PVD apparatus and method

Abstract

According to the present invention, there is provided a physical vapor deposition (PVD) apparatus, comprising: a PVD chamber; a target; a substrate support in the chamber, the substrate support comprising an upper rotatable portion and a lower fixed portion, the upper rotatable portion having an upper surface on which a substrate can be supported; an RF source configured to supply an RF signal having an RF power to the lower portion; and an arrangement for rotating the upper portion during a PVD process performed in the chamber; wherein the upper portion is spaced apart from the lower portion such that RF power supplied to the lower portion is capacitively coupled to the upper portion.

Description

Technical Field

[0001] The present invention relates to a physical vapor deposition (PVD) apparatus. The present invention also relates to a related method of performing PVD. Background Art

[0002] Physical vapor deposition (PVD) is widely used for depositing high-purity thin films (metals and dielectrics) for use in the microelectronics and related industries. A typical PVD process occurs under reduced pressure in a vacuum chamber in the presence of an inert gas (e.g., Ar), where the target material is sputtered onto a substrate by applying a potential difference between a target cathode and an anode. Positively charged Ar+ ions are attracted to the target and "sputter" material from the target. By positioning the substrate (e.g., a circular silicon wafer) near the target, some of the sputtered material is deposited onto the substrate.

[0003] In the microelectronics industry, PVD modules are incorporated into integrated platforms where multiple steps can occur in a specific order. These platforms are commonly referred to as "cluster tools". Such platforms incorporate multiple modules around a central transfer module where a vacuum robot can move substrates between processing modules. The processing modules can contain one or more PVD modules (potentially utilizing different targets) and / or can contain preheat chambers, etch chambers, and chemical vapor deposition (CVD) chambers. Substrates are transported into and out of the transfer module via a load lock or a vacuum cassette elevator (VCE).

[0004] The PVD module needs to produce a film with fixed specifications during the life of the target and continue to meet the film specifications when the target is replaced. The characteristics that need to be controlled are film thickness, defect rate, stress, resistivity, texture, or even alloy composition. Ultimately, the film specifications will be device-specific. The thin film thickness uniformity on or within a wafer (WIW) is one of the most critical metrics of a PVD system because an undesirable variation in the uniform film thickness can lead to poor device performance. Typically, this can be best represented by the %1sigma (or %1σ) uniformity metric related to the standard deviation. This metric is commonly referred to as the WIW non-uniformity and is expressed as a percentage. In an ideal situation, the thickness of the deposited film would be equal at all points on the wafer surface (0%1σ is ideal). Thickness measurements are taken radially across the wafer surface such that 49 points are equally spaced with one central point and three concentric circles. Typically, the thickness of the wafer is measured at each of the 49 points, where each point represents an equal portion of the total wafer area minus a 5 mm edge exclusion (EE) zone.

[0005] Existing deposition techniques result in a deposition WIW uniformity deviation equal to or greater than 0.5%1σ. This is partly due to factors such as the practical difficulty of designing a completely radially symmetric PVD chamber, constraints on the overall chamber size, and the accumulation of tolerances in critical chamber components.

[0006] In a PVD system, a wafer is typically placed on a wafer support that is directly opposite a target assembly. Deposition uniformity depends primarily on: target width and magnetron design; controlling the distribution of material ejected from the target; and target-to-wafer separation, which can collimate the ion flux reaching the wafer surface. As the target-to-wafer separation increases, uniformity improvement can be achieved, but at the cost of a reduced deposition rate. In demanding multi-layer deposition sequences, such as in MRAM, off-axis rotation of the wafer support has been proposed to achieve improved uniformity for very thin films (i.e., films with a thickness of a few nanometers). However, this would result in a large chamber with complex hardware and a low deposition rate, which is not suitable for more conventional PVD depositions. Another problem is that it is difficult to achieve good RF coupling with the rotating components. Thus, for those PVD processes that require applying an RF bias to the substrate support, existing technology systems that utilize a rotating wafer support are particularly problematic. SUMMARY OF THE INVENTION

[0007] Accordingly, there is a need for a new method to improve thickness uniformity in PVD depositions. It is desirable to achieve this without compromising the deposition rate and without changing the basic geometry of the PVD chamber. It is desirable to achieve this while maintaining an effective and reliable substrate bias voltage. It is desirable to achieve this while maintaining effective and reliable temperature control. In at least some embodiments of the present invention, the present invention addresses the above problems, desires, and requirements.

