DE2911503A1 - METHOD FOR PRODUCING STRUCTURES FROM POSITIVE PHOTO PAINT LAYERS WITHOUT INTERFERING INTERFERENCE EFFECTS - Google Patents

Description

SIEMENS AKIIEiTGESELLSCHAET Our mark Berlin and Munich VPA 7g ρ 7 Q 4 ι pon

Process for the production of structures from positive photoresist layers without disruptive interference effects

The present patent application relates to a method for the production of structures from positive photoresist layers without disturbing interference effects on for integrated Semiconductor circuits provided substrates.

Processes of this type are used in semiconductor technology for the production of masks on photoresist layers. Such a method is known from DE-PS 25 34 795, for example. In this procedure will be Structures made of positive photoresist layers on a reflective, in particular with profile steps provided semiconductor substrate produced by. a positive photoresist layer on the substrate surface is applied, then exposed and developed, whereby the exposed areas are removed.

Edt 1 The / March 21, 1979

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To close tolerances of the lateral dimensions of the photoresist structures adhere to, it is necessary that the light intensity in the exposed areas as possible is the same, i.e. a variation in intensity within the exposed areas or of exposed Area to exposed area is undesirable. This is because a greater intensity leads to after development Use of positive resist for smaller dimensions of the photoresist structures and thus for electrical scattering Parameters or the failure of the semiconductor components produced in this way.

The light intensity "coupled" into the photoresist layer during exposure can now fluctuate locally, even if the areas to be exposed hit Light intensity is the same across all these areas. The reason for this different coupling are interference effects that occur when exposed to monochromatic light are particularly pronounced.

The cause of the intensity fluctuations causing the interference effects are in the photoresist thickness fluctuations to look for (even small fluctuations in thickness of 50 nm can lead to intensity fluctuations of up to lead to a paktor 2).

In the method described in DE-PS 25 34 iffi mentioned at the beginning, the uneven structure widths resulting from the differences in thickness are avoided by the fact that the photoresist layer prior to the actual exposure to monochromatic light of an intensity which is at least half an order of magnitude smaller than the average intensity is during the actual exposure, is uniformly pre-exposed over the entire area and then pre-developed, the pre-exposure time being selected so short that

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len, where the paint thickness is an integral multiple of half the wavelength of monochromatic light is, the removal rate remains lower than at the points where the paint thickness is an odd multiple of a quarter of the wavelength. The pre-development time is chosen so that at the points where the paint thickness is an odd multiple of a quarter of the wavelength, the lacquer thickness by an odd multiple of a quarter of the Wavelength is reduced. The actual exposure then takes place with a wavelength at which only produce minimum intensity levels on the paint surface.

The effect of different intensity coupling in the photoresist layer can also be reduced by exposure to broadband light or exposure to several wavelengths (RM Finnila, SC Su and AJ Braunstein, Soc. Photoopt. Instrum. Eng. J., Vol. 55, p. $ 8 (1974)).

It is also known that the effect of different intensity coupling in the photoresist layer the less pronounced, the less reflective the semiconductor substrate, the thicker the photoresist layer and the more the photoresist layer absorbs the light (D. Widmann, H. Binder: Linewidth Variations in Photoresist Patterns on Profiled Surfaces ", IEEE Transactions on Electron Devices, Vol. ED-22, Ho. 7, pp 467-471 (1975)).

It is the object of the present invention to provide a further method of the type mentioned at the beginning

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to the tolerance deviations caused by the different intensity coupling in the photoresist layer the lateral dimensions of the structures can be reduced in a simpler manner.

This object is achieved in that to reduce the effect of the different intensity coupling during exposure, the photoresist layer is combined with at least one additional, translucent layer before exposure, the thickness dg of this layer and its refractive index n _g that of the additional layer during exposure Layer prevailing wavelength A- "of the light used is adapted so that the light waves reflected from the substrate surface are no longer reflected back into the photoresist layer.

It is within the scope of the invention that the thickness dg and the refractive index n _{g of} the additional layer (s) meet the following conditions:
dg = (m - 1)

where m is a ⁴ whole positive number, ^ - _{g is} the wavelength of the light used in the exposure and n ,. is the refractive index of the photoresist.

In a modification of the proposed solution, one or more additional layer (s) with a thickness

7-

index η i ^ 1, 7 · η-τ can be used

cL_ = (with m = 1,2,3 ...) and a refractive

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In a further development of the inventive concept it is provided that the additional layer (s) on the To apply the photoresist layer located on the semiconductor substrate. But it is also possible to use the additional Layer (s) with a suitable thickness and suitable refractive index directly onto the semiconductor substrate and then then apply the photoresist layer. The layer can also consist of several thin layers with different Refractive indices exist. The thicknesses of the individual layers and their refractive indices can thus be combined that they have the same effect as the single layer previously described.

Further explanations of the invention can be found in FIGS. 1 and 2 and the associated descriptive text. It shows:

Figure 1 in a schematic representation of the incident Light wave 1 and the reflected light waves 2 and 3 for the Pail of a photoresist layer 5 on a reflective Semiconductor substrate 4 without an additional transparent layer 6 and FIG. 2 shows the arrangement a transparent layer 6 with a suitable thickness which is additionally applied to the photoresist layer 5 and suitable refractive index.

