JP2006057178A - Sputtering target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sputtering target having excellent oxidation resistance, corrosion resistance, electromigration resistance and stress migration resistance. <P>SOLUTION: Copper having a purity of ≥99.9999 wt.% excluding gas components is dissolved in an atmosphere having an oxygen content of ≤0.1 vol.ppm, and is further subjected to casting. The obtained ingot is subjected to machining and process annealing, and is subsequently subjected to organic cleaning and etching, so as to obtain the sputtering target. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sputtering target made of copper and a semiconductor element having a wiring formed using a sputtering target made of copper.

  Advances in LSI manufacturing technology in recent years have been remarkable, and with the realization of miniaturization of wiring width, the LSI has rapidly evolved from LSI to super LSI, and further to ultra-super LSI, and the miniaturization of wiring width has progressed for higher integration. . Copper (Cu) is particularly promising as a wiring material for next-generation LSIs that require fine processing with a line width of 0.3 μm or less, such as DRAM of 64 megabits or more.

  Conventionally, as an LSI wiring material formed on a silicon substrate, an Al alloy thin film has been widely used. However, an Al alloy wiring has a higher specific resistance than pure metal Al, and further, electromigration and Breakage due to stress migration, precipitation of Si at the contact portion, generation of hillocks due to heat treatment, and the like occur. Copper has been studied as a wiring material to replace such an Al alloy. Since copper has a lower electric resistance than Al, it can take a large current density and has a melting point of 400 ° C. or higher, so that it has an electromigration property. However, since the copper wiring has low oxidation resistance, the oxidation proceeds to the inside of the wiring when the interlayer insulating film is deposited, and the electric resistance tends to increase.

  In order to solve these problems, Patent Document 1 discloses a method for preventing oxidation during high-temperature treatment of copper by attaching an oxygen-containing insulating film so as to cover the copper wiring film at a temperature lower than the oxidation temperature of copper. Has been. Patent Document 2 discloses a technique for improving the oxidation resistance of copper by enlarging the crystal grain size by heat treatment after deposition of a copper film. Furthermore, Patent Document 3 discloses a technique for forming a film using copper alloys to which elements having different electronegativity are added.

Further, as described in Patent Document 4, it is also effective to add Ti and Zn as trace elements to copper. For example, the addition of Ti has corrosion resistance, increased adhesion strength to an element substrate, There is an effect of increased migration.
Japanese Patent Publication No. 5-87173 JP-A-3-1666731 JP-A-5-47760 JP-A-5-31424

  However, in the above-described technique, it is necessary to uniformly disperse the additive metal. For this reason, when creating a sputtering target in which Ti is added to copper having a purity of 99.9999% by weight, the ingot is rapidly cooled. Precipitation of additive elements must be prevented. For this purpose, a continuous casting apparatus capable of rapid cooling is required. Further, since the purity of Ti is as low as 99.99% by weight, there is a problem that unintended impurities are mixed and it is difficult to control the characteristics of the thin film.

  As described above, various technical improvements have been made in using copper wiring, but many problems remain and are not fully satisfactory.

  The present invention has been made in order to solve the above-mentioned problems. A sputtering target made of copper having a purity of 99.9999% by weight or more, and an oxidation resistance, an anti-resistance, wired using a sputtering target using copper. An object of the present invention is to provide a semiconductor element having copper wiring excellent in electromigration property and stress migration resistance.

  The sputtering target according to the first means is a sputtering target made of copper, and has a purity of 99.9999 weight excluding oxygen (O), nitrogen (N), and gas components of carbon (C) and hydrogen (H). % Copper or more.

  A semiconductor element according to the second means has a wiring formed using the sputtering target described in the first means.

  A semiconductor element according to a third means is a semiconductor element having a wiring formed using a sputtering target made of copper, and the wiring is formed by heat treatment at a temperature of less than 450 ° C. in a vacuum or in an inert gas atmosphere. The crystal grains are coarsened.

