Improved method of planarization of topologies in integrated circuit structures.

0001This invention relates to integrated circuit struc­tures. More particularly, this invention relates to an improved method for forming highly planarized oxide portions in integrated circuit structures.

0002In the conventional construction of integrated circuit structures, field oxide, for example, is usually grown on and into the surface of the sili­con substrate to provide oxide insulation between adjacent active devices by masking the active de­vice regions of the substrate and then oxidizing the remaining portions of the substrate.

0003In the formation of such oxide regions by oxidation of the silicon substrate, that is, by oxide growth rather than by deposition, the oxide grows down into the substrate as well as extending upwardly from the surface. For example, when growing an oxide layer of about one micron thickness, the oxide growth will extend down into the substrate about half the distance, that is, extend down about 0.5 micron below the original silicon substrate surface and also extend about 0.5 micron above the original silicon substrate surface, due to the fact that a given number of silicon atoms in crystalline silicon occupies less volume than the oxide of the same number of silicon atoms.

0004While this phenomena changes the vertical topology of the integrated circuit structure somewhat, the greater problem is that this expansion of the oxide volume also occurs laterally as well as vertically. Thus, as shown in the prior art structure shown in Figure 1, the field oxide grown in the unmasked regions of the substrate also extends partially into the masked regions of the substrate with both the downwardly and upwardly extent of the oxide tapering off the further the oxide extends lateral­ly, thus forming what is known in the industry as a "bird's beak".

0005This "bird's beak" region then narrows the active region of the substrate in between the field oxide portions in which active devices can be construc­ted, as shown in Figure 1, down to a width x with the width of the mask minus x representing the area of lateral encroachment of the grown oxide. To remedy this, the dimensions of the mask must be altered to accommodate this encroachment, i.e., the openings for the field oxide must be made smaller.

0006This, in turn, becomes a problem as the density of integrated circuit structures increase with VLSI. When the lines and spaces, for example, become less than one micron, problems of lithography occur. Furthermore, there may be yet further encroachment if the field implant, i.e., the doping beneath the field oxide, laterally migrates with the field oxide as it grows, thus reducing the active device region still further.

0007The problems associated with "growing" field oxide. regions in an integrated circuit structure has been recognized and attempts have been made to remedy these problems. For example, Chen et al, in an article entitled "A FULLY RECESSED FIELD ISOLATION TECHNOLOGY USING PHOTO-CVD OXIDE", published in IDEM 82 at pp. 233-236, discuss the use of a photo-­resist layer to etch a groove which is then filled with a photox-CVD oxide (photox) before removing the photoresist mask. Excess "photox" is then removed with the photoresist by liftoff.

0008Shibata et al, in an article entitled "A SIMPLIFIED BOX (BURIED-OXIDE) ISOLATION TECHNOLOGY FOR MEGABIT DYNAMIC MEMORIES", published in IDEM 83 at pp 27-­30, discuss forming isolation oxide by refilling anisotropically etched recesses in silicon sub­strates with deposited oxide. The original BOX process used two steps, a plasma SiO₂ lift-off in the first step and redeposition of CVD SiO₂ fol­lowed by planarization etch-back in the second step. The authors noted that this procedure works satisfactorily for recesses narrow in width, but fails to leave field oxide in wide open areas. The authors suggest using two resist layers with the first resist providing a mask over the oxide in the wide open areas and the second resist layer appa­rently acting as a planarizing layer.

0009We have found a more satisfactory way to form highly planarized field oxide regions between ac­tive regions in the substrate while eliminating the formation of the "bird's beak" encroachment exper­ienced with prior art field oxide growth. This method permits us to form highly planarized field oxide type separation between active regions, such as, for example, either active devices formed in the substrate or between stepped regions in an integrated circuit structure such as those which occur when conductive lines are formed over the substrate, whereby the topology of the resulting structure will minimize formations of such steps or other nonplanar structures, i.e., will result in a highly planarized integrated circuit structure.

0010We will describe a process for producing highly planarized oxide portions in an integrated circuit structure.

0011We will describe a process for producing highly planarized oxide portions in an integrated circuit structure using deposited oxide.

0012We will describe a process for producing highly planarized oxide por­tions in an integrated circuit structure using deposited oxide which is planarized to the level of adjacent portions of the integrated circuit struc­ture by applying a further layer of planarizing material over the structure.

