ETCHING POLYIMIDE RESIN LAYERS AND METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE HAVING A LAYER OF POLYIMIDE RESIN

Abstract: The susceptibility to etching of a polyimide resin layer is controlled by implanting ions into the layer. A high close of implanted ions, for example 1 × 10¹⁴ cm⁻² substantially prevents etching.

Description: ETCHING POLYIMIDE RESIN LAYERS AND METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE HAVING A LAYER OF POLYIMIDE RESIN This invention relates to etching polyimide resin layers and a method of manufacturing a semiconductor device having a layer of polyimide resin. Thermosetting polyimide resin is a material which can be used for forming an insulating layer in a semiconductor device having a multilayer wiring structure. The application of such polyimide resin material in a semiconductor device is disclosed in U.S. Patent No. 3,700,497. In its application in a semiconductor device, it is the heat resistivity of polyimide resin that is excellent as compared with that of other organic thermosetting resins. Further, polyimide resin can be etched with excellent reproduceability, particularly by an etching solution of the hydrazine system, and allows the formation of fine patterns. This is a very important advantage for the application of polyimide resin material in a semiconductor device. An etching technique using etching solution of the hydrazine system is disclosed in U.S. Patent No. 4,218,283. In addition to ordinary polyimide resin obtained by the condensation reaction of polyamic acid, polyimide-isoindroquinazolinedione (PIQ) as described in U.S. Patent No. 4,218,283 is also referred to in this specification as polyimide resin. When polyimide resin is used as an interlayer insulator in a multilayer wiring structure, it is often required repeatedly to form polyimide resin layers and to pattern the layers by selective etchings. In such a case, it is desirable that a previously formed polyimide layer pattern be insoluble with regard to the etching solution used in a succeeding etching process for forming a further polyimide layer pattern. The etching rate of polyimide can be changed by adjusting the composition of etching solution, but there has been no known effective means for changing the etching rate of a previously formed polyimide resin layer for a particular etching solution. If there could be provided a means for reducing the etching rate of a part of a polyimide resin layer, it would be useful in the manufacture of semiconductor devices. According to the present invention there is provided a method of modifying the susceptibility of a polyimide resin layer to etching, comprising implanting ions into the polyimide resin layer According to the present invention there is also provided a method of selectively etching a polyimide resin layer, comprising implanting ions into a selected portion of the layer, and etching the layer with an etchant, the selected portion being rendered less susceptible to etching by the etchant by virtue of the implanted ions. According to the present invention there is further provided a method of manufacturing a semiconductor device, comprising the steps of: forming a polyimide resin layer on a substrate, implanting ions into a portion of the polyimide resin layer, to substantially decrease the susceptibility of the said portion of the polyimide resin layer to etching, and carrying out selective etching of the polyimide resin layer so that etching is substantially blocked in the said portion of the polyimide resin layer. According to the present invention there is moreover provided a method of manufacturing a semiconductor device having a multilayer wiring structure, comprising the steps of: forming a first-level wiring layer on- a substrate, forming a first polyimide resin layer on the substrate to form an even surface, with at least a part of the-first-level wiring layer being exposed through the first polyimide layer, implanting ions into the first polyimide resin layer to substantially decrease its susceptibility to etching, forming a second polyimide resin layer on the implanted first polyimide resin layer and the first-level wiring layer, selectively etching kind of polyimide resin, and any kind of polyimide resin including PIQ disclosed in the above mentioned prior art reference can be used. The etching rate of a polyimide resin layer having suffered ion implantation can be reduced to such a degree as to make the layer substantially completely resistant to an etching solution of the hydrazine system. The ion implantation can be selectively carried out for a desired region of a polyimide resin layer, depending on the structure