Method for producing a semiconductor device

Abstract: A semiconductor device is disclosed, in which a titanium nitride film (12) containing boron or carbon is provided between a semiconductor substrate (10) and an aluminum film (13). Non-reacted substances in the tita­ nium nitride film (12) are rendered inactive by boron or carbon contained in the titanium nitride film (12). Thus, it is possible to improve the barrier properties of the titanium nitride film (12) as mutual diffusion prevention film and also ensure good electric conduc­ tivity.

Description: This invention relates to a method of producing a semiconductor device, which can improve the barrier properties of a diffusion prevention film for preventing the mutual diffusion between silicon and metal and also between metal and metal and ensure satisfactory electric conductivity. In semiconductor devices, many contact sections or junctions between silicon and metal and between different metals are formed. When such a junction is elevated to a high temperature during manufacture of the semiconductor device, mutual diffusion between silicon and metal or between different metals takes place. In order to prevent mutual diffusion, various diffusion prevention films have been studied. Among the diffusion prevention films that have been studied, the TiN film is thought to be most promising. Now, an application of the TiN film as a mutual diffusion prevention film between a silicon diffusion layer and an aluminum film will be described. As shown in Fig. 1A, N-type diffusion layer 2 having a junction depth of 0.20 µm is-formed in P-type silicon substrate 1. Silicon oxide film 7 is formed by the CVD process on the surface of substrate 1. Then, oxide film 7 is selectively removed using a photoresist (not shown) as a mask to expose corresponding portions of diffusion layer 2. Thereafter, titanium nitride film 3 having a thickness of 1,000 angstroms (10Å = 1nm) is formed on diffusion layer 2 and oxide film 7. Then, an aluminum film 4 with a thickness of 1 µm is formed on titanium nitride film 3. Titanium nitride film 3 is formed in a spattering process in Ar/N₂ mixture plasma (N₂ : 60 %) using a titanium target. Aluminum film 4 and titanium nitride film 3 are patterned to form a diode, and the junction leak current therein is measured. The resultant structure is annealed at 500°C for 30 minutes before measurement of the junction leak current, and an abnormal junction leak current is measured. When a defective portion is observed in detail, a small alloy pit was found in diffusion region 2. It is found that the junction is damaged by this alloy pit due to the following reason. Barrier properties of titanium nitride (TiN) film 3 are lost by a certain reason, and mutual diffusion between aluminum (Aℓ) and silicon (Si) locally occurs. The cause of the alloy pit will be described with reference to Fig. 1B. A small amount of non-reacted titanium 5 is present in titanium nitride (TiN) film 3. Titanium nitride film 3 is polycrystalline and non-reacted titanium 5 gathers on a grain boundary of the crystal grains constituting titanium nitride film 3. Aℓ-Si mutual diffusion is accelerated through non-reacted titanium 5 gathering on the grain boundary, and alloy pit 6 is formed. As a result, junction leakage occurs. EP-A-0 127 281 describes a semiconductor device including an electrode having triple-layer electrode structure or a multilayer interconnecting structure comprising a contact (a lower conductive) layer of aluminium or its alloy which comes into contact with a silicon substrate, a barrier layer of refractory metal nitride (e.g. titanium nitride) and refractory metal (e.g. tungsten) and a (upper) conductive layer of aluminium or its alloy. The TiN-W barrier layer prevents over-dissolution of silicon into aluminum in spite of heat-treatment at a relatively elevated temperature. EP-A-0 009 397 describes a semiconductor device comprising a semiconductor substrate having an impurity of one conductivity type, a diffusion region extending from a major surface of said semiconductor substrate to an inside thereof, said diffusion region having an impurity of the opposite conductivity type; an interstitial transition element layer which is doped with an impurity of said opposite conductivity type and is formed on said major surface of said semiconductor substrate in ohmic contact with said diffusion region and a wiring electrode layer connected to said interstitial transition element layer. A method for manufacturing the semiconductor device