0013We will describe a process for producing highly planarized oxide portions in an integrated circuit structure using deposited oxide which is planarized to the level of adjacent portions of the integrated cir­cuit structure by applying a further layer of planarizing material over the structure and then subjecting the structure to polishing and etching steps, respectively, to form a substantially flat surface and remove the deposited oxide and and any remaining planarizing material down to the level of the underlying structure.

0014We will describe a highly planarized field oxide for an integrated circuit structure which is deposited in shallow openings provided in the underlying silicon substrate between active regions in said substrate by first forming such shallow openings in the sub­strate; depositing a layer of oxide which is thick­er than the depth of the shallow openings to form a conformal layer of oxide over the structure; form­ing a planarizing layer over the deposited oxide layer; mechanically polishing the structure to remove the planarizing layer over the highest reg­ions at least down to the highest level of the underlying deposited oxide; etching the exposed oxide down to a level approximately equal to the original height of the lowest portion of the unex­posed area of the oxide layer; mechanically polish­ing the structure further to remove the remaining portions of the planarizing layer; and then etching the remaining structure down to the level of the top surface of the active regions of the substrate to thereby form a highly planarized structure com­prising oxide portions in the substrate level with the substrate level in the active region of the substrate.

0015a highly planarized integrated circuit structure comprising a raised or stepped pattern interleaved with oxide portions formed by deposit­ing an oxide layer over an integrated circuit structure containing such a raised pattern, the oxide layer having a thickness greater than the thickness of the raised pattern, to form a confor­mal layer of oxide over the structure; forming a planarizing layer over the deposited oxide layer; mechanically polishing the structure to remove the planarizing layer over the highest regions at least down to the highest level of the underlying depos­ited oxide; etching the exposed oxide down to a level approximately equal to the original height of the lowest portion of the unexposed area of the oxide layer; and then mechanically polishing the structure further to remove the remaining portions of the planarizing layer to result in a highly planarized top surface. Optionally the remaining structure may be etched down to the level of the top surface of the raised pattern to thereby form a highly planarized structure with oxide in the spaces between the exposed raised pattern.

0016The features of the invention will be apparent from the following description and accompanying drawings.

Brief Description of the Drawings

0017<ul id="ul0001" list-style="none"><li>Figure 1 is a fragmentary vertical cross-section of a prior art structure showing the formation of a "bird's beak" by growth of field oxide regions in a silicon substrate which encroach into the active device region of the substrate.</li><li>Figure 2 is a fragmentary vertical cross-section showing an early stage of a first embodiment of the invention wherein a silicon substrate has been masked to cover active regions of the substrate and openings have been etched in the silicon substrate through the mask openings.</li><li>Figure 2A is a fragmentary vertical cross-section of an alternate step in the process to produce the structure of Figure 2 showing an optional field implant before forming the openings for the field oxide.</li><li>Figure 2B is a fragmentary vertical cross-section of the structure of Figure 2A showing a further field implant after forming openings for the field oxide.</li><li>Figure 3 is a fragmentary vertical cross-section showing the structure shown in Figure 2 at a later stage of the process with the mask removed and a conformal oxide layer deposited over the substrate and in the etched away openings in the substrate.</li><li>Figure 4 is an enlarged fragmentary vertical cross-­section of a portion of the structure of Figure 3 showing the difference between the depth X₁ of the etched area and the minimum thickness X₂ of the oxide layer over the structure, with X₃ represent­ing an intermediate level between X₁ and X₂.</li><li>Figure 5 is a fragmentary vertical cross-section of the structure of Figure 3 after a layer of planar­izing material has been deposited over the confor­mal oxide layer.</li><li>Figure 6 is a fragmentary vertical cross-section showing the structure of Figure 5 mechanically or chemically/mechanically polished to remove suffic­ient planarizing material to expose the highest portions of the underlying conformal oxide layer.</li><li>Figure 7 is a fragmentary vertical cross-section showing the structure of Figure 6 after an etch which removes oxide at a faster rate than planariz­ing material which therefore leaves high spots of oxide capped with planarizing material where the slower etching planarizing material shields the underlying oxide and the oxide not covered by plan­arizing material removed down to a level X₃.</li><li>Figure 8 is a fragmentary vertical cross-section showing the structure of Figure 7 after a second polishing step to remove the planarizing material/­oxide high spots.</li><li>Figure 9 is a fragmentary vertical cross-section showing the structure after performing the final step of this embodiment showing the structure of Figure 8 with further conformal oxide removed by a second etch until the top surface of the active regions of the substrate are exposed leaving a highly planarized structure.</li><li>Figure 10 is a fragmentary vertical cross-section of an alternate embodiment showing, under the dotted line, residual planarizing material which occurs when the conformal oxide layer thickness is less than X₂.</li><li>Figure 11 is a fragmentary vertical cross-section of another second embodiment of the invention show­ing a structure with a raised pattern formed over an integrated circuit structure.</li><li>Figure 12 is a fragmentary vertical cross-section showing the structure of Figure 11 with a conformal layer of oxide deposited thereon.</li><li>Figure 13 is a fragmentary vertical cross-section showing a further step of this embodiment with a layer of planarizing material deposited over the conformal layer of the structure of Figure 13.</li><li>Figure 14 is a fragmentary vertical cross-section showing polishing of the structure of Figure 13 until the highest portions of the underlying con­formal layer are exposed.</li><li>Figure 15 is a fragmentary vertical cross-section showing the structure of Figure 14 after an etch which removes oxide at a faster rate than planariz­ing material, which therefore leaves high spots of oxide where the slower etching planarizing material shields the underlying oxide.</li><li>Figure 16 is a fragmentary vertical cross-section showing the structure of Figure 15 after a second polishing step to remove the oxide high spots and form a highly planarized structure.</li><li>Figure 17 is a fragmentary vertical cross-section showing a further, but optional, etching step per­formed on the structure of Figure 16 to remove sufficient additional conformal oxide to expose the top surface of the raised pattern thereunder resul­ting in formation of a highly planarized structure.</li></ul>

