JP2006028642A - Internal wiring of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-purity single crystal copper which, when formed into a film and applied as a wiring onto an Si substrate, can give a semiconductor device having fine wirings highly resistant to corrosion in virtue of the merits, i.e., EM resistance and SM resistance, of copper, to provide a sputtering target made from the obtained single crystal copper, and to provide a semiconductor element having a wiring made from a film of the target. <P>SOLUTION: High-purity copper having a purity of at lowest 99.9999 wt% and having a total content of silver and sulfur of at highest 0.1 ppm is used as a starting material. This is placed in a raw material crucible 5 set in an electric furnace 1 and is melted. The molten copper is dropped into a lower single crystal mold 6 through a molten copper drop port 4 on the bottom of the crucible 5. In the meantime, the temperature is controlled by means of middle and lower heaters 10, 11 and 12, and the quartz cylinder 3 is evacuated by means of a vacuum system 2. The furnace 1 has on its bottom a heat-insulating trap 8 surrounded with a water-cooling flange 7 through which cooling water 9 passes. The high-purity single crystal copper desirable as a target material for forming a wiring in a semiconductor element accumulates in the single crystal mold 6 of this apparatus. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor device wiring film forming target with improved reliability and a copper wiring used for an internal wiring of a VLSI. Conventionally, as a VLSI wiring material, a metal alloy having low electrical resistance and high adhesion to Si has been generally used. However, along with the miniaturization of wiring due to high integration of LSIs, the reliability of elements due to disconnection due to electromigration (EM), stress migration (SM), etc. has become a problem.

  In order to solve this problem, development of a wiring material to replace the Al alloy has been studied, and a copper material has been used as one of them. Since copper has a low electrical resistance of 2/3 that of Al, the current density can be increased compared to Αl, and the melting point is higher than 400 ℃ compared to Αl, so when used as internal wiring for VLSI, It is regarded as a promising wiring material for electro migration (EM) and stress migration (SM).

  As a result, copper wiring has been formed using a sputtering target made of oxygen-free copper or electrolytic copper. However, since these copper materials have a purity of about 99.99%, they can be obtained. The purity of the resulting thin film was also inferior. In tests conducted using such low-purity wiring materials, EM resistance and SM resistance, which are the merits of copper, are lost, and low corrosion resistance becomes a problem. The following methods have been proposed.

  For example, as described in JP-A-5-31424 (Patent Document 1), a high-purity copper having a purity of 6N (99.9999%) or more is used as a raw material, and a small amount of Ti (titanium) and Zn (zinc) is contained. A method of adding as an element has been devised. However, this method complicates the manufacturing process of the raw material ingot, resulting in an increase in the target product cost. Further, as described in Japanese Patent Laid-Open No. 3-166931 (Patent Document 2), the crystal grain boundary of the copper wiring is coarsened by heat treatment to reduce the crystal grain boundary that becomes an oxidation progress path, and the oxidation resistance A method for improving the performance has been devised, but this method has a problem that the process cost of the LSI increases because the heat treatment is performed after the film formation.

As the wiring width is reduced, wiring defects due to abnormal discharge during film formation and the generation of holes called pinholes have become serious problems. As a result of diligent research on this cause, it has been found that the process of manufacturing a conventional target had a cause of reducing the quality of the target. Below, the manufacturing process of the conventional copper target is demonstrated.
(1) A copper ingot as a raw material is machined to a predetermined size by forging and rolling. At this time, the cast structure is destroyed by subjecting the ingot to strong processing to obtain a rolled sheet having a fine texture of 1 mm or less having no orientation.
(2) The rolled plate is subjected to heat treatment as necessary, and after being subjected to surface grinding, outer shape processing, and washing, becomes a target. In the target processed in this way, the structure is a collection of fine crystals of 1 mm or less by processing, so that the crystal grain boundary has oxide, sulfide, or Impurities are present in aggregate. When film formation is performed using such a poor target with low purity, oxides and sulfides mixed in the film cause corrosion. In addition, the electric field concentrates on the crystal grain boundary, causing abnormal discharge, and granular copper (hereinafter referred to as particles) is released from the grain boundary part and adheres to the film formation surface. Such deposits become pinholes in the thin film wiring and cause a short circuit between the wirings. For these reasons, in the prior art, it was not possible to make full use of excellent features such as EM resistance and SM resistance, which are merits of copper.
JP-A-5-31424 JP-A-3-1666731

