METHOD FOR MANUFACTURING OF A SEMICONDUCTOR DEVICE

Abstract: There is disclosed a method for manufacturing of a semiconductor wafer (1), preferably suitable for a wafer (1) with 300 mm in diameter or larger. After depositing at least one encapsulating material layer (14, 14') over the front side and back side of the wafer (1), the material layer (14) over the front side of the wafer (1) is etched selectively to form a predetermined structure in one of the following process steps. Wafer warpage is caused as a result of unequal wafer bowing stress of the material layer (14, 14'). By removing the material layer (14') over the back side of the wafer (1) partially or completely in accordance with the desired reduction of the bowing stress wafer warpage is reduced. When applying e.g. a lithographic process over the front side of the wafer (1) in the further curse of the manufacturing process, non-linear overlay distortions caused by wafer warpage are minimized.

Description: Description Method for manufacturing of a semiconductor device The present invention relates to a method for manufacturing of a semiconductor device using a wafer with deposited material layers causing wafer bowing stress, wherein in particular said wafer is of at least 200mm in diameter. In the technical process of manufacturing semiconductor devices from wafers (e.g. disks on the basis of silicon) it is common and necessary to apply a lithographic process frequently in the process. In the lithographic process the overlay performance depends on the wafer conditions . Overlay er- rors may derive e.g. from applying hot processes or processes like CMP (chemical mechanical polishing) and have negative influence on the overlay performance. The errors usually occur as residuals visible on the wafer surface after definite process steps. They can be divided into linear and non-linear overlay errors, whereby only linear or systematic overlay errors can be corrected by varying machine parameters of the exposure tools such as a stepper by optimization of the stepper parameters . Non-linear overlay errors, which usually cannot be corrected automatically by the manufacturing tools, cause high rework rates resulting in general in a loss of yield. As some of these errors are not correctable, even the rework may show no success . Beside the aforementioned effects causing non-linear overlay errors, a new root cause especially came up with the wafer technology using wafers of at least 200mm in diameter. In process steps where the front side and the back side of the wafer is deposited with at least one material layer having tensile or compressive stress such as nitride, polysilicon or different types of oxides, mechanical stress causes wafer warpage, e.g. as a result of forming a structure over the front side of the wafer by etching parts of the material layer. It has been observed that the scale of warpage increases with a larger diameter of the wafer. Due to a significant misalignment in the lithographic process after e. g. an element isolation process non-linear overlay errors may occur. Other problems in manufacturing may arise with processes that use electrostatic chucks or physical clamping rings for hol- ding the wafer during etch or thin film depositon processes. Warped wafers coming into these processes cause robotic wafer handling failures due to vacuum sealing problems or process faults due to leakage of backside cooling gases on the electrostatic chuck. In diffusion operations, precise loading of the wafers into the boats that are inserted in the furnace are affected by warped wafers resulting in wafer breakage or chipping, damage to the boat, or dropped wafers. Operations such as wet chemical processing that load wafers into holders by vacuum clamping on the wafer backside are also impacted by warped wafers. In CMP operations, warped wafers cause process non-uniformity errors due to the warpage affecting the polishing of the entire wafer surface. Further processes that can be impacted in their performance by wafer warpage are ion implantation processes, mask making or metrology processes. In US 5,856,230 there is disclosed a method for making a field oxide, by which wafer warpage is minimized when a local oxidation of silicon process is applied to a large wafer. A material layer having a compressive stress and a nitride are laminated over the back side of the wafer, so that the compressive stress of the material layer complementarily interacts with the tensile stress of the nitride. The method comprises the steps of depositing an oxide layer and the material layer over the front side and the back side of the wafer in addition to the standard LOCOS-process steps. The effects herein may be an increase of manufacturing costs and an increase of process time. In view of the prior art it is an object of the present invention to provide a method for manufacturing of a semiconductor device using a wafer, that is in particular of at least 200mm in diameter, which reduces or prevents the problems of the aforementioned processes caused by wafer warpage, the method being applicable to multiple process sequencies of semiconductor manufacturing with respect to low costs and process time. This object is solved by a method for manufacturing of a semiconductor device according to claim 1. Further advantageous features, aspects and details of the invention are evident from the dependent claims. According to the present invention, a method for manufacturing of a semiconductor device is provided using a wafer, comprising the steps of - depositing at least one encapsulating material layer over the front side and the back side of the wafer, - etching said material layer selectively over the front side of the wafer to form a predetermined structure, thereby causing wafer warpage as a result of bowing stress of said material layer, - removing said material layer over the back side of the wafer