Liquid mixture and method for selectively wet etching silicon germanium

A liquid mixture for etching a substrate includes a first liquid comprising one of: (i) percarboxylic acid comprising 3 to 70 mass. % of the liquid mixture; or (ii) carboxylic acid comprising 3 to 70 mass. % of the liquid mixture and at least one liquid selected from a group consisting of hydrogen peroxide comprising 3 to 30 mass. % of the liquid mixture and ozone comprising 0.5 to 5 mass. % of the liquid mixture; a water drawing agent comprising 2 to 40 mass. % of the liquid mixture; hydrofluoric acid comprising 0.05 to 3 mass. % of the liquid mixture; and water comprising 0 to 60 mass. % of the liquid mixture. The liquid mixture may be used to etch silicon germanium relative to silicon, silicon dioxide and silicon nitride.

FIELD

The present disclosure relates to a liquid mixture for etching and more particularly to methods for selectively wet etching silicon germanium relative to other materials using the liquid mixture.

BACKGROUND

Substrate processing systems are used to deposit, etch and otherwise treat materials on substrates such as semiconductor wafers. Examples of etching processes include dry etching, vapor etching and/or wet etching. In some examples, one exposed material of the substrate may need to be etched selectively relative to one or more other exposed materials of the substrate.

In one application, silicon germanium (SiGe) needs to be etched selectively relative to silicon (Si), silicon nitride (SiN or Si3N4) and silicon dioxide (SiO2) to reveal Si nanowires. When selecting the etching process, selectivity between Si and SiGe is a primary consideration. However, there should also be sufficient selectivity to avoid material loss of other materials such as SiO2and SiN. For example, material loss constraints for the 7 nm technology node (and smaller nodes where the Si nanowires may be used) should be less than 10-20 A for Si and SiO2and less than 10 A for SiN.

When using dry etching processes, there is limited selectivity between SiGe and Si, which causes material loss on the Si nanowire. Vapor etching processes using hydrochloric acid (HCl) are slow and typically require a minimum of 30 minutes of processing time. Both techniques are followed by a wet process (such as a wet clean process using dilute hydrofluoric acid (HF)) and a channel oxidation process, which is typically performed using wet treatment with water and ozone.

When using wet etching processes to etch SiGe, it is very challenging to provide sufficient selectivity such that only SiGe is etched while Si, SiO2and/or SiN are not etched. Existing chemistries for selectively etching SiGe relative to Si do not have sufficient selectivity relative to SiO2and SiN.

SUMMARY

A liquid mixture for etching a substrate includes a first liquid comprising one of: (i) percarboxylic acid comprising 3 to 70 mass. % of the liquid mixture; or (ii) carboxylic acid comprising 3 to 70 mass. % of the liquid mixture and at least one liquid selected from a group consisting of hydrogen peroxide comprising 3 to 30 mass. % of the liquid mixture and ozone comprising 0.5 to 5 mass. % of the liquid mixture; a water drawing agent comprising 2 to 40 mass. % of the liquid mixture; hydrofluoric acid comprising 0.05 to 3 mass. % of the liquid mixture; and water comprising 0 to 60 mass. % of the liquid mixture.

In other features, the water drawing agent comprises sulfuric acid. The carboxylic acid is selected from a group consisting of acetic acid, formic acid, propionic acid and butyric acid. The percarboxylic acid is selected from a group consisting of peracetic acid, performic acid, perpropionic acid, and perbutyric acid. The percarboxylic acid comprises 10 to 55 mass. % of the liquid mixture. The carboxylic acid comprises acetic acid.

In other features, the carboxylic acid comprises 10 to 55 mass. % of the liquid mixture. The hydrogen peroxide comprises 6 to 20 mass. % of the liquid mixture. The water drawing agent comprises 2 to 40 mass. % of the liquid mixture. The hydrofluoric acid comprises 0.1 to 1.5 mass. % of the liquid mixture. The water comprises 5 to 50 mass. % of the liquid mixture.

In other features, the method includes providing a substrate comprising silicon germanium, silicon and at least one material selected from a group consisting of silicon dioxide and silicon nitride; and selectively etching the silicon germanium relative to the silicon and the at least one material by applying the liquid mixture of claim1to the substrate.

