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  • Development Of Magnetron Sputtering Titanium Target Material
    Nov 07, 2018

    Development of magnetron sputtering titanium target material

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    As an important functional film material in the field of electronic information, high-purity titanium has rapidly increased in recent years with the rapid development of China's integrated circuits, flat panel displays, and solar energy industries. Magnetron sputtering technology (PVD) technology is one of the key technologies for the preparation of thin film materials. High-purity titanium sputtering targets are the key consumables in the magnetron sputtering process and have broad market application prospects. As a high value-added coating material, titanium target has strict requirements in terms of chemical purity and microstructure. It has high technical content and difficult processing. China's target manufacturing enterprises started relatively late in the field of high-end target manufacturing. The purity of raw materials is relatively backward, and there are certain gaps in the core process technologies such as tissue control and process molding. For the downstream high-end applications, the development of high-performance titanium sputtering targets is an important measure to realize the independent research and development of key materials in the electronic information manufacturing industry and to promote the transformation and upgrading of the titanium industry to the high-end.


    Titanium target application and performance requirements

    Magnetron Sputtering Ti targets are mainly used in the electronics and information industries, such as decorative coatings for integrated circuits, flat panel displays and home improvement automotive industries, such as glass decorative coatings and wheel decorative coatings. Different industries have different requirements for Ti targets, including: purity, microstructure, welding performance, and dimensional accuracy. The specific requirements are as follows:

    1) Purity: Non-integrated circuit: 99.9%; For integrated circuits: 99.995%, 99.99%.

    2) Microstructure: For non-integrated circuits: the average grain size is less than 100 μm; for integrated circuits: the average grain size is less than 30 μm, and the ultrafine grain average grain size is less than 10 μm.

    3) Soldering performance: For non-integrated circuits: brazing, monomer; for integrated circuits: monomer, brazing, diffusion soldering.

    4) Dimensional accuracy: Non-integrated circuit: 0.1mm; Integrate circuit: 0.01mm.

    1.1 Ti target for integrated circuits

    The purity of integrated circuit Ti targets is mainly greater than 99.995%, and currently relies mainly on imports. In 2013, China's IC industry achieved sales revenue of 250.8 billion yuan and imports amounted to 231.3 billion US dollars, making it the largest imported commodity in China for the first time. In 2014, the sales revenue of the integrated circuit industry was 267.2 billion yuan, and the import volume still reached 217.6 billion US dollars. Targets for integrated circuits account for a large share of the global target market.

     Ti target raw materials: High-purity Ti production is mainly concentrated in the United States, Japan and other countries, such as the United States Honeywell, Japan's Toho, Japan's Osaka titanium industry; domestic start later, after 2010 Beijing Nonferrous Metal Research Institute, Zunyi Titanium, Ningbo Chuangrun has successively launched domestically produced high-purity Ti products, but the stability of the products has yet to be improved.

     Structure development of Ti target: The early chip foundry has a large profit margin, mainly using a 100-150mm magnetron sputtering machine, and the power is small, the sputtering film is thick, the chip size is large, and the performance of the single target is large. It can meet the requirements of the use of the machine at that time. At that time, the Ti target for integrated circuits was mainly 100-150mm monomer and combined target, such as the typical 3180 type and 3290 type target. In the second stage, according to Moore's Law, the chip line width is narrowed. The chip foundry mainly uses a 150-200mm sputtering machine. In order to increase the profit margin, the sputtering power of the machine is increased, which requires the target size to increase. At the same time, it maintains high thermal conductivity, low price and certain strength. In this period, the Ti target is mainly composed of aluminum alloy back plate diffusion welding and copper alloy back plate brazing and welding, such as typical TN, TTN type, Endura 5500 type and other targets. . In the third stage, with the development of integrated circuits, the chip line width is further narrowed. At this time, the chip foundry mainly uses a 200-300mm sputtering machine. In order to further increase the profit margin, the sputtering power of the machine is increased, which requires the target. The size is increased while maintaining high thermal conductivity and sufficient strength. In this period, the Ti target is mainly made of copper alloy back plate diffusion welding, such as the mainstream SIP type target.

