Abstract:
Sparking is suppressed during high-frequency sputtering by a high-frequency generator ( 5 ) which has a controlled switching unit ( 13 ) that is connected upstream in relation to the output of the generator. A high-frequency supply signal that is generated at the output of the high-frequency generator is stopped for plasma discharge (PL) for a short time, by the switching unit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of international application no. PCT/IB00/01195, filed Aug. 29, 2000, and claims priority on German application no. DE 199 49 394.4, filed Oct. 13, 1999. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to an electric supply unit, a sputtering installation as well as a method for reducing arcing during sputtering, and further a fabrication method. 
     The present invention builds on the following problem. The findings gained according to the invention, can be generally applied for HF-supplied sputtering processes. 
     During magnetron sputtering of ITO layers of oxide targets and supply of the plasma discharge, combined of HF and DC, the development of arcs is sporadically observed. This is not surprising, for the occurrence of such arcs is known in the case of DC sputtering of electrically poorly conducting materials, be that for sputter etching or for sputter coating. Several different approaches are known in order to avoid the development of arcs during DC sputtering, which could considerably damage workpieces during sputter etching as well as during sputter coating. For example the DC supply is superimposed by an HF supply component or work is carried out through operating point stabilization in so-called intramode or the DC supply is chopped so that the plasma discharge path is intermittently short-circuited across a relatively low-ohmic current path, while the DC supply is cut out. 
     It is thus all the more surprising that, in spite of the HF supply superimposed on the DC supply, said arcing was observed and an arc once developed continued to burn even if, according to experience from DC-supplied sputtering technology, the DC supply component had been deactivated. 
     SUMMARY OF THE INVENTION 
     The present invention builds on the surprisingly resulting task of suppressing the arc development during HF sputtering—generally sputter coating or sputter etching—at least so fast that the workpiece being worked is not damaged. 
     For this purpose, a supply unit of the type described in the introduction is proposed, which is developed according to the invention. Consequently, the supply unit according to the invention is developed such that the HF supply of the sputter plasma discharge is briefly deactivated. 
     In a first preferred embodiment of the supply unit according to the invention the switching unit controlling the deactivation comprises a control input, which is operationally connected with the output of an arc detection unit. It thereby becomes possible to deactivate the high-frequency supply of the plasma discharge immediately when an arc is developing. 
     The HF generator provided for the supply comprises in the conventional manner an electric supply unit which, for example, converts an input-side mains voltage into a DC supply voltage for the succeeding HF oscillator. 
     In a preferred embodiment of the unit according to the invention the switching unit provided for the deactivation according to the invention of the high-frequency supply succeeds said supply unit internal to the HF generator, i.e. it is disposed between the output of said supply unit and that of the HF generator. This can take place succeeding said generator supply unit up to the output side of an impedance matching unit provided conventionally and, in the present case, considered to be part of the generator. 
     In a preferred embodiment of the supply unit according to the invention equipped with an arc detection unit the latter comprises a DC potential measuring unit, whose output is operationally connected with the input of a preferably adjustable threshold value detection unit, whose output, in turn, acts as the output of the arc detection unit. 
     It is known that even with the exclusive HF supply of a plasma discharge, DC potentials—DC potential drops across the electrode dark spaces, essentially constant DC potential along the remaining plasma path—are generated along the plasma discharge path, whose values change detectably when a low-ohmic arc path is generated. 
     In a further preferred embodiment of the supply unit according to the invention the deactivation time of the HF supply is maximally 40 μsec., preferably even maximally 30 μsec. 
     It is thereby attained that, on the one hand, an arc in the process of developing is extinguished or, as will yet be explained, cannot even form and simultaneously a stable discharge is immediately continued in operation. 
     In a further preferred embodiment it is attained, in particular when the deactivation of the HF supply triggered by arc detection is provided, that, in addition to the previously described rapid switching in again, after the detection of the arc development, the HF supply is rapidly switched out such that the arc which is in the process of developing cannot fully develop. This is attained thereby that the time interval between arc detection and switching-out of the high-frequency supply is maximally 50 μsec, preferably maximally 30 μsec. 
