PVD Method and Apparatus

Abstract

A substrate is positioned on a substrate supporting upper surface of a substrate support. An arrangement of permanent magnets is positioned beneath the substrate supporting upper surface so that permanent magnets are disposed underneath the substrate. The deposition material is deposited into the recesses formed in the substrate by sputtering a sputtering material from a target of a magnetron device. While depositing the deposition material, the arrangement of permanent magnets provides a substantially uniform lateral magnetic field across the surface of the substrate which extends into a region beyond a periphery of the substrate to enhance resputtering of deposited material deposited into the recesses.

Claims

1. A method of depositing a deposition material into a plurality of recesses formed in a substrate by Physical Vapour Deposition (PVD) comprising the steps of: positioning the substrate on a substrate supporting upper surface of a substrate support, wherein an arrangement of permanent magnets is positioned beneath the substrate supporting upper surface so that permanent magnets are disposed underneath the substrate; and depositing the deposition material into the recesses formed in the substrate by sputtering a sputtering material from a target of a magnetron device; in which, during the step of depositing the deposition material, the arrangement of permanent magnets provides a substantially uniform lateral magnetic field across a surface of the substrate which extends into a region beyond a periphery of the substrate to enhance resputtering of deposited material deposited into the recesses.

2. The method according to claim 1, wherein the arrangement of permanent magnets is positioned beneath the substrate supporting upper surface so that permanent magnets are additionally disposed beyond the periphery of the substrate.

3. The method according to claim 1, wherein the target and the substrate are separated by a gap of 2.5 to 7.5 cm.

4. The method according to claim 3, wherein the target and the substrate are separated by a gap of 2.5 to 4 cm.

5. The method according to claim 1, wherein a DC power is applied to the target to sputter the material with an applied power density of 0.1 to 5 Wcm.sup.2.

6. The method according to claim 5, wherein the applied power density is 0.25 to 1 Wcm.sup.−2.

7. The method according to claim 1, wherein the arrangement of permanent magnets is moveable and, during the step of depositing the deposition material, the arrangement of permanent magnets is subjected to a motion which allows the substantially uniform lateral magnetic field to be provided.

8. The method according to claim 7, wherein the motion that the moveable arrangement of permanent magnets is subjected to is rotation.

9. The method according to claim 8, wherein the moveable arrangement of permanent magnets is rotated at 2.5 to 15 rpm.

10. The method according to claim 9, wherein the moveable arrangement of permanent magnets is rotated at 5 to 10 rpm.

11. The method according to claim 7, wherein the motion that the moveable arrangement of permanent magnets is subjected to is a reciprocating motion.

12. The method according to claim 1, wherein the substantially uniform lateral magnetic field, which is provided across the surface of the substrate and extends into the region beyond the periphery of the substrate, has a magnetic field strength in the range 100-500 Gauss (0.01-0.05 Tesla).

13. The method according to claim 1, wherein Ar and/or He is used as a process gas during the step of depositing the deposition material.

14. The method according to claim 1, wherein an RF power is applied to the substrate to produce a DC bias of 100 to 500 V during the step of depositing the deposition material.

15. The method according to claim 1, wherein the step of depositing the deposition material is performed at a chamber pressure in the range 2 to 150 mTorr.

16. The method according to claim 1, wherein the deposition material is Ti, TiN, Ta, TaN, W, WN, Co, Ru or Cu.

17. The method according to claim 1, wherein the deposition material is deposited by reactive sputtering using hydrogen, nitrogen or oxygen.

18. The method according to claim 1, wherein the recesses are vias.

19. A Physical Vapour Deposition (PVD) apparatus for depositing a deposition material into a plurality of recesses formed in a substrate comprising: a chamber; a magnetron device comprising a target disposed in the chamber from which a sputtering material can be sputtered; and a substrate holder configured to hold a substrate of pre-defined dimensions comprising a substrate support disposed in the chamber; in which: the substrate support comprises a substrate supporting upper surface and an arrangement of permanent magnets positioned beneath the substrate supporting upper surface so that, in use, permanent magnets are disposed underneath the substrate; and wherein the arrangement of permanent magnets is configured to provide, in use, a substantially uniform lateral magnetic field across the surface of the substrate which extends into a region beyond a periphery of the substrate to enhance resputtering of deposited material deposited into the recesses.

20. The PVD apparatus according to claim 19, wherein the arrangement of permanent magnets is positioned beneath the substrate supporting upper surface so that permanent magnets are additionally disposed beyond the periphery of the substrate.

21. The PVD apparatus according to claim 19, wherein, in use, the target and the substrate support are separated by a gap of 2.5 to 7.5 cm.

22. The PVD apparatus according to claim 19, wherein the arrangement of permanent magnets is moveable, and the apparatus further comprises a mechanism configured to subject the arrangement of permanent magnets to a motion which allows the substantially uniform lateral magnetic field to be provided in use.

