AIR GAP DIELECTRIC IN SELF-ALIGNED VIA STRUCTURES

Abstract: A high speed interconnect structure and methods for making the structure are provided. The interconnect structure includes a first metallization layer having a plurality of metallization lines (120) and a conductive via metallization layer defined over the first metallization layer. The conductive via metallization layer is configured to define self-aligned conductive vias (140). A non-conformal oxide layer (200) is defined over the first metallization layer and the conductive via metallization layer such that air gaps (202) are positioned between the plurality of metallization lines (120). A cap oxide layer (204) is then defined over the non-conformal oxide (200). In this example, a CMP operation can be performed to expose the top surfaces of the conductive vias before a next metallization layer is defined. It should be noted that air gaps (202) are defined without the problems associated with conductive via misalignment.

Description: AIR GAP DIELECTRIC IN SELF- ALIGNED VIA STRUCTURES bv Inventor Subhas Bothra CROSS REFERENCE TO RELATED APPLICATIONS This application is a 35 U S C § 120 continuation-in-part of pending US patent application seπal no 08/884,795 (Attorney Docket No VLSI 2901) filed June 30. 1997, entitled "PROCESS FOR MAKING SELF-ALIGNED CONDUCTIVE VIA STRUCTURES." and naming Subhas Bothra and Jacob Haskell as inventors The contents of this pending application are incorporated herein by reference for all purposes BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to semiconductor circuits and, more particularly, to a method for making and the resulting structure having high speed interconnect lines that incorporate air-gaps. 2. Description of the Related Art Interconnect structures of integrated circuits (ICs) generally take the form of patterned metallization lines that are used to electπcally interconnect devices and to provide interconnection with external circuitry By way of example, IC devices may include metal oxide semiconductor ("MOS") devices having diffused source and dram regions separated by channel regions, and gates located over the channel regions In practice, an IC chip may include thousands or millions of devices, such as MOS transistors One problem with conventional metal interconnect structures is misalignments introduced in the photolithography process Via holes are typically defined through a dielectπc layer with the purpose of forming an ''electπcal" metal contact between a layer underlying the dielectπc layer and a layer overlying the dielectπc layer. As circuits become increasingly smaller and dense, interconnect structures between successive patterned metal layers have also become ever more dense. Unfortunately, conventional photolithography techniques are also being pushed to their limit, which has had the effect of introducing misalignments between patterned layers. Figure 1A is a cross sectional view of a conventional semiconductor device having a misaligned metal contact 28. The semiconductor device includes a semiconductor substrate 10 having diffusion regions 12 and a polysilicon gate 14 defined between the diffusion regions. A first dielectπc layer 19 is deposited over the semiconductor substrate 10, the diffusion regions 12 and the polysilicon gate 14. Via holes are defined through the first dielectπc layer 19 down to the polysilicon gate 14 and the diffusion region 12 (i.e., source/drain) The via holes are then conductively filled with tungsten or metal to define conductive contacts 16 and 18. In this example, conductive contacts 16 and 18 are somewhat misaligned, but no significant electπcal problem occurred in this case. However, seπous misalignments are shown to have occurred in the patterning of a conductive contact 28, which is defined through a second dielectπc layer 22. As can be appreciated, these type of misalignments are becoming ever more prevalent as device feature sizes continue to shπnk. As illustrated, the misalignment of conductive contact 28, which is used to interconnect a metal- 1 line 24 to a metal-2 line 30. may cause electπcal shorts between adjacently patterned features. By way of example, when interconnect density patterns increase, layout "design rules" that are used by designers to determine the closest possible inter-feature spacings are necessaπly pushed to their limits. That is, although features are designed to be adequately spaced apart to avoid electπcal shorts between features, misalignments (which are unavoidable in dense photolithography patterning) will cause features to be laid out in arrangements that seπously violate minimum inter-feature separations dictated the design rules. It is also known that interconnect speed is dependent on many factors such as metal density, the number of metal levels, mterconnect lengths, interconnect geometry, active device characteπstics, etc. However, for a given interconnect system, the speed is directly determined by the interconnect resistance, the capacitance and the dπve current. From the mateπal aspect, the dominant factor is the permittivity of the dielectπc (or insulating mateπal) mateπal used in the interconnect system The dielectπc mateπal surrounds the interconnect lines and contπbutes