Patent Application
20230097276
The invention refers to an apparatus comprising a DC-pulsed cathode array according to claim 1 and to a process to deposit a coating with a respective apparatus according to claim 18.
While use of rotating-cathode arrays is widespread with pass-through vacuum deposition plants for large area coatings as for instance in the glass coating industries, high quality coating equipment and processes for layer deposition on static substrates, e.g. in the flat panel industry, still needs improvement in terms of uniformity of the coatings and/or productivity of the equipment used. One main reason is the occurrence of a swing induced thickness asymmetry in diagonally opposed deposition areas with reference to a cathode axis YCj when two or more neighboring targets of a cathode array are operated with swivel mounted magnet systems to improve deposition uniformity under and between rotating cathodes along a central area on both sides of substrate axis X normal to YCj. This makes it necessary to provide a considerably higher volume of the deposition chamber to be used than necessary with comparable two-dimensional planar magnetron configurations. Due to non-uniformity issues arisen by that effect, as discussed in detail with
A (maximum) swivel angle ±β here defines the maximum angular deflection of a swivel mounted magnetic system out of a swivel plane PTS defining the middle or center of the overall deflection. The overall deflection is defined by the total swivel angle 2 β. A swivel plane of target n comprises respective cathode axis YCj and forms an angle α with the substrate plane S. During a sputter deposition process the magnetic system is moved from one extreme position to the other, i.e. from +β to −β or reverse. This can be effected once or repeatedly in a constant or stepwise manner. Note that speed may vary with time or the hold time can be different for every step, where each step refers to a different position of the magnetic system, so that dwell time of the magnetic system can be different for the positive and the negative angle-sector (i.e. +β to zero and −β to zero, where zero defines the position of the swivel plane which can be pivoted or non-pivoted from a zero position of the magnetic system which is in opposition to the substrate plane S).
An essentially equidistant distance TSD of the outer target diameter to the substrate surface in the following means that each shortest distance TSD1 to TSDn of the outer target diameter DT of the n-cathodes to the substrate plane S does not deviate from a mean value MTSD={Σk=1nTSDk}n−1 more than two millimeters, therewith for each TSD1 to TSDn the following applies: (MTSD−2 mm)≤TSKs=1 . . . n≤(MTSD+2 mm).
This can be seen as the maximum difference allowable at the end of target life, whereas with an all new targets configuration the difference will be essentially smaller, e.g. about zero millimeters. This refers at least to all targets driven with pulsed DC-sources and swivel angle β>0.
The substrate plane S is defined by the surface of a flat substrate, e.g. a wafer, which can be mounted to the substrate pedestal. The plane itself however extends over the limited extension of the substrate surface.
A normal distance TSC or TSD between a longitudinal axis of the cathode or an outer target diameter and the substrate plane S is the shortest distance between the respective longitudinal axis YCj or the respective outer target diameter DTk and the substrate plane.
A pedestal is a substrate support designed to support an essentially flat substrate of maximal dimensions x*y (x times y) or smaller. To support a substrate in a static way means the pedestal is designed to hold a substrate in such a way that it is not moved during a deposition process.
A bipolar pulsed or a bipolar power supply means a power supply which can provide at least a voltage reversal, e.g. after each negative pulse a relative short positive pulse or spike follows to clear potentially damaging charge buildup, thereby reducing or avoiding incidence of electric arcs. Although such pulses sequences will be seen as the standard sequence in the following, alternatively, bipolar pulses of different asymmetric or symmetric pulse patterns, with or without offset-time (pause) between pulse-cycles can be used up to different process needs.
The use of the terms inward and outward refers to directions towards and away from a center plane YZ, according to the figures. Center plane YZ usually is a symmetry plane of the cathode array.
The use of the terms up, upwards and down, downwards or lower and higher or the like refers to the Z-axis according to the drawings as shown in the figures but not mandatory to a possible direction of a cathode or substrate when mounted. Both can be mounted also in various different positions of a vacuum chamber, e.g. on a top, on a bottom, or a sidewall of the vacuum chamber however will be always mounted in a position essentially facing each other, e.g. top versus bottom or on two opposite sides of the chamber.