     In a further preferred embodiment the switching unit provided according to the invention is developed in the manner of a monostable unit. Triggered by a detection signal at the output of the provided arc detection unit, the high-frequency supply is thereby deactivated for the preferably adjustable time interval, and subsequently is again switched in. If subsequently, acquired by the arc detection unit, measured values indicating arcs continue to be present, the HF supply is again deactivated. Controlled by the arc detection, a repetitive switching in and out of said supply occurs, until the arc detection unit no longer triggers the switching-out of the supply. But the supply switch-out remains to be dependent on the detection of at least one arc in the process of developing. 
     But in a further preferred embodiment this is circumvented thereby that in free-running mode the HF supply is repetitively deactivated for brief periods of time. 
     In a further preferred embodiment of the supply unit according to the invention, in addition to said HF generator, a DC generator is provided, whose output signal is superimposed onto that of the HF generator. 
     The DC generator further preferred comprises also a controlled switching unit, by means of which the DC supply signal can be deactivated for a brief time. 
     If, for the triggering or deactivation of the HF supply an arc detection unit is provided, the latter can also drive the deactivation of the DC supply. It is understood that this can also take place directly or thereby that in mutual time dependence, as will yet be explained, HF and DC supply can be deactivated or switched in. 
     At the supply unit according to the invention the mutually dependent time driving of the provided controlled switching units takes place such that the DC supply is deactivated before the HF supply. The HF supply is switched in again before or after the DC supply, preferably after. 
     The supply unit according to the invention is realized in a preferred embodiment utilizing a DC supply of type “Pinnacle” by the firm Advanced Energy. 
     Preferred embodiments of the sputter installation according to the invention are specified in the claims as are preferred embodiments of the method according to the invention. 
     The present invention, furthermore, relates to a fabrication method, by means of which the resulting sputtered—sputter-etched or sputter-coated—structural components can be produced with increased quality or with significantly reduced rejects due to at least strongly reduced effects of arcs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the invention will be explained by example in conjunction with Figures. Therein depict: 
     FIG. 1 is a schematic and function block/signal flow diagram of a first embodiment of the supply unit according to the invention, operating according to the method according to the invention, in a sputter installation according to the invention for the fabrication according to the invention, with free-running arc prevention; 
     FIG. 2 in a representation analogous to FIG. 1 of a further development with DC and HF supply; 
     FIG. 3 is a schematic diagram building on the technology depicted in FIG. 1 of an embodiment with supply deactivation controlled by arc development; 
     FIG. 4 is a schematic diagram building on the technology according to FIG. 2 of an embodiment of supply interruption triggered by arc development; and 
     FIG. 5 is a diagram of a further embodiment of the technology explained in conjunction with FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In conjunction with a simplified function block/signal flow diagram, in FIG. 1 is schematically shown a first embodiment of the supply unit according to the invention switched into a sputter chamber conjointly forming a sputter installation according to the invention. 
     The sputter chamber  1  can be a sputter coating chamber or a sputter etching chamber, therein, as shown, a diode sputter chamber or (not shown) a triode or even multi-electrode sputter chamber. 
     In any case and as sufficiently known, in the sputter chamber  1  a plasma discharge path PL is provided between at least two electrodes. 
     The type and structure of the sputter chamber  1  is of secondary importance for the present invention, but it is essential that at least a portion of the plasma discharge supply takes place by means of HF energy. According to FIG. 1, a supply unit  3  according to the invention is provided. It comprises an HF generator  5  with a power supply unit  7 , an HF oscillator unit  9 , and an active or passive, optionally adjustable matching unit  11  (matchbox). According to the invention between an output  7   a  of the power supply unit  7  and an output  5   a  of the generator  5 , which is connected with the plasma discharge path PL, a controlled switching unit  13  is provided, for example, according to the depiction of FIG. 1, directly preceding output  5   a . The switching unit  13  comprises a control input  13   S  which is connected with output  15   a  of a freely oscillating clock generator  15 . With the freely oscillating clock generator  15  the switching unit  13  is switched during first time intervals t A  such that at output  5   a  the HF supply is switched out and, during second time intervals t B , is switched in. With respect to the clock ratios is recommended: 
     duty cycle: (t B /(t B +t A ))≧0.9 
     deactivation times: t A ≦100 μsec. 
