JP5457794B2 - Al-based alloy sputtering target - Google Patents

Description

  The present invention relates to an Al-based alloy sputtering target useful for forming wiring films and electrode films used in flat panel displays such as liquid crystal displays. In the following description, the liquid crystal display will be mainly described, but the application of the present invention is not limited to this.

  A liquid crystal display (LCD), one of the semiconductor devices, can be thinner, lighter, and consume less power than a conventional display device that uses a cathode ray tube. Recently, it has become mainstream as a display device. In such LCD, a TFT liquid crystal in which a thin film transistor (TFT) serving as a pixel switch is incorporated is mainly used.

  Various characteristics are required for the thin film electrode used as a part of the TFT and the metal thin film constituting the wiring connected to the thin film electrode, and in particular, the signal delay is caused by the recent trend toward larger LCD or higher definition. In order to prevent this, lower wiring resistance is becoming an important characteristic.

  An example of such a metal thin film material having low wiring resistance is pure Al. However, pure Al does not have sufficient heat resistance. Therefore, when a metal thin film using pure Al is subjected to a thermal history of about 200 to 400 ° C. in the process of forming an insulating film in the LCD manufacturing stage, the substrate and the thin film Compressive stress resulting from the difference in thermal expansion coefficient from the above becomes mobility, and minute irregularities called hillocks are generated on the surface, which may cause short circuit or disconnection between wirings.

  Thus, various techniques have been disclosed so far to solve the problem of hillock generation. For example, Patent Document 1 discloses a semiconductor made of an Al alloy containing 1.0 to 15 atomic% of a rare earth element such as Nd. An electrode is disclosed. Patent Document 2 discloses a wiring film or an electrode film formed of an Al-based alloy containing 1.0 to 10 atomic% of Fe, rare earth elements, or the like. Further, Patent Document 3 discloses an Al-based alloy thin film containing 0.1 to 3.0 atomic% Fe and 0.5 to 3.0 atomic% Si. However, since the Al-based alloys disclosed in these documents have a high alloy element content, they can cope with further lower wiring resistance (particularly, reduction in wiring resistance after heat treatment) as the liquid crystal panel becomes larger. There were cases where it was not possible.

  On the other hand, in Patent Document 4, Fe and Si are 0.001 to 0.01% by mass and Cu is 0.0001 to 0.01 as an Al alloy sputtering target used for forming a thin film electrode, a thin film wiring, and the like. An Al alloy sputtering target containing 5% by mass and having an average crystal grain size of 5 mm or less is disclosed. Since the metal thin film obtained by using such a sputtering target has a smaller amount of alloy elements than the metal thin films described in Patent Documents 1 to 3, the wiring resistance can be reduced while the amount of alloy elements is reduced. As a result, the hillock resistance may be reduced. Further, in order to reduce the crystal grain size (5 mm or less) and suppress the occurrence of splash during sputtering, Cu is an essential component in addition to Fe and Si.

  Furthermore, in Patent Document 5, as a technique for suppressing the occurrence of splash at the time of sputtering, in an Al-based alloy sputtering target containing a refractory metal such as Ti, Zr, Cr, etc., the one with lower hardness (Hv ≦ 25) suppresses splash. It is stated that it can be done.

Japanese Patent No. 2733006 Japanese Patent No. 2727967 Japanese Patent No. 40091165 JP 2007-63621 A Japanese Patent No. 3410278

  The present invention has been made in view of the circumstances as described above, and its purpose is to have low wiring resistance (wiring resistance after receiving a thermal history of about 300 ° C. is 3.7 μΩcm or less) and excellent hillock resistance. Another object of the present invention is to provide an Fe- and Si-containing Al-based alloy sputtering target that is useful for forming a metal thin film and that can further suppress the occurrence of splash during sputtering.

  The Al-based alloy sputtering target of the present invention that has solved the above problems is characterized by containing 0.0010 to 0.4 mass% Fe and 0.0010 to 0.50 mass% Si.

