JP5069201B2 - target - Google Patents

Description

This invention better uniformity of the film (uniformity), it is possible to improve the quality of sputtering deposition, about the sputtering target can be further significantly improve manufacturing yield.

In recent years, sputtering that forms a coating of metal or ceramic material has been used in many fields such as electronics, corrosion-resistant materials and decoration, catalysts, and production of cutting / polishing materials and wear-resistant materials.
The sputtering method itself is a well-known method in the above field, but recently, particularly in the field of electronics, a sputtering target such as a metal or an alloy suitable for forming a film having a complicated shape or forming a circuit is required. Has been.

In general, such a metal or alloy target is forged or annealed (heat treated) of an ingot or billet in which a metal or alloy raw material is melted and cast by a melting means such as an electron beam, and further rolled and finished (machinery, polishing, etc.) It is processed into a target.
In such a manufacturing process, forging of an ingot or billet destroys the cast structure, diffuses and disappears pores and segregation, and further recrystallizes by annealing, thereby increasing the density and strength of the structure. it can.
The melt-cast metal or alloy ingot or billet has a crystal grain size of about 50 mm. The cast structure is destroyed by forging or recrystallization annealing of an ingot or billet, and almost uniform and fine (100 μm or less) crystal grains are obtained. However, there is a problem that the coarse crystals persist to the final product.

When sputtering is performed, the finer and uniform the target crystals are, the more uniform film formation is possible, and a film having stable characteristics can be obtained.
Therefore, the presence of irregular crystal grains in the target that occurs during forging, rolling, and subsequent annealing changes the sputter rate, thereby affecting the uniformity of the film and improving the quality of sputter film formation. The problem of degrading can occur.
In addition, the use of a forged product that remains strained causes deterioration in quality and must be avoided as much as possible.

On the other hand, when a metal or alloy target is sputtered using a magnetron sputtering device, only a specific area along the magnetic field line is particularly eroded (generally, erosion progresses to a donut shape), and as the erosion progresses to the end point of sputtering, it gradually becomes steeper. Go.
The surface area of the target increases in a portion where erosion progresses particularly, and the difference in surface area from other areas becomes significant. This difference in surface area results in a difference in sputter rate, where the film is formed thicker at the substrate (wafer) location facing the part where the surface area increases and spatter concentrates, and conversely, it is formed thinner at the part where there is little spatter. It tends to be.
This not only results in the formation of a non-uniform film on a single wafer, but also causes the problem that the film thickness varies from the beginning to the end of a large number of wafers to be sputtered. That is, the uniformity of sputter deposition is reduced.
As a method for improving the uniformity of such sputter film formation, it has been proposed to make the structure as uniform as possible in general, and in particular to align the crystal orientation over the entire thickness direction of the target. However, there is a problem that the reduction in the uniformity of the sputtered film due to the change in the surface area cannot be solved only by aligning the crystal orientation.

Generally, high purity metals and alloys of about 4N to 8N are used for the target, but such high purity metals are very expensive. For example, depending on the material, if it is increased by 1N, the price may be 5 to 10 times higher. For these reasons, improving the yield in the target manufacturing process is a very important issue.
In addition, in order to improve the characteristics of the sputtered film, it is necessary to control the metallographic structure as described above. This is due to plastic processing such as forging and rolling, and heat treatment processes such as annealing and recrystallization. Achieved.
Iron, tantalum, and the like can be plastically processed in the cold, but are easily oxidized (oxygen diffuses), and must be heat-treated in a vacuum or in a non-oxidizing atmosphere, even in a high vacuum (10 ⁻⁴ to 10 ⁻⁶ torr). Therefore, the surface contamination layer (oxide layer) must be removed mechanically or chemically (such as pickling) before and after the heat treatment.
In particular, since the contaminated layer on the surface must be completely removed after the final heat treatment, a considerable thickness must be removed from both sides of the target, resulting in a significant decrease in yield.

