Method and apparatus for depositing a material

Abstract

A method is for depositing a dielectric material on to a substrate in a chamber by pulsed DC magnetron sputtering with a pulsed DC magnetron device which produces one or more primary magnetic fields. In the method, a sputtering material is sputtered from a target, wherein the target and the substrate are separated by a gap in the range 2.5 to 10 cm and a secondary magnetic field is produced within the chamber which causes a plasma produced by the pulsed DC magnetron device to expand towards one or more walls of the chamber.

Claims

1. A PVD apparatus for depositing a dielectric material on a substrate from a metallic target by pulsed DC magnetron sputtering comprising: a cylindrical chamber having a target backing plate; a rotating magnetron device which produces one or more primary magnetic fields in a vicinity of the metallic target located at a top of the chamber, wherein a sputtering material is sputtered from the metallic target, wherein the metallic target is powered by a pulsed DC magnetron device positioned on an opposite side of the target backing plate from the metallic target and outside the cylindrical chamber, wherein the metallic target has a target width; a DC power supply that provides a pulsed DC power to the metallic target from 1-10 kW; an RF driven substrate support disposed in the chamber which is orientated parallel to a surface of the metallic target at a distance from 2.5 cm to less than or equal to 5 cm and axially aligned with the metallic target, wherein a rotational path of the magnetron device behind the metallic target extends to beyond a diameter of a substrate on the substrate support, wherein the substrate support has a substrate support width, and wherein the target width is greater than the substrate support width; a gas inlet; a secondary magnetic field production device positioned around a body of the chamber between the metallic target and the substrate support which produces an axial secondary magnetic field that causes a plasma to expand towards a wall of the chamber, wherein the secondary magnetic field production device includes an electromagnet, wherein a density of field lines of the secondary magnetic field, in a cross sectional plane of the chamber in which an upper surface of the substrate support lies, is greatest in a region radially outwardly of the substrate adjacent the wall of the chamber, wherein the electromagnet is positioned such that the field lines extend axially along the wall of the cylindrical chamber, and wherein the electromagnet is disposed outside the chamber and extends around the wall of the chamber; and a controller configured to control the secondary magnetic field production device so that a secondary magnetic field is produced within the chamber while the dielectric material is deposited from the metallic target to produce an increase in thickness at a peripheral portion of the substrate, wherein the controller is further configured to control the pulsed DC power to the metallic target to be from 1-10 kW, a pulse frequency to be from 5-100 kHz, and a pulse duration to be from 1-10 sec, and wherein the controller is further configured to operate the electromagnet using a DC current from 10-20 Amps such that the electromagnet has a magnetic field strength of 330-660 Amp turns.

2. The apparatus according to claim 1, wherein the substrate support is configured to support a substrate having a width which is 150 mm or greater.

3. The apparatus according to claim 1, wherein the electromagnet is a single electromagnet that produces a magnetic field which steers electrons towards the wall of the chamber to produce a drift electric field which steers ions away from the peripheral portion of the substrate.

4. The apparatus according to claim 1, wherein the electromagnet includes a series of electromagnets having aligned polarities so that all of the electromagnets produce magnetic fields which steer electrons towards the wall of the chamber to produce a drift electric field which steers ions away from the peripheral portion of the substrate.

5. The apparatus according to claim 1, wherein the electromagnet is at least partly a same height as the substrate support in the chamber.

6. The apparatus according to claim 1, wherein the metallic target includes aluminum.

7. The apparatus according to claim 1, wherein the gas inlet is in fluid communication with at least one gas source, wherein the at least one gas source includes argon and/or nitrogen.

8. The apparatus according to claim 1, wherein the dielectric material is aluminum nitride or silicon oxide.

9. The apparatus according to claim 1, wherein the controller is configured to control a pressure of the chamber from 1-10 mT during the depositing with an argon flow from 5-40 sccm, and wherein the controller is configured to control a negative bias potential of an RF power supply in electronic communication with the substrate support on which the substrate is disposed to be from 20-45 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of apparatus and methods in accordance with the invention will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 shows AlN film thickness as a function of wafer radial position for a prior art deposition process;

(3) FIG. 2 is a semi-schematic cross sectional view of a portion of a prior art DC magnetron system being used to deposit AlN;

(4) FIG. 3 shows a PVD apparatus of the invention;

(5) FIG. 4 is a semi-schematic cross sectional view of a portion of a DC magnetron system of the invention being used to deposit AlN;

(6) FIG. 5 shows AlN film thickness as a function of wafer radial position for a number of DC current values in the DC coil; and

(7) FIG. 6 shows within wafer non-uniformity of deposited AlN film for a number of DC current values in the DC coil.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) FIG. 3 shows a PVD apparatus of the invention, depicted generally at 30. The apparatus 30 comprises a chamber 32 which contains a DC magnetron device 34, a target 36 from which material is sputtered by the magnetron device 34, and a substrate support 38 which supports a substrate (not shown) on which a desired material is deposited. The apparatus 30 further comprises a coil 40 which is disposed around the main body portion of the chamber 32. In the embodiment shown in FIG. 3, the chamber is cylindrical, although in principle other chamber shapes and other coil cross sectional shapes might be utilised. For presentation simplicity, other common aspects of magnetron sputtering devices, such as gas inlets and outlets are not shown in FIG. 3.

(9) Pulsed DC power is applied to the target 36 from a DC power supply 42. DC power is applied to the coil 40 by a coil DC electrical supply 46 which enables the applied current to be varied. RF power is applied to the substrate support 38 from a RF power supply 44 in order to negatively bias the substrate support. Typically, the substrate support 38 is driven at 13.56 MHz out of convention, although the invention is not limited in this regard. The operation of the power supplies 42, 44, 46 is controlled with a controller 48. The controller 48 may be a computer having a suitable graphical user interface.

