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EnglishViews: 169 Author: Site Editor Publish Time: 2023-05-10 Origin: Site
When our target is damaged, there are two situations. If there is only a slight crack, we can bond the target to the back plate so it can be keep up used; if the damage is serious, the target will not be used, and we need to find the supplier to rework one. If it is "target poisoning", we can use an intermediate frequency source or radio frequency source to beat the target for an hour or two, then take out the target, polish it with sandpaper, remove the surface pollutants, and it will be restored.
Preparatory work
Sputtering Target crack
Firstly, we have to prepare a backing plate, it should be noted that the choice of the backing plate needs to be based on the characteristics of the target material, the reasonable choice andbonding of the target backing plate can improve the service life of the target and the efficiency of the coating, it also can improve the film coefficient achievement rate.
Backing plate materials: Copper, Aluminum, Titanium, Molybdenum, Stainless steel, etc.
Secondly, it is the choice of bonding types, the commonly three bonding types we used are adhesive, solder and high temperature welding (including brazing and diffusion welding). We need to choose the applicable bonding types according to the target material.
Sputtering Target “poisoning”
1. Preparing the vacuum environment, ensuring that the vacuum chamber does not leak, cleaning the interior, removing volatile components, etc;
2. Must use medium frequency power supply or RF power supply.
3. Sandpaper.
4. Dust interrupter with good vacuum performance.
Sputtering target damage can be divided into two types, one is physical fracture, that is, target cracking, target cracking usually occurs in ceramic sputtering targets such as oxides, carbides, nitrides and chromium, antimony, bismuth and the other brittle materials; the other is "target poisoning", which means that the target reacts and the composition changes. Reactive sputtering will deposit on the surface of the substrate, target and other structures, and the accumulation of film deposited on the target surface will cause target poisoning. For example, in the TiN process, the Ti target reacts with N2 to form TiN. After the process is completed, there is a layer of TiN on the surface of the Ti target. This phenomenon becomes target poisoning.
There is a difference between the cooling water temperature used in production and the actual water temperature of the coating line, which leads to cracking of the target during use. Generally speaking, slight cracks will not have a great impact on coating production. However, when the target has obvious cracks, the charge is easily concentrated on the edge of the crack, resulting in abnormal discharge on the surface of the target. Discharging will lead to slag falling, abnormal film formation, and increased product scrapping.
Ceramic or brittle material targets always contain inherent stress. These internal stresses can be generated during the development of target manufacturing. Furthermore, these stresses are not completely relieved by the annealing process, as this is an inherent property of these materials. During sputtering, gas ions are bombarded to transfer their momentum to target atoms, providing enough energy to escape from the lattice. This exothermic momentum transfer raises the temperature of the target, potentially reaching extremely high temperatures at the atomic level. These thermal shocks will increase the internal stress already developed in the target by many times. In this case, the target may break if heat is not properly dissipated.
Target poisoning is due to the fact that positively charged ions gather on the target surface during the sputtering process and are not neutralized. The negative bias voltage on the target surface gradually decreases, and finally the strike does not work. The main factor affecting target poisoning is the ratio of reactive gas to sputtering gas. Excessive reactive gas will lead to target poisoning.
During the reactive sputtering process, the sputtering channel region on the target surface is covered by reaction products or the reaction products are stripped to re-expose the metal surface. If the rate at which the compound is formed is greater than the rate at which the compound is stripped, the area covered by the compound increases. In the case of a certain power, the amount of reaction gas involved in compound formation increases, and the compound formation rate increases.
If the amount of reaction gas increases excessively, the compound coverage area increases, and the reaction gas flow rate cannot be adjusted in time, the rate of compound coverage area increase cannot be suppressed, and the sputtering channel will be further covered by the compound. When the sputtering target is completely covered by the compound , the target is completely poisoned.
Positive ion accumulation: when the target is poisoned, a layer of insulating film is formed on the target surface. When the positive ions reach the cathode target surface, due to the barrier of the insulating layer, they cannot directly enter the cathode target surface, but accumulate on the target surface, which is easy to produce arc discharge caused by cold field ---Arc strike, so that the cathode sputtering cannot go on.
