# Patent

## Title
Method for forming insulation film

## Abstract

A method for forming an insulation film having filling property on a semiconductor substrate by plasma reaction includes: vaporizing a silicon-containing hydrocarbon having a Si—O bond compound to provide a source gas; introducing the source gas and a carrier gas without an oxidizing gas into a reaction space for plasma CVD processing; and forming an insulation film constituted by Si, O, H, and optionally C or N on a substrate by plasma reaction using a combination of low-frequency RF power and high-frequency RF power in the reaction space. The plasma reaction is activated while controlling the flow of the reaction gas to lengthen a residence time, Rt, of the reaction gas in the reaction space.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of U.S. patent application Ser. No. 11/437,951, filed May 19, 2006, which is a continuation-in-part of U.S. patent application Ser. No. 11/294,319, filed Dec. 5, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 10/412,363 filed Apr. 11, 2003, now U.S. Pat. No. 7,064,088, which is a continuation-in-part of U.S. patent application Ser. No. 10/317,239 filed Dec. 11, 2002, now U.S. Pat. No. 6,881,683, which is a continuation-in-part of U.S. patent application Ser. No. 09/827,616 filed Apr. 6, 2001, now U.S. Pat. No. 6,514,880, which is a continuation-in-part of (i) U.S. patent application Ser. No. 09/243,156 filed Feb. 2, 1999, now abandoned, which claims priority to Japanese patent application No. 37929/1998 filed Feb. 5, 1998, (ii) U.S. application Ser. No. 09/326,847 filed Jun. 7, 1999, now U.S. Pat. No. 6,352,945, (iii) U.S. patent application Ser. No. 09/326,848 filed Jun. 7, 1999, now U.S. Pat. No. 6,383,955, and (iv) U.S. patent application Ser. No. 09/691,376 filed Oct. 18, 2000, now U.S. Pat. No. 6,432,846, all of which are incorporated herein by reference in their entirety. This application claim s priority to all of the foregoing under 35 U.S.C. § 119 and § 120.


BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a semiconductor technique and more particularly to a silicone polymer film used as a low-k (low dielectric constant) film on a semiconductor substrate, which is formed by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of the Related Art
Because of the recent rise in requirements for the large-scale integration of semiconductor devices, a multi-layered wiring technique attracts a great deal of attention. In these multi-layered structures, however, capacitance among individual wires hinders high speed operations. In order to reduce the capacitance it is necessary to reduce relative dielectric constant of the insulation film. Thus, various materials having a relatively low relative dielectric constant have been developed for insulation films.
Conventional silicon oxide films SiOx are produced by a method in which oxygen O2 or nitrogen oxide N2O is added as an oxidizing agent to a silicon source gas such as SiH4 or Si(OC2H5)4 and then processed by heat or plasma energy. Its relative dielectric constant is about 4.0.
Alternatively, a fluorinated amorphous carbon film has been produced from CxFyHz as a source gas by a plasma CVD method. Its relative dielectric constant ε is as low as 2.0-2.4.
Another method to reduce the relative dielectric constant of insulation film has been made by using the good stability of Si—O bond. A silicon-containing organic film is produced from a source gas under low pressure (1 Torr) by the plasma CVD method. The source gas is made from P-TMOS (phenyl trimethoxysilane, see below), which is a compound of benzene and silicon, vaporized by a babbling method. The relative dielectric constant ε of this film is as low as 3.1.




