FR2936094A1 - ETCHING METHOD USING MULTILAYER MASKING STRUCTURE - Google Patents

Abstract

The method of etching a target layer comprises forming on the target layer (1) a multilayer structure (2) having an inorganic hard mask layer (4) disposed on said target layer (1), itself covered by a mask (5) comprising a network of nanometric patterns. The inorganic hard mask layer (4) has a thin metal oxide layer less than or equal to 10 nm thick. The network of nanometric patterns of the mask (5) is transferred into the target layer (1) by successive etchings.

Description

1

TECHNICAL FIELD OF THE INVENTION The invention relates to a method of etching an array of nanometric patterns on a target layer ensuring a vertical transfer of the structures. The method includes forming on the target layer a multilayer structure having an inorganic hard mask layer disposed on the target layer. This layer is covered by a mask comprising the network of nanometric patterns. The method also comprises the transfer, in the target layer, of the network of nanometric patterns of the mask by successive etchings. State of the art

Faced with the miniaturization of electronic devices and in particular, in order to meet the dimensional specifications of future generations of integrated circuits, optical lithography technologies, such as 193 nm photolithography or photolithography using UltraViolet extreme radiation (EUV) or electronic lithography ( (e-beam), have developed considerably to allow to transfer a network of patterns on a substrate, in particular of silicon.The development of nanotechnologies has made it possible to push back the resolution limits of conventional techniques, notably MP Stovkovich and aI, describe in the article "Block copolymers and lithography" (materials today, Sept 2006, vol 9, n ° 9, P.20-29), a grapho-epitaxy technique, based on the integration of diblock copolymers in the conventional lithography, to improve the resolution of this technology and to achieve di pattern sizes of about 20 nm. In these circumstances, 2

the use of diblock copolymers requires working at a limiting thickness of about 30 nm in order to obtain a great uniformity in the size of the patterns. With such thicknesses, the etch selectivity is then no longer good enough to directly transfer the mask to the substrate.

To preserve the integrity of the patterns made, laws of the transfer to the substrate, new nano-structuring techniques have been developed. These techniques make it possible to obtain multilayer mask structures that improve the quality of the pattern transfer at the nanoscale to the substrate. Thus, Wai-kin Li et al, in the article Creation of sub-20nm contact using a diblock copolymer, has 300 mm wafer for complementary metal oxide semiconductor applications (J. Vac, Sci Technol, B25 (6), Nov / Dec 2007 1982 - 1984) discloses a method of forming an array of patterns smaller than 20 nm in size from a poly (styrene-block-methylmethacrylate) diblock copolymer designated PS-b-PMMA. This article also mentions a three-layer structure corresponding to the stack of the polymer layer on a double layer of hard mask, one of silicon nitride and the other of silicon oxide. This structure allows the transfer of the pattern grating, made in the polymer layer, to the substrate with a relatively high aspect ratio. Nevertheless, the selectivity is not good enough to allow satisfactory dimensional control.

Likewise, patent application WO2007 / 103343 describes, more particularly, a three-layer structure consisting of an amorphous carbon layer forming a first hard mask, an inorganic layer forming a second hard mask and a light-sensitive resin which allows to define the patterns by optical lithography. The etching process using this masking structure includes a stripping step to reduce the size of the transferred patterns but only up to about 63 nm.

Object of the invention

The object of the invention is to propose an etching method using a multilayer masking structure and specific etching plasmas, allowing the transfer of a network of nanometric patterns with a high resolution and a good dimensional control, while by overcoming the disadvantages of the prior art.

According to the invention, this object is achieved by the fact that the inorganic hard mask layer comprises a thin layer of metal oxide with a thickness of less than or equal to 10 nm.

According to a preferred embodiment, the multilayer structure comprises an organic hard mask layer disposed into the target layer and the inorganic hard mask layer.

