Patent Application
20250207241
This application claims priority to United Kingdom Patent Application No. 2319929.2, filed on Dec. 22, 2023, the disclosure of which is incorporated herein by reference.
This disclosure relates to a Physical Vapour Deposition (PVD) apparatus. Specifically, the present disclosure relates also to an associated method of performing PVD.
Physical Vapour Deposition (PVD) is widely used for the deposition of high purity thin films, both metals and dielectric, for use in microelectronics and related industries. A typical PVD process occurs at reduced pressure in the presence of an inert gas such as Ar in a vacuum chamber where a target material is sputtered onto a substrate by applying a potential difference between the target cathode and an anode. Positively charged Ar+ ions are attracted to the target and “sputter” material from the target. By positioning a substrate, such as a circular silicon wafer, in the vicinity of the target some of the sputtered material is deposited onto the substrate.
In the microelectronics industry, a PVD module is incorporated into an integrated platform where multiple steps can occur in a specific sequence. These platforms are commonly known as “cluster tools”. Such platforms incorporate a number of modules around a central transport module where a vacuum robot can move substrates between the process modules. The process modules could comprise one or more PVD modules (potentially utilizing different targets) and/or could comprise pre-heat chambers, etch chambers and Chemical vapour deposition (CVD) chambers. Substrates are transported into and out of the transport module through load locks or vacuum cassette elevators. (VCEs).
It is necessary that the PVD module produces films to a fixed specification for the lifetime of the target and, when the target is changed, continues to meet the film specification. Properties that need to be controlled are film thickness, defectivity, stress, resistivity, texture or even composition of alloys. Ultimately the film specification will be device specific. Thin film thickness uniformity across a wafer, or within wafer (WIW), is one of the most critical metrics for a PVD system as unwanted variation in the thickness of a homogeneous film could result in undesirable device performance. Typically, this can be best represented by a % 1 sigma (or % 1σ) uniformity metric which is related to the standard deviation. This metric is often referred to as WIW non-uniformity and is expressed as a percentage. In an ideal case, the thickness of the deposited film would be equal at all points on the wafer surface (0% 1σ being ideal). Thickness measurements are conducted radially across the wafer surface such that 49-points are arranged with a centre point and three concentric rings equidistantly spaced. The thickness of the wafer is typically measured at each of the 49 points with each point representing an equal portion of the total area of the wafer less the 5 mm edge exclusion (EE) zone.
Prior art deposition technologies result in deposition WIW homogeneity deviations equal to or greater than 0.5% 1σ. This is due in part to factors such as the practical difficulty of designing a fully radially symmetric PVD chamber, constraints on overall chamber size and the accumulation of tolerances in key chamber components.
In PVD systems, wafers are typically placed upon a wafer support directly opposite a target assembly. Deposition uniformity is largely governed by: target width and magnetron design; the control of the distribution of material ejected from the target; and target to wafer separation which can produce collimation of the flux of ions arriving at the wafer surface. As target to wafer separation increases, uniformity improvements can be achieved but at the expense of a reduced deposition rate. In demanding multi-layer deposition sequences such as in MRAM, off-axis rotating wafer supports have been proposed to achieve improved uniformity for very thin films (i.e. films of several nm thickness). However, this results in large chambers with complex hardware and low deposition rates which are not suitable for more conventional PVD depositions. A further problem is that it is very difficult to achieve good RF coupling to a rotating part. Prior art systems utilizing a rotating wafer support are thus particularly problematic for those PVD processes that require an RF bias to be applied to a substrate support.
What is required therefore is a new way to improve thickness uniformity in PVD depositions. It is desirable for this to be achieved without compromising deposition rates and changing the basic geometry of the PVD chamber. It is desirable for this to be achieved while maintaining effective and reliable substrate bias voltage. It is desirable for this to be achieved while maintaining effective and reliable temperature control. The present disclosure, in at least some of its embodiments, addresses the above-described problems, desires and requirements.