As a conventional metal or alloy sputtering target or high-purity metal or alloy production method, a target made of aluminum, gold, platinum, copper, nickel, palladium and their alloys having a face-centered cubic lattice (FCC) has been proposed. (For example, refer to Patent Document 1).
Further, a 99.95 wt% tantalum sputtering target having a (100) equiaxed crystal structure and a maximum particle size of 50 microns or less manufactured by rolling and forging processes is disclosed (for example, see Patent Document 2).
Further, a high-purity tantalum target having a fine structure capable of uniform sputtering, in particular, an average crystal grain size of 100 μm or less, and (111) <uvw> is preferentially oriented in the thickness direction of the target. A high-purity tantalum target having a crystal structure is disclosed (for example, see Patent Document 3).

Japanese National Patent Publication No. 5-508509 JP-T-2002-518593 US Pat. No. 6,313,233

  In order to solve the above problems, the present invention improves the crystal orientation structure of the target, improves the uniformity of the film when performing sputtering, and improves the quality of sputter film formation. Furthermore, it is an object to obtain a sputtering target that can significantly improve the manufacturing yield.

The present invention
1. 1. A target characterized in that the crystal orientation changes from the sputtering surface of the target toward its back surface. A target whose crystal orientation is changing from the sputtering surface of the target toward the back surface thereof, and having a crystal structure in which the crystal orientation of the sputtering surface of the target or the back surface thereof is (222) preferential. 2. Target to be used Two flat targets cut in half from the center plane of the target material, and the two cut targets are characterized in that the crystal orientation changes in the thickness direction with the cut plane being plane-symmetric. Target to be used 4. The target material is cut in half from the center plane of the target material, and is a flat plate-like target. The two cut targets have the crystal plane changed in the thickness direction with the cut plane as plane symmetry, and the target A target characterized by having a crystal structure in which the crystal orientation of the sputtering surface or the back surface thereof is (222) preferential.

The present invention also provides:
5. 5. The target according to any one of 1 to 4 above, wherein the main crystal structure is a metal or alloy having a body-centered cubic lattice (BCC). 6. The target according to any one of 1 to 5 above, which is a metal selected from iron, tantalum, niobium, molybdenum, tungsten, and vanadium, or an alloy containing these metals as a main component. 7. The target according to any one of 1 to 6 above, wherein the average crystal grain size of the target is 250 μm or less. 8. The target according to any one of 1 to 7 above, wherein the average crystal grain size of the target is 80 μm or less. The target according to any one of 1 to 7 above, wherein the target has an average crystal grain size of 30 to 60 μm.

 In the flat target, the present invention cuts in half from the center surface of the target material to form two targets, and the crystal structure in which the crystal orientation located on the center surface of the target material before cutting is preferentially (222). By improving the crystal orientation structure of the target, improving the uniformity of the film when performing sputtering, improving the quality of sputter deposition, and further improving the production yield It has the outstanding effect that the sputtering target which can improve remarkably, and its manufacturing method can be obtained.

In the target manufacturing method of the present invention, in a flat target, the target material is cut in half from the center surface to obtain two targets. The target material after cutting in half is used as a target by surface finishing such as cutting and polishing. That is, after the final heat treatment or the like (after completion of metallographic structure control), it is divided into halves, and no plastic working is performed thereafter.
As means for improving the yield, for example, it is conceivable to manufacture the target into a columnar (particularly cylindrical) material and slice it. However, the target diameter has been increasing in recent years, and it is almost impossible to produce a target material having a columnar shape and a fine crystal grain size due to restrictions such as a forging device.

