Patent Application
20130178061
The disclosure of Japanese Patent Application No. 2012-001319 filed on Jan. 6, 2012 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
The present invention relates to a method of manufacturing a porous film and a method of manufacturing a semiconductor device.
Along with the progress of miniaturization of semiconductor devices, the requirement for lowering the permittivity of interlayer insulating films has been revealed. As a technique of lowering the permittivity of an interlayer insulating film, there is a technique of forming an interlayer insulating film by a porous insulating film.
Note that, in Japanese Patent No. 4160277 (Patent Document 1), there is a description of processing a low permittivity insulating film containing carbon by plasma having at least one reducing gas selected from H2 gas diluted with N2, CO, CO2 and NH3. In Japanese Patent Laid-Open Nos. 2000-332010 (Patent Document 2) and 2000-277507 (Patent Document 3), there is a description of making an insulating film be porous by vacuum annealing or plasma annealing, and after that, subjecting the surface to processing with H2 plasma.
In Japanese Patent No. 3768480 (Patent Document 4), there is a description that a trench for embedding wiring is formed in an interlayer insulating film, and after that, plasma processing is performed using He/H2 gas or He gas. In Japanese Patent Laid-Open No. 2009-004408 (Patent Document 5), there is a description that a trench for embedding wiring is formed, then plasma processing is performed using a gas containing hydrogen or ammonia, and after that, plasma processing is performed using a gas containing fluorocarbon.
In a process of manufacturing a semiconductor device, occasionally, there is a case where time lapses, after the formation of a porous insulating film, until processing for covering the surface thereof is performed. However, as a result of the examination by the inventor, when a porous insulating film is formed and is held in the state for a long time, it was found that there is a case where the permittivity of the porous insulating film increases. Consequently, in order to improve reliability of semiconductor devices, it is necessary to suppress the increase in the permittivity of a porous insulating film being stored for a long time.
According to an embodiment, a porous insulating film is formed through the use of an organic silica (also referred to as siloxane) raw material containing a hydrocarbon group. The surface of the porous insulating film is subjected, prior to the embedding of wiring, to plasma processing through the use of a processing gas containing an inactive gas and a reducing gas.
According to the above-mentioned embodiment, it is possible to suppress the increase in the permittivity of the porous insulating film along with the lapse of time.
Hereinafter, embodiments of the invention will be explained using the drawings. Note that, in all the drawings, the same sign is given to the same constituent, and the explanation thereof is omitted appropriately.
First, as shown in
Next, as shown in
The hydrocarbon group contains, for example, an unsaturated carbon compound, but it may contain a saturated carbon compound. Specifically, the hydrocarbon group is a vinyl group, an allyl group, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group or a tertiary butyl group, but is not limited to these.
The skeleton of the organic silica raw material is, for example, a cyclic organic silica raw material, but is not limited to this. When the skeleton of the organic silica raw material is cyclic organic silica, the organic silica raw material is shown by Formula (1) below.
In the Formula (1), n is 2 to 5, and Rx and Ry are each any of hydrogen, an unsaturated hydrocarbon group and a saturated hydrocarbon group. Each of the unsaturated hydrocarbon group and the saturated hydrocarbon group is, for example, any of a vinyl group, an allyl group, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group and a tertiary butyl group.
Meanwhile, in the above-mentioned Formula (1), n may be set to 3 or 4, Rx may be set to a vinyl group and Ry may be set to an isopropyl group.
The porous insulating film 120 having been formed here has a carbon content of not less than 20% in the atom number, preferably not less than 40% in the atom number. In addition, in the porous insulating film 120, an average pore diameter is not more than 1 nm. When setting the average pore diameter of the porous insulating film 120 to be not more than 1 nm, moisture absorption of the porous insulating film 120 can be suppressed.
