Patent Application
20240011180
The disclosure relates to a distribution system for a process fluid and an electric current for an electrolytic surface treatment of a substrate, a distribution module for a process fluid and an electric current for an electrolytic surface treatment of a substrate and a distribution method for a process fluid and an electric current for an electrolytic surface treatment of a substrate.
Electroplating, e.g. of copper, is a frequently used technology in many different industries, especially in the semiconductor related industries. Due to the simplicity and scalability of the process, electroplating is used to metallize surfaces or parts of surfaces of various types of substrates having various sizes.
In order to achieve adequate film quality and uniformity during the electroplating process, it is necessary to guarantee a very well balanced electrical current distribution over the surface area as well as a uniform and adequate metal-ion supply through an electrolyte to the surface to be plated. As the substrate is covered with extremely small and sensitive device structures, no direct electrical contact can be made within the substrate area, except within narrow regions at substrate edges. Therefore, an electrically conductive seed-layer is required to distribute the current from the contacts of the substrate edges throughout the surface.
The main challenge associated with the seed-layer and the uniformity of the electrical current distribution over the surface area is called “terminal effect”. The terminal effect describes a potential drop across a surface area, which can occur due to a relatively high resistivity of such a seed-layer, which is usually required for the electroplating process of a substrate. Depending on the seed-layer material, its thickness and the distance between the plating area and the electrical contact at the edge of the substrate, a potential drop of several volts is likely to occur. Such potential drop from the substrate edge to the area to be plated results in a highly non-uniform current density distribution leading to an extremely non-uniform plating thickness distribution, primarily characterized by a thicker plating at the substrate edges.
Additional challenges associated with the current distribution that need to be faced, especially with increasingly smaller structures, may be the equilibration of the current distribution between substrate areas with a very high-density of tiny structures and areas with a low density of rather larger structures to be electroplated.
In the prior art, several technologies address the mitigation of the macroscopic terminal effect, which addresses the “center-to-edge” potential drop, by adding a thief cathode. However, the thief cathode as used in the prior art has only provided limited success. Therefore, the overall non-uniformity problem is not yet fundamentally solved.
Hence, there may be a need to provide an improved distribution system for a process fluid and an electric current for electrolytic surface treatment of a substrate, which allows increasing the plating uniformity, particularly for applications in high performance devices, particularly with very small, device structures.
This problem is solved by the subject-matters of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the aspects of the disclosure described in the following apply also to a distribution system for a process fluid and an electric current for an electrolytic surface treatment of a substrate, a distribution module for a process fluid and an electric current for an electrolytic surface treatment of a substrate, and a distribution method for a process fluid and an electric current for an electrolytic surface treatment of a substrate.
According to the present disclosure, a distribution system for a process fluid and an electric current for an electrolytic surface treatment of a substrate is presented. The distribution system comprises a distribution body, a primary cathode, and a secondary cathode. The distribution body comprises several openings for the process fluid and the electric current, wherein the several openings are arranged at a front face of the distribution body, the front face being directed to the primary cathode. The primary cathode and the secondary cathode are arranged to attract the electric current and to guide the electric current to the substrate, preferably to predefined areas of the substrate to be treated. The secondary cathode comprises several cathode pixels, wherein the several cathode pixels are distributed in an array to be aligned with at least an area of the substrate to be treated. Additionally, the several cathode pixels are individually controllable for adjusting a distribution of the electric current at the substrate.
The secondary cathode may be spaced apart from the primary cathode and may comprise several cathode pixels being distributed in an array to be aligned with an area of the substrate to be treated. This arrangement may enable a localized control and tuning of the current density distribution, particularly with a tuning resolution down to the sub-μm range. The individually controllable cathode pixels may enable a very localized adjustment and tuning of the current density distribution all over a surface of the substrate to be treated, not only at the edge areas of the substrate. Therefore, the distribution system may allow effecting the edge-to-center/center-to-edge as well as the current density distribution within the substrate to be plated. Furthermore, the distribution system according to the disclosure may enable the plating of non-rotating substrates as well as of rotating substrates.
