Method of forming double pattern in a structure

A semiconductor structure including a double patterned structure and a method for forming the semiconductor structure are provided. A negative photoresist layer is formed on a positive photoresist layer, which is formed over a substrate. An exposure process is performed to form a first exposure region in the positive photoresist layer and to form a second exposure region in the negative photoresist layer in response to a first and a second intensity thresholds of the exposure energy. A negative-tone development process is performed to remove portions of the negative photoresist layer to form first opening(s). The positive photoresist layer is then etched along the first opening(s) to form second opening(s) therein. A positive-tone development process is performed to remove the first exposure region therefrom to form a double patterned positive photoresist layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese patent application No. CN201210062205.3, filed on Mar. 9, 2012, and entitled “METHOD FOR FORMING SEMICONDUCTOR STRUCTURE”, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to the field of semiconductor manufacturing and, more particularly, to a double patterned structure and a method for forming the double patterned structure.

BACKGROUND OF THE DISCLOSURE

In semiconductor device manufacturing, lithographic and etching processes are repeatedly performed to form patterned structures. For example, a photoresist layer may be firstly formed on a substrate to be processed, then exposure and development processes are performed to form openings in the photoresist layer. The substrate is exposed through the openings. Thereafter, the substrate is etched by using the patterned photoresist layer as a mask to form a desired pattern in the substrate.

In the development process, portions of the photoresist are exposed by light penetrating through a photo mask and the chemical characteristics of the exposed portions of the photoresist layer may be changed. In a case that a positive photoresist layer is used, the exposed portions are altered from insoluble to soluble. In a case that a negative photoresist layer is used, the exposed portions are altered from soluble to insoluble. Therefore, some portions of the photoresist layer are removed in the development process and the pattern on the photo mask is transferred onto the photoresist layer.

In a practical manufacturing process, the smallest distance between two neighboring components of a final device (the distance is named as “pitch”) depends on a resolution ratio of the exposure system. The smaller the ratio is, the smaller the pitch can be. With smaller pitch, semiconductor devices can be better integrated.

Conventional methods for reducing a pitch in a semiconductor device include use of a double patterning technology, which includes litho-etch-litho-etch (LELE) processes and dual-tone development (DDT) processes.

In a LELE process, two lithographic processes and two etching processes must be performed to one substrate to form a pattern thereon. Although the pitch between two neighboring components in the pattern may be obtained smaller, processing complexity is added because two lithographic processes and two etching processes must be performed.

In a DDT process, a photoresist layer is formed on a substrate and then exposed to form a dual pattern. Then, a positive-tone development and a negative-tone development are performed to the photoresist layer having the dual pattern therein. Such process is difficult to control because the positive-tone development and the negative-tone development may affect each other.

Therefore, there is a need to provide a double patterned structure and a simplified method for forming the double patterned structure with easy control of formation.

SUMMARY

According to various embodiments, there is provided a method for forming a semiconductor structure. The semiconductor structure can be formed by forming a positive photoresist layer over a substrate and forming a negative photoresist layer on the positive photoresist layer. An exposure process can be performed to form a first exposure region in the positive photoresist layer and a second exposure region in the negative photoresist layer. A negative-tone development process can be performed to remove portions of the negative photoresist layer outside of the second exposure region to form one or more first openings to expose the positive photoresist layer. The positive photoresist layer can be etched along the one or more first openings to form one or more second openings through both the negative photoresist layer and the positive photoresist layer to expose the substrate. The second exposure region of the negative photoresist layer can be removed and a positive-tone development process can be performed to remove portions of the positive photoresist layer in the first exposure region to form a double patterned positive photoresist layer.

According to various embodiments, there is also provided a semiconductor structure. The semiconductor structure can include a substrate and a double patterned positive photoresist layer disposed over the substrate. The double patterned positive photoresist layer can be formed by forming a positive photoresist layer over a substrate and forming a negative photoresist layer on the positive photoresist layer. An exposure process can be performed to form a first exposure region in the positive photoresist layer and a second exposure region in the negative photoresist layer. A negative-tone development process can be performed to remove portions of the negative photoresist layer outside of the second exposure region to form one or more first openings to expose the positive photoresist layer. The positive photoresist layer can be etched along the one or more first openings to form one or more second openings through both the negative photoresist layer and the positive photoresist layer to expose the substrate. The second exposure region of the negative photoresist layer can be removed and a positive-tone development process can be performed to remove portions of the positive photoresist layer in the first exposure region to form the double patterned positive photoresist layer.