is also provided. According to WO-86/01640, titanium carbonitride has been discovered to be an effective diffusion barrier material for use in metallization structure for MOS integrated-circuit devices. A layer of the material deposited under aluminum prevents deleterious aluminum-silicon or aluminum-silicide interactions. The structure described includes a silicon semiconductor substrate of a first conductivity type with a surface layer with an impurity region. The titanium carbonitride film is applied over said substrate and contains at least one of boron and carbon. An object of the invention is to provide a method of producing a semiconductor device which can further improve the barrier properties of the diffusion prevention film for preventing the mutual diffusion between silicon and metal and also between different metals and ensure satisfactory electric conductivity. The object of the invention is solved by a method of producing a semiconductor device including: a semiconductor substrate of a first conductivity type which has a surface layer with an impurity region of a second conductivity type; forming a nitrified film of high melting point metal including non-reacted high melting point metal contained therein by chemical sputtering using a high melting point metal target in a gas mixture of nitrogen, argon and methane or diborane at a volume ratio of 20/20/3 SCCM and a pressure of 3 x 10⁻¹ Pa, respectively, forming a metal film on said nitrified high melting point film and producing metal carbide or metal boride in the nitrified film of high melting point metal by the reaction of said non-reacted high melting point metal and carbon or boron, by means of an annealing heat treatment. According to the invention, non-reacted substances in the nitrified high melting point metal film are rendered inactive by boron or carbon contained in the nitrified high melting point metal film. Consequently, it is possible to improve the barrier properties of the nitrified high melting point film and ensure satisfactory electric conductivity. The dependent claims include further features of embodiments of the invention. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1A is a sectional view of a conventional semiconductor device having a titanium nitride film; Fig. 1B is a sectional view for explaining formation of an alloy pit in the conventional semiconductor device shown in Fig. 1A; Fig. 2A is a sectional view of a semiconductor device manufactured in accordance with the method of the present invention; Fig. 2B is a sectional view showing a state after the semiconductor device of Fig. 2A is annealed; Fig. 3A is a sectional view of a semiconductor device having a diode structure using a carbon-containing titanium nitride film; Fig. 3B is a sectional view showing a state wherein the semiconductor device of Fig. 3A is annealed to cause non-reacted titanium to react with carbon to obtain titanium carbide; Fig. 4 is a sectional view of a semiconductor device having a diode structure by using a titanium film and a titanium nitride film; and Fig. 5 is a sectional view of a semiconductor device having a CMOS structure by using a titanium film and a titanium nitride film. A semiconductor device having a nitrified high melting point film manufactured by the method according to a first embodiment will be described below. As shown in Fig. 2A, titanium nitride film 12 having a thickness of 100 nm (1,000 Å) and serving as a nitrified high melting point film is formed on P-type silicon substrate 10. Aluminum film 13 is formed on titanium nitride film 12. Titanium nitride film 12 is formed by chemical sputtering using a titanium target. Sputtering is performed in on N₂/Ar/CH₄ mixture plasma of a gas mixture of N₂ (nitrogen), Ar (argon), and CH₄ (methane) at an N₂/Ar/CH₄ volume ratio of 20/20/3 SCCM and a total pressure of 3 x 10⁻¹ Pa. Non-reacted titanium 14 and carbon 15 are contained in titanium nitride film 12. Aluminum film 13 is formed on titanium nitride film 12. After aluminum film 13 is formed, the resultant structure is heat-treated or annealed at 500°C for 30 minutes. Aluminum film 13 and titanium nitride film 12 are removed and the number of alloy pits is measured with a microscope. No pits are observed. The alloy pit is not formed due to the following reason, as shown in Fig. 2B. Non-reacted titanium 14 in titanium nitride film 12 reacts with carbon 15 to form titanium carbide (TiC) 16. The resultant structure is annealed at 500°C for 30 minutes, and an increase in the leak