FR2578065A1 - METHOD FOR IMAGE ENHANCEMENT IN POSITIVE PHOTOGRAPHIC RESERVE MATERIAL BY IMAGE INVERSION - Google Patents

Abstract

THE INVENTION CONCERNS PHOTOLITHOGRAPHY TECHNIQUES. AN IMAGE INVERSION PROCESS INTENDED TO FORM A NEGATIVE IMAGE ON A SURFACE BY USING A POSITIVE PHOTOGRAPHIC RESERVE MATERIAL INCLUDES IN PARTICULAR THE FOLLOWING OPERATIONS: THE RESERVE MATERIAL IS EXPOSED TO ACTINIC RADIATION 3, THROUGH A MASK, TO FORM AN ACID IN THE EXPOSED PARTS; THE RESERVE MATERIAL IS THEN SUBJECTED TO A TREATMENT WITH A HEATED AMINE VAPOR 4, WHICH MAKES THE ACID INSOLUBLE IN ALKALINE SOLUTIONS AND RELATIVELY INSENSITIVE TO SUBSEQUENT EXPOSURE TO LIGHT; THE ENTIRE SURFACE IS SUBJECTED TO A GENERAL EXPOSURE 5; AND THEN DEVELOPED RESERVE MATERIAL 6 TO REMOVE THE PARTS EXPOSED DURING THE GENERAL EXPOSURE. APPLICATION TO THE MANUFACTURING OF INTEGRATED CIRCUITS.

Description

In the semiconductor industry, the manufacture of

  The use of integrated circuits makes extensive use of photographic resist material processes to define preselected circuit images of predetermined dimensions on a surface of a substrate. This is accomplished by a photolithography technique,

  in which a photo layer is formed on the surface

  a pattern corresponding to the structure of the cir-

  cooked, by means of an appropriately masked mask. A subsequent development operation then defines the

  desired openings in the resist material photosen-

  sible, so that the discovered regions of the substrate surface can be treated, while the

  remaining regions are protected against treatment.

  i5 Initially, masks were preferably used

  negative images and photographic reserve materials

  than negative in the manufacture of chips. However,

  inherent limitations of photoresists

  negative effects have proved insurmountable. These defects include limited resolution, use

  of a negative image, light-field masks

  and solvents which cause difficulties

  related to the environment and regulation.

  Processes employing positive photoresists have therefore replaced negative processes, and they use positive image masks generally having darker fields, and

  positive photoresists' which become

  are soluble in aqueous base solutions when exposed to light. The materials of

  Positive photographic reserves are usually

  killed from resins of the type "Novolak" soluble in

  alkalis, or similar substances, which have been

  paired with sensitizers such as diazide

  o-quinone and suspended in solvents

  such as ethyl acetate- "Cello-

  The absorption of light energy between 300 nm and

  450 nm results in a loss of nitrogen, which forms an intermediate

  highly reactive diary which rearranges into a ketene compound. After a short time (in the range of a few picoseconds), the ketene reacts with

  any water available to form an indene-carboxylic acid

  than. This desired end product is soluble in an aqueous base, while the unexposed and unreacted quinone diazide is relatively insoluble. Immersion in an alkaline developer removes regions

  exposed and creates the positive image of the mask.

  In many of the photoresist materials

  The only significant difference in commercial positive graphs is the nature of the monomeric or polymeric structures with which o-quinone diazide is combined. It is important to note, however, that each of the commercial products has been extensively researched and documented, so that important properties such as shelf life, variation of the

  reaction rate as a function of light exposure

  re, density, viscosity, etc. The definition of these properties makes it possible to accurately and faithfully repeat the

  process using the reserve material photogra-

  which is an essential requirement in the manufacture of

cation of integrated circuits.

  There has been renewed interest in recent years in the use of negative image processes to overcome the limitations of imaging and processing techniques using positive photoresists, and

  improve adhesion, reduce the effects of stationary waves

  to improve the contrast of the reserve material and

  the resulting resolution, increase the properties of

  protection against implantation, etc. For example, U.S. Patent No. 4,104,070 discloses a process for providing a negative image of positive resist material,

  based on a positive photographic resist material.