Detailed Description of the Invention

0018The invention provides an improved method for form­ing highly planarized topologies in integrated circuit structures wherein oxide is used between active or conductive regions formed in or on an integrated circuit structure. In the illustrated embodiments, the process of the invention is shown, by way of illustration and not of limitation, as applied either to the formation of a highly planar­ized integrated circuit structure having field oxide deposited between active regions in a silicon substrate; or in forming a highly planarized struc­ture with a raised pattern such as, but not limited to, metal lines formed over an integrated circuit structure previously formed in and on a substrate, with oxide between or upon the raised pattern.

0019Referring now to Figure 2, a silicon substrate 2 is shown with a photoresist mask 10 thereon over ac­tive regions to be formed in the substrate and having openings 14 in mask 10 conforming to desired field oxide regions to be formed in silicon sub­strate 2. As shown in Figure 2, openings 8a and 8b have already been etched in silicon substrate 2 through mask openings 14 to a depth of, for exam­ple, from about 0.45 to about 0.55 microns.

0020Before forming mask 10 over substrate 2, an oxide layer 4 may be grown on the surface of substrate 2 to a thickness of, for example, 300-500 Angstroms, as shown in Figure 2, followed by deposition of about 1000 to about 2000 Angstroms, preferably about 1300 to about 1500 Angstroms, of silicon nitride 6 which may form an optional etch block for subsequent etching steps. Since the layer of oxide is used merely as an underlying layer for the optional nitride etch block layer, elimination of nitride layer 6 can also result in elimination of oxide layer 4 as well if desired. Alternatively, if desired, oxide layer 4 may be used beneath resist mask 10 even when nitride layer 6 is omit­ted.

0021Openings 8a and 8b are etched in silicon substrate 2, in one embodiment, by an anisotropic etch, such as a reactive ion etch (RIE) process, to form substantially orthogonal sidewalls, that is, side­walls normal to both the plane of the substrate surface prior to the etch and normal to the bottom of openings 8a and 8b.

0022In a variation of this embodiment, where it is desired to perform a field implant beneath the field oxide region to be formed in openings 8a and/or 8b etched in substrate 2, for example, when forming an n-channel device where undesirable in­version in the substrate can occur, the substrate may be implanted prior to forming the field oxide, as shown in Figures 2A and 2B.

0023As shown in Figure 2A, a first implantation and diffusion doping of substrate 2 may be carried out prior to any etching step through openings 14 in mask 10. By conductive this doping step prior to the etching step, some of the dopant will laterally scatter and diffuse into the edge of the adjacent active device region of the substrate as shown at 20, representing a crucial area where voltage in­version should be avoided. This doping step, for example, may be carried out by implanting boron followed by diffusion at between about 800 and 900°C for at least 15 minutes to result in a final boron concentration high enough to prevent field inversion, typically 10¹⁶ cm⁻³.

