PVD apparatus and method

Abstract

To provide a method for improving thickness uniformity in PVD depositions.SOLUTION: A Physical Vapor Deposition (PVD) apparatus comprising: a PVD chamber; a target; a substrate support in the chamber comprising an upper rotatable portion having an upper surface on which a substrate can be supported and a lower stationary portion; 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 and lower portions are spaced apart so that RF power supplied to the lower portion is capacitively coupled to the upper portion.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Physical vapor deposition (PVD) is widely used for depositing high-purity thin films, such as those of metals and dielectrics, used in microelectronics and related industries. A typical PVD process is performed at low pressure in a vacuum chamber in which an inert gas, such as Ar, is present, and a 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 the material is "sputtered" from the target. By placing a substrate, such as a circular silicon wafer, near the target, some of the sputtered material is deposited on the substrate.

[0003] In the microelectronics industry, a PVD module is incorporated into an integrated platform in which a plurality of processes can be performed according to a specific procedure. Such platforms are well known as "cluster tools". In this type of platform, since a plurality of modules are around a central transport module, a substrate can be moved between those process modules by a vacuum robot. Those process modules can be provided with one or more PVD modules (potentially those using different targets), and / or can be provided with a preheating chamber, an etching chamber, and a chemical vapor deposition (CVD) chamber. The substrate is transported into and out of the transport module through a load lock or a vacuum cassette elevator (VCE).

[0004] What is necessary is that the PVD module produces a film that meets the fixed specifications throughout the entire life of the target, and continues to meet the film specifications even when the target is changed. The characteristics that must be controlled include film thickness, defect rate, stress, resistivity, texture, and even alloy composition. Ultimately, the film specifications will be device-specific. Wafer cross-sectional thin film thickness uniformity, i.e., within-wafer (WIW), is one of the most important metrics for a PVD system, because unwanted fluctuations in homogeneous film thickness can lead to defective device performance. Usually, this can be best expressed by the %1 sigma (i.e., %1σ) uniformity metric 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 deposited film thickness would be equal at all points on the wafer surface (an ideal %1σ of 0). Thickness measurements are taken across the wafer surface in a radial direction, such that 49 points are arranged in a central point and three concentric circles spaced equally apart. Usually, the wafer thickness is measured at each of these 49 points, and each point represents an equal portion of the entire area of the wafer excluding the edge exclusion (EE) zone less than 5 mm.

[0005] In conventional deposition technologies, deposition WIW homogeneity deviations with a %1σ of 0.5 or more occur. This is due in part to factors such as the practical design difficulties of a fully radially symmetric PVD chamber, constraints on the overall chamber dimensions, and the accumulation of tolerances in the main chamber components.

[0006] In a PVD system, a wafer is usually placed on a wafer support directly opposite the target assembly. There are factors that significantly affect the deposition uniformity, including the target width and magnetron design, control of the distribution of the emitted material from the target, and the target-to-wafer spacing that can parallelize the ion beam arriving at the wafer surface. Increasing the target-to-wafer spacing can achieve improved uniformity, but at the cost of a reduced deposition rate. In the multi-layer deposition procedures required for MRAM etc., an off-axis rotating wafer support has been proposed to achieve improved uniformity for ultra-thin films (i.e., films with a thickness of several nm). However, this leads to an increase in the size of the chamber, complexity of the hardware, and a decrease in the deposition rate, which is not suitable for more conventional PVD depositions. A further problem is that it is very difficult to achieve good RF coupling to the rotating part. Conventional systems using a rotating wafer support are particularly problematic in PVD processes of the type that require applying an RF bias to the substrate support.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, there is a need for a new method for improving thickness uniformity in PVD deposition. It is desirable to achieve this without sacrificing the deposition rate and without changing the basic geometry of the PVD chamber. It is desirable to achieve this while maintaining an effective and highly reliable substrate bias voltage. It is desirable to achieve this while maintaining effective and highly reliable temperature control. In the present invention, according to at least some of its embodiments, it addresses the above-described problems, expectations, and requirements.

