Method of fabricating integrated circuit

A method of fabricating an integrated circuit includes the following steps. A first reticle is used to form a first pattern and a first alignment mark and a second reticle is used to form a second pattern and a second alignment mark in a same layer. A third reticle is aligned to the first alignment mark and the second alignment mark, to obtain an overlay correction value; additionally, a third reticle is aligned to the first alignment mark to obtain a first overlay correction value, a third reticle is aligned to the second alignment mark to obtain a second overlay correction value, and a total overlay correction value is obtained by trading off the first overlay correction value and the second overlay correction value. The third reticle is used to form a third pattern by aligning the third reticle with the total overlay correction value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method of fabricating an integrated circuit, and more specifically to a method of fabricating an integrated circuit relating to the alignment of photoresist patterns.

2. Description of the Prior Art

In the fabrication of semiconductor integrated circuits (ICs), semiconductor devices are connected by several metallic interconnecting layers commonly referred to as multi-level interconnects. A damascene process is a convenient and predominant method for forming the multi-level interconnects. The damascene process includes etching a dielectric material layer to form trench and/or via patterns, filling the patterns with conductive materials such as copper, and performing a planarization process. Thus a metal interconnect is obtained.

Photolithography is an essential process in the fabrication of semiconductor ICs. Principally, photolithography forms designed patterns such as implantation patterns or layout patterns on at least a reticle, and then precisely transfers such pattern to a photoresist layer by exposure and development steps. Subsequently, by performing semiconductor processes such as ion implantation, etching processes, or deposition, the complicated and sophisticated IC structure is obtained.

With the miniaturization of semiconductor devices and corresponding progress in fabrication methods, conventional lithography processes have met a bottleneck due to printability and manufacturability. To meet the requirements of device design rules which continue to push the resolution limits of existing processes and tooling, a double patterning technique (DPT) has been developed. This is one of the most promising lithography technologies for 32 nanometer (nm) node and 22 nm node patterning since it can increase the half-pitch resolution by up to 200% using current infrastructures.

SUMMARY OF THE INVENTION

The present invention provides a method of fabricating an integrated circuit, which forms two patterns by a double patterning process and then forms a pattern overlapping the two patterns by aligning a reticle exposing the pattern to both the two patterns, in order to get a compromising correction value.

The present invention provides a method of fabricating an integrated circuit including the following steps. A first reticle is used to forma first pattern and a first alignment mark and a second reticle is used to form a second pattern and a second alignment mark in a same layer. A third reticle is aligned to the first alignment mark and the second alignment mark, to obtain an overlay correction value. The third reticle is used to form a third pattern by aligning the third reticle with the overlay correction value.

The present invention provides a method of fabricating an integrated circuit including the following steps. A first reticle is used to forma first pattern and a first alignment mark and a second reticle is used to form a second pattern and a second alignment mark in a same layer. A third reticle is aligned to the first alignment mark to obtain a first overlay correction value. A third reticle is aligned to the second alignment mark to obtain a second overlay correction value. A total overlay correction value is obtained by trading off the first overlay correction value and the second overlay correction value. The third reticle is used to form a third pattern by aligning the third reticle with the total overlay correction value.

According to the above, the present invention provides a method of fabricating an integrated circuit, which forms a first pattern and a second by double patterning processes, and then aligns a third reticle to a first alignment mark and a second alignment mark for forming a third pattern overlapping both the first pattern and the second pattern, to obtain an overlay correction value. Therefore, the third pattern can be formed by aligning the third reticle with the overlay correction value.

Additionally, a third reticle may be individually aligned to the first alignment mark and the second alignment mark; a first overlay correction value can thereby be obtained by only aligning the third reticle to the first alignment mark and a second overlay correction value can be obtained by only aligning the third reticle to the second overlay correction value. A total overlay correction value can be obtained by trading off the first overlay correction value and the second overlay correction value. The third pattern can be formed by aligning the third reticle with the total overlay correction value.

To sum up, the third pattern can be formed by aligning the third reticle to both the first and the second patterns to get a compromising correction value.

DETAILED DESCRIPTION

FIG. 1schematically depicts a top view of an ideal pattern formed on an integrated circuit according to an embodiment of the present invention. As shown inFIG. 1, a first pattern110and a second pattern210are formed on a substrate10. In this embodiment, the substrate10is a wafer having multilayers formed thereon and the first pattern110and the second pattern210are formed in a same layer15on the substrate10. However, in another embodiment, the first pattern110and the second pattern210may be formed indifferent layers. More precisely, the first pattern110and the second pattern210are interconnect patterns, such that the layer15may be an inter-metal dielectric (IMD) while the first pattern110and the second pattern210are interconnect patterns formed therein. In another embodiment, the first pattern110and the second pattern210may be polysilicon gate patterns or contact patterns, and the layer15is an inter-layer dielectric (ILD), depending upon practical requirements. A third pattern310is formed to overlap the first pattern110as well as the second pattern210. In this embodiment, the third pattern310is a via pattern formed in different layers from the first pattern110and the second pattern210serving as the interconnect patterns, but it is not limited thereto. The first pattern110is parallel to the second pattern210. The first pattern110and the second pattern210are arranged alternately, and a pitch P1between each line of the first pattern110and the second pattern210is the same.