of semiconductor device to be manufactured. When a plurality of levels of polyimide resin layer patterns are to be formed on a substrate, the process of forming an upper polyimide resin pattern should take place after the execution of ion implantation into the surface of a lower polyimide resin pattern. In some cases, the execution of local ion implantation using an adequate masking layer such as a resist layer on a single level polyimide resin layer may be useful, depending on the device structure. Reference is made, by way of example, to the accompanying drawings, in which: Figure 1 is a graph illustrating the relationship between ion implantation dose and resultant etching rate of polyimide resin, and Figures 2A to Figure 2G are schematic sectional views illustrating a process for manufacturing a semiconductor device having a multilayer wiring structure in accordance with an embodiment of the present invention. Figure 1 is a graph illustrating the etching rate of ion implanted polyimide resin# layer. The graph of Figure 1 is plotted from information obtained by following the procedures described below-for polyimide resin layers subjected to various ion implantation- doses. The polyimide resin used in each case was synthesized through a curing process using a polyimide prepolymer consisting of polyamic acid marketed by the trade name of SP 760 from Toray Kabushishiki Kaisha. A prepolymer solution having a concentration of nonvolatile component of 14.6% the second polyimide resin layer to form a through hole therein, in which a part of the first-level wiring layer is exposed, and forming on said second polyimide resin layer a second-level wiring layer which is connected to the first-level wiring layer through the through hole. The present invention provides for the selectable reduction of the etching rate of a polyimide resin layer with regard to a particular etching solution. This can be made use of in a process for manufacturing a semiconductor device having a polyimide resin layer. This invention provides a method of reducing the etching rate of a part of the polyimide resin layer. An embodiment of the present invention can provide a method of protecting from damage, during the formation of -an upper polyimide pattern, a lower polyimide pattern already formed, in a manufacturing process for a semiconductor device having a multilayer wiring structure using polyimide resin as the interlayer insulator. A method of manufacturing a semiconductor device in accordance with an embodiment of the present invention includes a process for implanting an ion species into a part of a polyimide resin layer formed on a substrate, thereby selectively reducing the etching rate of the implanted area of the polyimide resin. There is no particular limitation on the species of ion which may be implanted, but it is convenient to use impurity ions such as arsenic ions, phosphorus ions and boron ions because they are in general use in the manufacture of semiconductor devices. Implantation energy can also be determined freely to a value larger than the lower limit causing sputtering, namely to a value almost equal to 10 ReV or more. In order to cause a substantial change of etching rate, it is necessary to implant the ions with a dosage of 1 x 1013 cm-2 or more, desirably 1 x 1014 cm As to the polyimide resin of which the etching rate is control by such ion implantation, there is no particular lgaitation on the was coated on a silicon substrate, preliminary curing was carried out at a temperature of 1500C and 2000 in air, thereafter further curing was carried out for 30 minutes at a temperature of 4500C in a nitrogen ambient and thereby the coated layer was converted into a polyimide resin layer. Then, boron difluoride ions (BF2+) were implanted onto the polyimide resin layer. The implantation energy was 100 KeV. Various dose amounts were employed as shown on the horizontal axis in Figure 1. The etchant used in each case was composed of 16 wt% ethylenediamine (98% aqueous solution) and the rest hydrazine hydrate (98% aqueous solution). This solution was kept at 35 C and etching of the ion implanted polyimide resin layer was carried out. The results are shown in the graph of Figure 1. As will be clear from this graph, when dosage exceeds 1 x 1013 cm 12, the etching rate of polyimide resin is substantially reduced and when ion implantation is carried out with a dosage of 1 x 1014 cm 2, the resultant polyimide resin is very nearly not etched at all. In other cases ion implantation was carried out using ion species other than BF2+, as indicated in Table 1, which also indicates change of the etching rate for different dose amounts. The