  In this process, the positive photoresist material described above is modified by the addition of a

  imidazole compound, such as 1-hydroxyethyl-2-alkylimidazo

  line. The imidazole compound decarboxylates the reaction product and the remaining indene is a dissolution inhibitor which is more hydrophobic than the

  reserve of origin. The exposed region becomes insolent

  and subsequent operations of general exposure and

  of development remove the regions not exposed to

  gine. This process has a significant disadvantage that the imidazole compound is highly unstable. Imidazole forms a suspension rather than

  solution, with the photographic reserve material posi-

  This leads to difficulties in maintaining a uniform dispersion of imidazole throughout the reserve material. In addition, imidazoline reacts chemically with

  quinone diazide, which affects the properties of

  sensitivity. The positive photoresist material thus becomes difficult to handle and its reactivity is less predictable. These limitations make the process

  absolutely not suitable for a manufacturing process.

  The invention generally consists of one

  original cessation to form a negative image using

  a mask corresponding to a negative image, and a material

  re of positive photographic reserve. An essential feature of the process is that it uses an original image inversion operation after exposure

  to obtain the negative image, without resorting to a modification

  cation of the positive photoresist material. The process also provides image enhancement by mastering the geometric configuration of portions of the photographic resist material that

define the image.

  The image inversion method for forming a negative image on a surface using a

  positive photographic reserve includes a first ope-

  surface forming a coating of a positive photoresist containing a sensitizer, such as o-quinone diazide, which

  forms an acid under the influence of exposure to

  actinic act. The resist is treated to form a uniform layer by drying, moderate baking or other known techniques. The layer is then exposed

  photographic reserve material by means of

  actinic activity, through a mask or similar structure

  to form an image, and the exposed parts react

  acid, such as an indene-carboxylic acid

  that which is soluble in aqueous base solutions.

  An important process operation is the exposure of the photoresist to a heated amine vapor treatment which neutralizes the acid in the reaction product, for example by decarboxylation of the indene carboxylic acid. . Indene or the remaining analogue substance is a potent dissolution inhibitor. Treatment with amine vapor also renders light-exposed regions relatively insensitive to subsequent exposure to light. Steam treatment is followed by a

  general exposure of the whole surface, to make

  parts of the photographic resist material that were not originally exposed because they were protected by the mask. The photoresist material is then grown in an alkali developer to remove the parts exposed to general exposure. The remaining regions of photographic resist material are constituted by the exposed portions through the mask, in relief relative to the

  surface, and they define the negative image of the

  origin through the mask. Thus, the invention takes advantage of the advantages of image formation by a dark field mask, while also using the properties of

  generally higher standards of photoresists

positive graph.

  The invention will be better understood when reading

  the following description of an embodiment and in

  Referring to the accompanying drawings in which: Figure 1 is a functional block diagram of the process of forming negative photolithographic images by the use of positive photoresist compounds; Figs. 2-6 are a sequential series of elevational representations of a substrate, showing various stages in the process shown in Fig. 1; Fig. 7 is a simplified representation of high intensity imaging exposure through a narrow mask aperture; Fig. 8 is a simplified representation of a low intensity imaging exposure through a narrow mask aperture, and Fig. 9 is a representation in the form of

  a synoptic diagram of the aptitude of the process of invention

  to define the contrast and the geometric configuration of the slopes in the region corresponding to the image and in the regions other than that of the image, by variations

treatment parameters.

  The invention generally consists of one

  image inversion to create negative images

  on the surface of a substrate using materials

  res of positive action photographic resist, in a process of photolithography. Referring to the block diagram of FIG. 1 and to the sequential sections of FIGS. 2-6, it will be noted that the preparatory operation consists in selecting a suitable substrate 11, for example silicon dioxide, aluminum, or other, and prepare on it a clean surface 12 and generally flat shape. Operation 1 The operation 1 shown in Figure 1 consists of

  to be applied to the surface 12, by any treatment

  A commercially positive photoresist containing a sensitizer which forms an acid under the effect of exposure to actinic radiation, such as o-quinone diazide or an equivalent . We can cite for such

  materials, in a non-limiting manner, the trade marks

  such as Shipley series 1300 or 1400 photographic resist materials; Kodak 800 Series; Hunt, series; etc. Operation 2 The operation 2 indicated in FIG.

  forming a layer 13 with the photoresist

  graphic, by extracting the solvent from the photographic resist material. This can be done by air drying at room temperature, or by steaming in a room.

  oven at moderate temperature, at 90 C, for about 30 minutes

  or in a similar way. The thickness of the layer 13 may be approximately 500 nm to 5000 nm or more

(Figure 2).

  Operation 3 The operation 3 indicated in FIG. 1 consists in exposing the photoresist layer 13

  through a mask 14, in a conventional manner, using

  actinic radiation, such as, but not limited to, ultraviolet light in the range of

at 500 nm (Figure 3).