Therefore, it is necessary to flatten by rolling or pressing. With this flattening, in particular, the body-centered cubic (BCC) metal can orient the (222) plane in the vicinity of the center plane, and such a target is resistant to variations in film uniformity as erosion progresses. It has been found that there is an inhibitory effect and the uniformity throughout the spatter life is stable. The inventor has already filed a patent application for this effective invention (see Japanese Patent Application No. 2002-274308). Details regarding the operational effects of the present invention relating to uniformity will be described later.
In order to solve the difficult effect of improving uniformity and improving yield, it is important to cut in half (divided into two equal parts). Not only can the crystal grain size become larger and the grain size cannot be controlled, but also a target with the same change in crystal orientation cannot be produced.

Although it does not specifically limit regarding the cutting method, It must be a cutting method with little heat influence. If there is much heat influence, the amount of cutting of this heat affected layer (contaminated layer) will increase, and conversely the yield will decrease. It is possible to use methods such as wire cutting, water jet cutting, and electric discharge cutting that can cut a plurality of sheets at the same time with little margin.
The sputtering target manufacturing method of the present invention is particularly effective for a metal or alloy whose main crystal structure is a body-centered cubic lattice (BCC). Specifically, it can be applied to a metal selected from iron, tantalum, niobium, molybdenum, tungsten, and vanadium, or an alloy containing these metals as a main component.

The two cut targets of the present invention can be a sputtering target having a structure in which the cut plane is plane-symmetric and the crystal orientation is changed in the thickness direction. In addition, the crystal orientation positioned on the center plane of the target material before cutting can be a target having a crystal structure in which (222) is preferred.
Further, as this condition, the crystal structure in which the (222) orientation is preferential from the position of 30% of the thickness of the target material before cutting toward the center plane of the target material, and the thickness of the target material before cutting From the position of 20% toward the center plane of the target material (222) The crystal structure in which the orientation is preferential, and further from the position of 10% of the thickness of the target material before cutting toward the center plane of the target material ( 222) The two cut targets having a crystalline structure in which orientation is preferential. These structures have the effect that the uniformity throughout the sputtering life is stabilized.
This position can be appropriately adjusted depending on the size or shape of the tantalum target or the desired film forming conditions.

When two flat (disc-shaped) sputtering targets cut in half from the center surface of the target material are used, they can be used as targets whose crystal orientation changes from the sputtering surface toward the back surface.
In particular, two targets can be used as targets in which the cut plane is symmetrical and the crystal orientation is changed in the thickness direction. In this case, a structure having a crystal structure in which the crystal orientation of the sputtering surface of the target or the back surface thereof is (222) preferential can be obtained.
As for the crystal orientation, (222) can be set as the preferential orientation as described above, but the (222) orientation may not be extended to the periphery of the target. The peripheral part of the target is less affected by erosion and does not reach the latter stage of sputtering.
The average crystal grain size of the target can be 250 μm or less, particularly 80 μm or less, and further 30 to 60 μm.

In the conventional target, when (110), (200), and (211) are in the main orientation, the film formation rate (deposition) is relatively fast, so that the productivity is improved and it is rather preferable. However, erosion proceeds substantially along the magnetic field lines after the start of sputtering. That is, erosion progresses in a donut shape on the plane of the target, and gradually becomes steeper, but the surface area of the target increases at a portion where erosion progresses particularly, and the difference in surface area from other areas becomes significant.
The difference in surface area is the difference in the amount of sputtering, that is, the sputtering rate, and the film is formed thick at or near the position of the substrate (wafer) facing the portion where the surface area increases and the spatter concentrates. The problem is that a small portion is formed thinly, resulting in a decrease in the uniformity of the sputtered film.

However, the target having the crystal structure of (222) preferential orientation on the surface (initial erosion surface) of the present invention can remarkably reduce such a decrease in the uniformity of the sputtered film. Such a phenomenon is not necessarily elucidated, but is considered as follows.
The structure of the (222) orientation of the target of the present invention has a characteristic that the deposition rate (deposition) is slower than other orientations.
This meaning is very large, and the (222) oriented structure serves to make uniform the total thickness of the film formed on the substrate in the initial stage of sputtering and the film thickness distribution in the wafer, and to prevent the deterioration of uniformity.