It has been found that drawbacks of state of the art apparatuses can be essentially diminished by the use of an apparatus according to claim 1 or by applying a process according to claim 18. Surprisingly the relative usable coating area of cathode arrays can be remarkable extended together with an efficient improvement of uniformity issues, e.g. with reference to the thickness of the coatings.
In a first embodiment of the invention an apparatus for sputter deposition of material on a substrate comprises:
In a further embodiment of the apparatus the following applies to a maximum substrate or a maximum support boundary dimension ymax which is parallel to longitudinal axes Y:
(TLA−3.9 MTSD)≥ymax≥(TLA−2 MTSD)
Especially (TLA−3.5 MTSC)≥ymax(TLA−2.5 MTSD) whereat TLA is the length of an active region on the target surface, MTSD is the mean shortest distance between the outer target diameter DTn and the substrate plane S. As an example the maximum substrate/boundary dimensions can be ymax=TLA−3 MTSD. This means that the targets protrusion at each “y”-side of the x*y-plane can be as small as about the 1.5-fold of the distance MTSD between the target plan S and the outer diameter of the target(s) DT or MTn. The latter referring to the mean outer diameter of the target(s) driven with a pulsed power supply and a swivel angle β>0. This however is essentially smaller than any state-of-the-art protrusions needed for sputtering on stationary substrates which usually need at least a fourfold protrusion of the targets to avoid swing induced thickness asymmetry.
It should be mentioned that a geometric target length can be about the same or bigger than the active target length, that is TLA≈TL or TLA≤TL, whereat TL stands for the total target length.
The mean value MTSD may correspond approximately or exactly to the values of the particular distance values TSDk=1 . . . TSDn between the respective outer target diameter and the target plane, i.e. MTSD≈TSDk=1 . . . ≈TSDn and therewith fall under the definition of an essentially equidistant distance TSD, see above with definitions. Therewith the outer target diameters DT are arranged essentially equidistant in a normal distance TSD from a substrate plane S. This will be the case when all targets are new or even at the end of the target life as long as all targets are made of the same material and essentially driven with the same power, which is favorably with reference to process efficiency.
In a further embodiment the distance TTT between the axes of neighboring cathodes or electrodes is equal for all distances TTTk−n between neighboring cathodes or electrodes, e.g. in a plane in parallel to the substrate plane S.
In a further embodiment of the invention the cathodes may be spaced equidistantly in a distance TSC from the substrate plane S.
In a further embodiment distance TSCo of at least one or both outer cathodes to the target plane S can be different to the distance TSCi of the inner cathodes to the target plane S.
An angle α between swivel plane PTs and the substrate plane S may be defined by: 40°≤α≤100°.
For a maximum swivel angle β of the at least one swivel mounted magnetic system the following applies: 0°≤|β|≤80°, e.g. 20°≤|ββ≤70°, whereas values near the higher limits apply to an a near or at 90°. The maximum swivel angle β thereby defines a maximal deviation of the magnetic system out of the swivel plane PTs. An alignment of the magnet system towards a neighboring cathode should be avoided for obvious reasons. That means that swivel angles ±β as any swivel angles between should be in line of sight with the substrate plane S without intersecting a neighboring cathode.
In a preferred embodiment the outer swivel plane PTSo will be inclined to the substrate plane S in an angle αo=50±10°. It should be noted that the inclination of the outer swivel planes PTSo will be always directed towards the substrate plane S and towards the central plane YZ, that is inwards directed. Therewith the maximum swivel angle βo of the two outer cathodes can be chosen from 30° to 50°, that is 30°≥|βo|≤50°, e.g. βo=±40° from the swivel plane PTso, or a total swivel angle 2βo=80°. In this case the inner swivel plane PTSi could be inclined to the substrate plane S in an angle αi=90±10° with a maximum swivel angle βi of the inner magnet systems of 50°≥|βi|≤70°, e.g. βi=±60° referring to a total swivel angle 2βi=120°.
In a further embodiment the pulsed power supply can be a bipolar pulsed power supply. The bipolar pulsed power supply may be configured as a dual magnetron supply, the outputs of different polarity being electrically connected with the inputs of two neighboring cathodes, here named electrodes, as in this case the neighboring electrodes act alternatingly as cathode and anode.