The disclosed method requires one exposure process and one photo mask. Manufacturing cost can be saved. In the one exposure process, a first exposure region and a second exposure region are respectively formed in the positive photoresist layer and the negative photoresist layer. A pattern of the negative photoresist layer is transferred to the positive photoresist layer by an etching process, and a pattern of the positive photoresist layer is formed by removing the first exposure region therefrom in a development process. Therefore, a double patterned structure is formed in the positive photoresist layer. The process is simple with high accuracy. In addition, because development processes are respectively performed to the negative photoresist layer and the positive photoresist layer, there are no interactions between the development processes. Such process is easy to control with good topography for the formed double pattern.

In some embodiments, removing the remaining negative photoresist layer, e.g., by a negative-tone development process or other suitable processes, and etching the positive photoresist layer along the first openings are performed simultaneously. Processing steps and manufacturing costs can further be reduced.

DETAILED DESCRIPTION OF THE DISCLOSURE

Reference will now be made in detail to exemplary embodiments of the disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. For illustration purposes, elements illustrated in the accompanying drawings are not drawn to scale, which are not intended to limit the scope of the present disclosure. In practical operations, each element in the drawings has specific dimensions such as a length, a width, and a depth.

FIGS. 1-7are cross-sectional views of intermediate structures illustrating a current litho-etch-litho-etch (LELE) process for forming a double patterned structure.

Referring toFIG. 1, a substrate100is provided. A target layer109is formed on the substrate100. A first photoresist layer101is formed on the target layer109. A first photo mask20with a nonopaque part21and an opaque part22is provided. Exposure light30penetrates through the nonopaque part21to expose the first photoresist layer101to form a first exposure region102therein.

Referring toFIG. 2, a first photoresist layer101ahaving one or more first openings103is formed, after a first development process is performed to remove the first exposure region102(shown inFIG. 1).

Referring toFIG. 3, the target layer109is etched along the first openings103using the first photoresist layer101aas a mask to form one or more second openings104.

Referring toFIG. 4, the first photoresist layer101a(shown inFIG. 3) is removed. A second photoresist layer105is formed on the target layer109and the substrate100. A second photo mask40with a nonopaque part41and an opaque part42is provided. The exposure light30penetrates through the nonopaque part41to expose the second photoresist layer105to form a second exposure region106therein.

Referring toFIG. 5, a second photoresist layer105ahaving one or more third openings107is formed after a second development process is performed to remove the second exposure region106(shown inFIG. 4).

Referring toFIG. 6, the target layer109is etched along the third openings107using the second photoresist layer105aas a mask to form one or more fourth openings108in the target layer109.

Referring toFIG. 7, the second photoresist layer105a(shown inFIG. 6) is removed. As such, by employing the LELE process, a double patterned layer is obtained by performing two lithographic processes and two etching processes. However, the process is complex and expensive.

A simplified method for forming a double patterned structure is provided. In the method, a substrate is provided and a positive photoresist layer is formed over the substrate. A negative photoresist layer is then formed over the positive photoresist layer. An exposure process is performed to expose the negative photoresist layer and the positive photoresist layer with an exposure energy having a first intensity threshold and a second intensity threshold. The first intensity threshold is higher than the second intensity threshold. A first exposure region is formed in the positive photoresist layer in response to the exposure energy having the first intensity threshold, and a second exposure region is formed in the negative photoresist layer in response to the exposure energy having the second intensity threshold. The second exposure region is wider than the first exposure region. Thereafter, a first development process is performed to remove portions of the negative photoresist layer outside of the second exposure region to form first openings to expose the positive photoresist layer. The positive photoresist layer is etched along the first openings to form second openings to expose the substrate. The remaining negative photoresist layer in the first development process is removed. And then, a second development process is performed to remove portions of the positive photoresist layer in the first region. A double patterned positive photoresist layer is formed.