  The semiconductor element according to the fourth means is characterized by having both the characteristics of the second means and the third means at the same time.

  The fifth means is characterized in that in the semiconductor element described in the third means or the fourth means, the size of crystal grains of the coarsened wiring is 2 μm or more.

  A sixth means is the semiconductor element according to any one of the third to fifth means, wherein the length / width value of the crystal grain length of the coarsened wiring is 6 or more, and the length / thickness value. Is 2.5 or more.

  In the sputtering target manufacturing method according to the seventh means, oxygen having a purity of 99.9999% by weight or more excluding oxygen (O), nitrogen (N), and carbon (C) and hydrogen (H) gas components is vacuumed. It has the melt | dissolution process melt | dissolved in an inside or inert gas atmosphere, and the casting process which casts the melt | dissolved copper in a vacuum or an inert gas atmosphere.

  A method for manufacturing a semiconductor element according to an eighth means is characterized by including a wiring step of forming a wiring using the sputtering target described in the first means.

  A method for manufacturing a semiconductor element according to a ninth means is a method for manufacturing a semiconductor element having a wiring step of forming a wiring by using a sputtering target made of copper, and is 450 or 450 in an inert gas atmosphere. It is characterized by having a heat treatment step for coarsening the crystal grains of the wiring at a temperature lower than ° C.

  The method of manufacturing a semiconductor device according to the tenth means is characterized in that both the characteristics of the eighth means and the ninth means are simultaneously provided.

  The eleventh means is characterized in that, in the semiconductor element manufacturing method according to the ninth means or the tenth means, the coarsening is performed until the size of the crystal grain of the wiring becomes 2 μm or more.

  The twelfth means is the semiconductor element manufacturing method according to any one of the ninth to eleventh means, wherein the length / width value of the crystal grains of the wiring is 6 or more and the length / thickness value. It is characterized in that coarsening is performed until the value becomes 2.5 or more.

As described above, according to the present invention, by using copper having a purity of 99.9999% by weight or more excluding gas components as a raw material, it has characteristics such as low impurities, high thermal conductivity at low temperature, and low resistance. A sputtering target can be created.

In addition, the wiring of a semiconductor element having wiring formed using a sputtering target made of copper is coarsened by heat treatment at a temperature of less than 450 ° C. in vacuum or in an inert gas atmosphere. The oxidation resistance, electromigration resistance and stress migration resistance can be made excellent.

  As a result of newly investigating the oxidation progress mechanism of the copper wiring film by the research of the present inventors, the oxidation proceeds from the grain boundary, and the low recrystallization temperature which is one of the characteristics of high-purity copper and It was found that the wiring having a pseudo single crystal or a crystal with a crystal grain coarsening utilizing the grain coarsening effect has high oxidation resistance.

  A copper wiring formed by sputtering a sputtering target made of copper having a purity of 99.9999% by weight or more excluding gas components (O, N, C, H) is formed at 450 ° in vacuum or in an inert gas. By growing crystal grains in the wiring by heat treatment at a temperature lower than C, characteristics excellent in oxidation resistance, electromigration resistance, and stress migration resistance are exhibited.

  The sputtering target is prepared by the method shown below.

  Copper having a purity of 99.9999% by weight or more excluding gas components (O, N, C, H) is used. The reason for this is that if a material having a purity lower than this is used, a small amount of impurities act and a predetermined effect cannot be obtained. Moreover, it is because the thing contained as a trace impurity in these cannot be removed by the process after melt | dissolution.

  For the above purity, the gas components (O, N, C, H) are excluded in the metal in the case of five nines indicating normal purity, that is, 99.999% by weight or six nines 99.9999% by weight. Gas components contained, for example, oxygen gas if O, O component constituting oxide, carbide, gas, hydrocarbon if C, S sulfide, sulfite, gas, H if S Water, gas, ammonia gas, hydride, and the like can be mentioned, but these gas components are not usually analyzed, and the purity is displayed from the analysis result of the metal component, so the actual purity is unknown. Therefore, in this specification, it represents with the purity except a gas component (O, N, C, H).