Anode disappearance: When the target is poisoned, an insulating film is also deposited on the grounded vacuum chamber wall, and the electrons reaching the anode cannot enter the anode, resulting in the phenomenon of anode disappearance.
Its physical explanation is as follows:
❶ In general, the secondary electron emission coefficient of metal compounds is higher than that of metals. After the target is poisoned, the surface of the target is all metal compounds. After being bombarded by ions, the number of secondary electrons released increases, which improves the conduction of the space ability, and reduces the plasma impedance, resulting in a lower sputtering voltage, thereby reducing the sputtering rate. The sputtering voltage of magnetron sputtering is between 400V-600V. When target poisoning occurs, the sputtering voltage will be significantly reduced.
❷ The sputtering rate of the metal target and the compound target is different. Generally, the sputtering coefficient of the metal is higher than that of the compound, so the sputtering rate is low after the target is poisoned.
❸ The sputtering efficiency of reactive sputtering gas is inherently lower than that of inert gas, so when the proportion of reactive gas increases, the overall sputtering rate decreases.
Generally, slight cracks will not have a great impact on coating production. However, when the target has obvious cracks, the charge is easily concentrated on the edge of the crack, resulting in abnormal discharge on the surface of the target. Discharging will lead to slag falling, abnormal film formation, and increased product scrapping.
To prevent target cracking, an important consideration is heat dissipation. This requires a water cooling mechanism to remove unwanted thermal energy from the target. It can bring thermal shock to the target by increasing the power in a short time. In addition, it is also possible to bond the target to a backing plate, which not only provides support for the target, but also facilitates better heat exchange between the target and the water. If the target is cracked but bonded to the backing plate, it can still be used without issue.
Maybe you can use a copper plate to paste the fragments of the target and then polish the target so that the broken areas have minimum exposure to plasma. The second step is very important because when the plasma hits the target area, the power suddenly breakdown to zero. Obviously, the film quality will be affected if breakdown is frequent. Although it may help solve the problem when the target is broken, it is still a remedy. To avoid target from breaking, you need to give a target bonding service to the target. It is necessary for those brittle targets.
Many materials perform better when bonded. Bonding the target to the backplate allows for better cooling, increases target stability, and allows continued sputtering after minor cracks have occurred.
The commonly used target bonding methods are glue, solder and high temperature welding (including brazing and diffusion welding).
Adhesive bonding
Silver glue bonding is the lowest cost technique and uses specialized thermally and electrically conductive epoxies to bond the target to the backplane. This technique requires surface treatment of the target and backplate, and the bonded target has low residual stress and is easy to rework. However, silver colloidal bonding has the disadvantage of relatively high thermal resistance, which limits the usable power density of the sputtering target and thus limits the deposition rate.
Solder bond
Solder has low thermal resistance relative to silver adhesive bonding and can operate at higher deposition rates. The most common solder filler material we used is indium, it has the advantage of having high thermal conductivity and a relatively low melting point and modulus of elasticity, which reduces residual stress after bonding. Its low melting point also simplifies rework of the bond and allows reuse of the backplane. The whole bonding process can be carried out in the air, so the bonding cost is reduced.
High temperature welding
Techniques such as high-temperature welding (a combination of brazing and diffusion welding) are a third technique that can be employed. These processes are performed at temperatures above 500°C and require the use of vacuum or controlled atmosphere ovens. With brazed joints, the joint is achieved by melting a brazing alloy at the joint to form the joint. For diffusion bonding, fillers are not used, but bonding is achieved by heating the backing plate at high pressure to a temperature at which interdiffusion with the target occurs. The result is a very low thermal resistance, usually close to or lower than that of the master alloy, and allows the highest possible power density. The use of high temperature soldering techniques is limited by several factors. There's more expense associated with that, plus unless the backsheet's material coefficients of expansion are very closely matched, the bond will be under extreme stress. In addition, it cannot be reworked after binding, which means that the backplane cannot be reused.
