Patent Application
20080113108
The present invention relates to plasma enhanced chemical vapor deposition (PECVD) processes. In particular, but not by way of limitation, the present invention relates to systems and methods for controlling electromagnetic radiation during the PECVD process.
The process of depositing films using PECVD is well known and has been employed for many years. PECVD is used in several industries to deposit non-conductive and conductive films on a variety of substrates, including glass, semiconductor wafers, and plasma display panels.
These films vary widely in quality and chemistry. With regard to quality, films made of the same material can vary widely in density and purity. That is, depending upon the PECVD parameters, the type of PECVD system, and the system inputs, films can increase or decrease in quality.
In some cases, variations in film quality and chemistry are unintentional. But in other cases, film chemistry can deliberately be altered to create films with particular properties and characteristics. For example, PECVD process parameters such as radical density, pulsing frequency, duty cycle, gas pressure, and temperature can be varied to change film chemistry.
As the control over these process parameters improves, new applications become available for films and film quality for existing applications increases. Despite current process controls, the PECVD industry continues to search for new and better ways to control film chemistry. Accordingly, systems and methods are needed to more finely control film chemistry. Similarly, new films are needed that can be produced as a result of finely controlled film chemistry.
Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.
A system and method for coating a substrate with a film is described. One embodiment includes a process that provides a substrate on which to deposit a film; generates a plasma to produce radicals from a support gas; produces the radicals from the support gas; disassociates a precursor gas using the radicals; deposits material from the disassociated precursor gas on the substrate; and controls the amount of electromagnetic radiation to which the deposited material is exposed.
Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein:
Referring now to the drawings, where like or similar elements are generally designated with identical reference numerals throughout the several views, and referring in particular to
Referring now to
The electrons emitted from the antenna 135 causes the O2 gas to ionize and form a plasma 155. This plasma 155 causes a cascade reaction, thereby forming more ions and fractionalized O2 gas (radicals). These radicals then travel through the neck 150 connecting the remote plasma chamber 130 to the plasma chamber 105. Once in the plasma chamber 105, the radicals collide with the HMDSO molecules, breaking them into SiOx, H, OH, etc.
For this embodiment, a perfect film would include only SiO2. However, waste particles such as OH, H2O and SiOH form during the disassociation and deposition process. And these particles also deposit upon the substrate and growing film. When the growing film is SiO2, these impurities reduce its dielectric properties but may also introduce flexibility into the film. Similar changes result in other types of films.
Most of the impurities produced during the PECVD process are actually pumped out of the process chamber rather than deposited upon the substrate. However, in most processes, enough impurities deposit upon the substrate to significantly change the film chemistry.
Those of skill in the art will understand that a remote plasma source can be used for other thin films besides the dielectric SiO2 layer. This process is shown for illustration purposes only.
Referring now to
These types of flaws in thin films are found in nearly all film chemistries and are not limited to SiO2 dielectrics. And although these films are functional for some purposes, these flaws limit the film's ability and life span in many instances. For example, these impurities and gaps cause thin films to crack and reduce their desired electrical properties.
In some instances, films may actually benefit from a carefully added amount of impurities. But this process of adding impurities must be carefully controlled or the film quality will suffer significantly.
Referring now to
This embodiment of a conventional PECVD system includes a process chamber 175, an antenna 180, a dielectric sheath 185, a supporting gas supply 190, a precursor gas supply 195, and a substrate 200. Although not shown, this system could also include a substrate support. Again, this type of PECVD system is well known in the art and not described in great detail herein.
Although this PECVD system should work almost identically to the remote PECVD system shown in
It was recently discovered that part of the reason for this increase in film quality was due to electromagnetic radiation, and in particular ultraviolet radiation, radiated outward from the plasma formed around the antenna. In a remote PECVD system, the electromagnetic radiation was blocked from reaching the substrate and the growing film. But in the direct PECVD system, the radiation from the plasma could directly bombard the substrate and the growing film. This bombardment was discovered to significantly affect the chemistry of the growing film. In some instances, the electromagnetic radiation bombardment enhanced the quality of the film. However, in other cases, the electromagnetic radiation bombardment could actually disrupt the growth of the film.
As previously discussed, the PECVD industry is always searching for new and better ways to control the PECVD process and more finely tune the chemistry of the deposited films. And conventionally, the PECVD industry controlled process parameters such as radical density, pulsing frequency, duty cycle, gas pressure and temperature. In accordance with embodiments of the present invention, the additional process parameter of electromagnetic radiation can also be controlled.
By controlling the amount of electromagnetic radiation, including UV radiation, to which the growing film is exposed, film chemistry can be more finely controlled. Moreover, the substrate can be preconditioned by controlling the amount of electromagnetic radiation to which the substrate is exposed prior to depositing the film. In both instances, the amount of electromagnetic radiation can be significantly and quickly varied during the course of film production. Alternatively, the amount of electromagnetic radiation can be set for a desired film chemistry. This ability to vary electromagnetic radiation during the film production allows film chemistry to be finely controlled and changed as the film is grown.
Referring now to
In one embodiment, this radiation assist device 215 is an ultraviolet source that is controlled by a computer or manually by a user. The UV source output could be linked to any of the process parameters commonly used to control film quality. For example, the UV source could be linked to radical density so that the UV source is at a high output level when radical density is at its lowest point and UV could be at its lowest point when radical density is at its highest point. Those of skill in the art could determine how to adjust the process parameters and the UV output to achieve their unique, desired film chemistries.
In this embodiment it is assumed that the electromagnetic radiation radiated from the plasma around the antenna 235 is not sufficient to achieve the film properties desired. Accordingly, an assist device 225 is added to provide extra electromagnetic radiation as needed. This electromagnetic radiation assist device 225 could also be manually controlled or computer controlled and timed to operate with other conventional process parameters.
This embodiment assumes that the electromagnetic radiation produced by the plasma surrounding the antenna 285 is sufficient to sufficiently alter film chemistry. In fact, this embodiment assumes that at times the electromagnetic radiation produced by the plasma may be more than is needed to adequately alter film chemistry. Accordingly, the shutters 310 in this embodiment can be opened, restricted, or closed as the process parameters demand. The shutters 310 are designed to block the passage of electromagnetic radiation. As with the previously described radiation sources, the shutters can be linked to other process parameter controls to finally control film chemistry. Shutters can include any device that restricts electromagnetic radiation, including UV radiations.
In some instances, control of electromagnetic radiation alone can produce the desired film chemistries. But as previously described, in other instances, the electromagnetic radiation is controlled in conjunction with other process parameters such as radical density, power modulation, duty cycle, pulsing frequency, pulse shape, gas pressure, and radical density. In particular, as previously described, one novel method of using UV control involves linking the amount of UV at the film to the radical density.
For example, if a SiO2 dielectric layer is being deposited, the UV could be linked to the density of O1 and O3 radicals at a particular point in time. As the radical density decreases, the amount of UV could be increased to prepare the surface of the film as the deposition rate lowers, and as the radical density increases, the UV could be reduced to allow more material to be deposited unencumbered by added energy sources.
Referring now to
Notably, embodiments that use power waveform contouring to control the amount of ultraviolet radiation need not include any type of radiation shield. Although some embodiments of the present invention can also include a radiation shield.
Additionally, controlling the contour of the pulse shape also enables control over the wavelength of the produced ultraviolet radiation. And in some embodiments, the wavelength is controlled independently of the amount of ultraviolet radiation produced.
In conclusion, the present invention provides, among other things, a system and method for PECVD and controlling the PECVD process. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.
