Method for reforming a substrate surface

Abstract: The present invention relates to a method for reforming a surface of a base layer before thin film deposition, wherein a base thermal SiO 2 film 1a is exposed to any gas for reforming the surface of the base layer selected from the group consisting of AX 4 , AH n Cl 4-n and AR n X 4-n (in which, a represents any one selected from the group consisting of Si , Ge and Sn, X represents any one selected from the group consisting of I, Br, F and Cl and R represents any one of C m H 2m+1 , and an accompanying character "n" is any one of 1, 2 or 3 and an accompanying character "m" is a natural number).

Description: BACK GROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reforming a base surface before thin film deposition, a method for manufacturing the semiconductor device and an equipment for manufacturing the same, and more particularly to the method for reforming the base surface before the thin film deposition, the method for manufacturing the semiconductor device and the equipment for manufacturing the same in the thin film deposition by CVD (Chemical Vapor deposition) method using O 3 /TEOS (Tetraehylorthosilicate) system reaction gas (the gases containing O 3 and TEOS). 2. Description of the Prior Art Recently, it is often known that a property of the film formed on the base layer is greatly influenced depending upon a surface condition of the base layer. Especially, a film property of CVD film deposited by the CVD method using O 3 /TEOS system gas for thin film deposition depends upon the surface condition of the base layer greatly. For example, the growth rate of the thin film is reduced remarkably and the deposited film becomes porous in case that the surface of the base layer is hydrophilic. Therefore, the fluidity, the flatness, the embedding ability and the step-coverage ability of the film deposited on a surface of a base layer are lowered. It is thought that such deposition irregularity is caused by that an intermediate generated in the reaction of O 3 gas and TEOS gas is a polymer with hydrophilicity, and it is shown that a film can not be deposited on the surface of the base layer in case that the surface of the base layer is hydrophilic. As methods destroying a dependence on the surface of the base layer described above, there have been (1)a method by plasma processing using the gases such as NH 3 , H 2 or the like, (2)a method using the insulating film formed using a low concentration of O 3 as the base layer, (3)a method using the insulating film formed by a plasma CVD method as the base layer, (4)a method processing the surface of the base layer before the thin film deposition with alcohol, or the like. However, there are the problems as described below in the mentioned-above method. That is, (1)In the method by plasma processing using the gases such as NH 3 , H 2 or the like the good film in the embedding ability and the step-coverage ability has been not deposited, when depositing film on very narrow regions such as via-holes and contact holes. (2)In the method using the insulating film formed by a plasma CVD method as the base layer, it has been difficult to form the insulating film being used as the base layer on the very narrow regions such as the via-holes and the contact holes. (3)In also the method using the insulating film formed by the plasma CVD method as the base layer, it has been difficult to form the insulating film being used as the base layer on the very narrow regions such as the via-holes and the contact holes as the same as the item (2). (4)In the method processing the surface of the base layer before the thin film deposition with alcohol, the effect of reform is poor in reproduction, in addition, the effect of reform processing of the base surface can not be maintained. From US-A 5,080,933 a method for selectively depositing polysilicon on a semiconductor surface is known. In this method, after a silicon substrate is exposed to a single crystal inhibitor gas, a polycrystalline silicon is formed on the silicon substrate exposing to a silicon containing gas and a source of hydrogen. N 2 or Ar is used as the single crystal inhibitor gas. Furthermore, SiH n Cl 4-n by which the polycrystalline silicon can be selectively formed on the silicon substrate is used as the silicon containing gas. US-A-5,365,877 describes a method for forming a semiconductor layer on a semiconductor substrate in which the semiconductor layer is formed on the semiconductor substrate rotating the semiconductor substrate. SiH n Cl 4-n is used as a reaction gas. GB-A 1,044,041 describes