polyimide resin used in each case, and etching conditions in each case, were the same as those selected for theeuperiments upon which the graph of Figure 1 is based. Table 1 Ion species Acceleration Dosage etching rate energy Arsenic (As +) 180 KeV 1x1014 atm/cm2 0.02 pm/min 1x1015 n to 0 Phosphorus (P+) 80 KeV 1x1014 " 0.05 1x1015 ". to 0 Boron (B+) 25 KeV lx1014 0.3 1x1015 n to to 0 From Table 1, it is clear that the same result as illustrated in Figure 1, can be obtained even when the ion species or the ion implantation energy is changed. Namely, etching rate is largely changed (reduced) at 14 -2 a dosage of 1 x 10 cm and moreover etching is substantially prevented in polyimide resin implanted with ions with a dose amount of 10 cm or more. Here, it should be noted that the important characteristics of polyimide resin for application in a semiconductor device, such as heat resistivity and electrical insulating properties, do not suffer any substantially deterioration at a dosage of about 1 x 10 cm Therefore, the above method for controlling the etching rate of polyimide resin layer by ion implantation can be adapted for manufacture of a semiconductor device. For example, the manufacture of a bipolar type semiconductor device having a multilayer wiring structure by - a- process embodying the present invention is explained hereinbelow with reference to Figure 2. First, as shown in Figure 2A, a substrate is prepared by the following steps:- a base diffusion region 22 and an emitter diffusion region 23 etc. are formed, using ordinary processes, on the semiconductor substrate, for example in a silicon epitaxial layer 21, whilst a lower SiO2 insulating film 24 is formed on the silicon epitaxial layer 21, and moreover electrode windows 25 and 26, etc. for the base diffusion region 22 and the emitter diffusion region 23, are formed on the lower SiO2-insulating film 24, and lower Al wirings 27a, 27b etc., which are connected respectively to the base diffusion region 22 and emitter diffusion region 23 etc., in the electrode windows 25 and 26, are formed on the lower SiO2 insulating film 24. Thereafter, as shown in Figure 2B, a first polyimide layer 28 is formed on the substrate of Figure 2A by spin coating polyamic acid solution and by a step curing process. The layer 28 is of such a thickness as to perfectly embed therein the lower Al wirings 27a and 27b etc. Desirable conditions for the use of the polyamide acid Sup¯ 760 (trade name of a product supplied by Toray Kabushiki Kaisha) as employed in the experiments upon which Figure 1 is based, are as follows. With adjustment of viscosity of the polyamic acid solution to 700 cp, spin coating is carried out by rotating the substrate at 4000 rpm. For curing the coated solution, a step curing is carried out with three steps each of 30 minutes and at 1500C, 2000C and 4500C respectively. The polyimide layer formed has a thickness of 1.3cm. Thereafter, as shown in Figure 2C, the first polyimide layer 28 is evenly removed from the surface until the upper surface of the lower Al wirings 27a, 27b is perfectly exposed. This is effected for example by ordinary oxygen cho2) plasma processing. At this time, any dent part or indentation having been formed between the lower wirings 27a, 27b is filled in by the first polyimide layer 28. The, boron difluoride ions (BF2+) with a dosage of 1 X 1015cm 2 '2or so are implanted, for example with an acceleration energy of about 100 KeV, into the surface of the substrate to be processed and, as shown in Figure 2D, a high concentration implantation region 29 of BF f is formed on the surface of the first poly + imide layer 28. In this case, a very shallow BF2 implanted region 29' is also formed at the upper surface of the lower Al wirings 27a, 27b, but it does. not cause deterioration of the quality of the wiring surfaces. Next, as shown in Figure 2E, a second polyimide layer 30 is formed, to a thickness of about lSm, on the first polyimide layer 28 and upper surfaces of lower Al wirings 27a, 27b etc. through a step curing process similar to that mentioned above using the same material as that of the first polyimide layer 28 and by executing spin coating at 4500 rpm. Thereafter, as shown in Figure 2F, a negative resist film 32 of the rubber system having an etching window 31 (for example for forming a wiring connection window giving access to a desired surface region of the lower wiring 27b) is formed by an ordinary photo process on the second polyimide layer 30. Then, with the photo-resist film 32 used as a mask, selective etching is carried out for the second polyimide layer 30 by an ordinary wet etching method using a polyimide etching solution