DE10259322B4 - A method of forming an alignment mark in an opaque layer on a substrate - Google Patents

Abstract

A method of forming an alignment mark in an opaque layer (100) on a substrate, comprising the steps of:
Providing the substrate comprising a surface (91) and a first (10) and a second (20) trench, the first trench (10) having a first width and a first depth and the second trench (20) having a second width and a second width second depth and wherein the first width is greater than the second width and / or the first depth is greater than the second depth,
- applying a first layer (50) comprising a first material having a thickness such that the second trench (20) is complete due to its smaller width and / or depth and the first trench (10) only partially due to its greater width and / or depth is filled,
Applying a second layer (30) comprising a second material which has a selectivity in an etching process with respect to the first material,
- Adjusting the thickness of the ...

Description

The The invention relates to a method for forming an alignment mark in an opaque Layer on a substrate, in particular on a semiconductor wafer.

Around preferably high positional accuracies of structures to be formed in one layer relative to a pre-plane on a substrate such as a semiconductor wafer to achieve so-called in the lithographic projection Alignment marks (alignment marks) for aligning the substrate uses. These are along with the structures in the concerned ones Layer layers formed and serve the exact position determination for a Justieroptik of the respective exposure device used in the implementation of a subsequent exposure.

The subsequent exposure takes place in a photosensitive resist which, for this purpose, is currently being structured Layer is applied. The layer to be structured is located in turn, above the pre-structured, already structured Layer within which said alignment marks are e.g. when deep, wide compared to the structural elements of the circuit trenches are arranged.

often For example, the layers to be patterned have the property translucent, i. transparent at the wavelength to be the light used by the alignment optics. The same generally also applies to the resist, so that means the alignment optics through the resist and the layer to be structured through the alignment marks detected in the underlying layer and their positions can be measured.

Various Materials, especially those that are electrically conductive, such as such as metals to form metal tracks or poly-silicon, find Application in the manufacturing processes which are opaque, i. non-transparent are the light used by the alignment optics. In this case can arranged in already covered layers alignment marks not be recognized. However, it is possible that in the presence of a corresponding surface topography just before applying the layer to be structured surface topography immediately in the new surface the now applied, to be structured layer reflects. In this case, the position of the alignment mark is based on the current surface topography identified.

at the production of structures with particularly small structural widths However, there is an effort to make the exposure as possible flat surface to perform on a substrate. Namely, prevail substantially identical focus conditions across the surface, so that one high image contrast is achieved.

To For this purpose, for example, a chemical-mechanical polishing step applied to an existing surface topography, to be structured layer. Through this polishing step However, at the same time the possibility of recognizing Alignment marks significantly diminished when opaque layers be applied.

you As a result, it increasingly turns into, in the underlying Layers alignment marks as trenches with extra large ones To form latitudes and / or depths. The widths of these trenches are compared to those that serve the structural elements of the circuit, so big enough, that these trenches are the Alignment marks through the deposition process of the currently to be structured Do not shift to a complete one backfilling the alignment mark leads. In the polishing process becomes thus a flat surface created at the positions of the alignment marks by recesses due to the unfilled trenches is marked.

However, further problems arise in this context. As in the 1 and 2 the example of the formation of a shallow trench isolation (STI, 21 ) with subsequent planarization, the surface is in an environment of not completely filled trenches 10 the alignment marks in the chemical-mechanical polishing process by erosion 101 impaired.

1 shows in monocrystalline silicon 1 a trench formed by a substrate 10 , which represent alignment marks, and trenches 20 , which with an HDP (high-density plasma) oxide 50 to form the shallow trench isolation 21 are completely filled. Outside the trenches 10 . 20 is the monocrystalline silicon 1 the substrate is a pad nitride forming the surface of the provided substrate 40 arranged. In the not to scale drawing is the ditch 10 from the oxide 50 only partially filled.

In 2 is the planarized surface resulting from the polishing process 91 shown. Due to incomplete backfilling of the trench 10 with the oxide 50 become the upper trench edges, especially the pad nitride 40 in the vicinity of the trenches 10 heavily attacked and eroded. Microscope examinations, for example of semiconductor wafers on which memory modules are formed, show that after the planarization process, the memory structures located near the saw frame area of an exposure field (kerf) are replaced by a memory array such erosion are badly affected. It can thus lead to a significant reduction in the yield in semiconductor production.