current is not measured. Since titanium is reacted with carbon at 200°C to 400°C, titanium and carbon are converted into titanium carbide (TiC) during annealing at 500°C for 30 minutes. As a result, improvement of the carrier properties of the nitride film has been completed. When titanium nitride film 12 is formed by chemical sputtering using a plasma of an N₂/Ar gas mixture and a titanium target, i.e., when methane is not used, alloy pits are formed at a density of 200 pits/mm². In order to examine the junction leak current characteristic of the titanium nitride film formed in this embodiment, fabrication of a semiconductor device having a diode structure shown in Fig. 3A will be described. Referring to Fig. 3A, N-type diffusion layer 11 having a junction depth of 0.2 µm is formed in P-type silicon substrate 10. Silicon oxide film 17 is formed on diffusion layer 11 and silicon substrate 10 by CVD (Chemical Vapor Deposition). A photoresist pattern (not shown) is formed on silicon oxide film 17, and silicon oxide film 17 is selectively etched using the photoresist pattern as a mask, thereby exposing diffusion layer 11. 100 nm(1,000-Å) thick titanium nitride film 12 as a nitrified high melting point film is formed on diffusion layer 11 and oxide film 17. Aluminum film 13 is formed on titanium nitride film 12. Titanium nitride film 12 is formed by mixing carbon therein, as previously described. In this case, non-reacted titanium and carbon are present in titanium nitride film 12 shown in Fig. 3A. Therefore, the non-reacted titanium and carbon are reacted with each other during annealing at 500°C for 30 minutes to obtain titanium carbide 16 shown in Fig. 3B. In a diode structure shown in Fig. 3B, even if annealing is performed at 500°C for 30 minutes prior to junction leak current measurement, no junction leakage is detected. According to a second embodiment, a titanium nitride film is formed on a silicon substrate by chemical sputtering in a plasma generated by using a titanium target in an Ar/N₂ gas mixture containing diborane (B₂H₂) in place of methane (CH₄) in the same amount of methane. An aluminum film is formed on the titanium nitride film and non-reacted titanium in the titanium nitride film is bonded to boron, and titanium boride (TiB₂) is formed. In this case, the barrier properties of the titanium nitride film can be improved, and no alloy pits are formed. In the second embodiment, since the alloy pit is not formed, the junction leak current property of the titanium nitride film can be improved. In practice, a diode structure as in the first embodiment is formed in order to evaluate the barrier properties of the titanium nitride film, and the resultant structure is annealed at 500°C for 30 minutes. In this case, no junction leakage is detected, and the barrier properties of the titanium nitride film can be greatly improved. According to another example, a titanium nitride film is formed on a silicon substrate by sputtering in a plasma generated by using an Ar (argon)/N₂ (nitrogen) gas mixture (N₂: 60%) when a titanium target containing 0.3% of boron is used. An aluminum film is formed on the titanium nitride film. The titanium nitride film is annealed to cause the non-reacted titanium in the titanium nitride film to react with boron to obtain titanium boride (TiB₂). In order to evaluate the barrier properties of the titanium nitride film in the same manner as in the first and second embodiments, the resultant structure is annealed at 500°C for 30 minutes. No junction leakage occurs, and the barrier properties of the titanium nitride film can be greatly improved. In the first and second embodiments, the non-reacted titanium in each titanium nitride film is reacted with boron or carbon to produce titanium boride (TiB₂) or titanium carbide (TiC) at a temperature of about 300°C. The substrate may be kept at a temperature of 300 to 400°C during formation of the titanium nitride film, and titanium boride (TiB₂) or titanium carbide (TiC) may be formed simultaneously when the titanium nitride film is deposited. After the titanium nitride film may be deposited, the resultant structure may be annealed and the aluminum film may be deposited thereon. Boron or carbon may be contained in the titanium target in the form of titanium boride (TiB₂) or titanium carbide (TiC). Alternatively, boron or carbon may be contained in the form of a boron or carbon compound excluding titanium boride (TiB₂) or titanium carbide (TiC) to improve the barrier properties of the titanium nitride film. A