[0008] According to a first aspect of the present invention, there is provided a physical vapor deposition (PVD) apparatus comprising:

[0009] a PVD chamber;

[0010] a target;

[0011] a substrate support in the chamber, the substrate support comprising an upper rotatable portion and a lower fixed portion, the upper rotatable portion having an upper surface on which a substrate can be supported;

[0012] an RF source configured to supply an RF signal having RF power to the lower portion; and

[0013] an arrangement for rotating the upper portion during a PVD process performed in the chamber;

[0014] wherein the upper portion is spaced apart from the lower portion such that the RF power supplied to the lower portion is capacitively coupled to the upper portion.

[0015] In this way, improved substrate plate thickness uniformity is achieved by rotating the substrate on the upper part while maintaining RF coupling with the static lower part. Surprisingly, it has been found that excellent thermal coupling can also be achieved, with the advantage that the temperature of the upper part can be easily controlled. The substrate support can be implemented as a compact assembly structure that does not require any additional modifications inside the chamber. This makes the process implementation more efficient as it does not change the process conditions inside the chamber.

[0016] The upper part and the lower part can be spaced apart with a gap of less than 3 mm. The upper part and the lower part can be spaced apart with a gap in the range of 0.5 to 1.5 mm. The gap can be changed to optimize the capacitive coupling of the RF power.

[0017] The upper part can be positioned on a plurality of non-conductive bearings that also contact the lower part. The bearings can be dielectric-coated bearings, such as dielectric-coated steel bearings, or dielectric bearings, such as silicon nitride bearings.

[0018] The arrangement for rotating the upper part can include a source of rotational motion. The source of rotational motion can be coupled to a rotatable shaft that is drivingly connected to the upper part.

[0019] The lower part of the substrate support can include a platform portion that is spaced apart from the upper part. The platform portion can be supported by support rods. The rotatable shaft can extend through the support rods.

[0020] The lower part can be electrically isolated from the chamber by a dielectric break structure.

[0021] The apparatus can further include an upper sheath that surrounds the periphery of the upper part of the substrate support. The upper sheath can contact the upper part, at least during use in PVD. Thus, during use in PVD, the upper sheath can be driven by the RF power coupled to the upper part.

[0022] The upper sheath can include an upper surface that is coplanar with the upper surface of the upper part. In this way, the substrate can be supported by both the upper part and the upper sheath. The upper surface can include an inner edge that defines an annular region in which the upper surface of the upper part is disposed.

[0023] The apparatus can further include a lower sheath that surrounds the periphery of the lower part of the substrate support and is spaced apart therefrom. When the apparatus includes support rods, the lower sheath can surround the periphery of the platform portion and the support rods.

[0024] The lower sheath can be electrically connected to the chamber.

[0025] The upper sheath and the lower sheath are spaced apart by a dark space gap. The dark space gap can be 2 mm or less. The dark space gap can be 1 mm or less.

[0026] The upper sheath and the lower sheath may be formed of metal (such as aluminum or stainless steel).

[0027] The lower portion of the substrate support may include one or both of a resistive heater element and a fluid cooling conduit.

[0028] When the device includes a platform portion, the platform portion may accommodate a resistive heater element and a fluid cooling conduit.

[0029] The target can be of any suitable type. The target may be formed of metal. It is extremely important to use RF bias for the substrate support during PVD of the metal, and thus the excellent control of the RF bias provided by the present invention is particularly advantageous in these applications.

[0030] The target may be sputtered by any suitable technique, such as DC sputtering, pulsed DC sputtering, or RF sputtering. As is well known in the art, the target may include a magnetron.

[0031] The device may further include a controller. The controller may control process parameters during PVD. The controller may be configured to control the device to perform the method of the second aspect of the present invention.

