Semiconductor Manufacturing Process Technologies:
Thin Film Deposition & Photoresist Strip
Thin Film Deposition Technologies
Integrated circuits, or semiconductors, are generally built on a silicon wafer substrate, and include a large number of different components such as transistors, capacitors and other electronic devices. These components are connected on the silicon wafer by multiple layers of wiring, called interconnects. To build an integrated circuit, transistors are first fabricated on the surface of the silicon wafer. Wiring and insulating structures are then added as alternating thin-film layers in a series of manufacturing process steps. Typically, a first layer of dielectric material is deposited on top of the transistors. If the conductive material used is aluminum, subsequent metal layers are deposited on top of this base layer, etched to create the conductive lines that carry the electricity, and then covered with dielectric material to create the necessary insulation between the lines. Following each deposition step, a planarization or polishing process is employed to achieve a flat surface for the manufacturing steps that follow. To construct copper wires, the manufacturing process used is a mirror image of that described for aluminum: the dielectric is etched and the copper wiring is deposited within the etched insulator. Building either copper or aluminum wiring requires these manufacturing steps to be repeated many times. Advanced chip designs may require more than 500 process steps.
Our semiconductor manufacturing products are used in a number of different manufacturing process steps. Our advanced deposition systems use chemical vapor deposition (CVD), physical vapor deposition (PVD), and electrochemical deposition (ECD) processes to form the interconnects in an integrated circuit. Our High-Density Plasma CVD (HDP-CVD)and Plasma-Enhanced CVD (PECVD) systems employ chemical plasma to deposit dielectric material within the gaps formed by the etching of aluminum, or as a blanket film which can be etched with patterns for depositing conductive materials into the etched dielectric. Our CVD Tungsten systems are used to deposit small tungsten conductive lines or plugs between layers of metal. Our PVD systems deposit conductive aluminum and copper metal layers by sputtering metal atoms from the surface of a target source. Our Electrofill ECD systems deposit copper to form the conductive wiring on integrated circuits using copper interconnects.
The following paragraphs describe these semiconductor manufacturing processes in more detail.
In the CVD process, manufacturers place wafers in a reaction chamber, introduce a variety of pure and precisely metered gases into the chamber, and then add a form of energy to activate a chemical reaction that deposits a film on the wafers. The CVD process is the traditional method used to deposit dielectric films on wafers. Manufacturers also use CVD to deposit conductive metal layers, particularly tungsten, as it is difficult to deposit such layers on devices with very small features when using conventional PVD or other deposition technologies.
PVD, also known as “sputtering,” is a process in which ions of an inert gas such as argon are electrically accelerated in a high vacuum toward a target of pure metal, such as tantalum or copper. Upon impact, the argon ions sputter off the target material, which is then deposited as a thin film on the silicon wafer. PVD processes are used to create the barrier and seed layers in copper damascene interconnect applications, as well as conductive aluminum wires in a subtractive aluminum manufacturing process.
Electrochemical Deposition Process
Electrochemical deposition, or ECD, is a wet chemistry process used to build the copper primary conductive wires in advanced integrated circuits. Electrochemical deposition uses a copper electrolytic solution to create lines and vias in a dielectric layer which has been etched with the pattern of the circuitry, in a process called copper damascene. These films are deposited on a surface which has been prepared with a copper diffusion barrier layer to prevent copper migration into the adjacent dielectric films, and a copper seed layer to facilitate ECD nucleation--in both cases, these barrier and seed films are deposited using PVD technology.
Deposition-Related Process Technologies
The ultraviolet thermal processing (UVTP) step is a complementary process to the dielectric PECVD process, and is use to treat deposited films to either increase the strain on the film to improve the switching speed of the transistor, or in the case of low-k dielectric films, to increase the hardness of the deposited film to improve packaging reliability. The UVTP chamber resembles a PECVD reactor, but uses a combination of thermal heat and ultraviolet light radiation to change the physical characteristics of the deposited film to achieve one of these results.
Photoresist Strip Processes
Chip manufacturers use photoresist strip technologies to remove photoresist from a wafer’s surface after the photolithographic circuitry patterning process, in order to remove any film residues and particles before proceeding with the next deposition step in the manufacturing process. Both wet chemistry and dry chemistry strip processes may be used in semiconductor manufacturing. In dry strip a combination of plasma energy and gaseous chemistries are combined to achieve the desired result. We offer two different variants of dry strip systems, one for high volume removal of bulk photoresist, and the other for selective removal of residues with very low silicon loss on the substrate.