Patent Application
20200291526
The present invention relates to a device for improving the homogeneity of a deposited metal layer during electroless metallization of a target surface of at least one workpiece, e.g. with copper, nickel, palladium, silver, or gold, as well as the alloys thereof, according to the preamble of claim 1.
Electroless metal deposition from an electrolyte solution is basically known in the semi-conductor, solar, and nanotechnology sectors. Electroless metallization of objects, for example structured wafers, has significant advantages over galvanic metallization with respect to the resistance as well as the homogeneity and conformity of deposition technology and the properties of the achievable layers. It is advantageous that no devices are necessary for electrical contacting of the objects to be coated. In addition, the parallel processing of several objects by means of a batch process is a decisive advantage for increasing the production rate per unit of time. Due to the purely chemical deposition process, a seed layer on the objects is not absolutely necessary.
The process of electroless depositing of a metal layer requires a metal plating solution with a reducing agent, a metal source, and a chelating agent, wherein—in addition to control of the bath composition—parameters such as the pH value, the temperature, and the composition of the metal plating solution can also be adjusted with great accuracy, because initiation of a chemical reaction by means of a catalyst is extremely sensitive to the process temperature. The reaction can proceed autocatalytically or as an exchange or displacement reaction.
Typically, the operating temperature of the electroless electrolyte solution is in a range close to the autocatalysis temperature for spontaneous self-decomposition of the electroless electrolyte solution. The occurrence of self-decomposition of the electroless electrolyte solution leads to metal deposition not only onto desired regions, i.e. the substrate surface to be coated, but also onto surfaces of the metallization equipment such as the reactor cell, the electrolyte solution tank, the supply lines, and the like. In pronounced cases of self-initiated decomposition, essentially the entire metal content of the electrolytes is quickly reduced to a pure metal, which potentially causes clogging of all of the lines and tubes and of the processing basin. As a consequence of this, great effort is required in order to clean the metallization equipment in a wet-chemical manner with, for example, nitric acid and other chemicals, wherein all the expensive electrolyte components are lost at once. In addition, the resulting waste, which may be toxic in some cases, must be disposed of, which further significantly contributes to the operating expenses of the electroless metallization process.
The devices for electroless metallization known from the prior art are not designed as single-wafer systems but are for batch processes in order to increase the achievable production rate. In order to simultaneously process a plurality of wafers, they are placed in holders, or carriers, in a basin, which contains the electrolyte solution. Typically, the wafers are positioned vertically upright in the carriers, wherein the electrolyte solution is continuously circulated in the basins in order to ensure a uniform distribution of the reactants within the basin.
Typically, the electrolyte solution is placed in the basin from below via a central inlet and can be removed at the upper side and supplied for circulating and heating. The removal can be implemented, for example, via simple overflow into an overflow basin.
With the assemblies known from the prior art, the inlet for the electrolyte solution is arranged in the base of the container, wherein the inlet is designed as a single inlet port with additional diffuser plate. This diffuser plate has flow-optimized inlet openings in the form of concentric circles or differently arranged inlet openings.
With the devices known from the prior art, it is considered to be disadvantageous that the layer thickness of the deposited metal varies across a wafer and that there are also differences from wafer to wafer within a batch. The reasons for this are the variations in the surface potential of the circuits on the wafer and the hydrodynamics of the solution with respect to the surface, which leads to a reduction in the concentration of reactive electrolyte components over the surface of the objects to be metallized.
Thus, the object of the present invention is to provide a device for the batch processing of wafers, which enables more uniform layer depositing within a wafer as well as from wafer to wafer, particularly for large wafers with diameters of up to 300 mm.
This object is achieved by means of a device having the features of claim 1. Advantageous refinements are the subject matter of the dependent claims.
An assembly according to the invention for electroless metallization of a target surface of at least one workpiece comprising a container for receiving an electrolyte solution; an inlet for the electrolyte solution, said inlet arranged in the base of the container, wherein the inlet is designed as an inlet port with an additional diffuser plate; an outlet which is arranged on an upper side of the container; and a receiving area for holding the at least one workpiece is characterized in that the diffuser plate is formed as a first assembly and a second assembly, which is identical to the first assembly, of a respective plurality of circular inlet openings, wherein the assemblies at least partially but not completely overlap, and the inlet has at least two inlet ports.