  Operation 4 Operation 4 of Figure 1 involves exposing the photoresist material 13 to a vapor which is a chemical base. Steam can consist of

  amine and can be obtained from tetrahydroxide

  methylammonium, triethanolamine, anhydrous ammonium hydroxide, or a similar substance. We complete the

  treatment for a sufficient period of time and at a

  sufficient for the base vapor to react with the acid reaction product in the exposed regions 16 of the photoresist material and render these

  insoluble regions and relatively insensitive to an expo-

  later in the light. This treatment requires about 0.6 to 200 minutes at a temperature of 10O C-200 C

  (Figure 4). The vapor exposure reaction favors

  rised by the increase in temperature and

  pressure. The pressure can range from a value close to the vacuum to a value greater than

atmospheric pressure.

Operation 5

  The operation shown in FIG.

  then submit the entire surface of the

  layer of photographic resist material 13 at an exhibition

  general assembly, using actinic radiation

  uniform in a wide range of exposure intensity.

  All previously masked regions 17 are exposed and react to exposure by becoming soluble in suitable developing solvents for

  classic development of photoresist

(Figure 5).

Operation 6

  Operation 6 shown in FIG.

  is developing the layer of photoresist

  classic way for a positive photographic reserve material, using solutions

  conventional development, after which a rinse is carried out

  drying and drying. The resulting structure includes the

  parts 16 of the photographic resist material layer

  that 13 that adhere to surface 12 in regions in

  which the exposure was initially carried out

  towards the mask, while the remaining parts 17 are completely dissolved, and the surface 12 is exposed in these regions. The parts 16 thus constitute the negative of the image defined by the mask 14, formed in relief on the

surface of the substrate.

  It should be noted that the operation of exposure to amine vapor heated in a vacuum-heated oven, such as the Star 2001 / IR model manufactured by Imtec Products, Inc., Sunnyvale, can be accomplished. , California. However, other processing techniques may be used, working at normal pressure or at higher pressure, in combination with appropriate temperatures, as is known from

the skilled person.

  An important advantage of the process described above is that a negative image is formed using an unmodified positive photoresist. Thus, in the frequent situations in which a mask defining a negative image gives a darker field than a mask defining a positive image, the first of these masks can be used to help minimize reflections and diffractions.

  which degrade the geometrical configuration and the dimensions

the final image.

  In addition, the process of the invention provides

  an unrealizable mastery so far as far as

  contrast, geometric configuration and precision

  dimensional dimension and the resolution of the elements of

  ge. This progress in the micro-photolithography technique is due to the fact that the intensity and total energy of the actinic radiation projected in the initial image exposure operation are directly related to the definition of the upper part of the elements of the image. the image, while the intensity and total energy of actinic radiation

  used in the general exposure operation are directly

  related to the slope of the sidewalls and the

  the base of the elements of the image. By way of example, FIG. 7 will show an exemplary image exposure through a slot of one micron in an opaque mask 14 to expose the

  photographic reserve matter 17. Because of the proximity

  Between the wavelength of the exposure light and the width of the slit, diffraction effects and notable stationary wave patterns appear in the portion of the photoresist material.

  below the opening 21. During the exhibition

  According to the image projection light, at wavelengths corresponding to the sensitivity of the conventional resist materials, the main diffraction effect spreads the incoming light and irradiates a groove which widens at increasing depths. In fact, side lobes 22

  which diverge laterally from the vertical projection

  of the aperture 21 are significantly exposed, although they are not exposed as completely as the photographic resist material contained in the

  vertical projection of the opening. The corresponding part

  the vertical projection of the aperture is generally completely exposed over the entire thickness of the

reserve matter.

  Increasing or decreasing the image projection exposure, relative to the nominal exposure,

  which faithfully reproduces the shape of the mask, creates respec-

  Increasing or decreasing dimensions in the upper part of the image 23. If exposure is decreased from normal, the entire width of the vertical projection of the aperture is not irradiated completely. . Image projection exposure energies may radiate an image completely to the full depth of the resist layer, while the side-lobe portions 24 are only partially exposed, as shown in FIG.

  figure 8. In addition, attenuation and depth effects

  focus factor produces a negative exposure gradient as depth increases to the interface

  between the reserve material and the surface. Thus, the inten-

  The total energy of the initial exposure can define volumes 22 or 24 in which partial exposure takes place. We can actually define and master a

  continuum of variation of exposure below the opening

mask.

