EP1425790A2

EP1425790A2 - Means and method for structuring a substrate with a mask

Info

Publication number: EP1425790A2
Application number: EP01978136A
Authority: EP
Inventors: Robert Kachel; Gerhard Franz
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2001-09-11
Filing date: 2001-09-11
Publication date: 2004-06-09
Also published as: WO2003027767A2; US20050020072A1; WO2003027767A3

Abstract

Means and method for structuring a substrate by means of a multi-layered mask (1, 2, 3, 4), characterised in that the mask comprises at least one layer (1) made from a wet-structured dielectric which is resistant to a dry-etching. An undesirable etching of the substrate is thus avoided.

Description

description

Means and method for structuring a substrate with a mask

The invention relates to a means for structuring a substrate with a mask according to the preamble of claim 1 and a method according to the preamble of claim 5.

In the manufacture of structures for microelectronics, a substrate is processed with dry etching in many cases in order to produce these structures. Typical dry etching processes are e.g. Plasma etching, reactive ion etching or ion beam etching.

In these methods, a plasma acts on the substrate, e.g. a wafer, one that is coated with an exposed photoresist (resist). For the exact transfer of a structure to the substrate, in order to achieve good etching results, even with high DC potentials in the plasma system, it is necessary that the edges of the photoresist are as vertical as possible. If the order of magnitude of the structure to be etched is greater than the thickness of the photoresist, it occurs during the so-called post-beacon step or at the latest when structuring due to surface tension effects

Rounding of the photoresist. This means that the material under the photoresist is laterally inaccurately etched during the structuring.

To avoid these structural inaccuracies, a so-called 3-layer resist has been developed as a multi-layer mask, in which a so-called bottom resist is applied to the substrate. In addition, the bottom resist is provided with a dielectric mask made of Si0 ₂ or Si ₃ N ₄ . This mask can then be patterned _4/0 ₂ plasma in a CF eg. To do this, however, it is necessary to apply a further photoresist layer to the dielectric layer (hereinafter referred to as textured lacquer layer). Thus, the “3-layer resist has a layering (from above) of structural lacquer, Si0 ₂ / Si ₃ N ₄ mask layer, bottom resist. With such a 3-layer mask, vertical photoresist flanks of up to 5 7 μ were generated (see G. Franz, J. Vac. Sci. Technol. A16, 1542 (1998); G. Franz, F. Rinner; J. Vac. Sci. Technol. A17, 56 (1999))

However, when structuring metal, in particular platinum layers of a substrate, it was found that when structuring the botto resist, the underlying metal (here platinum) can be sputtered, because the end point of the etching can only be detected spectroscopically when an etching has already taken place, ie L5 if platinum has already been sputtered. Sputtering distributes the platinum on the substrate, which is undesirable. So-called “micro-masking” occurs in the subsequent etching step in the semiconductor.

The object of the present invention is to create a means for structuring a substrate with a mask and a method for structuring a substrate with a mask, in which undesired etching and sputtering of material of the substrate is avoided 5.

This object is achieved according to the invention by an agent with the features of claim 1.

The fact that a mask has at least one layer with or from a dielectric which can be wet-structured and is resistant to dry etching prevents the substrate lying under the mask from being etched.

It is advantageous if the dielectric has at least a proportion of Si0 ₂ , Si ₃ N ₄ , Al ₂ 0 ₃ , SiO _x N _γ (silicon oxynitride) and / or Ti0 ₂ or entirely from one of these Substances. Layers with or from these substances can easily be deposited on substrates.

It is advantageous if the layer with or from the dielectric has a thickness of 30 to 50 nm.

It is particularly advantageous if the layer with or from the dielectric is arranged below a bottom resist of a 3-layer resist, since particularly good flanks can be produced in a photoresist.

The object is also achieved by a method having the features of claim 5.

The fact that at least one layer of the mask is applied from a dielectric that can be wet-structured and from a dielectric that is resistant to dry etching. The layer can have a dielectric or consist of it. An etching stop for the underlying substrate is thus efficiently implemented.