FIG. 1: Depending on the phase position between the light sources and 3, a different amount of intensity is coupled into the photoresist layer 5 located on the substrate 4. Maximum coupling occurs when the phases are identical. This is the case when the thickness dr of the photoresist layer 5 satisfies the condition: _{- L} = (m − 1). | _L ,
where m = T, Z, 3, 4 ... A ^ is the exposure

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length of time in the photoresist 5 .. It is / i- ^ = /? _T

where % is the wavelength of light in a vacuum and nr the

Refractive index of the photoresist are. 5

Calculation of shaft 3 (according to Figure 1):

Let the amplitude of the electric field vector of waves 2 and 3 be E ₂ and E ~, respectively.

According to the Fresnel relation, E, n _L - 1
E ₂ = S ₁ -TT

For example, for the AZ 1350 photoresist from Shipley, n ^ = 1.68 (at /? _Ύ = 436 mn). This results in E ₅ / E ₂ = 0.254.

Figure 2: The calculation of shafts 3 'and 3' 'results according to the Fresnel relationship:

(for η = ⁿ L + 1 ) *)

E ₀ n _L + n _s 3η,. + 1 ' ^s

j ₁ ^
E ₂ I ₂ "3n ^ + 1

^E 2 «= ⁿ a - 1 = ⁿ L - E ₂ T n _s + 1 D ₁ , +

+ 2)

J _{2 2 1} + 3; (3n _L + i;

*) Example: for n-r = 1.68, η should be between 1.25 and 1.4 lie.

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= ^Ε 2 = ²ⁿ L

+ 1

iit _ \ '-> * τ. τ * -) ν · "τ. - 1) E ₂ E ₂ ^ E ₂ ""X3n _L + 1 r (Hj ₁ +3)

If d _s = (m - \ ). ^ P. (m = 1, 2, 3, ...), the waves E ₃ and E _{3 are} out of phase. It is then

E ₃ ^ E ₃₁ , _ E ₃ , ^ (2n _L + 2) ² (n _{I |} - 1) _ (n ^ - 1) "~" = T ₀ (3n _Ti + ir (n _T. + 3;

Pur n _L = 1.68 (valid for AZ 1350 H) results

E ^ E ^ _n E ,,
2 -2-g 2i. = 0.1144-0.1125 = 0.0019

Compared to the case in which no additional, transparent layer 6 lies over the photoresist layer 5, the result is an almost complete extinction of the wave 3 (wave 3 = sum of wave 3 ¹ and wave 3 ^fI ).

The one on the photoresist or between the photoresist and the semiconductor substrate applied additional, translucent layer 6 (layer thickness in the range from 30 to 100 nm)

pe can be an organic or inorganic layer, preferably consisting of fluorides, which is produced by means of spin coating or dip coating or vapor deposition, for example in the plasma of reactive gases such as CF., CClF ₃ , SiF ,, C ₂ Fg, Cl ₂ , BCl ₃ or by means of a Vacuum coating process has been applied. These layer (s) must either be removed before development in a solvent that does not attack the lacquer, or they must be soluble in the developer.

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The method according to the teaching of the invention is distinguished from that known from DE-PS 25 34 795 Procedure is characterized by its ease of implementation and its reproducible results.

2 figures

10 claims

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Claims (10)

vp _A 79 P 7 0 4 1 FRG Claims Process for the production of structures from positive photoresist layers without disruptive interference effects on substrates intended for integrated semiconductor circuits, characterized in that, in order to reduce the effect of the different intensity coupling during exposure, the photoresist layer is combined with at least one additional, light-permeable layer prior to exposure, the Thickness d of this layer and its refractive index η is adapted to the wavelength ε> of the light used during exposure in the additional layer so that the light waves reflected from the substrate surface are no longer reflected back into the photoresist layer. 2. The method according to claim 1, characterized in that the thickness d _e and the refractive index n "of the additional layer (s) meet the following conditions · »_ N _T + 1 d_. = (m - £) - * ψ and η = where m is a positive integer, / t is the wavelength of the light used during exposure in the additional layer and n _{T is} the refractive index of the photoresist. 3. The method according to claim 1, characterized in that the thickness d "and the Refractive index η of the additional layer (s) as follows Conditions suffice d _s = m % ψ- and n _g ^ 1.7 n _L , 030039/0495 ORiOINAL INSPECTED 79 P 7 0 4 I FRG where m is a whole positive number, Λ_ is the wavelength of the light used during exposure in the additional layer and n _{L is} the refractive index of the photoresist.
5 4. The method according to claim 1 to 3, characterized in that the additional Layer (s) is applied to the photoresist layer located on the semiconductor substrate. 5. The method according to claim 1 to 3 »characterized in that the additional Layer (s) is applied directly to the semiconductor substrate and only then the photoresist layer. 6. The method according to claim 1 to 5, characterized in that for the additional Layer (s) an organic or inorganic material, preferably consisting of fluorides, with a smaller Refractive index is used as the photoresist, which either prior to developing the exposed photoresist layer can be removed with a solvent resistant to the photoresist layer, or in the developer the photoresist layer is soluble. 7. The method according to claim 1 to 6, characterized in that the additional Layer by spinning or dipping or vapor deposition or by means of a vacuum coating process is applied. 8. The method according to claim 1 to 7, characterized by the use of reaction products generated in the plasma from reactive gases such as CF ^, CClF ^, SiF ^, C ₂ Fg, CIp, BCl ^ ₅ as additional layer (s). 030039/0495 79 P 7 O h 1 BRO 9. The method according to claim 1 to 7, characterized in that alkali fluorides or Magnesium fluoride can be used. 10. The method according to claim 1 to 9, characterized in that the layer thickness of the additional layer (s) is set to a range from 30 to 100 nm. 03O039 / 0A95