Preparation method of high-purity planar copper target material

Abstract

The invention relates to the technical field of semiconductor sputtering, and provides a preparation method of a high-purity planar copper target material, which comprises the following steps: preheating a high-purity copper ingot, and forging and stretching the high-purity copper ingot in the preheating process; carrying out first heat treatment on the forged and stretched high-purity copper ingot; preheating the high-purity copper ingot subjected to the first heat treatment again, and forging and stretching the preheated copper ingot; carrying out secondary heat treatment on the forged and stretched copper ingot; performing cold forging on the high-purity copper ingot subjected to the second heat treatment to form a copper plate blank, and performing third heat treatment on the copper plate blank to further refine the crystal grains of the copper plate blank and further rationalize the crystal grain orientation; then rolling the copper plate blank to form a copper target blank, and micronizing crystal grains again through extrusion deformation in the rolling process; and finally, the copper target blank is machined, and the high-purity copper target is formed.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor sputtering, and in particular to a method for preparing a high-purity planar copper target material. Background Art

[0002] With the rapid development of the electronics and information industries, semiconductor manufacturing and ultra-large-scale integrated circuits have increasingly higher requirements for the materials of sputtering metal targets, which have become the main factor affecting the performance of chip applications. Among them, copper targets are widely used due to their extremely high electrical conductivity, excellent thermal conductivity, corrosion resistance, resistance to electromigration and extremely low dielectric constant. They are used to reduce the resistance of interconnects between electronic devices and improve their computing speed. They have become an indispensable key material for the development of semiconductors and related microelectronics industries.

[0003] The working principle of magnetron sputtering is to use an accelerated ion flow with high energy to bombard the surface of the target material. The sputtered target atoms are deposited on the surface of the substrate in the form of a thin film, thereby realizing the coating process of the substrate material. Magnetron sputtering is used in various chips, displays, information storage and various electronic control devices. In the prior art, copper target is a commonly used target in the vacuum sputtering process.

[0004] For the organizational structure of the target material, producing a copper target with small and uniform grains, dense interior, no defects and small grain orientation difference has a great influence on the performance and application environment of sputtering products, so the requirements for the composition and preparation process of the material are extremely strict. The copper target with fine grain size has a more uniform thickness distribution of the sputtered film and can improve its sputtering rate. Obtaining a similarly oriented organization on the basis of controlling the grain size is also an important condition for achieving high-quality coating. In the prior art, the preparation of copper target materials is mainly to control its microstructure organization through the cooperation of deformation processes such as hot forging, rolling, and static pressing to prepare high-purity target materials with fine grain size, good flatness and surface roughness, thereby improving its target material utilization rate and reducing production costs. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing a high-purity planar copper target material to solve the problems in the background technology.

[0006] Based on the above purpose, the present invention provides a method for preparing a high-purity planar copper target, characterized in that it includes the following steps:

[0007] Step 1, using a copper ingot with a purity greater than 99.999%, preheating the high-purity copper ingot, and forging the high-purity copper ingot during the preheating process;

[0008] Step 2, performing a first heat treatment on the forged high-purity copper ingot;

[0009] Step 3, performing a second forging on the high-purity copper ingot after the first heat treatment;

[0010] Step 4, performing a second heat treatment on the high-purity copper ingot that has undergone the second forging and stretching;

[0011] Step 5, cold forging the high-purity copper ingot subjected to the second heat treatment into a copper plate blank;

[0012] Step 6, performing a third heat treatment on the cold forged copper plate blank;

[0013] Step seven, rolling the copper plate blank subjected to the third heat treatment to form a copper target material blank;

[0014] Step eight, mechanically processing the copper target blank to form a high-purity copper target.

[0015] Preferably, the preheating temperature in step 1 is 700° C.-900° C., and the insulation time is 2-4 hours.