[0032] According to a second aspect of the present invention, there is provided a method of performing PVD, comprising the steps of:

[0033] Placing a substrate on a substrate support in a PVD chamber, the substrate support including an upper rotatable portion and a lower fixed portion, the upper rotatable portion having an upper surface on which the substrate can be supported;

[0034] Supplying an RF signal having RF power to the lower portion;

[0035] While the upper portion rotates and the lower portion is fixed, performing a PVD process to deposit a material onto the substrate by sputtering a target, wherein the RF power supplied to the lower portion is capacitively coupled to the upper portion.

[0036] The upper portion may rotate at a speed in the range of 1 to 10 rpm.

[0037] The targets may overlap and radially extend beyond the substrate support.

[0038] The temperature of the upper portion may be controlled by controlling the temperature of the lower portion.

[0039] When the substrate support includes an upper sheath and the upper sheath includes an upper surface, the substrate may radially extend beyond an inner edge, the upper surface including an inner edge defining an annular region, wherein the upper surface of the upper portion is disposed in the annular region.

[0040] The substrate can be a semiconductor substrate, such as a silicon substrate. The semiconductor substrate can be a silicon wafer or a wafer of another semiconductor material.

[0041] For the avoidance of doubt, whenever reference is made in this text to the terms ‘comprising’ or ‘including’ and similar terms, the invention is also to be understood as encompassing the more restrictive terms, such as ‘consisting of’ and ‘consisting essentially of’.

[0042] Although the invention has been described above, the invention encompasses any inventive combination of the features set out in the description above or below, the drawings or the claims. For the avoidance of doubt, any feature disclosed in relation to a first aspect of the invention may, where appropriate, be combined with any feature disclosed in relation to a second aspect of the invention, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0044] Figure 1 is a semi-schematic cross-sectional view through a PVD deposition apparatus according to the invention;

[0045] Figure 2 shows the process sequence;

[0046] Figure 3 shows thickness profiles for (a) deposition using a stationary platen of the prior art and (b) deposition using a rotating substrate support according to the invention;

[0047] Figure 4 shows, for a thin film metal layer of molybdenum deposition, the relationship between the applied platen RF power and the thickness non-uniformity (% 1σ) and the average specific resistivity;

[0048] Figure 5 shows the average local stress and the full stress range (in MPa) as a function of the process pressure (mTorr) for the applied platen RF power (0 W to 300 W) for molybdenum deposition;

[0049] Figure 6 shows the thickness non-uniformity (% 1σ) and the average specific resistivity ρ (μΩ.cm) repeatability in 20 wafer processing runs; and

[0050] Figure 7 shows the thickness non-uniformity (% 1σ), the average specific resistivity and the average specific resistivity non-uniformity (% 1s) as a function of the molybdenum film thickness. DETAILED DESCRIPTION

[0051] Figure 1Shows the PVD apparatus of the present invention 1, which includes a sputtering target 2 within a metal grounded vacuum chamber 3. The vacuum chamber 3 is evacuated through a vacuum port 4. A substrate 5 (usually a wafer) to be processed is centered on a substrate support 8. More precisely, the wafer is placed on the upper surface of the rotatable portion 6 of the upper part of the substrate support 8. For processing a wafer substrate, the upper part may be in the form of a platen or a similar structure. The substrate support 8 further includes a lower stationary portion 9, 11 and a series of bearings 14 located on top of the lower portions 9, 11. The upper portion 6 rests on the bearings 14, which serve to space the upper portion 6 from the lower portions 9, 11. The bearings 14 are non-conductive, such as dielectric-coated steel bearings or dielectric bearings formed of a suitable material such as silicon nitride. The bearings 14 may be located in any convenient position, such as towards the periphery of the lower portions 9, 11 or near their center or a combination of both. There is no direct contact between the lower surface of the upper portion 6 and the upper surface of the lower portions 9, 11 except through the bearings 14. This defines a gap of approximately 1 mm between the lower surface of the upper portion 6 and the upper surface of the lower portions 9, 11.

[0052] The lower portion is formed by a platform portion 9 located on a support rod 11. A resistance heater, a fluid cooling path, and a thermal monitoring device (such as a thermocouple) are located in the fixed platform portion 9. A shaft 13 passes through an internal passage in the lower portions 9, 11 without contacting the lower portions. The shaft 13 contacts the upper portion. In use, the shaft 13 is rotated by a suitable source of rotational motion (such as a motor or actuator) located outside the vacuum chamber 3 (not shown), thereby causing the upper portion 6 and the substrate 5 located thereon to rotate. A vacuum seal for the rotating shaft 13 is achieved by using an "O" - ring seal between the shaft 13 and the internal passage in the lower portions 9, 11.

