DE1915085C3 - Process for improving the adhesion of photoresist materials to oxide surfaces and its application - Google Patents

Description

4o

The invention relates to a method for improving the adhesion of photoresist materials Oxide surfaces, in particular on silicon dioxide surfaces used in semiconductor technology.

In the manufacture of various articles, it is often necessary to protect certain areas e ner oxide surface, while others Flädien same surface for further treatment or further process steps are exposed It is gen example, in _the production of Halbleiteranordnun- ₅ c in which a semiconductor substrate is covered with an oxide layer, it is often necessary to remove certain parts of the oxide layer in order to be able to embed suitable dopants into the underlying semiconductor substrate by diffusion. This technology is characteristic of halftone arrangements, such as npn and pnp field effect tractors. Such transistors are obtained by diffusion of suitable dopants from the gas phase in half-bodies made of monocrystalline silicon. wobc, the corresponding half-liter rulers in. «. In order to preserve the separate half-items necessary for the working method. allowed the diffusion only in hcsiunrntcn Bercidun of the silicon body stattfindon These selected areas of the silicon body wcrck η norma-diffusion of the impermeable Dotiemngsstoffe The D usionsmasken ^lu _be SiIidumkörper coverage of the oxide layer with a gleichförm.gen ER- I and in which subsequently the corresponding Öffhalten _{> through which the} doping

now en s underlying silicon body

| ° £ _f £ can lose. Coated ial to form these openings have """^ _{Oxidsdlicht w} ith a gen as photoresist _Mater, which on exposure

becomes polymerized and insoluble. This photoresist- ^ y ^m ™ [ _selectively exposed so that the polymeriscm ^ ^ areas above the oxide layer

T, "finds which are to be protected later during the subsequent ^ f" ^{11 ".} The nichtpolyme- ^ '""^s' _o ° ^s _{of the} unexposed portions of the photoresist ™ ^1C _{Major (± a} solvent in which the poly _{m (r. P} ici rtp resist is not soluble, removed. Subse- ™™ _{"to the no} t protected areas of OxidI "! ♦ _by a suitable etchant such example-V. Fiußsäure, to produce the corresponding instance ™" ™ ⁵ ^

ρ ^'S _urde now been found that the during the etching

^: "_{Rtf> n} silicon dioxide surface of the photoresist

masKiei ic .- ^ ^ ^ _{oxide surface to rol} .

aie khu ^ e ^ ^^ take off. This leads to *. n _nt etching of the silicon dioxide layer below a υ. * _the photoresist, so dali after the

the beautiful _boundary layers that arise

um ^u , ' ^s _d deterioration in properties

^ " ^e ^.", | ' _foren result. Especially in the case of J " _d : _f ^r _f ^a _e J _transistors , for the formation of which at least i ftffnuneen are generated in the oxide surface _{dje dmdi diffusion of the} corresponding

J " ^ss ^ _ierungssto ff _e source and drain are formed Uot.erunfe ^ ^^ ^^ inadequate Aus" _{affect the} width of source and drain and thus also the width of the gate located between source and drain. Since at the same diffusion regions 2 are generated and the diffusing additives spread in the silicon body, growing at _"lnPr deteriorated resolution nsbesondere at a ^{vcr te} ^ ^ ^ ¹ _{DJE Wahrsche} inlichkeit of Drawn Ringer uaieu 'within the transistors.

^{tre 's} "* ™" ¹ V _"Prob lem was recognized, tried

, "A , Lt by heating before the following man first ^ f _f ^ ™ _wi 4 _{cn photoresist} ^g _and

f ^^ VcrbLcrn to allow the encryption ^ Ä / runider resolution by rolling or Suei ccmeruiig _the oxide surface to

^Abhe f " ^de "'"° _vorh eri _R e warming was, however, ^ \ _Γ ξ effect largely ab-« ehandlunR and from the upper ^ -in particular-

, such as Phos- _{Finfiuss sjd WU}

Pjorpcn oxide

hn '7'"^"
layer. ¹ yes

per ausfeget'-n.llens ode
high is I '\

_{Hcradic of} the etching solution län- ^ ^ ^^ ^ _M _

Photoresists especially previous areas

SwSSLg is not only

^^ J ^ MilJ to improve the Hafein unzum. ^ ™ _a terialien on the oxide covering ie tores, ma _the ^ ^^

flat o. cs you e sen _upper mL

nung d 1 ^^^ "" ^ _{; iur} improvement of the

unc

surfaces to apply a layer of adhesive to the oxide surfaces. However, one of the known adhesives so far none completely satisfactory. Those adhesives that have good adhesive properties are usually toxic and highly reactive with air and water vapor and also require prior treatment Warming.

The object of the invention is a method for improving the adhesion of photoresist materials to oxide surfaces so that they do not roll off or lift off during the etching.
The object of the invention is achieved by a method which is characterized in that a hexaalkyldisilazane-containing adhesive is applied to the oxide layer and the photoresist is applied to this.