to the parasitic capacitance of the mterconnect. This parasitic capacitance is directly proportional to the dielectπc constant of the insulator As is well known, a reduction in the dielectπc constant results in increased interconnect speed and also lowers the power dissipated in the interconnects (i.e., the different metal layers) This realization has led to substantial activity in the field of low dielectπc constant mateπals for applications in integrated circuits The relative dielectπc constant of silicon dioxide (the most commonly employed insulator in integrated circuits) is about 4.0 All of the mateπals currently being researched for applications as low dielectπc constant mateπals have relative dielectπc constants in the range of 2.0 to 4.0. The mateπal with the lowest dielectπc constant, however, is air, with a relative dielectπc constant of 1. Thus the use of air as the dielectπc would provide the most benefit. This, of course, has been widely recognized in the industry. Recently, the use of air-gaps between metal lines has been proposed as a possible solution. See for example an article entitled "USE OF AIR GAP STRUCTURES TO LOWER INTRALEVEL CAPACITANCE" by J.G Fleming, et al., DUMIC Conference 222D/97/0139 (1997), which defines conventional uses of air-gaps to lower the dielectπc constant This article is incorporated herein by reference. Although the implementation of air-gaps can help in reducing capacitance, the fabπcation of conventional air-gaps is not practical for several reasons. One such reason is that the size and location of the formed air-gaps depend on the spacing between adjacent metal interconnect lines When the spacings grow to a particular width, the air-gaps extend upward (i.e , are formed at a higher level) above the level of the metal lines. Duπng subsequent CMP processing the air-gaps can open up trapping residues and or forming stπngers at subsequent via metal deposition, which can result in yield reductions. Figure IB illustrates a problem that may occur when air-gaps are intentionally fabπcated between metal lines and misalignments in the conductive vias occur. For instance, a substrate 50 is shown having metal lines 54 and 56. A dielectπc layer 52 is then deposited over the metal lines 54 and 56 such that an air-gap 62 is formed. In this example, the air-gap 62 is shown to have moved above the metal lines 54 and 56, however, the level of the dielectπc layer 52 is still thick enough that the air-gap 62 is not exposed due to a chemical mechanical polishing (CMP) operation that is used to planaπze the top of dielectnc layer 52. Because misalignments in conductive vias 58 and 60 is common, when the via holes are formed through the dielectπc layer 52, a path to the air-gap 62 is defined As shown in a top view of Figure IC. the misalignment of the via holes used to form the conductive vias 58 and 60 can be at different location along the metal lines 54 and 56. It should be noted that when the via holes are defined and the path to the air-gap 62 is made, process gases and other chemicals can get trapped within the air-gap 62. Still further, when a tungsten deposition is performed to fill the via holes, the tungsten deposition, which is a chemical vapor deposition (CVD) operation, can cause tungsten to line the inner walls 64 of the air-gap 62. When this happens, a conductive link can be formed through the tungsten covered air-gap 64 and the conductive vias 58 and 60 may inadvertently be electπcally connected (i.e., causing an electπcal short). If this occurs, the entire fabπcated circuit can fail to operation for its intended purpose, which will therefore cause a significant drop in yield. Accordingly, in view of the foregoing, there is a need for a method for making high speed interconnect structures that incorporate air-gaps, however, without having the problems associated with conductive via misalignment. SUMMARY OF THE INVENTION Broadly speaking, the present invention fills these needs by providing a method of making high performance interconnect structures having air-gaps. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are descπbed below. In one embodiment, an interconnect structure is disclosed. The interconnect structure includes a first metallization layer havmg a plurality of metallization hnes and a conductive via metallization layer defined over the first metallization layer. The conductive via metallization layer is configured to define self-aligned conductive vias A non-conformal oxide layer is defined over the first metallization layer and the conductive via metallization layer such that air gaps are positioned between the plurality of metallization hnes. A cap oxide layer is defined over the non-conformal oxide In this embodiment, a CMP operation can be performed to expose the top surfaces of the conductive vias before a next metallization layer is defined. It should be noted that air gaps are defined without the problems associated with conductive via misalignment. In another embodiment, a method of making an interconnect structure is disclosed. The method includes providing a substrate and forming a plurality of metallization lines on a first level. Self-aligned vias are then formed over the plurality of metallization