JP5439349B2 - Method for producing Cu film - Google Patents

Description

  The present invention relates to a method for producing a Cu film.

  In recent years, the semiconductor industry represented by LSI has been progressing rapidly. In 64M-bit DRAMs, logic elements, and semiconductor elements thereafter, the precision required for microfabrication technology is increasing more and more as higher integration, higher reliability, and higher functionality progress. With the increase in density and speed of such integrated circuits, the width of metal wiring formed mainly of Al or Cu is becoming ¼ μm or less. In order to cope with such wiring, improvement of wiring technology is underway.

  That is, application of a dual damascene (DD) wiring technique, which is different from the conventional wiring technique, is being studied. In the DD technique, a metal mainly composed of Al or Cu as a wiring material is formed on a wiring groove formed in advance in a base film using a sputtering method, a CVD method, a plating method, or the like, and CMP (Chemical Mechanical Polishing) is performed. This is a technique for removing excess wiring metal by the method.

  As a wiring material as described above, Cu whose resistivity is lower than that of Al is becoming mainstream, and Cu wiring is generally used in semiconductor devices such as logic. An advantage of Cu wiring is that it has superior electromigration resistance compared to Al wiring. When Cu wiring is applied, it is essential to provide a barrier metal layer for the purpose of preventing diffusion of Cu into Si.

  TiN has generally been used as a barrier metal for semiconductor elements, but recently TaN has been proposed as a barrier material for Cu wiring, and TaN is effective for preventing diffusion of Cu into Si. It is becoming clear. Therefore, the TaN film is being applied to the barrier layer for Cu wiring. Since Cu wiring is mainly formed by a plating method, a specific process for forming Cu wiring is as follows. That is, a TaN film is formed as a barrier layer in a wiring groove or hole, and a Cu plating seed layer (Cu film) is formed thereon by sputtering or the like, and then Cu constituting the wiring is formed by plating.

  The state of the Cu seed layer described above, in other words, the Cu sputtering state during formation of the seed layer has a great influence on Cu plating. That is, if the Cu seed layer is not formed as a complete continuous film in the groove or hole, it is etched by the plating solution, and Cu cannot be grown well during plating. In addition, in the Cu seed layer that is not continuous, since no current flows during plating, the chemical reaction is not promoted and Cu may not be filled.

  Semiconductor device design rules are becoming increasingly finer, and grooves and holes with aspect ratios exceeding 4 are becoming common. In order to cope with such a device, the conventional collimation sputtering method, long-distance sputtering method, low-pressure sputtering method and the like have limitations, and development of a new sputtering technique is indispensable. Thus, as a new sputtering method for forming the Cu seed layer, a Cu self-ion sputtering method has attracted attention.

The self ion sputtering method is a method in which Cu itself is ionized and the discharge is self-maintained by the generated Cu ⁺ ions, that is, self-sustain discharge is performed. In the self-ion sputtering method for self-sustaining discharge of Cu, no rare gas such as Ar or Kr used in the normal sputtering method is required, so that Cu atoms, Cu ⁺ ions, neutral particles, etc. are not bent in the flight direction. Continue to go straight to the board. That is, the directivity is superior to the conventional sputtering method, and there is no etching action by Ar ions or Kr ions, so that a Cu film can be satisfactorily formed in a groove or hole having a large aspect ratio.

By the way, in the sputtering of Cu to which the self ion sputtering method is applied, in order to improve the straightness of Cu ⁺ ions, it is general to apply a bias voltage to the substrate side. That is, first, the inside of the chamber is set to a high vacuum, a negative voltage is applied to the target side, and an initial plasma is generated while flowing a rare gas such as Ar or Kr. At the same time, a negative voltage is applied to the substrate side. Next, the rare gas is stopped and the discharge is maintained by Cu ⁺ ions themselves.

  However, when self-sustained discharge is generated using a conventional Cu target, when the bias voltage to the substrate side is increased, the balance between the target and the substrate is lost, and plasma is not generated if the film is formed for a long time. As a result, there is a problem that the discharge is stopped as a result. If such a problem occurs in a mass production line for semiconductor devices, a large amount of defective products will be generated, and the manufacturing yield of semiconductor devices will be greatly reduced.

  The present invention has been made to cope with such a problem, and in applying the Cu self-ion sputtering method, it is possible to stabilize the plasma state and maintain the self-sustained discharge for a long time. The purpose is to provide a target.

The method for producing a Cu film of the present invention is to produce a Cu film by a self-ion sputtering method of Cu using a sputtering target made of high-purity Cu. The high-purity Cu contains at least one element selected from Ag and Au, and the total content of the Ag and Au is in the range of 0.5 to 50 ppm, and is selected from the Ag and Au. The variation in the content of at least one element is within ± 30% of the target as a whole.