  As described above, the copper wiring material used for the VLSI wiring is required to have extremely high purity. In particular, when an alkali metal such as sodium or potassium is present in the wiring as an impurity, the breakdown voltage of the oxide film is deteriorated, and the reliability of the element is significantly lowered. From such a viewpoint, a sputtering target using high-purity copper produced by electrolytic purification or zone purification as a raw material has been manufactured and studied as a film forming material. However, not only the contamination in the processing process cannot be completely eliminated, but also a problem that oxides, sulfides, and impurities are concentrated and accumulated at the grain boundaries as the processing structure.

  Such impurities cause corrosion due to reaction with moisture or the like entering from the outside of the LSI package. The trace amount of oxygen released during film formation oxidizes the film to increase the resistivity, and causes the occurrence of corrosion due to oxidation. In addition, due to abnormal discharge that occurs from the grain boundary as a starting point, particles are generated, causing a short circuit between the wirings. The present invention has been made in view of the above circumstances. When a wiring is formed by sputtering using high-purity copper as a target, the copper is excellent in EM resistance, SM resistance, oxidation resistance, and corrosion resistance. A thin film wiring is provided.

  The inventors of the present invention have intensively studied to solve such problems. As a result, a high purity copper obtained by dissolving and solidifying in an atmosphere having an oxygen concentration of 0.1 ppm or less using high purity copper having a purity of 99.9999 wt% or more as a base metal. It has been found that these problems can be solved by using a pure copper single crystal, and the present invention has been achieved. That is, the first of the present invention is a sputtering target made of single crystal copper having a purity of 99.9999 wt% or more; the second is oxygen of 0.05 ppm or less, hydrogen of 0.2 ppm or less, and nitrogen of 0. The first sputtering target is characterized by having 5 ppm or less, carbon 0.01 ppm or less, and a purity of 99.9999 wt% or more; a third is a single crystal copper having a purity of 99.9999 wt% or more (111 And 4) a method for producing a sputtering target characterized in that the target material is obtained by polishing in a direction after cutting in the direction; and the fourth is a method using a sputtering target made of single crystal copper having a purity of 99.9999 wt% or more. It is a semiconductor internal wiring characterized by having a film wiring.

  The present invention is a semiconductor element having a sputtering target obtained by processing a novel high-purity copper single crystal and wiring formed using the target, and has an initial disconnection rate and a disconnection failure rate compared to conventional products. A low VLSI copper wiring can be obtained.

The high-purity copper single crystal used as a sputtering target for wiring of a semiconductor element in the present invention uses high-purity copper having a purity of 99.9999 wt% or more with a total content of silver and sulfur being 0.5 ppm or less as a starting material. After being put in the raw material crucible in the vacuum furnace, heated and melted (first step) at a vacuum degree of 1 × 10 ⁻³ Torr or lower and a furnace temperature of 1085 ° C. or higher through the bottom of the raw material crucible and the melting dropping hole. After flowing into the single crystal template to be connected, the single crystal template is sequentially cooled to obtain a high-purity copper single crystal having an inner diameter of 4 inches in which the O ₂ gas component and the N ₂ gas component are 1 ppm or less in total. .