Each cathode of the cathode array can be connected to a dedicated pulsed power supply, e.g. bipolar, or to a dual magnetron supply. As an example with a four cathodes array the inner cathodes may be connected to the opposite polarities of a dual magnetron supply. Due to the alternating nature of their polarity these cathodes are referred to as electrodes. At the same time the outer cathodes can be connected to dedicated bipolar pulsed DC-supplies. The dual magnetron supply being synchronized with the dedicated bipolar power supplies. For further examples see
In a further embodiment least one or both outer power supplies may be DC supplies.
The pedestal can be electrically isolated to hold the substrate on a floating potential during the deposition process, alternatively the pedestal can be electrically grounded.
Usually an inventive apparatus may comprise a gas distribution system for providing one or more process gases. The anode may be a ground anode formed by the process chamber and may comprise also respective electrically connected elements like shieldings, liners or similar.
The invention also refers to a process to deposit a coating comprising the use of an inventive apparatus as described above, whereat a substrate is mounted to and positioned with the pedestal in the deposition chamber. When vacuum has been applied to the deposition chamber and a process gas introduced to the chamber, e.g. until a reference pressure has been reached, deposition of a coating on at least one flat substrate within the dimensions x*y in the target plane S is started by applying a pulsed target power to at least one cathode of the array.
By applying inventive processes a coating thickness uniformity unifT within the substrate dimensions x*y of unifT≤5% can be produced. Where uniformity is defined as
unif=(Max−Min)/(2*Mean)
with Max and Min being the respective highest and lowest value measured.
Each cathode may be driven by a separate power supply which can be all pulsed power supplies or a combination of at least one pulsed power supply, e.g. for the inner cathode(s), and DC supplies, e.g. for the outer cathodes.
At least one power supply may be a bipolar power supply.
In a further embodiment two neighboring cathodes, here electrodes can be driven by a bipolar power supply in a dual magnetron configuration with an output of different polarity connected to each neighboring electrode. As an example, the inner cathodes of a four cathodes array or alternatively the right and the left cathode pair of such an array can be driven by a respective bipolar power supply in a dual magnetron configuration.
Using inventive processes as described also Chrome (Cr), copper (Cu), tantalum (Ta), titanium (Ti), tungsten (W), tungsten titanium (WTi) coatings, where a strong expression of swing induced thickness asymmetry has been observed with state of the art processes and equipment, can be deposited with Cr, Cu, Ta, Ti, W, WTi targets having a reduced sidewise protrusion over the substrate surface.
The pedestal can be mounted electrically floating, electrically grounded, or on a defined bias potential given by a bias generator which can supply an RF-voltage.
The invention is further directed to the use of an inventive apparatus or process to manufacture a product comprising a coating having a uniformity unifR of the specific resistance R [Ωm] of unifR≤5% and/or a thickness uniformity unifT≤5% within the substrate dimensions x*y.
It should be mentioned that two or more embodiments of the apparatus according to the invention may be combined unless being in contradiction. Which means that all features as shown or discussed in connection with only one of the embodiments or examples of the present invention and not further discussed with other embodiments or examples can be seen to be features well adapted to improve the performance of other embodiments of the present invention too, as long such a combination cannot be immediately recognized as being prima facie inexpedient for the man of art, as for instance using a ground and floating bias at the same time or similar. Therefor with exceptions as mentioned all combinations of features of certain embodiments or examples can be combined with other embodiments or examples even when such features are not mentioned explicitly.
