Semiconductor Processes And Equipment: Thin Film Deposition Processes And Equipment

Thin film deposition is the deposition of a nano-sized film on the substrate, and then with the repeated processes such as etching and polishing, many stacked conductive or insulating layers are made, and each layer has a designed circuit pattern. In this way, semiconductor components and circuits are integrated into chips with complex structures.

There are three main categories of thin film deposition:

◈ CVD (Chemical Vapor Deposition)

◈ PVD (Phicial Vapor Deposition)

◈ ALD (Atomic Layers Deposition)

Let's take a closer look at thin film deposition technologies from these three categories.

 

Chemical Vapor Deposition Process

Chemical vapor deposition (CVD) forms a thin film on the surface of a substrate through thermal decomposition and/or the reaction of gaseous compounds. The film layer materials that can be made by the CVD method include carbide, nitride, boride, oxide, sulfide, selenide, telluride, as well as some metal compounds, alloys, etc.

Chemical vapor deposition is currently an important microscopic manufacturing method because it has the following characteristics:

1. Wide range of deposits: metallic and non-metallic films can be deposited, as well as films with multi-component alloys, as well as ceramic or compound layers as required.

2. The CVD reaction is carried out at atmospheric pressure or low vacuum, and the diffraction of the coating is good, and it can be evenly coated for deep holes and fine holes on surfaces with complex shapes or workpieces.

3. It can obtain a thin film coating with high purity, good compactness, low residual stress and good crystallization. Due to the mutual diffusion of reaction gases, reaction products and substrates, a well-adhesive film can be obtained, which is important for surface reinforcement films such as surface passivation, corrosion resistance and wear resistance.

4. Since the temperature at which the film is grown is much lower than the melting point of the film material, it is possible to obtain a highly pure, fully crystallized film layer, which is necessary for some semiconductor coatings.

5. By adjusting the parameters of deposition, the chemical composition, morphology, crystal structure and grain size of the cladding can be effectively controlled.

6. The equipment is simple, easy to operate and maintain.

7. The reaction temperature is too high, generally 850~1100 °C, and many matrix materials cannot withstand the high temperature of CVD. Plasma or laser-assisted technology can be used to reduce the deposition temperature.

The chemical vapor deposition process is divided into three important stages：

1,The reaction gas diffuses to the surface of the matrix

2,The reaction gas is adsorbed on the surface of the matrix

3,A chemical reaction occurs on the surface of the matrix to form solid deposits and the resulting gas-phase by-products are detached from the surface of the matrix

The most common chemical vapor deposition reactions are: thermal decomposition reaction, chemical synthesis reaction and chemical transport reaction. The main reaction processes of CVD are as follows:
i). Polysilicon

SiH4 -> Si + 2h2 (600℃)

Deposition Speed 100 - 200 nm /min

Phosphorus (phosphine), boron (diborane) or arsenic gas can be added. Polysilicon can also be doped with diffusion gas after deposition.

ii). Silicon Dioxide

SiH4 + O2→SiO2 + 2h2 (300 - 500℃)

SiO2 is used as an insulator or passivation layer. Phosphorus is usually added to obtain better electron flow properties. When silicon is present in oxygen, SiO2 grows thermally. Oxygen comes from oxygen or water vapor. The ambient temperature requirement is 900 ~ 1200°C. The surface of the silicon wafer after selective oxidation is shown in the figure below:

Both oxygen and water diffuse through the existing SiO2 and combine with Si to form additional SiO2. Water (steam) diffuses more easily than oxygen, so it grows much faster using steam. Oxides are used to provide an insulating and passivation layer to form the transistor gate. Dry oxygen is used to form gates and thin oxide layers. Steam is used to form a thick oxide layer. The insulating oxide layer is usually around 1500 nm, and the gate layer is usually between 200 nm and 500 nm.

iii). Siicon Nitride

3SiH4 + 4NH3 -> Si3N4 + 12H2

Chemical Vapor Deposition CVD Equipment

There are three basic types of CVD reactors:

◈ APCVD: Atmospheric pressure CVD

◈ LPCVD:Low pressure CVD,LPCVD

◈ UHVCVD: Ultrahigh vacuum CVD

◈ LCVD: Laser CVD

◈ MOCVD:Metal-organic CVD

◈ CVD (PECVD

The schematic diagram of the equipment for the low-pressure CVD process is shown in the figure below.

The diagram below shows the structure of an ion-enhanced CVD plant used to deposit carbon and prepare a diamond-like coating.