On the other hand, when a target having a crystal structure of (222) preferential orientation is used on the back side of the present invention, (110), (200), (211) are main orientations on the surface (initial erosion surface). Therefore, along the magnetic field lines, erosion rapidly progresses in a donut shape on the target surface.
This is not different from the conventional erosion, and the erosion part becomes steeper gradually upon receiving the erosion. This also changes the sputter rate in the plane of the target, thereby reducing the uniformity of the sputtered film.
Since the erosion surface has a large undulation as described above, the target surface area of the portion further increases, and the decrease in uniformity tends to increase at an accelerated rate.

However, when a target having a (222) -oriented structure is used on the back side of the present invention, a (222) -oriented structure appears on the erosion surface from the middle of the progress of erosion to some extent. As described above, the (222) oriented structure has a characteristic that the deposition rate (deposition) is slower than other orientations.
Therefore, the (222) -oriented structure that appears in the middle of the substrate undergoes rapid progress of steep and non-uniform (partial) erosion, but the (222) -oriented structure, which has a slow deposition rate (deposition), cancels out the substrate. The film thickness is uniform and the film thickness distribution in the wafer is uniformed to prevent a decrease in uniformity.
Since the erosion of the target surface has progressed to some extent, the external appearance of the target does not seem to be so different from that of the conventional one. However, it was confirmed that there was a large difference in film formation uniformity.

(222) From which point of the target thickness the crystal structure in which the orientation is preferential can be arranged, depending on the target thickness, area size, and required film formation conditions, The (222) orientation can be arbitrarily selected from the position of 30%, the position of 20% of the thickness, or the position of 10% of the thickness toward the center plane.
In a situation where erosion has progressed to some extent, it is desirable to have a (222) -oriented crystal structure. In a target having a uniform structure from the surface to the center, erosion of the surface occurs non-uniformly as described above, so it can be said that film formation uniformity cannot be ensured.
In the previous application (Japanese Patent Application No. 2002-274308), the present inventors have developed a sputtering target having a crystal structure in which (222) orientation is preferential from the position of 30% of the target thickness toward the center plane of the target. Proposed. This is superior to the conventional one in improving the uniformity of the film (uniformity). However, the (222) orientation part is formed at the later stage of sputtering, that is, when the erosion surface is the steepest and the surface area is large. As a result of the appearance of the same orientation as the surface, the effect of suppressing the deterioration of the uniformity of the (222) orientation may be lost.
However, the present invention has a feature that the (222) orientation is maintained up to the joint surface, so that the effect of the (222) orientation is maintained and can be used until the life end.
As described above, both of the case where a target having a crystal structure of (222) preferential orientation on the front surface (initial erosion surface) and a target having a structure of (222) orientation on the back side are formed on the substrate. It has the effect of making the total thickness of the film and the film thickness distribution in the wafer uniform, and preventing a decrease in uniformity.
Since the target of the present invention has a structure capable of remarkably improving the manufacturing yield, it goes without saying that it can be used without sticking to the use form of the target having the (222) priority orientation as described above.

The sputtering target of the present invention is manufactured by the following process. This manufacturing process can be appropriately changed according to the other metal or alloy material, and is not limited to the following manufacturing conditions.
First, a metal or alloy raw material (usually using a high purity metal of 4N5N or more) is melted by electron beam melting or the like, and this is cast to produce an ingot or billet.
Next, this ingot or billet is crystallized in which (222) orientation is preferential from the position of 30% of the target thickness, the position of 20% of the thickness, or the position of 10% of the thickness toward the center plane of the target. A series of processes such as hot forging, cold forging, rolling, annealing (heat treatment), and finishing are performed so that a structure is formed.
In this way, a crystal in which the (222) orientation is preferentially in a disc shape at the center of the target, that is, directly below the initial erosion site of the target or at a position that becomes an erosion site when sputtering proceeds or in the vicinity thereof. An organization can be formed.