Brief description of the drawings

Other advantages and features will emerge more clearly from the following description of the particular embodiments of the invention given as non-restrictive examples and represented in the accompanying drawings, in which:

Figures 1 to 7 show, schematically and in section, different successive steps of a first embodiment of a method of etching a multilayer structure.

Figures 8 to 12 show, schematically and in section, different successive steps of a second embodiment of a method of etching a multilayer structure. 3 4

Description of particular embodiments

According to a first embodiment, the method of etching a target layer 1, illustrated by way of example, in FIGS. 1 to 7, comprises the formation of a multilayer structure 2 on the target layer 1 (FIG. 1). The multilayer structure 2 consists of a stack of layers. As shown in FIG. 1, the multilayer structure 2 comprises successively (from bottom to top in FIG. 1), an organic hard mask layer 3, disposed on the target layer 1, an inorganic hard mask layer 4, disposed on the organic hard mask layer 3 and a mask 5 comprising a network of nanometric patterns.

The target layer 1 is the layer in which the network of nanometric patterns of the mask 5 is to be transferred. This target layer 1 is primarily intended for producing printed circuit devices, nanoelectronic devices or nanoporous structures. This target layer 1 may correspond, for example, to a silicon layer, a metal layer or an insulator. The organic hard mask layer 3 and the inorganic hard mask layer 4 are deposited successively, full plate, on the target layer 1, according to any known method. This deposit may, for example, be achieved by physical vapor deposition (PVD), sputtering, evaporation or plasma-enhanced chemical vapor deposition (PECVD). The organic hard mask layer 3 is, advantageously, a thin layer, typically having a thickness of between 10 and 500 nm and advantageously between 25 and 75 nm, for example 50 nm. This organic hard mask layer 3 is preferably a carbon layer, advantageously consisting of amorphous carbon.

The inorganic hard mask layer 4 consists of a thin layer of metal oxide, less than or equal to 10 nm thick. The preferred metal oxides are oxides of hafnium, aluminum, yttrium or zirconium. The use of a very thin inorganic hard mask layer 4 (less than 10 nm) avoids the practice of too aggressive etching, which can deteriorate the integrity of the network of nanometric patterns of the mask 5.

The mask 5 is produced by any known method, for example, by deposition and optical lithography or photolithography. In the case of an electronic lithography, the presence of a thin layer of metal oxide 4 allows better dimensional control of the network of nanometric patterns. Indeed, the electronic lithography of insolating a resin by means of an electron beam without using a prior mask is subject to a charging effect. The thin layer of metal oxide 4 then promotes the dissipation of the electrical charges and thus reduces this charging effect. The mask 5 is advantageously made of a polymeric material. The mask 5 made of polymeric material can be obtained by known lithography techniques using self-organized materials, for example diblock copolymers, in particular of the PS-b-PMMA type. Since the critical dimension is the dimension of the smallest geometric patterns (line width, contact, trench, etc.), the mask 5 has an array of patterns having a critical dimension of less than or equal to 50 nm, preferably less than or equal to 20 nm. This critical dimension corresponds in Figure 1 to the length L of the patterns. The increase in the resolution of the network of nanometric patterns generally induces a decrease in the thickness d of the mask 5. In these critical dimension ranges, the thickness d of the mask 5 is less than or equal to 50 nm, more particularly less than or equal to 30 nm.

After completion of the multilayer structure, according to FIG. 1, the network of 30 nanometric patterns is transferred from the mask 5 to the target layer 1, by successive etchings. As shown in FIG. 2, the pattern network existing within the mask 5 is first transferred to the inorganic hard mask layer 4 by a first plasma etching. This is, advantageously, a reactive ion etching ("reactive ion etching" note RIE). In particular, the plasma is a mixture of chlorine and boron chloride and / or chlorosilane, more particularly a mixture of chlorine (Cl 2), boron trichloride (BCI 3) and / or tetrachlorosilane (SiCl 4), which may be associated with the plasma. to a rare gas like argon. This etching then exposes certain parts of the organic hard mask layer 3, not covered by the network of nanometric patterns. The etching is carried out under conditions of low ion bombardment in capacitively or inductively coupled reactors. In the case of an inductively coupled reactor, the etching is performed with a low self-biasing voltage to have an ion energy of less than 50 eV. These etching conditions, very little aggressive for the mask 5, ensure the transfer of the network of nanometric patterns without deterioration of these patterns. Thus, even with very small mask thicknesses, ie less than 30 nm, the integrity of the network of nanometric patterns is retained.