  In the melting and casting of copper, the continuous casting method described in JP-A-5-31424 can be used, but a batch method in which the casting is performed after the melting alone may be used, and impurities are mixed during the melting. In order to avoid this, any melting furnace or casting furnace with measures for mixing impurities can be used.

  The melting atmosphere is in an inert gas or vacuum. This is because a part of the trace impurities present in the copper can be volatilized and removed, and when dissolved in the air, it reacts with oxygen in the atmosphere to produce copper oxide to contaminate the copper.

  During casting, it is necessary to carry out in an inert gas atmosphere or vacuum for the same reason as during melting. This atmosphere is continued until the metal is solidified and cooled. The cooling may be either rapid cooling or slow cooling, but rapid cooling is preferable.

  The solidified metal (ingot) obtained by casting is subjected to mechanical processing such as rolling, forging and cutting as necessary to obtain a sputtering target.

  Thin film formation processing is performed using this sputtering target.

  The formed thin film wiring is heat-treated at a temperature of less than 450 ° C. in a vacuum or an inert gas.

  As the heat treatment atmosphere, it is desirable to carry out in a vacuum or in an inert gas in order to avoid the inclusion of oxygen in the atmosphere.

  In this embodiment, high purity argon is used as the inert gas. U grade (6N = 99.9999%, impurity 0.1 ppm or less) manufactured by Taiyo Toyo Oxygen Co., Ltd. was used for this high purity argon. The concentrations of O, N, C, and H in argon are as follows.

O = <0.1 ppm
N = <1 ppm
C = <0.1 ppm
H = <0.1 ppm
Depending on the composition of the wiring material only by this heat treatment, the thin film wiring may be oxidized by the residual oxygen that is slightly present in the atmosphere to form an oxide film layer.

  One of the features of the present invention is that the heat treatment temperature is lower than 450 ° C.

  When the heat treatment temperature is high, peeling of the wiring portion occurs due to a difference in thermal expansion between the wiring material and the base material, or stress migration is caused due to residual stress.

  Although the residual stress can be lowered and the specific resistance can be lowered by the heat treatment, the wiring formed using high-purity copper undergoes recrystallization of copper.

  Thereby, a wiring having a pseudo single crystal or a crystal with coarse crystal grains can be obtained.

  Hereinafter, examples and comparative examples according to the present invention will be described in detail with reference to the drawings.

Example 1
In this example, a sputtering target was prepared from copper having a purity of 99.9999% by weight excluding gas components (O, N, C, H) using a batch type casting furnace, and wiring was performed using this sputtering target. An example is shown when a copper wiring is heat-treated at 100 ° C. for 1 hour in high-purity argon.

  FIG. 1 is a flowchart showing a processing flow of a method for manufacturing a sputtering target according to the present embodiment.

  FIG. 2 is a schematic cross-sectional view of the batch type casting furnace used in this example. The following description will be made with reference to the schematic cross-sectional view of FIG.

  About 10 kg of copper 22 having a purity of 99.9999% by weight excluding gas components was charged into the high-purity carbon crucible 21 shown in FIG. The crucible 21 used was previously calcined at 1500 ° C. for 5 hours in an ultra-high purity argon atmosphere.

  After repeating the evacuation of the melting chamber and high-purity argon gas replacement several times, the heating and melting were started. Then, after the raw material copper 22 was completely dissolved, it was gradually cooled from the bottom of the crucible 21 to be solidified. The obtained ingot had a cylindrical shape with a diameter of 10 cm and a thickness of 14 cm, the ingot had no casting defects, and the ingot was close to a single crystal. This was processed into a thickness of 3 cm by forging as a raw material.