The layer of or with the dielectric is advantageously applied to the substrate before the application of a bottom resist layer of a 3-layer resist.

It is also advantageous if after structuring the bottom resist using a dry etching method, in particular an RIE method, the layer is etched from or with the dielectric using wet chemistry.

Particularly efficient wet chemical etchants for the dielectric are phosphoric acid (H ₂ P0 ₄ ) for sputtered A1 ₂ 0 ₃ , hydrofluoric acid (HF) or ammonium-buffered HF (HF / NH ₄ F) for Si-containing dielectrics. It is advantageous if the phosphoric acid is diluted 1: 1 with water and has a temperature of 70 ° C. In a further advantageous embodiment of the method according to the invention, the layer made of or with the dielectric is used as an etching stop, in particular in an automated method.

The invention is explained in more detail below with reference to the figures of the drawings using several exemplary embodiments. Show it:

1 shows a schematic sectional view of a substrate with an embodiment of the structuring agent according to the invention;

Fig. 2 structuring result with a known 3-layer resist;

3 structuring result with a known 3-layer resist after removal of the resist;

Fig. 4 EDX spectrum for a structure produced using a known method and using the method according to the invention.

1, which is not to scale, is a section through an embodiment of the invention

Represented for structuring a substrate 20. The substrate 20 here is a semiconductor material (e.g. silicon or a III-V semiconductor) with a platinum layer. This is particularly inventive for the III-V semiconductors used in the field of optoelectronics

Appropriate means and the inventive method.

The structuring means here is a multi-layer mask 1, 2, 3, 4. Since this mask 1, 2, 3, 4 is made up of four layers, this is also called a quadro-level layer.

According to the invention, a layer 1 is made on the substrate 20 arranged a wet chemical structurable dielectric, wherein the selected dielectric is resistant to dry etching processes for the photoresist of an overlying layer.

Such a dielectric layer 1 can consist, for example, of Si0 ₂ , Si ₃ N, SiO _x N _γ , A1 ₂ 0 ₃ and / or Ti0 ₂ or have portions of these substances.

It is this dielectric layer 1 that at a

Structuring overlying layers 2, 3, 4 prevents the substrate 20 from being etched; it acts as an etch stop. Any etching that is used as an etch stop e.g. a noble metal (for example Au, Ag, Pt) or a refractory metal (for example Co, Mo, W, Ti on semiconductors) has the disadvantage that the material removed from this layer is deposited in the immediate vicinity with the formation of "micromasking" is very annoying for the subsequent etching, and layer 1 made of or with a dielectric which can be removed by wet chemistry avoids this undesirable effect.

The method according to the invention for producing the structuring agent provides that this dielectric layer is applied before another layer of the multilayer mask layer is applied.

This agent according to the invention and the corresponding methods for producing this agent are suitable for setting the end point of an etching very precisely (to the nanometer). In the case of known methods, the end point of an etching can only be determined inaccurately, since in order to detect the end point, the material underneath must be detectable in the plasma, ie removal must have already taken place. Although the dielectric is also slightly removed, it can be removed quantitatively in the subsequent wet etching. The negative consequences of undesired ablation are shown in FIG. 3.

A known 3-layer resist mask 2, 3, 4 is arranged above the dielectric layer 1 in FIG. 1.

As mentioned, a bottom resist 2 with a relatively high layer thickness (for example several micrometers) is structured by means of a dry etching process. For this purpose, a mask layer 3 made of Si0 ₂ or Si ₃ N _{4 is} provided. A

Structural lacquer layer 4 in turn serves to structure the mask layer 3.

FIG. 2 shows a trace of an SEM image of such a 3-layer resist layer known per se. The

Here, substrate 20 has a platinum layer, on which an approximately 7.3 μm thick bottom resist 2 layer is arranged.

A very thin cover layer made of Si ₃ N as a mask layer 3 is arranged above the bottom resist 2.

Fig. 3 shows a tracing of an SEM on which shows the structure shown in Fig. 2 after dry etching.