  It is important to note that in the parts

  partially exposed photoresist

  part of the quinone diazide or an inhibitor

  reacted so as to form an indene-

  carboxylic acid or other acid, while a

  ble of the inhibitor did not react. Invert treatment

  The reaction with the steam will set the reaction product, but the subsequent general exposure will then make at least a portion of the remaining inhibitor soluble. It results

  that parts 22 and 24 exposed marginally could

  be virtually dissolved during the development of

  to remain practically intact, depending on the level of general exposure energy applied

  to the photographic reserve material and according to the

  inhibitor tee which then remains. The effectiveness of the process

  the general exposure, which can be easily controlled, interacting with the exposure variation continuum in the resist material, selectively and accurately removes or retains virtually any

  part of the exposed regions. The general exposure operation

  This determines the angle, profile, and slope of the image walls as well as the basic dimensions of the image. In fact, by carefully defining the parameters of the process, including the temperature of the reversal treatment by the steam, the concentration, the pressure

  and the duration of steam application, as well as the energy

  of general exposure, it can be determined whether the

  22 or 24 remain in the developed image, being preserved wholly or partially. These parts generally define not only the walls

  sloping sides and lower outer parts -

  (the base) elements of the image, but also the edge portions of the upper surface of the elements of the image. These physical characteristics are directly related to the contrast of the image and are controlled by the

  drying conditions and initial exposure, the conditions

  exposure to steam, general exposure and

  Development. Because we can define beforehand

  and reproducible these parameters of the process, the pro-

  The present invention provides improved images in which the configuration can be precisely adapted.

  geometry of the picture elements to the specific use

  than in the manufacture of integrated circuits. As

  for example, an image aperture of one micron in a mas-

  that can be reproduced with a slightly narrowed geometric configuration, giving an image line width

  0.5 micron or less. This effect is an improvement

notable image.

  Figure 9 shows in a very simple form

  the determination of these geometric properties by variations in the process of the invention. When the more intense image exposure (Fig. 7), indicated at A in Fig. 9, is followed by a relatively intense overall exposure, indicated at D, the side portions 22 are substantially eliminated, and the fully exposed vertical projection gives an image element profile 27 having a planar upper surface with well defined edges and sidewalls which are generally vertical. In fact, the sidewalls can converge inward when the general exposure increases. If the intense image exposure, indicated in A, is followed by a relatively low overall exposure, indicated in F,

  the resulting picture element profile 29 retains the surface

  this superior plane and a good definition of the edges, with

  side walls inclined outwards, in direct

  a significantly enlarged base.

  When a weak image exposure (Figure 8),

  indicated in C in Figure 9, is followed by a

  general, indicated in D, the element profile

  resulting image is defined by a significant removal

  of the parts 24. The structure 26 thus comprises a

  narrow and flat upper part and a base part.

  A weak image exposure, indicated in C, followed by a low general exposure, indicated in F, gives a profile 28 of the final structure in which the parts

  24 are practically intact. The picture element 28 co.m-

  takes a narrow upper extent and a basic portion

with inclined flanks.

  It should be noted that the simplified representations of Figure 9 are extreme cases, and that there is a continuum of variation in the exposure treatments. In addition, this fine control of the final image is available without systematic deformation over the entire range of current dimensions in the manufacture of integrated circuits, from less than a micron to more than 10 microns. We must compare the extreme cases to a

  nominal image exposure, indicated in B, and an exposure

  Nominal general assembly, indicated at E, which gives an image element profile 30 having sidewalls

  vertical surfaces, an upper surface that is gener-

  horizontally, and a good definition of the upper edges

  laughing. The dimensions of this image element reproduce the dimension of the corresponding element of the mask.

Example

  A 500 nm thick thermal oxide layer was formed on a silicon substrate by techniques known in the art. The oxide surface was coated with photographic resist material

  (Shipley 1470), using a coating device

  by MTI centrifugation, to form a 1000 nm thick layer. Substrate was then subjected to moderate baking in a convection oven,

90OC for 30 minutes.

  The substrate was then subjected to imaging exposure in a TRE-800 type exposure device, using a mask bearing a test pattern having 0.75-100 micron picture elements. The resist-coated substrate exposed to a treatment with heated amine vapor was then subjected to

  produced by one of the substances indicated in the Opera-

  4 above, in a heated vacuum oven (Star 2001 / IR). The steam exposure was carried out at 90 ° C for 105 minutes. The substrate was then exposed to

  a general exposure of ultraviolet light from

  500 mJ / cm 2, using a broadband ultraviolet light source. The substrate was then grown in an aqueous alkali solution (Shipley MF-314) and rinsed in a MTI spray / circulation device. We then completed the process

  by conventional steaming at high temperature.