  By this forging, the structure of the ingot was refined and became a fine polycrystal suitable for the sputtering target.

  Next, after removing the contaminated layer on the surface of the ingot with nitric acid, the processing strain was removed by annealing at 135 ° C. for 30 minutes in a high purity argon atmosphere. The crystal grain size of the ingot after annealing was 1 mm or less. Next, it cross-rolled and processed into the board of thickness 7mm. The obtained rolled plate was subjected to surface grinding and external processing to form a disk having a diameter of 6 inches and a thickness of 5 mm. Next, after washing the disk with an organic solvent, the disk was etched with dilute nitric acid to obtain a sputtering target.

  Impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. As a result, the impurity metal component was the same as the analysis value of the raw material, and the analysis result is shown in the table of FIG.

A copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the sputtering target obtained as described above. At this time, the film was deposited on the Si substrate under an argon gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W. Next, heat treatment was performed at 100 ° C. for 1 hour in a high purity argon gas atmosphere. By this treatment, the crystal grains of the copper wiring changed from 0.1 μm to 2.1 μm before and after the heat treatment.

Next, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method. This sample was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an atmospheric temperature of 200 ° C., and the disconnection failure rate was measured. As a result, the disconnection failure rate of the sample was 0.3%, and the result is also shown in the table of FIG.

(Example 2)
In this example, a sputtering target was prepared from copper having a purity of 99.9999% by weight excluding gas components (O, N, C, H) using a batch type casting furnace, and wiring was performed using this sputtering target. An example when heat treatment is not performed on the copper wiring is shown.

  A copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the sputtering target described in Example 1. The film forming conditions are the same as in Example 1. The detailed method is the same as that in the first embodiment, and will not be described.

For the thin film sample, a SiN protective film having a thickness of 0.8 μm was deposited by the CVD method without performing the heat treatment described in Example 1. This sample was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an atmospheric temperature of 200 ° C. As a result, the disconnection failure rate of the sample was 1.0%, which is also shown in the table of FIG.

(Example 3)
In this example, a sputtering target was prepared from copper having a purity of 99.99999% by weight excluding gas components (O, N, C, H) using a batch casting furnace, and wiring was performed using this sputtering target. An example is shown when a copper wiring is heat-treated at 100 ° C. for 1 hour in high-purity argon.

  The same procedure as described in Example 1 was used except that copper having a purity of 99.99999% by weight was used. Since a sputtering target creation method, a copper wiring method, an impurity metal analysis method, and a disconnection failure rate measurement method are the same as those in Example 1, they are omitted.

  The analysis result of the impure metal material and the measurement result of the disconnection failure rate are also shown in the table of FIG. At this time, the disconnection failure rate was 0.15%.

Example 4
In this example, a sputtering target was prepared from copper having a purity of 99.99999% by weight excluding gas components (O, N, C, H) using a continuous casting furnace, and wiring was performed using this sputtering target. An example is shown when a copper wiring is heat-treated at 100 ° C. for 1 hour in high-purity argon.

  FIG. 1 is a flowchart showing a processing flow of a method for manufacturing a sputtering target according to the present embodiment.

  FIG. 4 is a schematic cross-sectional view of the continuous casting furnace used in this example. The following description will be made with reference to the schematic cross-sectional view of FIG.

  Unlike the casting apparatus shown in FIG. 2, the continuous casting furnace shown in FIG. 4 includes a mold 43 (hereinafter referred to as a die) for shaping and solidifying the copper melted in the carbon crucible 41.

  The melting and casting of the copper 42 was performed according to the following procedure. About 8 kg of copper 42 having a purity of 99.9999% by weight excluding gas components was charged in a crucible 41 and a die 43 which had been calcined at 1500 ° C. for 5 hours in an ultrahigh purity argon atmosphere.

