltage diagram

The figure above is a current-voltage diagram showing the current that can pass through the diode at different voltages. The red line in the figure represents a silicon diode and the blue line represents a Germanium diode. Niobium, like silicon, is also a good semiconductor material. The diode has a value called the threshold voltage. Above this value, the diode starts to conduct. For a silicon diode, this value is 0.7V. For a germanium diode, this value is 0.2V [3]. There is also a value called breakdown voltage. This value will be mentioned when we talk about rectification.

After doing these preparations, we can finally talk about transistors. There are billions of transistors in the CPU, but these billions of transistors have exactly the same structure and only the connections are changed. The transistor used by the CPU can have its own name: MOSFET.

IV. Metal Oxide Semiconductor Field Effect Transistor (MOSFET)

In 1926, when the Northern Expedition against the Northern Warlords launched by the Guangdong National Government was in full swing, in the United States across the ocean, the physicist Julius Edgar Lilienfeld had applied for an important influence on the development of electronics in the next century. Patents - Method and Apparatus for Controlling Electric Currents is the first time this patent has proposed the working principle of the Field Effect Transistor. From then on to 1960, although two generations of field-effect semiconductor devices - JFET and MOSFET have come out in succession, China has no contribution to this. Until today, China's semiconductor industry still lags behind the world level.

Method and apparatus for controlling electric currents.png

Method and apparatus for controlling electric currents

The full name of the MOSFET is horrible. Its English name is called Metal-Oxide-Semiconductor Field-Effect Transistor. The Chinese name is Metal-Oxide Semiconductor Field Effect Transistor. I hope you can also appreciate the charm of MOSFETs - low to negligible power consumption, extremely simple structure and processing technology and engaging working principles.

We noticed that the MOSFET is a field effect transistor. What is the field effect? We have all learned the magnetic field in the early days and we know that the opposite sex attracts the opposite sex. For electronics, electric fields are also generated. Like the electric field and the magnetic field, it is the same-sex repulsion and the opposite sex attracts electrons. The electrons will repel electrons, but electrons will attract holes, and vice versa. This statement is very simple and just gives the students a concept. In the following sections I will detailed introduction of the electric field.

electric field.png

electric field

We all know that the role of the transistor is to control large currents with a small current. So transistors generally have three pins. Two are responsible for current input and output, and one is responsible for controlling the opening and closing. The point is how to turn it on and off. We have to make the input impedance as large as possible. What is the input impedance? The input impedance is the resistance value from the control pin to the output pin. If the input impedance is low, the current on the control pin will easily flow out of the output pin. There will be a little bit of each control turn on and off. Electricity flows out of the output pins, which is a waste. If the input impedance is large, then the current on the control pin does not easily flow out of the output pin, because the resistor plays a role in blocking the current flow. The ideal state is that the input impedance is infinite, so that the control current consumes no energy at all, and the power consumption of the CPU can be reduced to almost zero.

MOSFETs use a very magical way to control the current. Its input pin and output pin are connected by two independent N-shaped semiconductors. The two N-shaped semiconductors are filled with a P-shaped semiconductor. Above the middle P-shaped semiconductor, there is a thin layer of silicon dioxide. (Oxide) Insulating layer, above is a metal plate, the metal plate is connected to the control pin.

So it is called metal/oxide/semiconductor/field effect/transistor.

MOSFET structure.png

MOSFET structure

In the MOSFET, we refer to the input pin as source G, the output pin as drain D, the control pin as gate G, and the bottom bulk P-shaped semiconductor as substrate B[4]. When no voltage is applied to the gate, we can see that there are two PN junctions between source-substrate-drain stages. These two PN junctions isolate the source and drain stages from which current flows. No direction can be circulated.

N+ semiconductor channel

N+ semiconductor channel

However, if we apply a positive voltage like the gate, then the positive charge on the gate metal plate will attract the P-type semiconductor and the N-type semiconductor negatively charged electrons. Then, the area near the insulating layer is filled with carriers (electrons). It is known that the semiconductor material containing electrons is an N-type semiconductor. Although the substrate is essentially a P-type semiconductor, since the substrate has a very high concentration For electrons, we can think of the P-type semiconductor in that region as an N-type semiconductor containing free electrons. We call this region the Channel. Since the semiconductors between the source and drain stages are now of the same nature and are all N-type semiconductors, current can freely flow between the two pins.



Analysis

V. N+ type semiconductor

In fact, the semiconductors used here in the source and drain stages are not yet ordinary N-type semiconductors. Here, N+ semiconductors heavily doped with phosphors are used. They contain a large amount of free electrons and can make more electrons able to be gated. The pole attracts, increasing the width of the channel, making it easier to pass the current. We can find that the gate and the drain are insulated, which means that its input resistance is very high. It can be said that if it is not the invention of MOSFET, the electricity generated in the world can not afford several computers. The emergence of MOSFETs has enabled millions of millions of transistor processors to enter millions of homes. Its simple structure also allows ordinary people to have powerful computing power.

Just as our world is made up of atoms, the electronic world is made up of MOSFETs. No matter what is complicated, its essence is simple and beautiful. I hope that this section will inspire the students to inspire you to continue to explore the charm of electronic circuits.This video explained mechanics of chips and formation types of chips:

Mechanics of chips formation and types of chips 


Book Recommendation

  • Fundamentals of Machining Processes

Machining remains a hugely important process in modern engineering and manufacturing practice, and students need to be aware of the vast host of methods and technologies available to meet all sorts of precision and surface finish requirements. 

--by Hassan Abdel-Gawad El-Hofy 

  • The Chip : How Two Americans Invented the Microchip and Launched a Revolution

Barely fifty years ago a computer was a gargantuan, vastly expensive thing that only a handful of scientists had ever seen. The world’s brightest engineers were stymied in their quest to make these machines small and affordable until the solution finally came from two ingenious young Americans. Jack Kilby and Robert Noyce hit upon the stunning discovery that would make possible the silicon microchip.

--by T.R. Reid



Relevant information about "From Sand to Chip - Chip Formation Process"

About the article "From Sand to Chip - Chip Formation Process", If you have better ideas, don't hesitate to  write your thoughts in the following comment area. You also can find more articles about electronic semiconductor through Google search engine, or refer to the following related articles.

8 comments

    • maya on 2018-4-3 15:01:07

    Good article~

    • sarmaya on 2018-4-3 15:39:28

    The chip formation process is the same for most machining processes, and it has been researched in order to determine closed-form solutions for speeds, feeds, and other parameters which have in the past been determined by the "feel" of the machinist.

    • Tony on 2018-4-3 15:41:05

    the shear direction is directly influenced by the rake face deformation and friction processes. The shear direction influences the heating and straining of the chip in the primary process. In terms of metal cutting theory, this means that shear stress and shear direction must be determined simultaneously. Such theoretical analyses are usually based on the mechanics of the process.

    • Martin on 2018-4-3 15:43:50

    metal cutting including Discontinuous Chip,Continuous Chip and Sheared Chips

    • lukarma on 2018-4-3 15:46:54

    Hello~ Could I ask a question that what is continuous chip formation in drilling?

      • author on 2018-4-3 15:48:22
        author

      Re:

      The formation of coil continous chips in drilling often leads to chip disposal problems. 

    • carrot on 2018-4-6 16:46:34

    I like it!!

    • Anna on 2018-4-9 15:45:23

    Good articles! Detailed content

    • And on 2018-4-9 15:47:04

    Excellent!

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