partially from said back side in accordance with the desired reduction of the bowing stress, - applying in the further course of the manufacturing process a lithographic process to the front side of the wafer, a CMP process or a process that uses electrostatic, physical clamping or vacuum clamping for holding the wafer . The provided method is applicable to a multiple processes comprising the aforementioned sequencies of process steps. The provided method therefore is applicable e.g. in DRAM technologies and in processes for manufacturing logic cir- cuits or micromechanic components. The effect of reducing wafer warpage can be observed significantly at wafers of at least 200mm in diameter. Especially with using wafers of 300mm in diameter and larger the wafer warpage caused by ma- terial layers plays a fairly important role for the performance of the aforementioned processes, in comparison to effects caused by processes such as CMP or hot processes, because of the different thickness-to-area-ratio. Furthermore the problem of overlay distortions caused by wafer warpage can be observed especially at backend of-line lithography processes (BEO ) . In lithographic processes, there is a reduced amount of de- focus or non-linear overlay errors as a result of reduced wa- fer warpage. Thus, process improvements can be observed with no or less rework rates and a reduction in yield loss. Concerning the other aforementioned processes, as a result of reduced wafer warpage there are no or less robotic wafer handling failures or process faults impacted by wafer warpage. Precise loading of the wafers into boats that are inserted in a furnace is improved. In CMP operations, reduced process non-uniformity errors due to wafer warpage can be achieved. Further it is not necessary to deposit a novel kind of layer interacting with the stress of the encapsulating material layer. This results in low costs and process time. It takes into account that for several reasons it can be disadvantage- ous to deposit multiple layers over the back side of the wafer. This could take influence on other processes or prevent the wafer surface from having a flat back side which could be necessary with regard to the requirements of the wafer or stepper chuck. According to the present invention, said material layer or material layers can be removed completely or partially depen- ding on the process and its requirements according to the reduction of the warpage. In case of removing the layers partially, which helps to destress the wafer, the corresponding process time can be shortened. For partial removal, the layer is removed within a circular area from the back side of the wafer by suitable etching techniques. The layer is still present within the area surrounding said inner circular area. For example, said material layer or material layers can be formed of nitride, polysilicon or all known variations of oxides such as BPSG or siliconoxide . They all have more or less compressive or tensile stress to cause wafer warpage. Advantageously, in a lithographic process the invention redu- ces the necessity of non-linear correction algorithms with respect to reduced software and measurement capacity and therefore reduced process cycletime. It eliminates the root cause with the effect that no compensation of the symptoms is necessary. Over all a better product quality can be achieved. According to an embodiment of the present invention, the deposition and the removal of the material layer on the back side is part of a common DRAM process forming gate contact interconnects over the front side of the wafer, said wafer comprising a silicon substrate with active areas at that stage. For forming gate contacts the back side layer may be removed partially or completely according to the desired amount of reduction of bowing stress. The accompanying sequence of process steps is described with respect to the drawings be- low. In a preferred embodiment, said material layer or material layers are removed by spin etch processing using an acid process . In a spin etch tool preferably a chemical consisting of HF (e.g. 49% HF at 40°C) etches the layers on the back side of the wafer. In the aforementioned DRAM process, the process time could be about 360 seconds to remove as much ni- tride as necessary to reduce the wafer warpage to acceptable levels. To take it off completely it can take about 720 seconds, for example. Thereby it has to be taken into account that the attack on the wafer edge on the front side of the wafer should be minimized. In a further embodiment of the invention, the wafer bowing stress of the material layer on the back side is relieved by removing the material layer by a plasma backetch processing in a single wafer tool or batch tool with the front side of the wafer protected by a removable protective material . Preferably, said protective material can be formed of a film such as photoresist or other suitable removable film. Advantageously the process uses plasma processing to remove the back side films using chemistries that are known in the art to achieve rapid throughputs. After the processing, the front side protecting film is removed by a solvent, ashing or other cleaning processes . According to another embodiment, said material layer is removed by liquid acid processing in a immersion tank in a single wafer tool or batch tool with the front side of the wafer protected by a removable protective material. Advantageously, the process uses an acid, acids, or other chemical combina- tions to remove the back side films using chemistries that are known in the art to achieve rapid troughputs . After the processing, the front side protecting film is removed by solvent, ashing or other cleaning processes. In a further embodiment, said material layer is removed by a vapor phase processing in a single wafer tool or batch tool. Preferably, the process uses an acid vapor, vapor of various