PVD Process

Under vacuum conditions, the material on the surface of the material source (solid or liquid) is vaporized into gaseous atoms, molecules or parts ionized into ions by physical methods, and a thin film with a special function is deposited on the surface of the matrix through a low-pressure gas (or plasma) process. Physical vapor deposition can not only deposit metal films and alloy films, but also can deposit compounds, ceramics, semiconductors, polymer films, etc. The basic principle of physical vapor deposition technology can be divided into three process steps: (1) Vaporization of the plating material: even if the plating material evaporates, sublimates or is sputtered, that is, through the vaporization source of the plating material. (2) Migration of atoms, molecules or ions of the plating material: After the atoms, molecules or ions supplied by the gasification source collide, a variety of reactions will be generated. (3) Deposition of plating atoms, molecules or ions on the substrate. The process of physical vapor deposition technology is pollution-free and has few consumables. The film is uniform and dense, and the binding force with the substrate is strong. The technology is widely used in aerospace, electronics, optics, machinery, construction, light industry, metallurgy, materials and other fields, and can prepare coatings with wear-resistant, corrosion-resistant, decorative, conductive, insulation, light conductivity, piezoelectricity, magnetism, lubrication, superconductivity and other characteristics. There are also a variety of processes for physical vapor deposition:

◈ Thin Film Vacuum Coating

◈ PVD-Sputtering

◈ Ion-Coating

Below we describe the process technologies for each of these three types of methods.

◈ Thin Film Vacuum Coating

Principle: Thin Film Vacuum Coating is a technology that heats and evaporates the plating target under vacuum conditions, so that a large number of atoms and molecules are vaporized and leave the liquid plating material or leave the solid plating surface (or sublimation), and finally deposit on the surface of the substrate. In the whole process, the gaseous atoms and molecules will migrate directly to the matrix with few collisions in a vacuum, and are deposited on the surface of the matrix to form a thin film. The evaporation methods include resistance heating, high-frequency induction heating, electron beam, laser beam, ion beam high-energy bombardment plating material, etc.

Thin Film Vacuum Coating is one of the most ancient technology of PVD.

Evaporation source: The plating material is heated to the evaporation temperature and vaporized, this heating device is called an evaporation source. The most commonly used evaporation sources are resistance evaporation sources and electron beam evaporation sources, and the evaporation sources for special purposes include high-frequency induction heating, arc heating, radiation heating, laser heating evaporation sources, etc. Process: The basic process of vacuum evaporation is as follows:

Pre-plating treatment: including cleaning of plating parts and pretreatment. The specific cleaning methods include cleaning agent cleaning, chemical solvent cleaning, ultrasonic cleaning and ion bombardment cleaning. Specific pretreatment includes static removal, primer coating, etc.

Furnace loading: including vacuum chamber cleaning, cleaning of plating hangers, installation and debugging of evaporation sources, and coating of gowns.

Vacuuming: Generally, the first rough pumping to more than 6.6Pa, the pre-stage maintenance vacuum pump of the diffusion pump is opened earlier, and the diffusion pump is heated. After the preheating is sufficient, open the high valve and pump it to a background vacuum of 6×10-3Pa with a diffusion pump.

Baking: Bake the plated parts to the desired temperature.

Ion bombardment: the vacuum degree is generally 10Pa~10-1Pa, the ion bombardment voltage is 200V~1kV negative high voltage, and the departure time is 5min~30min,

Pre-melting: Adjust the current to pre-melt the plating material, and degassing for 1min~2min.

Evaporative deposition: Adjust the evaporation current according to the requirements until the end of the desired deposition time. 8. Cooling: The plated parts are cooled to a certain temperature in the vacuum chamber.

9. Furnace: After picking, close the vacuum chamber, vacuum to 1×10-1Pa, and the diffusion pump is cooled to the allowable temperature before turning off the maintenance pump and cooling water.

◈ PVD-Sputtering

Sputtering coating refers to the use of energy-obtained particles (such as argon ions) to bombard the surface of the target material under vacuum conditions, so that the atoms on the surface of the target material can obtain enough energy to escape, this process is called sputtering. The sputtered target is deposited on the surface of the substrate, which is called sputtering coating.

Argon (Ar) atoms can be ionized into argon ions (Ar+) by filling argon (Ar) in a vacuum environment and discharging argon at high voltage. Under the action of the electric field force, the argon ions accelerate the bombardment of the cathode target made of plating material, and the target will be sputtered out and deposited on the surface of the workpiece.

Sputtering coating can be divided into DC sputtering, radio frequency sputtering and magnetron sputtering, and the corresponding glow discharge voltage source and control field are high-voltage direct current, radio frequency (RF) alternating current and magnetron (M) field, respectively.

Sputtering coating, high deposition speed, good process repeatability, easy automation, suitable for large-scale architectural decoration coating and functional coating of industrial materials. Sputtering coatings also play an important role in the manufacture of integrated circuits and semiconductor devices.

With the development of high-tech and emerging industries, there are many new and advanced highlights in physical vapor deposition technology, such as multi-arc ion plating and magnetron sputtering compatibility technology, large rectangular long-arc targets and sputtering targets, non-equilibrium magnetron sputtering targets, twin target technology, ribbon foam multi-arc deposition winding coating technology, strip fiber fabric winding coating technology, etc., the use of complete sets of coating equipment, to the computer automated, large-scale chemical industry scale development.