  The dissolution of the copper 22 was performed after evacuation of the melting chamber and high-purity argon gas replacement were repeated several times. A copper lump 44 (hereinafter referred to as a starter bar) having the same dimensions as that of the die 43 was previously inserted into the die 43 for the purpose of guiding the molten metal. In addition, oxygen-free copper having a purity of 99.9999% by weight excluding the same gas components as the base material was used for the starter bar. At the time of dissolution, the starter bar 44 was cooled by a water cooling jacket 45 to prevent dissolution. The dissolved copper flows into the die 44 by the molten metal pressure (self-weight) and is welded to the starter bar 44. The copper welded to the starter bar was pulled out by the draw roll 46 while rapidly solidifying the molten metal in the die 44. The casting speed at this time was 45 mm / min.

  The dimensions of the obtained ingot were the same as the dimensions of the die 44, and were 15 mm thick, 150 mm wide, and 400 mm long. Moreover, the crystal grain size of the obtained ingot was about 1 mm, which was almost the same as the processed structure after forging shown in Examples 1 to 3.

  Next, after etching the surface with nitric acid, it was processed into a rolled plate having a thickness of about 7 mm by cross rolling. The obtained rolled plate was subjected to surface grinding and external processing to form a disk having a diameter of 6 inches and a thickness of 5 mm. Next, after washing the disk with an organic solvent, the disk was etched with dilute nitric acid to obtain a sputtering target.

  Impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. As a result, the analytical value of the impurity metal component was the same as that described in Example 1. The analysis results are also shown in the table of FIG.

A copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the sputtering target obtained as described above. At this time, the film was deposited on the Si substrate with an argon gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W. Next, heat treatment was performed at 100 ° C. for 1 hour in a high purity argon gas atmosphere. By this treatment, the crystal grains of the copper wiring changed from 0.1 μm to 2.2 μm before and after the heat treatment.

Next, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method. This sample was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an atmospheric temperature of 200 ° C., and the disconnection failure rate was measured. As a result, the disconnection failure rate of the sample was 0.3%, and the result is also shown in the table of FIG.

(Comparative Example 1)
In this comparative example, a sputtering target was prepared from copper having a purity of 99.99 wt% excluding gas components (O, N, C, H) using a batch casting furnace, and wiring was performed using this sputtering target. An example is shown when a copper wiring is heat-treated at 100 ° C. for 1 hour in high-purity argon.

  In addition, since the method of producing an ingot using the batch type casting furnace shown in FIG. 2 is the same as that of Example 1 except for the purity of the raw material copper, a description thereof will be omitted.

  Below, the process after obtaining an ingot is demonstrated.

  The obtained ingot was processed into a thickness of 3 cm by forging. Next, after removing the contaminated layer on the surface of the ingot with nitric acid, the processing strain was removed by annealing at 350 ° C. for 30 minutes in a high purity argon atmosphere. The crystal grain size of the ingot after annealing was 1 mm or less. (Then, cross rolling was performed to form a plate having a thickness of 7 mm.) The obtained rolled plate was subjected to surface grinding and outer shape processing to obtain a disk having a diameter of 6 inches and a thickness of 5 mm. Next, after washing the disk with an organic solvent, the disk was etched with dilute nitric acid to obtain a sputtering target.

  Impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. As a result, the impurity metal component was the same as the analytical value of the raw material. The analysis results are also shown in the table of FIG.

A copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the sputtering target obtained as described above. The film formation conditions at this time were the same as those in Example 1, and the film was deposited on the Si substrate with an argon gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W. Next, heat treatment was performed at 100 ° C. for 1 hour in a high purity argon gas atmosphere. The change in the crystal grain size of the copper wiring was not observed before and after this heat treatment, and remained at 0.1 μm to 0.2 μm.

Next, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method. This sample was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an atmospheric temperature of 200 ° C., and the disconnection failure rate was measured. As a result, the disconnection failure rate of the sample was 3.0%, and the result is also shown in the table of FIG.

