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EnglishALD Precursor Applications
1. Integrated Circuits
1.1 Metal Interconnects and Contact Layers/Plugs
Aluminum interconnects have been used for a long time. However, with the continued frequency reduction, lower resistance materials are needed to reduce RC delay. Today, copper interconnects are the choice for most devices. However, for GaAs devices, gold interconnects are usually chosen.
The plug interconnects the silicon to the metal. Since the plug is very short, the chemical and thermal stability of the plug material is more important. Tungsten is the preferred material for the plug due to its relatively low resistivity, high melting point and strong inertness. The use of diborane (B2H6) can enhance the nucleation of tungsten, which helps to reduce the size of the device.
ALD Precursors: TMAl, Mo(CO)6, BTMMo, W(CO)6, BTMW, Ru(EtCp)2
1.2 Seed layer
As device size shrinks, the seed layer needs a copper alternative. During atomic layer deposition, it can be observed that copper nucleates in an island-like manner, which will produce a discontinuous film with high resistivity, so recent research has focused on precious metal materials such as Ru, Pt and Ir.
ALD Precursor: Ru(EtCp)2
1.3 Low-k dielectric materials
Maintaining high-speed performance while shrinking device size is a challenging task due to limiting factors such as RC delay and power consumption. Therefore, low-k dielectric materials are used as contact layers to reduce parasitic capacitance.
ALD Precursors: TEOS, TDMASi, BEMASi, DiPASi, SiCl4, HTEOS, BTBASi
1.4 Barrier layer
Transition metal nitrides such as TiN, TaN and WN are common barrier materials for metal interconnects. For example, diffusion of copper into silicon can lead to deep traps that degrade device performance. In addition, barrier materials seal interconnects from contamination. In the early stages when aluminum interconnects dominated, TiN was used for a long time. However, for copper interconnects, alternatives such as TaN and WN are needed.
ALD Precursors: TiCl4, TDMATi, PDMATa, W(CO)6, BTMW, TBHy, UDMHy
1.5 High-k dielectric materials
As device size continues to shrink, high-k dielectric materials in MOSFETs allow for greater physical thickness to maintain higher channel electron mobility than SiO2. Similarly, as DRAM device size shrinks, capacitance continues to decrease, so high-k dielectric materials are needed to ensure sufficient capacitance. HfO2 has a dielectric constant of 25 and has been widely used, while TiO2 has a dielectric constant of 80.
ALD precursors: TMAl, TiCl4, TDMATi, PDMATa, TEMAZr, TDMAHf
1.6 Capacitor Electrodes
The electrode material that connects the capacitor in the DRAM cell needs to have low resistivity and be easy to etch. A common choice is TiN, while Ru and Nb are being studied as alternatives.
ALD precursors: TMAl, TiCl4, TDMATi, PDMATa, TBHy, UDMHy, Ru(EtCp)2
1.7 Phase change materials
Phase change RAM (PRAM) is a promising non-volatile memory device. It has high read/write speed, good scalability and low power consumption. Ge2Sb2Te5 can be selected as the phase change material.
ALD precursors: GeCl4, TMGe, TDMASb, TTMSiSb, MATe, DETe
2. Perovskite Photovoltaic Cells
The self-limiting nature of the ALD process allows for the deposition of highly conformal, dense coatings on arbitrarily complex substrates or structures, making ALD the method of choice for coating battery materials and perovskite photovoltaic cells.
The perovskite photovoltaic cell route is very promising, but to achieve industrial application, several challenges must be overcome, such as interface charge recombination, ion migration, material diffusion and humidity sensitivity. Currently, ALD process research is mainly focused on the manufacture of isolation layers and functional layers.
Small portable electronic devices are powered by lithium batteries that degrade by lithium ion consumption at the solid electrolyte interface and dissolution of the cathode material. One possible way to slow down the degradation is to deposit Al2O3 on the cathode, thereby reducing the degradation.
ALD Precursors: TMAl, TTBAl
3. Transparent Conductive Materials
Transparent conductive materials use crystalline oxides and achieve conductivity by choosing the right dopants. Common examples are Al-doped ZnO, F-doped InO (FTO) and Sn-doped InO (ITO). Downstream applications are diverse, such as photovoltaic plating, electrodes in (touch) displays and OLEDs.
In capacitive touch screens, both sides of the insulating glass are coated with ITO. Touching the cover glass surface with a finger, a capacitive stylus or a conductive glove generates an electric charge that is resolved at the x and y positions of the ITO.
ALD precursors: TMAl, DADI, TESn, TMGa, DMZn, Cp2Mg