lines. A conformal oxide layer is then deposited over the plurality of metalhzation lines and the self-aligned vias, such that air-gaps are formed at least between some of the plurality of metallization lines. The air-gaps therefore provide for higher speeds and performance for the mterconnect structure. In this preferred embodiment, the method also includes depositing a cap oxide layer over the conformal oxide layer to fill high aspect ratio regions without forming voids and then performing a CMP operation down to the conductive vias. In yet another embodiment, an interconnect structure of a semiconductor chip is disclosed The interconnect structure includes (a) a metallization layer havmg a plurality of metallization lines defined over an under-layer, (b) a conductive via metallization layer defined over the first metallization layer, such that the conductive via metallization layer defines self-aligned conductive vias; (c) a non-conformal oxide layer defined over the first metallization layer, and the conductive via metallization layer defines air gaps that are positioned between at least some of the plurality of metallization lines; and (d) an HDP oxide layer defined over the non-conformal oxide. The HDP oxide layer is configured to fill topographical vaπations between the conductive via metallization layer before a CMP operation is performed Other aspects and advantages of the invention will become apparent from the following detailed descπption, taken in conjunction with the accompanying drawings, illustrating by way of example the pπnciples of the invention BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be readily understood by the following detailed descπption m conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements Figure 1A is a cross sectional view of a conventional semiconductor device having a misaligned metal contact Figure IB illustrates a case in which misalignments can cause openings m air-gaps formed between metallization lines Figure IC is a top view of Figure IB, in which the conductive via formation caused the deposition of tungsten within the air-gap and resulted in an electπcal short Figure 2 is a cross sectional view of a semiconductor substrate having a number of active devices and fabπcated layers in accordance with one embodiment of the present invention Figure 3 shows the cross sectional view of Figure 2 after an etch stop layer is deposited over a top barπer layer in accordance with one embodiment of the present invention Figure 4 shows the cross sectional view of Figure 3 after a conductive via metallization layer and an anti-reflective layer have been successively deposited over the etch stop layer in accordance with one embodiment of the present invention Figure 5A shows the cross sectional view of Figure 4 after a hard mask layer and photoresist layer have been successively deposited over the anti-reflective layer m accordance with one embodiment of the present invention. Figure 5B is a three dimensional view of the top most layers deposited over the first dielectπc layer in accordance with one embodiment of the present invention. Figure 5C shows the resulting structure after etching operations are performed in Figure 5B in accordance with one embodiment of the present invention Figure 5D illustrates another etching operation used to remove a portion of the etch stop layer in accordance with one embodiment of the present invention. Figure 5E shows a via photoresist mask pattern formed over the remaining hard mask layer and another etching operation in accordance with one embodiment of the present invention. Figures 5F through 51 are top views illustrating other representative mterconnect patterns that may be defined throughout a surface of a semiconductor device and associated via photoresist mask patterns in accordance with one embodiment of the present invention. Figure 5J illustrates the remaining hard mask pattern used to define the location of the conductive via structures in accordance with one embodiment of the present invention. Figure 5K illustrates the resulting interconnect line and aligned conductive via structure formed over the interconnect line in accordance with one embodiment of the present invention. Figures 6A-6C illustrate a method for making air-gaps between metallization layers and self-aligned vias Figures 7A-7C illustrate an alternative method for depositing oxides layers to form air-gaps between metallization lines and self-aligned vias. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An invention for a method of making high speed interconnect structures is disclosed. In the following descπption, numerous specific details are set forth in order to provide a thorough understanding of the present invention It will be understood, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details In other instances, well known process operations have not been descπbed in detail in order not to unnecessaπly obscure the present invention In the following discussion will first include reference to Figures 2-5K, which define methods for making self-aligned via structures Figures 6A-7C will then focus on the fabπcation of air-gaps between metallization lines that implement the self-aligned via structures. Figure 2 is a cross sectional view of a semiconductor substrate 100 having a number of active devices and fabπcated layers m accordance with one embodiment of the present invention. As shown, the semiconductor substrate 100 has diffusion regions 112 formed into the semiconductor substrate 100 and associated polysilicon gates 114. Also shown is a field oxide 113 typically implemented to separate adjacent active devices in a semiconductor design A first dielectπc layer 119 is deposited over portions of the semiconductor substrate 100, diffusion regions 112, polysilicon gates 114, and field oxide 113 Generally, first dielectπc layer 119 may be any commonly used dielectπc, such as a deposited silicon dioxide (SiO ) layer that is subsequently planaπzed to provide a substantially even top surface for subsequently deposited layers By way of example, the first dielectπc layer 119 may be planaπzed using a chemical mechanical polishing (CMP) technique, or any other suitable technique suitable to provide a substantially planer top surface Once planaπzed. a bottom barπer layer 120c is deposited over the first dielectπc layer 119 to a preferred thickness of between about 100 angstroms and about 800 angstroms. More preferably, the bottom barπer layer 120c is deposited to a thickness of between about 150 angstroms and 500 angstroms, and most preferably to a thickness of about 200 angstroms. In this embodiment, the bottom barπer layer 120c is a titanium nitride (TiN) layer evenly deposited over the top surface of the first dielectπc layer 119. Of course, other suitable barrier layers may be used as well, such as titanium (Ti), or a titanium/titanium nitπde (Ti/TiN) combination. Once the bottom barπer layer 120c has been deposited, an interconnect metallization layer 120b, which is preferably an aluminum/copper (Al/Cu) mixture containing about 99.5% aluminum and about 0.5% copper is deposited over the bottom barπer layer 120c. The interconnect metallization layer 120b is preferably deposited to a thickness of between about 3,000 angstroms and about 10.000 angstroms, and more preferably between about 4,000 angstroms and 7,000 angstroms, and most preferably about 5,000 angstroms. Next, a top barπer layer 120a, which is preferably titanium nitπde (TiN) having a thickness of between about 100 angstroms and 800 angstroms, and more preferably between about 150 angstroms and 600 angstroms, and more preferably about 300 angstroms is applied over the interconnect metallization layer 120b. The top barrier layer 120a may also be a combination of titanium and titanium nitride (Ti/TiN). Further, the top barrier layer 120a is a good anti-reflective layer (ARC) material that assists in improving photolithography patterning precision. As will be described below, layers 120a, 120b, and 120c will be subsequently patterned to form a first level of metallization interconnect lines, that may be used to interconnect devices formed in semiconductor substrate 100. Accordingly, conductive vias down to the polysilicon gates 114 and diffusion regions 112 are not shown for ease of descπption. Figure 3 shows the cross sectional view of Figure 2 after an etch stop layer 130 is deposited over the top barner layer 120a in accordance with one embodiment of the present invention. Etch stop layer 130 is preferably a titanium tungsten (TiW) layer having a thickness of between about 200 angstroms and 1,000 angstroms, and more preferably between about 300 angstroms and about 800 angstroms, and most preferably about 600 angstroms. In another embodiment, the etch stop layer 130 may also be a tungsten (W) layer or a tungsten suicide (WSi,) layer suitable for stopping a C10BCL etch chemistry, which will be descπbed m greater detail below with reference to Figure 5B and table A Figure 4 shows the cross sectional view of Figure 3 after a conductive via metallization layer 140b and a top barπer layer 140a have been successively deposited over the etch stop layer 130 Preferably, conductive via metallization layer 140b is an aluminum/copper (Al/Cu) mixture similar to that of mterconnect metallization layer 120b descπbed above Preferably, conductive via metallization layer 140b is deposited to a thickness of between about 3,000 angstroms and about 10,000 angstroms, and more preferably between about 4,000 angstroms and 7,000 angstroms, and most preferably about 5,000 angstroms Once conductive via metallization layer 140b has been deposited to an appropπate thickness, the top barπer layer 140a, being a titanium nitπde (TiN) layer is deposited to a thickness of between about 100 angstroms and about 800 angstroms, and most preferably between about 150 angstroms and about 600 angstroms, and most preferably about 300 angstroms In this embodiment, top barπer layer 140a is similar to that of top barπer layer 120a, which may also be a combination of titanium and titanium nitπde (Ti/TiN) As mentioned above, the top barπer layer 140a is a good anti-reflective layer (ARC) mateπal that assists in improving photolithography patterning operations As will be shown below, conductive via metallization layer 140b and top barπer layer 140a will be subsequently patterned to define self-aligning conductive vias which are preferably used to electπcally interconnect