Please help me to answer. Thank you so muchh Module 5 - In our process experimen
ID: 494659 • Letter: P
Question
Please help me to answer. Thank you so muchh Module 5 - In our process experiments we found pressure and RF power had a strong impact on the sputter deposition rate. In HDP CVD deposition, we use a plasma to provide highly reactive free radicals to speed the chemical deposition reaction, and to provide ions to directionally physically (sputter) etch the surface to allow the deposition to fill holes better. Discuss what you think are the important HDP system plasma controls, and how they control the deposition characteristics. Be sure to make clear the relationship between control and effect. Cross-section 1: deposition of SiO_2 with regular CVD shows that surface deposits block holes (vias) and spaces between features causing "breadloafing" which leaves voids (keyholes) Cross-section 2: HDP CVD preferentially etches at a 45 degree angle which tends to remove the "breadloaf" features, which keeps the space/via open and allows full deposition and complete "gap fill" (over)Explanation / Answer
In manufacturing insulated semiconductors silicon oxide is used as the insulating film. Among the techniques to deposit silicon oxide film, thermal chemical vapor deposition (CVD) or plasma chemical vapor deposition are most widely used. In themal CVD reactive gases are supplied to the substrate surface under heat induced chemical reaction to form a film whereas in plasma CVD a controlled plasma is used to produce the desired film. Due to small sizes of the semiconductors the film coating is not uniform resulting in the gaps between adjacent conductive lines.
To avoid this problem currently high density plasma CVD (HDP CVD) is used in forming the insulation layer. HDP CVD consists of a simultaneous sputter etch and chemical vapor deposition unlike low density plasma CVD. As the processes for manufacting semiconductors continues to scale down to sub-quarter micron technology, the HDP process has been widely used for the gap-fill of small geometry metal spacing in the inter-metal dielectric (IMD) process.
HDP CVD system form a plasma that is approximately two orders of magnitude or greater than the density of a standard CVD system. HDP CVD systems operate at lower pressure ranges than low density plasma systems.
The HDP-CVD systems employ low chamber pressure which provides active species a long mean-free-path and reduced angular distribution. These factors, in combination with the plasma’s density, contribute to a significant number of constituents from the plasma reaching even the deepest portions of closely spaced gaps, providing a film with improved gap-fill capabilities as compared to flms deposited in a low density plasma CVD system.
The films deposited by HDP-CVD techniques are attributed to have improved gap-fll characteristics as compared to films deposited by other CVD techniques due to the occurrence of sputtering simultaneous with film deposition. The sputtering element is promoted by the plasma’s high density and slows deposition on certain features, such as the corners of raised surfaces, thereby contributing to the increased gap-fill ability of HDP deposited films.
Anothe factor that promotes the sputtering effect is introduction of argon or a similar heavy inert gas in HDP-CVD systems. Those systems typically employ an electrode within the substrate support pedestal that enables the creation of an electric field to bias the plasma toward the substrate. The electric field can be applied throughout the HDP deposition process to generate sputtering and provide better gap-fill characteristics for a given film.
One known way to improve the gap-fill capability of silicon oxide films is to add a fuorine-containing source gas
to the process gas. Fluorine atoms are known to etch silicon oxide and it is known that the inclusion of fluorine into a silicon oxide deposition process results in etching simultaneous With deposition Which in turn can improve the deposited film’s gap-fill capability. The incorporation of fuorine into a silicon oxide film also has a primary benefit of reducing the dielectric constant of the deposited film. A silicon oxide film (also referred to as a silicate glass layer)
that includes fluorine is often referred to in the industry as a fluorine-doped silicon oxide film or as a fluorosilicate glass (FSG) layer. It is also known that the dielectric constant of an FSG layer is generally related to the amount of fluorine incorporated into the film. Higher fluorine concentrations result in a lower dielectric constant and lower fluorine concentrations a higher dielectric constant. If fluorine concentrations become too high, however, stability issues may arise. Generally, FSG films having sufficient stability for integrated circuit applications have a fluorine content of between 4—8 atomic percent and a dielectric constant between 3.3 and 3.6. Undoped silicon oxide fillms, on the other hand, generally have a dielectric constant in the range of 4.0 and 4.2.