[0053] The substrate support 8 is centered relative to the target at the base of the vacuum chamber 3, where a ceramic breaker 12 electrically isolates the substrate support 8 from the vacuum chamber 3. An RF signal having RF power is applied to the lower portions 9, 11 using an RF generator 16. The RF generator 16 is connected to an annular connector 17, which is attached to the support rod 11. An RF matching box (not shown) is also provided. Thereby, RF power is applied to the lower portion 9, which is capacitively coupled to the upper portion 6 to provide a DC bias on the substrate 5. The DC bias increases the ion bombardment of the wafer surface by the plasma generated during sputtering to control film characteristics, such as WIW thickness non-uniformity, stress, and specific resistivity.

[0054] The substrate support 8 includes a rotatable upper part 6, a shaft 13 for rotating the upper part, a lower part 9, and a support rod 11. The upper part 6, the lower part 9, and the support rod 11 are all formed of a suitable metal (such as stainless steel). In principle, the support rod does not need to be formed of a conductive material, but it is advantageous to use metal to manufacture the support rod because it is easier to match the thermal expansion coefficients of the support rod and the upper part, enabling the substrate support to function effectively at the high temperatures encountered during PVD.

[0055] The apparatus further includes an upper sheath 7 and a lower sheath 10. The upper sheath can be an annular upper platen cover 7 resting on the periphery of the upper part 6, whose upper surface is coplanar with the upper surface of the upper part 6, such that in use the substrate 5 can also be supported on the upper sheath 7. The lower sheath 10 can be a tubular structure surrounding the base of the support rod 11 and the lower part 9 but spaced apart from the bases of the support rod 11 and the lower part 9. The lower sheath 10 is grounded to the chamber 3, while the upper sheath is electrically floating. The upper sheath 7 is separated from the lower sheath 10 by a dark space gap. The dark space gap is typically less than 1 mm under typical operating conditions because plasma discharges may occur between the RF-charged upper sheath 7 and the grounded lower sheath 10 when RF is applied to the substrate support. Both the upper sheath 7 and the lower sheath 10 are metallic, such as aluminum or stainless steel. The sheaths 7, 10 can be textured to hold the PVD film and minimize particle generation.

[0056] The substrate 5 enters / leaves the chamber through an isolation valve 15 and is raised and lowered onto the substrate support 8 by a conventional lift assembly (not shown), which is located near the wafer periphery or more centrally within the wafer support. When located on the substrate support, the wafer extends beyond the inner edge of the upper sheath 7, typically by a few millimeters (1 - 4 mm). Considering the thermal expansion of the materials used at the high temperatures encountered during processing, the size of the gap between the inner edge of the upper sheath 7 and the upper part 6 is designed to maintain a small gap of approximately 0.5 mm to facilitate removal of the shield.

[0057] In Figure 1 a DC power supply 19 connected to the target 2 is shown. However, the PVD process used can be any desired process, such as DC sputtering, pulsed DC sputtering with a magnetron assembly, or RF sputtering. The target 2 extends beyond the diameter of the substrate 5 to improve film uniformity and is isolated from the grounded chamber 3 by an annular ceramic breaker 18. When testing with a 200 mm diameter wafer, a target with a diameter of 332 mm is used to improve film uniformity.

[0058] Figure 2A typical process sequence is shown. The process sequence assumes that the target has been adjusted. At 200, the wafer is placed on the lift pins in the processing chamber. This can be achieved, for example, in a cluster tool using a vacuum transfer robot. The wafer is then lowered onto the top of the platen. Then, before starting wafer rotation at step 204, the required process conditions, pressure, gas flow, and temperature are established at step 202. At 206, rapid successive target power and substrate bias are applied, and PVD is started. When the desired thickness has been reached, the target and bias power are disconnected at 208, and rotation is stopped at 210. Chamber transfer pressure is achieved by stopping the gas flow into the chamber and pumping down to the required pressure (step 212). When the transfer pressure is achieved, the slit valve opens, the wafer is raised from the top of the platen by the lift pins, and removed from the chamber at 214 by the vacuum robot. The rotational speed of the platen rotation can be automatically controlled using a controller that employs a software algorithm to ensure an integer number of rotations during the deposition process, thus ensuring fully optimized results. A typical rotational speed is 1 - 10 rpm. If required, the alignment of the recess in the rotating platen top with the lift pin position is also automatically controlled by the controller and control software.