to the patterned interconnect lines formed from the first metallization layers 120a, 120b, and 120c Figure 5A shows the cross sectional view of Figure 4 after a hard mask layer 150, which is preferably a silicon nitπde (SiN) layer, is deposited over the top barπer layer 140a in accordance with one embodiment of the present invention Preferably, the hard mask is deposited to a thickness of between about 500 angstroms and about 2,000 angstroms, and more preferably between about 700 angstroms and about 1,500 angstroms, and most preferably about 1,000 angstroms In one embodiment, hard mask layer 150 will be subsequently used for patterning the resulting conductive vias formed from patterning conductive via metallization layer 140b and top barπer layer 140a as shown in Figure 5J below Other suitable mateπals for hard mask layer 150 may be a silicon dioxide (SιO0 layer or a silicon oxy nitπde (SiON) layer deposited to about the same thickness as the silicon nitπde (SiN) layer After the hard mask layer 150 has been deposited, a photoresist layer 160 is spin coated over the top surface of hard mask layer 150 In one embodiment, the photoresist layer 160 is applied to a thickness of between about 3,000 angstroms and about 15,000 angstroms, and more preferably between about 4,000 angstroms and about 9,000 angstroms, and most preferably about 5,000 angstroms In general, the photoresist thickness is selected such that some photoresist remains over the hard mask 150 as shown in Figure 5C Figure 5B is a three dimensional view of the top most layers deposited over the first dielectπc layer 119 in accordance with one embodiment of the present invention For ease of understanding, only the top most layers will be shown in Figures 5B through 5K to illustrate the advantageous self-aligning features of conductive vias formed over a lower metallization line. At this point, photoresist layer 160 has been patterned using conventional photolithography techniques to define an outline of the desired metallization interconnect line feature geometπes patterned from layers 120a, 120b, and 120c (e g , as shown in Figure 5K below) Once photoresist layer 160 is patterned as shown, the semiconductor wafer is subjected to two etching operations (Etch-1) The first etching operation takes advantage of an O0CHF chemistry (descπbed in table C below), which is well suited for etching through exposed regions of hard mask 150 layer Once the hard mask layer 150 etch is complete, a second CL/BCL etch chemistry (descπbed in table A below) is used to etch through the top barπer layer 140a and conductive via metallization layer 140b However, as mentioned above, etch stop laver 130 is preferably well suited to stop the etching chemicals from removing any more mateπal once the conductive via metallization layer 140b is removed Figure 5C shows the resulting structure after the etching operations of Etch-1 are performed in Figure 5B in accordance with one embodiment of the present invention. This perspective therefore illustrates that the conductive via metallization layer 140b and top barπer layer 140a are completely removed in those regions where the patterned photoresist layer 160 was not protecting the underlying surface After the Etch-1 process, a photoresist layer 160' will remain having a thickness of between about 1,000 angstroms and about 2,500 angstroms, and most preferably about 2,000 angstroms. Most importantly, the etch chemistnes used to etch through hard mask layer 150, top barπer layer 140a and conductive via metallization layer 140b do not substantially penetrate etch stop layer 130 because the second Cl/BCL, etch chemistry does not etch titanium tungsten (TiW), tungsten (W), or tungsten si cide (WSi,) well. Figure 5D illustrates another etching (Etch-2) operation used to remove the etch stop layer 130 in accordance with one embodiment of the present invention. Preferably, a BC /SF 6 chemistry descπbed in table B below is used to remove etch stop layer 130. Once Etch-2 removes the etch stop layer 130 over regions not protected by the patterned photoresist 160' and hard mask 150, the top barπer layer 120a will be exposed. Duπng Etch-2, most of the patterned photoresist 160' will be substantially removed, but the underlying hard mask 150 will also assist in protecting the top barπer layer 140a and the conductive via metallization layer 140b. However, to ensure that no photoresist 160' remains, a conventional resist stπpping operation is performed before proceeding to the next operation. Figure 5E shows a photoresist mask pattern 152 formed over hard mask layer 150 and another etching operation (Etch-3) in accordance with one embodiment of the present invention Photoresist mask pattern 152 is preferably patterned over a portion of hard mask 150 to protect selected regions of hard mask 150 from the Etch-3 operation, which is used to define the location of self-aligned conductive vias. Specifically, the resulting conductive vias (i.e , formed form conductive via metallization layer 140b and top barπer layer 140a) will he under the photoresist mask pattern 152 As shown, the photoresist mask expeπenced a slight misalignment (i.e., shift to the πght). These misalignments are common, and are becoming ever more severe