0024Alternatively, as shown in Figure 2B, after the etching of opening 8′ (which may be carried out to the same depth as openings 8a and 8b), a second doping step may be carried out to dope the newly exposed substrate surfaces over or against which the field oxide will be deposited. As shown in Figure 2B, advantageously sidewall 9 of substrate opening 8′ will be formed by adjusting the aniso­tropic etch slightly to form sidewalls with an inward slope of about 3-5 degrees to facilitate doping of sidewalls 9 of opening 8′. The bottom and sidewalls of substrate 2 exposed by opening 8′ may then be doped with boron to a concentration sufficient to prevent field inversion, typically 10¹⁶ cm⁻³.

0025After forming openings 8a and 8b (or 8′), mask 10 is removed and, as shown in Figure 3, a conformal layer of oxide 30 is deposited over the entire structure to a thickness sufficiently in excess of the depth of openings 8a and 8b so that the level of oxide in the lowest point in the widest opening 8b is above the highest point in the adjoining active regions of the substrate, including any layers, such as oxide 4 or nitride 6 thereon, which were shown in Figure 2.

0026It will be noted that the height of oxide layer 30 over wide area 8b is not as high as over narrower etched area 8a. As previously discussed with re­spect to the prior art, when wide areas are etched and then filled with oxide to form a field oxide region, oxide layer 30 tends to conform to the underlying topography. Since the eventual struc­ture, in accordance with the invention, will be highly planarized, it is important to the practice of the present invention that the thickness of oxide layer 30 over wide area 8b exceed the depth of area 8b from the unetched surface. This is illustrated in the enlarged region of Figure 3 shown in Figure 4 wherein the depth of etched area 8b from the surface is represented by X₁ while the thickness of oxide layer 30 over area 8b is repre­sented by X₂.

0027In accordance with the invention, the thickness of oxide layer 30 over wide area 8b (X₂) must be greater than the depth X₁ of area 8b. The differ­ence between X₁ and X₂ is preferably from about a minimum of about 0.15 microns up to about 0.45 microns. Greater thicknesses of oxide may be used, if desired, but are unnecessary. Thus, for exam­ple, when the depth of area 8b is about 0.5 mi­crons, the thickness of oxide layer 30 over area 8b will range from about 0.65 up to 0.95 microns.

0028Preferably, the deposited oxide is highly conform­al, such as, for example, tetraethyl orthosilicate (TeOS), which is deposited at a temperature of from about 700 to about 750°C. Alternatively, the de­posited oxide may comprise a low pressure chemical vapor deposition (CVD) oxide layer deposited at a temperature of from about 350 to about 450°C.

0029As shown in Figure 5, a planarizing layer 40, preferably comprising polysilicon, is then depos­ited over conformal oxide layer 30. Planarizing layer 40 may comprise any material which will pol­ish at a faster rate than oxide and which may be selectively etched at a rate less than or equal to that of the conformal oxide. In addition to poly­silicon, for example, aluminum metal may be used for planarizing layer 40.

0030Planarizing layer 40 will be described hereinafter as polysilicon layer 40 by way of illustration and not of limitation. The thickness of polysilicon layer 40 should typically be at least equal to or greater than the depth of the etched area in the substrate X₁, though thinner polysilicon films also are feasible.

0031After deposition of polysilicon layer 40, the structure is mechanically or chemically/mechanical­ly polished, using, for example, a sufficiently flat abrasive means so that only the highest points of the structure are contacted without the abrasive means conforming to depressed areas.

0032The abrasive means used in the polishing step may comprise either a purely mechanical polish using, for example, as a polishing material an aqueous slurry of finely divided Al₂O₃ or SiO₂ particles, with the pH adjusted to about 7, spread on a flat teflon disk, or the polishing material may also include a minor amount of a hydroxide such as KOH or NaOH added in a sufficient amount to increase the pH to about 9-11.

0033This first polishing step is carried out until the highest portions of underlying conformal oxide layer 30 are exposed leaving polysilicon portions 40a and 40b over lower levels of oxide layer 30, as shown in Figure 6. A typical selectivity of >200:1 can be obtained for polysilicon to oxide removal by chemical/mechanical polishing.