acids or other chemical vapor combinations to remove the back side films using chemistries that are known in the art to achieve rapid throughputs. After the processing, the front side protecting film is removed by solvent, ashing or other cleaning processes. In some tool designs, the front side of the wafer may be adequately protected such that front side protection is not required. Otherwise the front side of the wafer has to be protected by a removable protective material before starting the process . According to another embodiment, said material layer is removed by CMP processing with the front side of the wafer protected by a removable protecting material. Advantageously, the process uses a slurry or slurry materials, composed of abrasive materials that chemically facilitate the removal by physical means, that are known in the art to achieve rapid throughputs. After the processing, the front side protecting film is removed by solvent, ashing, physical peelback of protecting films or other cleaning processes. The invention will be explained in detail by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein Figure la shows a wafer with layers on the back side causing wafer bowing stress, Figure lb shows a wafer after reduction of the wafer bowing stress, Figure 2 shows residuals as a result of non-linear overlay distortions in a lithographic process, Figure 3a-g show schematic cross sectional views showing a process of making gate contact interconnects on a silicon wafer with active areas. Figure la shows a wafer 1 and a stepper chuck 2, where said wafer 1 is placed upon. Since the front side and the back si- de of the wafer 1 are deposited with a material layer causing bowing stress, e. g. with a nitride layer, with the material layer structured over the front side, the bowing stress on the back side is larger than the opposite bowing stress on the front side. The result of the unequal bowing stress is wafer warpage, in case of figure 1 causing the ends of the wafer 1 to lift off the stepper chuck 2. Disadvantageously, defocus of patterns on the wafer surface and non-linear overlay errors could arise when applying a lithographic process to wafer 1. Figure lb illustrates said wafer 1 after reduction of the wa- fer bowing stress. For example, by etching the material layer over the back side of the wafer 1 partially in accordance with the desired reduction of the bowing stress, wafer warpage of wafer 1 is reduced. Thus, this results in reduced defocus and non-linear overlay errors in a lithographic process . Figure 2 shows residuals on the surface of wafer 1 as a result of non-linear overlay distortions in a lithographic process schematically illustrated by small vectors showing the positions of said residuals. The stepper parameters are already optimized to eliminate linear overlay distortions. Figure 3a-g schematically illustrate a process of making gate contact interconnects on a silicon wafer with active areas. The present invention is applicable advantageously to said process. Nevertheless, the invention can also be used in other processes with the problem of wafer warpage in correlation with reduced process performance. First, as shown in figure 3a, the wafer 1 comprising a silicon substrate 10 with active areas is deposited with layers of gate oxide 11, polysilicon 12, which is doped with phosphorus, and metal 13, namely tungsten silicon in this case, on the front side. For example, the polysilicon layer 12 and the metal layer 13 are deposited by a CVD process. Then, typically, in a furnace diffusion process encapsulating material layers 14 and 14', herein formed of nitride, are deposited over the front side and the back side of the wafer 1, respectively. Figure 3b is a cross section after structures of photoresist 15 have been formed on the nitride layer 14 over the front side in a lithographic process. Thereafter, a predetermined structure of gate contact interconnects 30 (GC-interconnects) according to the structure of photoresist 15 is formed, illustrated in figure 3c, by etching said deposited layers. Wafer warpage is caused as a result of unequal wafer bowing stress. In the following process steps, as shown in figure 3d, there is deposited a thin insulating layer 16 such as nitride or oxide on the GC-interconnects 30 over the front side of the wafer 1. Preferably, said insulating layer 16 is for means of protecting the GC-interconnects 30 in the following various ion-implantation process steps over the front side of the wa- fer 1. Thereafter, according to an embodiment of the present invention, the process of back side etching is performed to remove the nitride layer 14' partially. Thereafter, the gaps formed by the structure of the GC-interconnects 30 on the wafer surface are filled with a deposited insulating layer 17 such as oxide. The following process step is a CMP processing step for planarizing said insulating layer 17. As shown in figure 3e, again an insulating layer 18 such as oxide is deposited over the front side of wafer 1. Preferably, said insulating layer 18 is formed of another type of oxide as the insulating layer 17 between the aforementioned gaps to perform a selective etch processing of both oxides in one of the following processing steps. Thereafter, another lithographic process is applied over the front side of wafer 1 to form a structured mask for the following etch processing, as indicated with photoresists 19 in figure 3f . The performance of said lithographic process is improved by the preceeding back side etch processing with the result of reduced wafer warpage. Thereby, several kinds of lithographic processes are applicable such as optical lithography, ion lithography, X-ray lithography or lithography with electron beam. Finally, as shown in figure 3g, contacts 20 to the implanted areas 21 of the substrate 10 are formed by applying several process steps of etching, measuring and cleaning.

