FIELD

Embodiments of the present disclosure relate to systems and methods for passivating a workpiece using a plasma chamber, and more particularly, to passivating the workpiece using implantation while minimizing the etching of the workpiece.

BACKGROUND

Semiconductor workpieces are often implanted with dopant species to create a desired conductivity. Plasma implantation is an effective method of doping or otherwise modifying surfaces of a semiconductor device to form devices, such as transistors.

As geometries continue to get smaller, new issues arise that affect the performance and reliability of these smaller transistors. For example, for advanced transistors, gate reliability, specifically negative bias temperature instability (NBTI) is one of the critical parameters for device performance and reliability. The issue of gate oxide reliability is even more critical as the industry migrates to more advanced channel materials such as high germanium concentrated SiGe films.

Gate oxide reliability is mainly related to the defects and trap states at the gate oxide interface and the performance can be enhanced by passivating these defects. For example, these defects can be passivated using species such as hydrogen, deuterium and fluorine.

These species can be introduced using a number of different processes. In certain embodiments, ion implantation is used to introduce these species. There are several advantages of this approach, as high doping levels can be achieved at a high dose rate, thus enabling cost of ownership advantages, at especially low implant energies.

However, implantation of a workpiece using a plasma-based process can be challenging, due to the presence of radicals and excited species along with the ions during the implant process. The radicals and excited species can lead to excessive etching of the surface layers and thus adversely affecting the device performance.

Therefore, an apparatus and method that enables the implantation of species to passivate a workpiece without etching the surface of that workpiece would be beneficial. Further, it would be beneficial if this method did not add significant time or cost to the overall semiconductor fabrication process.

SUMMARY

An apparatus and method of processing a workpiece is disclosed, where a sacrificial capping layer is created on a top surface of a workpiece. That workpiece is then exposed to an ion implantation process, where select species are used to passivate the workpiece. While the implant process is ongoing, radicals and excited species etch the sacrificial capping layer. This reduces the amount of etching that the workpiece experiences. In certain embodiments, the thickness of the sacrificial capping layer is selected based on the total time used for the implant process and the etch rate. The total time used for the implant process may be a function of desired dose, bias voltage, plasma power and other parameters. In some embodiments, the sacrificial capping layer is applied prior to the implant process. In other embodiments, material is added to the sacrificial capping layer during the implant process.

According to one embodiment, a method of passivating a portion of a workpiece is disclosed. The method comprises disposing the workpiece in a plasma chamber; applying a sacrificial capping layer to a top surface of the workpiece; creating a plasma comprising a passivating species within the plasma chamber, wherein the passivating species is selected from the group consisting of hydrogen, deuterium, fluorine and gas mixtures containing hydrogen, deuterium or fluorine as a diluent or primary processing gas and wherein ions, radicals and excited molecules of the passivating species are generated; performing an implant process wherein the ions of the passivation species are implanted through the sacrificial capping layer and into the portion by applying a bias voltage to the workpiece, and wherein during the implant process, the radicals and excited molecules etch the sacrificial capping layer; and terminating the implant process when a desired dose of passivating species has been implanted, wherein at termination of the implant process, a thickness of the sacrificial capping layer is less than 5 angstroms or all of the sacrificial capping layer has been completely removed and less than 10 angstroms of the workpiece has been etched. In certain embodiments, the sacrificial capping layer is applied in the plasma chamber during a capping period by introducing a capping species, and creating a plasma comprising the capping species while the bias voltage is disabled. In some embodiments, the capping period is prior to the implant process. In some embodiments, additional sacrificial capping layer is applied during the implant process by flowing the capping species into the plasma chamber. In some further embodiments, the flow of the capping species is continuous throughout the implant process. In some further embodiments, the flow of the capping species is pulsed during the implant process. In some further embodiments, the bias voltage is varied when the capping species is flowing into the plasma chamber during the implant process. In certain embodiments, the implant process is terminated after a predetermined time, where the predetermined time is determined based on the passivating species and the desired dose of passivating species. In some embodiments, a warning is generated if an output of a metrology system indicates that the workpiece is being etched. In certain embodiments, the implant process is terminated based on an output from a metrology system indicating that the workpiece is being etched. In certain embodiments, an initial thickness of the sacrificial capping layer is determined based on an etch rate of the sacrificial capping layer and a total duration of the implant process. In some further embodiments, the initial thickness is adjusted based on chamber metrology, number of workpieces processed, or hours of operation to compensate for varying etch rate. In certain embodiments, the thickness of the sacrificial capping layer is between 5 angstroms and 100 angstroms. In certain embodiments, when the bias voltage is applied, the bias voltage is a pulsed DC voltage between 0.1 and 10 kV.

According to another embodiment, a method of passivating a portion of a workpiece is disclosed. The method comprises applying a sacrificial capping layer to a top surface of the workpiece in a chamber, wherein a thickness of the sacrificial capping layer is between 5 angstroms and 100 angstroms; disposing the workpiece in a plasma chamber, wherein the plasma chamber is different from the chamber; creating a plasma comprising a passivating species within the plasma chamber, wherein the passivating species is selected from the group consisting of hydrogen, deuterium, fluorine and gas mixtures containing hydrogen, deuterium or fluorine as a diluent or primary processing gas and wherein ions, radicals and excited molecules of the passivating species are generated; performing an implant process wherein the ions of the passivation species are implanted through the sacrificial capping layer and into the portion by applying a bias voltage to the workpiece, and wherein during the implant process, the radicals and excited molecules etch the sacrificial capping layer; and terminating the implant process when a desired dose of passivating species has been implanted. In certain embodiments, the chamber heats the workpiece to a temperature near the temperature of the implant process; and grows the sacrificial capping layer by flowing a gas while the workpiece is being heated.

According to another embodiment, a method passivating a portion of a workpiece is disclosed. The method comprises flowing a capping species into the plasma chamber, within which a workpiece is disposed; energizing the capping species to generate a plasma, wherein, during a capping period, a bias voltage is not applied to the workpiece, so as to create a sacrificial capping layer on a top surface of the workpiece; flowing a passivating species into the plasma chamber wherein the passivating species is selected from the group consisting of hydrogen, deuterium, fluorine and gas mixtures containing hydrogen, deuterium or fluorine as a diluent or primary processing gas; performing an implant process, to implant passivating ions into the workpiece, wherein the implant process is defined as a period of time when a bias voltage is applied to the workpiece while a plasma comprising the passivating species is being generated; adding material to sacrificial capping layer by flowing the capping species into the plasma chamber during the implant process; and terminating the implant process. In certain embodiments, the implant process is terminated when a desired dose of passivating ions has been implanted. In certain embodiments, at termination of the implant process, a thickness of the sacrificial capping layer is less than 5 angstroms or all of the sacrificial capping layer has been completely removed and less than 10 angstroms of the workpiece has been etched. In certain embodiments, the flow of the capping species is continuous throughout the implant process. In certain embodiments, the flow of the capping species is pulsed during the implant process. In some further embodiments, the bias voltage is varied when the capping species is flowing into the plasma chamber during the implant process. In certain embodiments, wherein the amount of material added is varied based on chamber metrology, number of workpieces processed, or hours of operation to compensate for varying etch rate. In some further embodiments, the capping species flows through a mass flow controller to the plasma chamber and the amount of material is carried by adjusting a flow rate of the capping species, the frequency at which the mass flow controller is actuated, or the duty cycle of the mass flow controller.