    Ti target processing and manufacturing: The early domestic and international markets were basically monopolized by large target manufacturers such as the United States and Japan. After 2000, the domestic manufacturing industry gradually entered the target market, and began to import high-purity Ti raw materials to process low-end targets. In recent years, domestic Ti target manufacturing enterprises have developed rapidly, and their market share has gradually expanded to Taiwan, Europe and the United States, etc. If there are two companies, Yanyijin and Jiangfeng Electronics, focus on target manufacturing for many years. Domestic target manufacturing companies are also working with domestic magnetron sputtering machine manufacturers to develop targets to promote the development of the domestic integrated circuit magnetron sputtering industry.

    1.2 Ti target for flat panel display

    The flat panel display includes a liquid crystal display (LCD), a plasma display (PDP), an electroluminescent display (E-L), and a field emission display (FED).

    At present, the liquid crystal display LCD market is the largest in the flat panel display market, with a share of more than 90%. LCD is considered to be the most promising flat panel display device, and its appearance has greatly expanded the application range of displays. From notebook monitors, desktop monitors, high-definition LCD TVs and mobile communications, various new LCD products are impacting. People's living habits and promote the rapid development of the world's information industry. TFT-LCD technology is a technology that combines microelectronic technology and liquid crystal technology. It has become the mainstream technology of flat display, and it is divided into AL-Mo, AL-Ti, Cu-Mo and other processes.

    The film of the flat panel display is mostly formed by sputtering. Targets such as Al, Cu, Ti, and Mo are the main metal targets for flat panel displays, and the purity of Ti targets for flat panel displays is greater than 99.9%. This raw material can be made in China. The size of the planar Ti target for the TFT-LCD6 generation line is relatively large, and the structure uses a copper alloy water-cooled backing plate target, and a CLP panda is used.

    At present, China's self-built world's highest generation line - Hefei 10.5 generation line mainly produces large-size ultra-high-definition liquid crystal display, with a design capacity of 90,000 glass substrates per month, glass substrate size of 3370×2940mm, total investment of 40 billion yuan, 2018 The second quarter of the year, the use of sputtering machines and the corresponding technology and targets is still uncertain.

    2 Magnetron sputtering Ti target preparation technology

     According to the production process, the raw material preparation technology of the Ti target can be divided into two categories: electron beam melting smelting (abbreviation EB blank) and vacuum consumable electric arc furnace smelting blank (abbreviation (VAR) blank). In the target preparation process, In addition to strict control of material purity, density, grain size and crystal orientation, the heat treatment process conditions and subsequent molding processes must be strictly controlled to ensure the quality of the target.

     For high-purity Ti raw materials, the high-melting impurity elements in the Ti matrix are usually removed by melt electrolysis, and further purified by vacuum electron beam melting. Vacuum electron beam melting is to bombard the metal surface with a high-energy electron beam, and then the temperature gradually rises until the metal melts. The element with large vapor pressure will preferentially volatilize, and the element with small vapor pressure remains in the melt, and the impurity element and the matrix The greater the difference in vapor pressure, the better the purification effect. The vacuum refining after melting has the advantage of removing impurity elements in the Ti matrix without introducing other impurities. Therefore, when 99.99% of electrolytic Ti is smelted by electron beam in a high vacuum environment (10-4 or more), the impurity element (Fe, Co, Cu) whose saturated vapor pressure in the raw material is higher than the saturated vapor pressure of the Ti element itself will preferentially volatilize. The content of impurities in the matrix is reduced to achieve the purpose of purification. A combination of the two methods can provide a high purity metal Ti having a purity of 99.995 or more.

