Method for preparing carbon doped oxide insulating layers

[0002] The present invention relates to a method for preparing carbon doped oxide insulating layers, and semiconductor devices incorporating such layers.

[0003] Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal layers, capacitance increases. To address this problem, insulating materials that have a relatively low dielectric constant are being used in place of silicon dioxide (and other materials that have a relatively high dielectric constant) to form the dielectric layer that separates the metal lines.

[0004] One material that may be used to form such a low k dielectric layer is carbon doped oxide. Using this material instead of silicon dioxide to separate metal lines may yield a device having reduced propagation delay, cross-talk noise, and power consumption. Carbon doped oxides have been prepared by plasma enhanced chemical vapor deposition (“PECVD”) using gases that provide a source of silicon, oxygen, and carbon. Examples of source gases that have been used included dimethylmethoxysilane and alkyl silanes such as methylsilane, trimethylsilane, and tetramethylsilane. While these source gases produce carbon doped oxides having acceptable k values, it would be desirable to produce carbon doped oxides having even lower k values.

[0005] The present invention is a method for forming carbon doped oxide layers by chemical vapor deposition using a source gas that includes:

[0006] (a) an alkyl-alkoxysilane having the formula (R¹)_n(R²O)_4−nSi where R¹and R²are lower alkyl groups, e.g., having between 1 and 4 carbon atoms, inclusive, and n is an integer between 0 and 3, inclusive, with the proviso that when R¹and R²are methyl groups, n is not equal to 2; or

[0007] (b) a fluorinated alkoxysilane having the formula (R³O)_nSiF_4−nwhere R³is a lower alkyl group, e.g., having between 1 and 4 carbon atoms, inclusive, and n is an integer between 1 and 3, inclusive.

[0008] These source gases may be used alone or in combination with each other. They may also be used in combination with other gases that provide a source of oxygen, silicon, and/or carbon.

[0009] In the method of the present invention, a carbon doped oxide insulating layer is formed on a substrate. The substrate may be any surface, generated when making a semiconductor device, upon which the carbon doped oxide insulating layer may be formed. The substrate may include, for example, active and passive devices that are formed on a silicon wafer such as transistors, capacitors, resistors, diffused junctions, gate electrodes, local interconnects, etc. The substrate may also include insulating materials (e.g., silicon dioxide, either undoped or doped phosphorus (PSG) or boron and phosphorus (BPSG); silicon nitride; silicon oxynitride; silicon carbide; carbon doped oxide; an organic containing silicon oxide; or a polymer) that separate such active and passive devices from conductive layers that are formed on top of them, and may include various types of conductive layers.

[0010] The carbon doped oxide layer is formed on top of the substrate. Preferably, it contains between about 5 and about 50 atomic % carbon. It is formed using chemical vapor deposition techniques such as PECVD and a gaseous feed that provides a source of carbon, oxygen, and silicon.

[0011] In one embodiment, the source gas includes an alkyl-alkoxysilane having the formula (R¹)_n(R²O)_4−nSi where R¹and R²are lower alkyl groups, e.g., having between 1 and 4 carbon atoms, inclusive, and n is an integer between 0 and 3, inclusive, with the proviso that when R¹and R²are methyl groups, n is not equal to 2. Examples of such materials include methyltrimethoxysilane, tetramethoxysilane, trimethylmethoxysilane, and combinations thereof.

[0012] In another embodiment, the source gas includes a fluorinated alkoxysilane having the formula (R³O)_nSiF_4−nwhere R³is a lower alkyl group, e.g., having between 1 and 4 carbon atoms, inclusive, and n is an integer between 1 and 3, inclusive. Examples of such materials include fluorinated methoxysilane, fluorinated ethoxysilane, and combinations thereof.

[0013] These source gases may be used alone or in combination with each other. They may also be used in combination with other gaseous sources of carbon, oxygen, and/or silicon. Examples include hydrocarbon gases such as methane, ethane, etc.; alkylsilanes such as methyl, dimethyl, trimethyl, and tetramethylsilane; and dimethyldimethoxysilane.

[0014] The operating conditions for the PECVD reactor, including temperature, pressure, RF, and power, are selected to produce a carbon doped oxide layer having the requisite k value and thickness. Typical thicknesses range from about 300 to about 3,000 nanometers. The k values are preferably no greater than 2.5. In general, it is desirable to obtain a k value as low as possible.

[0015] Following deposition of the carbon doped oxide layer, it may be desirable in some cases to cure the layer to outgas volatile species, e.g., hydrogen and loosely bonded organic components. Additional layers may then be formed on the carbon doped oxide layer using conventional semiconductor fabrication processes.

[0016] Although the foregoing description has specified certain steps, materials, and equipment that may be used in such a method, those skilled in the art will appreciate that many modifications and substitutions may be made. Accordingly, it is intended that all such modifications, alterations, substitutions, and additions be considered to fall within the spirit and scope of the invention as defined by the appended claims.