When dry etching with oxygen, the thin

Platinum coating of the substrate 20 is sputtered on, so that this platinum is deposited on the flanks of the 3-layer mask 2, 3, 4. After the mask 2, 3, 4 has been removed, this sputtered platinum remains as a kind of “fence” 30.

Not inconsiderable amounts of platinum can be sputtered, since conventional mass spectrometers cannot detect platinum due to its high atomic weight. Platinum is also not sufficiently converted into volatile compounds for detection by other methods. All of this makes it difficult to prove an end point of the etching. Although no coherent layer is formed during the deposition (redeposition) of the material (here platinum), dot masks are nevertheless formed, which lead to “needle or grass formation” in a subsequent etching step.

The example of a platinum layer on a substrate shows how the exposed material forms an etching stop in a reactive etching process (here etching with oxygen), since it has no chemical affinity for the etching gas. But the material is removed by physical sputtering and deposited again.

In order to prevent this, the wet-chemical structurable dielectric layer 1, which is resistant to dry etching, is inserted as an additional etching stop layer. This layer 1 can be removed by wet chemistry. The agent according to the invention and the method according to the invention can thus be used for any type of structuring with etching stop but also with end point detection (accuracy not better than 1 nm). A speech position is avoided.

4 shows an EDX spectrum (Energy Dispersive X-Ray Analysis) in which the signals of a structuring with a 3-level resist (curve A) and an inventive quadro-level mask (curve B) are shown. The platinum peak of curve A shows (labeled Pt) that 1 platinum is present in a 3-layer mask without a dielectric layer according to the invention. When using the quadro-level technique according to the invention, i.e. with the electrical layer 1, no significant sputtering of platinum can be detected; there was no etching of the platinum layer on the substrate 20.

The dielectric layer 1 according to the invention can thus also be used for automatic control of the manufacturing process. Once portions of the dielectric layer the etching step is stopped. The traces of the dielectric are then removed in a subsequent wet etching.

The embodiment of the invention is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable which make use of the agent according to the invention and the method according to the invention even with fundamentally different types.

LIST OF REFERENCE NUMBERS

1 layer of wet-structurable dielectric

2 bottom resist

3 mask layer

4 structure paint layer 20 substrate

30 fence made of sputtered platinum

Claims

claims

1. Means for structuring a substrate with a mask, characterized in that the mask has at least one layer (1) with or made of a dielectric which can be wet-structured and is resistant to dry etching.

2. Composition according to claim 1, characterized in that the dielectric has at least a proportion of Si0 ₂ , Si ₃ N ₄ , SiO _x Nγ, Al ₂ 0 ₃ and / or Ti0 ₂ or consists entirely of one of these substances.

3. Means according to claim 1 or 2, characterized in that the layer (1) with or from the dielectric has a thickness of 30 to 50 nm.

4. Agent according to at least one of the preceding claims, characterized in that the layer (1) with or from the dielectric is arranged below a bottom resist (2) of a 3-layer resist (2, 3, 4).

5. A method for structuring a substrate using a mask, characterized in that at least one layer (1) of the multilayer mask has or consists of a dielectric which can be wet-structured and resistant to dry etching.

6. The method according to claim 5, characterized in that the layer (1) with or from the dielectric before the application of a bottom resist (2) layer of a 3-layer resist (2, 3, 4) on the substrate (20 ) is applied.

7. The method according to claim 6, characterized in that after the structuring of the bottom resist (2) with a dry etching process, in particular an RIE process, the layer (1) is etched with or from the dielectric using wet chemistry.

8. The method according to claim 7, characterized in that the wet chemical etching of the layer (1) from or with a dielectric with phosphoric acid (H ₂ P0 ₃ ), hydrofluoric acid (HF) or ammonium-buffered HF (HF / NHF).

9. The method according to claim 8, characterized in that the phosphoric acid is diluted 1: 1 with water and has a temperature of 70 ° C.

10. The method according to at least one of claims 5 to 9, characterized in that the layer (1) made of or with a dielectric used as an etching stop, in particular in an automated process.