    For the purity of 99.9% Ti raw materials, the 0-stage sponge Ti is smelted in a vacuum consumable electric arc furnace, and then hot forged blanks are used to form a small-sized blank. The metal Ti raw materials prepared by the two methods are controlled by thermomechanical deformation to control the microstructure of the entire sputtering surface, and then processed into a magnetron sputtering Ti target for processing integrated circuits through machining, binding, cleaning and packaging processes. For a Ti target with a particularly high requirement for a 300 mm machine, the sputtering surface of the target before pre-packaging is also pre-sputtered to reduce the target time (Burning Time) of the target mounted on the sputtering machine.

    The target prepared by the integrated circuit Ti target preparation method has a complicated process and a relatively high cost.

    3. Technical requirements for Ti targets

    In order to ensure the quality of the deposited film, the quality of the target must be strictly controlled. After a large number of practices, the main factors affecting the quality of the Ti target include purity, average grain size, crystal orientation and structural uniformity, geometry and size.


    3.1 purity

    The purity of the Ti target has a great influence on the properties of the sputtered film.

     The higher the purity of the Ti target, the less the impurity element particles in the sputtered Ti film, resulting in better film properties, including corrosion resistance and electrical and optical properties. However, in practical applications, different uses of Ti targets have different purity requirements. For example, Ti targets for general decorative coatings are not critical in terms of purity, and Ti targets have a much higher purity requirement in fields such as integrated circuits and display bodies. The target serves as a cathode source in sputtering, and impurity elements and pore inclusions in the material are the main sources of contamination of the deposited film. The stomatal inclusions are basically removed during the non-destructive testing of the ingot. The pores that are not removed will cause the tip discharge phenomenon (Arcing) during the sputtering process, which will affect the quality of the film. The impurity element content can only be analyzed in the full element. The test results show that the lower the total impurity content, the higher the purity of the Ti target. In the early days, there was no standard for high-purity titanium sputtering targets in China, which was based on the requirements of Ti target manufacturers at home and abroad. After 2013, the standard "YS/T893-2013 high-purity titanium sputtering targets for electronic films" was issued. The requirements for different impurity content and total impurity content of three purity Ti targets are specified. This standard is gradually standardizing the purity requirements of the chaotic Ti target market.

    3.2 Average grain size

    Usually, the Ti target has a polycrystalline structure, and the grain size can be on the order of micrometers to millimeters. The sputtering rate of the fine-sized crystal target is faster than that of the coarse-grain target, and the target having a small difference in grain size on the sputtering surface is splashed. The thickness distribution of the deposited film is also relatively uniform. It has been found that if the grain size of the titanium target is controlled to be less than 100 μm and the change in grain size is kept within 20%, the quality of the film obtained by sputtering can be greatly improved. The average grain size of the Ti target for integrated circuits is generally required to be within 30 μm, and the average grain size of the ultrafine grain Ti target is 10 μm or less.


    3.3 Crystal orientation

    The metal Ti is a close-packed hexagonal structure, and since the Ti target atoms are preferentially sputtered in the direction in which the atoms are most closely arranged in the sputtering, the method of changing the crystal structure of the target can be achieved in order to achieve the highest sputtering rate. Increase the sputtering rate. At present, most of the integrated circuit Ti target sputtering surface {1013} crystal face family is more than 60%, the grain orientation of the target produced by different manufacturers is slightly different, and the crystal orientation of the Ti target is uniform to the thickness of the sputtered film layer. The impact is also greater. The film size of the flat display and the decorative coating is relatively thick, so the grain orientation requirements of the corresponding Ti target are relatively low.


    3.4 Structural uniformity

    Structural uniformity is also one of the important indicators for examining the quality of targets. For the Ti target, not only the sputtering plane of the target but also the normal direction component, grain orientation and average grain size uniformity of the sputtering surface are required. Only in this way, the Ti target can obtain a Ti film having uniform thickness and reliable quality and uniform grain size in the same time period.


