JP2770822B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device , and more particularly to a semiconductor device having a wiring formed of a laminated film including a titanium nitride film and an aluminum film as constituent elements. The present invention relates to a method for manufacturing a semiconductor device suitable for manufacturing a semiconductor device . [0002] According to a method for producing an aluminum thin film by a low pressure chemical vapor deposition method (LPCVD method) using, for example, an organic aluminum compound as a raw material as a compound containing aluminum, high purity and excellent coverage are obtained. The formation of an aluminum thin film is possible in principle. [0003] Therefore, research and development of an LPCVD method and an apparatus for application to formation of a wiring aluminum thin film of a miniaturized semiconductor device have been actively promoted.
An LPCVD method and an apparatus for forming an aluminum thin film using triisobutylaluminum (TIBA), which is a kind of conventional organoaluminum compound, as a raw material are described in, for example, Solid State Technology December, 1982, pp. 62-65 (Solid). State Te
chnology, December (1982) pp 62-65). [0004] The aluminum thin film formed by the conventional LPCVD method and apparatus is said to have excellent coverage and extremely high purity, but the formed aluminum thin film has a rough surface. When viewed microscopically, there is a problem that considerable irregularities occur on the surface of the thin film. Further, there is also a problem that the irregularities on the surface are not always reproduced even when the aluminum film is repeatedly formed under the same conditions using the same apparatus. Although the cause of the deterioration of the smoothness of the aluminum thin film is unknown, the smoothness of the film surface is largely changed by the sample surface activation treatment performed on the sample before the aluminum film is formed. This sample surface activation treatment is performed for the purpose of promoting the nucleation of aluminum on the sample surface.
Typical solid state technology of D method 12
In the method described in the month issue (1982), the activation treatment is performed because the heated sample is related to titanium tetrachloride. (Hereinafter referred to as titanium tetrachloride treatment.) The inventors have found that this titanium tetrachloride treatment is not always the best activation treatment, and is susceptible to slight differences in the material of the sample and its surface state. It has been found that this is a cause of unevenness or insufficient reproducibility. When the LPCVD method of aluminum is applied to the formation of an aluminum thin film for a wiring of a semiconductor device, it is necessary to improve the thermal stability of the connection between the aluminum wiring and the silicon substrate in the miniaturized contact hole. It is becoming essential to insert a barrier layer between silicon. As a barrier layer, for example, a titanium nitride film formed by a reactive sputtering method has been proposed, but the reactive sputtering method lacks coverage, so that a barrier layer having a thickness required as a barrier layer is formed at the bottom of a vertically processed minute through hole. It is extremely difficult to form a titanium nitride film. Also, in the reactive sputtering method, a titanium nitride film is formed thicker on the through hole than on the bottom, so that an aluminum film is formed thereon by an LPCVD method.
Attempting to embed the through-hole with aluminum also has a problem that a cavity is generated inside the through-hole. Furthermore, the LPCVD method of aluminum has a great feature that it does not damage semiconductor devices due to plasma discharge. However, if the device is damaged by using a reactive sputtering method to form a barrier layer, Another problem is that the advantages of the LPCVD method of aluminum cannot be utilized. It is indispensable to establish a method of forming a barrier layer having a coverage comparable to that of an aluminum film by the LPCVD method in order to put the LPCVD method of aluminum to practical use. The conventional LPCVD method and apparatus do not take this point into consideration, so that their application to semiconductor devices is greatly restricted. An object of the present invention is to form a barrier layer having excellent coverage on a sample, and to form a high-quality aluminum film on the barrier layer by LPCVD with good reproducibility without performing a special activation treatment. It is another object of the present invention to provide a method for manufacturing a semiconductor device having a low contact resistance. The object of the present invention is to form an aluminum film by forming a film having titanium on the bottom and titanium nitride on the sample by LPCVD on the sample. Achieved. The most preferable result is obtained when titanium tetrachloride and ammonia are used as the raw materials of the titanium nitride film and triisobutylaluminum is used as the raw material of the aluminum film. However, other raw materials such as titanium tetrachloride and nitrogen are used as the raw materials of the titanium nitride film. Alternatively, trimethylaluminum, triethylaluminum or the like may be used as a raw material of the aluminum film. As a method for forming a titanium nitride film, a plasma enhanced chemical vapor deposition (PCVD) method can be used instead of the LPCVD method. Further, an optical CVD method using a light source that emits vacuum ultraviolet light may be used. In the light CVD method, a chemical reaction is promoted by light energy, so that a titanium nitride film can be formed at a lower temperature and at a higher speed than in a normal LPCVD method. The titanium nitride film formed by chemical vapor deposition (CVD) functions as a barrier layer between aluminum and silicon. Further, it was found that the titanium nitride film formed by the CVD method had excellent coverage, and the thickness of the film formed on the bottom of the through hole was almost equal to the thickness of the film formed on the top of the through hole. Therefore, L is formed on the titanium nitride film.