It has surprisingly been found that this adhesive layer, the toxicity of which is very low and which is non-corrosive, is significantly improved compared to previously known adhesive layers Properties related to the rolling or lifting of the photoresist layers from oxide surfaces in a subsequent etching of the underlying oxide layers.

Further details and advantages of the present invention can be found in the following description, can be seen in the drawings and examples.

The F i g. 1 to 8 show successive work steps for the production of field effect transistors according to the method of the present invention. For the sake of simplicity, there are only work steps for the production of MOS field effect transistors shown.

In FIG. 1, an oxide layer 1 is applied to a silicon body 2 consisting of a single crystal. This oxide layer can be produced by known methods, such as, for example, by vapor deposition of silicon dioxide on the silicon substrate, chemical oxidation of the silicon surface with oxygen. Steam, air or other oxidizing agents or by thermal decomposition of siloxane. The thickness of the oxide layer can be between a few hundred or several hundred thousand Å and is dependent on the specific manufacture and purpose of the oxide layer. One method for producing the oxide layer is, for example, the oxidation of the silicon substrate with oxygen at a temperature between about 10 and 50 ° C., with about 2 liters of oxygen / min flowing past a silicon wafer for about 16 hours. After the oxide layer has been produced, an adhesive layer 3 consisting of a hexaalkyldisilazane is applied, which consists, for example, of hexamethyldisilazane. The adhesive layer can be applied either directly or in a mixture with a solvent such as, for example, trifluorotrichloroethane, using known coating processes. For example, the adhesive can be applied in a whirling process, in which a certain amount of the substance is spread onto the wafer and this is then evenly distributed by the centrifugal force at 3000 to 6000 rpm. The adhesive can also be applied by dipping the wafer in a solution of the adhesive. Another good practice is to expose the wafer to an atmosphere of the vaporized adhesive for a time and at a temperature sufficient to obtain the desired thickness. In the method described here, the adhesive only needs to be applied in a thickness of up to a few Å, preferably only in a molecular layer thickness.
A suitable photoresist 4 (see FIG. 2) is then applied to the adhesive layer 3. A plurality of photoresist materials can be firmly bonded to the oxide layer via the adhesive layer in accordance with the method of the invention. Among these photoresist materials, compositions based on polyvinyl cinnamate, polyisoprene, natural rubber resins, formaldehyde novolak resins, cinnamylidene or polyacrylic esters are particularly useful. These photoresist materials include a commercially available polyvinyl cinnamate-based photoresist having a molecular weight of 14,000 to 115,000; a partially cyclized poly-cis-isoprene having an average molecular weight of 60,000 to 70,000; a photoresist based on a natural rubber resin, a photoresist based on an m-cresol-formaldehyde novolak resin, and photoresist materials based on cinnamylidene or poly-styryl acrylic ester. These photoresist materials normally contain small amounts of a photoinitiator which decomposes under the action of ultraviolet light to generate free radicals which initiate the polymerization reaction. Suitable photoinitiators, which are given, for example, in US Pat. No. 2,732,301, are 2,6 bis- (p-azidobenzylidene) -4-methylcyclohexanone, diazooxides, such as the 1-oxo-2-diazo-5-sulfonate ester of naphthalene and thioazo compounds such as 1-methyl-2-mchlorobenzoylmethylene - /? - naphthothiazoIin.
The thickness of the photoresist to be applied depends on the particular photoresist and the coating technique used. Usually thicknesses between 8000 and 20000 Å are assumed. The photoresist is then exposed in the desired light pattern of the source-drain structure 5 (FIG. 2). While the distance between source and drain was previously limited by the substrate to the oxide layer that appeared during the etching process, according to the method of the present invention, both can now be much closer together. The only limitation for this distance is the degree of expansion of the dopants diffused into the silicon body. The unpolymerized areas of the photoresist are then removed with a suitable solvent, such as methylene chloride, and the surface of the wafer is then exposed to an etching solution to etch the oxide. Usable etching solutions through which the openings 5a in FIG. 3 are obtained are, for example, hydrofluoric acid buffered with ammonium fluoride; Mixtures of nitric acid, acetic acid and hydrofluoric acid. It was found that the photoresist layer remains firmly bonded to the oxide surface during the etching process and the undercut of the oxide surface is negligible - and drain areas 6 and 7, between which the gate is located. If boron is used as the p-type dopant, the diffusion with boron trioxide can be carried out for about 4 hours at 1250 ° C., with drain, source and gate being formed.