    3.5 Geometry and dimensions

    Mainly reflected in processing accuracy and processing quality, such as processing size, surface flatness, roughness and so on. If the mounting hole angle deviation is too large, it cannot be installed correctly; the small thickness will affect the service life of the target; the sealing surface and the sealing groove size will be too rough, which will cause problems in the vacuum after the target is installed, causing serious water leakage; The roughening treatment of the surface can make the surface of the target full of convex tips. Under the action of the tip effect, the potential of these raised tips will be greatly increased, thereby breaking the dielectric discharge, but the excessive protrusion is for sputtering. The quality and stability are unfavorable.


    3.6 welding joint

    At present, there are many papers on the research of Ti/Al dissimilar metal diffusion welding. Generally, the diffusion welding of high melting point titanium and low melting point aluminum materials is mainly based on vacuum diffusion bonding technology of one-way or two-way pressure or thermal isostatics. The pressure technology realizes the high-pressure medium-low temperature direct diffusion connection of titanium and aluminum metal materials. There are many domestic manufacturers of Ti/Cu and Cu alloy welding, but there are few research papers.

    4, Ti target prospects

    Global target manufacturing bases are rapidly gathering in Asia. With the rapid development of high-tech industries such as domestic semiconductor integrated circuits, flat panel displays and decorative coatings, China's target market is expanding, and it has gradually become one of the world's largest demand areas for thin film targets. Development offers opportunities and challenges.

    In recent years, under the leadership of the integrated circuit industry fund, the national science and technology major projects (01, 02, 03) and local funds, the investment in the integrated circuit industry can be described as hot. According to statistics, only in the two years from 2015 to 2016, domestic It has announced that there are as many as 44 wafer production lines under construction or planned to start, including 300mm, 18mm, 200mm20, and 150mm. Driven by this huge market demand, the target industry will surely attract the attention and attention of relevant research institutes and enterprises in China, and invest in manpower, material resources and financial resources to develop and produce magnetically controlled splash targets.

     As a unique branch of the target field, Ti targets are used in both semiconductor Al and Cu processes, and are widely used in the liquid crystal display industry and decorative coating industry. At present, the bases for R&D and production of Ti targets are mainly concentrated in Beijing, Guangdong, Jiangsu, Zhejiang and Gansu. Due to the limitations of target raw material purity, production equipment and process research and development technology, China's Ti target manufacturing industry is still in its infancy. Domestic Ti target production enterprises are basically low in quality and technology, using traditional processing methods and relying on price to win. Low-grade sputtering target producers, or limited-cost foundry processing plants. The production scale is small, the variety is single, and the technology is still unstable. So far, China (including Taiwan, China) has only a few professional companies that produce targets, such as Yanyijin, Jiangfeng Electronics, etc., which produce Ti targets far. Far from meeting the needs of market development, a large number of Ti targets still need to be imported from abroad. The raw materials of high-purity metal Ti targets have already achieved breakthroughs, but most of them have to rely on imports.

     As a special-purpose material, Ti target has a strong application purpose and a clear application background. Metallurgical purification technology for detachment from metal Ti, EB vacuum melting technology, non-destructive testing technology for Ti ingots, impurity analysis technology for high-purity Ti, preparation technology for Ti target, preparation technology for sputtering machine, sputtering process and film performance testing technology The study of the Ti target itself does not make any sense. The development and production of Ti targets and subsequent application improvements involve a whole industry chain from upstream raw materials to industrial midstream equipment manufacturers and target manufacturers to develop and downstream Ti target coating chips. The relationship between the performance of the Ti target and the properties of the sputtered film is beneficial to obtaining the film properties that meet the application requirements, and is also beneficial for better use of the target, fully exerting its effects, and promoting the development of the target industry.

    At present, the integrated circuit industry is booming in China. Opportunities and challenges coexist. If we can't seize the opportunity to localize target manufacturing, film manufacturing and testing equipment, the gap between China and the international level will surely become larger. It is not only unable to recapture the domestic market occupied by foreign investors, but also to compete in the international market.