The disclosed method requires one exposure process and one photo mask, which saves cost in manufacturing. In addition, because development processes are respectively performed to the negative photoresist layer and the positive photoresist layer without affecting one another, the process is easy to control. This is beneficial for obtaining a double patterned structure with good topography.

FIG. 8is a flow chart of an exemplary method for forming a double patterned structure according to various disclosed embodiments. The exemplary method depicted inFIG. 8is illustrated herein in detail with reference to the accompanying drawings, including, e.g.,FIGS. 9-16. Specifically,FIGS. 9-16are cross-sectional views of intermediate structures illustrating a process for forming a double patterned structure according to various disclosed embodiments.

The substrate300may include monocrystalline silicon, monocrystalline germanium, GeSi, SiC, and/or III-V group compounds such as GaAs, InP, or the like. For example, the substrate300may be a silicon-on-insulator (SOI) substrate or a germanium-on-insulator (GOI) substrate. Specifically, semiconductor devices may be formed on the substrate300including, for example, MOS transistors, diodes, capacitances, inductances, and the like.

In Step S202ofFIG. 8and still referring toFIG. 9, a target layer310, an anti-reflection coating (ARC) layer301, a positive photoresist layer302, and a negative photoresist layer303are successively formed on the substrate300as shown inFIG. 9.

The target layer310is formed on a top surface of the substrate300. The target layer310may include an insulating material including, for example, silicon dioxide, silicon nitride, silicon carbide, silicon oxynitride, and/or the like. Alternatively, the target layer310may include a conductive or semi-conductive material including, for example, metal, metal oxide, metal nitride, metal oxynitride, metal silicide, silicon, polysilicon, and/or the like. Of course, the target layer310may include any other suitable materials.

The target layer310may include a single-layer structure or a multi-layer stack structure. The target layer310may include at least one of the conductive material and/or the insulating material.

The ARC layer301is formed on the target layer310by applying a spin-on process or a deposition process. The ARC layer301may have a thickness in a range from about 100 Å to about 1500 Å. The ARC layer301is adapted for eliminating standing wave effect, which may occur in a subsequent exposure process as a result of the optical reflection and optical interference. This allows subsequent-formed photoresist layers to have desired topography, e.g., for sidewalls.

The ARC layer301may be an organic ARC layer or an inorganic ARC layer. The inorganic ARC layer includes materials such as Ti, titanium oxide, titanium nitride, chromium oxide, carbon, amorphous silicon, silicon nitride, silicon nitride oxide, silicon carbon, and/or the like. The organic ARC layer includes photo-absorption materials and/or polymer materials. In some cases, the organic ARC layer may include silicon. In one embodiment, the ARC layer301is a bottom anti-reflection coating (BARC) layer.

The positive photoresist layer302is formed on the ARC layer301and the negative photoresist layer303is formed on the positive photoresist layer302. The negative photoresist layer303has a thickness in a range from about 500 Å to about 3000 Å. The positive photoresist layer302has a thickness in a range from about 500 Å to about 3000 Å.

Each of the negative photoresist layer303and the positive photoresist layer302is formed by, e.g., applying a spin-on process, in a same process or a different processes. Specifically, the spin-on process is performed as follows. The positive photoresist layer302is coated on the ARC layer301in a coating chamber; then, a first post application baking (PAB) process is performed to bake the positive photoresist layer302to remove some solvent thereof; then, the negative photoresist layer303is coated on the positive photoresist layer302; and then, a second PAB process is performed to the negative photoresist layer303to remove some solvent thereof. In each PAB process, the temperature is controlled within a range from about 50° C. to about 200° C. for a processing time within a range from about 20 seconds to about 200 seconds. After each PAB process, the substrate300can be cooled to the room temperature.

In various embodiments, prior to coating the positive photoresist layer302on the ARC layer301, the substrate300and the ARC layer301are dehydrated in order to enhance the adhesion between the ARC layer301and the positive photoresist layer302. This dehydration may be performed by treating the substrate300with hexamethyldisilazane gas in a high temperature environment.

The positive photoresist layer302may include, e.g., a resin, a photo acid generator (PAG), a base quencher, a solvent, an additive, and/or the like. The negative photoresist layer303may include a radiation-induced cross-linking negative resist, a radiation-induced polymerization negative resist, and/or a radiation-induced polarity change negative resist.