  The high-purity Cu preferably has a total content of Fe, Ni, Cr, Ti, Al, Na and K as impurity elements of 10 ppm or less. The target is preferably joined to a backing plate.

  An example of the Cu film is a Cu wiring. Moreover, as said Cu film | membrane, Cu seed layer of Cu plating wiring is mentioned, for example.

  The Cu film is preferably a Cu film of an electronic device. Examples of the electronic device include a semiconductor device, a SAW device, TPH, and LCD.

Since Cu has high ionization efficiency, the discharge can be self-maintained (self-sustained discharge) by Cu ⁺ ions. However, only the self-sustained discharge with Cu ⁺ ions results in an unstable plasma state when the discharge is sustained for a long time. In particular, when a large bias voltage is applied to the substrate side, self-sustained discharge due to Cu ⁺ ions tends to be unstable.

  Therefore, in the sputtering target (Cu target) of the present invention, Ag and Au having higher ionization efficiency than Cu are contained in the high purity Cu constituting the range of 0.005 to 500 ppm (total content of Ag and Au). As)). Ag or Au promotes the ionization efficiency of Cu, in other words, plays a role of supplementing the self-sustained discharge of Cu. Therefore, the self-sustained discharge of Cu can be stably maintained for a long time.

  According to the sputtering target of the present invention, when applying the Cu self-ion sputtering method, it is possible to stabilize the plasma state and maintain the self-sustaining discharge for a long time. This greatly contributes to the improvement of the manufacturing yield and reliability of the Cu wiring.

It is a figure for demonstrating the measuring method of Ag and Au content and its variation in the sputtering target of this invention.

  Hereinafter, modes for carrying out the present invention will be described.

  The sputtering target of the present invention is made of high-purity Cu containing at least one element selected from Ag and Au in a mass ratio of 0.005 to 500 ppm as a total amount of Ag and Au. By containing such a range of Ag and Au in high-purity Cu, it is possible to significantly improve the sustainability of self-sustained discharge in Cu self-ion sputtering.

  In the present invention, the reason why the total content of Ag and Au in the sputtering target (Cu target) made of high-purity Cu is defined in the above range is as follows.

Since Cu has a very high ionization efficiency, Cu itself ionizes and returns to the target to perform self-sustained sputtering. In other words, Cu has a characteristic that sputtering of Cu is continued while maintaining self-sustained discharge. According to such Cu sputtering based on the self-ion sputtering method, since no rare gas such as Ar or Kr exists in the discharge space, the sputtered Cu atoms, Cu ⁺ ions, neutral particles, etc. bend the flight direction. Without going through the process, it goes straight to the substrate. That is, the directivity very excellent compared with the conventional sputtering method is obtained. Further, by applying a negative charge (bias voltage) to the substrate side, more Cu ⁺ ions reach the substrate while having a straight direction.

However, when a conventional high-purity Cu target is used, if the discharge is continued for a long time, the plasma falls into a very unstable state, and the discharge is eventually cut off. In order to avoid the disappearance of such a self-sustaining discharge, it is effective to increase the number of Cu + ions released from the Cu target. As a result of various studies on this point, it has been found that Ag and Au having high ionization efficiency effectively act against an increase in the number of generated Cu ⁺ ions.

That is, since the ionization efficiency of Ag and Au is higher than that of Cu, the ionization efficiency of Cu can be promoted. In other words, Ag and Au play a role to supplement the self-sustained discharge of Cu. As a result, the self-sustained discharge of Cu can be stably maintained for a long time. In particular, in order to improve the rectilinearity of Cu ⁺ ions, even when a negative charge (bias voltage) is applied to the substrate side, the self-sustained discharge of Cu is supplemented with Ag or Au having high ionization efficiency, so Self-sustained discharge can be stably maintained for a long time.

  However, when the content of Ag and Au in high-purity Cu exceeds 500 ppm as a total of these, a compound of Cu and Ag or Cu and Au is formed, and the specific resistance of the Cu film formed using the Cu target is low. It will increase. On the other hand, if the total content of Ag and Au is less than 0.005 ppm, the effect of promoting the ionization efficiency of Cu cannot be obtained effectively. The total content of Ag and Au in the high-purity Cu is more preferably in the range of 0.01 to 100 ppm, and further preferably in the range of 0.5 to 50 ppm.

  Moreover, in the sputtering target of the present invention, the variation in the content of Ag and Au is preferably within ± 30% of the entire target. Thus, since the ionization efficiency of Cu can be promoted as a whole target by suppressing variation in the content of Ag and Au with respect to the whole target, the self-sustained discharge of Cu can be maintained more stably. It becomes possible. The variation in the Ag content or Au content in the Cu target is more preferably within ± 15%, and more preferably within ± 10%.