Here, the pore diameter of the porous insulating film 120 can be measured using, for example, a SAXS (Small Angle
X-ray Scattering) method. Specifically, when the porous insulating film 120 is irradiated with X-rays, the X-rays are led to diffuse scattering by pores in the porous insulating film 120. The scattering profile is determined according to the density and the distribution of the pore diameter in the porous insulating film 120. Therefore, on the basis of the SAXS profile, the average pore diameter in the porous insulating film 120 can be measured.
Note that, the porous insulating film 120 may be formed from an organic silica material not having a cyclic organic silica skeleton. In this case, the porous insulating film 120 is made porous by using, for example, porogen.
Next, as shown in
The processing aims mainly at processing chemically the surface of the porous insulating film 120 by using ions or radicals generated from the reducing gas. Therefore, the vicinity of the surface layer of the porous insulating film 120 preferably avoids physical damages (that is, does not suffer shock by ions) as much as possible. For that purpose, the inactive gas is preferably as light as possible, for example, He. However, even when an inactive gas other than He such as Ar is used, by adjusting generation conditions of the plasma (pressure, power, interval between electrodes, etc.), it is possible to suppress damage of the porous insulating film 120. As a result, hydrocarbon components near the insulating film surface layer are kept, and thus high durability against process stresses (etching, asking, etc.) given in subsequent processes is exerted.
Furthermore, as the reducing gas, at least one of H2, CO and NH3 can be used. However, the reducing gas may be a gas other than these. Moreover, in the plasma processing, the ratio of the reducing gas contained in a gas to be introduced into the processing vessel is from not less than 5% to not more than 75%.
Next, as shown in
Subsequently, as shown in
Next, as shown in
Subsequently, the inside of the wiring trench 123 and the inside of the via hole 125 are embedded with an electroconductive film 128. The electroconductive film 128 is, for example, a metal film including Cu as a main component, and is formed by, for example, a plating method. At this time, the electroconductive film 128 is formed also over the barrier metal film 127 located over the insulating film 121. After that, the electroconductive film 128 is heat-treated. Under heat treatment conditions at this time, the temperature is 200° C. to 400° C. and the time period is 30 sec to 30 min. Consequently, crystalline grains of the electroconductive film 128 grow large.
Next, as shown in
Subsequently, as shown in
Meanwhile, when forming the porous insulating film 120, a plurality of organic silica raw materials may be used. Since organic materials in which n is set to 3 or 4 in the structure shown by the Formula (1) are easy to be manufactured, many of which are chemically stable, and have a relatively small cyclic skeleton structure, the use of a raw material obtained by mixing a plurality of these gives a better result.
For example, there may be used, as a first organic material, a compound in which, in the structure shown in the above-mentioned Formula (1), n is 3, Rx is a vinyl group and Ry is a methyl group (2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane) or Rx is a vinyl group and Ry is an isopropyl group (2,4,6-triisopropyl-2,4,6-trivinylcyclotrisiloxane), and there may also be used, as a second organic material, a compound in which, in the structure shown in the above-mentioned Formula (1), n is 4, Rx is a vinyl group and Ry is an isopropyl group (2,4,6,8-tetraisopropyl-2,4,6,8-tetravinylcyclotetrasilo xane) or Rx is a vinyl group and Ry is a methyl group (2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxan e). In this case, the ratio of the first organic silica material to the second organic silica material is preferably set between 1:9 and 9:1. The example, in the case where Rx is a vinyl group and Ry is an isopropyl group, includes a mixture obtained by mixing, at 4:3, the first organic silica material having the cyclic organic silica of n=3 in a side chain and the second organic silica material having the cyclic organic silica of n=4 in a side chain, the cyclic organic silicas of n=3 and n=4 being, respectively, (2,4,6,8-triisopropyl-2,4,6,8-trivinylcyclotrisiloxane) and (2,4,6,8-tetraisopropyl-2,4,6,8-tetravinylcyclotetrasilo xane). To the cyclic organic silica of n=3, three vinyl groups are bound, and to the cyclic organic silica of n=4, four vinyl groups are bound. By setting the mixing ratio of the two to be 4:3, it is possible to make the mixture have a stoichiometric composition in which the number of vinyl groups is made equal (12=4×3=3×4).