23. The PVD apparatus according to claim 22, wherein the mechanism is a rotation mechanism for rotating the moveable arrangement of permanent magnets.

24. The PVD apparatus according to claim 19, further comprising a controller which is configured to control the PVD apparatus.

25. The PVD apparatus according to claim 19, further comprising the substrate positioned on the substrate supporting upper surface of the substrate support.

Description

DESCRIPTION OF THE DRAWINGS

[0041] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0042] FIG. 1 is a semi-schematic cross sectional view of a via (a) without a constriction at the opening of the via and (b) with a constriction at the opening of the via;

[0043] FIG. 2 is a semi-schematic view of an apparatus of the invention;

[0044] FIG. 3 is a semi-schematic view of the substrate holder of FIG. 2 including an arrangement of permanent magnets;

[0045] FIG. 4 is a SEM (scanning electron microscope) image of a via with a titanium layer deposited using a prior art ionized PVD apparatus;

[0046] FIG. 5 shows developed DC bias as a function of RF bias power and Target power;

[0047] FIG. 6 is a SEM image of a via with a titanium layer deposited using an apparatus of the invention with Ar process gas;

[0048] FIG. 7a shows SEM images of the top and FIG. 7b shows the base of a via with a titanium layer deposited using an apparatus of the invention with He process gas; and

[0049] FIG. 8a shows a schematic representation of a via with a PVD deposited titanium layer showing 15 measurement points and FIG. 8b shows the thickness of the titanium layer, presented as % coverage values, at the 15 measurement points for PVD performed using the apparatus of the invention and a prior art ionized PVD apparatus and measured using a TEM (transmission electron microscope).

DETAILED DESCRIPTION OF THE DISCLOSURE

[0050] In FIG. 2 shows a PVD apparatus 200 of the invention. A wafer 240 is positioned on a substrate supporting surface of a chuck 202 or platen within a vacuum chamber 204. The chuck 202 is part of a substrate support 206. Within the chuck 202 and below the wafer and the substrate supporting surface is an arrangement of permanent magnets, shown generally at 208. This arrangement is described in more detail below in relation to FIG. 3. The apparatus further comprises an RF power source 210, which is connected to the substrate support 206 to provide an RF bias on the wafer 240. The RF power source 210 typically operates at 2-20 MHz (usually 13.56 MHz out of convention), although an RF electrical signal of any suitable frequency, such as 380-400 kHz, could be used. Temperature control is achieved through resistive heating and fluid based cooling is achieved through a connection 212 which allows a cooling fluid to be flowed into and out of the chuck 202 in a manner well known to the skilled reader. One or more process gases enters the chamber through line isolation valve 214 and gas line 216. The process gas or gases can comprise one or more Noble gases such as Ar, He, Ne, Kr, Xe. He and/or Ar can be used with good results as described later. A reactive gas such as nitrogen, oxygen or hydrogen can be used as part of a reactive sputtering process. The line isolation valve 214 and line 216 are connected to a suitable gas manifold (not shown) which can deliver the desired process gas or gases. The apparatus is evacuated through an opening 218 same numeral as apparatus using a suitable vacuum pumping system (not shown). Wafer loading/unloading occurs through a slot valve 220. A target 222 is situated opposite the wafer 240 at the top of the chamber 204. The target 222 is driven by a negative DC power supply 224 and isolated from the grounded metal chamber through the use of dielectric isolation 226. Typically, the target is circular. A rotating magnet assembly 228 is positioned behind the target 222. The rotating magnet assembly 228 comprises permanent magnets 230 which help to trap electrons in the vicinity of the target 222 and provide full face erosion of the target 222. The target 222, rotating magnet assembly 228 and power supply 224 constitute a magnetron device which allows sputtering to take place. As explained in more detail below, the substrate support 206 provides capacitive coupling of RF and also magnetic enhancement of the resputtering process.