0034The structure is then selectively etched using an etchant system, such as, for example, a reactive ion etch (RIE), using CHF₃ chemistry with the oxy­gen level adjusted to favor oxide removal over polysilicon removal or by a wet etch such as hydro­fluoric acid (HF) diluted in water (H₂O) to a volume ratio of, for example, 40:1 H₂O/HF. For the case of an RIE etch, for example, the etch ratio may be preferably adjusted to provide an etch ratio of, for example, about 5:1 to about 10:1, oxide to polysilicon etch removal rate, i.e., to remove oxide at a rate 5-10 times faster than the polysil­icon etch removal rate. Referring to Figure 7, the etch step is carried out for a sufficient time to etch back the oxide layer down to a level X₃ which is higher than X₁ but less than X₂ by an amount not exceeding approximately 0.1 microns as will be discussed below. It will be noted that solid lines 32 indicates the edge of oxide layer portions 30a and 30b when a dry etch such as an RIE etch is used while dotted lines 34 indicate the edge of oxide layer portions 30a and 30b when a wet etchant is used.

0035It should be noted with regard to this etch step that the minimum as deposited thickness of polysil­icon planarizing layer portion 40b over etched area 8b is related to (1) the step height X₁ of the etched substrate, (2) the etch ratio of oxide re­moval to polysilicon removal, and (3) the amount of polysilicon removed in the polishing step over area 8b by the following formula: P_min = X₁/E_ratio + M where: P_min = minimum thickness of planarizing layer 40; X₁ = depth of the etched area in the sub­strate from the surface which is ap­proximately equal to the amount of oxide removed to reach level X₃; E_ratio = etch ratio of oxide layer 30 to planarizing layer 40; M = thickness of polysilicon removed by polishing step.

0036This relationship ensures that as the oxide is selectively etched, the polysilicon will be etched at a sufficiently slow rate, relative to the thick­ness of the polysilicon so that all of the poly­silicon will not be removed before the selective etch is stopped and so that none of the oxide beneath the polysilicon in region 8b is removed.

0037This relationship is important because the selec­tive etch step is intended to lower the overall oxide level (in the regions not covered by poly­silicon) to a height X₃ which is below X₂, and higher than X₁. While eventually all of the oxide will be removed down to the level of the unetched or active regions of the substrate, to ensure the highly planarized surface which characterizes the process of the invention, more control of the re­moval of the last portions of the oxide can be maintained by using a second polishing step to remove the remainder of the polysilicon as will be described below followed by uniform removal of oxide over the entire surface area

0038This selective etch step just described will result in high spots of polysilicon 40a and 40b bordered by minor oxide portions left on the structure due to the selectivity of the preceding etch step as shown in Figure 7 with minor oxide portions 30a and 30b left in those portions of oxide layer 30 shielded by polysilicon portions 40a and 40b.

0039These polysilicon portions 40a and 40b, as well as remaining oxide portions 30a and 30b are then re­moved by a second polishing step, which again may be either mechanical or chemical/mechanical. This polishing step is carried out until the level of these high spots is reduced to reach a level some­where between X₂ and X₃, and until all of the polysilicon planarizing layer 40 (40a and 40b) is removed leaving a thin oxide layer 30c, as shown in Figure 8.

0040The oxide layer 30 is then further etched to expose and planarize the structure down to the level of the adjoining active regions of the substrate, as shown in Figure 9. This etch step is preferably carried out using either the RIE or wet etching methods described previously.

0041The foregoing describes the process when the lowest level of oxide layer 30, as deposited, will be X₂, the lev the bottom of the widest etched away regions 8b. In some instances, however, narrower openings or etched away areas may not be filled with oxide up to the level of X₂ which, in turn, means that some planarizing material will remain in these low reg­ions after the second polishing step of the poly­silicon or other planarizing material. This is shown under the dotted line as 31 in Figure 10.

0042When region 31 in Figure 10 is filled with polysil­icon, which then still remains after the second polishing step discussed above, this problem may be solved as follows. The additional polysilicon remaining at 31 may be removed by dividing the final etch step into two steps with the first step comprising a 1:1 oxide to silicon etch whereby the polysilicon in region 31 will be removed at the same rate as the surrounding oxide. The ratio would then be changed, after all of the polysilicon in region 31 was removed, back to the selective oxide ratio, e.g. 5:1 to 10:1, so that the final etch could still be stopped when the active (unetched) region of the silicon substrate was reached as in the earlier described embodiment.

0043Turning now to Figures 11-17, another embodiment of the process of the invention is shown commencing with Figure 11 wherein an integrated circuit struc­ture 60, which may include previously formed active devices in or on the surface of a substrate, such as a silicon substrate, is shown provided with a raised pattern 70 over the substrate surface.