◈ Ion-Coating

The basic principle of ion coating is to use plasma ionization technology under vacuum conditions to partially ionize the atoms of the plating material into ions, and at the same time produce many high-energy neutral atoms. A negative bias is applied to the substrate to be plated, so that under the action of deep negative bias, ions are deposited on the surface of the substrate to form a thin film.

With the help of inert gas glow discharge, the ion coating makes the plating material (such as metal titanium) gasify and evaporate and ionize, and the ions are accelerated by the electric field to bombard the surface of the workpiece with higher energy, at this time, if carbon dioxide, nitrogen and other reaction gases are introduced, TiC and TiN covering layers can be obtained on the surface of the workpiece, and the hardness is as high as 2000HV.

Ion coating is one of the most widely used coating processes in the physical vapor deposition method.

Its advantages are as follows：

①The adhesion between the film layer and the matrix is strong, and the reaction temperature is low.

②The film layer is uniform and dense.

③Good winding plating under negative bias pressure.

④No contamination.

⑤A wide range of substrate materials are suitable for ion plating.

With the development of ion coating technology, many different ways of ion coating technology have emerged, such as: reactive ion plating, plasma coating, multi-arc ion plating, etc. I won't go through them all here.

PVD Equipment

Physical vapor deposition equipment includes vacuum evaporation coaters, vacuum sputter coaters, and vacuum ion coaters.The figure below shows the structural principle of the vacuum evaporation coater

The following figure shows the schematic diagram of the equipment structure of sputter coating

The following figure shows the structural schematic diagram of the ion coating equipment

ALD Process

ALD：Atomic Layers Deposition is a high-precision thin film deposition technology based on chemical vapor deposition (CVD), which is a technology that deposits material materials layer by layer on the surface of a substrate in the form of a single atomic film based on chemical vapor phase.Unlike conventional CVD, ALD is deposition in which the reaction precursors are alternately deposited, and the chemical reaction of the new atomic film is directly related to the previous layer, so that only one layer of atoms is deposited in each reaction.

Only one layer of atoms is deposited in each reaction, which is self-limiting, allowing the film to be deposited on the substrate conformal and pinhole-free. As a result, the thickness of the film can be precisely controlled by controlling the number of deposition cycles.

ALD depositable materials include metals, oxides, carbon (nitrogen, sulfur, silicon), various semiconductor materials, and superconducting materials. As the integrated circuits become more and more integrated and smaller, high dielectric constant (high k) gate dielectrics are gradually replacing traditional silicon oxide gates, and the aspect ratio is getting larger and larger, which puts forward higher requirements for the step coverage ability of deposition technology, so ALD has been increasingly adopted as a new deposition process that can meet the above requirements.

An ALD cycle can be divided into four steps：

The first precursor gas is introduced into the substrate, and adsorption or chemical reaction occurs with the surface of the substrate;

Flush the remaining gas with inert gas;

Introduce the second precursor gas; chemical reaction with the first precursor gas adsorbed on the surface of the matrix to form a coating, or the product reacting with the first precursor and the matrix continues to react to form a coating;

Wash away the excess gas with inert gas again.

Features and advantages of ALD technology:

Excellent three-dimensional conformality: ALD produces a film that is consistent with the shape of the original substrate, i.e. the film can be deposited uniformly on a concave-like surface. Therefore, it is suitable for substrates of different shapes; Uniform three-dimensional film, consistent shape and conformality are the unique advantages of ALD technology.

High flatness: The surface is pinhole-free, and the bottom-up growth mechanism determines the pinhole-free nature of the film, which is valuable for blocking and passivation applications.

Excellent adhesion: The chemical adsorption of the precursor to the substrate surface ensures excellent adhesion

Low thermal budget (low deposition temperature): Thin film growth can be performed at low temperatures (room temperature to 400°C), which is very attractive for temperature-constrained polymer devices and biomaterial coatings

High accuracy: The thickness of the substrate film can be controlled simply and precisely by controlling the reaction cycle, and the thickness accuracy of the film can reach the thickness of one atom.

ALD Equipment

The process temperature of ALD equipment is 50~500°C, which can work under normal pressure, but it tends to work under low pressure (0.1~10Torr) conditions. ALD can be divided into hot atomic deposition and plasma-enhanced atomic layer deposition (PEALD) according to different energy supply methods. Thermal ALD relies on thermal energy to excite two or more precursors to react chemically. In order to provide sufficient reaction activation energy, thermal atomic layer deposition equipment generally works in the range of 200~500°C.

The picture below shows a single-wafer ALD device

0020-24896 COVER RING 6" SST 101 AL

 

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