This problem can be circumvented consuming, including by the incomplete backfill of the trench 10 resulting depression 81 in the surface of the oxide 50 with another layer, a so-called cap layer 39 on the oxide 50 is filled. In an additional lithographic exposure step with subsequent etching back and removal of the resist applied thereto, the now completely filled trench can be filled using a specially provided block mask 10 be opened again after an unproblematic polishing step, so that for the alignment optics, the topography of the alignment marks in the trenches 10 becomes visible again. The avoidance of the resulting by erosion particles and yield problems must be paid for by an expensive and time-prolonging manufacturing process.

From the publication US 6,153,492 A For example, a method is known in which the contrast of alignment marks after deposition and re-planarization of a tungsten layer is increased by both the trenches of the alignment marks as well as contact holes in an upper region are respectively re-etched or etched back. This results in trench edges opposite the trench filling, which are transmitted in a recess in a subsequently deposited layer of aluminum and thus are easier to detect. The etch back in the contact hole is not a problem because the etchback in the upper region of the contact hole is filled by the aluminum metallization.

A likewise in US 6,153,492 A According to the alternative provided, instead of etching back into the tungsten-filled trenches of the alignment marks and contact holes, etching back the oxide layer surrounding the trenches. As a result, the former trench content, the tungsten layer, protrudes beyond the surface of the oxide layer and thus forms an edge for the exposure of a subsequently applied aluminum layer, which likewise reflects in a high contrast in its surface. In order that the filled contact hole does not project beyond the oxide layer, the etching back can be limited by a resist to an environment of the alignment mark.

It is the object of the present invention, the effort and the costs for the process of opening Aligning marks forming trenches below to be patterned, opaque layers to reduce. It is also an object of the present invention, the quality of the structuring process an opaque layer to increase.

The Task is solved by a method of forming an alignment mark in an opaque layer on a substrate, comprising the steps of: providing the substrate, comprising a surface and a first and a second trench, wherein the first trench a first width and a first depth and the second trench one second width and second depth, and wherein the first Width is larger is the second width and / or the first depth is greater than the second depth is applying a first layer comprising a first material having a thickness such that the second trench due its lesser width and / or depth is complete and the first ditch due its greater width and / or depth is only partially filled, applying a second layer comprising a second material having a selectivity in an etching process over the first material, adjusting the thickness of the second layer in the Applying such that the first dig completely filled by the second layer is, chemical-mechanical polishing of the substrate to the exposure the surface of the substrate under to form a flat surface over the first and second trenches, etching the second material selectively to the first material for the partial opening of the first trench, applying the opaque layer to the plane surface and in the opening of the first trench, so that the Adjusting mark formed as a recess of the opaque layer above the opening becomes.

In front the implementation of the chemical-mechanical polishing process are not completely with the first layer, in particular a STI oxide, filled first ditches, which represent positions of alignment marks in a substrate filled by a second layer. This second layer has the special property of being selective in an etching process across from the trenches backfilled etched first layer to be able to. Selective means here that it gives an etching process, at which the etching rate the material of the second layer is many times higher, as the etching rate the first or further layers, which are superficially exposed are.

In the subsequent polishing process, the surface of the substrate surrounding the first trench of the alignment mark is not eroded, since there is essentially no opening or depression due to the filling of the wider or deeper trench. The polishing process results in a backplanarization such that the original surface of the substrate is exposed. Substrate is here, for example, serving as a basis for a wafer monocrystalline silicon with one or more arranged thereon layers, such as a thin oxide and / or pad nitride layer understood.

The trenches are in the monocrystalline silicon and arranged thereon Layers of the provided substrate formed. After backplaning is the first, the alignment mark forming trench with parts of the first and the second layer filled. As the second, the formation of structural elements such as the flat Trench isolation trenches have already been completely filled with the first layer, as they have a lesser second Width and / or depth as the first width and / or depth of the first trenches have the alignment marks, these trenches have no share of the second Material of the second layer.

If in detail the depth, the width or a combination of both the criterion for the backfilling the first and the non-filling of the second trench, depends in particular from the currently set process parameters in the deposition process of the first Shift or even earlier deposited layers. In the majority of cases will the different current depth of the trench of the alignment mark relative to the trench of a structural element to be filled crucial for the Functioning of the method according to the invention be.

With an etching process, which the material of the second layer selectively to that of the first layer be etched now the trenches the alignment marks at least in the occupied by the second layer Room shares etched. Depending on the selected Ätzselektivität be also etched back some other areas of the substrate surface, but the etch depths are comparatively low.