  Here, Ag content or Au content in the sputtering target of this invention is taken as the value measured by the method shown below. That is, as shown in FIG. 1, for example, the center part (position 1) of a disk-shaped target, and the positions near the outer periphery (positions 2 to 9) on four straight lines that pass through the center part and are divided equally. A test piece having a length of 10 mm and a width of 10 mm was taken from a position at a half distance (positions 10 to 17), and the amount of Ag or Au in these 17 points was measured. A value obtained by averaging the measured values is set as the Ag content or Au content of the target. The amount of Ag or Au is measured based on the ICP-MASS method.

  Further, the variation in the Ag content or Au content of the entire target is determined from the maximum value and the minimum value of the Ag content or Au content obtained from the 17 test pieces described above, {(maximum value−minimum value) / (Maximum value + minimum value)} The value obtained based on the formula of 100 is assumed to be indicated.

  As described above, the sputtering target of the present invention is characterized in that the total content of Ag and Au in high-purity Cu is in the range of 0.005 to 500 ppm. The amount of impurity elements excluding Ag and Au in the high-purity Cu constituting the target may be included to some extent as long as it is about the level of a general high-purity metal material.

  However, in order to reduce wiring resistance and the like, in the present invention, it is preferable to use high-purity Cu having a total content of Fe, Ni, Cr, Ti, Al, Na, and K as impurity elements of 10 ppm or less. In other words, a value obtained by subtracting the total content (% by mass) of Fe, Ni, Cr, Ti, Al, Na, and K from 100% [100− (Fe% + Ni% + Cr% + Ti% + Al% + Na%) + K%)] is preferably 99.999% or higher.

  The sputtering target of this invention can be produced as follows, for example. That is, first, high-purity Cu that is a raw material for forming a Cu sputtering target is prepared. High-purity Cu is, for example, electrolytically refined natural copper and further purified by a vacuum induction melting method to obtain an ingot. The billet size is, for example, 100 to 500 mm in diameter. At this time, Ag or Au is added based on the Ag content or Au content of the target. In adding Ag and Au, the addition amount is set in consideration of the Ag amount and Au amount in the Cu raw material.

  Next, the obtained Cu ingot is subjected to plastic working by forging and rolling. The processing rate at the time of plastic processing is, for example, 50 to 98%. According to plastic working at such a processing rate, appropriate thermal energy can be given to the ingot, and homogenization (reduction in variation) of Ag and Au can be achieved by this thermal energy. In addition, the thermal energy at the time of processing plays a role in matching the arrangement of crystal lattices, and thus effectively acts on the removal of minute internal defects. In the plastic working process, an intermediate heat treatment may be performed as necessary. Thereafter, heat treatment is performed at a temperature in the range of 200 to 500 ° C. for 1 hour or longer. By this heat treatment, variations in Ag and Au in the target material can be further reduced.

  The high-purity Cu material thus obtained is machined into a desired disk shape or the like, and this is joined to a backing plate made of, for example, Al. For bonding to the backing plate, diffusion bonding, brazing bonding, or the like is applied. The temperature during diffusion bonding is preferably 600 ° C. or lower. Further, the brazing joining is performed using a known In-based or Sn-based bonding material. The sputtering target of the present invention is obtained by machining the target material obtained here into a predetermined size.

  The sputtering target of the present invention can be used for forming a wiring film of various electronic devices, but is particularly suitable for forming a Cu seed layer of a Cu plating wiring by applying a Cu self ion sputtering method. . The Cu film formed by using the sputtering target of the present invention and applying the self ion sputtering method of Cu is excellent in the straightness of the sputtered particles, so it can be formed well in grooves and holes having a large aspect ratio. Can do. In addition, since the stability of the sputtering process based on the Cu self-ion sputtering method can be greatly increased, the reliability of the device manufacturing process can be improved, and the manufacturing yield of the device can be improved. be able to.

  The above-described technology based on the present invention is extremely effective for semiconductor devices and the like that are rapidly being highly integrated and densified by DD wiring and the like, and the high density wiring is highly reproducible with high reliability. It can be realized well. This greatly contributes to improving the manufacturing yield of the ultra-highly integrated semiconductor device and stabilizing the manufacturing process. Further, the Cu film formed by the sputtering target of the present invention is not limited to a semiconductor device, but can be applied to various electronic components such as a SAW device, a TPH, and an LCD device.

  Next, specific examples of the present invention and evaluation results thereof will be described.

Example 1, Comparative Example 1 , Reference Example 1
First, 16 types of Cu ingots were produced in which the content of each element of Ag, Au, Fe, Ni, Cr, Nb, Ta, Co and Al was changed. These Cu ingots were subjected to cold forging and cold rolling, and further heat-treated under conditions of 250 ° C. × 120 min. Thereafter, brazing joining was applied to join the Al backing plate, and further machined to obtain 11 types of Cu sputtering targets having a diameter of 320 mm and a thickness of 10 mm. In addition, about content of each element, it analyzed by ICP (Emission-spectral-analysis apparatus: Seiko Instruments company make, SPS1200A).