[0051] FIG. 3 is a cross sectional view of the chuck 202 of FIG. 2 with the wafer 240 in position. FIG. 3 shows an arrangement of permanent magnets 300, 302 which can be used to provide enhanced deposition and resputtering. The wafer 240 to be processed is positioned on the substrate supporting surface 304 of the chuck 202. The chuck 202 comprises a lower part 306 and an upper part 308. The upper part 308 is an annular ring which carries the substrate supporting surface 304. The upper part 308 is attached to the lower part 306, and together the lower part 306, upper part 308 and substrate supporting surface 304 form a cavity within the chuck 202. Within the cavity, the array of the permanent magnets 300, 302 is positioned on a rotating plate 310 which is attached to a shaft 312. The rotating plate 310 rotates above the lower part 306 while the shaft 312 passes through an aperture in the lower part 306 to permit the shaft 312 to be rotated by a suitable drive mechanism (not shown). As shown in FIG. 3, the magnets 300, 302 in the array are arranged along a linear cross sectional axis with alternate North 300 and South 302 polarities. Adjacent magnets of alternate polarity are separated by a spacing 314. It will be appreciated that FIG. 3 is a cross sectional view which shows the arrangement along a single cross sectional axis. In practice, the arrangement of permanent magnets is a two dimensional (2D) array of suitable configuration which extends underneath the entire lower surface of the wafer substrate 240 and can also extend beyond the periphery of the substrate. The arrangement of permanent magnets provides strong local magnetic fields. Typical values of the magnetic field are 100-500 Gauss (0.01-0.05 Tesla) at the surface of the wafer 240 extending beyond the edge of the wafer.

[0052] The lower 306 and upper 308 parts of the chuck 202 and the main plate-like body of the substrate supporting surface 304 are typically fabricated using a metal such as aluminium or an alloy such as an aluminium alloy. The outermost portion of the substrate supporting surface 304 which is in contact with the wafer 240 can be coated with a CrO.sub.2 coating to provide improved thermal performance. Surfaces can be frame sprayed or roughened by other means to retain sputtered material as is known to the skilled reader. Rotation of the array of permanent magnets enables a uniform lateral magnetic field to be produced at the wafer surface which in turn gives rise to excellent centre to edge uniformity of deposition across the wafer.

[0053] Experiments were performed using the apparatus shown in FIGS. 2 and 3 with a target to wafer separation of 4 cm. Excellent base and sidewall coverage of high aspect ratio vias was achieved. The vias had an aspect ratio (depth of the feature/diameter of the feature) of greater than to 24:1 and a diameter of 0.5 micron. A 332 mm diameter Ti target was used to deposit thin Ti barrier layers on 200 mm diameter silicon wafers operating at low target powers (<5 W/cm.sup.2) without any additional plasma enhancement of the material sputtered from the target. Under these conditions, the system is operating without a high density of ionized Ti being emitted from the target (in other words, without a high ion fraction in the plasma). This is in contrast to prior art ionized PVD systems. The small target to wafer separation of 4 cm would be expected to result in a significant amount of sputtered material reaching the wafer with non-normal incidence. It is anticipated that target to wafer separations of 2.5-7.5 cm would operate in a similar fashion. Beyond this range of target to wafer separations it is possible that uniformity and deposition rate would be a concern unless ionized PVD techniques were employed.

[0054] Surprisingly, it was found that it was possible to avoid closure of the via openings during deposition and achieve excellent base and sidewall coverage of these very high aspect ratio features, due to an enhanced etch performance. One set of experiments were performed with the following operating conditions: 82 mTorr Ar pressure; 0.4 kW Target power (0.46 W/cm.sup.2); 120V DC Bias; rotation of the array of permanent magnet at ca. 5-10 rpm. The resulting step coverage results are shown in Table 1, which indicates that excellent centre to edge uniformity was achieved in the high aspect ratio features. It is notable that even at the edge of the wafer, minimal shadowing (caused by the via profile) was observed. It is believed that enhanced resputtering of material on the wafer surface and within the deep features avoided closure of the vias, and enabled good base coverage and excellent sidewall coverage.

TABLE-US-00001 TABLE 1 Comparison of step coverage measured by SEM at the wafer centre and edge. Wafer Wafer Centre Edge Field  100%  100% Side wall  3.8%  6.6% Corner 10.8% 11.9% Bottom 15.7% 13.1%

[0055] A performance comparison was made between the apparatus of the invention shown in FIGS. 2 and 3, and the prior art i-PVD module manufactured by the applicant (an advanced HiFill™ PVD module on a Sigma fxP™ PVD apparatus, which is commercially available from SPTS Technologies Limited, located in Newport, South Wales, UK).

[0056] In the prior art advanced HiFill™ PVD chamber, a high platen DC bias and solenoid coils surrounding the chamber are used in conjunction with a long throw design to improve step coverage. Ti deposition into high aspect ratio vias (25:1) was performed using 1 mT Ar process gas at 40 kW target power (46 W/cm.sup.2), with 450 W RF bias (resulting in 110V DC bias) combined with a target to substrate distance of ca. 350 mm. As shown in FIG. 4, good base coverage ([thickness of coverage at base of feature/thickness in the field]%) of up to 19% that of the field (232 nm) was achieved. However, only a very small amount of this material is resputtered onto the sidewalls at the bottom of the via, giving only 2% coverage.