A further method uses a porous structure made in the film. An insulation film is produced from an inorganic SOG material by a spin-coat method. The relative dielectric constant E of the film is as low as 2.3.
However, the above noted approaches have various disadvantages as described below.
First, the fluorinated amorphous carbon film has lower thermal stability (370° C.), poor adhesion with silicon-containing materials and also lower mechanical strength. The lower thermal stability leads to damage under high temperatures such as over 400° C. Poor adhesion may cause the film to peel off easily. Further, the lower mechanical strength can jeopardize wiring materials.
Oligomers that are polymerized using P-TMOS molecules do not form a linear structure in the vapor phase, such as a siloxane structure, because the P-TMOS molecule has three O—CH3 bonds. The oligomers having no linear structure cannot form a porous structure on a Si substrate, i.e., the density of the deposited film cannot be reduced. As a result, the relative dielectric constant of the film cannot be reduced to a desired degree.
In this regard, the babbling method means a method wherein vapor of a liquid material, which is obtained by having a carrier gas such as argon gas pass through the material, is introduced into a reaction chamber with the carrier gas. This method generally requires a large amount of a carrier gas in order to cause the source gas to flow. As a result, the source gas cannot stay in the reaction chamber for a sufficient length of time to cause polymerization in a vapor phase.
Further, the SOG insulation film of the spin-coat method has a problem in that the material cannot be applied onto the silicon substrate evenly and another problem in which a cure system after the coating process is costly.
In view of the above, various techniques of forming low-k silica insulation films have been developed.
In order to reduce wiring resistance, copper wiring is widely used in combination with low-k silica insulation films. However, copper tends to migrate or diffuse into the silica insulation films. Diffusion of Cu is significantly promoted by heat. In order to prevent this problem, a barrier film for blocking diffusion of Cu is formed between the silica insulation film and copper wiring. Conventionally, SiC is mainly used as a barrier film. However, the dielectric constant of such a barrier film is relatively high, and thus when forming the barrier film, the barrier film increases the effective dielectric constant of the integrated layers including the barrier film. Thus, ideally, the thickness of the barrier film is reduced as much as is practically possible while maintaining Cu-diffusion blocking ability.
In order to determine whether a barrier film is effectively usable, a heat resistance test where a sample is placed an atmosphere at 400° C. for 14 hours is conducted in view of device manufacturing processes. Further, because diffusion of Cu is also promoted when electricity is applied, an electric resistance test is also conducted. As a simple test in place of the above tests, the quality of a barrier film can be evaluated by placing a sample in an atmosphere at 400° C. for four hours and measuring a thickness where Cu penetrates and diffuses in the barrier film. In this test, if the thickness of a Cu-diffused portion of the barrier film is 20 nm or less, the barrier film is considered to be good.
In addition, in order to inhibit oxidation of Cu wiring due to absorption of moisture by a barrier film, impurities such as N or O are introduced into SiC constituting the barrier film. However, SiCN or SiCO tends to have a high dielectric constant such as 4.5-5.0. If SiC containing no impurities is used, the dielectric constant can be reduced, but the barrier film of SiC entails the moisture absorption problem.
Thus, conventionally, no silicon carbide film (herein “silicon carbide” includes pure SiC and non-pure SiC such as SiCOH) having a low dielectric constant such as 4.0 or less and having effective Cu-diffusion blocking ability has been obtained.
As described above, copper has been used in digital integrated logic circuits because as compared with Al, Cu has low electrical resistivity and it can decrease wiring delay times (high response speed or switching speed). In memory devices, wiring delay times have not been a problem, and thus Al has been still used for wring. Unlike Cu, Al can be dry-etched and Al wiring does not require damascene processes. Thus, using Al wiring is advantageous. However, wiring pitch or node becomes small (e.g., a wiring pitch of 45-100 nm), it is expected that low wiring delay times of Al wiring will be a problem.
Therefore, a principal object of this invention is to provide a method for forming an improved insulation film which has a low dielectric constant and excellent padding (filling) ability in Al wiring, for example. Conventional low-k films do not have good padding ability.
In view of the fact that properties such as fine structures, padding effect in an aluminum/low-k structure for Al wiring or a shallow trenched isolation (STI) structure, and controlling elastic modulus are required for insulation films, another object of this invention is to provide a method for forming an insulation film that has a low dielectric constant, fine structures, good padding property (filling grooves or holes without creating voids), and appropriate levels of elastic modulus.
A further object of this invention is to provide a method for forming an insulation film that is a silicon carbide doped with oxygen having a high density and a low dielectric constant.
A still further object of this invention is to provide a method for effectively forming an insulation film without requiring complicated processes.
SUMMARY OF THE INVENTION
One aspect of this invention for achieving one or more of the above objects (although the objects are not intended to limit the present invention) may involve a method for forming an insulation film on a semiconductor substrate by using a plasma CVD apparatus including a reaction chamber, which method comprises a step of directly vaporizing a silicon-containing hydrocarbon compound expressed by the general formula SiαOβCxHy (α, β, x, and y are integers) or SiαOβHpNq (α, β, and p are integers, q is an integer of 0-2) and then introducing it to the reaction chamber of the plasma CVD apparatus, a step of introducing an additive gas, the flow volume of which is substantially reduced, into the reaction chamber and also a step of forming an insulation film on a semiconductor substrate by plasma reaction wherein mixed gases made from the vaporized silicon-containing hydrocarbon compound as a source gas and the additive gas are used as a reaction gas. It is a remarkable feature that the reduction of the additive gas flow also results in a substantial reduction of the total flow of the reaction gas. According to the above embodiment of the present invention, a silicone polymer film having a micropore porous structure with low dielectric constant can be produced.
In an embodiment, the present invention is drawn to an insulation film that may be formed as described above on a semiconductor substrate, that may be in contact with aluminum, tungsten, or tungsten silicon wiring, and that may have characteristics described above.
In embodiments of the present invention, by using an organo silicon having a Si—O bond as a source gas which flows at a decreased flow rate to lengthen the residence time (defined below), plasma reaction is carried out in a gaseous phase in a reaction chamber to form an insulation film having fine structures, and by additionally applying low-frequency RF power, the film density (e.g., more than 1.30 g/cm3, preferably 1.35 g/cm3 or greater, more preferably 1.4 to 2.0 g/cm3 including 1.5, 1.6, 1.7, 1.8, 1.9, and values between any two numbers of the foregoing) can be controlled without increasing a dielectric constant (e.g., less than 3.5, preferably 3.3 or lower, more preferably 2.8 to 3.2 including 2.9, 3.0, 3.1, and values between any two numbers of the foregoing). Although the following explanation does not intend to limit the present invention, by using the precursor having at least one Si—O bond in a molecule for forming a silicon carbide film (e.g., SiCOH), it becomes possible to stabilize Si with an O-terminal and/or a C-terminal. If a precursor having no Si—O bond, such as 3 MS or 4 MS, is used with an oxygen-supplying gas, the molecules are dissociated in a plasma and Si tends to have an H-terminal and/or OH-terminal which is unstable.
Also, by reducing the distance between the electrodes, using low-frequency RF power mixed with high-frequency RF power, and/or using a reaction gas containing no oxygen-supplying gas and/or crosslinking gas, a silicon carbide film (Si—C based structure), not a low-k film (Si—O based structure), can be formed, and the film density can increase.
In an embodiment, the distance between the electrodes may be 10 mm to 50 mm, including 15 mm, 20 mm, 25 mm, 30 mm, preferably 20 mm to 25 mm, in another embodiment, 10 mm to 14 mm.
Conventional SiC has a relatively low dielectric constant but does not sufficiently block moisture penetration, whereas conventional SiCN or SiCO has a relatively high dielectric constant but can effectively block moisture penetration. This may be because the conventional SiC has a low density of 1.1-1.3 g/cm3 as compared with the conventional SiCN or SiCO having a density of 1.8-2.0 g/cm3. In an embodiment, the insulation film has as low a dielectric constant as that of SiC or lower than that of SiC, but the insulation film has as high Cu-diffusion blocking ability and as high dry etching selectivity against a low-k film as SiCN or SiCO (having a dielectric constant of 4.0 to 4.5) which are formed using 3 MS or 4 MS as a precursor gas. The insulation film according to an embodiment of the present invention has a high density and thus exhibits high etching-selectivity as compared with a low-k film (an etching selectivity against a low-k film may be in the range of 5-10) and also exhibits low Cu-penetration thickness (which may be 5-15 mu as measured under the Cu-diffusion blocking test). Thus, in an embodiment, the insulation film can effectively be used for memory devices.
Further, by adding an additive gas, elastic modulus of the insulation film can be improved. When the insulation film serves as a barrier film, preferably, the barrier film has compressive stress in view of wiring stress and adhesion to an Al layer.
Further, when the average temperature of the reaction (in an embodiment, the temperature of the susceptor) is controlled at −50° C. to 100° C. (−50° C. to 50° C. in an embodiment, 50° C. to 100° C. in another embodiment) during the plasma treatment, the insulation film can possess good filling property (padding property) so that even if a surface having holes or wiring grooves on which the insulation film is deposited has a high aspect ratio such as 1/3 to 1/10 (e.g., a Shallow Trench Isolation (STI) structure formed in a Si substrate) or a wiring pitch of 100 nm or less (e.g., 45 mn to 100 nm for an Al/low-k structure), the insulation film can fill in the holes or grooves without creating voids (as a low-k film or an oxide film). When the temperature is low, the precursor which is once vaporized when entering the reaction chamber becomes in an activated liquid state in the vicinity of a substrate surface, and thus the depositing film can exhibit excellent step coverage and filling property.
Further, in order to further improve filling property (padding property), an auxiliary gas constituted by C and H or C, H, and O such as isopropyl alcohol or acetone may be added to the reaction gas at a flow rate of 10 sccm to 200 sccm (including 20 sccm, 30 sccm, 50 sccm, 80 sccm, 100 sccm, 150 sccm, and ranges between any two numbers of the foregoing). In an embodiment, the flow rate of the auxiliary gas may be greater (e.g., 1.2 times to 20 times greater; including 2 times, 5 times, 10 times, and ranges between any two numbers of the foregoing) than the flow rate of the source gas.
Further, in order to further improve filling property by improving affinity between an underlying layer and an insulation film, the method may further comprise, as a preliminary treatment, introducing an auxiliary gas which is one or more selected from the group consisting of He, O2, and a gas constituted by C, H, and optionally O into the reaction space for plasma treatment of the semiconductor substrate (at a low temperature so that an activated liquid formed from the auxiliary gas can preliminarily cover a three-dimensional structure and then mixed with an activated liquid subsequently formed from the reaction gas) before introducing the reaction gas. In an embodiment, as the gas constituted by C, H, and optionally O, the additive gas used at the deposition stage can be used. The preliminary treatment is effective specifically when the underlying layer has a hydrophobic surface, for example, and in that case, by the preliminary treatment, the surface can be changed from a hydrophobic state to a hydrophilic state. The characteristics of the insulation film are typically not affected by the preliminary treatment. The preliminary treatment of the substrate can be conducted under conditions set for forming an insulation film thereon except that no silicon-containing hydrocarbon compound is used and higher RF power (2-fold to 5-fold) may be used as compared with the RF power (e.g., 27 MHz) for depositing an insulation film (which may be in the range of 100 W to 1,000 W, e.g., 200 W to 500 W). The auxiliary gas may be isopropyl alcohol or acetone and can include an inert gas such as He. The flow rate of each auxiliary gas may be 10 sccm to 200 sccm (including 20 sccm, 30 sccm, 50 sccm, 80 sccm, 100 sccm, 150 sccm, and ranges between any two numbers of the foregoing). The above auxiliary gas can be used in any combination. If the preliminary treatment is conducted, no auxiliary gas may be added to the reaction gas for depositing an insulation film.
In an embodiment, by a combination of the above preliminary treatment for improving affinity between an underlying layer and an insulation film and the above deposition process using an additive gas a CxHyOz gas for reducing the viscosity of the reaction gas, the filling property or padding property of the insulation film (oxide film or low-k film) can significantly be improved.
Additionally, the method may further comprise annealing the substrate having the insulation film, thereby curing the insulation film.
The insulation film may contain N. In that case, the method may further comprise introducing an additive gas which is at least one selected from the group consisting of N2, NH3, and N2O. The additive gas may be introduced at a flow rate of 50 sccm to 3,000 sccm (including 100 sccm, 500 sccm, 1,000 sccm, 2,000 sccm, and ranges between any two numbers of the foregoing).
In another aspect, the present invention provides a method for forming an interconnect structure, comprising the steps of: (i) forming a three-dimensional structure for interconnect in a substrate; and (ii) forming an insulation layer on a surface of the three-dimensional structure using any of the foregoing method. In the above, in an embodiment, the step of forming a three-dimensional structure may comprise forming a layer of aluminum, tungsten, or tungsten silicon as a wiring layer and etching the layer in a pattern.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.



BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention.
FIG. 1 is a schematic diagram illustrating a plasma CVD apparatus usable forming an insulation film according to the present invention.
FIG. 2 is a schematic diagram showing a UV curing apparatus according to an embodiment of the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In an embodiment of the present invention, an insulation film may be formed on a low-k film or on a Cu layer or formed on a surface of a via and/or trench in a damascene process as a barrier film, or on a three-dimensional structure of Al, tungsten, or tungsten silicon (or any other wiring materials) which can be processed by dry-etching. The insulation film may be formed using the same source gas as those used for forming a low-k film formed by the method described below in an embodiment. In that case, the insulation film and the low-k film can continuously be formed using the same equipment, thereby eliminating particle contamination problems and increasing productivity.
In an embodiment, the present invention provides a method for forming an insulation film on a semiconductor substrate by plasma reaction, comprising the steps of: (i) vaporizing a silicon-containing hydrocarbon compound to provide a source gas, said silicon-containing hydrocarbon compound comprising a Si—O bond in a molecule; (ii) introducing a reaction gas comprising the source gas and a carrier gas without an oxygen-supplying gas into a reaction space for plasma CVD processing wherein a semiconductor substrate is placed; and (iii) forming an insulation film constituted by Si, C, O, and H on the substrate by plasma reaction using a combination of low-frequency RF power and high-frequency RF power in the reaction space, wherein the plasma reaction is activated while controlling the flow of the reaction gas to lengthen a residence time, Rt, of the reaction gas in the reaction space, wherein 100 msec ≦Rt,
Rt[s]=9.42×107(Pr·Ts/Ps·Tr)rw2d/F
wherein:
Pr: reaction space pressure (Pa)
Ps: standard atmospheric pressure (Pa)
Tr: average temperature of the reaction (K)
Ts: standard temperature (K)
rw: radius of the silicon substrate (m)
d: space between the silicon substrate and the upper electrode (m)
F: total flow volume of the reaction gas (sccm).
The above embodiment further includes the following embodiments:
The residence time (Rt) may be in the range of 100 msec to 150 msec (including 110 msec, 120 msec, 130 msec, 140 msec, and values between any two numbers of the foregoing).
The reactive group may be selected from the group consisting of alkoxy group, vinyl group, amino group, and acid radical. The silicon-containing hydrocarbon compound may have the formula SiaObHcNx (wherein a, b, c are integers, x is 0, 1, or 2). In an embodiment, the silicon-containing hydrocarbon compound may have the formula SiαOα−1R2α−β+2(OR′)β wherein α is an integer of 1-3, β is an integer of 0-3, R is C1-6 hydrocarbon attached to Si, and R′ is C1-6 hydrocarbon unattached to Si. R′ may be CnH2n+1 wherein n is an integer of 1-3. R and/or R′ may independently be hydrogen. R and/or R′ may independently contain vinyl group. The silicon-containing hydrocarbon compound comprising a Si—O bond in a molecule includes, but is not limited to, the following:




(In the formula, R1, R2, R3 and R4 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, and at least one of R1 and R3 may include CH═CH, wherein trimethoxysilane is included.)




(In the formula, R1, R2, R3 and R4 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, and at least one of R1 and R3 may include CH═CH)




(In the formula, R1, R2, R3, R4, R5, and R6 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, and at least one of R1, R3, R4, and R6 may include CH═CH)




(In the formula, K1, R2, R3, R4, R5, and R6 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, and at least one of R1, R3, R4, and R6 may include CH═CH, wherein 1,1,3,3-tetramethyldisiloxane and hexamethyldisiloxane (Si2OC6H18, HMDSO) are included)
Further, a chemical structure of Sip(OR)2p+2 (wherein p is an integer of 1-3, R is H or C1-6 hydrocarbon) can be used, such as the following structure.




(In the formula, R1, R2, R3, R4, R5, and R6 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, and at least one of R1, R3, R4, and R6 may include CH═CH)
Further, as the silicon-containing hydrocarbon compound, a compound having the formula SiR(OR′)3 or (Si—O)3R6 wherein R and R′ are independently H or C1-6 hydrocarbon attached to Si can be used, such as the following structure:




(In the formulae, R, R2, R3, and R4 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, wherein triethoxysilane (TES, HSi(OC2H5)3) is included.)




(In the formulae, R1, R2, R3, R4, R5, and R6 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, wherein octamethylcyclotrisiloxan (OMCTS, Si3O3C6H18) is included.)
In another embodiment, the silicon-containing hydrocarbon compound may have a chemical structure of SimR2m+2 (wherein m is an integer of 1 or 2, R is H or C1-6 hydrocarbon), such as the following structure.