The invention shall now be further exemplified with the help of figures. Figures are drawn exemplarily for mere demonstrative purposes only and therefore do not show actual equipment dimensions, nor do they show details known to the man of art but not essential for the understanding of the present invention. Same numbers and reference signs refer to same features also with different figures. Apostrophes and subscripted indices “i” for features of an inner cathode, and “o”, for features of an outer cathode, or numbers refer to alternatives or specific features of a specific cathode. The figures show:
With inner cathode 2 and outer cathode 4 the shaft 33 of the cathode axes YC2,YC4 and transmission spokes 34 are shown, whereas with outer cathode 1 and inner cathode 3 inner and outer swivel planes PTSi, PTSo (dash-pointed lines) and respective inner and outer swivel angles ±βi, ±βo (dashed lines) are shown exemplarily. The cathode arrangements 1,2 with magnetic systems 9,10 can be seen as mirrored in the YZ-plane to respective arrangement 3,4 with magnetic systems 11,12. The angle αi of the inner swivel planes PTSi is normal to the substrate plane S, whereas the angle αo of the outer swivel planes PTSo are inclined at nearly 45° to the substrate plane S, so that planes PTSo are oblique downward and to the central plane YZ seen from axes YCo. Where indices “i” and “o” refer to inner and outer cathodes and respective dimensions, angles, swivel planes and the like. The maximum of the magnet swing out of the swivel planes PTS is given by respective angles ±β. Outer swivel angles ±β are about 20°, inner swivel angles ±βi are about 40°, which each can be varied up to the respective process needs. It should be mentioned that for many processes in the semiconductor industry, due to the thin layers, e.g. from some nanometers to about 500 nm, and high process efficiency which means a high cathode power applied, usually one magnet swing between the maximum positions, i.e. from +β position to −β position will suffice to deposit the required layer thickness. The swivel movement can be realized in a constant or a stepwise manner. Speed may vary or hold time may be different with consecutive swivel positions so that dwell time of the magnet system may vary and be different for instance for angle range +β to zero and range zero to −β. As shown with
Cathodes 1,2,3,4 with mounted targets 5,6,7,8 are of the same size, respective of the same diameter DT, arranged in equal distance TTT (i.e. TTTi=TTTo) from each other and in equal distance TSD (i.e. TSD1= . . . =TSD4) or at least in approximately equal distance MTSD−±2 mm from the target plane S. Alternatively, as shown in dotted lines, the position of the outer cathodes 1′, 4′ with targets 5′,8′ can be moved vertically, e.g. lowered as shown, so that the distance TSDo′ of the outer targets 1′, 4′ to the target plane is different to the distant TSDi of the inner targets 2,3 to the target plane S. In addition, position of the outer cathodes 1′, 4′ with targets 5′,8′ can be moved sidewise, e.g. towards the middle as shown, so that the distance TTTi between two inner targets is different to the distant TTTo between an outer target to the next inner target. Alternatives as discussed may help to improve layer uniformity parameters like (thickness or specific resistance) in an x-direction, e.g. when length x of the centrally positioned substrate would be shorter than the distance between the two outer axes in an arrangement of equal distances as shown with cathodes 1,2,3,4, or more formally expressed:
for: TTT=TTTk=1 . . . =TTTn (here n=3)
and at the same time: TSD≈TSDk=1≈ . . . ≈TSDm (here m =4) and TSC=TSCo=TSci.
Therefore, an arrangement as shown with dotted cathodes 1′,2′,3′,4′ would allow to adjust the nearest distance of the outer cathodes to the substrate surface to be coated, e.g. to a distance value |TSDi| according to the normal distance TSDi of the inner cathodes 2 and 3. In such case of different target to substrate plane distances, the longer distance has to be used to calculate the minimum value of the target protrusions or to calculate the maximum y-value for the substrate area for a given cathode array. Such an arrangement may be helpful also when the outer cathodes are driven with a different power, e.g. with higher or lower power, or a different power supply like an AC or a DC-supply, see below.
As a counter-pole to the cathodes a ground anode 19 is provided encompassing the cathode array. This can be realized by respective liners or shields, e.g. encompassing and/or forming essentially the whole inner surface of the deposition chamber 31 with the exception of the cathodes 1,2,3,4 and the pedestal 15 for the substrate 14.
The pedestal encompasses further an isolation or an isolated ESC 16 to allow a biased, e.g. RF, grounded or floating substrate potential, up to the respective process needs. A cooling/heating circuit comprising a cooling or heating fluid inlet 17, and a fluid outlet 18 may be provided. Usually water will be used as cooling liquid.
The pedestal may be further provided with a back-gas supply 20 to enhance thermal transfer from the pedestal 15 to a flat substrate 14 mounted to it or vice-versa. A back-gas supply 20 may comprise a gas supply for at least one inert gas, e.g. He and/or Ar and at least one gas inlet 21a leading to the surface of the pedestal 15, e.g. in the surface of the isolated ESC 16. Alternatively, there may be several inlets or gas distribution ducts, e.g. leading from a center towards further outside pedestal or ESC surface areas and having a flow area to transport back-gas with a low flow resistance. The ducts may be in part or even completely open to the backside of the wafer and being connected to shallow but wide gas channels, e.g. from 10 μm to 100 μm, or 50±10 μm depth, having a considerable higher flow resistance than the ducts and covering an essential area of the pedestal/ESC surface to provide an effective thermal transfer between the wafer and the pedestal/ESC surface via the back-gas. Alternatively, the wafer may be positioned on spacers in a close distance above the pedestals or the ESCs surface, e.g. according to the channel depth as mentioned, thereby forming another kind of channel between the wafer and the pedestal/ESC. With both variations the substrate may be further positioned on a surrounding projection, e.g. a gasket to allow a higher back-gas pressure. In a further embodiment the projection may be provided with small outlet openings to the process atmosphere or a back-gas outlet 21b may be provided to lead the back gas directly to the pump socket 22 of the high vacuum pump 23.
Elevation rods 24 allow to move the pedestal in a vertical direction, e.g. to load the substrate 14 to the pedestal in a lowered position (not shown), to close the deposition chamber 31 and/or adjust the substrate to cathode distance in an upper position as shown.
A process gas inlet 36 for inert sputter gases like Argon, Neon and/or Krypton and, if reactive processes should be performed to deposit compounds of the target material, respective reactive gases comprising e.g. nitrogen, carbon, or oxygen, can be connected to a gas distribution system 37 to distribute process gasses evenly in the deposition chamber 31.
In
Attention should be given to the different power supply systems the apparatuses of
Contrary to that with
In a further embodiment shown in
In
In table 1 the key dimensions of two inventive apparatuses for two different substrate geometries are shown. Both apparatuses are of a modified Clusterline PNL type. For apparatus 1 (Appar.1), which is based on a Clusterline PNL500 model, substrates in the range of 500±15 m×500±15 mm could be coated with a three cathodes array. For apparatus 2 (Appar.2), which is based on a Clusterline PLN600 model, substrates in the range of 600±20 m×600±20 mm could be coated with a four cathodes array.
The formula defines respective target protrusions as used per side of the respective substrates. Targets having a diameter DT from 140 mm to 160 mm have been used. Using such apparatuses, DC-power supplies for state of the art processes and bipolar pulsed DC-power supplies for inventive processes have been used with targets comprising swivel mounted magnetic systems. Parameters as shown in table 2 have been applied to show that swing induced thickness asymmetry could be effectively improved to enlarge the substrate surface in both y directions.
Applying such parameters, coating properties could be reached as shown in table 3.
With parameters as listed above a thickness distribution as shown in
In
In case of a pivoted magnetic system at Υ=60° from the zero position towards the central ZY-plane, the thickness maximum can be found shifted sidewise towards the center at about 325 mm, the substrates center being at 300 mm. Measuring points for deposition with a magnetic system in zero position are square and denominated DC Υ=0°, measuring points for deposition with a pivoted magnetic system are circular and denominated Υ=60°. A middle thickness of about 375 nm can be calculated from
From there a thickness uniformity unifT(Υ=0°)=±1.5% can be deduced for a deposition in the zero position of magnetic system, whereas the thickness uniformity achieved with the pivoted magnetic system was very poor with uniformity unifT(Υ=60°)=±7.8. At the same time the distribution is highly asymmetric being thin at one end and thick at the other end of the y-coordinates. It should be noted again that these measurements were made on one x-coordinate of maximum thickness only. Taking into account a thickness distribution of the whole substrate surface it is clear that despite optimization programs for the thickness distribution along a central x-coordinate, as shown with
In
The results of surface area measurements of the thickness uniformity on a 600 m×600 mm glass substrate with an edge exclusion of 10 mm for DC sputtering showing distinct swing induced thickness asymmetry is shown in
The same measurement on a respective glass substrate coated with a pulsed-DC process according to the present invention however resulted in a mean thickness of about 205 nm and a uniformity unifT<5.0 between the minimum and the maximum value, which is more than 30% better than the uniformity of the DC-process. Especially in the side areas between with 200≥y and 400≤y topographic differences are remarkably lowered.
Experimental results as shown with
| Number | Date | Country | Kind |
|---|---|---|---|
| 00291/20 | Mar 2020 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/052305 | 2/1/2021 | WO |
