Silicon Valley Microelectronics offers a variety of metal films deposited on both silicon and non-silicon substrates. SVM has nearly 30 years of experience performing metallization for companies all over the world. Metallization is the deposition of a thin metal film over a dielectric film on a substrate. These films form interconnecting metal lines on a silicon wafer for use in microchip fabrication. These films are often accompanied by some kind barrier material, depending on the metal deposited and the substrate’s end use. If the wafer is being used for integrated circuit (IC) fabrication, this is the final processing step the wafer will go through before it is ready to function as a microchip.
While there are several different techniques to deposit metals, the basic process flow is as follows:
- Grow a dielectric layer on the starting substrate. The most common dielectric layers are silicon nitride (SiN) and silicon dioxide (SiO2), although most dielectric films will work, depending on the project requirements and end use. The role of these layers are to separate conductive metal lines from each other, which can lead to device malfunction.
- Lithography, TSV etch, or photoresist. Using a photomask or selective etch, shallow lines are cut into the dielectric film to create channels for the metal to be deposited.
- Deposit target metals and use CMP to planarize the metal film.
- Repeat steps 1 through 3 for additional metal films. Depending on the application, up to 20 different metal layers can be deposited on a single wafer.
SVM Metals Deposited:
- Aluminum (Al)
- Copper (Cu)
- Gold (Au)
- Tin (Sn)/Indium Tin Oxide (ITO)/Tin Alloys
- Platinum (Pt)
- Nickel (Ni)
- Silver (Ag)
While these metals make up most of SVM’s metal film deposition, we have 27 years of experience working with different vendors to provide the deposition of nearly 20 different metals for a range of applications. Please contact us if you don’t see the film your project requires.
Aluminum has traditionally been the most common metal for interconnects, although copper has recently taken over due to its thermal capabilities and superior resistance to electromigration, or the unwanted movement of electrons. Copper naturally has a low resistivity and is the among the most conductive metals, which also make it an ideal material for IC fabrication.
Metal Deposition Methods:
For wafer metallization, there are two categories of ways to deposit material, either physical deposition or chemical deposition. The device specifications, budget and time constraints must all be considered when deciding which method to use.
There are three types of physical deposition: evaporation, sputtering, and spin-on (casting).
Evaporation – This is a very popular method for depositing metals due to its cost effectiveness and overall simple process. The deposition rate is determined by the pressure and temperature in the furnace, as well as the atomic mass of the material to be deposited. This method is performed by vaporizing the source material in a vacuum, then sending it through a vacuum tube to the wafer, where the material lands and condenses back into a solid state, leaving the desired film.
Sputtering – Sputtering is a deposition technique that uses a furnace and charged plates in order to deposit the target material. There are 2 types of sputtering: DC sputtering, which uses a direct current in order deposit the film, and RF sputtering, which avoids the problem of charge build up by alternating the potential from positive to negative during deposition.
Spin-on (Casting) – First, the metal is dissolved in a solution, then it is applied to the substrate by spinning the wafer. The spin rate of the substrate will determine film thickness and uniformity.
Chemical Vapor Deposition (CVD) – Chemical vapor deposition is a very common film deposition technique used for many different films across almost all applications. Of the several types of CVD, LPCVD and PECVD are the most common methods to deposit metals. This method requires loading wafers into a furnace where the environment is changed to facilitate deposition of the target material.
Electrolytic deposition (AKA electrodeposition, electroplating) – Electrolytic deposition of wafers is a very similar process to electroplating other metals or material. This method first requires the metal source to be connected to a positively charged electrode, while the substrate is placed at a negatively charged electrode. After both the plating material and substrate have been connected to electrodes, they are placed in an electrolytic solution for film deposition. Once both parts are submerged, a DC charge is sent to the anode (positively charged electrode), which oxidizes the metal and a dissolves it into the solution. The negative charge of the substrate attracts positively charge ions in the film to create a uniform film. To ensure cleanliness, this entire process takes place in a clean room, and the plating solution is continuously filtered to prevent unwanted particles from damaging the wafer.
Epitaxy – The target film stack is grown using liquid phase, vapor phase, or molecular beam epitaxy. To grow epitaxial layers, the desired material is mixed with a solvent then deposited onto the target wafer in an environment similar to a CVD furnace. Epitaxial layer growth techniques differ from each other based on the physical state the material is when it’s deposited.
Barrier metals are extremely thin films that go between dielectric layers and metal films to prevent diffusion, crosstalk, electromigration and ultimately, device malfunction. An ideal barrier material is thermally stable, with low electric resistance. It must also bond well to silicon, promote adhesion at the silicon/metal film junction, and be thermally stable at temperatures over 1000°C, with a similar coefficient of expansion to silicon. While there is no perfect barrier material, polysilicon, silicides and some refractory metals have the right characteristics to protect these metal layers.
Common Refractory Metals for Barrier films:
Silicide Barrier films:
WSi2 – Tungsten disilicide
TiSi2 – Titanium disilicide
NiSi – Nickel Silicide
CoSi2 – Cobalt disilicide
PtSi – Platinum silicide
TaSi2 – Tantalum disilicide
MoSi2 – Molybdenum disilicide
For more information on wafer metallization or to request a quote to have metal films deposited, please CONTACT SVM today. For a small sample of our stock wafers to deposit metals on, please visit our ONLINE INVENTORY.