a method of manufacturing semiconductor devices in which, after a semiconductor layer is formed on a semiconductor substrate, a silicon oxide film is formed on the semiconductor layer continuously without taking it outside the film forming apparatus. SiH 4 or SiHCl 3 is used as a film forming gas. From the article "Dichlorosilane effects on low-temperature selective silicon epitaxy", Applied Physics Letters 58 (1991), 7 January, no. 1, New York, US, a method for forming a silicon layer on a silicon film forming surface is known. It is disclosed that the silicon film forming surface is process by a process gas in which a low concentration of SiH 2 Cl 2 is added in H 2 gas before the film formation of this silicon layer on a silicon film forming surface. Summary of the Invention The present invention is defined by the features of the independent claims. Advantageous embodiments of the present invention are set forth in the subclaims. The object of the invention is to provide a method for reforming a base surface before the thin film deposition, a method for manufacturing the semiconductor device and an equipment for manufacturing the same, capable of maintaining the effect by means reform of the base layer surface, of improving the fluidity, the flatness, the embedding ability and the step-coverage ability of the film deposited on the surface of the base layer and, especially, of improving the embedding ability and the step-coverage ability of the film formed in the very narrow regions such as the via-holes and the contact holes of the base layer. In the invention, reform of the surface of the base layer in a reaction chamber is performed by the gas for reform of the base layer surface containing a halogen element, and subsequently, film deposition can be performed on the surface of the base layer reformed by the gas for thin film deposition. According to experiments of the inventor of this application, it has been found that when reform of the surface of the base layer is performed by the gas for reform of the base layer surface containing a halogen element, the effect of reform of the base layer surface can be maintained for the long term as compared to the prior art, in addition, the fluidity, the flatness, the embedding ability and the step-coverage ability of the film formed on the reformed surface of the base layer can be improved. Especially, the embedding ability and the step-coverage ability of the film formed in the via-holes or the like could be improved, even though there are the very narrow-concave regions such as the via-holes and the contact holes in the base layer. Moreover, the fluidity, the flatness, the embedding ability and the step-coverage ability of the film formed on the surface of the base layer thereof can be improved, when reform of the surface of the base layer is performed while heating the base layer. Especially, it was confirmed that the effect further can be increased when setting a heating temperature at 100 °C or more upon reform of the surface. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A to FIG. 1C are sectional views showing a method for reforming a base surface of embodiment of the invention. FIG. 2 is a view showing a condition of a base thermal SiO 2 film surface soon after forming the base thermal SiO 2 film, according to the method for reforming the base surface of the embodiment of the invention. FIG. 3A and FIG. 3B are views showing a condition of the base thermal SiO 2 film surface before reforming according to the method for reforming the base surface of the embodiment according to the invention. FIG. 4A to FIG. 4F are views showing a reaction of the base thermal SiO 2 film and a reaction gas SiCl 4 according to the method for reforming the base surface of the embodiment according to the invention. FIG. 5 is a schematic construction view showing a CVD thin film deposition equipment of a cold wall system, which can be used in the method for reforming the base surface of the invention. FIG. 6 is a side view showing a detail of reforming gas supply means provided on the equipment for manufacturing the semiconductor device for use in the invention. FIG. 7A and FIG. 7B are section views showing a reaction equipment of a hot wall system which can be used as the equipment for manufacturing the semiconductor device employing the embodiment of the invention. FIG. 8 is a section view in case of that a O 3 /TEOS SiO 2 film is formed after reform processing according to the embodiment of the invention. FIG. 9 is a section view in case of that a O 3 /TEOS SiO 2 film is formed without performing reform