JPH0715902B2 - A safe way to etch silicon dioxide - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention generally relates to silicon (S
i) A method for etching native silicon dioxide (SiO ₂ ) from the surface of a substrate, and more specifically, a method for etching native SiO ₂ using anhydrous ammonium fluoride (NH ₄ F).

[0002]

2. Description of the Related Art When a surface of a silicon substrate is exposed to ambient air, a natural SiO ₂ spontaneously occurs on the surface.
A layer is formed. Many semiconductor (eg, low temperature epitaxy, polysilicon deposition, silicidation) processes require that the silicon wafer surface be free of any native SiO ₂ . During the last few years, a number of different methods for removing specific SiO ₂ by etching a Si surface have been developed. The most commonly used SiO
_{One of the two} etching techniques is to use hydrofluoric acid (H
F) (wet or dry). But,
The use of liquid or gaseous HF has major drawbacks for semiconductor manufacturers due to its high toxicity and corrosivity. Due to the high toxicity of HF, semiconductor manufacturers are
It is necessary to implement safety procedures and safety devices to prevent damage by F gas. Due to the strong corrosive nature of HF, semiconductor manufacturers need to utilize non-corrosive materials for storage vessels and plumbing for delivering HF gas to the etching chamber. Generally more expensive than uncharacterized containers and piping.

Nishino et al., 1989 Dry Prcess Symposium
IV-2, with 90-92 (1989), intrinsic SiO ₂ from a silicon substrate
A method of selectively etching is disclosed. This method uses nitrogen hydride and fluorine atoms generated by microwave discharge of NH ₃ and NF ₃ . In the etching method of Nishino et al., NH ₄ ⁺ and F ⁻ are first reacted with polarized Si atoms of ionic SiO ₂ to form a film of (NH ₄ ) ₂ SiF _{6 on} the substrate surface. When heated to 100 ° C. or higher, the (NH ₄ ) ₂ SiF ₆ coating vaporizes, leaving an oxygen-free silicon surface. The method of Nishino et al. Is not ideal as it still requires the corrosive gas to be brought into the reaction chamber. Furthermore, in the method of Nishino et al., First, the wafer temperature is kept at 100 ° C. or lower to form an etching film on the substrate surface, and then heating is performed at 100 ° C. or higher to remove etching products. Nishino, etc.
From the beginning, it was confirmed that when the temperature was kept at 100 ° C. or higher, the coating did not adhere and the SiO ₂ etching did not occur. Therefore, the method of Nishino et al. Requires semiconductor manufacturers to manage timing and temperature control parameters.

[0004]

It is an object of the present invention to provide a method of removing native SiO ₂ from a silicon surface using anhydrous NH ₄ F.

[0005]

According to the present invention, anhydrous N 2
Etch the native SiO ₂ from the silicon surface using H ₄ F. A source of NH ₄ F is provided in the etching chamber along with the substrate to be cleaned. When heated, anhydrous NH ₄ F sublimes to produce HF gas and NH ₃ gas.
Next, this HF gas is transferred to the surface of the silicon substrate
O ₂ is removed by etching.

[0006]

EXAMPLE Anhydrous NH ₄ F is used at a temperature of 100 ° C. or higher, 1 to
At a pressure of about 10 torr, it sublimes according to the following formula. NH ₄ F _(c) → HF _(g) + NH _{3 (g)}

Anhydrous NH ₄ F is a form of aqueous NH ₄ F that readily absorbs water and is a less reactive form when exposed to air.
Converted to F, it is inherently safer than gaseous or aqueous HF. Aqueous NH ₄ F is used to make a buffered HF solution and does not form gaseous HF when heated or evaporated. Anhydrous NH ₄ F is available from Aldrich Chemical, Sigma Chemical, Alfa
It is commercially available from various manufacturers such as Chemical.

The present invention contemplates placing a silicon substrate having a unique SiO ₂ layer to be etched away in an etching chamber with a container of anhydrous NH ₄ F (such as an ampoule). When a container of anhydrous NH ₄ F is heated above the sublimation point, HF gas is generated, which etches SiO ₂ from the surface of the silicon substrate.
The NH ₃ gas generated during sublimation may also act as an electron donor in the reaction and assist the etching.
Controlling the supply of HF gas to etch SiO ₂ controls the temperature to which the container of anhydrous NH ₄ F is exposed (ie, modulating the temperature above or below the sublimation point when HF gas is needed, Alternatively, it can be achieved by similar steps). If necessary, additional water vapor can be added to aid in the etching of SiO ₂ , but care must be taken not to convert anhydrous NH ₄ F to aqueous NH ₄ F before the generation of HF gas. In order to prevent the re-growth of SiO ₂ , the subsequent processing steps including adhesion etc.
Immediately after etching the O ₂ layer, it is preferable to carry out in the same chamber or another chamber under vacuum connected to the etching chamber.

In a test experiment, a silicon substrate with a thermally grown SiO ₂ layer was placed adjacent to a container of anhydrous NH ₄ F. Keep the substrate at ambient temperature and dry with anhydrous NH ₄ F.
It was heated to a temperature of 0 ° C. and sublimated to form HF gas and NH ₃ gas. It was observed that the SiO ₂ on the substrate surface was etched at a rate of 30 Å / min.

[0010]

According to the present invention, S can be effectively and safely
Inherent SiO ₂ can be removed from the i surface by etching.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location 9272-4M 21/306 D (72) Inventor Richard Anthony Conti United States 10549, Munt Kisco, NY Fox Wood Circle 47 (72) Inventor David Edward Kotecki United States 12533, Hopewell Junction, New York, Sylvan Lake Road 37 (72) Inventor Andrew Herbert Simon United States 12524, Fishkill, NY, Green Hill Drive 31 Sea

Claims (6)

[Claims] 1. A step of placing a silicon substrate having a silicon dioxide layer formed thereon in an etching chamber, a step of supplying anhydrous ammonium fluoride into the etching chamber, and a step of removing the anhydrous ammonium fluoride. Heating to a temperature above its sublimation point to produce a gas species that etches the silicon dioxide on the silicon substrate, and etching or cleaning the silicon dioxide. 2. The method of claim 1, wherein the gas species produced in the heating step comprises hydrogen fluoride. 3. The method according to claim 1, wherein the anhydrous ammonium fluoride is heated to 100 ° C. or higher in the heating step. 4. The method of claim 1, further comprising the step of maintaining the silicon substrate at a temperature below the temperature required to sublime the anhydrous hydrogen fluoride. 5. The method of claim 1, wherein the heating step comprises adjusting the temperature at which the anhydrous ammonium fluoride is heated to adjust the etching rate of the silicon dioxide layer. Method. 6. The method further comprises depositing a layer of material on the silicon substrate after removing the silicon dioxide layer, the depositing step being performed immediately after the anhydrous ammonium fluoride heating step. The method according to Item 1.