Courtesy : Lam Research
- Deposition is when a thin layer of material is added to the surface of a wafer
- Each deposition process varies depending on the material and the purpose it serves on a chip
Microchips are fabricated by repeating thousands of steps. During the fabrication process, very thin layers of materials are deposited onto a silicon wafer, then etched [Etch Essentials] to create a pattern. As the deposition and etch processes are repeated, a complex series of these patterns are created to control the flow of electricity that allows a chip to perform its function. Lam has been in the deposition market for nearly 45 years and remains one of the top suppliers in the world for deposition tools.
- Deposition refers to the manufacturing process by which a thin layer of material is added to a chip.
Deposition processes are primarily used for two purposes:
- Metal deposition: A layer of conductive material is deposited on a wafer to create a path through which electricity can travel freely.
- Dielectric deposition: A layer of electrically insulating material is deposited on a wafer to ensure electricity is blocked from traveling where it should not flow.
Think of metal deposition as the process of laying roads where cars are allowed to travel, and dielectric deposition as the process of setting up guidelines and barriers to route the flow of traffic.
Common Methods
Many different methods of deposition exist. Each application will have different requirements, but a key consideration is whether the surface to be deposited on is planar or whether it has topography such as trenches and holes. Some of the more common methods of deposition in semiconductor manufacturing include:
Chemical vapor deposition (CVD) uses reactive gases at high temperature. The wafer is placed in a chamber, heated, and the high temperature causes the gases to breakdown and form a solid on the wafer surface.
- CVD can create layers of conductive, non-conductive, or semiconducting materials, so it finds wide applications in semiconductor manufacturing.
- CVD can in many cases deposit well both on planar and non-planar structures.
Electrochemical deposition (ECD) is the process by which a wafer is submerged in a liquid containing positive ions of a metal, then connected to a power source. When the wafer is charged, metal ions in the liquid are attracted and adhere to the wafer, forming a thin layer of the conductive material.
- The ECD process is a cousin of plating for bumpers, however to precisely form high quality, void free metal in the very small gaps on a chip requires the special chemical techniques used in ECD are needed.
Physical vapor deposition (PVD) is a process where individual atoms are knocked off a target material by ion bombardment causing the atoms to travel and adhere to the wafer’s surface. In some cases, some of the atoms can be ionized which allows them to be directed more precisely, which is important when topography is involved.
- PVD can deposit a wider range of materials than CVD at low cost because no specialized chemicals are needed.
- However, the atoms in PVD spray onto the wafer from above and therefore are subject to shadowing effects when non-planar structures are present. This leads to varying thickness within a gap and prevents void free filling. PVD is therefore usually limited to thin liners or to applications where no topography exists on the wafer.
Ultraviolet thermal processing (UVTP) uses a combination of ultraviolet (UV) radiation with thermal energy to modify films to improve their properties.
- UVTP’s primary market is to improve the quality of low dielectric constant materials, making them more robust to withstand further processing. Low dielectric constant materials are needed to reduce the time delays in the interconnections on the chip.
Pulsed laser deposition (PLD) uses a high-powered pulsed laser to strike a target material causing a plasma plume. The plume is directed toward a substrate where a film is deposited consisting of the target material.
- PLD allows more precise control of the composition of complex materials, improving their performance.
Depending on the desired speed and precision of the final product, a manufacturer will employ any number of the above deposition methods.
CVD Variations
Because CVD requires extremely high temperatures, variations of the CVD process have emerged:
Plasma-enhanced CVD (PECVD) is a chemical vapor deposition process that uses plasma to enhance the reaction rather than temperature. Plasma is created by generating an electric field in the reactor to crack the molecules present – exactly what happens in a fluorescent tube or neon light. The fragments of these molecules are much more reactive than the original molecules themselves.
- PECVD therefore generally allows lower temperature processing than when using purely thermal methods. Often, the materials already present on the wafer before a CVD step cannot withstand the high temperature step required for a CVD process.
- The higher reactivity of the precursors when cracked in plasma also allows for much higher rate than with CVD, thereby dramatically lowering the cost of the deposition. This is especially important for very thick films such as those used in 3D NAND and packaging. Lam’s Vector Strata tool for instance dominates the market for the very thick ONON films deposited for 3D NAND.
- PECVD can also make advantageous use of ion bombardment to improve film quality which allows us to make excellent insulators, barriers and etching hard masks with it.
Atomic-layer deposition (ALD) is a highly precise process that deposits up to one layer of atoms at a time. This is done by putting the wafer in a reactor chamber and then alternating its exposure to a solid forming gas and a reacting gas. ALD is useful in creating uniform coatings with sub-nanometer thickness control for the most complex structures.
- During ALD, the gas molecules react with the surface until all available surface sites are consumed, resulting in self-limiting growth. Given enough time, ALD can then ensure a uniformly thick coating in the smallest gap and on the most complex topography.
High-density plasma CVD (HDP-CVD) uses a plasma like in PECVD, but the plasma is supercharged, creating a higher density of ions. The process involves doing deposition and etch simultaneously to allow the filling of small gaps with insulating material.
- The etch in HDP-CVD is needed to be able to remove deposition in unwanted areas so that the gaps can fill properly. The purpose of the higher density plasma is to allow a faster etch rate so that the etch can keep pace with a high deposition rate and therefore provide low-cost process.
All these methods listed play important roles in the fabrication of high-performance and energy-efficient chips that will power the AI era.
Lam’s Role
Lam offers many families of deposition systems:
VECTOR – Dielectric Film Deposition – Plasma enhanced CVD with high productivity multi-station reactor and isolated walls for improved particle control.
Striker– Dielectric ALD – Multi-station reactor design enabling atomic layer deposition of thin, conformal films with leading uniformity and repeatability at high productivity to meet the most demanding needs for small features and aggressive topography.
ALTUS – Metal ALD/CVD – Multi-station ALD/CVD deposition tool enabling leading productivity with superior fill and resistivity performance for the most aggressive topography in advanced devices.
SABRE & SABRE 3D – Metal ECD/ELD – Electrochemical deposition (ECD) and electroless deposition systems (ELD) for metallization. Advanced cell design with innovations in chemistry, waveform, and process control enabling for high deposition rate electrochemical deposition (ECD) for both small feature and large geometry metallization with excellent fill rate and stability.
SOLA – UVTP – Post-deposition treatment of insulating materials with UV radiation and heat. SOLA’s film treatments stabilize insulating material, improving chip performance.
SPEED – HDP-CVD – Deposits dielectric layers into gaps of varying sizes. SPEED products’ precise filling of these gaps with high quality film provides excellent insulation in between conducting lines.
Pulsus – PLD – Supports deposition of a wide range of materials. Pulsus delivers scandium aluminum nitride (ScAlN) films with the highest scandium content available. Pulsus products are especially effective for Specialty Technologies applications.
Reliant – CVD, HDP-CVD, PECVD, PLD – Supports a wide variety of manufacturing requirements by addressing numerous material and performance needs. By supporting these different technologies in a single offering, Reliant products extend fabs’ productive capabilities.