[0016] Preferably, the temperature of the first heat treatment in step 2 is 200°C-500°C, and the holding time is 0.5-3h:

[0017] Preferably, the temperature of the second heat treatment in step 4 is 200° C.-450° C., and the holding time is 0.5-2 h.

[0018] Preferably, the temperature of the third heat treatment in step six is ​​200° C.-400° C., and the holding time is 0.5-1 h.

[0019] Preferably, the rolling pressure in step seven is 2000KN-5000KN.

[0020] Preferably, the step seven rolling is performed by reversing rolling multiple times.

[0021] Preferably, the copper target material blank needs to be leveled before mechanical processing.

[0022] Preferably, the forging and stretching is performed in a three-punch and three-pull manner, with forging being performed in one direction each time, and the directions of the three forging and stretching are perpendicular to each other.

[0023] The beneficial effects of the present invention are as follows: the present invention first preheats the high-purity copper ingot and forges the high-purity copper ingot during the preheating process to initially destroy the coarse grains; then the forged high-purity copper ingot is subjected to a first heat treatment to release the thermal stress of the forged copper ingot, thereby refining the grains and rationalizing the grain orientation; then the high-purity copper ingot subjected to the first heat treatment is preheated again, and the preheated copper ingot is forged to destroy the coarse grains inside the high-purity copper ingot structure again, thereby refining the grains; then the forged copper ingot is subjected to a second heat treatment , so that the grains are evenly refined and the orientation is reasonable; the high-purity copper ingot after the second heat treatment is cold forged to form a copper plate blank and the copper plate blank is heat treated for the third time, so that the grains of the copper plate blank are further refined and the grain orientation is further rationalized; then the copper plate blank is rolled to form a copper target material blank, and the grains are further refined and the grain orientation is rationalized again through extrusion deformation during the rolling process; finally, the copper target material blank is machined to form a high-purity copper target material to meet the size requirements for semiconductor sputtering.

[0024] The temperatures of the first heat treatment and the second heat treatment of the present invention are both 200°C-500°C, and the holding times are 0.5-3h and 0.5-2h respectively. If the temperature is too low, it is easy for the damaged grains to be difficult to form crystal nuclei. If the temperature is too high, the nucleated grains grow too large and fail to meet the requirements of grain refinement. If the holding time is too long, the crystal nuclei grow too large. If the holding time is too short, the high-purity copper ingot will be heated unevenly inside and outside.

[0025] The temperature of the third heat treatment of the present invention is 200° C.-400° C., and the holding time is 0.5-1 h, so that the grains of the copper plate blank after cold forging are further refined and the grain orientation is further rationalized.

[0026] The rolling pressure range of the present invention is 2000KN-5000KN. If the pressure is too high, the grain orientation will be flat, which is not conducive to the sputtering process and the control of the sputtering direction of the target material. If the pressure is too low, the grain refinement will not meet the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 is a metallographic structure diagram of a high-purity planar copper target prepared in a specific implementation manner;

[0029] Figure 2 It is a schematic diagram of a high-purity planar copper target prepared in a specific implementation manner. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0031] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0032] This embodiment provides a method for preparing a high-purity planar copper target, comprising the following steps:

[0033] The general purity requirement of semiconductor copper target is 4N5 (99.995%) or above, for example, 5N (99.999%) or 5N5 (99.9995%). Therefore, the purity of the high-purity copper ingot used is 5N (99.999%) or above, and 5N5 (99.9995%) copper ingot is preferred in this embodiment. In this embodiment, the shape of the high-purity copper ingot is preferably cylindrical, and its size can be cut by sawing machine based on the raw material to achieve a size that is easy to handle;

[0034] S1, leveling the copper target blank;

[0035] The leveling in this step first detects the surface flatness of the copper target blank. If the flatness meets the machining requirements, machining is performed; if it does not meet the requirements, the copper target blank is straightened and leveled by a straightening machine to achieve the flatness requirements before machining.