     The controlled switching unit  13  can therein be developed as a series chopper (as shown) or as a parallel chopper, as indicated at  13   p  in dashed lines. 
     FIG. 2 shows a further embodiment according to the invention of the freely oscillating embodiment, already represented in principle in FIG. 1, inter alia of the supply unit according to the invention. 
     The same references are applied for the function blocks and signals, which were already described in conjunction with FIG.  1 . 
     Apart from the HF generator  5 , according to FIG. 2 the supply unit  23  according to the invention comprises a DC generator  25 . As shown, HF generator  5  and DC generator  25  can therein be supplied by the same supply unit  7 . 
     The DC generator  25  comprises a DC voltage generation stage  29 , succeeding it conventionally a low-pass filter unit  31 , and a controlled switching unit  33 . The output  25   a  of the DC generator and  5   a  of the HF generator  5  are superimposed at a superimposition stage  50 , which can also be formed by a conjointly connected electrode of the plasma discharge path PL according to FIG.  1 . 
     Just as the control input  13   S  of switching unit  13  is operationally connected with the clock generator  15 , so is a control input  33   S  of switching unit  33  operationally connected with the output  35   a  of a clock generator  35 . Therewith the DC supply signal is switched in and switched out at output  255   a  of the supply unit  23  or at DC output  25   a . During third time intervals t C  the DC supply is deactivated by clock generator  35 , during fourth time intervals t D  switched in. The two clock generators  15  and  35 , which can be realized entirely conjointly, are in principle operated in mutual time dependence, as shown with the synchronization unit  43 . 
     In a preferred embodiment, with respect to the time ratios t A  to t D , the following applies: 
     the time intervals t C  start before time intervals t A , i.e. the DC supply is switched out before the HF supply. 
     Preferably, further, the particular time interval t C  is terminated before t A  is terminated, i.e. the DC supply is switched in before the HF supply is switched in in both cases again. 
     Preferably the following time ratios apply: 
     0.25≦t C /t A ≦0.5. 
     In principle, the switch-in time intervals t B  and t D  are further significantly longer than the switch-out time intervals t A  or t C . 
     Based on the representations of FIGS. 1 and 2, many variants are open to a person skilled in the art for realizing the supply unit according to the invention such that primarily the HF supply is intermittently briefly deactivated and, if additionally a DC supply is provided, it is also deactivated synchronized with the HF supply deactivation. 
     In analogy to FIGS. 1 and 2, in each of FIGS. 3 and 4 a further preferred embodiment of the supply unit according to the invention is shown, in which the supply interruption in terms of HF, or HF and DC, does not take place freely oscillatingly but rather triggered by the detection of arc development in the sputter chamber. 
     With respect to FIGS. 3 and 4, only the differences with respect to FIGS. 1 and 2 will be described. 
     According to FIG. 3 an arc detection unit  60  is provided on the supply unit according to the invention. In a preferred embodiment, it acquires a DC potential DC PL , due to a plasma discharge. On a preferably adjustable threshold value unit  62  it is determined whether this monitored DC potential φ, for example the plasma potential, reaches the set threshold value SW, based on which conclusions are drawn regarding the development of an arc. The threshold value unit  62  triggers at the output side a time control unit  64 , which outputs, in the manner of a monostable multivibrator, a deactivation control signal of the preferably adjustable length t A  to the controlled switching unit  13 . Consequently, in this embodiment the HF supply is deactivated briefly, t A , if the development of an arc in the plasma discharge PL is detected, for example if the plasma potential decreases due to the low-ohmic arc conductive connection. 