(In the formulae, R1, R2, R3, R4, R5, and R6 are independently any of H, CH3, C2H5, C3H7, C6H5, C2H3, C3H5, C4H7, and C4H5, and at least one of R1, R3, R4, and R6 may include CH═CH, wherein 4MS (SiC4H12), divinyldimethylsilane (DVDMS), and hexamethyldisilane (Si2C6H18, HMDS) are included.)
In the above, the silicon-containing hydrocarbon compound contains no Si-O bond in its molecule. In an embodiment, the silicon-containing hydrocarbon compound may contain at least one reactive group selected from the group consisting of alkoxy group, vinyl group, amino group, and acid radical.
One or more of the silicon-containing hydrocarbon compounds represented by any of the aforesaid formulae can be used. For example, dimethyldimethoxysilane (DMDMOS, SiO2C4H12), diethyldiethoxysilane (DEDEOS, SiO2C8H20), phenyltrimethoxysilane (PTMOS, SiO4C9H14), 1,3-dimethoxytetramethyl disilane (DMOTMDS, Si2O3C6H18), and hexamethydisilane (HMDS, Si2OC6H18) are included. In an embodiment, cyclic silicon-containing hydrocarbon compounds having a Si—O bond can be used. Preferably, however, linear silicon-containing hydrocarbon compounds having a Si—O bond, more preferably, O—Si—O bond, may be used in an embodiment.
The carrier gas or inert gas may be one or more selected from the group consisting of He, Ar, Kr, and Xe. The carrier gas may be introduced at a flow rate of 10 sccm to 100 sccm (including 20 sccm, 40 sccm, 60 sccm, 80 sccm, and values between any two numbers of the foregoing). In another embodiment, the carrier gas may be introduced at a flow rate of 30 sccm to 10,000 sccm (including 100 sccm, 500 sccm, 1,000 sccm, 2,000 sccm, 5,000 sccm, and values between any two numbers of the foregoing, in an embodiment, 50 sccm to 3,000 sccm).
The method may further comprise introducing an additive gas selected from the group consisting of an oxidizing gas (e.g., O2) and a gas of CO2, H2, CxHyOz wherein x=1-5, y=2x or 2x+2, and z=0 or 1 (e.g., C2H4, C2H6, C3H6, C3H8, C2H8, C2H5(OH), and C3H7(OH)), into the reaction space when the source gas is introduced in order to further eliminate unstable bonds or terminals of Si.
In another embodiment, the additive gas may be at least one selected from the group consisting of H2 gas and a gas of CxHyOz wherein x=1-10, y=a natural number, and z=0, 1, or 2, which is introduced into the reaction space when the source gas is introduced. The above gases can be used singly or in any combination. These gases do not typically serve as an oxygen-supplying gas which supplies oxygen to be bound to Si (i.e., even if a molecule of the gas contains oxygen, the oxygen is insignificantly involved in formation of a basal structure of the resulting film) or crosslinking gas (i.e., a molecule of the gas is insignificantly involved in formation of a basal structure of the resulting film). In an embodiment, the additive gas may be selected from the group consisting of acetone, hexane, isoprene, and isopentan. The additive gas may be introduced at a flow rate of 10 sccm to 100 sccm (including 20 sccm, 40 sccm, 60 sccm, 80 sccm, and values between any two numbers of the foregoing). In another embodiment, the additive gas may be introduced at a flow rate of 10 sccm to 1,500 sccm (including 100 sccm, 200 sccm, 400 sccm, 600 sccm, 800 sccm, 1,000 sccm, and values between any two numbers of the foregoing, preferably 10 sccm to 900 sccm).
In the above, the additive gas of CxHyOz preferably has a viscosity of 0.2-2.3 mPa·s (as measured at 20° C. so that when the additive gas is mixed in the reaction gas, the viscosity of the reaction gas can be reduced, thereby improving filling property (padding property) in small gaps or holes in interconnect structures.
In an embodiment, an oxidizing gas may be added to the source gas. The oxidizing gas may be one or more selected from the group consisting of O2, O3, CO2, N2O, and H2O. The oxidizing gas may be introduced at a flow rate of 50 sccm to 3,000 sccm (including 100 sccm, 500 sccm, 1,000 sccm, 2,000 sccm, and values between any two numbers of the foregoing).
In an embodiment, the inert gas, the oxidizing gas, and the additive gas may be used in any combination (e.g., a flow ratio of [source gas]/[inert gas]/[oxidizing gas]/[additive gas]=[10]/[5-1000 (e.g., 10-700)]/[0-700 (e.g., 100-600)]/[10-300 (e.g., 100-200)]). In another embodiment, one or two of the inert gas, the oxidizing gas, or the additive gas may be excluded. In an embodiment where the preliminary treatment for improving affinity between an underlying layer and an insulation film is performed with use of a gas equivalent to the additive gas (this is effective for filling a small hole), the additive gas may be eliminated at the deposition stage. In another embodiment where the preliminary treatment is performed without use of a gas equivalent to the additive gas, the flow rate of the additive gas may be reduced at the deposition stage. For example, in the case of application of the preliminary treatment, a flow ratio of [source gas]/[additive gas] may be [10]/[0-100 (e.g., 0-50)].
The flow rate of the source gas can be adjusted according to the residence time (Rt), and in an embodiment, it may be 25-400 sccm (including 50 sccm, 100 sccm, 150 sccm, 200 sccm, 300 sccm, and values between any two numbers of the foregoing). The flow rate of the source gas may be at lest 30% of the total gas flow (including 40%, 50%, 60%, 70%, 80%, and values between any two numbers of the foregoing). In another embodiment, the source gas may be introduced at a flow rate of 5 sccm to 25 sccm (including 10 sccm, 15 sccm, 20 sccm, and values between any two numbers of the foregoing), and the flow rate of the source gas may be less than 30% of the total gas flow (including 5%, 10%, 20%, and values between any two numbers of the foregoing).
The low-frequency RF power may be 1%-50% of the high-frequency RF power (including 5%, 10%, 15%, 20%, 30%, 40%, and values between any two numbers of the foregoing). The low-frequency RF power may have a frequency of 2 MHz or less (e.g., 400 kHz, 430 kHz). The high-frequency RF power may have a frequency of 13.56 MHz to 60 MHz such as 13.56 MHz, 27 MHz, and 60 MHz (in an embodiment, 20 MHz or higher). In an embodiment, the total RF power may be 400 W or higher (450 W, 500 W, 750 W, 1000 W, and values between any two numbers of the foregoing).
The average temperature of the reaction (Tr) may be in a range of 323K to 823K.
The insulation film may be a silicon carbide film doped with oxygen. The oxygen content may be 5% to 30% (including 10%, 15%, 20%, 25%, and values between any two numbers of the foregoing). The insulation film may be composed further of N. The insulation film may be a barrier film for blocking Cu-diffusion. The barrier film may have a thickness of 25 nm to 70 nm (including 30 nm, 40 nm, 50 nm, 60 nm, and values between any two numbers of the foregoing; in another embodiment, 20 um to 100 um).
The space between the silicon substrate and the upper electrode (d) may be less than 0.014 m (including 0.012 m, 0.010 m, 0.008 m, 0.006 m, and values between any two numbers of the foregoing).
The substrate may have a via and/or trench is formed wherein the insulation film is to be formed on a surface of the via and/or trench. The substrate may have an exposed Cu layer on which the insulation film is to be formed. Because no oxygen-supplying gas is used, the insulation film can be deposited directly on a Cu layer.
In another aspect, the present invention provides a method for forming an interconnect structure, comprising the steps of: (i) forming a via and/or trench for interconnect in a substrate; (ii) forming a barrier layer on a surface of the via and/or trench using any method of the foregoing; and (iii) forming a Cu layer on the barrier layer. In the above, the via and/or trench may be formed by a single or dual damascene process.
In still another aspect, the present invention provides an insulation film obtainable by any method of the foregoing, constituted by Si, C, O, and H and having a density of more than 1.3 g/cm3 and a dielectric constant of 3.3 or less. In the above, the insulation film may be a silicon carbide doped with oxygen.
In all of the aforesaid embodiments and aspects, any element used in an embodiment or aspect can interchangeably or additionally be used in another embodiment or aspect unless such a replacement is not feasible or causes adverse effect.
Compounds which can be mixed include a compound having at least one Si—O bond, two or less O—CnH2n+1 bonds and at least two hydrocarbon radicals bonded with silicon (Si). A preferable silicon-containing hydrocarbon compound has formula:

SiαOα−1R2α−β+2(OCnH2n+1)β

wherein α is an integer of 1-3, β is 0, 1, or 2, n is an integer of 1-3, and R is C1-6 hydrocarbon attached to Si.
More specifically, the silicon-containing hydrocarbon compound includes at least one species of the compound expressed by the following chemical formula:




wherein R1 and R2 are one of H, CH3, C2H3, C2H5, C3H7 and C6H5, and m and n are any integer.

Except for the species indicated above, the silicon-containing hydrocarbon compound can include at least one species of the compound expressed by the following chemical formula:




wherein R1, R2 and R3 are one of H, CH3, C2H3, C2H5, C3H7 and C6H5, an n is any integer.

Except for those species indicated above, the silicon-containing hydrocarbon compound can include at least one species of the compound expressed by the following chemical formula:




wherein R1, R2, R3 and R4 are one of H, CH3, C2H3, C2H5, C3H7 and C6H5, and m and n are any integer.

Further, except for those species indicated above, the silicon-containing hydrocarbon compound can include at least one species of the compound expressed by the following chemical formula:




wherein R1, R2, R3, R4, R5 and R6 are one of H, CH3, C2H3, C2H5, C3H7 and C6H5, and the additive gases are argon (Ar), Helium (He) and either nitrogen oxide (N2O) or oxygen (O2).