FIG. 1shows an ideal pattern to be formed on an integrated circuit. As the scale of manufacturing processes of the integrated circuit becomes smaller and the wavelength of current exposure machines is limited, patterns such as interconnect patterns on the reticle are too close to each other. This leads to incorrect patterns developed on the wafer due to light interference, such that the integrated circuit fails. In order to solve the problem of incorrectly developed patterns on the wafer due to insufficient gaps between interconnect patterns and via patterns, a double patterning technique is utilized as follows.

A double patterning technique is used, for example, one interconnect pattern having a pitch of about 100 nm is split into two patterns both having a pitch of about 200 nm. The interconnect pattern with a 100 nm pitch can then be formed on an integrated circuit wafer by printing both patterns with the looser pitch into the same layer of photoresist. As shown inFIG. 2, a first feature110′ corresponding to the first pattern110and a second feature210′ corresponding to the first pattern210are respectively formed onto a first reticle110and a second reticle200, so that the first reticle110includes the first feature110′ and a first alignment mark120′ while the second reticle200includes the second feature210′ and a second alignment mark220′.

The first reticle100is used to form the first pattern110and a first alignment mark120in the layer15on the substrate10. This means the first pattern110is transferred from the first feature110′ and the first alignment mark120is transferred from the first alignment mark120′. Then, the second reticle200is used to form the second pattern210and a second alignment mark220in the layer on the substrate10. This means the second pattern210is transferred from the second feature210′ and the second alignment mark220is transferred from the second alignment mark220′. The order of exposing the first reticle100and the second reticle200to the layer15may be reversed.

In this embodiment, the first pattern110is a first interconnect pattern and the second pattern210is a second interconnect pattern, so that positions of interconnects in one single layer15can be defined by the first pattern110and the second pattern210. The methods of forming these interconnects are well known in the art, and are not described herein. In this case, the first pattern110is parallel to the second pattern210. Preferably, the first pattern110and the second pattern210divided by one single pattern in the same layer15are arranged alternately, so that a pitch P2between each line of the first feature110′ or a pitch P3between each line of the second feature210′ can be the same, and also be larger than a minimum pitch between lines of the first feature110′ or lines of the second feature210′, which are not arranged alternately. This means the first feature110′ and the second feature210′ can have looser pitches, but is not limited thereto.

It is emphasized that, as one single pattern is divided into the two patterns of the first pattern110and the second pattern210formed by respectively using the first reticle100and the second reticle200, a shifting S must occur between the first pattern110and the second pattern210. Dashed lines D represent the ideal position of the second pattern210. A pitch P4in a real case ofFIG. 2is different from the pitch P1in the ideal case ofFIG. 1.

A double patterning process is used to enhance feature density by using multiple lithographic processes to form a single layer. Thus, spacing between pattern features in the device can effectively be reduced even though the reticles used in the pattern transfer process may have comparatively larger feature spacing. When dealing with reduced pattern spacing, however, even slight errors in alignment between the pattern steps can affect the arrangement of the first and second patterns with respect to each other. Thus, conventional optical overlay targets and their attending measurement techniques may be insufficient to provide the necessary tolerances for double-patterning processes. As shown inFIG. 3, a third reticle300is used to form a third pattern310overlapping both the first pattern110and the second pattern210by aligning the third reticle300to the first alignment mark120. In this embodiment, the third pattern310is a via pattern while the first pattern110and the second pattern210are both interconnect patterns, and the third pattern may be formed in different layers from the first pattern110and the second pattern210.

The third pattern310corresponding to the first pattern110can overlap the first pattern110accurately due to aligning the third reticle300to the first alignment mark120, but the third pattern310corresponding to the second pattern210cannot overlap the second pattern210accurately because of the shifting S between the first pattern110and the second pattern210. Likewise, if the third pattern310is formed by aligning the third reticle300to the second alignment mark220instead, the third pattern310corresponding to the second pattern210can overlap the second pattern210accurately due to aligning the third reticle300to the second alignment mark220, but the third pattern310corresponding to the first pattern110cannot overlap the first pattern110accurately because of the shifting S between the first pattern110and the second pattern210. The shifting S of the third pattern310overlapping the second pattern210(or the first pattern110) may not be tolerant and achieve processing requirements.