  In the Al-based alloy sputtering target, the hardness (Hv) is 26 or more, or at least one element selected from the group consisting of Mn, Cr, Mo, and Nb is 0.001 to 0.1 mass. Including% is a preferred embodiment of the present invention.

  In the Al-based alloy sputtering target of the present invention, the content of alloying elements (Fe, Si, etc.) is appropriately adjusted, so that the excellent low wiring resistance (the wiring resistance after receiving a thermal history of about 300 ° C.) A metal thin film having both 3.7 μΩcm or less and hillock resistance can be formed. Further, by setting the hardness (Hv) of the Al-based alloy sputtering target to 26 or more, occurrence of splash during sputtering can be suppressed.

  The Al-based alloy sputtering target of the present invention (hereinafter sometimes simply referred to as “target”) contains 0.0010 to 0.4 mass% Fe and 0.0010 to 0.50 mass% Si. It is characterized by.

  When the composition of the target according to the present invention is compared with Patent Document 3 described above, in Patent Document 3, the lower limit of Si is 0.5% atomic% (≈0.52 mass%). This is different from the present invention in which the upper limit is 0.50% by mass or less. As will be described in detail below, according to the examination results of the present inventors, by controlling Fe and Si within the range specified by the present invention, it is possible to further reduce the wiring resistance after heat treatment, and to be excellent. It was also found that a target capable of providing a metal thin film having both hillock resistance was obtained. Further, when the composition of the target according to the present invention is compared with the above-mentioned Patent Document 4, in Patent Document 4, the upper limits of Fe and Si are both extremely reduced to 0.01% by mass, and Cu is added to the same extent. This is different from the present invention in which Cu is not added. Moreover, in patent document 4, although crystal grain size is refined | miniaturized by the trace amount addition of Fe, Si, and Cu, especially generation | occurrence | production of the splash at the time of sputtering is suppressed, according to examination of the present inventors, Cu It has been found that the occurrence of splash can be effectively suppressed by adding a suitable control of the hardness (Hv) of the target (Hv ≧ 26). That is, in Patent Document 4, the hardness (Hv) effective for suppressing the occurrence of splash is not established in a target containing a very small amount of Fe and Si as in the present invention.

  In the target of the present invention, by reducing or adjusting the content of alloying elements (Fe and Si) as compared with conventionally known targets, not only can the resulting metal thin film have low wiring resistance, but also hillock resistance. The mechanism that can improve this is not clear, but it is presumed as follows.

In general, low wiring resistance of an Al-based alloy is achieved by (1) precipitation in the post-process of an alloy element that has been dissolved in supersaturation during the film formation process (around 150 to 180 ° C.), and (2) grains by crystal grain growth. It is known that the effect of precipitation of solid solution elements (1) (reduction of the total solid solution amount of elements in the solid solution state) is particularly large. Yes.

  In addition, it is known that hillock suppression requires that a certain amount or more of a solid solution element maintain a solid solution state in crystal grains during a film formation process (around 150 to 180 ° C.).

  Therefore, in order to obtain a metal thin film having both low wiring resistance and high hillock resistance, a solid solution state of a certain amount or more of solid solution elements is maintained in the film formation process (around 150 to 180 ° C.), and the LCD is manufactured. It is necessary to promote the precipitation of the solid solution element in the step of forming the insulating film at the stage (200 to 400 ° C.).

  By the way, the present inventors have found that Fe, which is an alloy element in an Al-based alloy, precipitates at 220 to 250 ° C., Si has an effect of suppressing the growth of crystal grains, and Fe and Si are used as alloy elements. It has been found that the wiring resistance can be reduced by using together even if the film is formed in a low temperature region (see Patent Document 3). This is because the precipitation of alloy elements includes a body diffusion process in which dissolved atoms diffuse to the grain boundary and a process of agglomerating to a grain boundary triple point through the grain boundary, especially in the low temperature range (around 200 ° C.). Body diffusion rate is rate limiting. Therefore, the alloy element is rapidly precipitated by suppressing the crystal grain growth and reducing the diffusion distance of the solid solution element to the grain boundary.