It has been found that when an aluminum film is formed by the PCVD method, it is possible to completely fill the through hole with aluminum without forming a cavity inside. According to the study by the inventors, since the surface has an action of promoting the nucleation of aluminum, a high-quality aluminum film can be formed by LPCVD without performing a special surface activation treatment on the titanium nitride film. I understood. First, according to the conventional titanium tetrachloride treatment, the areal density of titanium atoms adsorbed on the sample surface, which is considered to have a function of promoting the nucleation of aluminum, remarkably depends on the material of the sample and its surface state, and therefore, the local The density distribution was also large. Therefore, the surface state of the aluminum film formed thereon by the LPCVD method greatly changed locally in accordance with the density distribution. Furthermore, since the density is still insufficient even in the part where titanium is considered to be densely adsorbed, the smoothness of the aluminum film surface on it is reduced by the conventional sputtering method or vacuum evaporation method. There was a problem that it was remarkably inferior to the properties. Further, the present inventors applied LPCVD to certain materials such as palladium deposited by electron beam deposition and titanium nitride formed by reactive sputtering without performing the above-mentioned titanium tetrachloride treatment. It has been found that aluminum can be deposited. In this case, the uniformity of the surface of the aluminum film on the sample was better than when the titanium tetrachloride treatment was performed, but the smoothness itself was still insufficient. On the other hand, it has been found that the CVD method of the present invention can form an aluminum film on the surface of the titanium nitride film which is much more excellent in smoothness than the method described above.
The reason for this is not clear, but is presumed to be due to the following reasons. Titanium atoms are uniformly distributed on the surface of the titanium nitride film formed by the CVD method, and the surface density of the titanium atoms can be set to an optimum value by adjusting the flow rate ratio of the source gas during CVD. LPCVD on the titanium nitride film
When an aluminum film is formed by the method, a high-quality film with a smooth surface can be obtained with good reproducibility. The smoothness of the surface of the aluminum film on the titanium nitride film formed by the CVD method is superior to that on the titanium nitride film formed by the reactive sputtering method. The causes may be as follows. In a conventional reactive sputtering method, argon and nitrogen are used as a sputtering gas. For this reason, argon and nitrogen are adsorbed on the surface of the formed titanium nitride film, but it is presumed that the function of promoting the nucleation of aluminum of titanium atoms on the film surface is weakened by the adsorption of such gas atoms or molecules. Also,
In the reactive sputtering method, it is extremely difficult to control the density of titanium atoms on the surface to an optimum value. The LPCVD method is optimal as the method for forming the titanium nitride film, but the PCVD method can provide an effect similar thereto.
The reason why the LPCVD method is more suitable is that the PCVD method desorbs water, oxygen, etc. from the inner wall of the reaction vessel due to the ion bombardment caused by the plasma discharge, thereby contaminating the surface of the titanium nitride film and reducing the surface density of titanium atoms. This is considered to be due to the occurrence of a local density distribution. Further, in order to eliminate the element damage due to the plasma discharge, it is necessary not to use the PCVD method for forming the titanium nitride film. It is desirable that the apparatus used in carrying out the manufacturing method of the present invention can form a titanium nitride film and an aluminum film continuously without exposing the sample to the atmosphere. It is presumed that the surface density of titanium atoms on the surface of the titanium nitride film is reduced by exposing the sample to the atmosphere, and a local density distribution is generated. Further, it is more preferable that the reaction vessel for forming the titanium nitride film and the reaction vessel for forming the aluminum film are separate from each other, more preferable results can be obtained. This is because if titanium tetrachloride remains in the reaction vessel, it reacts with the organoaluminum compound and the product is mixed into the aluminum film, resulting in deterioration of the aluminum film quality. The present invention will be described below in detail with reference to examples. Reference Example 1 A description will be given with reference to FIGS. This embodiment is an example in which the present invention is applied to the formation of wiring of a silicon integrated circuit. FIG. 1A shows a phosphor silicate glass (PSG) film 102 on a silicon substrate 101 by a CVD method.
This is a sample in which a contact hole 103 having an opening size of 0.7 μm square is vertically formed after forming a 1 μm thick. A high concentration of phosphorus is diffused into the surface of the silicon substrate 101 at the bottom of the contact hole 103. Surface carrier concentration is 2
× 10 ¹⁰ cm ^-3 . Such a sample is set in the manufacturing apparatus of the present invention shown in FIG. The apparatus shown in FIG. 2 has a titanium nitride reaction vessel 201 and an aluminum reaction vessel 202 separately, and is shut off by a shutoff valve 203 therebetween. Each of the reaction vessels 201 and 202 has a dedicated exhaust system 204 and 205, respectively. The evacuation systems 204 and 205 each include a trap for adsorbing unreacted titanium tetrachloride and triisobutylaluminum, and an evacuation pump and the reaction vessel 20.
