Dopant Gettering Semiconductor Processing by Excimer Laser

The invention provides a dopant gettering semiconductor processing technique for selectively photochemically activating an otherwise benign reactant to remove dopant from a substrate.

In various semiconductor processing operations, it is difficult to control various processing parameters, particularly thermally driven deposition, diffusion and the like. The resultant dopant concentration in the semiconductor substrate lattice in turn may vary, which is undesirable in high precision applications. In order to ensure sufficient dopant concentration and the desired electrical charactertistics, the semiconductor layer is typically overdoped, and then a gettering agent is used to remove some of the dopant to achieve the desired concentration.

The present invention provides a particulary simple and efficient dopant gettering technique which can be used to obtain a more uniform dopant concentration.

FIG. 1 schematically illustrates the semiconductor processing technique in accordance with the invention.

FIG. 2 shows various available excimer pulsed ultraviolet laser radiation wavelengths and peak power.

FIG. 3 shows a gas absorption spectrum.

FIG. 4 illustrates a particular species of the invention.

FIG. 1 illustrates a dopant gettering semiconductor processing technique for selectively activating an otherwise benign reactant to remove dopant from a semiconductor wafer substrate 2. Excimer pulsed ultraviolet laser radiation is provided from laser 4 at a discrete designated pulsed wavelength corresponding to a discrete designated excitation energy of an otherwise benign reactant gas such that the reactant is photolytically activated to remove dopant from substrate 2 without thermally driven pyrolytic reaction.

A conventional processing chamber 6 may be used, and semiconductor wafer substrate 2 is placed on a supporting pedestal 8 in the chamber which may have a resistance heater coil 10 or the like driven by a voltage source 12 for heating substrate 2 and/or a resistance heater coil 14 in chamber 6 for heating the interior thereof. These thermal processing elements are optional in the method of the present invention. Reactant gas is introduced into chamber 6 at port 16 from gas supply 18, and may be exhausted at port 20, all as is conventional. Chamber 6 typically has an observation window or port 22.

Excimer pulsed ultraviolet laser radiation from laser 4 is introduced into chamber 6 at 24 through port 22, and may be directed by mirrors 26 and 28 to impinge wafer substrate 2 substantially perpendicularly thereto. FIG. 2 shows various available excimer pulsed ultraviolet laser radiation wavelengths and peak power, and FIG. 3 shows an absorption spectrum of a reactant gas with absorption peaks at discrete designated excitation energy wavelengths. The excimer radiation wavelength is chosen according to the reactant gas absorption peaks, or vice versa. The narrow spectral output of the excimer laser enables highly specific electronic excitation of reactants, allowing selective breaking of a particular molecule's bonds, driving a predetermined controllable reaction. The excimer laser may be tuned to differentially break bonds of a desired type of gas molecule from a mixture of gases. The gas molecule bonds are broken photochemically with a photolytic reaction at a temperature ranging from room temperature to about 400.degree. C., rather than a thermally driven pyrolytic reaction wherein the gas molecule bonds are thermally agitated and vibrationally broken at substantially higher temperatures typically around 1,000.degree. C.

In a particularly desirable aspect of the invention, a plurality of otherwise benign reactants are provided, either in a gaseous mixture of plural gases from source 18, or a plurality of gas sources such as 30 and 18. The excimer pulsed ultraviolet laser radiation is provided at a plurality of different discrete designated pulsed wavelengths corresponding respectively to discrete excitation energies of the reactants from sources 30 and 18 for selectively choosing the dopant to be removed from substrate 2 according to the designated wavelength.

As shown in FIG. 4, a mask 32 may be provided over substrate 2, and the substrate is irradiated with the excimer laser radiation at 24 through mask 32 to activate the otherwise benign reactant only at selected areas such as 34 exposed by the mask to decrease dopant concentration only at such selected areas.

In one desirable species, substrate 2 has portions of phosphorous at 34, and the reactant is provided by silane gas SiH.sub.4. The excimer pulsed ultraviolet laser radiation is provided by an argon fluoride excimer laser at 193 nanometers or a krypton fluoride excimer laser at 248 nanometers corresponding to a discrete excitation energy of the silane gas photochemically breaking bonds of the gas photolytically activating and releasing hydrogen atoms which react with the phosphorous at 34 to produce a compound gas of phosphorous and hydrogen PH.sub.3 removing phosphorous from the substrate to decrease phosphorous concentration. The laser output is provided at up to 1 joule per pulse at up to 250 hertz.

The excimer pulsed ultraviolet laser radiation at the discrete designated wavelength photolytically reacts with the otherwise benign reactant gas in the chamber at a discrete gettering excitation energy photochemically breaking bonds of the gas to produce gettering agents such as the two hydrogen atoms as shown in FIG. 4 reacting with the substrate to remove dopant therefrom, all without thermally driven pyrolytic reaction. The gettering agent reacts with dopant in the substrate to form a gaseous compound, for example PH.sub.3 in FIG. 4, liberated from the substrate and benign to and unactivated by the discrete designated wavelength of the excimer pulsed ultraviolet laser radiation.

It is recognized that various alternatives and modifications are possible within the scope of the appended claims.