To the etching process For example, the planar planarized surface has only pits in the trenches of the alignment marks. Will now be an opaque layer applied, so transfers the Recess on the opaque Layer, as far as the deposition process has a sufficient conformity and the thickness of the deposited layer is not significantly greater than is the width and / or depth of the first trench. Based on this Recess can with an adjustment optics, the position of the alignment mark be recognized. To carry out the inventive method neither particles are damaged by eroding trench edges during a Planarization generated, still will be additional Mask steps needed, to avoid erosion.

The Light transmission the layer to be structured does not only refer to the optical or ultraviolet wavelength range, as for traditional Adjustment optics come into consideration. For exposure devices in the future Technology generations can Also such optics are considered, which in the X-ray, Ion or electron beam work. These definitions are included in the present invention.

Of the etching step according to the invention may also be a sum of subsequent separate etching steps For example, after an STI process, a first wet chemical Oxide etching process, then a wet chemical Nitride etching process and after Again, a wet chemical oxide etching process can be performed. A particular advantage arises if and only if the etching step according to the invention to expose the trade mark opening in Combination with an etching step to remove a superficial applied further layer, for example, the pad nitride or an oxide layer arranged directly on the monocrystalline silicon, carried out becomes.

The Applying the first layer may also include several substeps respectively comprising applying partial layers. For future technologies For example, it is provided that the process parameters during a Deposition in ge suitable manner to vary, so that a horizontal sequence of layered structures in such a first Shift setting.

The inventive method is not on the application of alignment marks for alignment in one exposure unit limited. Rather, in this document under an alignment mark and a measuring mark for determining the relative positional accuracy of two on a Substrate arranged, structured layer planes understood, generally after performing an exposure in one Microscope examined become.

The Invention will now be described with reference to an embodiment with the aid of Drawings closer explained become. Show:

1 - 2 Method steps for opening a filled adjustment mark according to a first example according to the prior art,

3 - 7 Method steps for opening a filled adjustment mark according to a second example according to the prior art,

8th - 11 Method steps for opening a filled alignment mark according to an embodiment of the invention according to the prior art.

The inventive method is particularly advantageous applicable to the structuring of poly-silicon tracks, which serve for gate contacting of the active regions of selection transistors, for example, trench capacitors. For this purpose, a substrate is provided, which is monocrystalline silicon 1 comprising, on which a thin oxide and in turn a pad nitride layer 40 is arranged, which can serve as an end mark for subsequent etching processes.

The Substrate is a semiconductor wafer on which memory cell arrays should be formed.

In the substrate provided already serving as a storage node trench capacitors (deep trenches) and active areas for forming selection transistors are arranged. The memory cells are separated from each other by a shallow trench isolation, for what purpose in the monocrystalline silicon 1 trenches 20 formed with shallow depths.

The width of these trenches 20 (in the following STI trenches or second trenches 20 ) have a structure width of 240 nanometers (nm). Before the shallow STI trenches are formed within the memory cell arrays, first trenches are formed 10 the alignment marks in the monocrystalline silicon 1 formed in the sawing frame of the exposure field, which includes, among other things, the memory cell array. For simplicity and not to scale are in 3 the trenches 10 and 20 drawn directly next to each other.

The profile of the trenches 10 and / or trenches 20 can be arbitrary, in particular, in addition to the rectangular profiles shown in the figures, V-shaped or U-shaped profiles, etc. are possible.

The first trenches 10 The alignment marks have a much greater depth than the STI trenches 20 or further trenches that are structured within the memory cell array or in its periphery. The width of the first trenches 10 is for example 1.2 microns. The depth is 1.5 μm. Trenches formed in the sawing frame area, which have a width of, for example, 0.5 μm and a depth of approximately 100 to 150 nm, exhibit the same properties as the second trenches when carrying out the method according to the invention with regard to backfilling 20 , The different depth of the originally for example up to 5 microns deep into the silicon etched trenches to form alignment marks is due to a different running filling profile, here of poly-silicon for backfilling trenches for storage capacitors (deep trenches), justified. In the embodiment, the trenches 10 By Marks indicative depth above, for example, 0.5 microns.

The depth of the trenches 10 . 20 one here a special role for the filling behavior. In shallow trench isolation (STI), the depth is by definition low, it is about 280 nm in the exemplary embodiments.