The residence time of the reaction gas is determined based on the capacity of the reaction chamber for reaction, the pressure adapted for reaction, and the total flow of the reaction gas. The reaction pressure is normally in the range of 1-10 Torr, preferably 3-7 Torr, so as to maintain stable plasma. This reaction pressure is relatively high in order to lengthen the residence time of the reaction gas. The total flow of the reaction gas is important to reducing the relative dielectric constant of a resulting film. It is not necessary to control the ratio of the source gas to the additive gas. In general, the longer the residence time, the lower the relative dielectric constant becomes. The source gas flow necessary for forming a film depends on the desired deposition rate and the area of a substrate on which a film is formed. For example, in order to form a film on a substrate [r(radius)=100 mm] at a deposition rate of 300 nm/min, at least 50 sccm of the source gas is expected to be included in the reaction gas. That is approximately 1.6×102 sccm per the surface area of the substrate (m2). The total flow can be defined by residence time (Rt). When Rt is defined described below, a preferred range of Rt is 100 msec≦Rt, more preferably 200 msec≦Rt≦5 sec. In a conventional plasma TEOS, Rt is generally in the range of 10-30 msec.

Rt[s]=9.42×107(Pr·Ts/Ps·Tr)rw2d/F

    
    
        wherein:
        Pr: reaction chamber pressure (Pa)
        Ps: standard atmospheric pressure (Pa)
        Tr: average temperature of the reaction (K)
        Ts: standard temperature (K)
        rw: radius of the silicon substrate (m)
        d: space between the silicon substrate and the upper electrode (m)
        F: total flow volume of the reaction gas (sccm)
    
    


In the above, the residence time means the average period of time in which gas molecules stay in the reaction chamber. The residence time (Rt) can be calculated at Rt=αV/S, wherein V is the capacity of the chamber (cc), S is the volume of the reaction gas (cc/s), and α is a coefficient determined by the shape of the reaction chamber and the positional relationship between the inlet of gas and the outlet of exhaust. The space for reaction in the reaction chamber is defined by the surface of the substrate (πr2) and the space between the upper electrode and the lower electrode. Considering the gas flow through the space for reaction, α can be estimated as 1⁄2. In the above formula, α is 1⁄2.
In this method, the source gas is, in short, a silicon-containing hydrocarbon compound including at least one Si—O bond, at most two O—CnH2n+1 bonds and at least two hydrocarbon radicals bonded to the silicon (Si). Also, this source gas is vaporized by a direct vaporization method. The method results in an insulation film having a low relative dielectric constant, high thermal stability and high humidity-resistance.
Further aspects, features and advantages will become apparent from the detailed description of the preferred examples which follows.
FIG. 1 diagrammatically shows a plasma CVD apparatus usable in this invention. This apparatus comprises a reaction gas-supplying device 12 and a plasma CVD device 1. The reaction gas-supplying device 12 comprises plural lines 13, control valves 8 disposed in the lines 13, and gas inlet ports 14, 15 and 16. A flow controller 7 is connected to the individual control valves 8 for controlling a flow of a source gas of a predetermined volume. A container accommodating liquid reacting material 18 is connected to a vaporizer 17 that directly vaporizes liquid. The plasma CVD device 1 includes a reaction chamber 6, a gas inlet port 5, a susceptor 3 and a heater 2 embedded therein which can be a coil in which a coolant or heating medium flows to control the temperature. A circular gas diffusing plate 10 is disposed immediately under the gas inlet port. The gas diffusing plate 10 has a number of fine openings at its bottom face and can inject reaction gas to the semiconductor substrate 4 therefrom. There is an exhaust port 11 at the bottom of the reaction chamber 6. This exhaust port 11 is connected to an outer vacuum pump (not shown) so that the inside of the reaction chamber 6 can be evacuated. The susceptor 3 is placed in parallel with and facing the gas diffusing plate 10. The susceptor 3 holds a semiconductor substrate 4 thereon and heats it with the heater 2. The gas inlet port 5 is insulated from the reaction chamber 6 and connected to an outer high frequency power supply 9. Alternatively, the susceptor 3 can be connected to the power supply 9. Thus, the gas diffusing plate 10 and the susceptor 3 act as a high frequency electrode and generate a plasma reacting field in proximity to the surface of the semiconductor substrate 4.
A method for forming an insulation film on a semiconductor substrate by using the plasma CVD apparatus comprises a step of directly vaporizing silicon-containing hydrocarbon compounds expressed by the general formula SiαOβCxHy (α, β, x, and y are integers) and then introducing it to the reaction chamber 6 of the plasma CVD device 1, a step of introducing an additive gas, whose flow is substantially reduced, into the reaction chamber 6 and also a step of forming an insulation film on a semiconductor substrate by plasma reaction wherein mixed gases, made from the silicon-containing hydrocarbon compound as a source gas and the additive gas, are used as a reaction gas. It is a remarkable feature that the reduction of the additive gas flow also renders a substantial reduction of the total flow of the reaction gas. This feature will be described in more detail later.
The additive gases used in this embodiment, more specifically, are argon gas and helium gas. Argon is principally used for stabilizing plasma, while helium is used for improving uniformity of the plasma and also uniformity of thickness of the insulation film.
In the method described above, the first step of direct vaporization is a method wherein a liquid material, the flow of which is controlled, is instantaneously vaporized at a vaporizer that is preheated. This direct vaporization method requires no carrier gas such as argon to obtain a designated amount of the source gas. This differs greatly with the babbling method. Accordingly, a large amount of argon gas or helium gas is no longer necessary and this reduces the total gas flow of the reaction gas and then lengthens the time in which the source gas stays in the plasma. As a result, sufficient plasma reactions occur in the vapor so that a linear polymer can be formed and a film having a micropore porous structure can be obtained.
In FIG. 1, inert gas supplied through the gas inlet port 14 pushes out the liquid reacting material 18, which is the silicon-containing hydrocarbon compound, to the control valve 8 through the line 13. The control valve 8 controls the flow of the liquid reacting material 18 with the flow controller 7 so that it does not exceed a predetermined volume. The reduced silicon-containing hydrocarbon compound 18 goes to the vaporizer 17 to be vaporized by the direct vaporization method described above. Argon and helium are supplied through the inlet ports 15 and 16, respectively, and the valve 8 controls the flow volume of these gases. The mixture of the source gas and the additive gases, which is a reaction gas, is then supplied to the inlet port 5 of the plasma CVD device 1. The space between the gas diffusing plate 10 and the semiconductor substrate 4, both located inside of the reaction chamber 6 which is already evacuated, is charged with high frequency RF voltages, which are preferably 13.4 MHz and 430 kHz, and the space serves as a plasma field. The susceptor 3 continuously heats the semiconductor substrate 4 with the heater 2 and maintains the substrate 4 at a predetermined temperature that is desirably 350-450° C. The reaction gas supplied through the fine openings of the gas diffusing plate 10 remains in the plasma field in proximity to the surface of the semiconductor substrate 4 for a predetermined time.
If the residence time is short, a linear polymer cannot be deposited sufficiently so that the film deposited on the substrate does not form a micropore porous structure. Since the residence time is inversely proportional to the flow volume of the reaction gas, a reduction of the flow volume of the reaction gas can lengthen its residence time.
Extremely reducing the total volume of the reaction gas is effected by reducing the flow volume of the additive gas. As a result, the residence time of the reaction gas can be lengthened so that a linear polymer is deposited sufficiently and subsequently an insulation film having a micropore porous structure can be formed.
In order to adjust the reaction in the vapor phase, it is effective to add a small amount of an inert gas, an oxidizing agent, or a reducing agent to the reaction chamber. Helium (He) and Argon (Ar) are inert gases and have different first ionization energies of 24.56 eV and 15.76 eV, respectively. Thus, by adding either He or Ar singly or both in combination in predetermined amounts, the reaction of the source gas in the vapor phase can be controlled. Molecules of the reaction gas undergo polymerization in the vapor phase, thereby forming oligomers. The oligomers are expected to have a O:Si ratio of 1:1. However, when the oligomers form a film on the substrate, the oligomers undergo further polymerization, resulting in a higher oxygen ratio. The ratio varies depending on the relative dielectric constant or other characteristics of a film formed on the substrate.
In an embodiment, subsequently, a curing process is performed on the semiconductor substrate taken out from the reactor using the UV cure apparatus shown in FIG. 2. The UV cure apparatus comprises a process chamber 11, a UV lamp 12, a susceptor 13, an exhaust port 14, and a gas inlet port 15. The UV lamp and a susceptor 13 are disposed parallel, and are heated by heaters embedded in them respectively. The semiconductor substrate 16, which is a workpiece, is placed on the susceptor 13 and is heated and held. Projected from the UV lamp whose wavelength range is selected from 172-250 nm, light is irradiated toward the semiconductor substrate 16. When the semiconductor substrate is irradiated, gases such as He, H2, N2, CO2, etc. are being introduced through the gas inlet port 15. As soon as pores are formed in the film with H, O, C, etc. being desorbed from a low-dielectric-constant structure, unstable bonds no longer exist; hence, a film having a lower dielectric constant and higher strength can be obtained.
As the UV cure apparatus, the apparatus disclosed in commonly assigned U.S. patent application Ser. No. 11/040,863 can be used, the disclosure of which is incorporated herein by reference in its entirety.
In an embodiment, subsequently, a curing process is performed on the semiconductor substrate taken out from the reactor by annealing under conditions where the susceptor temperature may be 300° C. to 900° C. (preferably 350° C. to 750° C.), the pressure may be 300 Pa to 1,000 Pa (preferably 600 Pa to 900 Pa), the flow rate of an inert gas such as N2 may be 0.5 SLM to 5 SLM (preferably 2 SLM to 4 SLM), and the duration may be 100 seconds to 1000 seconds (preferably 400 seconds to 800 seconds.
In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation.
EXAMPLE
Experiments were conducted as described below. The results are indicated in tables below. In these experiments, an ordinary plasma CVD device (EAGLE®-10, ASM Japan K.K.) was used as an experimental device wherein:

