WO2008015212A1

WO2008015212A1 - Novel hard mask structure for patterning features in semiconductor devices

Info

Publication number: WO2008015212A1
Application number: PCT/EP2007/057899
Authority: WO
Inventors: Marcel Eduard Irene Broekaart; Veronique De-Jonghe; François Leverd
Original assignee: Koninklijke Philips Electronics N.V.; St Microelectronics (Crolles 2) Sas
Priority date: 2006-08-02
Filing date: 2007-07-31
Publication date: 2008-02-07

Abstract

The present invention relates to a method for fabricating at least one feature, which has a target lateral width, in a substrate layer. The method allows fabricating a feature with a target lateral width in a substrate layer that is smaller than can be obtained with the used lithographic equipment. In comparison with known methods, it provides an increased resistance to temperatures typically used during processing, in particular, during a plasma etching step. The increased temperature resistance is achieved by using a layer structure that comprises an amorphous carbon layer on the substrate layer, a capping layer on the amorphous carbon layer, and a first resist layer structure on the capping layer. In this layer structure, a carbon contribution to the etching process, which is usually provided by a resist material, is provided by the amorphous carbon layer, which forms a hard mask on the substrate layer.

Description

Novel hard mask structure for patterning features in semiconductor devices

FIELD OF THE INVENTION

The present invention relates to a method for fabricating at least one feature, which has a target lateral width, in a substrate layer.

The invention also relates to a method for fabricating at least one first feature and at least one second feature in a substrate layer, the first and second features having a target lateral width and a mutual target lateral pitch.

BACKGROUND OF THE INVENTION

Most advanced patterning technologies often require a patterning of features, which are smaller than those which can be made by state-of-the-art lithographic equipment. Therefore, the challenges, which have to be met, are a reduction of lateral critical dimensions and/or a reduction of the lateral distance (pitch) between neighboring features in a substrate layer.

The critical dimensions of a feature comprise a lateral extension of the feature attained by the employed fabrication technology. In current advanced Complementary Metal-Oxide-Semiconductor (CMOS) technology, the minimum feature size of features like holes, trenches, and lines are linked to the characteristics of the used mask, photoresist material and scanner technology, which are employed for exposure and development of a photoresist layer used for patterning of a substrate layer. For reaching smaller feature sizes in a new generation of technology, a hitherto used photo-resist suitable for exposure at a given wavelength of light and associated equipment must be replaced by a photo resist suitable for exposure at a smaller wavelength, and suitable new equipment. This which in turn will be replaced in the next generation by a further photo-resist suitable and related equipment, and so on. For instance, photolithography has moved from 248nm wavelength to 193 nm, and on to a 193 nm- immersion technology for a stepwise increase of resolution, i.e. reduction of critical dimension.

As can be seen, each technological step forward requires a new generation of photoresist materials, which in the beginning are not always mature. Additionally, the associated masks and scanners constitute ever-increasing investment costs. On account of this situation, techniques were developed order to avoid or delay the investment into a new technology.

US 2005/0056823 Al describes a method for fabricating features in a substrate layer. The process comprises depositing an antireflective material layer on a substrate layer, in which the features are to be fabricated. On top of the antireflective material layer, a photoresist layer is deposited. The layer of antireflective material has general structural formula metal:carbon:hydrogen:inorganic element, an example of which is formed by the material Si:C:H:O. In contrast, the photoresist layer comprises carbon, hydrogen, and oxygen, and not any metal atoms, nor silicon. The patterning process involves a plasma etch step, which in US

2005/0056823 Al is used to deposit polymeric materials on the sidewalls of an opening in the radiation sensitive imaging layer in a gradually tapered configuration. This way, the lateral width is reduced from the original width of the opening in the exposed and developed radiation sensitive imaging layer to the target lateral width. The composition of the antireflective material can be tuned for attaining a desired reduction in the critical dimensions of the feature to be fabricated by the amount of sidewall taper used during the taper-etch step. However, the plasma etching step, due to the high temperatures induced by the plasma generated, can cause damage to the antireflective layer, and thus also introduce edge irregularities in the mask, which are transferred on to the features to be formed in the substrate layer.

It is therefore desirable to provide a layer structure for a tapered-etch process that has an increased resistance to plasma etching temperatures.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for fabricating at least one feature, which has a target lateral width, in a substrate layer that uses a mask layer structure with an increased resistance to high temperatures.

