KR20010015222A - Fabrication and bonding of copper and copper alloy sputtering targets - Google Patents

Abstract

PURPOSE: Disclosed is a copper or copper-alloy sputtering target having crystals of random orientation and fine, uniform grain size. CONSTITUTION: After heating is applied to high-purity copper and copper-alloy material to at least about 500 deg.C for at least about 1 hr, strain of at least about 40% is applied by hot working. Further, additional strain of at least about 40% is applied by cold working to form a target stock. Then, the target stock is annealed at least about 300 deg.C for at least about 1 hr. By this procedure, fine, uniform grain size of desired random crystal orientation can be obtained in the final sputtering target. Moreover, in order to maintain the microstructure of the target material, the target material is explosion bonded to a metallic backing plate. By using this sputtering target, electric properties necessary for interconnection can be provided and a high uniformity thin film of minimal particle can be formed by sputtering.

Description

Fabrication and bonding of copper and copper alloy sputtering targets

The present invention relates to a method for producing a copper and copper alloy sputtering target having particles that are fine, uniform in size, and having a random orientation, in which the present invention reduces particle generation in a sputtering process, and provides a semiconductor device and a circuit. The film uniformity on substrates, such as a semiconductor wafer used for manufacture of a film, is strengthened.

Sputtering refers to a process comprising coating a semiconductor wafer or other substrate mounted in a processing chamber, where the wafer is electrically biased against a sputter target made of a material to be sputtered spaced apart. Inert gas is introduced into the chamber at low temperature and an electric field is applied to ionize the gas. Ions from the gas impinge on the target and separate atoms from the target, which are then deposited onto a wafer or other substrate to be coated with the target material.

In the manufacture of sputter targets used in the semiconductor industry, particularly sputter targets used for physical vapor deposition of thin films on composite integrated circuits, film uniformity, high deposition rate, minimal particle generation during sputtering, and certain electrical It is desirable to provide a sputter target having characteristics. Aluminum and aluminum alloy sputter targets are commonly used to deposit electrically conductive thin films on integrated circuits for interconnection purposes. However, copper may be used in place of aluminum in the interconnect technology. Copper is more resistant to electromigration than aluminum and has higher electrical conductivity. Another advantage of interconnecting the films using copper and copper alloys is that both interconnect signal delay and power loss are reduced.

If the particles are large and uneven, the target performance will be reduced. In addition, film uniformity and sputter deposition rate are related to the crystallographic orientation of the sputtering target, which affects the dispersion of material discharged from the target. Further, sputtering of atoms from the target occurs along the dense direction of the target material, and if the particle direction is random, the uniformity of the sputtered film becomes good.

Conventional methods for producing aluminum or copper targets generate either a crystal structure oriented in the 200 or 220 direction and / or a large second phase alloy precipitation down to 10 μm. Targets with strong 200 or 220 crystal directivity result in films with poor uniformity. Therefore, the target preferably has a random or weak direction. Poor conductivity of the large second phase precipitation results in local arcing during sputtering, which causes large particles to be deposited on the wafer or high particle density.

In conventional target cathode assemblies, the target is attached to a non-adhesive backing plate, typically aluminum or copper, to form a parallel interface between the backplate and the sputter target in the assembly. The backing plate provides a means for maintaining the target in the sputtering chamber and provides structural stability to the target. The backplate is also generally water cooled to dissipate heat generated by ion bombardment of the target. In order to achieve good thermal electrical contact between the target and the backplate, these members are generally attached to each other using welding, soldering, diffusion bonding, clamping, screw fasteners or epoxy cement, or the like.

Solder joints are likely to separate during sputtering operations. In addition, because the soldering temperature is relatively low, the temperature range at which the target can be operated during sputtering is small. Therefore, solder bonded assemblies are more expensive and users spend a lot of time because the target must be used at a lower voltage level, and therefore the sputtering rate must be reduced to prevent separation of the target from the backplate.

Diffusion bonding with a roughened surface, such as by pretreatment or the like, provides stronger bonding but is time consuming to manufacture. In particular, since diffusion bonding proceeds at high temperatures, a change occurs in the microstructure obtained during the preliminary bonding process. Thus, even if fine particle size or random orientation can be achieved in the target fabrication step, the properties are lost by current diffusion bonding techniques. In copper and aluminum targets, the high temperatures applied during diffusion bonding have the effect of nearly doubling the particle size. Thus, variations and separation of microstructure and metallurgical properties are a serious disadvantage of conventional diffusion bonding techniques, which makes it undesirable to use them for copper target assemblies in sputter targets where small, uniform particles are desired.

In addition, using a monolithic sputter target without a backplate also makes it difficult to continually increase the target diameter needed to sputter large silicon wafers, and it is difficult to increase the required purity of the target material, both of which are monolithic. This increases the manufacturing cost of the food target.

Accordingly, there is a need to provide a method of manufacturing a copper target assembly having a sputter target of fine, equiaxed, uniform particle structure and random crystallographic structure strongly bonded to a nonmagnetic backplate.

According to the present invention, the metallurgical characteristics and particle size of the sputter target are not significantly changed by the bonding process, and the fine and random orientation directions bonded to the backplate by explosion bonding are formed so that the atomic bonding is formed between the target and the backplate. Provided is a high purity copper or copper alloy sputter target having particles of uniform size. To this end, in accordance with the principles of the present invention, high purity copper or copper alloy material is heated to at least 500 ° C. for at least 1 hour and then hot processed to apply at least about 40% strain. Thereafter, the material is additionally cold worked so that at least 40% additional strain is applied to form the target blank. The target blank is then annealed at a temperature of at least 300 ° C. for at least about 1 hour. The process according to the invention forms a preferred final sputter target having a fine and uniform particle size and having a random orientation. The surface of the target blank is preferably planarized, such as by pressing between two metal plates, and one or more of these planarized faces may be formed by one or more controlled explosions to maintain the microstructure of the target material. Explosion-bonded to the backplate of a suitable material. Sputter targets prepared and bonded according to the principles of the present invention have particles of size less than about 100 μm, preferably less than 50 μm, evenly distributed throughout the target and have a random crystallographic orientation. In addition, the particles of the sputter target have a aspect ratio of less than about 1.5, preferably less than about 1.0. Copper or copper alloy sputter targets processed according to the principles of the present invention provide high deposition rates, minimal particle generation during sputtering, and high film uniformity. In addition, by using explosive bonding techniques, the bond between the target and the backplate is significantly stronger, minimizing separation during sputtering, and also avoiding changes in the metallurgical properties of the sputter target during the bonding process.

The above and other objects and advantages of the present invention will become more apparent from the following detailed description.

High-purity copper or copper alloy sputter targets having fine, uniform particles and random orientation directions are produced by processes including heating, high temperature processing, cold working and annealing. This sputter target is bonded to the backplate by explosion bonding, whereby the size and direction of orientation of the particles of the sputter target material are not changed.

To this end, according to the principles of the present invention, the high purity copper or copper alloy material is heated for one hour at a temperature of about 500 ° C. or higher. The material may be ingots, slabs, plates or any other form suitable for subsequent machining operations. The material is preferably heated to a temperature in the range of about 500 ° C. to about 750 ° C. for about 1 to 2 hours. The atmosphere in which the material is heated is not of great importance. The material may be heated under routine conditions or under a protective atmosphere to minimize oxidation.

The copper or copper alloy material is then hot worked to undergo a strain of at least 40%, preferably about 50 to 70%, which is suitable for hot pressing, hot forging, hot rolling, isochannel angular extrusion or metal working operations. It is performed by some other way. The amount of processing used here is defined as the ratio between the pre-process thickness and the thickness reduction in terms of 100%, or as the amount of shear deformation applied to the material. The high temperature processing can be performed with an intermediate annealing step or without an intermediate annealing step. In addition, the atmosphere in which the material is hot processed is not critical. The hot processed material may then be cooled to near room temperature by air cooling, oven cooling, water cooling or cooling with other liquid media.

The hot worked material is then cold worked to a strain amount of at least about 40%, preferably about 50 to 70%, under ordinary conditions to form a target blank of final thickness. Known cold working techniques such as cold rolling, isochannel angular extrusion, forging and extrusion can be used for this purpose.

After cold working, the target blank is annealed for at least 1 hour at a temperature of about 300 ° C. or more, so that the target blank has the desired final microstructure with final fine uniform particles and random orientation. The particles preferably have a aspect ratio of about 1.5, preferably less than 1.0, defined as the ratio between the length and width of the particles, which is a property of equiaxed particles. The target blank is preferably annealed for about 1 to 4 hours at a temperature in the range of about 300 ° C to about 500 ° C. When a heating step is included, the target may be annealed under normal conditions or annealed in a protective atmosphere to minimize oxidation of the target material. The upper and lower end surfaces of the target blank may be flattened at elevated temperatures to avoid imparting additional processing to the target material, which is sufficient to flatten the surface but does not reduce the thickness of the target. By pressing between two opposing plates.

Since the process described above provides a desirable target microstructure that achieves minimal particle formation and good film uniformity during sputtering, additional manufacturing steps to complete the target assembly should be able to minimize deformation of the microstructure. In particular, the technique of joining the target to the backplate, and when machining the target to final dimensions, should avoid the addition of additional processing or high temperatures to the target material.

Thus, according to an additional principle of the invention, the target blank is exploded bonded to a backplate made of copper, aluminum or any other suitable metal or alloy. Suitable materials are those having good thermal conductivity, high strength, modulus of elasticity, and their coefficient of thermal expansion similar to copper. The explosive bonding comprises one or more controlled to position the surface of the target proximate to the surface of the backplate (ie, with a small gap therebetween) and to accelerate one or more of the surfaces towards each other. Is achieved by generating an explosion. The explosion bonding method is Paul S. filed as the same. It is described in detail in a US patent application entitled "Method for Bonding Sputtering Targets to Backplates" by Gilman et al.