By way of example, in the case of a layer of hafnium dioxide (HfO2), the inorganic hard mask layer 4 is etched by a BCI3 plasma in an inductively coupled reactor (ICP) under the following conditions: MTorr; 800W source power, 10W auto-polarization power, 50 ° C temperature, 0.1 Slm BCI3 output.

By way of example, in the case of an aluminum oxide layer (Al 2 O 3), the inorganic hard mask layer 4 is etched by a SiCl 4 / Cl 2 plasma in an inductively coupled reactor (ICP) under the following conditions pressure of 10 mTorr; power source of 500 W, no self-biasing power, temperature of 50 ° C, flow of SiCI4 of 0.02 Slm and

Cl2 of 0.08 SIm. A flow rate of 1SIm (1 standard liter / minute) corresponds to a flow equivalent to 1 liter per minute under standard conditions of pressure and temperature.

According to a variant, when the hard mask layer 4 is a thin layer of hafnium dioxide (HfO 2) having, for example, a thickness of less than 5 nm, it may advantageously be etched by a first chemical etching. The etching liquid used for this first etching is then hydrofluoric acid (HF) in liquid form. This etching has the advantage of being very selective vis-à-vis the mask 5. In practice, the assembly consisting of the target layer 1 and the multilayer structure 2 is immersed in a bath of hydrofluoric acid (HF) then removed after an immersion time of about 1 min. The small thickness of the thin metal oxide layer 4a, that is to say less than 5 nm, makes it possible to obtain anisotropic etching despite the isotropic character of a chemical etching.

The mask 5 is then removed according to techniques known to the nature of the mask 5 (Figure 3). A mask 5 made of carbon-rich material of the polystyrene or amorphous carbon type may, for example, be removed with an oxygen plasma (O 2) or with high temperature reducing plasmas, for example gaseous mixtures of hydrogen and carbon. helium (H2 / He) or hydrogen and argon (H2 / Ar) at 350 ° C or ammonia (NH3).

The organic hard mask layer 3 is then etched by a second plasma etch under low ion bombardment conditions. Preferably, the second etching is a reactive ion etching (RIE). The inorganic hard mask layer 4 which comprises the entire network of nanometric patterns is then used as a mask for etching the organic hard mask layer 3. As illustrated in FIG. 4, the network of nanometric patterns is transferred from the hard mask 8

The plasma used is preferably a gaseous mixture of hydrogen and one or more nitrogen and / or carbon compounds. For example, the plasma is a mixture of hydrogen (H2), nitrogen (N2) and methane (CH4). Since the inorganic hard mask layer 4 is not very sensitive to the plasma conditions used, it guarantees the durability of the network of nanometric patterns during this transfer. In the absence of this layer of inorganic hard mask 4, the selectivity of the etching being no longer good enough, the direct transfer of the pattern network from the mask 5 to the organic hard mask layer 3 would, because of the etching conditions too aggressive, a deterioration of the network of nanometric patterns.

According to one variant, the plasma is advantageously a gaseous mixture of oxygen, one or more halogenated compounds and an inert gas serving as a plasma support. For example, the plasma is a mixture of oxygen (O 2) and hydrobromic acid (HBr) and / or chlorine (Cl 2) and argon (Ar).