[0036] S2, preheating the high-purity copper ingot;

[0037] Before forging and stretching, the high-purity copper ingot is preheated. The preheating method is to put the high-purity copper ingot into a heating furnace and heat it to 890°C for 3 hours. In this temperature range, the high-purity copper ingot is conducive to subsequent forging and stretching. Specifically, if the temperature is too high, the grain size generated by recrystallization will be relatively large, so that the target material formed subsequently cannot meet the requirements of semiconductor sputtering. If the preheating temperature is too low, the subsequent forging and stretching will not be easy to process, and the effect on improving the internal performance of the high-purity copper ingot is not very obvious. Low-temperature forging and stretching will increase the risk of cracks. The forging and stretching process is mainly to make the copper ingot easy to plastically deform. The insulation time should not be too long. Long insulation time will cause the grain size generated by recrystallization of the copper ingot to be relatively large; short insulation time will cause uneven heating inside the copper ingot.

[0038] S3, then, the high-purity copper ingot in the preheating process is forged and stretched. The forging and stretching is to use an air hammer to beat the high-purity copper ingot along the surface of the high-purity copper ingot. The role of forging and stretching is to break the original coarse branch-shaped grains and columnar grains into fine grains, so that the original segregation, looseness, pores, slag inclusions, etc. inside the high-purity copper ingot are compacted, the inside of the copper ingot becomes more compact, and the plasticity and mechanical properties of the high-purity copper ingot are improved.

[0039] Considering that copper has a face-centered cubic structure, in order to destroy the coarse grains as quickly as possible in this step, the forging is carried out in a three-punch and three-pull manner, each time forging is carried out in one direction, and the directions of the three forgings are perpendicular to each other.

[0040] S4, the high-purity copper ingot after forging is subjected to the first heat treatment, the heat treatment temperature is 300°C, and the holding time is 1 hour. In this embodiment, within the temperature range of the first heat treatment, the broken grains after forging are recrystallized (the recrystallization temperature of pure copper is about 200°C-280°C). If the temperature is too low, it is easy for the damaged grains to be difficult to form crystal nuclei, and if the temperature is too high, the nucleated grains grow too large, which does not meet the requirements of grain refinement; if the holding time is too long, it will also cause the grains to grow too large, and if the holding time is too short, it will cause uneven heating inside and outside the high-purity copper ingot.

[0041] S5, after the first heat treatment, the high-purity copper ingot is preheated again, the high-purity copper ingot is placed in a heating furnace and heated to 890° C., kept warm for 1 hour, and the preheated copper ingot is forged and stretched to destroy the coarse grains inside the high-purity copper ingot structure again, so that the grains are refined;

[0042] S6, performing a forging and stretching process on the high-purity copper ingot in the preheating process again, and performing a second heat treatment after the forging and stretching;

[0043] The high-purity copper ingot that has been forged again is subjected to a second heat treatment, wherein the heat treatment temperature is 250°C and the heat preservation time is 2 hours. In the temperature range of the second heat treatment, the broken grains after forging are recrystallized (the recrystallization temperature of pure copper is about 200°C-280°C). If the temperature is too low, it is easy for the damaged grains to form crystal nuclei, and if the temperature is too high, the nucleated grains grow too large, which does not meet the requirements of grain refinement; if the heat preservation time is too long, the grains will grow too large, and if the heat preservation time is too short, the high-purity copper ingot will be heated unevenly inside and outside;

[0044] S7, cold forging the high-purity copper ingot after the second heat treatment to form a copper plate blank and performing a third heat treatment on the copper plate blank, so that the grains of the copper plate blank are further refined and the grain orientation is further rationalized;

[0045] The high-purity copper ingot after cold forging was subjected to a third heat treatment at a temperature of 250°C and a holding time of 0.5 hours, so that the grains of the copper plate blank after cold forging were further refined and the grain orientation was further rationalized.