The secondary cathode may be made from an electrically conducting material, preferably inert to the chemical environment of the electrolyte, e.g. inert metals, such as palladium, palladium-coated materials, platinum and/or platinized materials like tantalum, tungsten, and/or titanium, or may be made from the same material as a plating material to be used for the surface treatment of the substrate. For example, a Cu-comprising secondary cathode may be used when Cu is plated. Further, the secondary cathode may have a circular, square, rectangular, C-shaped, wire-shaped and/or partially electrically insulated shape. The secondary cathode may work as a thief cathode mitigating the terminal effect by increasing the plating-uniformity. Additionally, or alternatively, the secondary cathode may be formed by several pixels, wherein the pixels may be separate from each other, wherein each pixel may be individually controllable. Therefore, the secondary cathode may be referred as pixelated cathode. Further, the secondary cathode may be directed towards the primary cathode.
In an embodiment, the distribution system may further comprise at least a power source configured to apply individual voltage potentials to the cathode pixels to individually control the cathode pixels. Depending on the plating level on specific substrate areas, the voltage potential level can be adjusted at each cathode pixel. In an embodiment, at least some of the cathode pixels may be each connected to a single power source.
The cathode pixels may be each connected to the at least one power source by electrical connecting lines transmitting a potential from the at least one power source to the cathode pixels. Additionally or alternatively, the cathode pixels their selves can be at least partially formed as a wire. At least some of the cathode pixels may be together connected to a single power source. To sum it up, the cathode pixels may be each connected to the same power source, or the cathode pixels may be each connected to individual power sources, resulting in that the number of power sources corresponds to the number of cathode pixels. Alternatively, the power source may comprise several power outlets, each pixel being connected to an individual power outlet of the one power source. Additionally, or alternatively, the cathode pixels may be divided into several groups of pixels, wherein the pixels of each group may be connected to the same power source, but each group of pixels is connected to a separate power source.
In an embodiment, at least some cathode pixels being controlled by a single power source may have individual potentials. In this case, the cathode pixels may be configured to display a variety of different pixel potentials by providing variable resistances between the power source and the individual cathode pixel.
In an embodiment, the distribution system may further comprise at least a processing unit configured to control the at least one power source to apply the individual voltage potentials to the cathode pixels for individual durations.
In principle, each cathode pixel may be fabricated in a way to permit individual controllability of the applied potential and/or the duration of the applied potential. At least some of the cathode pixels may be grouped to arrays and each array is connected to one of several power sources for being applied with the same potential and same duration.
The power source(s) may have a cathodic potential or an anodic potential. In particular, the anodic potential may be used for achieving an improved pixelated reverse pulse plating or for cleaning the pixels from potentially deposited metal layers or particles. Additionally, or alternatively, the cathode pixels may be arranged at a rear face of the distribution body, wherein the rear face is opposite to the front face of the distribution body. Placing the cathode pixels at a rear face of the distribution body may be especially advantageous when the power source(s) has an anodic potential.
In an embodiment, the control for adjusting the distribution of the electric current at the substrate may be a physical arrangement of cathode pixels. Thus, the pixels may be arranged according to a predefined pattern, e.g. a photolithographic mask, which is used to create the pattern distribution on the substrate to be treated. Alternatively, the pixel pattern may be adjusted during plating process according to the plating levels of the substrate areas. This may be controlled by the user or by a control unit automatically. Additionally, or alternatively, the cathode pixels can be electrically tuned according to the substrate pattern densities and substrate irregularities. For instance, some cathode pixels may be deactivated (turned off) to prevent further attraction and guidance of the electric current to the substrate surface areas.
In an embodiment, the cathode pixels may be arranged at the distribution body. The cathode pixels may be arranged in or on a surface of the distribution body. In an embodiment, the cathode pixels may be arranged at the front face of the distribution body directed to the first cathode. For example, the cathode pixels may be mainly arranged around the openings at the front face. Thereby, the cathode pixels may be integrated into the distribution body surface through common processes used in the semiconductor and/or flat panel industry, like one or more photolithographic process sequences. Alternatively, at least some of the cathode pixels and electrical connecting lines may be manufactured on the surface via printing. The electrical connecting lines may be fabricated in a similar way as the (individual) cathode pixels.
The openings at the front face may be configured at least partially as jet holes directing the process fluid and/or the electric current towards the substrate to be treated and/or at least partially as connecting passages draining off the process fluid from the substrate to be treated. In an embodiment, the front face and the rear face of the distribution body may be connected by the connecting passages through the distribution body, wherein the cathode pixels are arranged at least partially around the connecting passages. The connecting passages may be configured to permit a backflow and with this a circulation of the process fluid through the distribution body. Arranging the cathode pixels around the connecting passaged can be an easy way to integrate the cathode pixels into the distribution body.