processing of the base surface according to the comparison example. DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, the embodiment of the invention will be described referring to the accompanying drawings. FIG. 5 is a schematic construction view showing a CVD thin film deposition equipment of a cold wall system which can be used in the method for reforming the base surface of the present invention and FIG. 6 is a side view showing detail of reforming gas supplying bombe. A holding table 62 for holding a silicon wafer 1 is provided in a reaction chamber 61 ( a chamber) made of stainless steel, and a heater (a heating means) for heating the silicon wafer 1 is embedded in the holding table 62. A conduit 68a introducing the O 3 /TEOS gases (gases for thin film deposition) supplied from a gas supply means 63 or the gas for reforming the base layer surface into the reaction chamber 61 and a gas distribution plate 64 discharging the O 3 /TEOS gases or the gas for reforming the base layer surface to the silicon wafer 1 on the holding table 62, said the gas distribution plate 64 being connected to the other end of said conduit 68a, are installed in the reaction chamber 61. Moreover, an exhaust equipment 65 for adjusting a pressure in the reaction chamber 61 is connected to the reaction chamber 61. The gas supply means 63 is comprised of a reforming gas supply means 66, a supply means of the gas for thin film deposition 67, a conduit 68b and a selecting valve 69 (a selection means). The reforming gas supply means 66 supplies the reforming gas in the reaction chamber 61 upon reforming the base surface, and the supply means 67 of the gas for thin film deposition supplies a mixed gas of the O 3 /TEOS gases of the gas for thin film deposition after reforming the surface of the base layer. The conduit 68b and 68c are connected to these two gas supply means 66 and 67 respectively, in addition, these conduits 68b and 68c are connected with the conduit 68a extending into the reaction chamber 61. The connecting ports of these three conduits 68b 68c and 68a are provided with the selecting valve 69 and the valve selects a flow passage so as to allow to conduct the flow passage introducing the gas for reforming from the conduit 68b to the conduit 68a or to conduct the flow passage introducing the gas for thin film deposition from the conduit 68c to the conduit 68a. The gas for reforming or the gas for thin film deposition are introduced into the reaction chamber 61 through the conduit 68a selectively by selection of the flow passage by the selecting valve 69. The detailed structure of the reforming gas supply means 66 is as follows: namely, the reforming gas supply means 66 comprises an evaporation container 72 in which liquid sources such as liquid SiCl 4 , SiBr 4 , SiF 4 are accommodated and a temperature regulator 71 for adjusting a temperature of the liquid sources in the evaporation container 72, said the temperature regulator being provided around the evaporation container 72 as shown in FIG. 6. Moreover, the reforming gas supply means 66 comprises the conduit 68d for introducing N 2 , H 2 or Ar gas as carrier gas into the liquid sources in the reaction container 72 and the conduit 68b introducing a source gas (a reforming gas) generated by allowing to bubble the carrier gas in the liquid sources outside the evaporation container 72. A flow meter 73 for measuring flow rate of N 2 , H 2 or Ar gas and a valve 74 for performing flow regulation are provided on the conduit 68d and a valve 75 for performing flow regulation of the reforming gas is provided on the conduit 68b. The reforming gas generated in the evaporation container 72 is introduced into the reaction chamber 61 through the conduit 68b. Subsequently, the method for reforming the base surface of the embodiment of the present invention will be described. FIG. 1A to FIG. 1C are sectional views showing a method for reforming a base surface of embodiment of the present invention. FIG. 2 is a view showing a condition of a base thermal SiO 2 film surface soon after forming the thermal SiO 2 film as the base layer (hereinafter referred to as a base thermal SiO 2 film also) is formed, FIG. 3A and FIG. 3B are views showing a conditions of the base thermal SiO 2 film surface before reforming and FIG. 4A to FIG. 4E are views showing a reaction of the base thermal SiO 2 film and the reforming gas SiCl 4 at the base thermal SiO 2 film surface. First, the silicon wafer 1 is fed in an oxidation furnace to be heated at 1100 °C within an oxygen atmosphere. By this treatment, the surface of the silicon wafer 