When forging, recrystallization annealing, and rolling are performed to form a (222) orientation-oriented crystal structure in the center of the target, the target forging, recrystallization annealing, and rolling can be adjusted even if the forging, recrystallization annealing, and rolling conditions are adjusted. It is difficult to form a crystal structure in which (222) orientation is preferential to the periphery.
Although the portion without the (222) orientation of the target can be excised, there is a problem that the yield decreases. However, since the erosion hardly progresses at the peripheral portion and is not a portion that particularly affects the film formation, the peripheral portion can be (222) oriented in a disc shape except the peripheral portion.

Furthermore, as for forging conditions, a metal or alloy target material having the above structure can be efficiently produced by repeating forging and recrystallization annealing two or more times. Further, sufficient forging is required to form a crystal structure in which the (222) orientation is preferential, but it is particularly effective to perform forging by repeating upsetting and forging.
Furthermore, it is effective to process into a flat target by cross rolling after forging (multi-directional rolling) and heat treatment. Although the annealing conditions vary depending on the metal material, it is generally desirable to perform recrystallization annealing at a recrystallization temperature to 1673K after forging an ingot or billet. The recrystallization annealing at a recrystallization start temperature to a temperature of 1673 K may be performed once, but the target cast structure can be obtained more effectively by repeating twice.

If the annealing temperature exceeds 1673K, the temperature loss is large and is wasted.
With these, a crystal structure in which (222) orientation is preferential from the position of 30% of the target thickness, the position of 20% of the thickness, or the position of 10% of the thickness toward the center plane of the target material is provided. A metal or alloy sputtering target material can be obtained, and a tantalum target material having an average crystal grain size of 250 μm or less, 80 μm or less, or 30 to 60 μm can be produced.

Next, the target material manufactured in this way is cut in half from the center plane to obtain two targets. Of course, in the above process, it is manufactured as a target material having a thickness sufficient for taking two sheets. Before or after the cutting, the upper surface and the lower surface of the target material are ground and / or polished to remove the contaminated layer, the work-affected layer, and the like to obtain a clean surface.
The cutting allowance of the cut surface is usually about 0.15 to 0.4 mm, which is an extremely small amount compared to the ground surface of the surface, and the cut surface itself is close to the clean surface. Very small amount. Therefore, overall, it can be said that it can be said that grinding on almost one side is sufficient. This significantly improves the target yield per unit.

  Next, examples will be described. In addition, a present Example is for showing an example of invention, This invention is not restrict | limited to these Examples. That is, other aspects and modifications included in the technical idea of the present invention are included.

Example 1
A tantalum raw material having a purity of 99.997% was melted with an electron beam and cast into an ingot having a length of 1000 mm and a diameter of 200 mmφ. The crystal grain size in this case was about 50 mm. Next, the ingot was cold-tightened and forged to 110 mmφ and then cut to form a billet having a thickness of 110 mm and a diameter of 110 mmφ. The billet was forged and forged cold, then recrystallized and annealed at a temperature of 1173K, cold-kneaded and forged again, and recrystallized and annealed at a temperature of 1173K again.
Next, the forged ingot is cold-rolled (multi-direction), subjected to strain removal and recrystallization heat treatment at 1173K, a target material having a thickness of 25 mm and 380 mmφ is obtained, and finish machining is performed to obtain a thickness of 17.65 mm. 350 mmφ target material.

Through the above steps, the uniformity of having a crystal structure with a preferential (222) orientation and an average crystal grain size of 45 μm from the position of 30% of the target thickness toward the center plane of the target. An excellent tantalum target material can be obtained.
The contaminated layer of 1.825 mm was removed from both sides of the target material having a thickness of 17.65 mm and 350 mmφ, and wire was cut from the center surface. The cutting allowance for this cutting was 0.3 mm. Then, the cut surface was chamfered by 0.5 mm to prepare two targets having a thickness of 6.35 mm.
When producing these two targets, the loss of the thickness of the material by cutting and cutting was 4.95 mm in total. This is a yield increase of about 12% as compared with the case where a single normal target material shown in Comparative Example 1 is subjected to double-side grinding. The results are shown in Table 1.