In an embodiment, the secondary cathode may be separate to the distribution body and positioned adjacent to the distribution body in a direction towards the substrate.
Thus, the secondary cathode may be implemented as a stand-alone system. As the simplest example of such a stand-alone system, the secondary cathode may correspond to a mostly electrically isolated wire with an electrically non-isolated tip. In a more typical example, multiple cathode pixels may be physically connected together in a predefined specific geometric constellation, preferably defined by and aligned with the requirements of an “open area density” distribution on the substrate. This stand-alone system can be placed between the distribution body and the primary cathode to enable the tuning of the current density distribution all over the substrate to be treated, and in particular to enable the tuning of the current density distribution for individual areas and/or individual device structures of the substrate to be treated.
The “open area density” may define the density degree of open areas and/or the size of those open areas in a predefined area of the substrate. The open areas may be configured to be the areas of the substrate to be treated or plated. When a constant potential may be applied on the whole substrate, the current distribution, particularly the distribution of electrons, may depend on the density degree and/or the size of the open areas, wherein the distribution of the electrons may affect the current density and thereby the amount of the plating material being deposited in this area. Different current densities in different areas of the substrate may lead to different amount of deposited plating material in the different areas resulting in a non-uniform distribution of the plating material. Thus, providing the pixels with different potentials may allow controlling the current density distribution to achieve a uniform current density distribution and thus, a uniform distribution of the plating material.
In an electrical sense, the cathode pixels may not be electrically connected with each other, but individually controllable through being individually electrically connected to individual power supplies, as described above, or to one power supply having adequate multiple power outlets. In specific cases, the cathode pixels may also be grouped as to enable electrical power control on various groups of cathode pixels.
Furthermore, the secondary cathode may preferably be placed in a first predefined distance to the distribution body and in a second predefined distance to the substrate. The first predefined distance may be equal to the second predefined distance. Alternatively, the first predefined distance may be different to the second predefined distance. The predefined first and second distances may be dependent on the plating material and/or the size of the substrate and/or the process fluid and/or the open area density distribution of the device structures on the substrate to be plated. Further, the first and the second predefined distances may be constant or correspond to a predefined range, within the distances may be adaptable during the treatment of the substrate. Alternatively, the distance of each cathode pixel to the substrate may be defined independently and be adjusted depending on the plating requirement of the corresponding substrate area. Adapting the distances of the secondary cathode, particularly the second distance to the substrate may influence the current density distribution. The smaller the second distance, the more accurately controllable the influence on the current density distribution. The secondary cathode may be aligned substantially parallel to the distribution body and/or may be configured to be aligned with the substrate in-line, flush and not outside the substrate. On the other hand, the secondary cathode may have alternating distance to the distribution body and/or the substrate.
Preferably, the secondary cathode may be configured to be aligned to a main area of substrate, e.g. a center of substrate, covering at least part of the substrate. The surface of the secondary cathode may preferably be substantially parallel or angled to the surface of the substrate to be treated, but not perpendicular.
The secondary cathode may have approximately the same dimensions as the substrate, or the dimensions of the secondary cathode can be dynamically adjusted to the substrate dimensions through turning on and off predefined pixels.
In a further embodiment, the secondary cathode may be arranged on an inert plate shield. The inert plate shield may be composed of a chemically inert material. A chemically inert material may be defined as not chemically reactive in the electrolyte. Therefore, the inert plate shield may not interfere with the chemical process for plating the surface of a substrate. When the secondary cathode is arranged on the inert plate shield, the cathode pixels can also be integrated with the plate shield placed in-between the primary cathode and the distribution body and can be rotated in cooperation and/or coordinated with a substrate rotation. Thus, the plate shield may work as a carrier plate for the cathode pixels allowing a more flexible arrangement of the cathode pixels.
In an embodiment, the inert plate shield may be attachable to the substrate holder and movable with the substrate. In particular, this can enable the secondary cathode to be movable with the substrate, e.g. during loading and unloading into and from a plating chamber and/or during agitation movements, such as agitation movements with high as well as with low frequencies, introduced to the substrate. In cases where the pixels are arranged on or within plate shields, specific arrangements have to be made for warranting electrical connections to the individual pixels.