  On the other hand, when the present inventors further studied, it was found that the combined use of Fe and Si may reduce the hillock resistance. This is presumably because Fe reacts with Si to form a FeSi-based composite and precipitates during the film formation process, and the solid solution state of a certain amount or more of the solid solution element cannot be maintained. It was.

  From the above, in the present invention, by further reducing the Si content in the Al-based alloy as compared with Patent Document 3, the amount of Fe that reacts with Si and precipitates in the film formation process decreases, and the solid content is reduced. It is thought that the solid solution state of the dissolved element could be maintained and deterioration of hillock resistance could be suppressed. Moreover, since the amount of Fe used for precipitation decreases, even if the amount of Fe added is reduced, a solid solution Fe amount of a certain amount or more can be secured. For this reason, the amount of alloy elements in the Al-based alloy can be reduced as a whole, and it is considered that low wiring resistance can be achieved while maintaining excellent hillock resistance.

  Hereinafter, the Al-based alloy sputtering target of the present invention containing 0.0010 to 0.50 mass% of Si and 0.0010 to 0.4 mass% of Fe will be described in detail.

(Alloy element)
As described above, Si contained in the target of the present invention has a function of suppressing the growth of crystal grains and promoting the precipitation of other solid solution elements (Fe, Mn described later, etc.). By making 0.0010 to 0.50 mass%, the above-mentioned action can be effectively exhibited. Moreover, it can prevent that Fe forms and precipitates a FeSi type composite.

  If the Si content is less than 0.0010% by mass, precipitation of solid solution elements cannot be promoted even after a thermal history in the subsequent process such as the formation of an insulating film, and the wiring resistance of the resulting metal thin film is reduced. May not. In addition, since the amount of the solid solution component in the metal thin film becomes too small, the solid solution state of a certain amount or more of the solid solution element cannot be maintained in the film forming process, and the hillock resistance may be lowered. On the other hand, when the Si content exceeds 0.50 mass%, precipitation of Fe used together with Si is promoted, and a solid solution state of a certain amount or more of solid solution elements cannot be maintained in the film formation process. The hillock resistance of the metal thin film may be reduced. Moreover, the amount of alloy components in the metal thin film may increase, leading to an increase in wiring resistance. The content of Si is preferably 0.01% by mass or more (more preferably 0.03% by mass or more), and preferably 0.25% by mass or less (more preferably 0.1% by mass or less). .

  As described above, Fe contained in the target of the present invention can maintain a solid solution state during the film formation process, and thus improves the hillock resistance of the obtained metal thin film. Moreover, it precipitates at 220-250 degreeC, and it contributes also to low wiring resistance by promoting the growth of a crystal grain accompanying it. The said effect | action can be exhibited effectively by making the content rate of Fe into 0.0010-0.4 mass%.

  If the Fe content is less than 0.0010% by mass, a certain amount of solid solution element cannot be secured in the film formation process, and the hillock resistance of the resulting metal thin film may be lowered. If the Fe content exceeds 0.4% by mass, the amount of alloying elements in the metal thin film increases, so that the wiring resistance may not decrease. The Fe content is preferably 0.01% by mass or more (more preferably 0.05% by mass or more), and is preferably 0.38% by mass or less (more preferably 0.35% by mass or less). preferable.

  As described above, the target of the present invention reduces the amount of alloy components Si and Fe as a whole compared to Patent Document 3 and reduces the amount of alloy components in the metal thin film, thus providing further wiring resistance. Can be reduced.