    
    
        rw (radius of the silicon substrate): 0.1 m
        d (space between the silicon substrate and the upper electrode): 0.024 m or 0.020 m
        Ps (standard atmospheric pressure): 1.01×105 Pa
        Ts (standard temperature): 273 K
    
    


The thickness of each insulation film was set at 50 nm, except that the thickness of each insulation film for measuring a dielectric constant was set at 200 nm.
An insulation film was formed on a concave-convex surface of aluminum which had an aspect ratio of 1/3 to 1/10. Filling property of the film was evaluated by observing a cross section of the interconnect structure with a scanning electron microscope.
Example 1
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 400° C.
    DM-DEOS (dimethyldiethoxysilane) flow rate: 100 sccm
    He flow rate: 70 sccm
    27 MHz RF applied: 1600 W
    Reactor pressure: 600 Pa
    Dielectric constant: 2.9
    Modulus: 20 GPa
    Film stress: 40 MPa (tensile)
    Space between the silicon substrate and the upper electrode: 0.024 m
    Residence time: 320 msec.


The thin film formed on the substrate was then cured using a curing apparatus shown in FIG. 2 under the following conditions, and the cured film had the following properties:

    UV curing process: Wavelength: 172 nm, 3-10 mW/cm2, Susceptor temperature: 300° C., N2: 5 SLM, Pressure: 45 Torr, Time: 70 sec.
    Dielectric constant: 3.0
    Film shrinkage: 5.3%
    Modulus: 25 GPa
    Film stress: 55 MPa (tensile)
    Filling property (Padding property): Voids were observed in a padded area.


Example 2
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 10° C.
    DM-DEOS (dimethyldiethoxysilane) flow rate: 10 sccm
    He flow rate: 650 sccm
    O2 flow rate: 500 sccm
    Isopropyl alcohol flow rate: 150 sccm (isopropyl alcohol has a viscosity of 2.27 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.024 m
    Residence time: 118 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 450° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 2.7
    Film shrinkage: 10.3%
    Modulus: 6 GPa
    Film stress: 55 MPa (tensile)
    Filling property (Padding property): Voids were not observed in a padded area which showed good filling property of the film.


Example 3
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 110° C.
    DM-DEOS (dimethyldiethoxysilane) flow rate: 10 sccm
    He flow rate: 700 sccm
    O2 flow rate: 200 sccm
    Isopropyl alcohol flow rate: 150 sccm (isopropyl alcohol has a viscosity of 2.27 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.024 m
    Residence time: 113 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 400° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 2.6
    Film shrinkage: 12.3%
    Modulus: 8 GPa
    Film stress: 60 MPa (tensile)
    Filling property (Padding property): Voids were not observed in a padded area which showed good filling property of the film.


Example 4
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 0° C.
    TRES (triethoxysilane) flow rate: 10 sccm
    He flow rate: 650 sccm
    O2 flow rate: 0 sccm
    Isopropyl alcohol flow rate: 150 sccm (isopropyl alcohol has a viscosity of 2.27 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.020 m
    Residence time: 153 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 700° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 3.9
    Film shrinkage: 30%
    Film stress: 0 MPa (tensile)
    Filling property (Padding property): The film (oxide film) was able to be deposited selectively inside the holes.


Example 5
As a preliminary treatment (for improving padding property of an insulation film), a substrate was treated with a plasma using a plasma CVD apparatus shown in FIG. 1 under the following conditions:

    Susceptor temperature: 0° C.
    Isopropyl alcohol flow rate: 40 sccm
    He flow rate: 150 sccm
    27 MHz RF applied: 1200 W
    Reactor pressure: 800 Pa


An insulation film was then formed on the substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 0° C.
    DM-DMOS (dimethyldimethoxysilane) flow rate: 30 sccm
    He flow rate: 650 sccm
    O2 flow rate: 500 sccm
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.020 m
    Residence time: 105 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 450° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 2.8
    Film shrinkage: 10%
    Modulus: 9 GPa
    Film stress: 70 MPa (tensile)
    Filling property (Padding property): Voids were not observed in a padded area which showed good filling property of the insulation film.


Example 6
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 0° C.
    TRES (triethoxysilane) flow rate: 50 sccm
    He flow rate: 500 sccm
    O2 flow rate: 1,000 sccm
    Isopropyl alcohol flow rate: 150 sccm (isopropyl alcohol has a viscosity of 2.27 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.020 m
    Residence time: 153 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 700° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 3.9
    Film shrinkage: 30%
    Film stress: 0 MPa (tensile)
    Filling property (Padding property): The film (oxide film) was able to be deposited selectively inside the holes.


Example 7
As a preliminary treatment (for improving affinity between an underlying layer and an insulation film), a substrate was treated with a plasma using a plasma CVD apparatus shown in FIG. 1 under the following conditions:

    Susceptor temperature: 0° C.
    He flow rate: 1,000 sccm
    27 MHz RF applied: 250 W
    Reactor pressure: 1,000 Pa
    Reaction time: 30 seconds


An insulation film was then formed on the substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 0° C.
    TRES (triethoxysilane) flow rate: 50 sccm
    He flow rate: 500 sccm
    O2 flow rate: 500 sccm
    Isopropyl alcohol flow rate: 150 sccm (isopropyl alcohol has a viscosity of 2.27 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.020 m
    Residence time: 104 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 700° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 3.9
    Film shrinkage: 30%
    Film stress: 0 MPa
    Filling property (Padding property): The film (oxide film) was able to be deposited exclusively inside the holes.


Example 8
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 0° C.
    TRES (triethoxysilane) flow rate: 10 sccm
    He flow rate: 650 sccm
    O2 flow rate: 0 sccm
    Acetone flow rate: 150 sccm (acetone has a viscosity of 0.32 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.020 m
    Residence time: 153 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 700° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 3.9
    Film shrinkage: 20%
    Film stress: 30 MPa
    Filling property (Padding property): The film (oxide film) was able to be deposited exclusively inside the holes.