consisting of hydrazine solution or a mixed solution of hydrazine and ethylenediamine and thereby the wiring connection window (through hole) 33 is formed in the layer 30 in which window the upper surface of the lower Al wiring 27b is exposed. In this case, as shown in the Figure, even if some misalignment occurs between the wiring connection window 33 and the lower Al wiring 27b, no indentations are formed in the displaced (exposed) polyimide resin (see 'y'} as a result of over-etching because the high + BF2+ concentration of the region 29 formed at the upper surface of the first polyimide layer 28 gives a very high resistivity to etching to exposed the region Y- Thereafter, as shown in Figure 2G, upper wiring, for example an upper Al wiring 34, which comes into contact with the lower Al wiring 27b at the wiring connection window 33, is formed on the second polyimide layer 30 by an ordinary method such as vacuum evaporation or sputtering and selective etching etc. In a-method embodying the present invention, no step is formed between.the first polyimide layer 28 exposed within the wiring connection window 33 and the upper surface of the lower Al wiring 27b as a result of misalignment between the wiring connection window 33 and the lower Al wiring 27b. Therefore defects such as cracks do not occur at the upper Al wiring 34 in the wiring connection window 33. According to the present invention, in order to selectively reduce the etching rate of a polyimide resin layer, ion implantation into the layer is carried + + + out. Preferably, impurity ions such as As , P , B BF2+ are implanted with a dosage of 1 x l014cm or more. As a result, the polyimide resin layer has a resistivity to etching by an etchant containing hydrazine. This method can be used for preventing occurrence of unwanted etching in the process of forming a through hole when using polyimide resin as an interlayer insulator for a multilayer wiring structure.

Claims: CLAIMS: 1. A method of modifying the susceptibility of a polyimide resin layer to etching, comprising implanting ions into the polyimide resin layer. 2. A method of selectively etching a polyimide resin layer, comprising implanting ions into a selected portion of the layer, and etching the layer with an etchant, the selected portion being rendered less susceptible to etching by the etchant by virtue of the implanted ions. 3. A method of-manufacturing a semiconductor device, comprising the steps of: forming a polyimide resin layer on a substrate, implanting ions into a portion of the polyimide resin layer, to substantially decrease the susceptibility of the said portion of the polyimide resin layer to etching, and carrying out selective etching of the polyimide resin layer so that etching is substantially blocked in the said portion of the polyimide resin layer. 4. A method as claimed in Claim 1, 2 or 3, in which the ions are implanted with dosage of more than 1 x 10 13cm#2. 5. A method as claimed in Claimed 1, 2, 3 or 4, in which the said ions are impurity ions selected from the group consisting of arsenic ions, phosphorus ions, boron ions and boron difluoride ions. 6. A method as claimed in Claim 2 or 3, in which the said etching is carried out using an etchant containing hydrazine. 7. A method of manufacturing a semiconductor device having a multilayer wiring structure, comprising the steps of: forming a first-level wiring layer on a substrate, forming a first polyimide resin layer on the substrate to form an even surface, with at least a part of the first-level wiring layer being exposed through the first polyimide layer, implanting ions into the firsi polyimide resin layer to substantially decrese its susceptibility to etching, forming a second polyimide resin layer on the implanted first polyimide resin layer and the first-level wiring layer, selectively etching the second polyimide resin layer to form a through hole therein, in which a part of the first-level wiring layer is exposed, and forming on said second polyimide resin layer a second-level wiring layer which is connected to the first-level wiring layer through the through hole. 8. A method as claimed in Claim 7, wherein the first polyimide resin layer is formed by a process which comprises the steps of: forming a polyimide resin coating over the first-level wiring layer on the substrate, and removing evenly a surface portion of said polyimide resin coating to expose the first-level wiring layer.

Inventors: SHINGU, MASATAKA C/O FUJITSU LIMITED, TSUKADA, SABURO C/O FUJITSU LIMITED, UCHIYAMA, NOBUHIRO C/O FUJITSU LIMITED
Applicants: FUJITSU LIMITED
Application year: 1982
Main classification: H01L21
IPC codes: H01L21, C09K13, H01L23