[0046] S8, since the temperature of the third heat treatment will not make the nucleated grains grow too large, this temperature is suitable for plastic deformation of the copper plate blank, so the high-purity copper plate blank is rolled after the third heat treatment;

[0047] Copper is a face-centered cubic. During the magnetron sputtering process of the target material, atoms with a crystal orientation of (110) are easily sputtered to the sputtering substrate. In this step, the content of crystal grains with a crystal orientation of (110) formed by the high-purity copper target material is controlled by appropriate pressure. Too much pressure will cause the crystal grain orientation to be flat and elongated, and too little pressure will make the grain refinement fail to meet the requirements. In this step, when rolling the high-purity copper slab, it is preferred that a two-roll reversible rolling mill with a pressure range of 2000KN-5000KN is used for rolling, and the proportion of the crystal orientation (110) formed by the high-purity copper target material reaches 50%-80%.

[0048] The rolling process is implemented as follows: placing the high-purity copper sheet stock in a roller platform device and performing plastic deformation by extrusion molding. The rolling adopts forward extrusion, that is, the extrusion direction is consistent with the flow direction of the high-purity copper sheet stock. In addition, during the rolling process, the high-purity copper sheet stock needs to be reversed and rolled until the required size is controlled.

[0049] By reasonably controlling the extrusion rate and setting a suitable extrusion deformation rate, the forming size of the copper plate blank can be accurately controlled, further achieving the purpose of grain refinement and reducing the surface roughness of the target material, and preparing for the production of target materials that meet the size requirements.

[0050] S8, machining the copper target blank to form a high-purity copper target;

[0051] Machining includes rough machining, fine machining and other processes to produce target products that meet the requirements; among them, rough machining uses wire cutting to take out the round copper target, and then uses CNC to perform milling surface processing on the round target; fine machining uses a CNC lathe to fine-turn the surface of the rough-machined target, so that the surface roughness, accuracy and smoothness of the target meet the target requirements.

[0052] like Figure 1 and 2 As shown, the average grain size of the prepared planar copper target is 19um, the grains are evenly distributed and the density is high.

[0053] It should be understood by those skilled in the art that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-purity planar copper target, characterized in that: The following steps are included: Step 1, using a copper ingot with a purity greater than 99.999%, preheating the high-purity copper ingot, and forging the high-purity copper ingot during the preheating process; Step 2, performing a first heat treatment on the forged high-purity copper ingot; Step 3, preheating the high-purity copper ingot after the first heat treatment again, and performing a second forging after preheating; Step 4, performing a second heat treatment on the high-purity copper ingot that has undergone the second forging and stretching; Step 5, cold forging the high-purity copper ingot subjected to the second heat treatment into a copper plate blank; Step 6, performing a third heat treatment on the cold forged copper plate blank; Step seven, rolling the copper plate blank subjected to the third heat treatment to form a copper target material blank; Step eight, mechanically processing the copper target blank to form a high-purity copper target.

2. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: The preheating temperature in step 1 and step 2 is 700° C.-900° C., and the insulation time is 2-4 hours.

3. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: The temperature of the first heat treatment in step 2 is 200° C.-500° C., and the insulation time is 0.5-3 h.

4. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: The temperature of the second heat treatment in step 4 is 200°C-450°C, and the insulation time is 0.5-2h.

5. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: The temperature of the third heat treatment in step six is ​​200° C.-400° C., and the insulation time is 0.5-1 h.

6. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: The rolling pressure in step seven is 2000KN-5000KN.

7. The method for preparing a high-purity planar copper target according to claim 6, characterized in that: The step seven rolling is performed by reversing rolling for multiple times.

8. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: Before the copper target material blank is mechanically processed, the copper target material blank needs to be leveled.

9. The method for preparing a high-purity planar copper target according to claim 1, characterized in that: The forging and stretching is performed in a three-punch and three-pull manner, with forging being performed in one direction each time, and the directions of the three forging and stretching are all perpendicular to each other.

Images