Means for Solving the Problems

[0009] Provided by a first aspect of the present invention is a physical vapor deposition (PVD) apparatus, a PVD chamber, a target, a substrate support within the chamber, comprising a rotatable upper portion having an upper surface on which a substrate can be supported and a stationary lower portion, an RF source configured to supply an RF signal having a certain RF power to the lower portion, a device for rotating the upper portion when a PVD process is being performed within the chamber, and the upper portion and the lower portion are spaced apart such that the RF power supplied to the lower portion is capacitively coupled to the upper portion.

[0010] In this approach, while maintaining RF coupling with the stationary lower portion, rotation of the substrate on the upper portion achieves an improvement in substrate thickness uniformity. Surprisingly, it has been found that excellent thermal coupling can also be achieved, which advantageously allows the temperature of the upper portion to be rapidly controlled. The substrate support can be realized as a compact assembly structure, and no additional modification inside the chamber is required at all. Since the process conditions inside the chamber remain unchanged, this makes the process implementation more efficient.

[0011] The upper portion and the lower portion can be spaced apart with a gap of less than 3 mm. The upper portion and the lower portion can be spaced apart with a gap within the range of 0.5 - 1.5 mm. The capacitive coupling of the RF power can be optimized by varying the gap.

[0012] The upper portion can be positioned on a plurality of non - conductive bearings, and those bearings can be further brought into contact with the lower portion. Those bearings can be dielectric - coated bearings such as dielectric - coated steel bearings or dielectric bearings such as silicon nitride bearings.

[0013] The apparatus for rotating the upper part can be provided with a source of rotational motion. The source of rotational motion can be coupled to a rotatable shaft, and the rotatable shaft can be drivingly connected to the upper part.

[0014] The lower part of the substrate support can be provided with a platform part spaced apart from the upper part. The platform part can be supported by a support stem. The rotatable shaft can be extended into the support stem.

[0015] The lower part can be electrically separated from the chamber by a dielectric break structure.

[0016] The apparatus can further be provided with an upper sheath surrounding the periphery of the upper part of the substrate support. The upper sheath can be brought into contact with the upper part, at least during use in PVD. As a result, the upper sheath can be driven by the RF power coupled to the upper part during use in PVD.

[0017] The upper sheath can be provided with an upper surface coplanar with the upper surface of the upper part. In this configuration, the substrate can be supported by both the upper part and the upper sheath. An inner edge of the upper surface defines a ring, and the upper surface of the upper part can be disposed within the ring.

[0018] The apparatus can further be provided with a lower sheath surrounding and spaced apart from the periphery of the lower part of the substrate support. In an apparatus provided with a support stem, the lower sheath can surround the periphery of the platform part and the support stem.

[0019] The lower sheath can be electrically connected to the chamber. The upper sheath and the lower sheath can be spaced apart by a certain dark space gap. The dark space gap can be 2 mm or less. The dark space gap can be 1 mm or less.

[0020] The upper and lower sheaths can be formed of a metal, such as aluminum or stainless steel.

[0021] The lower portion of the substrate support can be provided with one or both of a resistive heater element and a fluid heat removal passage.

[0022] In an apparatus having a platform portion, a resistive heater element and a fluid heat removal passage can be accommodated in the platform portion.

[0023] The target can be of any suitable type. The target can be formed of a metal. The use of an RF bias for the substrate support during metal PVD is extremely important, i.e., the excellent RF bias control achieved by the present invention is particularly beneficial in that type of application.

[0024] The target can be sputtered by any suitable technique, such as DC sputtering, pulsed DC sputtering or RF sputtering. The target can be provided with a magnetron, as is well known in the art of the present case.

[0025] The apparatus can further be provided with a controller. By means of the controller, process parameters can be controlled during PVD. The controller can be configured to control the apparatus to execute the method of the second aspect of the present invention.