15 085

A second layer 1/1 of silicon dioxide about 1000 to 5000 Å thick can then be applied as shown in FIG. 4 specified, can be applied to the surface. For the sake of clarity, the two silicon dioxide layers 1 and IA are shown separately, although in reality they merge continuously. A layer of hexaalkyldisilazane 8 is now again applied to the silicon dioxide layer, as shown in FIG. 5 is shown. A photoresist layer 9 is then applied to this layer in a known manner and the desired pattern is produced in a known manner. The silicon dioxide is then etched in the open areas in a known manner with flood acid and the photoresist is then removed, so that an arrangement according to FIG. ft arises. Then an aluminum layer 10 is vapor-deposited onto the entire surface (FIG. 7) and then the photoresist layer 11 is applied over an adhesive layer, in which the desired pattern is produced in a known manner (FIG. 8). The aluminum is then etched away in the opened parts 11/1 of the photoresist pattern with a sodium hydroxide solution, so that the structure shown in FIG. 9 is produced. The aluminum then makes direct contact with the source and drain regions and is insulated from the gate by silicon dioxide, as is the usual structure of field effect transistors.

Although the invention has been described in its application to the manufacture of semiconductor devices it can also be used for other processes that require a layer of photoresist on top of a Oxide surface must be applied firmly. For example, the method according to the invention for the production of printed circuit cards, of thin-film memories, in which a film then through a Oxide surface is protected, in the gravure printing process as well as for the production of photo masks and can be used to coat glass plates.

It is believed that the disilazane in the adhesive reacts with the oxide of the surface, while the photoresist adheres firmly to the remainder of the molecule. The adhesive is general applicable and useful for improving the adhesion of photoresist materials to any Oxide surfaces such as silicon dioxide. Silicon rubber monoxide, aluminum oxide. Copper oxide, Beryllium oxide, titanium dioxide, zinc oxide. Nickel Oxide and Cobalt Oxide to name a few.

The examples given below serve to further describe the present invention.

50 parts by volume of hexamethyldisilazane are added to 50 parts by volume of tri-fluorotrichloroethane and mixed. A silicon wafer with a 3 to 5 μ thick silicon dioxide layer with a diameter of about 3.2 cm is then covered with the hexamethyldisilazane solution, and this is evenly distributed by rotation (4000 rpm) after 30 seconds for about 15 seconds. A photoresist composition based on partially cyclized poly-cis-isoprene containing about 6% di-n-butyl adipate is then applied to about ³ U of the front of the wafer, and then the wafer is again rotated for about 15 seconds exposed to a corresponding centrifugal force of 4000 rpm. The wafer is then kept at a temperature of about 100 ° C. for 10 minutes in order to increase the sensitivity of the photoresist and to remove any organic solvent that is still present. The thickness of the photoresist layer obtained was about 8000 A. After exposure of the photoresist layer and subsequent development

ίο the wafers were used to further manufacture a Semiconductor arrangement immersed in an etching solution. It was found that the photoresist was on the oxide surface adhered firmly and no rolling or lifting of the resist from the oxide surface could be seen.

Similar results were obtained if the photoresist was applied prior to application to the oxide surface was mixed with the adhesive and this mixture then applied to the oxide surface in one step instead of being applied in two steps as previously indicated.

Similar results were obtained with other hexaalkyldisilazanes as adhesives, wherein the alkyl group is a lower alkyl radical, for example a methyl, ethyl or propyl radical.

About the surprising improvements in adhesion when using the method according to the invention and to show the adhesive, hexamethyldisilazane was combined with other already known adhesives, as compared, for example, to chlorosilanes previously believed to have good adhesion of the photoresist layers produced on oxide layers. The one when comparing hexamethyldisilazane with dimethyldichlorosilane, trimethylchlorosilane

and phenoltrichlorosilane are shown in the table.

table

Chlorosilanes

Hexamethyldisilazane

Medium undercut in
Silicon dioxide 120 mm 0

Can be applied by

Immerse No yes

Pore formation Very low

Toxicity very toxic hardly toxic

Corrosive very corrosive- not corrosive-

Effect. Education rend

of HCl

Subsequent heating generally not required for about 15 minutes
good adhesion at 100 to 150 ¹ C

between photoresist and silicon dioxide substrate
receive

Duration, a few hours, a few weeks
rend the the
Photoresist solid
on the oxide
adheres

1 sheet of drawings

Claims (7)

Patent claims: 1. A method for improving the adhesion of photoresist materials on oxide surfaces, j characterized in that the oxide layer au an adhesive containing hexa-alkyl disilazane and on this, a photoresist is applied. 2. The method according to claim 1, characterized in that the hexaalkyldisilazane is hexamethyldisilazane or is hexaethyldisilazane. 3. The method according to claim 1, characterized in that that the adhesive is mixed with the photoresist and this mixture is applied to the oxide surface is applied. 4. Processor according to claim T, characterized in that that the oxide layer is silicon dioxide. 5. The method according to claim 1, characterized in that » indicates that photoresist materials based on polyvinyl cinnamate, polyisoprene, natural Rubber resin, formaldehyde novolak, cinnamylidene or polyacrylic ester can be used. 6. The method according to claims 1 to 5, characterized in that the photoresist em partially cyclized poly-cis-isoprene with a average molecular weight of 60,000 to 70,000 and containing azide as a photoinitiator is. . 7. Use of the method according to one or more of claims 1 to 6 for production of masking masks in semiconductor production. ^25th