Patent Application
20120027956
The present invention relates generally to semiconductor fabrication, and more particularly to nitride films.
Consumer electronics devices are driving trends in miniaturization. As consumers are demanding products with more processing power, and smaller physical size, there is a need to improve the performance of various integrated circuits. This need has pushed semiconductor technology and chip manufacturing towards advances that have resulted in a steady increase of the number of transistors on a single chip. This has continued to drive the feature size of semiconductors smaller and smaller.
One of the most frequently required processes in the fabrication of IC circuits is the nitride deposition process. Nitride films play an important role in semiconductor fabrication, and as semiconductor fabrication technology continues to advance, and feature size continues to reduce, there is a need for improved nitride films and methods for forming and modifying the nitride films.
In one embodiment of the present invention, a method of forming a nitride film is provided. The method includes performing a main film deposition using a high density plasma chemical vapor deposition tool. The main film deposition process comprises administering a first reactive source gas at a first main flow rate, a second reactive source gas at a second main flow rate, and an ion source gas at a third main flow rate.
The method further includes performing an ending film deposition process using the high density plasma chemical vapor deposition tool. The ending film deposition process comprises reducing the flow rate of the first reactive source gas from the first main flow rate to a first ending flow rate gradually over a ramp time interval, and maintaining acceleration power of the high density plasma chemical vapor deposition tool.
In another embodiment of the present invention, an alternate method of forming a nitride film is provided. This method includes performing a main film deposition process using a chemical vapor deposition tool and performing a post deposition conditioning process to remove a top layer of the nitride film.
In yet another embodiment of the present invention, an additional method of forming a nitride film is provided. This method includes the steps of performing a main film deposition process using a high density plasma chemical vapor deposition tool. The main film deposition process comprises administering SiH4 gas at a first main flow rate, N2 gas at a second main flow rate, and argon gas at a third main flow rate. An ending film deposition process is performed using the high density plasma chemical vapor deposition tool. The ending film deposition process comprises reducing the flow rate of the SiH4 gas from the first main flow rate to zero gradually over a ramp time interval, and maintaining acceleration power of the high density plasma chemical vapor deposition tool.
The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying figures (FIGs.). The figures are intended to be illustrative, not limiting.
Certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines which would otherwise be visible in a “true” cross-sectional view, for illustrative clarity.
Often, similar elements may be referred to by similar numbers in various figures (FIGs) of the drawing, in which case typically the last two significant digits may be the same, the most significant digit being the number of the drawing figure (FIG).
Throughout the descriptions set forth in this disclosure, lowercase numbers or letters may be used, instead of subscripts. Regarding the use of subscripts (in the drawings, as well as throughout the text of this document), sometimes a character (letter or numeral) is written as a subscript—smaller, and lower than the character (typically a letter) preceding it, such as “Vs” (source voltage) or “H2O” (water). For consistency of font size, such acronyms may be written in regular font, without subscripting, using uppercase and lowercase—for example “Vs” and “H2O”.
For the purpose of providing context for describing embodiments of the present invention, the prior art will be briefly discussed.
Excitation frequencies in the low-frequency (LF) range, usually on the order of hundreds of kHz, require several hundred volts to sustain the discharge. These large voltages lead to high-energy ion bombardment of surfaces. High-frequency plasmas are often excited at the standard 13.56 MHz frequency widely available for industrial use; at high frequencies, the displacement current from sheath movement and scattering from the sheath assist in ionization, and thus lower voltages are sufficient to achieve higher plasma densities. The low frequency excitation is sometimes referred to as the source power of the HDP-CVD tool, and serves to generate plasma. The high frequency excitation is sometimes referred to as the acceleration power or bias power, and is indicated symbolically as A in
The increased film density, plus the uncontrolled nature of the ending deposition phase can result in increased manufacturing defects which can adversely affect product yield. The increased density of top layer 204 (
The acceleration power of the HDP-CVD tool is maintained during the ending deposition phase. In one embodiment, the acceleration power is in the range of about 1000 W (watts) to about 1500 W, and has a frequency of 13.56 MHz. The source power, used to generate the plasma, is in the range of 3000 W-4000 W, with a frequency in the range of about 200 KHz to about 600 KHz.
In one embodiment, the flow rates of the gases used during the main deposition phase are as follows: The SiH4 flow rate ranges from about 50 to about 150 sccm (standard cubic centimeters per minute), with a preferred value of about 90 sccm. The N2 flow rate ranges from about 200 to about 500 sccm (standard cubic centimeters per minute), with a preferred value of about 310 sccm. The argon flow rate ranges from about 150 sccm to about 400 sccm with a preferred value of about 230 sccm. In another embodiment, helium is used as the inert gas in place of argon.
In one embodiment, the flow rates of the gases used during the ending deposition phase are gradually changed from the following values over a predetermined time interval, referred to as the ramp time interval. In one embodiment, the starting and ending limits for the flow rates of the gases are as follows: The SiH4 flow rate starts at about 90 sccm and ends at 0 sccm. The N2 flow rate starts at about 310 sccm and ends at about 0 sccm. The decrease in N2 flow rate during the ending deposition phase is optional. The argon flow rate starts at about 230 sccm and increases to about 600 sccm. The increase in argon serves to maintain stability of plasma during the ending deposition phase. In one embodiment, the ramp time interval is 3 seconds.
In process step 654, post deposition conditioning is performed. The post deposition conditioning process may comprise removal of a top layer of nitride by wet etch or RIE (reactive ion etch). In the case of a wet etch, the etchant used may comprise dilute HF (hydrofluoric acid) or hot phosphoric acid.
The arrows of flowchart 600 indicate various possible process sequences. One such sequence is to perform main deposition 650, followed by the ending deposition phase 652, as described previously, which prevents a dense top layer of nitride. Alternatively, a main film deposition process 650 is performed, followed by a post deposition conditioning step 654 to remove the dense top layer of nitride. Another embodiment comprises a combination sequence of main deposition 650 followed by ending deposition phase step 652 followed by a post deposition conditioning step 654.
As can now be appreciated, embodiments of the present invention provide the ability to fabricate nitride films having a constant density profile, meaning that the density of the top layer is essentially the same as the density of the bulk layer. In other embodiments, the parameters of the ending deposition phase are adjusted such that top layer is less dense than the bulk layer.
Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.) the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application.