1 is oxidized, whereby the thermal SiO 2 film 1a is formed as shown in FIG. 1A. This thermal SiO 2 film 1a becomes the base layer for thin film deposition. There are dangling bonds in Si of the surface of a base thermal SiO 2 film 1a soon after being formed as shown in FIG. 2. In this process, a plasma enhanced CVD method and a low pressure CVD method may be used. At this point of time, it is considered that there are occurred the conditions that the surface of the base thermal SiO 2 film 1a contacts with air (containing moisture) to hydrate to allow to bond Si and OH to form Si-OH bond as shown in FIG. 3A, or to allow to bond Si and H 2 O to form Si-H 2 O bond as shown in FIG. 3B. In any events, the base thermal SiO 2 film 1a becomes hydrophilic. Subsequently, the silicon wafer 1 is placed on the holding table 62 in the reaction chamber 61 as shown in FIG. 1B to be heated 100 °C or more by the heater built in the holding table 62. And then, the gas for reforming the base layer surface containing SiCl 4 is supplied from the reforming gas supply means 66 to the reaction chamber 61. The gas for reforming the base layer surface is discharged to the surface of the base thermal SiO 2 film 1a formed on the silicon wafer 1. At this time, it can be estimated that two kind of reactions are occurred between the base thermal SiO 2 film 1a and the gas for reforming the base layer surface on the surface of the base thermal SiO 2 film 1a as described below. A mark "×" in FIG. 1B shows the situation that this reaction is occurred. The situation of the reaction is described, dividing into the base thermal SiO 2 film 1a terminated by the Si-OH bond and the surface of the base thermal SiO 2 film 1a terminated by the Si-H 2 O bond. First, the situation of the reaction of the case being terminated by the Si-OH bond is illustrated. As shown in FIG. 4A, -H in -OH being bonded by Si-OH bond and -Cl in SiCl 4 are bonded on the surface of the heated base thermal SiO 2 film 1a by being exposed to SiCl 4 to generate HCl. By this reaction, O remains in the bond of Si of the surface of the base thermal SiO 2 film 1a, as well as -Cl is removed from SiCl 4 to generate SiCl 3 . Moreover, HCl generated is discharged out of the reaction region of the surface of the base thermal SiO 2 film 1a, since the temperature of the surface of the base thermal SiO 2 film 1a is 100 °C or more. SiCl 4 +OH - → SiCl 3 + HCl + O 2- . Oxygen and Si of the surface of the base thermal SiO 2 film 1a are bonded to result in SiO. Subsequently, SiCl 3 generated and Si-O of the surface of the base thermal SiO 2 film 1a react as shown in FIG. 4B, whereby Cl and O are replaced to generate SiOCl 2 and Si-Cl as shown in FIG. 4C. SiCl 3 + O 2- → SiOCl 2 + Cl - . By this reaction, hydrophobicity is appeared, since the surface of the base thermal SiO 2 film 1a is halogenated. Furthermore, even though Cl and O are remained as it is without being replaced, hydrophobicity is shown since the surface is oxidized as shown in FIG. 4D. Under the condition that Si of the surface of the base thermal SiO 2 film 1a is bonded with H 2 O, SiCl 4 and H 2 O react as shown in FIG. 4E to generate SiOCl 2 , HCl and Cl through the same reaction processes as described in FIG. 4A to FIG. 4D. SiCl 4 + H 2 O → SiOCl 2 + 2HCl + Cl - As a result, it is considered that since Si of the surface of the base thermal SiO 2 film 1a and Cl are bonded and the surface of the base thermal SiO 2 film 1a is chlorinated as shown in FIG. 4F, whereby hydrophobicity is appeared. After the reform processing described above, without providing processing such as cleaning on the surface of the base thermal SiO 2 film 1a, the transfer to a subsequent thin film deposition process can be performed. Therefore, the reforming gas is stopped in succession the reform processing described above, and the mixed gas of the O 3 /TEOS gases is supplied into the reaction chamber 61 as the gas for thin film deposition from the supply means 67 of the gas for thin film deposition. Moreover, the silicon wafer 1 is heated at approximate 400 °C to allow to react the O 3 and TEOS gases thermally. Holding the condition for the given time period, an O 3 /TEOS SiO 2 film 2 is formed on the base thermal SiO 2 film 1a as shown in FIG. 1. This O 3 /TEOS SiO 2 film 2 shows the SiO 2 film formed by making to react the O 3 gas and the TEOS gas. In this embodiment, the thin film deposition is performed using the gases after reforming the surface of the base thermal SiO 2 film 1a into hydrophobic, whereby the fluidity, the flatness, the embedding ability and the step-coverage ability of O 3 /TEOS SiO 2 film 2 formed can be improved. Especially, it has allowed to maintain the effect of the reform since using the reforming gas containing a halogen element. That is, even though after performing reform of the base surface, the surface of the base thermal SiO 2 film 1a is exposed to air for 24 hours subsequently to form the O 3 /TEOS SiO 2 film 2, the fluidity, the flatness, the embedding ability and the step-coverage ability of the O 3 /TEOS SiO 2 film 2 formed can be maintained. Hydrophobicity can be improved, since the temperature of the surface of the base thermal SiO 2 film 1a is 100 °C or more. In this case, it is considered that silanol (here, Si(OH) 4 is applicable) is generated in reforming process, and silanol is decomposed by the temperature of 100 °C or more. Moreover, when silanol is generated it takes long time to decompose silanol if being less than 100 °C, so that the time period to stay on the surface of the base thermal SiO 2 film 1a becomes long, whereby conversion from hydrophilicity to hydrophobicity becomes difficult. Hereinafter, the example actually embodied will be described referring to the FIG. 8. In this example, the invention is applied to the base layer in which there are grooves narrow in width. Moreover, for comparison, a comparison example deposited on the base layer without performing reform processing of the invention is shown in FIG. 9. FIG. 8 is a section view in case of that a O 3 /TEOS SiO 2 film is formed after performing reform processing on the base surface, and FIG. 9 is a section view in case of that a O 3 /TEOS SiO 2 film is formed without performing reform processing of the base surface. As shown in FIG. 8, a groove 3 of approximate 0.1 µ m in width and approximate 0.6 µ m in depth was formed on the silicon wafer 1 to form the base thermal SiO 2 film 1a on the surface of the silicon wafer 1 having this groove 3 to provide as the base layer. And then, the O 3 /TEOS SiO 2 film 2 is formed on the base layer surface thereof, and it was searched whether the embedding ability and the step-coverage ability of the O 3 /TEOS SiO 2 film 2 formed could be improved or not. Heating temperature is set at 1100 °C in order to form the base thermal SiO 2 film 1a. As the conditions for reform of the base surface, liquid SiCl 4 in 20 °C was used as a liquid source, and bubbling was performed for about 2 minutes by introducing N 2 gas into this SiCl 4 at the rate of 5 littler per min.. Moreover, heating temperature of the silicon wafer 1 was set at 250 °C. Moreover, in the conditions for thin film deposition of the O 3 /TEOS SiO 2 film 2, the ozone concentration in the gas for thin film deposition composed of the mixed gas of the O 3 /TEOS was set at a so called high concentration of O 3 concentration of 5 percent in O 2 , and heating temperature of the silicon wafer 1 was set at 400 °C. It is found from FIG. 8 that the O 3 /TEOS SiO 2 film 2 of which surface is planarized is formed without voids, when the O 3 /TEOS SiO 2 film 2 is formed after performing the processing using the method for reforming the base surface of this embodiment. In contrast with this, it is found that the voids are occurred, the surface of the film 2 becomes wavy, whereby a planarized film can not be obtained as shown in FIG.9, when the O 3 /TEOS SiO 2 film 2 is formed without reform processing of the base surface. As described above, the embedding ability and the step-coverage ability of the film 2 formed in the groove 3 can be improved, when the surface reform of the base layer 1a having the very narrow-concave regions such as the groove 3 is performed by the gas for reform of the base layer surface containing a halogen element. In this embodiment, although the same chamber 61 is used without separating the reaction chamber used for reforming the base surface and the reaction chamber used for depositing the O 3 /TEOS SiO 2 film 2, an individual reaction chamber may be used respectively. Moreover, the reaction chamber 61 may be a single wafer processing reaction chamber or a batch processing equipment of a furnace type. Furthermore, although the reaction equipment of a cold wall system is used in this embodiment, the reaction equipment may be a reaction equipment of a hot wall system as shown in FIG. 7 and a horizontal type furnace as shown in FIG. 7A or a vertical type furnace as shown in FIG. 7B. In this case, a heater or an infrared heating equipment provided on the vicinity of the reaction chamber can be used as the heating means of the hot wall system. Besides, although SiCl 4 in the gas expressed by a generalized formula