In an HDP (High Density Plasma) process, an electrically insulating oxide is applied to the substrate and into the trenches as the first layer 50 deposited. The thickness of the layer is 480 nm. In the HDP deposition method, a larger thickness of the first layer than on vertical surfaces is produced due to parallel sputtering processes on horizontal surfaces. The specified layer thickness refers to the thickness over a horizontal surface. In the embodiment of the present invention to be described, an HDP method is used, but other suitable deposition methods, especially those having a conformal deposition profile, are equally applicable to the invention.

For a better illustration of the advantages of the present invention is first in the 3 to 7 a prior art process sequence using an additional mask step to open the filled trench 10 shown. As in 3 is seen on the deposited with the HDP process oxide layer 50 a cap layer 39 deposited in such a way that the trench 10 the alignment mark to above the through the pad nitride layer 40 marked trench edge is filled.

Subsequently, a chemical-mechanical polishing (CMP) step is performed until the surface 91 the originally provided substrate, ie the pad nitride layer 40 is exposed ( 4 ). In the course of becoming a photosensitive layer 70 applied and exposed with a non-critical block mask, the exposed structures on the filled trenches 10 within the frame of the exposure fields. After developing and removing the exposed resist parts ( 5 ) will be in the first trenches 10 oxide present with the cap layer 39 etched back in a timed etching process. The cap layer is also an oxide with chemical and physical properties similar to those of the STI oxide 50 ( 6 ).

After removing the photosensitive layer 70 and the implementation of further process steps, for example wet chemical etching, oxidation, implantation, etc., is doped poly-silicon as an opaque layer 100 applied. Over the etched holes 180 the first trenches 10 any profile forms a depression 200 in the substantially conform abge different opaque layer 100 , After application of another, for the alignment optics translucent, photosensitive layer, this depression 200 in an alignment process (English: alignment) to determine the position of the alignment mark recognized and used.

On a comparison substrate, the inventive method is now applied. The starting point is the described, provided wafer with first trenches 10 (Alignment marks) and second trenches 20 (STI trenches), on and in which a 480 nm thick oxide layer 50 was deposited in an HDP process. In the opening 81 of the not completely filled in first trench 10 the alignment mark and on the oxide layer 50 becomes a flow-fill oxide 30 deposited. Unlike the STI oxide 50 is this flow fill oxide 30 have not been exposed to a high-temperature process. Its internal structure differs considerably from that of the STI oxide 50 as well as the oxide of the cap layer 39 according to the prior art. The flowfill oxide can thus be deposited with high selectivity in an etching process over the STI oxide 50 remove. 8th shows the condition after application. this second layer with high Ätzselektivität.

After performing the CMP step ( 9 ), in the memory cell array as well as in the context of a substantially flat surface 91 is prepared, a wet etching process is used. The original conformal layer thickness of the flow-fill oxide 30 was 160 nm. After a 24 second etch with BHF, the flow-fill oxide is 30 to a depth of 200 nm from the previous opening 81 in the STI oxide 50 away ( 10 ). At the same time, the STI oxide has 50 opposite the adjacent pad nitride 40 suffered a loss of about 40 nm in height due to etching losses (not shown). But this loss is tolerable. The etching selectivity achieved is thus about a factor of 5.

To repeatedly make the opening 81 in the first ditch 10 the alignment mark is therefore no additional mask step necessary. The pad nitride 40 and the STI oxide 50 remain almost unimpaired by the selective etching process. The pad nitride 40 is to be deducted in the present example below. The etching step required for this purpose can be advantageous with the etching step according to the invention for exposing the opening 81 be combined. For this purpose, the selectivity of the etching step according to the invention is set accordingly. The same applies to the combination with an etching step for the necessary adjustment of the height of the STI oxide 50 ,

It is also possible, instead of only the flow-fill oxide, to deposit a liner of, for example, poly-silicon and, for example, an oxide plug. By undercutting by means of a poly-silicon etch so the oxide plug from the opening 81 be removed.

It will now be the opaque layer 100 comprising poly-silicon, in which, due to a substantially conformal deposition, the shape of the opening 81 as a depression 201 transfers. As described above, based on this depression 201 , which is only slightly smaller than the recess 200 According to the prior art, for aligning the substrate or wafer by means of an alignment optics are used in an exposure device.

It it is clear that the in the embodiment materials described no limitation of the present invention represent. The one in the field of etching techniques Skilled average expert may instead of the flow-fill oxide for example, doped oxides, boron-silicate, boron-phosphorus silicate, so-called Low-k materials with low dielectric constant, ozone TEOS, amorphous or use poly-silicon.