This single crystal is cut in the (111) direction and then mirror polished to obtain a target. When the dissolved gas component of this single crystal is analyzed, oxygen (O) is <0.03 ppm, sulfur (S ) Was <0.01 ppm, hydrogen (H) was <0.2 ppm, and nitrogen was 0.5 ppm or less. Next, using a target having the above composition, an RF sputtering method is used to perform a discharge test at an Ar gas pressure of 1 × 10 ⁻² Torr or less, preferably 3 × 10 ⁻³ Torr, and a discharge power of 200 to 800 W. After coating a TiN film as a barrier film, a copper wiring having a thickness of 0.5 to 1.0 μm was formed, and then a SiN film was deposited as a protective film to obtain a semiconductor element.

  As described above, the single crystal sputtering target for forming a copper thin film of the present invention forms a copper thin film used as a copper wiring by a sputtering method, but has higher corrosion resistance, EM resistance, and SM resistance than the conventional method. It is excellent and has become a promising material for miniaturization of wiring of future semiconductor elements and the like. Hereinafter, although an Example demonstrates in detail, the scope of the present invention is not limited to these.

[Example 1]
A high-purity copper single crystal was obtained using the manufacturing apparatus shown in FIG. First, 10 kg of high-purity copper having a purity of 99.9999 wt% or more having a total content of silver and sulfur of 0.1 ppm or less as a starting material is placed in the raw material crucible 5, and the degree of vacuum in the furnace is 4 × 10 ⁻⁴ Torr. The raw material in the crucible was melted at a constant temperature of 1150 ° C. The dissolved copper is dropped into the single crystal mold 6 below from the melting dropping hole 4 provided at the bottom of the crucible, but the lower heater 12 is heated to 1000 ° C. at a rate of 0.5 ° C./min, and from 1000 ° C. to 15 ° C. The temperature was lowered at a rate of ° C./min to obtain 10 kg of a single crystal having a 4 inch diameter. Next, the obtained single crystal was cut in the (111) direction with an X-ray cut surface inspection apparatus and then mirror-polished to prepare a target having a diameter of 6 inches and a thickness of 5 mm. When the impurity analysis of this target was performed by glow discharge mass spectrometry, the impurity metal component was the same as the analysis value of the raw material, but the analysis value of the gas impurity was as shown in the table.

この場合ガス成分中炭素（Ｃ）および酸素（Ｏ）の分析は住友重機製サイクロトロンＣＹＰＲＩＳ３７０を用いて荷電粒子放射化分析で行い、窒素（Ｎ）はＬＥＣＯ社製ＲＨ−ＩＥで、また水素（Ｈ）は、ＬＥＣＯ社製ＴＣ−４８６を用いて燃焼熱伝導度法で求めた。このようにして得られた、６Ｎ−銅単結晶ターゲットを希硝酸を用いて、エッチングをおこなったが、結晶粒界は観察されず、加工を経ても単結晶が維持されたままであることが確認された。このターゲットについて、２結晶Ｘ線回折装置によりＸ線ロッキングカーブを測定した。その結果、ロッキングカーブの半値幅は、４０秒であった。

In this case, analysis of carbon (C) and oxygen (O) in the gas component is performed by charged particle activation analysis using a cyclotron CYPRIS370 manufactured by Sumitomo Heavy Industries, and nitrogen (N) is RH-IE manufactured by LECO, and hydrogen (H ) Was determined by the combustion thermal conductivity method using TC-486 manufactured by LECO. The 6N-copper single crystal target thus obtained was etched using dilute nitric acid, but no crystal grain boundary was observed, and it was confirmed that the single crystal was maintained even after processing. It was done. For this target, an X-ray rocking curve was measured with a two-crystal X-ray diffractometer. As a result, the full width at half maximum of the rocking curve was 40 seconds.

Next, using this target, a discharge test was performed by an RF sputtering method at an Ar gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 250 W and 500 W, respectively. In this case, the discharge state during film formation was observed with a multi-channel photo detector, and the occurrence of outgas and abnormal discharge was recorded. The results are shown in Table 2.