According to a first aspect of the disclosure there is provided a Physical Vapour Deposition (PVD) apparatus comprising:
In this way, improved substrate thickness uniformity is achieved by rotation of the substrate on the upper portion while maintaining RF coupling with the static lower portion. Surprisingly, it has been found that excellent thermal coupling can be achieved as well, with the advantage that the temperature of the upper portion can be readily controlled. The substrate support can be implemented as a compact assembly structure which does not require any additional modification inside the chamber. This makes process implementation more efficient as it does not change process conditions within the chamber.
The upper and lower portions can be spaced apart with a gap of less than 3 mm. The upper and lower portions can be spaced apart with a gap in the range 0.5 to 1.5 mm. The gap can be varied in order to optimize the capacitive coupling of RF power.
The upper portion can be positioned on a plurality of non-conductive bearings, the bearings also being in contact with the lower portion. The bearings can be dielectric coated bearings, such as a dielectric coated steel bearings, or dielectric bearings, such as silicon nitride bearings.
The arrangement for rotating the upper portion can comprise a source of rotational motion. The source of rotational motion can be coupled to a rotatable shaft, the rotatable shaft being in driving connection with the upper portion.
The lower portion of the substrate support can comprise a platform portion which is spaced from the upper portion. The platform portion can be supported by a support stem. The rotatable shaft can extend through the support stem.
The lower portion can be electrically isolated from the chamber by a dielectric break structure.
The apparatus can further comprise an upper sheath which surrounds a periphery of the upper portion of the substrate support. The upper sheath can be in contact with the upper portion, at least during use in PVD. As a result, the upper sheath can be driven by RF power coupled to the upper portion during use in PVD.
The upper sheath can comprise an upper surface which is co-planar with the upper surface of the upper portion. In this way, a substrate can be supported by both the upper portion and the upper sheath. The upper surface can comprise an inner edge defining an annulus in which the upper surface of the upper portion is disposed.
The apparatus can further comprise a lower sheath which surrounds a periphery of the lower portion of the substrate support and is spaced therefrom. When the apparatus comprises a support stem, the lower sheath can surround a periphery of the platform portion and the support stem.
The lower sheath can be in electrical connection with the chamber.
The upper and lower sheaths can be 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.
The upper and lower sheaths can be formed from a metal, for example aluminium or stainless steel.
The lower portion of the substrate support can comprise one or both of resistive heater elements and fluid cooling conduits.
When the apparatus comprises a platform portion, the platform portion can house the resistive heater elements and fluid cooling conduits.
The target can be of any suitable type. The target can be formed from a metal. The use of an RF bias to the substrate support during PVD of metals is extremely important, and therefore the excellent control of RF bias provided by the disclosure is particularly advantageous in these applications.
The target can be sputtered by any suitable technique, such as DC sputtering, pulsed DC sputtering or RF sputtering. The target can comprise a magnetron, as is well known in the art.
The apparatus can further comprise a controller. The controller can control the process parameters during PVD. The controller can be configured to control the apparatus to perform the method of the second aspect of the present disclosure.
According to a second aspect of the present disclosure there is provided a method of performing PVD comprising the steps of:
The upper portion can be rotated at a speed in the range 1 to 10 rpm.
The target can overlay and extend radially beyond the substrate support.
The temperature of the upper portion can be controlled by controlling the temperature of the lower portion.
When the substrate support comprises an upper sheath and the upper sheath comprises an upper surface comprising an inner edge defining an annulus in which the upper surface of the upper portion is disposed, the substrate can extend radially beyond the inner edge.
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.
For the avoidance of doubt, whenever reference is made herein to ‘comprising’ or ‘including’ and like terms, the present disclosure is also understood to include more limiting terms such as ‘consisting’ and ‘consisting essentially’.
Whilst the present disclosure has been described above, it extends to any inventive combination of the features set out above, or in the following description, drawings or claims. For the avoidance of doubt, any features disclosed in relation to the first aspect of the present disclosure may be combined with any features disclosed in relation to the second aspect of the present disclosure and vice versa as appropriate.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:
Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure.
Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include all values to the magnitude of the smallest value (either lower limit value or upper limit value) and ranges between the values of the stated range.
The steps of the method described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present disclosure. Thus, in an embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of such steps.