[0026] Provided by the second aspect of the present invention is a method of performing PVD, comprising: placing a substrate on a substrate support in a PVD chamber, the substrate support comprising a rotatable upper portion having an upper surface on which the substrate can be supported and a stationary lower portion; supplying an RF signal having a certain RF power to the lower portion; Executing a PVD process of depositing a material on a substrate by sputtering a target in a state where the upper part rotates and the lower part is stationary, and capacitively coupling the RF power supplied to the lower part to the upper part; It is a method having

[0027] The upper part can be rotated at a speed within the range of 1 to 10 rpm.

[0028] The target can be arranged above the substrate and radially expanded outside the substrate support.

[0029] The temperature of the upper part can be controlled by controlling the temperature of the lower part.

[0030] When the substrate support has an upper sheath and the upper surface of the upper part is arranged within the ring defined by the inner edge of the upper surface of the upper sheath, the substrate can be radially expanded beyond the inner edge.

[0031] The substrate can be a semiconductor substrate, for example, a silicon substrate. The semiconductor substrate can be a silicon wafer or a wafer of other semiconductor materials.

[0032] Undoubtedly, even when reference is made by terms such as "comprising" or "having" and the like, the present invention also includes more restrictive terms such as "configured" and "mainly configured" in interpretation.

[0033] Although the present invention has been described above, it extends to any novel combination of the features described so far or in the following description, drawings or claims. Undoubtedly, any feature disclosed in connection with the first aspect of the present invention can be combined with any feature disclosed in connection with the second aspect of the present invention, and vice versa.

[0034] Here, embodiments of the present invention will be described solely by way of example with reference to the following accompanying drawings.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3a

Figure 3b

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0036] Shown in Fig. 1 is the PVD apparatus 1 of the present invention, which is provided with a sputtering target 2 in a vacuum chamber 3 made of metal and grounded. The vacuum chamber 3 is pumped through a vacuum port 4. The substrate 5 to be processed is typically a wafer and is centrally placed on a substrate support 8. More specifically, the wafer is placed on the upper surface of the upper rotatable portion 6 of the substrate support 8. For the processing of the wafer substrate, the upper portion can be in the form of a platen or a similar structure. The substrate support 8 further includes lower stationary portions 9, 11 and a group of bearings 14 disposed on the tops of the lower portions 9, 11 thereof. The upper portion 6 sits on the bearings 14, and the function of these bearings 14 separates the upper portion 6 from the lower portions 9, 11. The bearings 14 are non-conductive, for example, dielectric bearings formed of a suitable material such as silicon nitride or dielectric-coated steel bearings. The bearings 14 can be located at any convenient position, such as near the periphery of the lower portions 9, 11, near the center thereof, 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 at the locations via the bearings 14. Thereby, a gap of about 1 mm is defined and formed between the lower surface of the upper portion 6 and the upper surface of the lower portions 9, 11.

[0037] The lower portion adopts a form in which a platform portion 9 is located on a support stem 11. A resistance heater, a fluid heat removal path, and a heat monitoring device such as a thermocouple are located in the stationary platform portion 9 thereof. The shaft 13 passes through the internal passage of the lower portions 9, 11 and is not in contact with the lower portions. The shaft 13 is in contact with the upper portion. In use, the upper portion 6 is rotated together with the substrate 5 located thereon by rotating the shaft 13 by a suitable rotational motion source (not shown) located outside the vacuum chamber 3, such as a motor or an actuator. The vacuum seal related to the rotating shaft 13 is achieved by using an O-ring seal between the shaft 13 and the internal passage of the lower portions 9, 11.

[0038] The location of the substrate support 8 is at the center as viewed from the target and at the base of the vacuum chamber 3, and the accompanying ceramic break 12 electrically isolates the substrate support 8 from the vacuum chamber 3. An RF signal having a certain RF power is applied to the lower portions 9, 11 using the RF generator 16. The RF generator 16 is connected to an annular coupler 17 attached to the support stem 11. An RF matching box (not shown) is also provided. The RF power is thus applied to the lower portion 9, and the lower portion 9 is capacitively coupled to the upper portion 6, and thus a DC bias is applied to the substrate 5. By this DC bias, the ion bombardment from the plasma generated during sputtering to the wafer surface can be increased, and film characteristics such as WIW thickness non-uniformity, stress, and resistivity can be controlled.