  The target of the present invention includes at least one element selected from the group consisting of Mn, Cr, Mo, and Nb in addition to the above Si and Fe as alloy elements (hereinafter simply referred to as “M element”). May be included). These elements may be used alone or in combination of two or more. M element can improve the hillock resistance of a metal thin film like Fe. In addition, since diffusion at a low temperature is fast, it is likely to be deposited during the film formation process, and a reduction in wiring resistance can be promoted by heat treatment during film formation (or after film formation). Furthermore, since the solid solubility limit in Al is small, even if a solid solution element (M element) remains in the metal thin film, it is difficult to contribute to an increase in wiring resistance.

  The content of the element M (single amount in the case of a single element, or the total amount of these elements in the case of including two or more elements) is 0.1% by mass or less (more preferably 0.03% by mass or less, more preferably 0.01% or less). (Mass% or less) is preferable. When the content of M element exceeds 0.1% by mass, the amount of alloy components in the metal thin film increases, which may increase the wiring resistance. The lower limit of the content of the M element is not particularly limited, but in order to effectively exhibit the above-described action, it should be 0.001% by mass (more preferably 0.002% by mass). Is preferred.

  The target of the present invention may further contain Ti or B as an alloy element. Thereby, the crack in the casting process at the time of target manufacture can be prevented, or refinement | miniaturization of a cast structure can be achieved. The content of Ti is preferably 0.0005% by mass or more (more preferably 0.002% by mass or more), and 0.05% by mass or less (more preferably 0.03% by mass or less). The B content is preferably 0.0001% by mass or more (more preferably 0.0004% by mass or more), and preferably 0.01% by mass or less (more preferably 0.006% by mass or less).

  The target of the present invention includes a predetermined amount of Si and Fe, the remainder being Al and an inevitable impurity Al-based alloy, and Si and Fe, further containing a predetermined amount of M element, and the balance being Al and an inevitable impurity Al group. An alloy or an Al-based alloy containing a predetermined amount of Si, Fe, M element, and Ti and / or B, with the balance being Al and inevitable impurities may be used.

(hardness)
The target of the present invention preferably has a hardness (Hv) of 26 or more. Thereby, the splash at the time of sputtering can be suppressed.

  In general, when the amount of impurities (alloy elements, etc.) in the target is 0.01% by mass or more, it is known that splash is likely to occur, but the Al-based alloy target containing Fe and Si of the present invention According to the above, it has been found that by setting the hardness (Hv) of the target to 26 or more, the splash at the time of sputtering can be suppressed even when the amount of impurities in the target is 0.01 mass% or more. Thus, although the mechanism that can suppress the splash when the hardness (Hv) is 26 or more is not clear, the surface roughness after machining may be affected as in the case of the Mo-W alloy. Guessed.

  The hardness (Hv) of the target of the present invention is more preferably 28 or more. The upper limit of the hardness (Hv) is not particularly limited, but it is technically difficult to make the hardness (Hv) exceed 60 in a low alloy system with a small amount of additive elements. A preferable upper limit is 50 (more preferably 40).

(Manufacturing method of sputtering target)
The method for producing the target of the present invention is not particularly limited, and examples thereof include a spray forming method and a melt casting method. In particular, in order to produce a target having a hardness (Hv) of 26 or more, the production cost is reduced. For this reason, it is preferable to prepare by a melt casting method.

  More specifically, the target of the present invention comprises a general melt casting, a soaking step, a rough hot rolling step, a finish hot rolling step, (winding step, unwinding step, stretcher if necessary) It can be manufactured by going through a process), a cutting process, a cold working process (if necessary), and a target working process in this order. In addition, in order to ensure a predetermined hardness (Hv), in each of the above steps, the rolling temperature is lowered, the winding temperature is lowered, the stretcher amount is adjusted, and the cold rolling rate is adjusted during cold working. Preferably it is done. A target having a hardness (Hv) of 26 or more can be produced by performing one or a combination of two or more processes or controls as necessary. In particular, the present invention is characterized in that the rolling temperature and the coiling temperature are lowered as compared with the conventional case (approximately 500 ° C. or higher). In addition, unlike the patent document 4, the target of this invention can abbreviate | omit the annealing process after a cutting | disconnection. Hereinafter, the preferable manufacturing method used for this invention is demonstrated in detail for every process.