Example 9
An insulation film was formed on a substrate using a plasma CVD apparatus shown in FIG. 1 under the following conditions, and the resultant thin film had the following properties:

    Susceptor temperature: 0° C.
    TRES (triethoxysilane) flow rate: 10 sccm
    He flow rate: 650 sccm
    O2 flow rate: 0 sccm
    Isoprene flow rate: 150 sccm (isoprene has a viscosity of 0.21 mPa·s at 20° C.)
    27 MHz RF applied: 250 W
    Reactor pressure: 666 Pa
    Space between the silicon substrate and the upper electrode: 0.020 m
    Residence time: 153 msec.


The thin film formed on the substrate was then annealed under the following conditions, and the annealed film had the following properties:

    Annealing process: Susceptor temperature: 700° C., N2: 3 SLM, Pressure: 800 Pa, Time: 600 sec.
    Dielectric constant: 3.93
    Film shrinkage: 21%
    Film stress: 40 MPa (tensile)
    Filling property (Padding property): The film (oxide film) was able to be deposited selectively inside the holes.


In the above, the filling property of the insulation film in Example 1 was not as good as in the other examples because no additive gas was used in the reason gas. In Examples 6 and 7, the conditions of depositing the insulation films were substantially identical, and in Example 7, the preliminary treatment was performed in order to improve affinity between the underlying layer and the insulation film. The preliminary treatment did no affect the characteristics of the insulation film itself, the insulation films in Examples 6 and 7 were substantially the same. However, because of the preliminary treatment in Example 7, the padding property in Example 7 appeared to be better than in Example 6 according to the observations. The preliminary treatment is expected to have changed the surface character from a hydrophobic state to a hydrophilic state. When the holes are small, the preliminary treatment using a hydrocarbon gas as the auxiliary gas is effective as shown in Example 5.
The present invention includes the above mentioned embodiments and other various embodiments including the following:
In the above, the reaction space should not be limited to a physically defined single section, but should include any suitable space for plasma reaction. That is, as one of ordinary skill in the art readily understands, the space is a functionally defined reaction space. The space may be comprised of a physically defined single section such as the interior of a reactor, or physically defined multiple sections communicated with each other for plasma reaction, such as the interior of a remote plasma chamber and the interior of a reactor. Further, the space includes the interior of piping connecting multiple sections through which a reaction gas passes. The interior of the reactor includes only the space used for plasma reaction. Thus, if only a part of the reactor interior is used for plasma reaction where the reactor is composed of multiple sections, only the part used for plasma reaction constitutes a reaction space. Further, the plasma reaction includes a preliminary reaction for plasma polymerization. For example, upstream of a reactor, heating a reaction gas (e.g., 150° C. to 500° C., preferably 200° C. to 300° C., in a pre-heater chamber), exciting a reaction gas (e.g., in a remote plasma chamber), or mixing an excited additive gas and a source gas (e.g., in a pre-heater chamber) is included in a preliminary reaction.
The source gas and the additive gas are separately introduced into the reaction space. The additive gas and the source gas can be mixed upstream of a reactor and introduced into the reactor. However, they can be introduced separately, depending on the configuration of a reactor. As long as the gases are not in a reactive state, regardless of whether the additive gas and the source gas are mixed or separated, the space where the gases are present does not constitute a reaction space. At a point where additive gas and the source gas are in contact in a reactive state, the reaction space begins. The reactive state includes states where the reaction gas is heated or excited, or the excited additive gas and the source gas are mixed, for example.
The plasma reaction comprises exciting the reaction gas and depositing the film on the substrate. As described above, the plasma reaction includes a preliminary reaction such as excitation of the reaction gas.
The reaction space comprises a space for exciting the reaction gas and a space for depositing the film. In this embodiment, the reaction gas can be excited in a remote plasma chamber installed upstream of a reactor, and the film is deposited on the substrate in the reactor. The source gas and the additive gas can be introduced into the remote plasma chamber. In this case, the reaction space is composed of the interior of the remote plasma chamber, the interior of the reactor, and the interior of the piping connecting the remote plasma chamber and the reactor. Because of using the interior of the remote plasma chamber, the interior of the reactor can be significantly reduced, and thus, the distance between the upper electrode and the lower electrode can be reduced. This leads to not only downsizing the reactor, but also uniformly controlling a plasma over the substrate surface. Any suitable remote plasma chamber and any suitable operation conditions can be used in the present invention. For example, usable are the apparatus and the conditions disclosed in U.S. patent applications Ser. No. 09/511,934 filed Feb. 24, 2000 and Ser. No. 09/764,523 filed Jan. 18, 2001, U.S. Pat. No. 5,788,778, and U.S. Pat. No. 5,788,799. The disclosure of each of the above is incorporated herein by reference in its entirety.
The excitation of the reaction gas comprises exciting the additive gas and contacting the excited additive gas and the source gas. The excitation of the reaction gas can be accomplished in the reactor or upstream of the reactor. As described above, both the source gas and the additive gas can be excited in a remote plasma chamber. Alternatively, the excitation of the reaction gas can be accomplished by exciting the additive gas in a remote plasma chamber and mixing it with the source gas downstream of the remote plasma chamber.
The reaction space comprises a space for heating the reaction gas and a space for exciting the reaction gas and depositing the film. In this embodiment, the reaction gas can be heated in a pre-heat chamber installed upstream of a reactor, the reaction gas is excited in the reactor, and film is deposited on the substrate in the reactor. The source gas and the additive gas can be introduced into the pre-heater chamber. In this case, the reaction space is composed of the interior of the pre-heater chamber, the interior of the reactor, and the interior of the piping connecting the pre-heater chamber and the reactor. Because of using the interior of the pre-heater chamber, the interior of the reactor can be significantly reduced, and thus, the distance between the upper electrode and the lower electrode can be reduced. This leads to not only downsizing the reactor, but also uniformly controlling a plasma over the substrate surface. Any suitable remote plasma chamber and any suitable operation conditions can be used in the present invention. For example, usable are the apparatus and the conditions disclosed in the aforesaid references.
The excitation of the reaction gas comprises exciting the additive gas and contacting the excited additive gas and the source gas. In this embodiment, the additive gas can be excited in a remote plasma chamber, and the source gas is heated in a pre-heater chamber where the excited additive gas and the source gas are in contact, and then the reaction gas flows into the reactor for deposition of a film. In this case, deposition of unwanted particles on a surface of the remote plasma chamber, which causes a failure of ignition or firing, can effectively be avoided, because only the additive gas is present in the remote plasma chamber. The source gas is mixed with the excited additive gas downstream of the remote plasma chamber. The reaction space may be composed of the interior from a point where the excited additive gas and the source gas meet to an entrance to the reactor, and the interior of the reactor.
The plasma reaction is conducted at a temperature of 350-450° C. However, the suitable temperature varies depending on the type of source gas, and one of ordinary skill in the art could readily select the temperature. In the present invention, polymerization includes any polymerization of two or more units or monomers, including oligomerization.
The formation of the insulation film is conducted while maintaining a gas diffusing plate at a temperature of 150° C. or higher (e.g., 150° C. to 500° C., preferably 200° C. 300° C.), through which the reaction gas flows into the reaction space, so that the reaction is promoted. In the above, the gas diffusing plate (or showerhead) may be equipped with a temperature control device to control the temperature. Conventionally, the temperature of the showerhead is not positively controlled and is normally 140° C. or lower when the temperature of the reaction space is 350-450° C., for example.
The residence time is determined by correlating the dielectric constant with the residence time. This embodiment has been described earlier. The following embodiments also have been described earlier:
The flow of the reaction gas is controlled to render the relative dielectric constant of the insulation film lower than 3.10.
Rt is no less than 140 msec.
It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention.