(Comparative Example 2)
This comparative example shows an example when the copper wiring wired using the sputtering target prepared in Comparative Example 1 is heat-treated at 400 ° C. for 1 hour in a high purity argon atmosphere.

  A copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the sputtering target described in Comparative Example 1. The film forming conditions are the same as in Example 1.

  Next, heat treatment was performed at 400 ° C. for 1 hour in a high purity argon gas atmosphere. The reason why the heat treatment temperature is set to 400 ° C. is to confirm the heat treatment effect at a recrystallization temperature of 350 ° C. or more of copper having a purity of 99.99% by weight. By this heat treatment, the crystal grains of the copper wiring changed from 0.06 μm to 0.8 μm.

Next, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method. This sample was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an atmospheric temperature of 200 ° C., and the disconnection failure rate was measured. As a result, the disconnection failure rate of the sample was 2.0%, and the result is also shown in the table of FIG.

(Comparative Example 3)
In this comparative example, a sputtering target was prepared from copper having a purity of 99.99% by weight excluding gas components (O, N, C, H) using a continuous casting furnace, and wiring was performed using this sputtering target. An example is shown when a copper wiring is heat-treated at 400 ° C. for one hour in a vacuum.

  The method for producing the ingot using the continuous casting furnace shown in FIG. 4 is the same as that in Example 4 except for the purity of the raw material copper and the starter bar copper. The starter bar used was 99.99% by weight of oxygen-free copper, the same as the base material.

  Below, the process after obtaining an ingot is demonstrated.

  The surface of the resulting ingot was etched with nitric acid to remove the attached carbon, and then processed into a rolled plate having a thickness of about 7 mm by cross rolling. The obtained rolled plate was subjected to surface grinding and external processing to form a disk having a diameter of 6 inches and a thickness of 5 mm. Next, after washing the disk with an organic solvent, the disk was etched with dilute nitric acid to obtain a sputtering target.

  Impurity analysis of the sputtering target was performed by glow discharge mass spectrometry. The measurement results are also shown in the table of FIG.

A copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the sputtering target obtained as described above. At this time, the film was deposited on the Si substrate with an argon gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W. Next, heat treatment was performed in a vacuum at 400 ° C. for 1 hour. By this treatment, the crystal grains of the copper wiring changed from 0.1 μm to 1.0 μm before and after the heat treatment.

Next, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method. This sample was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an atmospheric temperature of 200 ° C., and the disconnection failure rate was measured. As a result, the disconnection failure rate of the sample was 2.0%, and the result is also shown in the table of FIG.

(Other examples)
The present invention is not limited to the above-described embodiments, and various modifications are allowed.

  In the above examples, two types of copper having a purity excluding gas components of 99.9999% by weight and 99.99999% by weight were used, but the purity excluding gas components was 99.9999% by weight or more. If so, copper of other purity may be used.

  Moreover, in the said Example, although what used the high purity argon gas as an inert gas was shown, it can implement similarly even if it uses other inert gas.

  Furthermore, in the above embodiment, the wiring crystal grains are coarsened by heat treatment at temperatures of 100 ° C. and 400 ° C. However, the present invention can be similarly applied at other temperatures as long as the temperature is 450 ° C. or less. .

It is a flowchart which shows the flow of a process of the manufacturing method of the sputtering target which concerns on embodiment. It is a schematic sectional drawing of the batch type casting furnace which concerns on embodiment. It is the figure which showed the analysis value of the impurity metal component of the sputtering target which concerns on embodiment, and the disconnection defect rate of copper wiring with a table | surface. It is a schematic sectional drawing of the continuous casting furnace apparatus which concerns on embodiment.

Claims (2)

  A sputtering target comprising a polycrystalline copper having a purity of 99.9999 wt% or more excluding gas components (O, N, C, H).   2. The sputtering target according to claim 1, wherein a crystal grain size of the polycrystalline copper is 1 mm or less.

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