(Melting casting process)
The melt casting process is not particularly limited, and a process usually used for target production can be appropriately employed. For example, typical casting methods include DC (semi-continuous) casting, thin plate continuous casting (double roll type, belt caster type, propel type, block caster type, etc.).

(Soaking process)
In the soaking step, in order to ensure hardness, the soaking temperature is preferably about 350 to 500 ° C, and the upper limit is more preferably 450 ° C. The soaking time is preferably controlled to about 1 to 8 hours.

(Rough hot rolling process)
After the above-mentioned soaking, rough hot rolling is performed. In order to ensure hardness, the rough hot rolling start temperature is preferably about 350 to 500 ° C, and the upper limit is more preferably 450 ° C. Moreover, it is preferable to control the total rolling reduction to about 50 to 95%.

(Finish hot rolling process)
In the present invention, finish hot rolling is performed after rough hot rolling. In order to ensure hardness, the finish hot rolling start temperature is preferably about 200 to 500 ° C, and the upper limit is more preferably 400 ° C. Moreover, it is preferable to control the total rolling reduction to about 50 to 90%.

(Winding process, rewinding process)
In the present invention, after finishing hot rolling, winding and rewinding operations may be performed as necessary. The winding temperature is preferably about 200 to 450 ° C, and the upper limit is more preferably 400 ° C.

(Stretcher process)
In the present invention, after the finish hot rolling (or after the winding process and the rewinding process), a stretcher may be performed as necessary. The stretcher may be performed at room temperature. The processing rate is preferably 1% or more.

(Cold working process)
In the present invention, the target obtained through the above steps may be cut into an appropriate size and then cold worked as necessary to ensure hardness. It is preferable to control the processing rate to 5 to 50%.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

  First, the evaluation method used in the experimental example will be described below.

(hardness)
The hardness (Vickers hardness: Hv) of the sputtering target was measured using a Vickers hardness meter (AVK-G2 manufactured by Akashi Seisakusho Co., Ltd.).

(Hillock resistance)
Using a sputtering target, DC magnetron sputtering was performed on a Si wafer substrate (size: diameter 100.0 mm × thickness 0.50 mm) using a sputtering apparatus of “Sputtering System HSR-542S” manufactured by Shimadzu Corporation. The sputtering conditions are as follows.
Back pressure: 3.0 × 10 ⁻⁶ Torr or less Ar gas pressure: 2.25 × 10 ⁻³ Torr
Ar gas flow rate: 30 sccm, sputtering power: 150 W
Distance between electrodes: 51.6mm
Substrate temperature: room temperature

  After forming a positive photoresist (novolak resin: TSMR-8900, manufactured by Tokyo Ohka Kogyo Co., Ltd., thickness 1.0 μm, line width 10 μm) on the thin film surface by photolithography, a CVD apparatus is formed. Heat treatment was performed in a reduced-pressure nitrogen atmosphere (pressure: 1 Pa) and held at 270 ° C. for 15 minutes or 320 ° C. for 30 minutes.

  Next, the number of hillocks (hemispherical protrusions) generated on the stripe pattern surface portion and the cross-sectional portion (side portion) of the pattern is confirmed with an 10000 × electron microscope (SEM), and the objective lens is observed with an optical microscope. The number of hillocks in the field of view was measured by differential interference with a normal ski lens at a magnification of 50 × and eyepiece 10 ×, and the hillock density (number of hillocks per unit area) was determined.