It is another object of the present invention to provide a method for fabricating at least one first feature and at least one second feature in a substrate layer, the first and second features having a target lateral width and a mutual target lateral pitch, which uses a mask layer structure that has an increased resistance to high temperatures.

A first aspect of the invention is provided by the method of claim 1. Preferred embodiments are given in the dependent claims. According to the first aspect of the invention, a method for fabricating at least one feature, which has a target lateral width, in a substrate layer, comprises the steps: depositing an amorphous carbon layer on the substrate layer; depositing a capping layer on the amorphous carbon layer; - depositing a first resist layer structure on the capping layer; fabricating at least one first opening in the first resist layer structure, the first opening having a first lateral width larger than the target lateral width; taper etching the capping layer through the at least one first opening in the first resist layer structure, thus forming at least one second opening in the capping layer that has a tapered lateral width, which reduces from the first lateral width at an interface to the first resist layer structure to the target lateral width at an interface to the amorphous carbon layer; etching at least one third opening, which has the target lateral width, into the amorphous carbon layer through the at least one second opening in the capping layer; and etching the at least one feature into the substrate layer through the at least one third opening.

The method according to the first aspect of the invention allows fabricating a feature with a target lateral width that is smaller than can be obtained with the used lithographic equipment. In comparison with known methods, it provides an increased resistance to temperatures typically used during processing, in particular, during a plasma etching step.

The increased temperature resistance is achieved by using a layer structure that comprises an amorphous carbon layer on the substrate layer, a capping layer on the amorphous carbon layer, and a first resist layer structure on the capping layer. In this layer structure, a carbon contribution to the etching process, which is usually provided by a resist material, is provided by the amorphous carbon layer, which forms a hard mask on the substrate layer. Another carbon contribution can be provided by relevant gases that are in the plasma.

The method of the invention thus involves depositing two intermediate layers between the resist layer structure and the substrate layer to be patterned by etching: one capping layer and one amorphous carbon layer. Additional layers can be present, as will be explained in the context of preferred embodiments further below.

Features that can be fabricated in the substrate layer with the method of the present invention are structural elements formed in the substrate layer which include lines, holes, and trenches, but are not limited to these examples. Note that the term substrate layer is not to be interpreted in a limited manner, such as necessarily requiring a layer or film structure obtained, for instance, by deposition of a distinguished layer on a substrate wafer. A substrate layer in the sense of the present invention can also be formed by a substrate wafer as such, like a silicon wafer. The term resist is used herein in short for photoresist, as is usual in the art.

In the following, preferred embodiments of the method of the first aspect of the invention will be described. Unless stated otherwise explicitly, the embodiments can be combined with each other.

In a first preferred embodiment, the capping layer is made from the same material as the substrate layer. In this embodiment, the capping layer will be removed at the same time the substrate layer is etched. This way, an additional individual etching step for removing the capping layer can be saved.

Alternative embodiments employ a capping layer that is made of a material different from that of the substrate layer. Examples of alternative capping-layer materials are SiN, SiNOC, SiNC and Si (forming an alternative embodiment, if the substrate layer is not made of Si).

In a further embodiment, depositing the first resist layer structure on the capping layer is performed by depositing a single resist layer, which provides a particularly simple resist layer structure and thus allows shorter processing times. In an embodiment that forms an alternative to the embodiment of the previous paragraph, depositing the first resist layer structure comprises depositing a bottom antireflective coating (BARC) on the capping layer, and subsequently depositing a resist layer on the BARC layer. The use of a BARC layer minimizes reflection of light back into the resist layer during exposure, which would otherwise degrade the lateral solution of the lithography process. The BARC is in one embodiment a polymer with carbon. This can be removed in the same way as the resist, thus saving extra processing steps and chemistry.