As illustrated in FIG. 5, the inorganic hard mask layer 4 is removed by any known method. According to a variant not shown, the inorganic hard mask layer 4 remaining after the second etching is removed in the subsequent steps either by etching the target layer 1 or with the hard organic mask layer 3. The organic hard mask layer 3 , which comprises the entire network of nanometric patterns, is then used as a mask for etching the target layer 1. The network of nanometric patterns is then transferred from the organic hard mask layer 3 to the target layer 1, by a third 30 engraving (Figure 6). The etching of the target layer 1 is carried out according to any known method depending on the nature of the target layer 1. For example, 20 9

a target layer 1 made of silicon can be etched with a plasma formed of a gaseous mixture (HBr + Cl2 + O 2). For a target layer 1 of silicon oxide, a plasma formed of a fluorocarbon gas mixture can be used for etching. The organic hard mask 3 is then removed by any known method (FIG. 7).

According to a second embodiment, an additional layer is inserted into the multilayer structure 2 (FIG. 8). The inorganic hard mask layer 4 then consists of the thin metal oxide layer 4a, with a thickness of less than or equal to 10 nm and a dielectric layer 4b between the organic hard mask layer 3 and the thin film layer. metal oxide 4a. The dielectric layer 4b is advantageously a silicon oxide (SiO 2) layer. The thickness of the dielectric layer 4b is preferably less than or equal to about 20 nm. The method according to this second embodiment comprises an additional etching step, illustrated by way of example in FIGS. 9 to 12. The transfer of the network of nanometric patterns from the mask 5 to the thin metal oxide layer 4a is carried out according to FIG. same procedure as before.

The thin metal oxide layer 4a which comprises the entire network of nanometric patterns is then used as a mask for etching the dielectric layer 4b (FIG. 9). As illustrated in FIG. 10, the network of nanometric patterns is then transferred from the metal oxide thin layer 4a to the dielectric layer 4b by an intermediate plasma etching, preferably RIE etching, under conditions of low ion bombardment. The plasma used is a plasma comprising a fluorocarbon compound. For example, the plasma contains tetrafluoromethane (CF4), advantageously in the presence of an inert gas, for example argon. The thin metal oxide layer 4a is particularly resistant to fluorocarbon plasma. The existence of this dielectric layer 4b thus improves the selectivity of etching. 10

After removal of the remaining layer 4a, the dielectric layer 4b, which comprises the entire network of nanometric patterns (FIG. 11), is then used as a mask for etching the organic hard mask layer 3. As illustrated in FIG. the network of nanometric patterns is then transferred from the dielectric layer 4b to the organic hard mask layer 3, under the same conditions as the second plasma etching. After removal of the clielectric layer 4b, the network of nanometric patterns is transferred from the organic hard mask layer 3 to the target layer 1 according to a procedure identical to that of the first embodiment.

According to a variant, not shown, the dielectric layer 4b and the organic hard mask layer 3 are etched successively without removing the remaining layers respectively of metal oxide 4a and dielectric 4b.

The layers 4a and 4b are then eliminated at the same time either by etching the target layer 1 when the etching conditions are sufficiently aggressive or after etching the target layer 1, with the organic hard mask layer 3.

The choice of the embodiment of the etching process is dictated by the nature of the layers and the compatibility of the layers between them. Thus, the etching method according to the second embodiment is particularly suitable when the direct deposition of the metal oxide layer 4a on the organic layer 3 is difficult or impossible.

According to a third embodiment, not shown, the multilayer structure 2 consists of the inorganic hard mask layer 4 disposed directly on the target layer 1, itself covered by the mask 5 comprising the network of nanometric patterns. The organic hard mask layer 3 is then non-existent. As previously, the inorganic hard mask layer 4 can also comprise a layer

4b when the deposition of the metal oxide layer 4a on the target layer 1 is difficult to achieve. The transfer of the network of nanometric patterns from the mask 5 to the inorganic hard mask layer 4 is then carried out according to the same operating mode as the first mode, described above. The target layer 1 can then be etched according to any known method.

When the target layer 1 is etched with hydrofluoric acid, the etching plasmas of the inorganic hard mask layer 41 may be used to remove the remaining inorganic hard mask layer 4. The mask 5 is then consumed during the various etching steps.