Thus, the present invention is based on the knowledge that an improved supply of the electrolyte solution to the workpieces, particularly to wafers arranged in the assembly, can be achieved due to a supply of the electrolyte solution at several points, which are different from one another, with interconnected diffusers, and due to the use of several inlet ports, to the extent that a more homogenous distribution of the reactive electrolyte components (concentration distribution) can be achieved and thus a more homogenous layer deposition can be achieved as well over several wafers, which are arranged vertically, for example, in a wafer carrier in the container.
The first assembly and the second assembly can be arranged, for example, along a longitudinal axis of the container to the extent that an improved introduction is achieved over the longer sides of the wafer, along which the workpieces are typically arranged in rows. As a whole, it is advantageous when the diffuser plate is arranged centered in the base of the container such that a symmetrical construction is achieved. In this manner, the flow conditions toward the structured wafer surface can be optimized.
The inlet may further have at least three inlet ports for improving the aforementioned effects to the extent that further distribution optimization can be achieved when supplying the electrolyte solution.
In particular, a first inlet port may be aligned centered relative to the diffuser plate, and a second inlet port and a third inlet port advantageously may be aligned centered relative to the first assembly and to the second assembly, respectively.
The diffuser plate may have a baffle plate and/or a lower density of inlet openings in the area of the inlet ports to the extent that direct flow of the freshly supplied electrolyte solution and thus a local increase in concentration is avoided. In this manner, the homogeneity of the metal deposition can be improved over several workpieces.
Due to the use of individual pumps for each inlet, further optimization of the flow conditions can be achieved.
An especially simple design of the assembly can be achieved when all inlet openings have the same diameter. Alternatively, a concentration distribution can be achieved due to the different diameters of the inlet openings, for example with diameters increasing steadily as the distance away from the inlet ports increases.
In a preferred embodiment, a surface of the diffuser plate amounts to at least 95% of a base surface of the container and at least 3% open surface, due to the inlet openings, relative to the total surface of the diffuser plate.
The inlet ports may have respectively identical cross-sections, or the second inlet port and the third inlet port may have a cross-sectional surface of 45% of a cross-sectional surface of the first inlet port. Due to a change in the cross-sectional surface of the individual inlet ports, a concentration distribution within the container can likewise be influenced.
The inlet openings may be arranged, for example, in concentric circles or in a spiraling line.
The inlet openings in this case are equipped with chamfers at the drilled holes on both sides in order to further optimize the media distribution and in order to prevent interfering edges. The inlet openings are aligned vertically.
The diameters of the inlet openings in this case are executed so as to increase and be in the shape of a circle relative to the center and/or the baffle plate of the diffuser plate.
The present invention is extensively explained in the following by means of an exemplary embodiment with reference to the enclosed figures. The following is shown:
To this end, the diffuser plate 24 is arranged in a lower fourth of the container 13 such that the diffuser plate is arranged between the workpieces 10 and an inlet 20, which is formed by the inlet ports 21, 22, 23, and thus a distribution of the medium supplied via the inlet 20 is ensured. Because the electrolyte solution, which is used for the metallization of the workpieces 10 in this case, is continuously recirculated during implementation of the metallization process, i.e. the electrolyte solution, which flows out of the container 13 via an upper edge of the container 13, which forms an outlet 30 in this case, is captured and then is supplied back to the container 13 via the inlet 20 arranged on the base, the diffuser plate 24 ensures a distribution of concentration that is as homogenous as possible of the reactants contained in the electrolyte solution to the extent that homogenous metal deposition takes place.
It can be seen that the container 13, which is designed as a quartz glass container in this exemplary embodiment, is substantially in the shape of a cube and is surrounded by an overflow container 14 for capturing the medium flowing over the upper edge, which is formed as an outlet 30. The overflow container 14 has different connection ports, which are formed for guiding the electrolyte solution or as connections for cleaning the assembly. Furthermore, various attachment parts can be seen on the overflow container 14, which are designed, for example, for holding or implementing various retainers for the workpieces 10.
Finally,
In the present exemplary embodiment, the diffuser plate 24 is substantially shaped as a rectangle, wherein, in the view shown in
In addition,
The view of the diffuser plate 24 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 128 439.7 | Nov 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/083104 | 11/30/2018 | WO | 00 |