Each of the two alternative resist layer structures requires an individual combination of processing chemistry, which is known in the art as such, because the use of BARC layers in combination with a resist layer is known. According to a second aspect of the invention, a method is provided for fabricating at least one first feature and at least one second feature in a substrate layer, the first and second features having a target lateral width and a mutual target lateral pitch. The method comprises performing the process of the first aspect of the invention for fabricating at least one first feature in the substrate layer up until the step of etching at least one third opening. Subsequently, a step of removing the first resist layer structure is performed, keeping, however, the capping layer with the at least one second opening and the amorphous carbon layer with the at least one third opening defined in the process of the first aspect of the invention. Furthermore, the following steps are performed: - depositing a second resist layer structure on the capping layer; fabricating at least one fourth opening in the second resist layer structure, the fourth opening having the first lateral width and being arranged at the target lateral pitch from the first feature; taper-etching the capping layer through the at least one fourth opening in the second resist layer structure, thus forming at least one fifth opening in the capping layer that has a tapered lateral width, which reduces from the first lateral width at an interface to the second resist layer structure to the target lateral width at an interface to the amorphous carbon layer; etching at least one sixth opening, which has the target lateral width, into the amorphous carbon layer through the at least one fifth opening in the capping layer; and etching the at least one first feature and the at least one second feature into the substrate layer through the at least one third opening and the at least one sixth opening, respectively.

The method of the present of the invention allows providing neighboring first and second features with a mutual lateral distance (pitch) that is smaller than can be obtained by standard processing with a given lithographic equipment. In addition, the first and second feature themselves can be formed with lateral widths that are smaller than can be achieved by standard processing with a given lithographic equipment.

The method of the second aspect of the invention makes use of the features fabricated during the processing according to the method of the first aspect of the invention with a larger pitch. By positing a second resist layer structure on the capping layer and repeating the formation of openings in the same manner as during the previous processing, but with a lateral offset, at least one second feature fabricated in the substrate layer with a desired target pitch with respect to the first embodiment. In a preferred embodiment, a plurality of first features is fabricated and each second feature is arranged between a respective pair of neighboring first features at equal distance to each of the respective neighboring first features. By this processing, a periodic turn of identical features with smaller critical dimensions and with a smaller pitch than obtainable by standard lithographic processing can be achieved. Further preferred embodiments of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be explained in more detail with reference to the drawings in which

Figs. 1 to 6 show schematic cross sectional views of a substrate layer during different processing stages of an embodiment of the method of the first aspect of the invention, for fabricating exemplary features, which have a target lateral width; Figs. 7 to 12 show schematic cross sectional views of a substrate layer during different processing stages of an embodiment of the method of the second aspect of the invention, for fabricating exemplary first and second features with a target lateral width and a mutual target lateral pitch.

DETAILED DESCRIPTION OF EMBODIMENTS

Figs. 1 to 6 show schematic cross sectional views of a substrate layer 100 during different processing stages of an embodiment of the method of the first aspect of the invention, for fabricating exemplary features in the substrate layer 100, which have a target lateral width. For the purpose of the present example, the substrate layer 100 is to be patterned by the fabrication of trenches with a target lateral width. However, any feature can be fabricated by the method of the invention.

Fig. 1 shows a first intermediate processing step, in which the substrate layer 100 has been covered by a layer stack that is formed by an amorphous carbon layer 102, a capping layer 104, a bottom antireflective coating (BARC) layer 106, and a resist layer 108. The BARC layer and the resist layer form a first resist layer structure 110.

Subsequently, as shown in Fig. 2, the resist layer 108 is patterned by fabricating first openings 112, 114, and 116. At this time, the first openings extend only through the resist layer itself, and not through the BARC layer. Standard lithographic equipment and processing can be used for the formation of the first openings 112 to 116. The processing of the first openings as such is thus well known to a person skilled in the art. The first openings are generated with a first lateral width that is attainable with standard lithographic techniques. In a next step, cf. Fig. 3, the capping layer 104 is taper-etched using a chemistry that at the same time opens the BARC layer 106, thus finishing the formation of first openings in the resist layer structure 110 and at the same time providing second openings 118 to 122 in the capping layer 104. For this kind of etching, a dry etcher is advisable for achieving the best control of the critical dimensions: a CF₄ chemistry can be used for the BARC step, whereas the chemistry used for the taper etching depends on the capping material. A CF₄ZC_xF_y chemistry can be used for an oxide capping layer. A chemistry based on CH_xF_y can be used for a nitride capping layer. The chemistry used in the present processing generates a taper in the capping layer. That means, by way of example, that the second opening 118 in the capping layer 104 has the first lateral width of the first opening 112 at an interface 124 to the BARC layer 106 of the first resist layer structure 110, and a smaller, namely, a target lateral width at an interface 126 between the capping layer 104 and the amorphous carbon layer 102. The inclination of the sidewalls between the two interfaces 124 and 126 can be set by appropriate structural and processing parameters. The thickness of the capping layer can be selected to achieve a desired target lateral width at the interface 126.