また、パーティクルの測定は、Ｓｉ基板上にバリア膜としてＴｉＮ膜を被覆させ、０．８μｍ厚の銅薄膜を堆積させた後、銅薄膜の表面を電球にて照らし、薄膜表面のパーティクルの付着の有無を顕微鏡にて目視観察する事により評価した。その結果を表３に示した。

In addition, the measurement of particles is performed by coating a TiN film as a barrier film on a Si substrate, depositing a 0.8 μm thick copper thin film, illuminating the surface of the copper thin film with a light bulb, and The presence or absence was evaluated by visual observation with a microscope. The results are shown in Table 3.

また、放電中のプラズマ分光測定の結果、ターゲットよりの放出ガスは確認されなかった。

Further, as a result of plasma spectroscopic measurement during discharge, no gas released from the target was confirmed.

Next, a copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using this (111) -oriented 6N-copper single crystal target. The film formation conditions at this time were an Ar gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 250 W, which were deposited on the Si substrate. When the crystallinity of the obtained thin film was evaluated by a two-crystal X-ray diffractometer, the film was oriented to (111) and the half-value width was 100 seconds, which was almost a single crystal.

Next, as a protective film, a SiN film having a thickness of 0.8 μm was deposited by a CVD method to obtain a desired semiconductor element. In this case, when the initial disconnection rate due to pinholes or the like generated during the film formation was examined prior to the acceleration test, it was 0.09%. Next, an accelerated test for 2000 hours was performed at a current density of 1 × 10 ⁶ A / cm ² and an ambient temperature of 200 ° C. for the sample excluding the initial disconnection, and the disconnection failure rate was measured. As a result, the disconnection failure rate was as low as 1.0%.

[Example 2]
A 7N high purity copper single crystal having a 4 inch diameter was obtained under the same conditions as in Example 1 except that 7N high purity copper was used as a starting material, and was cut in the (111) direction using an X-ray cut surface inspection device. Then, mirror polishing was performed to prepare a target having a diameter of 6 inches and a thickness of 5 mm. When impurity analysis of the target was performed by glow discharge mass spectrometry, the impurity metal component was the same as the analysis value of the raw material, but the analysis value of the gas impurity was as shown in Table 4.

この様にして得られた７Ｎ−単結晶ターゲットを希硝酸を用いてエッチングをおこなったが、結晶粒界は観察されず加工を経ても単結晶が維持されたままであることが確認された。このターゲットについて、２結晶Ｘ線回折装置によりＸ線ロッキングカーブを測定したところ、ロッキングカーブの半値幅は４０秒であった。

The 7N-single crystal target thus obtained was etched using dilute nitric acid, but no crystal grain boundary was observed, and it was confirmed that the single crystal was maintained even after processing. When the X-ray rocking curve of this target was measured with a two-crystal X-ray diffractometer, the half-width of the rocking curve was 40 seconds.

Next, using this target, a discharge test was conducted by RF sputtering with Ar gas pressure of 3 × 10 ⁻³ Torr, discharge power of 250 W, and 500 W, and the number of abnormal discharges and the state of generation of particles were examined. As a result, the same results as in Table 2 and Table 3 described in Example 1 were obtained. As a result of plasma spectroscopy, no gas that seems to be emitted from the target was detected.

Next, a copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using the (111) -oriented 7N-single-crystal copper target. The film formation conditions at this time were an Ar gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W, which were deposited on the Si substrate. When the crystallinity of the obtained thin film was evaluated by a two-crystal X-ray diffractometer, it was oriented to (111) and the half-value width was 85 seconds, which was a thin film almost similar to a single crystal.

Then, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method to obtain a desired semiconductor element. In this case, when the initial disconnection rate due to pinholes and the like generated during the film formation was examined prior to the acceleration test, it was 0.09%. Next, the sample with the initial disconnection excluded 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 to be 0.5%. It was low.