[0059] Experimental results

[0060] Tests were conducted using a Sigma fxP TM PVD system (SPTS Technologies Limited, Newport, UK) configured to process 200 mm diameter wafers. Deposition tests were performed using a conventional platen assembly and the rotating platen assembly of the present invention to quantify the differences in thickness uniformity and resistivity of the metal deposition (in this case molybdenum (Mo)). A rotating substrate support of the type shown in Figure 1 was used. The rotating platen top and platen top shield are made of stainless steel. During the experiment, the target-to-wafer spacing, as well as the target size and magnetron configuration, remained constant. A standard rotating magnetron was used during deposition. The nominal target thickness deposited on a 200 mm silicon wafer was The deposition conditions were: DC target power 1 kW, pressure 13 mT, RF bias 300 W, deposition temperature 200 °C. The platen top rotated at 3 rpm. Thickness measurements were obtained using a MetaPULSE-G instrument (Onto Innovation), which is a non-destructive pump-probe picosecond photoacoustic technique suitable for thickness measurement of opaque metal films.

[0061] Figure 3 shows thickness maps (49-point polar plots, 200 mm, 5 mm EE) of (a) deposition using a stationary platen of the prior art and (b) deposition using the rotating substrate support of the present invention. The thickness non-uniformity % (1σ) and thickness range are reported in Table 1. For the same deposition process and duration, the thickness NU% and range of the rotating substrate support of the present invention are significantly improved. This shows that the non-radial uniformity observed in stationary platen deposition can be reduced without reducing the deposition rate or productivity.

[0062]

[0063] Table 1. Thickness non-uniformity and thickness range for static and rotating depositions.

[0064] The efficacy of the RF bias capability of the rotating substrate support can be seen in Figure 4 which shows the effect of platen RF power on thickness non-uniformity (% 1σ) and average specific resistivity for a molybdenum thin film metal layer deposited using the rotating substrate support. Increasing the platen RF power significantly helps to reduce the thickness non-uniformity to less than or equal to 0.1% 1σ and to reduce the average specific resistivity to 8.6 μΩ.cm (best result: 0.05% 1s at 250 W; ρ = 8.6 μΩ.cm). Sheet resistance measurements were made using the Resmap (RTM) four-point probe technique (Creative Design Engineering, Inc., Cupertino, CA, USA).

[0065] Figure 5 shows the variation of average local stress and full stress range measured using an FSM 128L (Frontier Semiconductor) stress mapping system over a wide process pressure range. More specifically, Figure 5 shows a comparison of average local stress and full stress range data (measured in MPa) as a function of process pressure (mTorr) for applied platen RF power (0 W vs. 300 W). Molybdenum deposition was carried out using a target power of 1 kW, a pressure of 13 mT, and 10 mm EE. Effective stress control of the Mo film can be achieved to the extent that the stress can be fine-tuned by adjusting the process pressure. As the pressure increases, the average stress can change from compressive to tensile.

[0066] Wafer-to-wafer (WTW) repeatability is also crucial in HVM. Uniformity both within a wafer and wafer-to-wafer is critical in all production environments. Figure 6Shows wafer-to-wafer (WTW) repeatability for 20 wafer runs. Thickness non-uniformity (% 1σ) and average specific resistivity ρ (μΩ.cm) are shown. There is 5 mm EE. Excellent thickness non-uniformity and average specific resistivity repeatability are observed.

[0067] Figure 7 Plots the effect of molybdenum film thickness on thickness non-uniformity (% 1σ), average specific resistivity, and resistivity non-uniformity (% 1s). For comparison, the bulk specific resistivity of molybdenum is approximately 5.4 μΩ.cm. Measurements are made on Mo films with thicknesses of 100, 500, 1000, and For decreasing thicknesses less than the average resistivity increases substantially. This is consistent with what is expected for polycrystalline films, as scattering effects due to roughness and grain boundaries dominate when the thickness approaches the mean free path of the conducting metal, which is on the order of tens of nanometers.