In Step S203ofFIG. 8and referring toFIG. 10, an exposure process is performed to expose the negative photoresist layer303and the positive photoresist layer302.

As shown inFIG. 10, a photo mask50is provided, exposure light32generated from an exposure system penetrates through portions of the photo mask50to expose the negative photoresist layer303and the positive photoresist layer302. The exposure light32is configured to have a first intensity threshold E1and a second intensity threshold E2lower than E1. Under the influence of E1, a first exposure region305is formed in the positive photoresist layer302. Under the influence of E2, a second exposure region304is formed in the negative photoresist layer303. The second exposure region304has a width “b” is larger than a width “a” of the first exposure region305. The first exposure region305is under the second exposure region304.

Specifically, the photo mask50has a nonopaque part51and an opaque part52. The exposure light32generated from the exposure system penetrates through the nonopaque part51to expose the positive photoresist layer302and the negative photoresist layer303.

In various embodiments, DUV (i.e., deep ultra violet) light, such as Krf excimer leaser (wave length: 248 nm), Arf excimer leaser (wave length: 193 nm), or the like, can be utilized as the exposure light32. F2leaser (wave length: 157 nm), EUV (i.e., extreme ultra-violet) light (wave length: about 13.5 nm), or ultra violet glow generated from ultra pressure mercury lamps such as g-beam, i-beam, and the like, may also by utilized as the exposure light32.

After the exposure light32penetrates through the nonopaque part51of the photo mask50, the exposure energy in a space between the substrate300and the photo mask50may include a sinusoidal distribution. Within a flat surface parallel to a surface of the substrate300, the closer to a central axis of the nonopaque part51central axis, the higher exposure energy may be as shown inFIG. 10. The exposure energy may reach a maximum value near the central axis of the nonopaque part51. And due to the boundary effect of the opaque part52, the exposure energy may degrade when departing from the central axis the nonopaque part51, and reach a minimum value near a central axis of the opaque part52.

The distribution of the exposure energy after the exposure light32penetrates through the photo mask50can be adjusted by tweaking power of the light source and/or the critical dimensions of the opaque part52and the nonopaque part51.

On the energy distribution curve as shown inFIG. 10, a relatively high value is selected as the first intensity threshold E1, which may range from about 70% to about 90% of a maximum value of the exposure energy; and a relatively low value is selected as the second intensity threshold E2, which may range from about 10% to about 40% of the maximum value of the exposure energy. For example, a ratio of E1to E2ranges from about 5:1 to about 2:1.

The exposure light32penetrates through the nonopaque part51to expose the negative photoresist layer303to form the second exposure region304in the negative photoresist layer303. Chemical reactions may occur in the negative photoresist layer303in response to exposure energy greater than or equal to E2. If the energy is lower than E2, the chemical reactions do not occur. For example, cross-linking reactions may occur in a radiation-induced cross-linking negative resist. Alternatively, polymerization reactions may occur in the radiation-induced polymerization negative resist. Therefore, the second exposure region304, which is intrinsic soluble, are changed to be insoluble. The insoluble second exposure region304cannot be removed by a negative-tone development, while other portions in the negative photoresist layer303, which are not exposed, can be removed by the negative-tone development. The width “b” of the second exposure region304equals to a width “d” of the distribution curve corresponding to the second intensity threshold E2, as shown inFIG. 10.

The exposure light32penetrates through the nonopaque part51to expose the positive photoresist layer302to form the first exposure region305in the positive photoresist layer302. As described above, the positive photoresist layer302includes a resin, a photo acid generator (PAG), a base quencher, a solvent, an additive, and/or the like. For example, the PAG may generate a photo acid when exposed to an exposure energy greater or equal to E1. If the exposure energy is lower than E1, the PAG does not generate photo acid. The generated photo acid reacts with the resin in the positive photoresist layer302, which changes the first exposure region305from an intrinsic insoluble status to a soluble status. Therefore, the first exposure region305can be removed by a positive-tone development. The base quencher in the positive photoresist layer302is adapted for controlling the reaction (e.g., terminating the reaction) between the photo acid and the resin in the positive photoresist layer302. The width “a” of the first exposure region305equals to a width “c” of the distribution curve corresponding to the first intensity threshold E1, as shown inFIG. 10.