[Comparative example]
The 6N high-purity copper single crystal obtained in Example 1 was used as a raw material and processed to a thickness of 3 cm by forging according to the flow sheet shown in FIG. 2 to make the structure of the single crystal ingot a fine polycrystal. Next, after etching with nitric acid, annealing was performed at about 135 ° C. for 30 minutes in a high purity argon atmosphere for the purpose of removing processing strain. The crystal grain size after annealing was 1 mm or less. Next, the plate thickness was set to 7 mm by cross rolling. The rolled plate was formed into a disk having a diameter of 6 inches and a thickness of 5 mm by surface grinding and outer shape processing, and this was subjected to organic cleaning, followed by etching with dilute nitric acid to obtain a target.

  When impurity analysis of the target was performed by glow discharge mass spectrometry, the impurity metal component was the same as the analysis value of the raw material, but the gas impurities were compared to Example 1 and Example 2 as shown in Table 1. It was quite expensive.

When an X-ray diffraction pattern was measured for this target, a plurality of diffraction lines were obtained, and no orientation in a specific direction was confirmed. Next, using this target, a discharge test was performed by an RF sputtering method with an Ar gas pressure of 3 × 10 ⁻³ Torr, a discharge power of 250 W, and 500 W. The number of abnormal discharges and the occurrence state of particles were performed in accordance with Example 1 and Example 2, and the results are shown in Tables 5 and 6. Compared to Example 1, the number of abnormal discharges and the number of particles generated are different. It is clear that there are many.

尚、プラズマ分光分析の結果、多結晶ターゲットをスパッターした場合、成膜中に、アルゴンガスと共に、Ｏ、ＣＯ、ＣＯ_X等のガス成分の存在が確認された。また、５００時間の放電試験後に、ターゲットの表面を観察したところ、結晶粒界の割れ（空隙）の部分に、電界集中が発生し異常放電したと思われる変色が観測された。

As a result of plasma spectroscopic analysis, when a polycrystalline target was sputtered, the presence of gas components such as O, CO, and CO _x along with argon gas was confirmed during film formation. Further, when the surface of the target was observed after the discharge test for 500 hours, discoloration that was thought to be caused by abnormal electric discharge due to electric field concentration was observed at the crack (void) portion of the crystal grain boundary.

Next, a copper wiring having a width of 0.3 μm and a thickness of 0.8 μm was formed by RF sputtering using this 6N-high purity copper polycrystalline target. The film formation conditions at this time were an Ar gas pressure of 3 × 10 ⁻³ Torr and a discharge power of 500 W, and a TiN film was deposited as a barrier film on the Si substrate, and then deposited. The particle size was as fine as 0.06 μm to 0.1 μm. The X-ray diffraction pattern also showed a plurality of diffraction lines peculiar to polycrystals, and no orientation was observed.

Next, a SiN film having a thickness of 0.8 μm was deposited as a protective film by a CVD method. Prior to the acceleration test, the initial disconnection rate due to pinholes and the like generated during film formation was examined and found to be 0.8%. Next, a sample with the initial disconnection excluded was subjected to an accelerated test for 2000 hours at a current density of 1 × 10 ⁶ A / cm ² and an ambient temperature of 200 ° C., and the disconnection failure rate was measured. % And even in comparison with Example 1.

It is a schematic diagram which shows schematic structure of the manufacturing apparatus of this invention target material. It is a flow sheet which shows the manufacturing process of a comparative example and the conventional target.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric furnace 2 Vacuum exhaust device 3 Quartz outer cylinder 4 Melting dripping hole 5 Raw material crucible 6 Single crystal mold 7 Water cooling flange 8 Heat insulation trap 9 Cooling water 10 Upper heater 11 Middle heater 12 Lower heater

Claims (3)

  A semiconductor internal wiring comprising a wiring formed by depositing a film on a Si substrate in an Ar gas atmosphere by an RF sputtering method using a sputtering target made of single crystal copper having a purity of 99.9999 wt% or more.   A semiconductor internal wiring having a wiring formed by being oriented in (111) using a sputtering target made of single crystal copper having a purity of 99.9999 wt% or more.   The semiconductor internal wiring according to claim 1 or 2, wherein the sputtering target is (111) oriented single crystal copper.

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