According to the present disclosure, also a distribution module for a process fluid and an electric current for an electrolytic surface treatment of a substrate is presented. The distribution module for a process fluid and an electric current for an electrolytic surface treatment of a substrate comprises a distribution body as described above, and a substrate holder. The substrate holder is configured to hold at least one substrate relative to the distribution body.
A convection chamber may be formed between the front face of the distribution body and the substrate surface, which is further laterally limited by means of a solid wall. The convection chamber may be advantageous for forcing a targeted back flow of the processing fluid through the distribution body (more specifically, through the connecting passages), and to create an isolated space for the electric current to reach the specific substrate areas without being interrupted by the processing fluid flow within the processing bath.
This arrangement may enable a localized control and tuning of the current density distribution, particularly with a tuning resolution down to the sub-μm range. The individually controllable cathode pixels may enable a very localized adjustment and tuning of the current density distribution all over a surface of the substrate to be treated, not only at the edge areas of the substrate. Furthermore, this arrangement may enable the plating of non-rotating substrates as well as of rotating substrates.
According to the present disclosure, also a distribution method for a process fluid and an electric current for an electrolytic surface treatment of a substrate is presented. The distribution method comprises the following steps, not necessarily in this order: providing a distribution body comprising several openings for the process fluid and the electric current, wherein the several openings are arranged at a front face of the distribution body, arranging a primary cathode and a secondary cathode to attract and guide the electric current to the substrate to be treated, wherein the primary cathode is directed to the front face of the distribution body and wherein the secondary cathode comprises several cathode pixels distributed in an array aligned with at least an area of the substrate to be treated, and individually controlling the cathode pixels for adjusting a distribution of the electric current at the substrate.
This distribution method may enable a localized control and tuning of the current density distribution, particularly with a tuning resolution down to the sub-μm range. The individually controllable cathode pixels may enable a very localized adjustment and tuning of the current density distribution all over a surface of the substrate to be treated, not only at the edge areas of the substrate. Thus, the distribution method according to the disclosure may enable the plating of non-rotating substrates as well as of rotating substrates.
Exemplary embodiments of the disclosure will be described in the following with reference to the accompanying drawings:
The connecting passages 6 are configured to direct a process fluid 18 (see
The secondary cathode 3 comprises several cathode pixels 13, the cathode pixels 13 being arranged on the front face 10 of the distribution body 2 between adjacent openings 4. The cathode pixels 13 are integrated into the front face 10. The integration of the cathode pixels 13 into the front face 10 of the distribution body 2 is made by common processes used in the semiconductor and/or flat-panel industry, e.g. photolithography, or printing.
The illustration of the cathode pixels 13 is simplified for visibility reasons and electrical contacts of the cathode pixels 13 as well as electrical connecting lines connecting the cathode pixels 13 to a power source (not illustrated) are not illustrated.
Although, the cathode pixels 13 are only illustrated as arranged at the front face 10 of the distribution body 2, the cathode pixels 13 can be arranged additionally or alternatively on the rear face 11 of the distribution body 2.
Each cathode pixel 13 is configured to permit an individual controllability of an electric potential applied by the power source. During the plating process, a cathodic potential is usually applied, but also the application of an anodic potential is possible, preferably for achieving an improved pixelated reverse pulse plating or for cleaning the cathode pixels 13 from potentially deposited metal layers or particles.
The distribution system 1 in combination with a substrate holder 17 (see
The cathode pixels 13 are arranged on the plate 15 in a predefined geometric constellation, which is defined by and aligned with the requirements of an “open area density” distribution on the substrate. The plate 15 comprising the cathode pixels 13 in a predefined constellation is placed between the distribution body 2 and the substrate 9 to enable the tuning of the current density distribution over the whole structured substrate 9.
The illustration of the cathode pixels 13 is also simplified for visibility reasons and electrical contacts of the cathode pixels 13 as well as electrical connecting lines connecting the cathode pixels 13 to a power source (not illustrated) are not illustrated.
A convection chamber is formed between the front face 10 of the distribution body 2 and the substrate 9 surface, which is further laterally limited by means of a solid wall 19. The convection chamber may be advantageous for forcing a targeted back flow of the processing fluid 18 through the distribution body 2 (more specifically, through the connecting passages 6), and to create an isolated space for the electric current to reach the specific substrate areas without being interrupted by the processing fluid flow within the processing bath 50.
It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features.
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.
In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20210367.7 | Nov 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/081410 | 11/11/2021 | WO |