(10) The problems with film uniformity associated with the deposition of materials such as AlN have been described above. The present inventors believe that they have found the reason for the reduced thickness of the deposited AlN film at the periphery of the wafer. Without wishing to be bound by any particular theory or conjecture, it is believed that the reduced film thickness at the periphery of the wafer is due to sputtering by positively charged ions. This is depicted in FIG. 2, which shows a portion of a DC magnetron system comprising a chamber 20 having a target backing plate 20a which acts as a lid portion. A target 22 is bonded to the target backing plate 20a. A pair of rotatable magnets 24 are positioned opposite the face of the target backing plate distant from the target 22. A wafer 26 is positioned on a platen 28 which can be RF driven to produce a negative DC bias. A mixture of argon and nitrogen is introduced into the chamber and a pulsed, negative, high DC voltage is applied to the target backing plate 20a/target 22 which thereby acts as a cathode. This creates a high density plasma which includes Ar and AlN ions. The wafer 26 sits inside the main erosion track of the cathode which is dictated by the rotating path of the magnets 24. It is believed that a proportion of the ions escape the negative glow of the plasma and move towards the platen 28. It is also believed that the negative bias on the platen 28 acts to attract positively charged ions such as Ar.sup.+ to the edge of the wafer 26, causing the deposited AlN film to be thinned in this region by sputter etching. Al and N cations may cause some sputter etching as well.

(11) FIG. 4 shows a portion of an apparatus of the invention which shares many of the features of the prior art apparatus shown in FIG. 2. Accordingly, identical numerals have been used in FIG. 4 to describe these shared features. The embodiment of the invention shown in FIG. 4 further comprises a multiple turn coil 29 which is positioned around the main body section of the chamber 20. The coil 29 is supplied with DC current from a DC electrical supply (not shown). FIG. 4 also shows secondary magnetic field lines which are generated by the energised coil 29. It can be seen that the magnetic field 21 lines generated in the interior of the chamber 20 extend generally axially along the chamber close to the chamber walls of the main body section. The effect of the secondary magnetic field generated by the coil 29 is to cause an expansion of the plasma towards the walls of the main body section of the chamber 20. Without wishing to be bound by any particular theory or conjecture, it is believed that the secondary magnetic field attracts electrons from the cathode which in turn sets up a drift electric field that steers ions away from the edge of the wafer 26. This reduces sputter etching at the edge of the wafer. Thus, it is believed that the invention can reduce the number of positive ions moving towards the wafer edge which would otherwise sputter etch the edge region of the wafer by steering these positive ions towards the chamber walls. As the number of positive ions impacting the edge region of the wafer is reduced, it is believed that the localised thinning effect in this region of the wafer caused by ion bombardment are also reduced. This results in improved deposited film uniformity.

(12) Experiments have been performed using apparatus in accordance with FIGS. 2 and 4 to deposit AlN films on silicon substrates. The deposition process conditions used as shown in Table 1.

(13) TABLE-US-00001 TABLE 1 Process Conditions for AIN Film Deposition Process Step Parameter (Typical) Parameter Range Pulsed DC power (kW) 5 1-10 Pulse frequency (kHz) & 10, 4 5-100, 1-10 duration (sec) Chamber Pressure (mT) 3 1-10 Gas flows (sccm) 20Ar/40N.sub.2 5-40Ar/5-80N.sub.2 Platen temperature ( C.) 150 100-400 Substrate bias (Volts) 35 20-45 Target to wafer separation (cm) ~4.5 3-9

(14) Various DC currents were applied to the coil producing the secondary magnetic field (corresponding to the coils 29 and 40 shown in FIGS. 4 and 3, respectively). More specifically 0 A, 10 A and 20 A currents were used in conjunction with a 33 turn coil. FIG. 5 shows the AlN deposited film thickness as a function of the radial position on the wafer for films deposited using these DC currents. The line 50 shows film thickness when no current was applied, the line 52 shows film thickness with a 10 A current, and the line 54 shows film thickness with a 20 A current. It can be seen that when a 20 A current was used to generate the secondary magnetic field, there was no drop off in AlN film thickness at the edge of the silicon wafer. FIG. 6 shows film within wafer (WIW) thickness non-uniformity expressed as 1 sigma % standard deviation for a 49 point polar measurement for 3, 5 and 10 mm edge exclusions (ee) as a function of DC coil current applied to the coil that generates the secondary magnetic field. The lines 60, 62, 64 correspond to the 3, 5 and 10 mm edge exclusions, respectively. FIG. 6 shows that with no applied DC current, the non-uniformity is high at 3 and 5 mm edge exclusion, which is due to the drop off in the film thickness at the wafer edge. At 20 A applied DC current, the within wafer non-uniformity is essentially the same for 3, 5 and 10 mm edge exclusion. It can be seen that for the system and process conditions associated with these experiments, the optimal secondary magnetic field is generated with an applied DC current of around 20 A. It can also be seen that excellent results are achieved. In fact, processing to a 3 mm edge exclusion is considered to be state of the art. The use of an electromagnet to generate a secondary magnetic field is advantageous, because it allows the strength of the field to be easily varied in order to achieve an optimal result. In the example provided herein, the optimised magnetic field is 3320=660 Amp turns. For any given implementation, the optimised magnetic field can be readily derived using the principles provided herein.

(15) The present invention can be applied to a wide range of PVD systems. It is possible to produce bespoke systems embodying the invention and it is also possible to readily retrofit existing PVD systems.