Claims: Claims 1. A method for manufacturing of a semiconductor device using a wafer (1) having a front side and a back side, said method comprising the steps of - depositing at least one encapsulating ' material layer (14, 14') over said front side and back side of the wafer (1), - etching said material layer (14) selectively over the front side of the wafer (1) to form a predetermined structure, thereby causing wafer warpage as a result of bowing stress of said material layer (14, 14')/ - removing said material layer (14') over the back side of the wafer (1) partially from said back side in accordance with the desired reduction of the bowing stress, - applying in the further course of the manufacturing process a lithographic process to said front side of the wafer (1) , a CMP process or a process that uses electrostatic, physical clamping or vacuum clamping for holding the wafer (1) . 2. A method for manufacturing of a semiconductor device according to claim 1, wherein said wafer (1) is of at least 300 millimeter in diameter . 3. A method for manufacturing of a semiconductor device according to anyone of claims 1 or 2 , wherein said material layer (14, 14') is formed of nitride. 4. A method for manufacturing of a semiconductor device ac- cording to claim 3, comprising the steps of - depositing a gate oxide layer (11), a polysilicon layer (12) and a metal layer (13) over the front side of the wafer (1), said wafer (1) comprising a silicon substrate (10) with active areas, - depositing said material layer (14, 14') over the front side and back side of the wafer (1) , - etching said layers (11, 12, 13, 14) selectively over the front side of the wafer (1) to form a predetermined structure of gate contact interconnects (30), - depositing an insulating layer (16) over said gate contact interconnects (30) over the front side of the wafer (1), - applying an ion implantation process over the front side of the wafer (1) , - etching said material layer (14') partially over the back side of the wafer, - depositing at least one insulating layer (17, 18) over the front side of the wafer (1) , - applying a lithographic process over the front side to form a structured mask (19) for the following etch processing to form contacts (20) to implanted areas (21) of said substrate (10) . 5. A method for manufacturing of a semiconductor device according to anyone of claims 1 to 4 , wherein said material layer (14') over the back side of the wafer (1) is removed by spin etch processing using an acid process . 6. A method for manufacturing of a semiconductor device according to anyone of claims 1 to 4 , wherein said material layer (14') over the back side of the wafer (1) is removed by plasma backetch processing in a single wafer tool or batch tool with the front side of the wafer (1) protected by a removable protective material. 7. A method for manufacturing of a semiconductor device according to anyone of claims 1 to 4 , wherein said material layer (14') over the back side of the wafer (1) is removed by liquid acid processing in an immersion tank in a single wafer tool or batch tool with the front side of the wafer (1) protected by a removable protective material . 8. A method for manufacturing of a semiconductor device according to anyone of claims 1 to 4 , wherein said material layer (14') over the back side of the wafer (1) is removed by vapor phase processing in a single wafer tool or batch tool . 9. A method for manufacturing of a semiconductor device according to anyone of claims 1 to 4 , wherein said material layer (14') over the back side of the wafer is removed by chemical mechanical polishing processing with the front side of the wafer (1) protected by a removable protective material .

Inventors: KNEUPEL INES, KRAXENBERGER MANFRED, MAUTZ KARL, SCHEDEL THORSTEN, SPULER BRUNO, KNEUPEL, INES, KRAXENBERGER, MANFRED, MAUTZ, KARL, SCHEDEL, THORSTEN, SPULER, BRUNO
Applicants: INFINEON TECHNOLOGIES AG, KNEUPEL INES, KRAXENBERGER MANFRED, MAUTZ KARL, MOTOROLA INC, SCHEDEL THORSTEN, SEMICONDUCTOR300 GMBH & CO KG, SPULER BRUNO, KNEUPEL, INES, KRAXENBERGER, MANFRED, MAUTZ, KARL, MOTOROLA INC., SCHEDEL, THORSTEN, SEMICONDUCTOR300 GMBH & CO. KG, SPULER, BRUNO
Application year: 2000
Main classification: H01L21
IPC codes: H01L21