with the need to pattern increasingly smaller features withm very tight tolerances. As such, a part of the photoresist mask 152 will be applied over parts of top barπer layer 120a and the side wall of conductive via metallization layer 140b and top barπer layer 140a Therefore, part of the hard mask 150 on the left side will be unprotected, thereby causing the formation of thinner conductive via structure as illustrated in Figure 6A below Once patterned with the photoresist, the Etch-3 is preferably used to remove regions of hard mask 150 that are un-covered with the photoresist mask pattern 152 As such, Etch-3 implements the aforementioned OJCHF chemistry descπbed in table C below. Figure 5F is a top view illustrating other representative patterns (i.e., interconnect lines) that may be defined throughout a surface of a semiconductor device In this example, a region 180 illustrates the exemplary photoresist pattern 152 defined over hard mask layer 150, and a portion of top barπer layer 120a. Also shown are other regions where conductive vias will ultimately reside under the photoresist mask patterns 152'. Because the resulting via structures of the present invention are self-aligned, and will not be defined outside of the contours (i.e., outline) of the underlying hard mask layer 150 (i.e., as shown in Figure 5K), the leakage currents and short circuit problems of the pπor art will no longer be present. Figure 5G is the top view of Figure 5F showing a photoresist pattern 152' defined next to the photoresist pattern 152 on an adjacent interconnect line As shown in Figure 6B below, even when adjacent conductive vias are designed m close proximity to each other, and the photoresist patterns nearly meet, the resulting conductive vias 140 will still be perfectly aligned with the underlying interconnect lines 120 In another embodiment, to avoid producing thinner vias caused by misalignments, the designer may simply implement a re-sizing of the reticle patterns used to define photoresist mask patterns 152 and 152' As shown in Figure 5H, a resize (Rs) is implemented to increase the size of the reticle mask used to pattern the photoresist layer, and to define a photoresist mask 152 and 152' that has a larger shape In this manner, the resulting photoresist mask pattern 152 shown in Figure 5E may completely cover the top surface of hard mask layer 150, where the resulting conductive via will reside after and Etch-4 is performed in Figure 5J below Figure 51 is the top view of Figure 5G after a re-sizmg is performed to increase the size of the photoresist patterns 152 and 152' However, because there are two adjacently positioned photoresist patterns 152 and 152' on adjacent interconnect lines, the photoresist mateπal will tend to merge In pπor art designs, when the via masks merged due to misalignments, the conductive vias would necessaπly be formed as one large conductive via that would produce an erroneous electπcal interconnection (i.e , the two adjacent interconnect lines would be accidentally shorted together) It is therefore important to realize that even if the photoresist patterns 152 and 152' merge as shown in Figure 51, the resulting vias will still be spaced apart and perfectly aligned as shown in Figure 6D below In Figure 5J, once the photoresist mateπal is stπpped off, a hard mask pattern 150' will remain over top barπer layer 140a, thereby defining a region underlying the hard mask pattern 150', where a resulting conductive via 140 will reside as shown in Figure 5K. Accordingly, duπng the Etch-4 operation, all regions not covered by hard mask pattern 150' and etch stop layer 130 will be removed, thereby defining a conductive interconnect line 120 and a conductive via 140 (with a remaining hard mask 150") That is, Etch-4 is preferably a C10BC1 chemistry (descπbed in table A below) that is well suited to etch through conductive via metallization layer 140b and top barπer layer 140a down to the etch stop layer 130, and through top barπer layer 120a, interconnect metallization layer 120b, and bottom barπer layer 120c down to the fist dielectπc layer 119 As a result, Figure 5K shows a resulting conductive interconnect line 120 having an overlying conductive via 140 that is perfectly self- aligned with the underlying conductive interconnect line 120 It should be appreciated that no via overlapping is expeπenced past the edge of conductive interconnect line 120 as in pπor art Figures 1A-1C Figure 6A illustrates a cross-sectional view of an interconnect line 120 on a first metallization level having self-aligned conductive vias 140, in accordance with one embodiment of the present invention. In this embodiment, in order to form conductive lines 120 having air gaps between adjacent metallization lines, a non- conformal oxide 200 is deposited over the interconnect lines 120 and the conductive vias 140 As shown, the non-conformal oxide 200 will form an air gap 202 between adjacent metallization interconnect lines 120 The air gaps 202 will therefore enable the performance of the mterconnect lines to increase to higher speeds due to the reduced intra-feature capacitance. In this embodiment, the non-conformal oxide 200 is preferably a plasma-enhanced chemical vapor deposited (PECVD) oxide