By the rerun explosion bonding method, a strong atomic / metallurgical junction in the form of corrugated tissue is generated at the interface between the sputter target and the backplate, and the metallurgical properties of the backplate material or sputter target, except for local deformations occurring at the corrugated junction interface. Does not cause a change. The explosion bonding process is carried out at an un elevated temperature, and the heat generated from the process does not have enough time to transfer to the backplate and the components of the target metal, so that an increase in heat to cause particle growth may occur with the target. It does not occur on the backplate metal. Thus, strong bonding is achieved while the fine, directional particles produced by processing the target blank are not changed by the explosion bonding process.

(Example)

The pure copper material is heated to a temperature of 650 ° C. for about 1 hour under ordinary conditions. The material is then 60% hot flashed under ordinary conditions without intermediate annealing. The pressed material is then cooled in air and reduced by 60% with cold rolling. The target blank is then annealed at 350 ° C. for 2 hours in normal conditions, flattened between two opposing plates and exploded bonded to an aluminum backplate. The sputter target / backplate assembly has an average particle size of about 25 μm and a aspect ratio of 0.95, which is obtained during target processing and maintained during the explosion bonding process. The crystallographic structures observed have equal ratios in the 111, 200, 220 and 311 directional directions.

Although the invention has been described in detail by way of example, the appended claims are not limited to these details. Those skilled in the art will readily appreciate additional advantages and modifications. Accordingly, the present invention should not be limited to the details of the representative methods and apparatus illustrated in this description. Accordingly, these details may be modified without departing from the spirit and scope of the applicant's invention.

In accordance with the present invention there is provided a copper sputter target that provides high deposition rates, minimal particle generation during sputtering, and high film uniformity. In addition, by using explosive bonding techniques, the bond between the target and the backplate is significantly stronger, minimizing separation during sputtering, and also avoiding changes in the metallurgical properties of the sputter target during the bonding process.

Claims (10)

Heating the material selected from the group consisting of copper and copper alloy to at least about 500 ° C. for about 1 hour, Hot working the material to apply at least about 40% strain; Cold working the hot worked material to apply at least about 40% strain to form a target blank; Annealing the target blank at a temperature of about 300 ° C. or more for about 1 hour to obtain fine and uniform particles in a random direction in the target blank; A method of manufacturing a copper sputtering target having fine and uniform particles in a random direction, comprising exploding bonding the target blank to the backplate such that the fine and uniform particles in the direction of direction in the target blank are substantially maintained. The method of claim 1, wherein the material is heated at a temperature between about 500 ° C. and about 750 ° C. for about 1 to 2 hours, The target blank is annealed for about 1 to 4 hours at a temperature between about 300 ℃ to about 500 ℃. Heating a material selected from the group consisting of copper and copper alloys at least about 500 ° C. for at least about 1 hour, Hot working the material to apply at least about 40% strain, Cooling the material at room temperature substantially; Cold working the hot worked material to apply at least about 40% strain to form a target blank; Annealing the target blank at an elevated temperature of at least about 300 ° C. for at least about 1 hour to ensure that the target blank has fine and uniform particles in a random direction; Planarizing the target blank at an elevated temperature, A method of manufacturing a copper sputtering target having fine and uniform particles in a random directing direction comprising exploding bonding the target blank to a backplate such that the fine and uniform particles in a random directing direction in the target blank are substantially maintained. The method of claim 3, wherein the material is heated at a temperature between about 500 ° C. and about 750 ° C. for about 1 to 2 hours, The target blank is annealed for about 1 to about 4 hours at a temperature between about 300 to about 500 ° C. A sputter target composed of a material selected from the group consisting of copper and copper alloys, A back plate atomically bonded to the surface of the sputter target, The sputter target is a copper target / backplate assembly having particles of less than about 100㎛ size uniformly diffused throughout the target, and having a random crystallographic orientation. 6. The copper target / backplate assembly of claim 5, wherein the particles of the sputter target have a aspect ratio of less than about 1.5. The copper target / backplate assembly of claim 5, wherein the particles of the sputter target have a size of less than about 50 μm. A sputter target composed of a material selected from the group consisting of copper and copper alloys, A back plate atomically bonded to the surface of the sputter target, The sputter target has a particle size of less than about 100㎛ uniformly diffused throughout the target, and has a random crystallographic orientation, The sputter target heats a copper or copper alloy material at about 500 ° C. or more for about 1 hour or more, hot processing the material to a deformation amount of at least about 40%, and at least about 40% of the hot processed material. Cold working to a strain to form a target blank, and annealing the target blank for about 1 hour or more at a temperature of about 300 ° C. or more, The bonding is achieved by explosion bonding, and wherein the crystallographic orientation and size of the particles of the sputter target are not deformed by explosion bonding. The copper target / backplate assembly of claim 8, wherein the particles of the sputter target have a aspect ratio of less than about 1.5. The copper target / backplate assembly of claim 10, wherein the particles of the sputter target have a particle size of less than about 50 μm.