In this manner, the chemical reaction in the negative photoresist layer303to form the second exposure region304therein may occur in response to the exposure energy greater than or equal to E2. The photo acid (along with its chemical reaction) in the positive photoresist layer302may be generated in response to the exposure energy greater than or equal to E1. E2is lower than E1. On the distribution curve shown inFIG. 10, the width “d” corresponding to E2is greater than the width “c” corresponding to E1. Therefore, after the exposure, the width “b” of the second exposure region304is greater than the width “a” of the first exposure region305.

For example, the second exposure region304may have the width “b” approximately 1.5 times to 4.5 times (e.g., about 3 times) of the width “a” of the first exposure region305. The widths of the exposure regions can be easily adjusted as desired. For example, when E1and E2are predetermined, the distribution of the exposure energy can be adjusted by adjusting power of the light source and/or the critical dimensions of the opaque part52and the nonopaque part51. The widths on the distribution curve respectively corresponding to E1and E2can be adjusted. Thus, the second exposure region304and the first exposure region305may have desired widths after exposure.

In an exemplary embodiment, the second exposure region304may have the width “b” of about 3 times of the width “a” of the first exposure region305, so that a double patterned positive photoresist layer including components with the same linear widths and pitches may be obtained.

In another exemplary embodiment, the second exposure region304may have the width “b” of less than about 3 times of the width “a” of the first exposure region305, so that the linear widths of the components may be smaller and the pitches may be larger. To the contrary, in another exemplary embodiment, the second exposure region304may have the width “b” of more than 3 times of the width “a” of the first exposure region305, so that the linear widths of the components may be larger and the pitches may be smaller.

After the exposure process, a post exposure baking (PEB) process may be performed to the positive photoresist layer302and the negative photoresist layer303to further control widths of the exposure regions and eliminate the standing wave effect.

In the PEB process, the temperature is controlled within a range from about 50° C. to about 200° C. for a processing time within a range from about 15 seconds to about 200 seconds. After the PEB process, the substrate300can be cooled to the room temperature.

In Step S204ofFIG. 8and referring toFIG. 11, a negative-tone development process is performed to remove a portion of the photo resist material from the negative photoresist layer303(shown inFIG. 10) to form one or more first openings306outside of the second exposure region304. The first openings306expose the positive photoresist layer302.

The negative-tone development process utilizes an organic solution as the developer which is also referred to as organic developer. The second exposure region304is insoluble in the organic developer, while other portions of the negative photoresist layer303are soluble in the organic developer and are removed to form the first openings306.

The organic developer includes one or more solvents selected from: a ketone solvent, such as octanon and the like; an ester solvent, such as butyl acetate, amyl acetate, Ethyl 3-Ethoxypropionate, butyl formate, propyl formate, and the like; an alcohol solvent, such as n-propyl alcohol, isopropyl alcohol, butyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, and the like; and a glycol ether solvent, such as ethylene glycol monomethyl ether, ether solvent, and the like. In an embodiment, the organic developer may further include surfactant.

After the negative-tone development process, the substrate300may be rinsed, e.g., using any suitable organic solutions. After the negative-tone development process, a thermal treatment may be performed to the substrate300to remove remaining water and solution therefrom to further enhance the adhesion between the negative photoresist layer and the underlying layer.

The negative-tone development process may also use aqueous alkali solution as the developer, which is also referred to as aqueous alkali developer. Similarly, the second exposure region304is insoluble in the aqueous alkali developer and the other portions of the negative photoresist layer303are soluble in the aqueous alkali developer and are removed to form the first openings306.

In various embodiment, alkali materials in the aqueous alkali developer may include one or more materials selected from: sodium hydroxide; potassium hydroxide; sodium carbonate; sodium silicate; sodium metasilicate; aqueous ammonia; primary amines such as ethylamine and/or n-propylamine; secondary amines such as diethylamine; tertiary amine such as triethylamine; alcoholamine such as dimethylethano; quaternary ammonium salt such as tetramethylammonium hydroxide (TMAH) and tetraethylammonium hydroxide (TEAH); and/or cyclic amine In one embodiment, the aqueous alkali developer is TMAH.

