This invention relates to apparatus for electrochemical deposition onto the surface of a substrate having features formed in that surface and to methods of performing such deposition.
Electrochemical deposition (ECD) is widely used in the manufacture of printed circuit boards, semi-conductors, devices and hard disk drive manufacture. In semi-conductor applications the process is often used for depositing Cu. In the prior art constructions and methods, a wafer is placed in a bath of chemicals—principally CuSO4/H2SO4 in H2O plus small quantities of organic additives. A DC potential is applied between an immersed metal electrode—typically Cu or Pt—and a continuous Cu seed layer, which has been pre-coated on a wafer, for example using a physical vapour deposition (PVD). Fluid is re-circulated in the bath to avoid depletion of the chemicals.
Cu+ ions are generated at the anode in the electrolyte. The substrate is negatively charged with respect to the metal anode with the result that Cu+ ions are attracted to the wafer surface.
When the surface of the wafer, or other substrate, being coated is not flat there are often small features such as channels or vias in the substrate, which result in it becoming difficult to maintain a uniform deposition rate within the small features. One particular example is that of Through Silicon Vias (TSVs) where relatively small vias from 100 μm to 1 μm with aspect ratios of 1:1 to 30:1 need to be filled with metal.
The current ECD procedures have a number of difficulties:
1. Separate baths, with different electrolyte compositions, are generally needed to allow for varying deposition rates as the process proceeds and, for example, the vias become less and less deep.
2. The depletion of chemicals and the agitation in the vicinity of the wafer and the need for chemical additives both to enhance and suppress deposition in respective selected areas on the substrate.
3. The current ECD systems are large complex pieces of tooling into which fragile wafers have to be inserted and removed from whilst maintaining cleanliness and flow timings.
4. The chemicals in each batch have to be maintained free of particles and the fluid has to be constantly replenished with the result that only a small part of the Cu in the chemicals is actually deposited.
The Applicant's invention helps to mitigate, in at least some embodiments, one or more of these problems.
From one aspect the invention consists in apparatus for electrochemical deposition onto the surface of the substrate having features formed in that surface and the substrate having a conducting seed layer pre-deposited on the feature incorporating surface, the apparatus including an anode electrode, a support for supporting the substrate with its one surface exposed at a location, the support and the anode electrode being relatively moveable to alter the gap between the anode electrode and the location to define a chamber between them; and an electrical power source for creating a potential difference across the gap characterised in that the apparatus further includes a seal for sealing with the seed layer to form a fluid chamber and a fluid inlet and outlet to the chamber.
The fluid inlet and outlet may be formed in the electrode or through passages in other parts of the chamber and respective valves may be provided for opening and closing the inlet and outlet.
The seal may be carried by the anode electrode or by the chamber which contains the anode. The depth of the chamber may be at least an order of magnitude less than its cross-sectional dimension. The anode electrode may support an electrical contact, electrically isolated from the anode, for contacting the seed layer to complete an electrical circuit.
The apparatus may further include a fluid supply for the chamber. In that case it may further include a control for varying the chemical composition of the fluid in accordance with the degree to which the features have been plated and/or for pulsing fluid into and out of the chamber. The power supply may be pulsed or continuous. Typically the electrode will be positive with respect to the seed layer.
From another aspect the invention consists in a method of electroplating a substrate having features in a surface including:
The depth of the chamber may be at least in order of magnitude less than its cross-sectional dimension. The potential difference created may be pulsed and the support may be cooled or heated relative to the electrolyte temperature.
The period between steps (d) and (e) may be less than or equal to 30 seconds. The method may include varying over time one or more of the chemical compositions of the electrolyte; the period between steps (d) and (e); the period of the creation of the potential difference; the magnitude of the potential difference and the volume of the chamber.
Although the invention has been defined above it is to be understood it includes any invented combination of the features set out above or in the following description.
The invention may be performed in various ways in specific embodiments will now be described with reference to the accompanying drawings in which:
Turning to
In use, a wafer 11, for example, is placed on the substrate table 12 and the electrode is moved into the position indicated in
The system has several advantages. First, because small amounts of fluid have been used efficiently, chemical consumption can readily be reduced. Secondly the period of dwell and the chemical composition of the electrolyte can be readily varied over time. As the features 22 begin to fill, the diffusion time for the Cu+ ions is reduced and this, for example, can be taken into account. Further the system is likely to reduce or remove the need for accelerators and suppressors. Further this variation does not require a number of different baths and the system can easily be tuned to the particular construction of the wafer or other substrate concerned.