The criteria for determining hillock resistance are ◎ when the hillock density is less than 3.0 × 10 ⁹ pieces / m ² , ○ when the hillock density is (3.0 to 9.0) × 10 ⁹ pieces / m ² , 9.0 The case where × 10 ⁹ pieces / m ² was exceeded was taken as ×.

(Wiring resistance)
After processing into a stripe pattern shape with a line width of 100 μm by the same method as the above-described method for producing the hillock resistance measurement sample, it was processed into a wiring resistance measurement pattern shape with a line width of 100 μm and a line length of 10 mm by wet etching. For the wet etching, a mixed solution of H ₃ PO ₄ : HNO ₃ : H ₂ O = 75: 5: 20 was used. In order to give a thermal history to this, after the etching process, a heat treatment is performed by holding the thin film at 270 ° C. for 15 minutes or at 320 ° C. for 30 minutes in a reduced-pressure nitrogen atmosphere (pressure: 1 Pa) in the CVD apparatus as in the hillock measurement. I did it. Thereafter, the specific resistance value was measured at room temperature by a four-probe method.

(splash)
The number of splashes (initial splash) generated when sputtering was performed under the above conditions was measured.

  Sixteen thin films were formed for one sputtering target. Therefore, sputtering was performed for 81 (seconds) × 16 (sheets) = 1296 seconds.

  Using a particle counter (manufactured by Topcon Co., Ltd .: wafer surface inspection device WM-3), the position coordinates, size (average particle diameter), and number of particles observed on the surface of the thin film were measured. Here, particles having a size of 3 μm or more are regarded as particles. Thereafter, the surface of the thin film was observed with an optical microscope (magnification: 1000 times), a hemispherical shape was regarded as a splash, and the number of splashes per unit area was measured.

Specifically, the above-described sputtering process for each thin film is performed in the same manner for 16 thin films while replacing the Si wafer substrate, and the average number of splashes is expressed as “number of occurrences of initial splash”. " In this experimental example, the case where the number of occurrences of the initial splash thus obtained was 20 / cm ² or less was evaluated as ◯, and the case where the number of occurrences of 21 / cm ² or more was evaluated as ×.

(Experimental Examples 1 to 11)
Various Al-based alloys shown in Table 1 (the balance being Al and inevitable impurities) were prepared. An ingot with a thickness of 500 mm was ingoted by DC casting, then soaked at 450 ° C. for 2 hours, and then reduced to 450 ° C. It was hot-rolled with a hot 90% amount, followed by finish rolling at 400 ° C. and a reduction amount of 70%, and wound on a coil at 350 ° C. Then, it rewinded and processed 3% with the stretcher, and cut | disconnected, and produced the sputtering target (rolled plate). For Experimental Example 6, cold working was performed. At that time, the rolling reduction was controlled to 20%.

  Using the obtained sputtering target, hardness and splash were evaluated by the above methods. Moreover, the hillock resistance and wiring resistance when it was set as the metal thin film were evaluated. The evaluation results are shown in Table 1.

According to the results, the target of the present invention containing 0.0010 to 0.4 mass% Fe and 0.0010 to 0.50 mass% Si is hillock resistant after any heat treatment at 270 ° C. or 320 ° C. It can be seen that the wiring resistance is low and the occurrence of splash during sputtering is reduced (Experimental Examples 1 to 6). In particular, it can be seen that a target further containing an M element as an alloy component is more excellent in hillock resistance (Experimental Examples 4 to 6). On the other hand, it can be seen that the hillock resistance is reduced in the target with the Fe and Si contents being too low (Experimental Example 7). Moreover, it turns out that wiring resistance becomes high when the content rate of either Fe or Si is outside the range of the present invention (Experimental Examples 8 to 11).

Claims (2)

An Al-based alloy sputtering target comprising 0.0010 to 0.4 mass% Fe, 0.0010 to 0.50 mass% Si, and 0.001 to 0.1 mass% Mn .   The Al-based alloy sputtering target according to claim 1, wherein the hardness (Hv) is 26 or more.