A method for wet etching a substrate, comprising providing a substrate comprising silicon germanium and at least one material selected from a group consisting of silicon, silicon dioxide and silicon nitride; and selectively etching the silicon germanium relative to the at least one material by applying the liquid mixture to the substrate.

A method for wet etching a substrate includes arranging the substrate on a spin chuck. The substrate comprises silicon germanium and at least one material selected from a group consisting of silicon, silicon dioxide and silicon nitride. The method includes rotating the substrate using the spin chuck; and applying the liquid mixture onto at least one surface of the substrate to selectively etch the silicon germanium relative to the at least one material by applying the liquid mixture.

In other features, the silicon germanium is etched at a ratio greater than or equal to 10:1 relative to the at least one material selected from a group consisting of silicon, silicon dioxide and silicon nitride. The silicon germanium is etched at a ratio greater than or equal to 10:1 relative to the silicon material, the silicon dioxide material and the silicon nitride material.

A liquid mixture for etching silicon germanium includes carboxylic acid comprising 3 to 12 mol/L of the liquid mixture; hydrogen peroxide comprising 1.5 to 7 mol/L of the liquid mixture; sulfuric acid 0.5 to 5 mol/L of the liquid mixture; hydrofluoric acid comprising 0.1 to 1 mol/L of the liquid mixture; and water comprising 4 to 50 mol/L of the liquid mixture.

In other features, a molarity of the carboxylic acid is higher than a molarity of hydrogen peroxide.

A method for wet etching a substrate includes providing a substrate comprising silicon germanium, silicon and at least one material selected from a group consisting of silicon dioxide and silicon nitride; and selectively etching the silicon germanium relative to the at least one material using the liquid mixture.

DETAILED DESCRIPTION

The present disclosure relates to a liquid mixture for wet etching a substrate to selectively etch silicon germanium (SiGe) relative to one or more other exposed materials and methods for applying the liquid mixture to a substrate. As used herein SiGe refers to any alloy containing silicon and germanium. In some examples, the other materials include silicon (Si), silicon dioxide (SiO2) and/or silicon nitride (SiN). The present disclosure also relates to the use of the liquid mixture to selectively etch SiGe on a substrate using a spin chuck.

In some examples, a liquid mixture for etching a substrate includes a first liquid comprising one of (i) percarboxylic acid comprising 3 to 70 mass. % of the liquid mixture; or (ii) carboxylic acid comprising 3 to 70 mass. % of the liquid mixture and at least one liquid selected from a group consisting of hydrogen peroxide comprising 3 to 30 mass. % of the liquid mixture and ozone comprising 0.5 to 5 mass. % of the liquid mixture. The liquid mixture further includes a water drawing agent comprising 2 to 40 mass. % of the liquid mixture. The liquid mixture further includes hydrofluoric acid comprising 0.05 to 3 mass. % of the liquid mixture and water comprising 0 to 60 mass. % of the liquid mixture.

In some examples, the water drawing agent comprises sulfuric acid. In some examples, the carboxylic acid is selected from a group consisting of acetic acid, formic acid, propionic acid and butyric acid. In some examples, the carboxylic acid comprises acetic acid. In some examples, the carboxylic acid comprises 10 to 55 mass. % of the liquid mixture.

In some examples, the percarboxylic acid is selected from a group consisting of peracetic acid, performic acid, perpropionic acid, and perbutyric acid. The percarboxylic acid comprises 10 to 55 mass. % of the liquid mixture.

In some examples, the hydrogen peroxide comprises 6 to 20 mass. % of the liquid mixture. In some examples, the water drawing agent comprises 2 to 40 mass. % of the liquid mixture. In some examples, the hydrofluoric acid comprises 0.1 to 1.5 mass. % of the liquid mixture. In some examples, the water comprises 5 to 50 mass. % of the liquid mixture.

Another liquid mixture for etching comprises 3 to 12 mol/L carboxylic acid; 1.5 to 7 mol/L hydrogen peroxide; 0.5 to 5 mol/L sulfuric acid; 0.1 to 1 mol/L hydrofluoric acid; and 4 to 50 mol/L water. In some examples, a molarity of the carboxylic acid is higher than a molarity of hydrogen peroxide. Another method for wet etching a substrate includes providing a substrate comprising silicon germanium at least one material selected from a group consisting of silicon, silicon dioxide and silicon nitride. The method includes selectively etching the silicon germanium relative to the at least one material using the liquid mixture.