A first preferred method of the present invention is presented as follows. As shown inFIG. 4, a third reticle300is aligned to both the first alignment mark120and the second alignment mark220instead, to obtain an overlay correction value for exposure. In other word, the overlay correction value is obtained by alignment, and for exposure later. The overlay correction value is obtained by treating the first pattern110and the second pattern210as one single pattern. Then, the third reticle300is used to form a third pattern310by a lithography apparatus through aligning the third reticle300with the overlay correction value. Since the overlay correction value is obtained by aligning the third reticle300to both the first alignment mark and the second alignment mark, the third pattern310can overlap both the first pattern110and the second pattern210in a compromising way. The shifting S of the third pattern310overlapping the second pattern210shown inFIG. 3can be shared by the shifting S1of the third pattern310overlapping the first pattern110and the shifting S2of the third pattern310overlapping the second pattern210shown inFIG. 4. In one case, the shifting S equals the sum of the shifting S1and the shifting S2, so that the shifting S1and the shifting S2can respectively fall into the tolerance and achieve processing requirements. The method of the present invention is not an in-line inspection, but an alignment method for exposure. After the exposure, an inspection is operated to verify the accuracy, thus the value may being corrected and then feed backed to the system.

A second preferred method of the present invention is also presented. In this embodiment, the third reticle300is aligned to the first alignment mark120and the second alignment mark220individually to obtain overlay correction values, respectively, instead of being aligned to both the first alignment mark120and the second alignment mark220by treating the first pattern110and the second pattern as one single pattern in order to obtain only one overlay correction value. In other words, the third reticle300is aligned to the first alignment mark120to obtain a first overlay correction value; and the third reticle300is aligned to the second alignment mark220to obtain a second overlay correction value. The first pattern110and the second pattern210are treated as different patterns to get their overlay correction values individually. In this case, the method of the present invention is not an in-line inspection, but an alignment method for exposure. After the exposure, an inspection is operated to verify the accuracy, thus the value may being corrected and then feed backed to the system.

A total overlay correction value is obtained by trading off the first overlay correction value and the second overlay correction value, wherein the total overlay correction value may be obtained via a computer system calculation. More precisely, the total overlay correction value may be an average value of the first overlay correction value and the second overlay correction value, or may be a weighting average value of the first overlay correction value and the second overlay correction value, but is not limited thereto. When the total overlay correction value is a weighting average value of the first overlay correction value and the second overlay correction value, the weighting in the x direction and y direction may be different. As shown inFIG. 4, the weighting in the x direction should be larger than the weighting in the y direction since the tolerance in the x direction is less than the tolerance in the y direction. In one case, the first overlay correction value and the second overlay correction value may be correction values of the first pattern110and the second pattern210in a same direction. In this case, the first overlay correction value and the second overlay correction value may be correction values of the first pattern110and the second pattern210only in the x direction since the tolerance in the y direction is much larger than the tolerance in the x direction; thus, the tolerance in the y direction can be omitted for simplifying processes by only focusing on the tolerance in the x direction.

In another case, the weighting of the first overlay correction value (or the second overlay correction value) is at least over 50% in the x direction and y direction due to the tolerance in the first overlay correction value (or the second overlay correction value) being larger than the tolerance in the second overlay correction value (or the first overlay correction value). In an extreme case, the total overlay correction value may be obtained by excluding one of the first overlay correction value and the second overlay correction value.

To summarize, the present invention provides a method of fabricating an integrated circuit, which forms a first pattern and a second pattern by double patterning processes, thus causing shifting between the first pattern and the second pattern, and then aligns a third reticle to a first alignment mark and a second alignment mark for forming a third pattern which overlaps both the first pattern and the second pattern, to thereby obtain an overlay correction value. The third pattern can be formed by aligning the third reticle with the overlay correction value.

Additionally, a third reticle may be aligned to the first alignment mark and the second alignment mark individually, thereby a first overlay correction value can be obtained by only aligning the third reticle to the first alignment mark and a second overlay correction value can be obtained by only aligning the third reticle to the second overlay correction value. A total overlay correction value can be obtained by trading off the first overlay correction value and the second overlay correction value. The third pattern can be formed by aligning the third reticle with the total overlay correction value. The total overlay correction value may be an average value of the first overlay correction value and the second overlay correction value; and the total overlay correction value may be a weighting average value of the first overlay correction value and the second overlay correction value, but is not limited thereto.

The third pattern can be formed by aligning the third reticle to both the first and the second patterns in many different ways to get a compromising correction value. The third reticle may be aligned to the first and the second patterns by treating the first and the second pattern as one single pattern, or the third reticle may be aligned to the first and the second patterns by treating the first and the second pattern as different patterns.