     If thereupon, through the time control unit  64  the HF supply is again switched in (t B ), the stable plasma discharge PL continues unless, via the detection unit  60 , continuously or again the development of an arc is being detected. If the latter is the case, the HF supply is again deactivated via the units  62 ,  64 . Repetitive switching-out of the HF supply takes place until no arcs are any longer detected. 
     It is understood that the detection unit  60 , shown in FIG. 3 schematically coupled to the sputter chamber  1  or its plasma discharge PL, can also, and this preferably, be operationally connected for acquiring the electric discharge conditions, directly with the feed lines to the discharge electrodes. 
     Building on FIG. 2, in FIG. 4 the corresponding arc development-controlled supply unit is schematically represented for the combined HF and DC supply. 
     According to FIG. 4, with the detection of at least the development of an arc via the detection unit  60  and the threshold value unit  62 , preferably, first, the time control unit  66 , in the manner of a monostable unit, is driven for the deactivation of the DC supply according to the deactivation time interval t C . As a function of the latter, preferably displaced by an adjustable time interval T, the HF supply is deactivated via the time control unit  68 . Within the DC deactivation phase t C  it is entirely possible to employ the HF supply repeatedly and, with further detection of an arc, to deactivate it again. 
     Building on FIG. 4, in FIG. 5 a further embodiment is depicted, according to which, in response to threshold values, DC and/or HF supply are deactivated. 
     According to this Figure, at the outside side of the detection unit  60  which receives potential DC PL, a check for reaching a first threshold value SW-DC is carried out on the threshold value unit  62   a  and for reaching a second threshold value SW-HF, on threshold value unit  62   b . Upon reaching the threshold value SW-DC, via the time control unit  66  the DC supply is deactivated and, upon reaching the threshold value SW-HF, via unit  68  the HF supply is deactivated. 
     It is understood that now several feasibilities are open to a person skilled in the art to provide, in the case of DC and HF supply, combinations of time control and threshold value control and to deactivate briefly DC and HF supply each optimally staggered in time. 
     In a preferred embodiment, arc detection unit  60 , threshold value unit  62 , and time setting unit  66  with the DC generator  25  are realized in the embodiment according to FIG. 4 or  5  employing a DC feed of type “Pinnacle” by the firm Advanced Energy. 
     If it is taken into consideration that conventionally DC signals are decoupled from the input of the HF oscillator and that, conversely, HF signals are isolated from the input of the DC generators, it is evident that in a preferred embodiment an HF arc detection unit is connected succeeding the HF oscillator and a DC arc detection unit succeeding the DC generator. In FIG. 4 this is shown in dashed lines at  60   DC  and  60   HF . Each of these acts onto their associated time setting units  66  (DC) or  68  (HF). 
     In the embodiment according to FIGS. 3 to  5  preferably, starting with the detection, i.e. with reaching the corresponding threshold value with the development of an arc, until the deactivation of the HF supply, a time interval T of ≦50 μsec is set. 
     In a preferred embodiment the supply unit according to the invention is combined with a sputter coating chamber, in particular preferred with a magnetron sputter chamber. The described supply is therein especially suitable for sputtering poorly conducting materials, in particular of metal oxides, therein in particular of ITO, preferably by magnetron sputtering. 
     In magnetron sputtering of ITO targets with an HF power density P HF  of 0.75 W/cm 2  and a DC supply power density P DC  of 0.75 W/cm 2  in an installation in principle built according to FIG. 4, starting with the detection of the arc development, the supply switch-out (HF and DC) already takes place after 500 μsec. With increased DC power density of 1.5 W/cm 2  this time interval was less than 1 μsec. 
     With the supply unit according to the invention, the sputter installation according to the invention or the method according to the invention, it becomes possible to operate HF sputter processes and in particular also HF/DC sputter processes under control even with tendencies to arcing. Due to the capability of limiting the arc event to less than 1 μsec, stable process operation is made possible. With the fabrication process according to the invention the quality of surfaces in sputter etching or sputter coating of said type is significantly increased and thus the number of workpiece rejects decreased. Damage through arcing on target, workpieces or on portions of the chamber wall are largely avoided. 
     While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.