1, Formation of metal compounds on the target surface
Where is the compound formed in the process of forming a compound from a metal target surface by a reactive sputtering process? Since the chemical reaction between the reactive gas particles and the target surface atoms produces compound atoms, which is usually exothermic, the reaction heat must have a way to conduct out, otherwise the chemical reaction cannot continue. Under vacuum conditions, heat transfer between gases is not possible, so the chemical reaction must take place on a solid surface. Reaction sputtering generates compounds on target surfaces, substrate surfaces, and other structural surfaces. Generating compounds on the substrate surface is the goal, generating compounds on other structural surfaces is a waste of resources, and generating compounds on the target surface starts as a source of compound atoms and becomes a barrier to continuously providing more compound atoms.
2, The impact factors of target poisoning
The main factor affecting the target poisoning is the ratio of reaction gas and sputtering gas, too much reaction gas will lead to target poisoning. Reactive sputtering process is carried out in the target surface sputtering channel area appears to be covered by the reaction compound or the reaction compound is stripped and re-exposed metal surface. If the rate of compound generation is greater than the rate of compound stripping, the compound coverage area increases. At a certain power, the amount of reaction gas involved in compound generation increases and the rate of compound generation increases. If the amount of reaction gas increases excessively, the compound coverage area increases. And if the reaction gas flow rate cannot be adjusted in time, the rate of compound coverage area increase is not suppressed, and the sputtering channel will be further covered by the compound, when the sputtering target is fully covered by the compound, the target is completely poisoned.
3, Target poisoning phenomenon
(1) positive ion accumulation: when the target poisoning, a layer of insulating film will be formed on the target surface, positive ions reach the cathode target surface due to the blockage of the insulating layer. Not directly enter the cathode target surface, but accumulate on the target surface, easy to produce cold field to arc discharge — arcing, so that the cathode sputtering can not go on.
(2) anode disappearance: when the target poisoning, grounded vacuum chamber wall also deposited insulating film, reaching the anode electrons can not enter the anode, the formation of anode disappearance phenomenon.
4, Physical explanation of target poisoning
(1) In general, the secondary electron emission coefficient of metal compounds is higher than that of metals. After target poisoning, the surface of the target is all metal compounds, and after being bombarded by ions, the number of secondary electrons released increases, which improves the conductivity of space and reduces the plasma impedance, leading to a lower sputtering voltage. This reduces the sputtering rate. Generally the sputtering voltage of magnetron sputtering is between 400V-600V, and when target poisoning occurs, the sputtering voltage is significantly reduced.
(2) Metal target and compound target originally sputtering rate is different, in general the sputtering coefficient of metal is higher than the sputtering coefficient of compound, so the sputtering rate is low after target poisoning.
(3) The sputtering efficiency of reactive sputtering gas is originally lower than the sputtering efficiency of inert gas, so the comprehensive sputtering rate decreases after the proportion of reactive gas increases.
5, Solutions for target poisoning
(1) Adopt medium frequency power supply or radio frequency power supply.
(2) Adopt the closed-loop control of the reaction gas inflow.
(3) Adopt twin targets
(4) Control the change of coating mode: Before coating, the hysteresis effect curve of target poisoning is collected so that the inlet air flow is controlled at the front of producing target poisoning to ensure that the process is always in the mode before the deposition rate drops steeply.
–This article is published by Guangdong Zhenhua Technology, a manufacturer of vacuum coating equipment.
Post time: Nov-07-2022