[0039] The substrate support 8 includes a rotatable upper portion 6, a shaft 13 for rotating the upper portion, a lower portion 9, and a support stem 11. The upper portion 6, the lower portion 9, and the support stem 11 are all formed of a suitable metal such as stainless steel. In principle, it is not necessary to form the support stem of a conductive material, but it is beneficial to manufacture the support stem using a metal, which makes it easy to match the thermal expansion coefficient of the support stem with that of the upper portion, and thus enables the substrate support to function effectively under the high temperatures encountered during PVD.

[0040] The device further comprises an upper sheath 7 and a lower sheath 10. The upper sheath can be an annular upper platen cover 7 seated on the periphery of the upper portion 6, and by making its upper surface coplanar with the upper surface of the upper portion 6, it becomes possible to support the substrate 5 on the upper sheath 7 during use. The lower sheath 10 can have a tubular structure that surrounds but is spaced from the support stem 11 and the base of the lower portion 9. The lower sheath 10 is connected to the ground of the chamber 3, and the upper sheath is electrically floating. The upper sheath 7 is separated from the lower sheath 10 by a certain dark space gap. The dark space gap under typical operating conditions is usually less than 1 mm, because a plasma discharge can occur between the upper sheath 7 on the RF acting side and the lower sheath 10 on the grounded side when RF is applied to the substrate support. Both the upper sheath 7 and the lower sheath 10 are made of metal, such as aluminum or stainless steel. The sheaths 7, 10 can be textured, which can serve to hold the PVD film and minimize particle generation.

[0041] The substrate 5 is taken in and out of the chamber via the isolation valve 15 and is lifted and lowered on the substrate support 8 by a conventional lift assembly (not shown) located near the wafer periphery or closer to the center within the wafer support. When placed on the substrate support, the spread of the wafer typically exceeds the inner edge of the upper sheath 7 by about several millimeters (1 - 4 mm). The gap between the inner 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 material, taking into account the thermal expansion of the materials used at the high temperatures encountered during processing.

[0042] The DC power supply 19 in FIG. 1 is connected to the target 2 as shown in the figure. However, the PVD process used can be any desired process such as DC sputtering, pulsed DC sputtering by a magnetron assembly, or RF sputtering. The target 2 extends beyond the diameter of the substrate 5 to improve film uniformity and is separated from the grounded chamber 3 by an annular ceramic break 18. When a 332 mm diameter target was used in tests with 200 mm diameter wafers, the film uniformity was improved.

[0043] A typical process procedure is shown in FIG. 2. In this process procedure, it is assumed that the target has already been conditioned. At 200, the wafer is placed on the lift pins in the process chamber. This can be achieved, for example, with a cluster tool using a vacuum transfer robot. Then, the wafer is lowered onto the top of the platen. After that, after the desired process conditions, pressurized gas flow, and temperature are established at 202, wafer rotation is started at 204. Without interruption, target power and substrate bias are applied at 206, and PVD begins. After the desired thickness is achieved, those target and bias powers are switched off at 208, and rotation is stopped at 210. By stopping the gas flow into the chamber and pumping to the desired pressure, the chamber transport pressure is achieved (step 212). When the transport pressure is achieved, the slot valve opens, and at 214, the wafer is lifted from the top of the platen by the lift pins and removed from the chamber by the vacuum robot. The rotation speed of the platen rotation can be automatically controlled using a controller, and according to the software algorithm employed by that controller, integer rotations during the deposition process can be ensured, and thus overall optimal results can be ensured. A typical rotation speed is 1 - 10 rpm. If necessary, the alignment of the depressions on the top of the rotating platen with respect to the lift pin positions is also automatically controlled by the function of that controller and the control software.