1, 202. Introduction sample 207
Is set on the sample stage 206 in the titanium nitride reaction vessel 201. The inside of the reaction vessel 201 is 5 × 1 by the exhaust system 204.
After evacuation to 0 ^-7 Torr, the sample 207 is heated by the heater in the heater table 209 via the sample table 206, and its surface temperature is maintained at 350 ° C. After a while, titanium tetrachloride inlet 2
Titanium tetrachloride and ammonia were introduced at a flow rate of 5 ml / min and 20 ml / min, respectively, from 11 and the ammonia inlet 212. Since the container storing titanium tetrachloride is kept at 10 ° C., the vaporized titanium tetrachloride does not condense before reaching the inlet 211. The pressure in the reaction vessel 201 was adjusted to 0.5 Torr by adjusting a conductance valve provided in the exhaust system 204. When this state was maintained for 8 minutes, a 100 nm titanium nitride film was formed on the sample 207, and the sample became as shown in FIG. Titanium nitride film 10
4 is also formed on the bottom and side walls of the contact hole 103 with the same thickness as the flat portion. When the titanium nitride film 104 was analyzed, the composition ratio of titanium and nitrogen was 1: 1 and the content of chlorine and oxygen contained in the film was 1 atomic% or less, respectively. The resistivity of the film was about 100 μΩ · cm. The introduction of titanium tetrachloride and ammonia was stopped, and the titanium nitride
After evacuating the inside of the chamber 1 to 5 × 10 ^-7 Torr again, the exhaust system 20
5. Open the shutoff valve 203 between the aluminum reaction container 202 and the gas exhausted to 5 × 10 ⁻⁷ Torr. Thereafter, the sample 207 is transferred to the aluminum reaction vessel 202 together with the sample table 206 using the transfer rod 208, and set on the heater table 210. Since the transfer rod 208 and the sample table 206 are fixed by screws, the cutoff valve 203 can be closed by separating the transfer rod 208 and moving the transfer rod 208 into the titanium nitride reaction vessel 201 again. The sample 207 is heated by the heat from the heater stage 210 heated in advance.
After the surface concentration was kept at 250 ° C., aluminum was deposited by introducing 70 ml / min of TIBA from the TIBA inlet. The pressure in the aluminum reaction vessel 202 was adjusted to 0.5 Torr by adjusting a conductance valve provided in the exhaust system 205. The deposition rate is 150 nm / min. By depositing for 5 minutes, as shown in FIG.
50 nm of aluminum film 105 is formed of titanium nitride film 104
Formed on The surface of the aluminum film 105 was almost smooth and the unevenness was suppressed to ± 50 nm. In a conventionally known method and apparatus, the thickness was ± 200 nm for the same film thickness.
Aluminum was also buried in the contact hole 103. Note that the embedding property in a minute contact hole strongly depends on the smoothness of the surface of the aluminum film. In the case of a film having insufficient smoothness, a film is formed with good coverage in a large contact hole, whereas a film having a small Cavities may occur in holes. In the method of the present invention, the coverage of the titanium nitride film is excellent, a titanium nitride film having a thickness substantially equal to that of the bottom portion is formed on the contact hole, and the smoothness of the aluminum film is significantly improved. Embedding is possible even for minute contact holes. FIG. 1D shows a pattern obtained by patterning the aluminum film 105 by a normal photolithography process. The resistivity of the aluminum film 105 is 2.8 μΩcm, and the contact portion in the contact hole 103 is not deteriorated by a heat treatment in nitrogen at 550 ° C. for 3 hours due to the barrier effect of the titanium nitride film 104.
The contact resistance of the 0.7 μm square contact hole 103 almost maintained the value before heat treatment of 1.3 × 10 ⁻⁷ Ωcm ² .
In addition, high concentration boron is diffused and the surface carrier concentration becomes 5 ×.
The contact resistance of a 0.7 μm square contact hole of 10 ¹⁰ cm ⁻² was 2.9 × 10 ⁻⁷ before and after the heat treatment.
Ωcm ² . (Embodiment 1) A description will be given with reference to FIGS. This embodiment is an embodiment in which the present invention is applied to wiring formation of a silicon integrated circuit. In carrying out this embodiment, the apparatus shown in FIG. FIG. 4 shows boron-phosphorus silicate glass (BP) on a silicon substrate 401.
