Magnetron sputtering technology is used in magnetron sputtering vacuum coating machine, but in the
coating process, flameout often occurs, commonly known as poisoning. Then why does the target poisoning appear and what causes it? Let me introduce it to you in the hope of
helping you.
First, the formation of target metal compounds.
Where
is the compound formed in the process of forming the compound from the metal
target surface by reactive sputtering? Because the active reaction gas particles collide with the target surface
atoms to generate chemical reaction to generate compound atoms, which is
usually an exothermic reaction, the heat generated by the reaction must be
conducted out, otherwise, the chemical reaction cannot continue. It is impossible to conduct heat conduction between gases under vacuum, so
chemical reaction must be carried out on a solid surface. The sputtering products are carried out on the target surface, substrate
surface and other structural surfaces. It is our goal to generate compounds on the substrate surface, while it is
a waste of resources to generate compounds on other structures. At first,
generating compounds on the target surface is the source of providing compound
atoms, and later it becomes an obstacle to continuously providing more compound
atoms.
Second: the influencing factors of target poisoning.
The
main factor affecting target poisoning is the ratio of reactive gas to
sputtering gas, and excessive reactive gas will lead to target poisoning. In the process of reactive sputtering process, the sputtering channel area
on the target surface is covered by reaction products or stripped to re-expose
the metal surface. If the rate of compound
formation is greater than the rate of compound stripping, the compound coverage
area increases. Under a certain power, the
amount of reaction gas involved in compound formation increases, and the
compound formation rate increases. If the amount of reactant gas
increases excessively, the compound coverage area will increase. If the
reactant gas flow rate cannot be adjusted in time, the rate of compound coverage area increase
will not be restrained, and the sputtering
channel will be further covered by the compound. When the sputtering target is
completely covered by the compound, the target will be completely poisoned.
Third: target poisoning.
(1)
positive ion accumulation: when the target is poisoned, an insulating film is
formed on the target surface. when the positive ions reach the cathode target
surface, they cannot directly enter the cathode target surface due to the
blocking of the insulating layer, but accumulate on the target surface, which
is easy to produce cold field-induced arc discharge-arcing, which makes cathode
sputtering impossible.
(2)
Anode disappearance: When the target is poisoned, an insulating film is also
deposited on the grounded vacuum chamber wall, and electrons reaching the anode
cannot enter the anode, resulting in anode disappearance.
Fourth: the physical explanation of target
poisoning.
(1)
Generally, the secondary electron emission coefficient of metal compounds is
higher than that of metal. 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 space conduction
ability and reduces the plasma impedance, resulting in a decrease in sputtering
voltage. Thereby reducing the
sputtering rate. Generally, the sputtering
voltage of magnetron sputtering is between 400v and 600v, and when target
poisoning occurs, the sputtering voltage will be significantly reduced.
(2) The
sputtering rate of metal target is different from that of compound target.
Generally, the sputtering coefficient of metal is higher than that of compound,
so the sputtering rate is low after target poisoning.
(3) The
sputtering efficiency of reactive sputtering gas is inherently lower than that
of inert gas, so the comprehensive sputtering rate decreases when the
proportion of reactive gas increases.
Magnetron sputtering vacuum coating machine, target
poisoning is very unfavorable for coating, which will cause many unnecessary
failures and losses. Because of the solution to
poisoning, coating experts have also developed a set of solutions to prevent
target poisoning, so as to solve this problem, and will give you a detailed
introduction next time.