With knowledge of the chemical and physical composition of the material of the first layer 50 which was the STI oxide in the exemplary embodiment, the person skilled in the art can select a suitable etching process with suitable etching parameters in order to achieve a desired etch selectivity for said materials. With knowledge of the present invention, it is also obvious to use materials other than the STI oxide 50 for filling the trenches 10 and 20 use.

It is particularly advantageous if the etch-selective material of the second layer has an etching selectivity both relative to the pad nitride and to the first material of the filled trenches 10 and 20 having.

The invention is not limited to an application for structuring opaque polysilicon 100 comprehensive wordlines. Rather, the application of the invention is especially in the structuring of higher metal levels into consideration. Opaque layers may, for example, also include other electrically conductive materials such as the metals mentioned, in particular copper, aluminum, or metal compounds such as tungsten silicide, etc., doped semiconductor materials, carbon, antireflective layer materials, etc. Especially the formation of metal layers is usually associated with a previously performed CMP process by which the topography of the alignment marks are affected can. Consequently, the invention is particularly advantageously applicable to the structuring of metal planes.

Claims (9)

Method for forming an alignment mark in an opaque layer ( 100 ) on a substrate, comprising the steps: - providing the substrate comprising a surface ( 91 ) and a first ( 10 ) and a second ( 20 ) Digging, the first trench ( 10 ) a first width and a first depth and the second trench ( 20 ) has a second width and a second depth, and wherein the first width is greater than the second width and / or the first depth is greater than the second depth, - applying a first layer ( 50 ) comprising a first material having a thickness such that the second trench ( 20 ) due to its smaller width and / or depth is complete and the first trench ( 10 ) is only partially filled due to its greater width and / or depth, - application of a second layer ( 30 ) comprising a second material which has a selectivity in an etching process with respect to the first material, - adjusting the thickness of the second layer ( 30 ) when applying such that the first trench ( 10 ) completely through the second layer ( 30 ), - chemical-mechanical polishing of the substrate to expose the surface ( 91 ) of the substrate and to form a planar surface over the first ( 10 ) and second ( 20 ) Trenches, - etching the second material selectively to the first material for partial opening ( 81 ) of the first trench, without the use of a resist or hard mask, - application of the opaque layer ( 100 ) on the flat surface and in the opening ( 81 ) of the first trench ( 10 ), so that the alignment mark as depression ( 201 ) of the light-impermeable layer above the opening ( 81 ) is formed. Method according to claim 1, characterized in that that at the application of the second layer at least a second material from the group comprising: doped or non-stoichiometric oxides or nitrides, Borosilicate gels, Boron phosphorous silicate glass, Flowfill oxide, low-k-materials, ozone-tetra-ethyl-ortho-silicate, poly-silicon be used. Method according to one of claims 1 or 2, characterized in that in the application of the first layer ( 50 ) a material comprising an undoped oxide or an oxi-nitride is used. Method according to Claim 3, characterized in that the first layer ( 50 ) to form a shallow trench isolation ( 21 ) is applied in a deposition process at elevated temperatures, in particular a high-density plasma, a chemical vapor deposition or a physically enhanced Dampfabscheideprozeß, or that the deposition process is followed by a high-temperature process, in particular annealing to densify the material of the first layer , Method according to Claim 4, characterized in that the substrate is provided with a layer ( 1 ) comprising monocrystalline silicon and a further layer arranged above it on the surface comprising a pad nitride ( 40 ), in which two layers ( 1 . 40 ) the first ( 10 ) and the second trench ( 20 ) are each formed. Method according to Claim 5, characterized in that the second material has an etching selectivity with respect to the pad nitride ( 40 ) and the oxide or oxi-nitride of the shallow trench isolation ( 21 ) is selected. Method according to one of claims 1 to 6, characterized in that the opaque layer ( 100 ) comprises a material from the group comprising metals, semiconductor materials, carbon, antireflective layer materials, amorphous or poly-silicon. Method according to claim 5, characterized in that - the opaque layer ( 100 ) Comprises poly-silicon, - a photosensitive layer ( 70 ) is applied, - the alignment mark is used for aligning the substrate in a projection device, - the opaque layer ( 100 ) for forming word lines for driving active regions on the monocrystalline silicon ( 1 ) is exposed with a structural pattern representing a dynamic memory. Method according to one of the preceding claims, characterized characterized in that the etching is wet-chemical or in a dry etching process.