0044Patterned layer 70 might, for example, comprise a 3000 to 10,000 Angstrom layer of a conductor, e.g., metal patterned to form metal lines or intercon­nects. When layer 70 comprises a conductor, it may comprise any conductor conventionally used in form­ing integrated circuit structures, such as, for example, aluminum, polysilicon, or tungsten, cap­able of withstanding the temperatures subsequently used in depositing the conformal and planarizing layers thereon.

0045Raised pattern 70 might also comprise the combina­tion of an insulating layer or step over a raised pattern of conductors, or might only comprise an insulating material. Patterned layer 70, however, will be described below, by way of illustration, and not of limitation, as a metal pattern.

0046As shown in Figure 12, a conformal layer of oxide 80, such as the previously described TeOS oxide, for use over materials which can withstand tempera­tures above 700°C, up to 750°C, or a lower tempera­ture CVD oxide, (e.g., deposited at about 350°C), is deposited over structure 60 and metal pattern 70 to a thickness which, in the widest area between metal lines, will again be a thickness X₂, as in the first embodiment which is greater than X₁, the thickness of the metal pattern 70. Usually, the thickness X₂ will be greater than the thickness X₁ by about 0.2 microns up to about 1.2 microns. The thickness of conformal oxide layer may vary, for example, from about 7000 to about 15,000 Angstroms.

0047As in the first embodiment, a layer of planarizing material 90 such as, for example, polysilicon is now deposited over the structure as shown in Figure 13. The minimum thickness of this polysilicon layer can be determined using the same equation for P_min previously described.

0048It should be noted here, that if a lower melting metal such as aluminum is used for metal pattern 70, then a lower deposition temperature TeOS oxide, e.g., one deposited at about 350°C, such as plasma TeOS, may be substituted for the previously des­cribed conformal oxide; and for the planarizing layer, a material such as tungsten may be deposited instead of the higher temperature polysilicon, or the polysilicon could be sputtered or plasma CVD deposited over oxide layer 80 at temperatures less than 350°C. For purposes of illustration, and not of limitation, the planarizing layer will be des­cribed hereinafter as polysilicon, as in the prev­ious embodiment.

0049The structure is now polished, similarly to the first polishing step of the first embodiment, to remove polysilicon until the highest areas of the underlying conformal oxide layer 80 are exposed as shown in Figure 14 leaving polysilicon portions 90a.

0050The structure is then etched, as in the first embodiment, using, for example, a wet etch or a reactive ion etch with an etchant system which will remove conformal oxide layer 80 and polysilicon 90a at a ratio of from about 5:1 to 10:1. This etch is carried out to remove oxide now to a level X₃ which, as in the first embodiment is higher than X₁, but lower than X₂ by not more than about 0.1 microns, e,g., about 0.5 microns of conformal oxide layer 80 may be removed for a metal thickness X₁ of 0.45 microns. As in the first embodiment, this etch ratio results in high spots or pillars of polysilicon 90a, having oxide portions 80a beneath, as shown in Figure 15.

0051The remaining polysilicon 90a and underlying or adjacent high oxide areas 80a are then removed by a second polishing step, as in the previous embodi­ments, resulting in the structure depicted in Fig­ure 16 with planarized oxide layer 80c covering the entire structure.

0052The structure is then again etched to remove all of the remaining conformal oxide over pattern layer 70 using, for example, a reactive ion etching system which will selectively remove oxide at a faster rate than the material forming pattern layer 70 until the upper surfaces of pattern layer 70 are exposed.

0053Alternatively, for cases in which it is desirable to have an oxide layer covering the conductor pat­tern, the final etch step can be omitted to result in the planarized structure as shown in Figure 16.

0054When the final etch step is performed, the result, as shown in Figure 17, is a highly planarized structure with oxide 80d formed between the lines of pattern layer 70 at the same level as pattern layer 70.

0055Thus, the invention provides an improved method for forming highly planarized topology in integrated circuit structures which may be used in forming highly planarized oxide regions adjacent active device regions in a substrate or a highly planar­ized structure of a raised pattern such as metal lines interleaved with oxide by utilizing a confor­mal oxide layer over which is applied a planarizing layer of preferably polysilicon followed by a first polishing of the structure and then a first etching of the conformal oxide layer followed by a second polishing step to remove remaining planarizing material followed by a second etching to remove oxide down to the highest level of the integrated circuit thereunder.

0056Having thus described the invention, what is claimed is: