Electroless plating apparatus with non-liquid heating source

An electroless plating apparatus is provided. The electroless plating apparatus includes a wafer holder; a chemical dispensing nozzle over the wafer holder; a conduit connected to the chemical dispensing nozzle; and a radiation source over the wafer holder.

TECHNICAL FIELD

This invention relates generally to methods and apparatus for electroless plating on semiconductor wafers, and more particularly to methods for controlling heating of semiconductor wafers during electroless plating in order to improve plating uniformity.

BACKGROUND

Electroplating and electroless plating can be used for the deposition of continuous metal layers as well as patterned metal layers. Electroless plating is often used as a preliminary step in preparing a seed layer for conventional electroplating. One of the process sequences used by the microelectronic manufacturing industry to deposit metals onto semiconductor wafers is known to as a “damascene” process. In such a process, via openings, trenches and/or other recesses, are formed in a dielectric layer and filled with a metal, such as copper. The wafer, with vias and trenches etched in the dielectric material, first receives a metallic seed layer, which is used to conduct electrical currents during a subsequent metal electroplating step. If a metal such as copper is used, the seed layer is disposed over a barrier layer material, such as Ti, TiN, etc. The seed layer is a very thin layer of metal typically formed by electroless plating. The subsequent plating on the seed layer is typically electroplating.

FIG. 1illustrates a conventional apparatus for electroless plating. Wafer2is placed on wafer holder4, which includes guide pins6for limiting wafer2. The chemical dispensing nozzle8, that dispenses plating chemicals, is connected to a chemical dispenser (not shown). Typically, Electroless plating is performed at elevated temperatures by conducting hot de-ionized (DI) water under wafer2, wherein wafer2may be in direct contact with the DI water. In a typical design, the hot DI water is conducted to the bottom center of a wafer, and then spread to the edges, as illustrated by the arrows. In addition, the plating chemicals may be heated before they are dispensed on the surface of wafer2.

It is known that temperatures affect chemical reactions, and thus the deposition rate in an electroless plating is also sensitive to the temperatures. In certain cases, for example, in the Ni—P electroless plating process, the deposition rate may increase as high as twofold for every 10-degree increase in the plating temperature. Therefore, it is preferred that the temperature at the surface of wafer2is uniform. However, in the conventional heating scheme, when hot DI wafer flows from the bottom center of wafer2to the edge, due to heat dissipation, the hot DI water may develop an increasingly lower temperature along its path. The edge portions of wafer2accordingly have a lower temperature as compared to the center portion. The temperature difference may be as high as 5 degrees centigrade. This causes a significant variation in deposition rates between the center portion and the edge portions of the wafer.

Therefore, an electroless plating apparatus for uniformly heating a wafer and methods for achieving the same are needed.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an electroless plating apparatus includes a wafer holder; a chemical dispensing nozzle over the wafer holder; a conduit connected to the chemical dispensing nozzle; and a radiation source over the wafer holder.

In accordance with another aspect of the present invention, an electroless plating apparatus for plating a wafer includes a wafer holder for holding the wafer; a chemical dispensing nozzle over the wafer; a water pipe having an end under the wafer; a focus reflector over the wafer; and at least one lamp attached to the focus reflector.

In accordance with yet another aspect of the present invention, a method for electroless plating a semiconductor wafer includes placing the semiconductor wafer on a wafer holder; heating the semiconductor wafer using a radiation source overlying the semiconductor wafer; and dispensing plating chemicals from a chemical dispenser onto the semiconductor wafer.

In accordance with yet another aspect of the present invention, a method for electroless plating a semiconductor wafer includes placing the semiconductor wafer on a wafer holder; placing a focus reflector over the wafer; attaching a plurality of lamps to the focus reflector; heating the semiconductor wafer with the lamps; conducting hot de-ionized water to a bottom surface of the semiconductor wafer; and dispensing plating chemicals on the semiconductor wafer.

An advantageous feature of the embodiments of the present invention is that the plated wafers will have a substantially uniform temperature on their surfaces. Thus, the deposition rate across the wafer is more uniform. Also, the present invention provides the ability for adjusting the plating rates by adjusting the temperatures on wafers.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 2schematically illustrates an exemplary electroless plating apparatus20, which includes a radiation source30for providing heat to wafer22. Wafer22is placed on wafer holder24. Guide pins26in wafer holder24are used to confine wafer22. In electroless plating processes, wafer holder24and wafer22swivel at a constant speed. Radiation source30may be any non-liquid heat source. For example, it may radiate any light with heating ability, such as infrared and/or far infrared lights. Radiation source30may include lamp filaments or coils.

In an exemplary embodiment, radiation source30includes lamps32formed in focus reflector34. Focus reflector34may have a circular shape, as shown inFIG. 3. A plurality of openings is formed in focus reflector34, in which lamps32are placed. Focus reflector34is preferably formed of materials having good heat-insulating ability and heat-reflecting ability, such as anodized stainless steel, and the like. Throughout the description, the term “lamp” refers to all heat sources that generate heat, even if the heat sources do not emit visible lights. Each of the lamps32may include a coil(s) or a filament(s) for heat generation. The coils or filaments may have a spiral shape extending from the bottom of the openings into the openings, and may even extend to the tops of the openings. Focus reflector34helps focus the heat generated by lamps32onto wafer22.

The electroless plating apparatus20may optionally include pipe40for conducting hot de-ionized (DI) water, wherein the hot DI water is preferably conducted to a center of the bottom surface of wafer22, and flows in the center-to-edge directions, as illustrated by arrows51. The hot DI water acts as an additional heat source for heating wafer22, and preferably has a temperature of between about 50° C. and about 90° C., and more preferably about 80° C.

FIG. 3illustrates a bottom view of radiation source30, in an embodiment wherein no hot DI water is provided, the distribution of lamps32is adjusted so that wafer22receives a uniform heat level throughout the wafer. This may be achieved by, for example, increasing the diameter of the radiation source30approximately to, or even greater than, the diameter of wafer22, and substantially evenly distributing lamps32in focus reflector34. In other embodiments wherein the hot DI water is provided, since the hot DI water will cause a temperature difference between the center portion and the edge portions of wafer22, the distribution of lamps32is adjusted so that radiation source30compensates for the temperature difference caused by the hot DI water. In an exemplary embodiment, from the center of radiation source30to its edge, the density of lamps32increases, so that the edge portions of wafer22receives more heat per unit area from radiation source30. Alternatively, lamps proximate edges of focus reflector34are provided with a higher power, while lamps proximate the center are provided with a lower power. As a result, the overall temperature across wafer22is substantially uniform.

Referring back toFIG. 2, lamps32are connected to power control unit42, which controls whether to turn on or off lamps32. In addition, power control unit42controls the power level provided to lamps32. In a first embodiment, power control unit42is used to adjust the plating rate for the entire wafer. For example, after a wafer is plated, the wafer is measured to determine the plating rate. If the plating rate is lower than desired, power control unit42increases the power to lamps32. Conversely, power control unit42reduces the power to lamps32if the plating rate is higher than desired. In a second embodiment, power control unit42is used to improve plating uniformity on wafers. For example, if the edge portions of a wafer have lower plating rates than the center portion, power control unit42increases the power to the lamps32in outer portions of radiation source30, and hence increase the plating rate in the outer portions of the wafers. Conversely, if the edge portions of wafer22have higher plating rates than the center portion, power control unit42reduces the power to lamps in outer portions of the radiation source30. The uniformity of temperatures and plating rates on different spots of wafer22is thus improved. The temperature uniformity of wafer22can also be determined and improved by using power control unit42.

Radiation source30is preferably integrated with a chemical dispensing system. In an embodiment, opening44(also referred to as chemical inlet port44) is formed at the center of radiation source30. Conduit46, which has a first end connected to a chemical dispenser (not shown) and a second end connected to chemical dispensing nozzle48, is attached through chemical inlet port44. In an electroless plating process, chemical dispensing nozzle48and the connecting conduit46move back and forth between a center portion and an edge portion of wafer22(as illustrated as arrow50). Accordingly, radiation source30also moves accordingly with chemical dispensing nozzle48.

The electroless plating apparatus20may also include shield plate52, which has the ability of blocking the heat generated by radiation source30from reaching the underlying wafer22. In the preferred embodiment, radiation source30is formed of a material have reflecting ability, for example, the same material as used in focus reflector34. Shield plate52is movable so that it may be moved out of the way when electroless plating is conducted, and moved into the heat path if electroless plating apparatus20is idle and/or no wafer is placed on wafer holder24. With such as scheme, radiation source30does not have to be turned off, and constant heat may be provided.

It is to be realized that radiation source30inFIGS. 2 and 3are only examples, and may have different structures, shapes, materials, etc, as long as they provide uniform heat to wafers to be plated or compensate for the temperature differences between the respective edges and centers of the wafers.FIGS. 4A and 4Billustrate a second embodiment, wherein lamps54are horizontally, rather than vertically, placed under focus reflector34.FIG. 4Aillustrates a cross-sectional view of radiation source30, which shows that lamps54are attached to the bottom of focus reflector34.FIG. 4Billustrates an exemplary bottom view of the radiation source30shown inFIG. 4A. Lamps54may be arranged in the form of rings, as is illustrated inFIG. 4B, or parallel to each other. In yet other embodiments, as shown inFIG. 5, radiation source30includes a plurality of lamps, each forming a loop.

In yet other embodiments, the radiation source may be separate from chemical dispense conduit46.FIG. 6illustrates individual lamps56placed in electroless plating apparatus20. Similar to the embodiment shown inFIG. 2, the individual lamps56are preferably distributed in such a way that the resulting wafer32has a top surface with a uniform temperature.

By using the embodiments of the present invention, the electroless-plated wafers may have a substantially uniform temperature on their surfaces. As a result, the uniformity of deposition rates across the wafers is improved. Also, the embodiments of the present invention may be used to adjust plating rates.