If the lateral width of the first openings 112 to 114 is at the resolution limit of the lithographic equipment used, the second openings 118 to 122 will have a target lateral width at the interface 126 to the carbon layer, which target lateral width is in fact smaller than the resolution limit of the lithographic equipment.

Subsequently, using the capping layer 104 as a hard mask, third openings 128 to 132 are etched in the amorphous carbon layer 102 through the first openings 112 to 116 and through the second openings 118 to 122. Since the tapered second openings 118 to 122 are used for etching the third openings 128 to 132, the lateral width of the latter openings in the amorphous carbon layer 102 has the smaller lateral width achieved by the taper-etching step. The result of this processing is shown in Fig. 4.

As a part of this processing, the resist layer 108 will also be etched at least in part. Since it is the patterning of the capping layer 104 that is decisive for the reduction of the lateral width from the first to the second openings, the resist layer 108 of the first resist layer structure 110 can be rather thin. If the resist layer 108 is chosen thin enough (not shown here), it will be completely removed during the step of etching the amorphous carbon layer 102. Subsequently, as shown in Fig. 5, the amorphous carbon layer 102 is used as a hard mask for etching the desired features with the reduced target lateral width. In the present embodiment, the features are formed by trenches 134 to 138.

The final reduced thickness of the amorphous carbon layer after this step depends on the resistance of the α-carbon hard mask to the etching chemistry and on the time requested to etch completely 134 to 138 trenches.

Note that by choosing the capping layer material identical to the material of the substrate layer 100, the capping layer will be etched at the beginning of the step for etching the trenches 134 to 138, thus also removing the BARC layer 106 and any remaining parts of the resist layer 108.

Finally, as can be seen in Fig. 6, the remaining amorphous carbon layer 102 is stripped in situ.

Figs. 7 to 12 show schematic cross sectional views of a substrate layer 200 during different processing stages of an embodiment of the method of the second aspect of the invention, for fabricating exemplary first and second features with a target lateral width and a mutual target lateral pitch.

Fig. 7 shows the substrate layer 200 at a first processing stage, i.e., covered an amorphous carbon layer 202, a capping layer 204, and a resist layer 208. In the present embodiment, no BARC layer is used. However, an alternative embodiment may make use of BARC layer to avoid or minimize reflections during exposure to light in the lithography processing.

In the subsequent processing, first, second, and third openings 212 to 214, 218 to 222, and 228 to 232, respectively, are formed in the layer stack of the resist layer 208, the capping layer 204, and the amorphous carbon layer 202. The resulting structure is shown in Fig. 8. It can be fabricated by lithography, using a taper-etch step in the capping layer 204, which is arranged on top of the amorphous carbon layer 202. In one embodiment, in which the capping layer is an oxide, the taper etching can be performed using an optimized C_xF_y chemistry. The tapered etch step in the capping layer is followed by a vertical over-etch through the second openings. Fig. 8 shows the lateral width W of the first opening 212 in comparison with the target lateral width TW of the third opening 228 in the amorphous carbon layer 202. As mentioned before, a target lateral width can be achieved by accordingly choosing the capping-layer thickness. The larger the capping-layer thickness, the smaller target lateral width TW that can be achieved. Subsequently, as shown in Fig. 9, the resist layer 208 is stripped, and a second resist layer 240 is deposited and laterally structured for preparing the formation of second features in the substrate layer 200. The second resist layer 240 is deposited on the capping layer 204 and provided with fourth openings 242 to 246. In the present example, the fourth openings 242 to 246 have the same lateral width W as the first openings 212 to 216. In other embodiments, the lateral width may be different.

The lateral pitch P between the fourth openings 242 and 244, and between the fourth openings 244 and 246 is chosen identical to that of the first openings, cf. Fig. 8. Thus, the second openings are provided at equal lateral distance to the second and third openings fabricated during the previous processing described in the context of Fig. 8.

Subsequently, as shown in Fig. 10, the processing of Fig. 8 is repeated in the fourth openings for fabricating tapered fifth openings 248 to 252 in the capping layer 204 and sixth openings 254 to 258 in the amorphous carbon layer.