target may be obtained by a combination of boron or carbon and titanium which does not contain boron or carbon, or a combination of titanium which does not contain titanium or carbon and a compound containing boron or carbon (e.g., titanium boride (TiB₂), titanium carbide (TiC), or BN (boron nitride)). A further example will be described below. A titanium nitride film is formed on a silicon substrate by an N₂ (nitrogen)/Ar (argon) mixture plasma generated by using a titanium target which does not contain boron. Boron ions are implanted in the titanium nitride film. An aluminum film is formed on the titanium nitride film. The resultant structure is annealed at 450°C to cause the non-reacted titanium to react with boron to form titanium boride (TiB₂), thereby inactivating titanium. When a dose of boron ions implanted in the titanium nitride film is set to be 1 x 10¹⁴ atoms/cm², alloy pits are formed at a density of 100 pits/mm². Similarly, when a dose of boron ions is set to be 1 x 10¹⁵ atoms/mm², the alloy pits are formed at a density of 5 pits/mm². In the further example , a diode structure is prepared and annealed at 500°C for 30 minutes. No leak current is detected, and the barrier properties of the titanium nitride film can be greatly improved. On the contrary, when ion implantation of boron is not performed, the alloy pits are formed at a density of 200 pits/mm². As compared with the case wherein boron is contained in the titanium nitride film, the boron-containing titanium nitride film has a better junction leak current characteristic. In the first and second embodiments, when the substrate is heated during formation of the titanium nitride film, resistivity ρ is as low as 180 µΩcm. However, when the titanium nitride film is formed while the substrate is not heated, resistivity ρ is 400 µΩcm. Therefore, the resistivity can be decreased when the substrate is heated during formation of the titanium nitride film, and a better result is obtained. According to the present invention, both boron and carbon can be contained in the titanium film and the resultant film can be so annealed as to improve the electrical characteristics such as the junction leak current characteristic. A structure is shown in Fig. 4 wherein a titanium film is formed between a carbon-containing titanium nitride film and an N⁺-type diffusion layer. This diode structure can be formed in the following process. Arsenic (Ar) ions are implanted in P-type silicon substrate 10 at an acceleration voltage of 40 keV and a dose of 5 x 10¹⁵ atoms/cm² to form N⁺-type high-impurity semiconductor layer 11. Silicon oxide (SiO₂) film 21 having contact hole 20 is formed on N⁺-type layer 2. Contact hole 20 has an area of 1 µm x 1 µm. 500-Å thick titanium (Ti) film 22 is formed on the exposed portion of N⁺-type layer 2 and on SiO₂ film 21. 1,000-Å thick carbon-containing titanium nitride film 12 is formed on titanium film 22 while the substrate is heated at 300°C. Aluminum (Aℓ) film 13 is formed on titanium nitride film 12. The resultant structure is annealed at 500°C for 30 minutes to convert titanium into titanium silicide (TiSi₂). In the diode structure prepared as described above, a contact resistance between the titanium nitride film and the titanium film (in practice, a titanium silicide film is formed) is measured to be 10 to 15 Ω. This measurement result entails the following facts. A contact resistance of a diode structure (Fig. 4) prepared by using a titanium film but not using a titanium nitride film which does not contain carbon is also 10 to 15 Ω. Even if the diode structure is obtained by using the carbon-containing titanium nitride film and the titanium film, the contact resistance characteristic is not degraded but is kept unchanged. In addition, since the junction leak current characteristic is improved by use of the carbon-containing titanium nitride film, use of the titanium film and the carbon-containing titanium nitride film, as shown in Fig. 4, can improve the electrical characteristics of the element. BF₂ ions are implanted in an N-type silicon substrate at an acceleration voltage of 50 keV and a dose of 5 x 10¹⁵ atoms/cm² to form a P⁺-type layer. Following the same procedures as in Fig. 4, a silicon oxide (SiO₂) film, a titanium (Ti) film, and a carbon-containing titanium nitride film, and an aluminum (Aℓ) film are sequentially formed on the substrate. A contact resistance of the carbon-containing titanium nitride film is measured to be 30 to 50 Ω. In this case, as compared with the conventional