[0057] Using the apparatus of the invention, it is possible to achieve a much higher degree of resputtering. With a target power of 0.25 kW (ca. 0.29 W/cm.sup.2), an RF power of 100 W and a chamber pressure of 3.5 mTorr, a bias of 110V is achieved. However, these conditions resulted in negligible resputtering at the bottom of the via. Base coverage was ca. 5%, which is worse than with the prior art system when a similar pressure was used and a similar DC bias was developed, albeit with a much higher target power This suggests that insufficient deposition is reaching the wafer.

[0058] It is to be noted that a larger degree of resputtering is useful only if the base coverage can be increased. This is because material must first be deposited onto the base of the via for it to be resputtered onto the sidewalls. To achieve a more conformal base coverage required fine tuning of the bias and target power. FIG. 5 shows DC bias as a function of RF bias power and target power using the apparatus of the invention. The developed DC bias in V is shown as a function of RF power in W for target powers of 0.25 kW 500, 0.5 kW 502 and 2 kW 504. As RF power is increased, very high DC bias values are achieved. However, it can be seen that DC bias does not increase with increasing target power for a given value of the RF power. In view of these results, we postulate that for a given RF power to the chuck, the rate of resputtering is relatively constant. This suggests that the values of the target power and RF power are important in achieving sufficient resputtering for a given target film thickness.

[0059] Significant improvement was made to base coverage by substantially increasing Ar pressure to 100 mTorr, to increase scattering, while increasing target power density to 0.4 W/cm2 and substrate DC bias to 123V as can be seen in FIG. 6. This gave a bottom coverage of 17% and also a bottom corner coverage of 12%, which is far superior to the prior art system.

[0060] The type of process gas used is another process parameter that can be used to control resputtering. As previously stated, when Ar is used as the process gas, a higher RF power results in enhanced resputtering due to the DC bias on the wafer. The RF power is seen to direct ionized material to the bottom of the via. However, it can be advantageous to selectively direct large quantities of a deposition material such as Ti to the bottom of a via without a large degree of resputtering. This is a way in which coverage of the via bottom may be increased substantially. The use of He gas was investigated using a very high RF power to direct Ti into the via. Due to the small mass of the He ions, the amount of resputtering would be relatively small. Thus, high RF powers could be used to direct Ti into the via without the via opening becoming closed due to resputtering. We found that this scheme works for high DC bias values of greater than 200V, where bottom sidewall coverage of ca. 50% that of the field was observed. FIG. 7 shows the excellent result achieved operating at 20 mTorr of He with 0.25 kW target power and 400 W RF bias producing a DC bias of 227V. This DC bias was high enough to sputter material from the bottom of the via (FIG. 7b) while avoiding closure of the via (FIG. 7a). Equivalent tests using Ar as the process gas resulted in the closure of the via. This occurred because material was resputtered into the via opening, resulting in closure of the via, before significant quantities of material could be deposited onto the bottom of the via. These results were taken as an indication that the use of the lighter process gas results in a lesser amount of resputtering but a higher degree of directionality.

[0061] FIG. 8(a) is a sketch of a Ti layer 802 deposited into a high aspect ratio feature 804 (25:1 aspect ratio, 0.5 micron diameter opening) using a hard mask 800. FIG. 8a also shows 15 TEM measurement points 1-15 for measuring the thickness of the Ti layer. FIG. 8b shows a plot of a series of high resolution TEM measurements of the Ti thickness taken at the 15 points shown in FIG. 8a following deposition of Ti using both the prior art i-PVD system 806 and the present invention 808 under conditions which were optimized for the feature. It can be seen that, at all points, the present invention provides improved coverage within the via when compared to the prior art system.

[0062] Without wishing to be bound by any particular theory or conjecture, we propose that the relatively strong (100-500 Gauss) uniform magnetic field substantially parallel with the wafer surface reduces electron loss from the RF driven platen assembly. In turn, this increases ionization for a fixed RF power. This produces a more dense plasma which can more efficiently resputter material that is present on the wafer surface and within the via. The magnetic field providing this enhancement in resputtering is not attenuated within the vias. This is in contrast to the immersed coil of prior art systems such as that described in US2018/0327893 A1, which lies above the wafer and provides an enhancement of the plasma in the vicinity of the wafer as long as the plasma is above the wafer. However, the plasma will diminish as it reaches within the via.

[0063] A relatively small target to wafer separation provides a high flux of sputtered material reaching the wafer even at relatively low target power densities (<5 W/cm.sup.2). Through judicious choice of process parameters such as pressure, target power, DC bias and process gas, excellent results can be achieved. A mixture of Ar and He (or other process gas mixtures) could be used to provide a desired process performance. The methodologies and information provided herein can be used directly or readily adapted by the skilled person through routine experimentation to provide excellent results when depositing materials into recessed features by PVD across a wide range of implementations and applications. For example, by introducing a reactive gas such as NO or O.sub.2, a nitride or oxide deposition could be achieved using the present invention.