Furthermore, in the above-mentioned process, when forming the porous insulating film 120, an oxidizing gas such as O2, CO2, CO, N2O, NO2 or the like may be added. The gas may be introduced into a processing vessel through the same piping as that for the organic silica raw material and the carrier gas, or may be introduced into the processing vessel through another piping. In addition, the amount of the oxidizing gas is preferably not more than ½ relative to the flow amount of the carrier gas, particularly not more than ⅓.
Moreover, after subjecting the surface of the porous insulating film 120 to plasma processing, and before forming the insulating film 121, the porous insulating film 120 may be subjected to curing processing using heat, electron beams, ultraviolet light or the like. In curing by heat, the substrate temperature is preferably made to be not less than 350° C. Moreover, in curing by electron beams, the acceleration energy of electron beams is preferably set to be from 1 to 30 keV, which gives a dose amount of 0.05 to 1.0 mC/cm2. Moreover, in curing processing using ultraviolet light, irradiation time is preferably set to be from 10 sec to 5 min. Meanwhile, as ultraviolet light, light of one arbitrary wavelength, light from a broadband light source, or a combination thereof (single wavelength+single wavelength, single wavelength+broadband, broadband+broadband) may be used. Furthermore, curing by heat may be performed at the same time as curing by electron beams or curing by ultraviolet light. The curing processing here is characterized by being curing processing for the porous insulating film.
Next, the function and effect of the embodiment will be explained using
In Comparative example 1, the relative permittivity of the porous insulating film 120 increases as the storage period becomes longer. The inventor considers the reason as described below. In order to lower the relative permittivity of the porous insulating film 120, it is preferable to increase the number of carbon atoms contained in the porous insulating film 120. For achieving the purpose, an organic silica raw material for forming the porous insulating film 120 is required to be caused to contain many carbons. As a result, hydrocarbon groups contained in the organic silica raw material have a large number of carbons.
Meanwhile, when the formation of the porous insulating film 120 is completed, the surface of the porous insulating film 120 is exposed to organic silica raw materials with a small degree of decomposition. As a result, the surface of the porous insulating film 120 is exposed to lots of undecomposed hydrocarbon groups. Apart of the hydrocarbon groups is, as shown in
In contrast to this, in the embodiment, the surface of the porous insulating film 120 is processed by plasma using a reducing gas. Consequently, hydrocarbon groups deposited on the surface of the porous insulating film 120 are removed. Accordingly, as shown in
Meanwhile, excessive sputtering is not preferable in the surface processing of the porous insulating film 120. In Comparative example 2, the surface of the porous insulating film 120 is removed by sputtering. Consequently, hydrocarbon groups having been deposited on the surface of the porous insulating film 120 are also removed. However, apart of carbons have escaped from the surface of the porous insulating film 120, and the film 120 is modified to a film of high relative permittivity. Consequently, the initial value of the relative permittivity of the porous insulating film 120 becomes high.
In contrast to this, in the embodiment, when subjecting the surface of the porous insulating film 120 to sputtering processing, for example, He is used as an inactive gas, etc. so as to avoid sputtering as much as possible. Consequently, as shown in
Meanwhile, whether the plasma processing according to the embodiment has been performed on the porous insulating film 120 or not can be detected by, for example, a method below.
First, the cross-section of the porous insulating film 120 is observed with a TEM (Transmission Electron Microscope). This method makes it possible to observe directly the presence or absence of a deposit on the surface of the porous insulating film 120.
In addition, the analysis of elements and chemical bonding states near the surface of the porous insulating film 120 by TEM-EELS (Electron Energy-Loss Spectroscopy) also makes it possible to observe the presence or absence of a deposit on the surface of the porous insulating film 120.