titanium nitride film which does not contain carbon, the electrical characteristics of the titanium nitride film which contains carbon are not degraded. The substrate may be heated to 400°C to 500°C during deposition of the titanium film to convert titanium into titanium silicide. Thereafter, a carbon-containing titanium nitride film may be deposited. Alternatively, a titanium silicide film may be directly deposited in place of the titanium film. The same contact resistance characteristics as described above can be obtained when a cobalt film is used in place of the titanium film. The same contact resistance characteristic as described above can also be obtained when a titanium silicide film or a cobalt silicide film is used. Fig. 5 shows a structure wherein the semiconductor device manufactured in accordance with the method of the present invention is applied to an LSI having a CMOS structure. 500-Å thick titanium film 33 (this film is converted into a titanium silicide film after deposition) at a substrate temperature of 500°C, 1,000-Å thick titanium nitride film 34 prepared by chemical sputtering using a titanium target while a nitrogen/argon/methane plasma is generated at an N₂/Ar/CH₄ volume ratio of 20/20/3 SCCH and a total pressure of 3 x 10⁻¹ Pa and the substrate is kept at 300°C, 0.8-µm thick Aℓ film 35 (or Aℓ-Si alloy film or an Aℓ-Si-Cu alloy film) are formed on source and drain regions 31 and 32 of an N-channel FET and source and drain regions 31 and 32 of a P-channel FET. When boron ions are implanted in the carbon-containing titanium nitride film, the barrier properties of the film are not degraded. It is therefore apparent that both carbon and boron may be contained in the titanium nitride film. In the first to fourth embodiments, the contact leak current, the resistivity and the contact resistance of the barrier film formed between the silicon diffusion layer and the aluminum film are evaluated. However, the TiN film manufactured in accordance with the method of the present invention is also effective as a diffusion prevention film formed between layers of metals, e.g., between titanium silicide (TiSi₂) and aluminum (Aℓ) or between titanium silicide (TiSi₂) and tungsten (W) in another metal system. In this system, the excellent barrier properties of the TiN film can be maintained at a high temperature of 900°C. The TiN film may also be used as a metal diffusion prevention film for a semiconductor substrate made of a material (e.g., gallium arsenide (GaAs)) excluding silicon.

Claims: A method of producing a semiconductor device including: a semiconductor substrate (10) of a first conductivity type which has a surface layer with an impurity region of a second conductivity type; forming a nitrified film of high melting point metal (12) including non-reacted high melting point metal (14) contained therein by chemical sputtering using a high melting point metal target in a gas mixture of nitrogen, argon and methane or diborane at a volume ratio of 20/20/3 SCCM and a pressure of 3 x 10⁻¹ Pa, respectively, forming a metal film (13) on said nitrified high melting point film (12) and producing metal carbide or metal boride in the nitrified film of high melting point metal by the reaction of said non-reacted high melting point metal (14) and carbon or boron (15) respectively, by means of an annealing heat treatment. A method according to claim 1, wherein said nitrified high melting point film (12) is a titanium nitride film. A method according to claim 1, wherein said nitrified high melting point film (12) is a hafnium nitride film. A method according to claim 1, wherein said nitrified high melting point film (12) is a tungsten nitride film. A method according to claim 1, wherein said semiconductor substrate (10) is a silicon substrate. A method according to claim 1, wherein said semiconductor substrate (10) is a gallium arsenide substrate. A method according to claim 1, wherein said metal film (13) is an aluminum film. A method according to claim 1, wherein a titanium film or a titanium silicide film is formed between said semiconductor substrate (10) and said nitrified high melting point film (12). A method according to claim 1, wherein a cobalt film or a cobalt silicide film is formed between said semiconductor substrate (10) and said nitrified high melting point film (12).

Inventors: OKUMURA KATSUYA C O PATENT DIV, OKUMURA, KATSUYA C/O PATENT DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1987
Main classification: H01L29
IPC codes: H01L29, H01L21, H01L23