We have unique experience in the target bonding service. Our bonding solutions include the use of thermal expansion-matched backing and target combinations (such as silicon sputtering targets on molybdenum backing) to minimize the potential for target cracking due to mismatched material combinations.
It is relatively easy to sputter metal atoms on the surface of the target, but it is not easy to sputter after turning the surface into metal oxide.
The ion bombardment makes the metal atoms on the target surface very active, and the target temperature rises, which greatly increases the reaction rate on the target surface. At this time, the target surface is undergoing two processes of sputtering and reaction to form compounds at the same time. If the sputtering rate is greater than the compound generation rate, the target is in a metal sputtering state; otherwise, the reaction gas pressure increases or the metal sputtering rate decreases, and the target may suddenly cause the compound formation rate to exceed the sputtering rate and stop sputtering.
Phenomenon: The target voltage cannot reach normal for a long time, and it has been in a low-voltage operation state, accompanied by arc discharge; the target surface shows white deposits or dense needle-like gray discharge traces.
To reduce target poisoning, you can start from the following aspects:
To prevent target poisoning, first of all, ensure that the vacuum chamber does not leak, clean the interior, and remove volatile components, etc.;
DC power supply must be replaced by intermediate frequency power supply or RF power supply;
Reduce the introduction of reactive gas, increase the sputtering power, clean up the pollutants (especially oil) on the target, and choose a dust-proof arc extinguisher with good vacuum performance, which can effectively prevent target poisoning;
Using double targets
Control the change of coating mode: Before coating, collect the hysteresis effect curve of target poisoning, so that the intake flow can be controlled at the leading edge of target poisoning, so as to ensure that the process is always in the mode before the deposition rate drops sharply.
Keep the target surface clean and the pumping speed high, the poisoning problem can be solved;
The target can be restored by hitting it for an hour or two with a neutral source or a radio frequency source. Remove the target and polish it with sandpaper.
As a material for making thin films for sputtering or film deposition technology, the sputtering target plays a vital role, but in actual use, if the operation is improper or the machine fails, the sputter target will be damaged. Focusing on heat dissipation and power increase can prevent target cracking; In vacuum environment, using proper sputtering power supply, increasing sputtering power and reducing the reaction gas inflow can prevent “target poisoning”. When the target material is damaged, repairing in the above way can prolong the service life of the target material.
More questions, don’t hesitate to contact us for solutions.
We provide sputtering targets for all elements in the periodic table, just tell us the required material & specification, we will offer you a satisfact product.
Frequently Asked Question About Sputtering Target
1. What is the purpose of using these target ? for what performance ?
The target is the material for making thin films. The target material bombarded by high-speed energetic particles, and used to obtain different film systems through the interaction of different lasers (ion beams) and different targets to achieve the functions of conduction and barrier.
Therefore, the target is also called "sputtering target". Its working principle is to use the ions generated by the ion source to gather and speed up in a vacuum, and use the formed high-speed ion beam to bombard the surface of the target to exchange kinetic energy. Atoms from the target surface are deposited on the substrate.
The target material is extracted from high-purity metal and then coated by sputtering process, and is used in chips, flat panel displays, solar cells, storage, optics and other fields.
2. What is the reason of Aluminium target flickering and sparking in mirror process ?
The surface of the target flashing spark, may be the target surface is too dirty, or the purity of the target itself is not enough, or the working environment parameters and other problems.
And it may be caused by the high temperature of the precision mirror spark machine：
1. As long as it is in use, its fire protection function must be turned on. Once strong light or flames are found, it will immediately call the police. If the temperature is too high, the fire extinguisher will automatically operate. At the same time, it is also necessary to check whether the fire extinguisher is normal before use. To avoid have an accident.
2. If the current used is too large, the spark will be very large during the discharge process. Try to use it with oil, which will be safer.
3. Short circuit: The short circuit is caused by the metal contact between the phase line and the neutral line or between the phase lines. When short-circuited, the temperature rises sharply, causing the insulating material to burn, causing a fire.
4. Long overload operation time: If the circuit of the equipment and the equipment operate beyond the rated value for a long time, it will cause problems with the accessories.