Note that in another embodiment, which is not shown here, the lateral pitch P between the fourth openings 242 and 244, and between the fourth openings 244 and 246 can be chosen different from that of the first openings.

Then, as shown in Fig. 11, the resist layer 240 is removed. By the processing up to this point, a hard mask is produced, which is formed by the capping layer 204 and the amorphous carbon layer 202 and which has openings with the reduced target lateral width TW and the reduced target lateral pitch TP. These target values would not be available to conventional lithographic processing.

If the capping layer 204 is fabricated from the same material as the substrate layer 200, the capping layer will be removed in the following etching step in parallel with the desired feature formation in the substrate layer 200. The chemistry that should be used at this point corresponds to that known from conventional processing in lithographic techniques, using the carbon of the amorphous carbon layer in way as the carbon present in a resist layer would be used. This way, desired features, in the present examples, trenches 260 can be formed in the substrate layer 200 by using the third openings 228 to 232 and the sixth openings 254 to 258 in the amorphous carbon layer 202, cf. Fig. 12.

In the present example, the second features have an identical shape as the first features. However, in other embodiments, the second features may differ from the first feature in their shape and/or cross-sectional profile. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single layer or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A method for fabricating at least one feature (134; 260), which has a target lateral width (TW), in a substrate layer (100; 200), comprising the steps of depositing an amorphous carbon layer (102; 202) on the substrate layer; depositing a capping layer (104; 204) on the amorphous carbon layer; - depositing a first resist layer structure (110; 208) on the capping layer; fabricating at least one first opening (112; 212) in the first resist layer structure, the first opening having a first lateral width (W) larger than the target lateral width (TW); taper etching the capping layer (104; 204) through the at least one first opening (112; 212) in the first resist layer structure (110; 208), thus forming at least one second opening (118; 218) in the capping layer that has a tapered lateral width, which reduces from the first lateral width (W) at an interface (124) to the first resist layer structure to the target lateral width (TW) at an interface (126) to the amorphous carbon layer; etching at least one third opening (128; 228), which has the target lateral width, into the amorphous carbon layer through the at least one second opening (118; 218) in the capping layer; and etching the at least one feature (134; 260) into the substrate layer (100; 200) through the at least one third opening (128; 228).

2. The method of claim 1 , wherein the capping layer (104; 204) is made from the same material as the substrate layer (100; 200).

3. The method of claim 1, wherein depositing the first resist layer structure on the capping layer is performed by depositing a single resist layer (208).

4. The method of claim 1, wherein, for etching the amorphous carbon layer (102; 202), an etchant is used that at the same time removes the first resist layer structure.

5. The method of claim 1, wherein depositing the first resist layer structure (110) comprises depositing a bottom antireflective coating layer (106) on the capping layer and subsequently depositing a resist layer (108) on the bottom antireflective coating layer.

6. The method of claim 1, wherein at least one second feature (262) in the substrate layer (200) is fabricated, which has the target lateral width (TW), the first and second features having a mutual target lateral pitch (TP), the method further comprising the following steps after the step of etching at least one third opening (228): selectively removing the first resist layer structure (208), thus keeping the capping layer (204) with the at least one second opening (218) and the amorphous carbon layer (202) with the at least one third opening (228); depositing a second resist layer structure (240) on the capping layer (204); fabricating at least one fourth opening (242) in the second resist layer structure (240), the fourth opening having the first lateral width (W) and being arranged at the target lateral pitch (TP) from the first feature; taper etching the capping layer (204) through the at least one fourth opening (242) in the second resist layer structure, thus forming at least one fifth opening (220) in the capping layer (204) that has a tapered lateral width, which reduces from the first lateral width (W) at an interface to the second resist layer structure (240) to the target lateral width (TW) at an interface to the amorphous carbon layer (202); etching at least one sixth opening (254), which has the target lateral width (TW), into the amorphous carbon layer (202) through the at least one fifth opening in the capping layer; and wherein during the step of etching the at least one first feature (260) also the at least one second feature (262) is etched into the substrate layer (200) through the at least one sixth opening (254).

7. The method of claim 6, wherein at a plurality of first features is fabricated, and wherein each second feature is arranged between a respective pair of neighboring first features at equal distance to each of the respective neighboring first features.

8. The method of claim 1, wherein the feature comprises a trench, a hole, or a line.