A pH value of the aqueous alkali developer can be within a range from about 9 to about 15. A time length for the negative-tone development process using the aqueous alkali developer can be within a range from about 10 seconds to about 300 seconds. After the development, the substrate300is rinsed with purified water.

In an exemplary embodiment, the negative photoresist layer303includes a radiation-induced polymerization negative resist or a radiation-induced polarity change negative resist and the negative-tone development process uses an organic developer, accordingly. In another exemplary embodiment, the negative photoresist layer303includes a radiation-induced cross-linking negative resist and the negative-tone development process uses the organic developer or the aqueous alkali developer, accordingly.

It is noted that the negative-tone development process, by either the organic developer or the aqueous alkali developer, does not affect the positive photoresist layer302underlying the negative photoresist layer303.

In Step S205ofFIG. 8and referring toFIGS. 12-13, the positive photoresist layer302is etched using the second exposure region304as a mask to form one or more second openings307. The second openings307are formed through the positive photoresist layer302and expose the ARC layer301. Thereafter, the remaining negative photoresist layer (i.e., the second exposure region304) is removed as shown inFIG. 13.

Etching the positive photoresist layer302to form the second openings307may be performed by, e.g., a reactive ion etching process using oxygen as an etching gas. In an embodiment, the etching gas further includes an inert gas including, such as, for example, He, Ne, N2, Ar, Xe, or a combination thereof.

In an embodiment, removing the remaining negative photoresist layer (i.e., the second exposure region304) and etching the positive photoresist layer302to expose the ARC layer301may be performed simultaneously in a same etching process. Therefore, processing steps and cost are further reduced. In some cases, to ensure that the ARC layer301is exposed through the second openings307, the positive photoresist layer302may be over etched during the etching process. In other exemplary embodiments, the remaining negative photoresist layer may be removed in a separate process from etching the positive photoresist layer302to expose the ARC layer301.

In Step S206ofFIG. 8and referring toFIG. 14, a positive-tone development process is performed to remove the first exposure region305(shown inFIG. 13) to form a double patterned positive photoresist layer302ashown inFIG. 14.

In the positive-tone development process, the first exposure region305is dissolved into the developer while other portions of the positive photoresist layer302are insoluble. Therefore, after the positive-tone development process, the first exposure region305is removed and the double patterned positive photoresist layer302ais formed.

In various embodiments, the positive-tone development process may also use the aqueous alkali developer as used in the negative-tone development process. In one embodiment, the aqueous alkali developer includes TMAH. A pH value of the aqueous alkali developer can be within a range from about 9 to about 15. A time length for the positive-tone development process using the aqueous alkali developer can be within a range from about 10 seconds to about 300 seconds.

After development, the substrate300is rinsed with purified water. Further, a thermal treatment may be performed to the substrate300to remove the remaining water and solution to further enhance adhesion between the positive photoresist layer and underlying layer.

In Step S207ofFIG. 8and referring toFIGS. 15-16, the ARC layer301and the target layer310are etched using the double patterned positive photoresist layer302aas a mask to form a double patterned semiconductor structure having openings308as shown inFIG. 15. Remaining ARC layer301may then be removed to leave a patterned target layer310ahaving a plurality of target layer structures309on the substrate300as shown inFIG. 16. Any suitable etching techniques can be used to etch and remove the ARC layer301and/or the target layer310.

In this manner, the disclosed method uses one exposure process and one photo mask. Manufacturing cost may be saved. In the one exposure process, a first exposure region and a second exposure region are respectively formed in the positive photoresist layer and the negative photoresist layer. A pattern of the negative photoresist layer is transferred to the positive photoresist layer by an etching process, and a pattern of the positive photoresist layer is formed by removing the first exposure region therefrom in a development process. Therefore, a double patterned structure is formed in the positive photoresist layer. The process is simple with high accuracy. In addition, because development processes are respectively performed to the negative photoresist layer and the positive photoresist layer, there are no interactions between the development processes. Such processes are easily controlled with good topography for the formed double patterned structure.

The embodiments disclosed herein are exemplary only. Other applications, advantages, alternations, modifications, or equivalents to the disclosed embodiments are obvious to those skilled in the art and are intended to be included within the scope of the present disclosure.