Moreover, the mass spectrometric analysis of a material having detached from the porous insulating film 120 (for example, the presence or absence of a carbonyl group) by TDS (Thermal Desorption Spectroscopy) also makes it possible to observe the presence or absence of a deposit on the surface of the porous insulating film 120.
In addition, the presence or absence of a deposit on the surface of the porous insulating film 120 can be observed also by TOF-SIMS (Time of fright Secondary Ion Mass Spectroscopy), ATR-FTIR (Attenuated total reflection Fourier Transform Infrared), XPS (X-ray Photoelectron Spectroscopy), AES (Auger Electron Spectroscopy) or XRR (X-ray Reflection). Among these, in ATR-FTIR, a prism having a high refractive index is brought into contact with a part to be analyzed, and infrared light is made to enter the prism. Consequently, an evanescent wave generated at the boundary of the prism and a sample is absorbed by the sample. Therefore, by analyzing emerging light, the presence or absence of a surface-adsorbed material can be detected.
Over the substrate 10, a multilayered wiring layer 300 is formed. The multilayered wiring layer 300 has a local wiring layer 302 and a global wiring layer 304. The local wiring layer 302 is a wiring layer for forming a circuit, and the global wiring layer 304 is a wiring layer for drawing power source wiring and ground wiring. The uppermost layer of the global wiring layer 304 serves as an Al wiring layer. The wiring layer includes an electrode pad. The wiring layer that forms the local wiring layer 302 and a part of layer of the global wiring layer 304 are formed by a damascene method.
In the embodiment, at least one interlayer insulating film of the local wiring layer 302, for example, interlayer insulating films constituting a wiring layer higher than the second layer are formed into the porous insulating film 120 in the first embodiment. However, all the interlayer insulating films constituting the local wiring layer 302 may be formed into the porous insulating film 120. Moreover, any of interlayer insulating films forming the global wiring layer 304 may be formed into the porous insulating film 120.
Subsequently, a method of manufacturing the semiconductor device will be explained. First, over the substrate 10, the element isolation film 20 is formed. Consequently, an element formation region is isolated. The element isolation film 20 is formed using, for example, an STI method, but may be formed using a LOCOS method. Next, over the substrate 10 located in the element formation region, a gate insulating film and a gate electrode are formed. The gate insulating film may be a silicon oxide film or may be a high permittivity film (for example, a hafnium silicate film) having a higher permittivity than the silicon oxide film. When the gate insulating film is a silicon oxide film, the gate electrode is formed from a polysilicon film. In addition, when the gate insulating film is a high permittivity film, the gate electrode is formed from a stacked film of a metal film (for example, TiN) and a polysilicon film. Furthermore, when the gate electrode is formed from a polysilicon film, in a process for forming the gate electrode, the passive element 14 is formed.
Next, on the substrate 10 located in the element formation region, extension regions of a source and a drain are formed. Subsequently, on a side wall of the gate electrode, a sidewall is formed. Next, on the substrate 10 located in the element formation region, impurity regions serving as a source and a drain are formed. In this way, over the substrate 10, the transistor 12 is formed.
Subsequently, over the element isolation film 20 and over the transistor 12, the multilayered wiring layer 300 is formed. At this time, in a process that forms any of wiring layers, the method shown in the first embodiment is used.
The embodiment can also give the same effect as that of the first embodiment. In particular, in the first embodiment, time-lag may be caused from the formation of an interlayer insulating film to the time when wiring is embedded into the interlayer insulating film, in some wiring layer. The length of the time-lag may change according to situations of a manufacturing line. According to the embodiment, even when the time-lag becomes long, as shown in
Hereinbefore, the embodiments of the invention are described referring to the drawings, but these are exemplifications of the invention, and various configurations other than those described above may also be adopted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-001319 | Jan 2012 | JP | national |