Next, this cut surface was diffusion bonded to the Cu—Cr alloy backing plate with the bonding side as a target / backing plate assembly.
When sputtering was performed using this tantalum target, the uniformity of the film (uniformity) was good, and the quality of the sputter film formation could be improved. The results are shown in Table 2.
In addition, the survey of uniformity is a survey of the distribution of sheet resistance. Since the sheet resistance depends on the film thickness, the distribution of the sheet resistance in the wafer (8 inches) was measured, thereby examining the distribution of the film thickness. Specifically, the sheet resistance at 49 points on the wafer was measured, and the standard deviation (σ) was calculated.
As is apparent from Table 2, in Example 1, the uniformity is good from the early stage to the late stage of sputtering.

(Example 2)
A tantalum target manufactured in the same manner as in Example 1 was diffusion bonded to a Cu—Zn alloy backing plate with the cut surface of the target as the erosion side to obtain a target / backing plate assembly.
When sputtering was performed using this tantalum target, the uniformity of the film (uniformity) was good, and the quality of the sputter film formation could be improved. The results are also shown in Table 2.
The results shown in Example 2 in Table 2 are the results of measuring the sheet resistance at 49 points on the wafer in the same manner as in Example 1 and calculating the standard deviation (σ). This Example 2 shows that there is little fluctuation in the resistance distribution in the sheet from the initial stage to the latter stage of sputtering, that is, there is little fluctuation in the film thickness distribution.

(Comparative Example 1)
Two tantalum target materials having a thickness of 17.65 mm and 350 mmφ were manufactured one by one by the same process as in Example 1, and the contamination layers of 1.825 mm on both sides were removed from both sides of the target material. When producing these two targets, the loss of the material thickness by cutting was 7.30 mm in total.
Compared with Example 1, the loss of the thickness of the two targets is 7.30 mm−4.95 mm = 2.35 mm, which is a significant increase (the loss increase for one target is 1.175 mm).
Next, this tantalum target was diffusion bonded to a Cu—Cr alloy backing plate to obtain a target / backing plate assembly.
When sputtering was performed using this tantalum target, the film uniformity (uniformity) was slightly inferior to that of the example. The results are shown in Table 2.
The results shown in Example 2 in Table 2 are the results of measuring the sheet resistance at 49 points on the wafer in the same manner as in Example 1 and calculating the standard deviation (σ). As is clear from Table 2, in Comparative Example 1, the uniformity is slightly worse from the middle stage to the latter stage of sputtering as compared with Examples 1 and 2, although it is generally good.

 In the flat target, the present invention cuts in half from the center surface of the target material to form two targets, and the crystal structure in which the crystal orientation located on the center surface of the target material before cutting is preferentially (222). By improving the crystal orientation structure of the target, improving the uniformity of the film when performing sputtering, improving the quality of sputter deposition, and further improving the production yield Can be remarkably improved, and is useful as a sputtering target and a method for producing the same.

Claims (4)

A target made of a metal selected from iron, tantalum, niobium, molybdenum, tungsten, vanadium whose main crystal structure is a body-centered cubic lattice (BCC), or an alloy containing these metals as a main component, and a divided surface is a target material The center plane of the two flat targets is the plane target, and (222) is oriented on the dividing plane with the other plane facing the dividing plane ( 222) A target having a structure with a relatively low degree of plane orientation . The target according to claim 1 , wherein the target has an average crystal grain size of 250 μm or less. The target according to any one of claims 1 to 2 , wherein an average crystal grain size of the target is 80 µm or less. The target according to any one of claims 1 to 3 , wherein the target has an average crystal grain size of 30 to 60 µm.