Although the apparatus has been described in terms of the deposition of Cu it can be used where other forms of ECD are utilised such as in the deposition of alloys for magnetic media and other films such as nano-laminates. The apparatus is particularly advantageous for the deposition of alloys as the depletion of components in the electrolyte fluids will not normally occur at the same rate.
By pulsing small volumes of fluid through the cavity, the electrolyte composition can be optimized throughout the plating cycle. Previously, this would normally have been achieved by moving a wafer between plating cells however due to practical considerations, the number of dedicated cells in one system, the electrolyte composition is typically a compromise to achieve process requirements at an acceptable throughput. A second advantage is that the depletion effects within TSV type features can be reduced. This is opposed to known agitation or re-circulating baths which at best case can achieve a boundary layer thickness of ˜10 μm above the wafer. Conventional fountain cells have boundary layers quoted at ˜60 μm. Within the TSV and the boundary layer transport is diffusion limited.
Conventional acid based Cu plating electrolytes consist of CuSO4, H2SO4, H2O and various organic additives. The additives tend to be suppressors (e.g. PEG) to reduce the deposition in the field areas, accelerators (brighteners such as SPS) which enhance deposition rate within the features to be filled and levelers to reduce deposition rate around sharp features e.g. at the top of a via. In
The new approach provides advantages over all of the issues identified and enables complex processes to be realised as the fluid streams could be rapidly changed. This would facilitate in-situ cleans or pre-deposition steps, subtle changes to the electrolyte as a function of time in the fill cycles or even laminate depositions (change material composition). Groups of modules could operate in series or parallel depending on the process requirements of each application.
The system designed is simplified over a conventional ECD system with wafer transport being minimised. All ECD steps could take place in one module. It might also be advantageous to carry out pre and post deposition steps in the same module though this would depend on the system configuration.
The ability to rapidly heat and cool the substrate temperature through the use of a chuck or ESC provides additional process flexibility over the current fluid bath approaches. It would also be possible to run the wafer and the process fluids at different temperatures. Something that it is not possible/very difficult to achieve in the conventional systems.
Ultrasonic or megasonic agitation of the cathode/cavity would be possible by attaching/coupling ultrasonic transducers to the cathode support. This could assist the process cycle by speeding up the removal of bubbles from the solution prior to deposition and the agitation of plating solutions during deposition. With the cathode assembly not being fully immersed in a plating solution the practical task of coupling the ultrasonic signal into the vicinity of the wafer surface becomes simpler to implement.
Using a 150 mm wafer with 200 nm PVD Cu seed layer the average bulk resistivity of electroplated Cu is 1.716 m-cm. This is indicative of a high quality Cu deposition for an as-deposited (not annealed) film. There is tight control of resistivity & thickness of the coating at 7.41 & 7.54% respectively across the wafer.
The wafer was placed 10 mm below a copper anode, in a horizontal orientation, with a conventional CuSO4/H2SO4+HCl chemistry (50 g/Ltr Cu, 100 g/Ltr H2SO4, ˜50 ppm Chloride ions) using a 15 mA/cm2 current density. The deposition cycle was 1200 sec with a deposition rate of 0.33 m/min. Anode to wafer (cathode) separation was 10 mm.
The presence of only Cu crystallographic peaks is once again indicative of a high quality ECD Cu film. The primary peak is the (111) orientation. This is similar to high quality PVD Cu films.
Number | Date | Country | Kind |
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1021326.2 | Dec 2010 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB2011/052437 | 12/8/2011 | WO | 00 | 8/15/2013 |
Publishing Document | Publishing Date | Country | Kind |
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WO2012/080716 | 6/21/2012 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
20010020583 | Woodruff | Sep 2001 | A1 |
20020029978 | Talieh | Mar 2002 | A1 |
20040104119 | Edelstein et al. | Jun 2004 | A1 |
20040124089 | Basol | Jul 2004 | A1 |
20040237896 | Hongo | Dec 2004 | A1 |
20050164495 | Chou et al. | Jul 2005 | A1 |
20100258444 | Weiner et al. | Oct 2010 | A1 |
Number | Date | Country |
---|---|---|
9901592 | Jan 1999 | WO |
Number | Date | Country | |
---|---|---|---|
20130313124 A1 | Nov 2013 | US |
Number | Date | Country | |
---|---|---|---|
61423154 | Dec 2010 | US |