AX 4 is used as the reforming gas, the other gas, for example, SiI 4 , SiBr 4 or SiF 4 expressed by a generalized formula AX 4 can be used. Furthermore, the gas, for example, SiHCl 3 , SiH 2 Cl 2 or SiH 3 Cl expressed by a generalized formula AH n Cl 4-n (the accompanying character "n" is any one of 1, 2 or 3) can be used. Moreover, the gas, for example, Si(C m H 2m+1 )Cl 3 , Si(C m H 2m+1 ) 2 Cl 2 , Si(C m H 2m+1 ) 3 Cl expressed by a generalized formula AR n X 4-n (the accompanying character "m" is a natural number) can be used. Moreover, in the generalized formula described above, A represents any one of Si , Ge or Sn, X represents any one of I, Br, F or Cl and R represents any one of C m H 2m+1 . Furthermore, although SiO 2 film is used as the insulating film formed on the base layer, any one of PSG (Phosphosilicate glass) film, BSG (Borosilicate glass) film or BPSG (Borophosphosilicate glass) film can be used. The mixed gas of O 3 and TEOS and TMP (Trimehtylphosphite : P(OCH 3 ) 3 ) or TMOP (Trimehtylphosphite : PO(OCH 3 ) 3 ) as the gas for thin film deposition where PSG film is deposited, the mixed gas of O 3 and TEOS and TMB (Trimehtylborate : B(OCH 3 ) 3 ) as the gas for thin film deposition where BSG film is deposited, and the mixed gas of O 3 and TEOS and TMB and TMP or TMOP as the gas for thin film deposition where BPSG film is deposited can be used. As described above, according to the present invention, after the surface of the base layer is exposed to the gas for reform of the base layer surface containing a halogen element to reform the surface of the base layer, the thin film deposition is performed on the surface of the base layer reformed by the gas for thin film deposition. The effect of reform of the base layer surface can be maintained, since the gas for reform of the base layer surface containing a halogen element is used. The micronization and the increase in density of the device can be also realized, since the excellent film in the embedding ability and the step-coverage ability can be deposited on the surface of the base layer 1a having the very narrow-concave regions in width such as the groove.

Claims: A method for reforming a base surface, wherein a surface of a thermal SiO 2 film or a SiO 2 film obtained by a plasma enhanced CVD method and a low pressure CVD method as a base layer (1a), on which base layer (1a) an insulating film (2) is formed after reforming, is exposed to a gas for reforming the surface of the base layer (1a) said gas being selected from the group consisting of AX 4 , AH n Cl 4-n and AR n X 4-n (in which, A is selected from the group consisting of Si, Ge and Sn, X is selected from the group consisting of I, Br, F and Cl and R represents any one of C m H 2m+1 , and an accompanying character "n" is any one of 1, 2 or 3 and an accompanying character "m" is a natural number), and wherein said base layer (1a) is heated during said reforming step to 100°C or more, and said insulating film (2) is one selected from the group consisting of SiO 2 film, PSG film, BSG film and BPSG film. A method for reforming a base surface according to claim 1, comprising concave regions (3) in said base layer (1a). A method for reforming a base surface according to claim 1, wherein said base layer (1a) is heated, while said surface of the base layer (1a) is exposed to said gas for reforming. A method for reforming a base surface according to claim 1, wherein said AX 4 is any one selected from the group consisting of SiCl 4 , SiI 4 , SiBr 4 and SiF 4 . A method for reforming a base surface according to claim 1, wherein said AH n Cl 4-n is any one selected from the group consisting of SiHCl 3 , SiH 2 Cl 2 and SiH 3 Cl. A method for reforming a base surface according to claim 1, wherein said AR n X 4-n is any one selected from the group consisting of Si(C m H 2m+1 )Cl 3 , Si(C m H 2m+1 ) 2 Cl 2 and Si(C m H 2m+1 ) 3 Cl (in which, an accompanying character "m" is a natural number). A method for manufacturing semiconductor device according to claim 1, wherein the insulating film (2) is formed on the surface of the base layer (1a) by a chemical vapor deposition method, after reforming the surface of said base layer (1a). A method for manufacturing semiconductor device according to claim 7 wherein a gas for thin film deposition for forming said insulating film is a mixed gas containing at least a TEOS gas and an O 3 gas.

Inventors: MAEDA KAZUO, MAEDA, KAZUO
Applicants: SEMICONDUCTOR PROCESS LAB CO, SEMICONDUCTOR PROCESS LABORATORY CO., LTD.
Application year: 1998
Main classification: C23C16
IPC codes: H01L21, H01L23, C23C16