The lower portion is formed of a platform portion 9 located on a support stem 11. Resistive heaters, fluid cooling pathways and thermal monitoring equipment such as thermocouples are located in the stationary platform portion 9. A shaft 13 passes through an internal passage in the lower portion 9, 11 without contacting the lower portion. The shaft 13 is in contact with the upper portion. In use, the shaft 13 is rotated by a suitable source of rotational motion located outside the vacuum chamber 3 (not shown), such as a motor or an actuator, thereby causing the upper portion 6 with the substrate 5 positioned on it to rotate. Vacuum sealing for the rotating shaft 13 is achieved by using “O” ring seals between the shaft 13 and the internal passage in the lower portion 9, 11.
The substrate support 8 is located centrally with respect to the target at the base of the vacuum chamber 3 with a ceramic break 12 electrically isolating the substrate support 8 from the vacuum chamber 3. An RF signal having an RF power is applied to the lower portion 9,11 using an RF generator 16. The RF generator 16 is connected to an annular connection 17 which is attached to the support stem 11. An RF matching box (not shown) is also provided. RF power is thereby 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 ion bombardment at the wafer surface from the plasma produced during sputtering to control film properties such as WIW thickness non-uniformity, stress and specific resistivity.
The substrate support 8 comprises the rotatable upper portion 6, the shaft 13 which causes the upper portion to rotate, the lower portion 9 and the support stem 11. The upper portion 6, lower portion 9 and the support stem 11 are all formed from a suitable metal such as stainless steel. In principle, the support stem does not need to be formed from a conductive material, but using a metal to manufacture the support stem is advantageous as it is easier to match the coefficients of thermal expansion of the support stem and the upper portion so that the substrate support functions effectively under the high temperatures encountered during PVD.
The apparatus further comprises an upper sheath 7 and a lower sheath 10. The upper sheath can be an annular upper platen cover 7 which rests on the perimeter of the upper portion 6 with its upper surface being coplanar with the upper surface of the upper portion 6 so 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 but spaced apart from the support stem 11 and the base of the lower portion 9. The lower sheath 10 is connected to the chamber 3 ground 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 as, with RF applied to the substrate support, a plasma discharge could occur between the RF live upper sheath 7 and the grounded lower sheath 10. Both upper and lower sheaths 7, 10 are metallic, for example aluminium or stainless steel. The sheaths 7, 10 can be textured to retain the PVD film and minimize the generation of particulates.
The substrate 5 enters/leaves the chamber through isolation valve 15 and is raised and lowered onto the substrate support 8 by a conventional lift assembly (not shown) either located near the perimeter of the wafer or more centrally within the wafer support. When situated on the substrate support the wafer extends beyond the internal edge of the upper sheath 7, typically by several mm (1-4 mm). The gap between the internal edge of the upper sheath 7 and the upper portion 6 is sized to maintain a small gap of about 0.5 mm to facilitate removal of the shielding, taking into account the thermal expansion of the materials used at the elevated temperatures encountered during processing.
In
A typical process sequence is shown in
Tests were performed using a Sigma fxP™ PVD system (SPTS Technologies Limited, Newport, UK) configured to process 200 mm diameter wafers. Deposition tests were carried out to quantify the differences in thickness uniformity and resistivity for metal deposition, in this case molybdenum (Mo), using a conventional platen assembly and a rotating platen assembly of the present disclosure. A rotating substrate support of the type shown in
The efficacy of the RF bias capability of the rotating substrate support can be seen in
Wafer to wafer (WTW) repeatability is also critical in HVM. Uniformity, both within wafer and wafer-to-wafer, is important in all production environments.
The present disclosure enables reliable independent control of the wafer bias voltage over a wide range of power and rotation speeds through capacitive coupling of RF from the stationary part of the substrate support to the rotating part. The close proximity of the upper portion to the lower portion also provides accurate temperature control of the wafer. This avoids the complications and concerns over reliability associated with rotation of the entire substrate support.
Although the present disclosure has been described with respect to one or more particular embodiments and/or examples, it will be understood that other embodiments and/or examples of the present disclosure may be made without departing from the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2319929.2 | Dec 2023 | GB | national |