[0044] [Experimental Results] The tests were performed using a Sigma fxP (trademark) PVD system (SPTS Technologies Limited, Newport, UK) configured to process 200 mm diameter wafers. Deposition tests were performed to quantify the differences in thickness uniformity and resistivity for metals deposited using a conventional platen assembly and the rotating platen assembly of the present invention, in this case molybdenum (Mo). A rotating substrate support of the type shown in FIG. 1 was used. The rotating platen top and platen top shield were made of stainless steel. The target-to-wafer spacing, target size, and magnetron configuration were not changed during the experiment. A standard rotating magnetron was used during deposition. The nominal deposition target thickness onto a 200 mm silicon wafer was 2000 angstroms (1 angstrom = 10 -10 m). Among the deposition conditions, the DC target power was 1 kW, the pressure was 13 mT, the RF bias was 300 W, and the deposition temperature was 200 °C. The platen top was rotated at 3 rpm. Thickness measurements were acquired using a MetaPULSE (registered trademark)-G instrument (Onto Innovation), a non-destructive pump probe picosecond laser acoustic technique suitable for measuring the thickness of opaque metal films.

[0045] Of the thickness maps shown in FIG. 3 (49-point polar plot, 200 mm, 5 mm EE), (a) is that for the case where deposition was performed using a conventional stationary platen, and (b) is that for the case where deposition was performed using the rotating substrate support of the present invention. The thickness non-uniformity (%1σ) and thickness range are as described in Table 1. With the same deposition process and duration, the rotating substrate support of the present invention significantly improves the thickness NU% and range. This suggests that the non-radial uniformity observed in stationary platen deposition can be reduced without a decrease in deposition rate or productivity.

Table 1

[0046] The efficacy of the RF bias capability of the rotary substrate support can be discerned in FIG. 4, which shows the effect of the platen RF power on the thickness non-uniformity (%1 sigma) and the average resistivity in a molybdenum thin film metal layer deposited using the rotary substrate support. Increasing the platen RF power is a great help, with the thickness non-uniformity decreasing to %1σ of 0.1 or less and the average resistivity decreasing to 8.6 μΩ·cm (best result: 0.05 of %1s at 250 W; ρ = 8.6 μΩ·cm). Sheet resistance measurements were performed using the Resmap (trademark) 4-point probe technique (Creative Design Engineering, Inc., Cupertino, California, USA).

[0047] FIG. 5 shows the changes in the average local stress and the full stress range measured using the FSM 128L (Frontier Semiconductor) stress mapping system over a wide process pressure range. More specifically, FIG. 5 shows the comparison results between the applied platen RF power (0 W vs. 300 W) of the average local stress and the full stress range data (measurement results in MPa) as a function of the process pressure (mTorr). Molybdenum deposition was performed using a target power of 1 kW, a pressure of 13 mT, and an EE of 10 mm. Effective stress control of the Mo film has been achieved to the extent that the stress can be finely adjusted by adjusting the process pressure. By increasing the pressure, the average stress can be transitioned from compression to tension.

[0048] Wafer-to-wafer (WTW) reproducibility is also crucial in HVM. Uniformity both within the wafer and wafer-to-wafer is important in any production environment. FIG. 6 shows the wafer-to-wafer (WTW) reproducibility over 20 wafer runs. The thickness non-uniformity (%1σ) and the average resistivity ρ (μΩ·cm) are shown. An EE of 5 mm is provided. Excellent thickness non-uniformity and average resistivity reproducibility have been observed.

[0049] FIG. 7 depicts the influence of the molybdenum film thickness on the thickness non-uniformity (%1σ), the average resistivity, and the resistivity non-uniformity (%1s). For comparison, the bulk resistivity of molybdenum is about 5.4 μΩ·cm. The measurements were made on Mo films with thicknesses of 100, 500, 1000, and 2000 angstroms. The average resistivity increases significantly at small thicknesses less than 500 angstroms. This is as expected for polycrystalline films, because as the thickness approaches the mean free path of a conductive metal on the order of tens of nanometers, the scattering effects due to roughness and grain boundaries become dominant.

