What is a semiconductor?
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Semiconductors are a type of material with conductivity between conductors and insulators, and their conductivity changes significantly with external conditions. This characteristic makes semiconductors the core material of modern electronic information industry.
From the perspective of band theory, the core difference between conductors, semiconductors, and insulators lies in their different bandgap widths. At a certain temperature, electrons on covalent bonds rely on thermal excitation to obtain energy and detach from the covalent bond, becoming quasi free electrons that move freely in the crystal. The minimum energy required to break free from covalent bonds is the bandgap width.
Hafnium, as the most important and almost irreplaceable application in semiconductors, is used to manufacture the gate dielectric layer in metal oxide semiconductor field-effect transistors (MOSFETs), specifically in the form of its oxide - hafnium dioxide (HfO ₂) or its silicides, nitrides (such as HfSiO, HfSiON).
Why must it be hafnium? --Solving the century old problem of "gate leakage"
Prior to the 45nm technology node, the gate dielectric layer of the transistor had been made of silicon dioxide (SiO ₂). As the size of transistors continues to shrink, the silicon dioxide layer must also be made extremely thin (only a few atomic layers thick), but this leads to a fatal problem: quantum tunneling effect.
Problem: The extremely thin SiO ₂ layer cannot effectively block electrons, resulting in current leakage from the gate into the channel. This will cause a sharp increase in chip power consumption, severe heat generation, and the end of Moore's Law.
Solution: Use "High-k" materials instead of SiO ₂. According to the law of capacitance, using High-k materials with thicker physical thickness but the same "electrical equivalent thickness" can maintain control over the channel while effectively blocking leakage current.
Hafnium oxide (HfO ₂) is the ultimate choice due to its unique comprehensive properties:
High dielectric constant (k value): The k value of HfO ₂ is about 25, much higher than the 3.9 of SiO ₂. This means that it can be made physically thicker, effectively suppressing gate leakage current caused by quantum tunneling and significantly reducing power consumption.
Good thermal stability: HfO ₂ can bond well with silicon substrates and maintain structural stability during subsequent high-temperature processes, without crystallization or adverse reactions with silicon.
Appropriate band shift: There is sufficient conduction and valence band shift between HfO ₂ and silicon, which can form a good energy barrier and effectively block charge carriers.
Compatible with existing processes: Although it is a new material, HfO ₂ can be deposited with high quality, uniformity, and conformability through atomic layer deposition (ALD), a technology compatible with CMOS processes, to meet the needs of large-scale production.
Conductor: In the energy band, the valence band overlaps with the conduction band or the valence band is not completely filled with electrons, resulting in a large number of freely moving electrons and strong conductivity.
Semiconductor: The valence band in the energy band is filled with electrons, but the bandgap width is relatively small. At absolute zero, semiconductors are non-conductive. When the temperature rises or there is light, a small number of electrons in the valence band are excited into the conduction band, leaving holes in the valence band. Under the action of an external electric field, both electrons and holes can participate in conduction.
Insulator: The valence band in the energy band is filled with electrons, but the bandgap width is large. At room temperature, almost no electrons can be excited to the conduction band, so the conductivity is extremely poor.
The first generation of semiconductor materials mainly refers to semiconductor materials such as germanium (Ge) and silicon (Si), which are mainly used for separating devices and chip manufacturing. In the 1950s, germanium dominated the semiconductor industry. In the late 1960s, silicon gradually replaced germanium and was widely used. Silicon has a large amount of reserves in nature. With the increasing maturity of large-scale silicon wafer preparation technology and silicon-based chip manufacturing processes, silicon-based chip technology has developed rapidly along Moore's Law, forming a huge chip industry. Most chips nowadays are silicon-based chips, such as CPUs, GPUs, memory, FPGAs, etc.
The second generation of semiconductor materials mainly refers to compound semiconductor materials, such as gallium arsenide (GaAs), indium antimonide (InSb), etc. Compared to silicon, compound semiconductor materials have large bandgap, low carrier concentration, good optoelectronic properties, as well as good heat resistance and radiation resistance. They are mainly used to manufacture high-speed, high-frequency, high-power luminescent electronic devices and are widely used in fields such as microwave communication, satellite communication, optical communication, optoelectronic devices, and satellite navigation. However, compound semiconductor materials are extremely scarce, with problems such as deep level defects, difficulty in preparing large-sized wafers, high prices, and toxicity, which limit the application of compound semiconductor materials to a certain extent.
The third-generation semiconductor materials are mainly represented by silicon carbide (SiC), gallium nitride (GaN), and zinc oxide (ZnO), which have wide bandgap characteristics, and are therefore also known as wide bandgap semiconductor materials. Wide bandgap semiconductor materials have characteristics such as high breakdown field strength, high saturation electron velocity, high thermal conductivity, high electron density, and high mobility. They are widely used in the manufacture of high-temperature resistant, high-frequency, high-power, and radiation resistant electronic devices, mainly in semiconductor lighting, 5G communication, satellite communication, optical communication, aerospace and other fields.
The fourth generation semiconductor materials have ultra wide bandgap and higher breakdown field strength than the third generation semiconductors, such as gallium oxide (Ga2O3), aluminum nitride (AIN), diamond (C), etc., hence they are called ultra wide bandgap semiconductor materials. Ultra wide bandgap semiconductor materials can withstand higher voltages and powers, making them suitable for manufacturing high-power electronic devices and high-performance RF electronic devices. However, the production and preparation of these materials are difficult, and the manufacturing process is not yet mature. For example, β - Ga2O3 can be prepared with good n-type Ga2O3 by doping donor elements such as Si, Ge, and Sn. However, due to the flat valence band, large effective mass, easy formation of self trapped holes, and self compensation effect of β - Ga2O3 material itself, p-type doping is difficult to achieve, making it impossible to prepare ideal homogeneous pn junctions.
Shaanxi Zhongheng Weichuang Metal Materials Co., Ltd., as a leading hafnium material manufacturer and global exporter in China, has always been committed to providing customers with high-quality and high-purity hafnium products. We insist on integrated operation from production to sales, without any intermediate links, to ensure that you can obtain reliable products directly supplied from the source at the most competitive price.
The company strictly controls every production process, and all hafnium materials meet international standards with solid and guaranteed quality. We have a professional customer service team that is always online to respond to your needs, providing worry free services throughout the entire process from technical consultation to after-sales support, ensuring smooth cooperation and peace of mind in procurement.
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