Using the 16 types of Cu sputtering targets thus obtained, sputtering method: self-ion sputtering, substrate-target distance: 300 mm, back pressure: 1 × 10 ⁻⁵ Pa, output DC: 25 kW, Ar: 2 sccm ( The sustainability of self-discharge by Cu ions was investigated under the conditions of 1 sec addition for generating discharge), sputtering time: 10 min, substrate bias: −15V. The discharge duration of each Cu sputtering target is shown in Table 1 together with the content of each element of the target.

表１から明らかなように、ＡｇやＡｕを所定の範囲で含有させたＣｕスパッタリングターゲット（実施例１）によれば、比較例１の各Ｃｕターゲットに対して、数倍以上の自己維持放電の持続性が得られることが分かる。

As is clear from Table 1, according to the Cu sputtering target (Example 1) containing Ag or Au in a predetermined range, the self-sustaining discharge of several times or more of each Cu target of Comparative Example 1 was observed. It can be seen that sustainability is obtained.

The ratio Comparative Examples 2, Reference Example 2
First, 10 types of Cu ingots with varying contents of Ag and Au were produced. Each of these Cu ingots was subjected to cold forging and cold rolling under various conditions, and further heat-treated under the conditions of 250 to 400 ° C. × 120 min. Thereafter, each of the Cu sputtering targets having a diameter of 320 mm and a thickness of 10 mm was obtained by applying brazing and joining with an Al backing plate and further machining. The content of each element was measured in the same manner as in Example 1. Moreover, the dispersion | variation in Ag and Au content was measured based on the method mentioned above.

Using the 10 types of Cu sputtering targets thus obtained, sputtering method: self-ion sputtering, substrate-target distance: 300 mm, back pressure: 1 × 10 ⁻⁵ Pa, output DC: 25 kW, Ar: 2 sccm ( The sustainability of self-discharge by Cu ions was investigated under the conditions of 1 sec addition for generating discharge), sputtering time: 10 min, substrate bias: −15V. Further, the specific resistance of the Cu film obtained by the above sputtering was measured. Table 2 shows the discharge duration of each Cu sputtering target and the specific resistance of the Cu film together with the content of each element of the target and its variation.

表２から明らかなように、ＡｇやＡｕを所定の範囲で含有させ、かつそれらのバラツキを低減したＣｕスパッタリングターゲットによれば、比較例２の各Ｃｕターゲットに対して、数倍以上の自己維持放電の持続性が得られ、さらに得られるＣｕ膜の比抵抗も小さいことが分かる。

As apparent from Table 2, the Ag or Au is contained in a predetermined range, and according to Cu sputtering coater Getting bets that reduce their variations, for each Cu target of Comparative Example 2, several times or more self It can be seen that sustain discharge sustainability is obtained, and the specific resistance of the obtained Cu film is also small.

Claims (10)

Using a sputtering target made of high purity Cu, a Cu film manufacturing method for manufacturing a Cu film by Cu self-ion sputtering,
The high-purity Cu contains at least one element selected from Ag and Au, and the total content of the Ag and Au is in the range of 0.5 to 50 ppm. At least one selected from Ag and Au A method for producing a Cu film, wherein the variation in the content of seed elements is within ± 30% of the target as a whole. In the manufacturing method of Cu film | membrane of Claim 1,
The high-purity Cu has a total content of Fe, Ni, Cr, Ti, Al, Na, and K as impurity elements of 10 ppm or less. In the manufacturing method of Cu film | membrane of Claim 1 or 2,
A method for producing a Cu film, wherein the target is bonded to a backing plate. In the manufacturing method of Cu film | membrane of any one of Claim 1 thru | or 3,
The method for producing a Cu film, wherein the Cu film is a Cu wiring. In the manufacturing method of Cu film | membrane of any one of Claim 1 thru | or 3,
The Cu film is a Cu seed layer of a Cu plated wiring. In the manufacturing method of Cu film | membrane of any one of Claim 1 thru | or 5,
The method for producing a Cu film, wherein the Cu film is a Cu film for an electronic device. In the manufacturing method of Cu film | membrane of Claim 6,
The method of manufacturing a Cu film, wherein the electronic device is a semiconductor device. In the manufacturing method of Cu film | membrane of Claim 6,
The method for producing a Cu film, wherein the electronic device is a SAW device. In the manufacturing method of Cu film | membrane of Claim 6,
The method for producing a Cu film, wherein the electronic device is TPH. In the manufacturing method of Cu film | membrane of Claim 6,
The method for producing a Cu film, wherein the electronic device is an LCD.

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