which will non-conformally deposit over both the interconnect line 120 and the conductive vias 140 Alternatively, the non-conformal oxide 200 can also be deposited using a high density plasma (HDP) deposition operation that operates in a chamber without the application of a bias power In either case, the non-conformal oxide 200 should be configured to leave air gaps 202 between adjacent interconnect lines 120. In this preferred embodiment, the separation between interconnect lines 120 is preferably between about 2,000 A and about 8,000 A, and most preferably about 4,000 A. Of course, the separation really depends on the particular IC design and the micron technology being implemented. It should be noted that as the separation between the interconnect lines 120 grows, the harder it will be to create the air gaps 202 between the interconnect lines 120. In this preferred embodiment, the non- conformal oxide 200 is preferably deposited to a thickness that is between a range of 1.000 A and about 5,000 A, and most preferably about 2,500 A. Figure 6B illustrates the structure of Figure 6A after an HDP deposition operation is performed in accordance with one embodiment of the present invention. The HDP deposition is configured to deposit an oxide 204 over the non-conformal oxide 200 As is well known, the HDP deposition will be configured to fill high aspect ratio regions without the formation of voids Thus, the oxide 204 should be configured to be deposited to a level that is higher than the topmost portion of the conductive vias 140 Once the oxide 204 has been deposited, the structure can be processed through a chemical mechanical polishing (CMP) operation to planaπze the top surface of the deposited oxide layers. Preferably, the CMP operation will be configured to remove the topmost portion of the oxide layer 204 and the non-conformal oxide 200 from over the conductive vias 140. It is also preferred that duπng the CMP operation, the hard mask 150" be removed to expose the metallization of the conductive vias 140 as illustrated in Figure 6C Once the CMP operation has been performed, a metallization layer 206 can be deposited over the entire surface and then followed by a patterning operation The patterning operation will be configured to define metallization features 206a and 206b, each in conductive contact with the conductive vias 140. In a most preferred embodiment, the conductive metallization lines 206a and 206b will also be a sandwich of metallization mateπal as discussed with reference to interconnect lines 120. As a result of implementing the self-aligned conductive vias of the present embodiment, it is also possible to integrate air gaps 202 between the mterconnect lines 120 without the worry of having misalignments m the conductive vias may infπnge upon the air gaps 202. That is, because there will be no misalignment between the interconnect lines 120 and the conductive vias 140, the air gaps 202 will not be exposed to misaligned via holes that may introduce gasses, processing chemicals, and the like, into the air gaps 202. Additionally, the problem of having the air gaps deposited with tungsten duπng the tungsten deposition operations will also be eliminated, thus avoiding the πsk of shorts along the interconnect lines 120. Figure 7A illustrates another embodiment of the present invention in which air gaps 202 are used along with self-aligned via structures. In this embodiment, after the non-conformal oxide 200 is deposited to form the air gaps 202. a hydrogen silsesquioxane (HSQ) layer is spm-coated over the non-conformal oxide 200. Thus HSQ layer 205 is essentially a spin-on-glass (SOG) mateπal which is designed to fill in higher aspect regions throughout the structure being spm-coated (or even out surfaces having large topographical vaπations). In this example, the HSQ layer 205 has filled in the region between the conductive vias 140 Once the HSQ layer is spin-coated, the method will proceed as shown in Figure 7B to an HDP deposition. The HDP deposition will therefore deposit an oxide 204 over the HSQ layer 205 as well as the non-conformal oxide 200. Now that the HDP oxide 204 has been deposited, a CMP operation is used to planaπze the top surface of the deposited oxides as shown in Figure 7C As mentioned above, the CMP operation is preferably configured to remove the oxide down to the topmost metallization portion of the conductive vias 104 Accordingly, the hard mask 150" is removed such that a good conductive contact can be made to a subsequently deposited and patterned metallization lines 206a and 206b Tables A through C below are provided to illustrate the exemplary parameters used in performing the vaπous plasma chamber etching operations descπbed as Etch- 1, Etch-2, Etch-3, and Etch-4 Although any type of plasma etcher may be used, prefeπed etchers may be obtained from Lam Research Corporation of Fremont, California In a specific example, a LAM Research 9600 SE may be used to perform the etching operations of Table A and Table B In a like manner, a LAM Research 4520XL may be used to perform the etching operations of Table C. Further, although the following parameters are associated with an exemplary "6 inch wafer," the parameters may be modified for application to substrates of varying sizes and shapes, such as those employed in the manufacture of semiconductor devices. Further yet, it should be understood that the advantageous self-aligning conductive vias descπbed herein may be fabπcated in 0.35, 0.25, 0.18, 0.15 and smaller micron technology processes. Although the foregoing invention has been descπbed in some detail for purposes of claπty of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restπctive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims. What is claimed is:

Claims: 1. An interconnect structure, compπs g: a first metallization layer having a plurality of metallization lines; a conductive via metallization layer defined over the first metallization layer, the conductive via metallization layer defining self-aligned conductive vias, a non-conformal oxide layer defined over the first metallization layer and the conductive via metallization layer defining air gaps positioned between the plurality of metallization lines; and a cap oxide layer defined over the non-conformal oxide 2. An interconnect structure as recited in claim 1, wherein the non- conformal oxide is one of a PECVD oxide and a non-biased HDP oxide. 3. An interconnect structure as recited in claim 1, further compπsing: an HSQ layer disposed over the non-conformal oxide layer and under the cap metallization layer. 4 An interconnect structure as recited in claim 1, wherein the cap metallization layer is an HDP oxide. 5 An interconnect structure as recited in claim 1, wherein a separation between the plurality of metallization lines vanes between about 2,000 angstroms and about 8.000 angstroms 6. An interconnect structure as recited in claim 1, wherein the non- conformal oxide layer has a thickness that is between about 1 ,000 angstroms and about 5,000 angstroms. 7. An interconnect structure as recited in claim 1, wherein the first metallization layer is defined at any level of an interconnect structure and the conductive via metallization layer is defined over the first metallization layer 8. A method of making an interconnect structure, compπsmg. providing a substrate; forming a plurality of metallization hnes on a first level, forming self-aligned vias over the plurality of metallization lines; and depositing a conformal oxide layer over the plurality of metallization lines and the self-aligned vias, such that air-gaps are formed at least between some of the plurality of metallization lines. 9. A method of making an interconnect structure as recited in claim 8, further compπsmg: depositing a cap oxide layer over the conformal oxide layer to fill high aspect ratio regions without forming voids. 10 A method of making an interconnect structure as recited in claim 9, wherein the cap oxide layer is deposited using an HDP oxide deposition technique. 11 A method of making an interconnect structure as recited in claim 9. further compπsing chemical mechanically polishing the cap oxide layer and the non-conformal oxide layer to expose the self-aligned vias. 12. A method of making an interconnect structure as recited in claim 11, further comprising: depositing a metallization layer over the polished cap oxide layer, the non- conformal oxide layer, and the exposed self-aligned vias; patterning the metallization layer to define metallization lines, at least one being in electπcal contact with the exposed self-aligned vias. 13. An interconnect structure of a semiconductor chip, compπsing: a metallization layer havmg a plurality of metallization lines defined over an under-layer; a conductive via metallization layer defined over the first metallization layer, the conductive via metallization layer defining self-aligned conductive vias; a non-conformal oxide layer defined over the first metallization layer and the conductive via metallization layer defining air gaps positioned between at least some of the plurality of metallization lines; and an HDP oxide layer defined over the non-conformal oxide, the HDP oxide layer being configured to fill topographical vaπations between the conductive via metallization layer. 14. An interconnect structure of a semiconductor chip as recited in claim 13, wherein the non-conformal oxide is one of a PECVD oxide and a non- biased HDP oxide. 15. An mterconnect structure of a semiconductor chip as recited in claim 14, further compπsing: an HSQ layer disposed between the non-conformal oxide layer and the HDP oxide layer. 16. An interconnect structure of a semiconductor chip as recited in claim 13, wherein a separation between the plurality of metallization lines vanes between about 2,000 angstroms and about 8,000 angstroms. 17. An interconnect structure as recited in claim 13, wherein the non- conformal oxide layer has a thickness that is between about 1,000 angstroms and about 5,000 angstroms. 18. An interconnect structure as recited in claim 13, wherein the under- layer is at least a portion of a metallization line, a conductive via, and an insulating layer.

Inventors: BOTHRA SUBHAS, BOTHRA, SUBHAS
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SEMICONDUCTORS INC, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS SEMICONDUCTORS, INC.
Application year: 2000
Main classification: H01L23
IPC codes: H01L21, H01L23