[0050] According to the present invention, highly reliable independent control of the wafer bias voltage can be achieved over a wide range of powers and rotational speeds through capacitive coupling of RF from the stationary part to the rotating part of the substrate support. Precise wafer temperature control is also achieved due to the prominent proximity of the upper part to the lower part. Thereby, reliability problems and concerns related to the rotation of the entire substrate support are avoided.

Claims

1. A physical vapor deposition (PVD) apparatus comprising: a PVD chamber; a target; a substrate support within the chamber, having a rotatable upper portion with an upper surface on which a substrate can be supported and a stationary lower portion; an RF source configured to supply an RF signal having a certain RF power to the lower portion; a device for rotating the upper portion when a PVD process is being performed within the chamber; wherein the upper portion and the lower portion are spaced apart such that the RF power supplied to the lower portion is capacitively coupled to the upper portion.

2. The apparatus according to claim 1, wherein the upper portion and the lower portion are spaced apart by a gap of less than 3 mm.

3. The apparatus according to claim 2, wherein the upper portion and the lower portion are spaced apart by a gap within the range of 0.5 to 1.5 mm.

4. The apparatus according to any one of claims 1 to 3, wherein the upper portion is located on a plurality of non-conductive bearings, and the bearings further contact the lower portion.

5. The apparatus according to any one of claims 1 to 4, wherein the upper portion rotating device comprises a source of rotational motion coupled to a rotatable shaft, and the rotatable shaft is drivingly connected to the upper portion.

6. The apparatus according to any one of claims 1 to 5, wherein the lower portion of the substrate support comprises a platform portion spaced apart from the upper portion.

7. The apparatus according to claim 6, wherein the platform portion is supported by a support stem.

8. The apparatus according to claim 7, wherein the upper portion rotating device comprises a source of rotational motion coupled to a rotatable shaft, the rotatable shaft is drivingly connected to the upper portion, and the rotatable shaft extends within the support stem.

9. The apparatus according to any one of claims 1 to 8, wherein the lower portion is electrically separated from the chamber by a dielectric break structure.

10. The apparatus according to any one of claims 1 to 9, further comprising an upper sheath surrounding the periphery of the upper portion of the substrate support.

11. The apparatus according to claim 10, wherein the upper sheath contacts the upper portion.

12. The apparatus according to claim 10 or 11, wherein the upper sheath has an upper surface coplanar with the upper surface of the upper portion, and the substrate can be supported by both the upper portion and the upper sheath.

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

14. The apparatus according to claim 13, wherein the lower portion of the substrate support comprises a platform portion spaced from the upper portion, the platform portion is supported by a support stem, and the lower sheath surrounds the periphery of the platform portion and the support stem.

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

16. The apparatus according to any one of claims 13 to 15, wherein the upper sheath and the lower sheath are spaced apart by a certain dark space gap.

17. The apparatus according to any one of claims 1 to 16, wherein the lower portion of the substrate support comprises one or both of a resistance heater element and a fluid heat removal passage.

18. The apparatus according to claim 17, wherein the lower portion of the substrate support comprises a platform portion spaced from the upper portion, and the resistance heater element and the fluid heat removal passage are accommodated in the platform portion.

19. A method of performing PVD, Placing a substrate on a substrate support in a PVD chamber, the substrate support comprising a rotatable upper portion having an upper surface capable of supporting the substrate thereon and a stationary lower portion. Supplying an RF signal having a certain RF power to the lower portion. Performing a PVD process of depositing a material on the substrate by sputtering a target with the upper portion rotating and the lower portion stationary, and capacitively coupling the RF power supplied to the lower portion to the upper portion. A method having the above steps.

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

21. The method according to claim 19 or 20, wherein the target is disposed above the substrate and radially expanded beyond the substrate.

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

Images