## Claims

1. A method for forming an insulation film on a semiconductor substrate by plasma reaction, comprising the steps of:
vaporizing a silicon-containing hydrocarbon compound to provide a source gas, said silicon-containing hydrocarbon compound comprising a Si—O bond in a molecule;
introducing a reaction gas comprising the source gas and a carrier gas into a reaction space for plasma CVD processing wherein a semiconductor substrate is placed; and
forming an insulation film constituted by Si, O, H, and optionally C or N on the substrate by plasma reaction using a combination of low-frequency RF power and high-frequency RF power in the reaction space, wherein the plasma reaction is activated while controlling the flow of the reaction gas to lengthen a residence time, Rt, of the reaction gas in the reaction space, wherein 100 msec≦Rt,


Rt[s]=9.42×107(Pr·Ts/Ps·Tr)rw2d/F


wherein:
Pr: reaction space pressure (Pa)
Ps: standard atmospheric pressure (Pa)
Tr: average temperature of the reaction (K)
Ts: standard temperature (K)
rw: radius of the silicon substrate (m)
d: space between the silicon substrate and the upper electrode (m)
F: total flow volume of the reaction gas (sccm).

2. The method according to claim 1, wherein said reactive group is selected from the group consisting of alkoxy group, vinyl group, amino group, and acid radical.

3. The method according to claim 2, wherein said silicon-containing hydrocarbon compound has the formula SiαOα−1R2α−β+2(OR′)β wherein α is an integer of 1-3, β is 0, 1, or 2, R is H or C1-6 hydrocarbon attached to Si, and R′ is H or C1-6 hydrocarbon unattached to Si.

4. The method according to claim 1, further comprising adding to the reaction gas an additive gas selected from the group consisting of H2 gas and a gas of CxHyOz wherein x=1-10, y=a natural number, and z=0, 1, or 2.

5. The method according to claim 4, wherein the additive gas is introduced at a flow rate of 10 sccm to 900 sccm.

6. The method according to claim 4, wherein the additive gas is CxHyOz wherein x=1-5, y=2x or 2x+2, and z=0 or 1 and introduced at a flow rate greater than that of the source gas.

7. The method according to claim 4, wherein the additive gas is CxHyOz which has a viscosity of 0.2-2.3 mPa·s as measured at 20° C.

8. The method according to claim 1, further comprising adding to the reaction gas an oxidizing gas.

9. The method according to claim 1, wherein the average temperature of the reaction (Tr) is in a range of 223K to 373K.

10. The method according to claim 1, wherein the insulation film is a silicon carbide film doped with oxygen.

11. The method according to claim 1, wherein the insulation film contains N.

12. The method according to claim 11, further comprising adding to the reaction gas an additive gas which is at least one selected from the group consisting of N2, NH3, and N2O.

13. The method according to claim 12, wherein the additive gas is introduced at a flow rate of 50 sccm to 3,000 sccm.

14. The method according to claim 1, wherein the substrate has an exposed surface on which the insulation film is to be deposited, which surface has a three-dimensional structure of aluminum, tungsten, or tungsten silicon.

15. The method according to claim 14, wherein the insulation film has a thickness of 25 nm to 70 nm.

16. The method according to claim 1, wherein the insulation film has a density of 1.3 g/cm3 or higher.

17. The method according to claim 1, wherein the space between the silicon substrate and the upper electrode (d) is less than 0.014 m.

18. The method according to claim 1, wherein the substrate has a via and/or trench is formed wherein the insulation film is to be formed on a surface of the via and/or trench.

19. The method according to claim 1, wherein the substrate has an exposed surface on which the insulation film is to be formed, which surface has an aspect ratio of about 1⁄3 to about 1/10.

20. The method according to claim 1, wherein the average temperature of the reaction (Tr) is in a range of 323K to 373K.

21. The method according to claim 1, wherein the average temperature of the reaction (Tr) is in a range of 223K to 323K.

22. The method according to claim 1, further comprising, as a preliminary treatment, introducing an auxiliary gas selected from the group consisting of He, O2, and a gas constituted by C, H, and optionally O into the reaction space for plasma treatment of the semiconductor substrate before introducing the reaction gas.

23. The method according to claim 22, wherein the auxiliary gas is He or a combination of He and isopropyl alcohol or acetone.

24. The method according to claim 1, further comprising annealing the substrate having the insulation film, thereby curing the insulation film.

25. The method according to claim 2, wherein said silicon-containing hydrocarbon compound has the formula SiR(OR′)3 or (Si—O)3R6 wherein R and R′ are independently H or C1-6 hydrocarbon attached to Si.

26. A method for forming an interconnect structure, comprising the steps of:
forming a three-dimensional structure for interconnect in a substrate; and
forming an insulation layer on a surface of the three-dimensional structure using the method of claim 1.

27. The method according to claim 26, wherein the step of forming a three-dimensional structure comprises forming a layer of aluminum, tungsten, or tungsten silicon as a wiring layer and etching the layer in a pattern.

28. A method for forming an insulation film on a semiconductor substrate by plasma reaction, comprising the steps of:
performing, as a preliminary treatment, plasma treatment of a semiconductor substrate which is placed in a reaction space for plasma CVD processing, using an auxiliary gas selected from the group consisting of He, O2, and a gas constituted by C, H, and optionally O;
vaporizing a silicon-containing hydrocarbon compound to provide a source gas;
introducing a reaction gas comprising the source gas, a carrier gas, and an additive gas into the reaction space, said additive gas being selected from the group consisting of H2 gas and a gas of CxHyOz wherein x=1-10, y=a natural number, and z=0, 1, or 2, into the reaction space; and
forming an insulation film constituted by Si, O, H, and optionally C or N on the substrate by plasma reaction using a combination of low-frequency RF power and high-frequency RF power in the reaction space, wherein the plasma reaction is activated while controlling the flow of the reaction gas to lengthen a residence time, Rt, of the reaction gas in the reaction space, wherein 100 msec≦Rt,


Rt[s]=9.42×107(Pr·Ts/Ps·Tr)rw2d/F


wherein:
Pr: reaction space pressure (Pa)
Ps: standard atmospheric pressure (Pa)
Tr: average temperature of the reaction (K)
Ts: standard temperature (K)
rw: radius of the silicon substrate (m)
d: space between the silicon substrate and the upper electrode (m)
F: total flow volume of the reaction gas (sccm).

29. The method according to claim 28, wherein the auxiliary gas is He or a combination of He and isopropyl alcohol or acetone.

30. The method according to claim 28, wherein said silicon-containing hydrocarbon compound has a formula of SimR2m+2 wherein m is an integer of 1 or 2, R is H or C1-6 hydrocarbon.

31. The method according to claim 30, wherein said silicon-containing hydrocarbon compound contains at least one reactive group selected from the group consisting of alkoxy group, vinyl group, amino group, and acid radical.

32. The method according to claim 28, wherein the additive gas is CxHyOz which has a viscosity of 0.2-2.3 mPa·s as measured at 20° C.

33. The method according to claim 32, wherein the additive gas is introduced at a flow rate of 10 sccm to 900 sccm.

34. The method according to claim 28, further adding an oxidizing gas to the reaction gas.

35. The method according to claim 28, wherein the average temperature of the reaction (Tr) is in a range of 223K to 373K.

36. The method according to claim 28, wherein the substrate has an exposed surface on which the insulation film is to be deposited, which surface has a three-dimensional structure of aluminum, tungsten, or tungsten silicon.

37. The method according to claim 28, wherein the substrate has a via and/or trench is formed wherein the insulation film is to be formed on a surface of the via and/or trench.

38. The method according to claim 28, further comprising annealing the substrate having the insulation film, thereby curing the insulation film.

39. A method for forming an interconnect structure, comprising the steps of:
forming a three-dimensional structure for interconnect in a substrate; and
forming an insulation layer on a surface of the three-dimensional structure using the method of claim 28.

40. The method according to claim 39, wherein the step of forming a three-dimensional structure comprises forming a layer of aluminum, tungsten, or tungsten silicon as a wiring layer and etching the layer in a pattern.