According to one variant, the target layer 1 is an inorganic layer, for example a dielectric layer. The plasma used for the etching of the target layer 1 can then be identical to that of the etching of the inorganic hard mask layer 4.

The etching method according to this third embodiment is particularly suitable for etching an inorganic layer, for example a dielectric layer or for etching a target layer 1 on a small thickness, advantageously a thickness less than 100 nm.

The etching processes described above are industrializable processes, suitable for masks with very high resolutions, developed at present to meet the requirements of miniaturization of integrated circuits and nanotechnologies. They make it possible to transfer a network of nanometric patterns from a very thin mask to a substrate with high selectivity and good dimensional control.

These etching processes are particularly suitable for producing nanostructures for applications in nanoscience.

Claims (16)

Revendications1. A method of etching a target layer (1) comprising forming on said target layer (1) a multilayer structure (2) having an inorganic hard mask layer (4) disposed on said target layer (1), -Even covered by a mask (5) comprising a network of nanometric patterns, and transfer in the target layer (1), the network of nanometric patterns of the mask (5) by successive etching, characterized in that said mask layer inorganic hard (4) has a thin layer of metal oxide (4a), less than or equal to 10 nm thick. 2. Method according to claim 1, characterized in that the metal oxide (4a) is selected from oxides of hafnium, aluminum, yttrium and zirconium. 3. Method according to one of claims 1 and 2, characterized in that the mask (5) is of polymeric material. 20 4. Method according to any one of claims 1 to 3, characterized in that the nanometric patterns of the network of the mask (5) have a critical dimension (L) less than or equal to 50 nm. 5. Method according to claim 4, characterized in that the critical dimension (L) is less than or equal to 20 nm. 6. Method according to any one of claims 1 to 5, characterized in that the mask (5) has a thickness less than or equal to 50 nm. 30 7. Method according to claim 6, characterized in that the mask (5) has a thickness less than or equal to 30 nm. 12 13 8. Method according to any one of claims 1 to 7, characterized in that the network of nanometric patterns is transferred from the mask (5) to the thin metal oxide layer (4a), under conditions of low ion bombardment, by a first plasma etching, with a plasma comprising a mixture of chlorine and boron chloride and / or chlorosilane. 9. Method according to any one of claims 1 to 7, characterized in that the metal oxide (4a) being hafnium dioxide (HfO2), the network of nanometric patterns is transferred from the mask (5) to the layer thin metal oxide (4a) by chemical etching with hydrofluoric acid. Method according to one of Claims 1 to 9, characterized in that the multilayer structure (2) comprises an organic hard mask layer (3) arranged between the target layer (1) and the inorganic hard mask layer ( 4). 11. The method of claim 10, characterized in that the organic hard mask layer (3) is a carbon layer having a thickness between 10 nm and 500 nm. 12. Method according to one of claims 10 and 11, characterized in that the inorganic hard mask layer (4) comprises, between the thin metal oxide layer (4a) and the organic hard mask layer (3). a dielectric layer (4b) having a thickness less than or equal to 20 nm. Method according to any one of claims 10 to 12, characterized in that the network of nanometric patterns is transferred from the inorganic hard mask layer (4) to the organic hard mask layer (3) by one second. plasma etching under conditions of low ion bombardment. 14. The method of claim 13, characterized in that the second plasma etching is performed with a plasma comprising a gaseous mixture of hydrogen and one or more nitrogen compounds and / or carbon. 15. The method of claim 13, characterized in that the second plasma etching is performed with a plasma comprising a gaseous mixture of oxygen and one or more halogenated compounds. 16. A method according to any one of claims 1 to 15, characterized in that the inorganic hard mask layer (4) having a dielectric layer (4b), the pattern network is transferred from the thin oxide layer. metal (4a) to the dielectric layer (4b) by plasma etching with an etching plasma comprising a fluorocarbon compound.