For example only, the liquid mixture may include both acetic acid (HAc) and peroxide (H2O2) to form peracetic acid. The peracetic acid in the liquid mixture provides etch selectivity of SiGe over Si. In some examples, a water withdrawing agent such as sulfuric acid is added to the liquid mixture to increase the rate of peracetic acid formation so that a stable mixture can be obtained in about an hour instead of over several hours. The water withdrawing agent also lowers the etch rate of SiO2and SiN. Lower sulfuric acid concentration is possible at the expense of reaction rate and material selectivity. Depending on the Si nanowire dimensions, the hydrofluoric acid (HF) can be used to change the SiGe etch rate.

In some examples, the liquid mixture comprises a ratio by volume of 15:15:0.16:4 of respectively HAc(99%):H2O2(30%):HF(49%):H2SO4(96%). Molarities for this example of the liquid mixture include 7.6M HAc, 4.3M H2O2, 0.13M HF, 2.15M H2SO4and 20M H2O.

The liquid mixture according to the present disclosure provides the desired etch selectivity. In some examples, the SiGe is etched at a ratio greater than or equal to 10:1 relative to Si, SiO2and/or SiN. In some examples, the SiGe is etched at a ratio greater than or equal to 10:1 relative to Si, SiO2and/or SiN.

The etch process described herein is relatively short (on the order of seconds/minutes) and can be followed in-situ by other steps to remove a thin SiO2layer on Si (to expose bare Si) and to oxidize the Si in water/ozone to grow a controlled channel oxide.

Referring now toFIGS. 1 and 1B, a spin chuck50that may be used to deliver the liquid mixture to selectively etch silicon germanium relative to silicon, silicon dioxide and/or silicon nitride is shown. InFIG. 1A, the spin chuck50includes a processing chamber52and a rotatable chuck56supporting a substrate58. A motor60rotates a shaft62connected to the rotating chuck56. A liquid delivery arm64and a nozzle66deliver liquid to a surface of the substrate58as the motor60rotates the shaft62connected to the rotatable chuck56. A valve72controls delivery of one or more liquids such as deionized (DI) water, the liquid mixture described above and/or other liquids from a liquid supply74. A controller76may be used to control the motor60, a motor70and the valve72during etching. InFIG. 1B, a rotational position of the liquid delivery arm64may be adjusted from a dispensing position to a storage position shown in dotted lines using the motor70.

Referring now toFIG. 2, a method100for wet etching a substrate includes providing a substrate and arranging the substrate on a spin chuck at110. In some examples, the substrate includes a SiGe and at least one material selected from a group consisting of Si, SiO2and/or SiN. In some examples, the substrate is etched to expose nanowires as will be described below. The method includes rotating the substrate using the spin chuck at114. At118, the method includes applying the liquid mixture onto at least one surface of the substrate. The liquid mixture selectively etches the SiGe relative to the at least one material. In some examples, the substrate58is rinsed at120after etching using the liquid mixture with water (such as deionized water (DI) water). After rinsing, the substrate58may be dried at122.

In some examples, the rotatable chuck58is rotated at a speed greater than or equal to 50 rpm. In other examples, the rotatable chuck58is rotated at a speed greater than or equal to 300 rpm. In other examples, the rotatable chuck58is rotated at a speed of 1000 rpm. In some example, the liquid mixture is dispensed as a free flowing liquid onto the substrate58. In some examples, the liquid mixture is dispensed at a temperature in a range from 10-40° C. (e.g. 25° C.).

Referring now toFIGS. 3A and 3B, an example of a substrate200that is etched to release nanowires is shown. InFIG. 3A, a substrate200includes a silicon substrate210. A silicon germanium layer214is arranged on the silicon substrate210. An active silicon layer218is arranged on the silicon germanium layer214. A silicon germanium layer222is arranged on the active silicon layer218. A silicon oxide layer232is arranged at opposite sides of the substrate. A silicon nitride mask230is arranged above the silicon germanium layer222. To expose the active silicon layer218, an etch process using the liquid mixture described above may be used.

InFIG. 3B, the substrate200is shown after the etch process is performed using the liquid mixture. The silicon germanium layers214and222are removed to expose the active silicon layer218. Additional etching and/or annealing may be performed to transform a profile of the active silicon layer222to a round cross-sectional shape.