[0068] The present invention achieves reliable independent control of the wafer bias voltage over a wide range of powers and rotational speeds through capacitive coupling of RF from a fixed part of the substrate support to a rotating part. The close proximity of the upper part to the lower part also provides precise temperature control for the wafer. This avoids problems of complexity and reliability associated with the rotation of the entire substrate support.

Claims

1. A physical vapor deposition (PVD) device, comprising: PVD chamber; Target; a substrate support in the chamber, the substrate support comprising an upper rotatable portion and a lower fixed portion, the upper rotatable portion having an upper surface on which a substrate can be supported; an RF source configured to supply an RF signal having RF power to the lower portion; as well as an arrangement for rotating the upper portion during a PVD process performed in the chamber; The upper portion is spaced apart from the lower portion such that RF power supplied to the lower portion is capacitively coupled to the upper portion.

2. The apparatus of claim 1, wherein the upper portion is spaced apart from the lower portion by a gap of less than 3 mm.

3. The apparatus of claim 2, wherein the upper portion is spaced apart from the lower portion by a gap in the range of 0.5 to 1.5 mm.

4. The apparatus of any one of claims 1 to 3, wherein the upper portion is positioned on a plurality of non-conductive bearings, the bearings also being in contact with the lower portion.

5. Apparatus according to any one of claims 1 to 4, wherein the arrangement for rotating the upper portion comprises a source of rotational motion coupled to a rotatable shaft, the rotatable shaft being in driving connection with the upper portion.

6. An apparatus as claimed in any preceding claim, wherein the lower portion of the substrate support comprises a platform portion spaced apart from the upper portion.

7. The apparatus of claim 6, wherein the platform portion is supported by support rods.

8. Apparatus according to claim 7 when dependent on claim 5, wherein the rotatable shaft extends through the support rod.

9. Apparatus according to any preceding claim, wherein the lower portion is electrically isolated from the chamber by a dielectric disconnect structure.

10. The apparatus of any preceding claim, further comprising an upper jacket surrounding a periphery of the upper portion of the substrate support.

11. The apparatus of claim 10, wherein the upper sheath is in contact with the upper portion.

12. An apparatus according to claim 10 or claim 11, wherein the upper jacket comprises an upper surface that is coplanar with the upper surface of the upper portion, such that a substrate can be supported by both the upper portion and the upper jacket.

13. The apparatus of any one of claims 10 to 12, further comprising a lower jacket surrounding a periphery of the lower portion of the substrate support and spaced apart therefrom.

14. Apparatus according to claim 13 when dependent on claim 7, wherein the lower jacket surrounds the periphery of the platform portion and the support rods.

15. Apparatus according to claim 13 or claim 14, wherein the lower sheath is electrically connected to the chamber.

16. The apparatus of any one of claims 13-15, wherein the upper jacket is separated from the lower jacket by a dark space gap.

17. An apparatus as claimed in any preceding claim, wherein the lower portion of the substrate support comprises one or both of a resistive heater element and a fluid cooling conduit.

18. Apparatus according to claim 17 when dependent on claim 6, wherein the platform portion houses the resistive heater element and fluid cooling conduit.

19. A method of performing PVD, comprising the steps of: placing a substrate on a substrate support in a PVD chamber, the substrate support comprising an upper rotatable portion and a lower fixed portion, the upper rotatable portion having an upper surface on which the substrate can be supported; supplying an RF signal having RF power to the lower portion; While the upper portion is rotated and the lower portion is fixed, a PVD process is performed to deposit material onto the substrate by sputtering a target, wherein RF power supplied to the lower portion is capacitively coupled to the upper portion.

20. The method of claim 19, wherein the upper portion is rotated at a speed in the range of 1 to 10 rpm.

21. A method according to claim 19 or claim 20, wherein the target overlies and extends radially beyond the substrate.

22. The method of any one of claims 19 to 21, wherein the temperature of the upper portion is controlled by controlling the temperature of the lower portion.

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