SG) shows a sample in which titanium nitride films 403, 404, and 405 are formed on a sample in which a vertical contact hole 406 having an opening size of 0.7 μm is opened after depositing a 1 μm film by a CVD method. A high concentration of phosphorus is diffused on the surface of the silicon substrate 401 at the bottom of the contact hole 406,
The surface carrier concentration is 2 × 10 ¹⁰ cm ⁻³ . FIG. 3 shows the flow rate of ammonia and the flow rate of titanium tetrachloride when forming the titanium nitride film. The flow rate of titanium tetrachloride is always 5m for 12 minutes
l / min is constant, but the ammonia flow rate is increased from 0 ml / min to 20 ml / min at a constant rate in the first 2 minutes, kept at 20 ml / min for 8 minutes, and then from 20 ml / min to 5 ml at a constant rate for 2 minutes. / Min. Twelve minutes after the start of gas introduction, the introduction of both gases was stopped. 403, 40 of such titanium nitride films 403, 404, 405
5 is a titanium-rich film, the composition of which changes along the thickness direction. The thicknesses of the titanium nitride films 403, 404, and 405 were 15 nm, 100 nm, and 20 nm, respectively. The surface density of titanium atoms depending on the surface of the titanium-rich titanium nitride film 405 is larger than the surface of the film in which the composition ratio of titanium and nitrogen is 1: 1 because the ammonia flow is changed as shown in FIG. Smaller than the surface. As a result of various studies on the manner of changing the flow rate of ammonia, the surface of the aluminum film formed on the titanium nitride film 405 became the smoothest in the case of the change shown in FIG. This is because the surface density of titanium atoms on the surface of the titanium-rich titanium nitride film 405 became optimum for forming an aluminum film having a smooth surface when the ammonia flow rate was changed as shown in FIG. When an aluminum film was formed to a thickness of 750 nm on the titanium nitride film 405 in the same manner as in Example 1, the surface irregularities were ± 15 nm, further suppressed than in Example 1. The titanium-rich titanium nitride film 403 has a function of reducing the contact resistance of the contact hole 403. The contact resistance of the 0.7 μm-square contact hole 403 is 1.0 × 10 ⁻⁷ Ωcm ² , and this value also changes by a heat treatment in nitrogen at 550 ° C. for 3 hours due to the barrier effect of the titanium nitride films 403, 404, and 405. Did not. The contact resistance of the 0.7 μm square contact hole in which boron was diffused so that the surface carrier concentration was 5 × 10 ¹⁵ cm ^-5 was 2.4 × before and after the heat treatment.
It was 10 ⁻⁷ Ωcm ² . In the above embodiment, a silicon substrate was used as a sample, but the same effect can be obtained by using another sample such as a gallium arsenide substrate. In particular, the effect of improving the smoothness of the aluminum film surface can be obtained even when using any sample such as a metal and an insulator. As a raw material of the titanium nitride film, other gases such as titanium tetrachloride and nitrogen may be used in addition to titanium tetrachloride and ammonia in the above embodiment.
If a PCVD method is used instead of the PCVD method, a corresponding effect can be obtained. The present invention is also applicable to a case where a titanium nitride film is formed by a photo CVD method using light energy from a light source that emits vacuum ultraviolet light. Furthermore, when using an organic aluminum compound such as trimethyl aluminum and triethyl aluminum other than triisobutyl aluminum used in the examples as a raw material of the aluminum film,
Alternatively, it is needless to say that a case where an inorganic aluminum compound such as aluminum chloride is used is also included in the present invention. According to the present invention, a barrier layer having excellent coverage is formed on a sample, and then a high quality aluminum film is formed on the barrier layer by LPCVD without special activation treatment. Can be formed with good reproducibility.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a reference example of the present invention. FIG. 2 is a diagram illustrating a reference example of the present invention. FIG. 3 is a diagram for explaining an embodiment of the present invention. FIG. 4 is a diagram illustrating an embodiment of the present invention. [Description of Symbols] 103: contact hole, 104: titanium nitride film, 1
05: aluminum film, 201: titanium nitride reaction vessel,
202: aluminum reaction vessel, 203: shut-off valve,
403: a titanium-rich titanium nitride film, 404: a titanium nitride film, 405: a titanium-rich titanium nitride film.

Claims (1)

(57) [Claims] Place a substrate with a step on the surface on a table in the container
Heating the substrate by a heating step provided in the container.
In a heated state, a gas containing titanium and nitrogen is removed by chemical vapor deposition.
It is response to said step portion, a method of manufacturing a semiconductor device characterized by a step of forming a titanium nitride film having a composition of titanium and nitrogen in the film thickness direction is changing. 2. 2. The method according to claim 1, wherein the step is an opening of a film. 3. 3. The method according to claim 2, wherein the film is an insulating film. 4. After the step of forming the titanium nitride film, a second
The method of manufacturing a semiconductor device according to any of claims 1 to 3, characterized in that a step of forming a conductive film. 5. The method according to claim 4, wherein the second conductive film is an aluminum film. 6. The method according to claim 1, wherein the base is heated by heating the base by the heating unit.