  It can be noted that after the establishment of the

  substrate in the Star 2001 / IR oven, and before the start

  In order to avoid steam exposure, the furnace can be programmed to vacuum-steam the resist layer and obtain the known advantages of

stoving after exposure.

  After this treatment, all ligies and all 2 micron spaces had a perfect resolution. In addition, all image lines up to 0.8 micron and spaces up to 0.7 micron had a sharp resolution. It can thus be seen that the process of the invention provides the following advantages: 1) Better resolution of existing material, which prior to invention was limited

  at 1.25 microns in the best conditions of focusing

  in the example under consideration; 2) The ability to produce an image free of systematic deformation throughout the microphotolithography range, from 10 microns to sub-micron pixels;

  3) A reduction in the effect of stationary waves

  res on the images; (4) The ability to benefit from the advantages of reverse polarity masks, such advantages including

  in a non-restrictive way, a better control of the dimensions

  Critical to the reduction of uncontrolled reflections from underlying surfaces, the

  possibility of use for a take-off treatment

  a layer formed by chemical vapor deposition, physical vapor deposition, plating, or in a similar manner, greater ability to detect underlying alignment marks, etc .; 5) The ability to master the definition of

  image by controlling the size, shape and slope of the picture elements; 6) The ability to produce an improved image by

an improvement of the contrast.

  It goes without saying that many modifications can be made to the process described and shown, without departing from the scope of the invention,

Claims (15)

  A method of forming a negative photoresist image on a substrate (11),   characterized in that it essentially comprises the opera- following   a substrate (1, 2) is applied to the substrate (11)   of positive photoresist (13),   containing a sensitizer which forms a reaction product   acidity under the effect of exposure to actinic radiation; subjecting the photoresist layer (13) to imaging exposure (3) with actinic radiation; we expose (4) the   substrate (11) to a material containing a base, which   tralizes the acid from the reaction product and makes the regions   of the relative photographic reserve material-   insoluble in aqueous alkaline solutions and relatively insensitive to subsequent exposure to actinic radiation; the photoresist layer is subjected to a general exposure (5) with actinic radiation, exposing all regions which have not been initially exposed or entirely   exhibited during the image exhibition; and we develop   (6) the image with a developer consisting of an alkali, to generally preserve the regions exposed to the image and to remove the regions of the   photographic reserve subject to the general exhibition.   Method according to claim 1, characterized in that the operation of exposing the substrate to a material containing a base (4) comprises exposing the   vapor substrate containing a base.   3. Method according to claim 2, characterized in that the vapor containing a base consists of a amine vapor.   4. Process according to Claim 3, characterized in that the exposure to amine vapor (4) is carried out   in a temperature range of about 10 C to 200 C.   5. Method according to claim 3, characterized in that the exposure to an amine vapor (4) is carried out for a duration of about 0.6 minutes to 200 minutes and at an equal pressure, greater or less than the atmospheric pressure. 6. Method according to claim 1, characterized in that the intensity of the general exposure (5) is   about 10-20 000 mJ / cm2 at the wavelength of sensi- maximum flexibility.   7. Process according to claim 6, characterized in that an increased intensity of the general exposure   (5) generally provides an increase in the number of   of slope, profile control and selection.   tivity of the wall angle for the image.   8. The method of claim 6, characterized in that an increased intensity of the general exposure   (5) generally provides an increase in the   geometric definition of the lower parts of the image, adjacent to the substrate (11).   9. Process according to claim 1, characterized   in that the intensity range of the training exposure   image (3) is about 10 to 3000 mJ / cm2 at the time of   maximum sensitivity of the reserve material.   10. Process according to claim 9, characterized   in that increased intensity of training exposure   image (3) generally provides an increase in   geometric dimensions and definition of the upper part of the image in the photographic resist material.   11. The process according to claim 1, characterized   in that it further comprises the step of stoving after exposure of the resist material, after the imaging exposure (3) and before the exposure operation to a material containing a base (4).   Method according to claim 6, characterized in that a reduced intensity of the general exposure (5) generally provides a larger base portion and   sloping side walls for the picture elements.   Method according to claim 9, characterized in that a reduced intensity of the training exposure   image (3) generally provides smaller   higher elements of the image elements.   A method of forming a negative photographic resist material image on a substrate (11), using a positive photoresist material   unmodified, characterized in that it comprises essentially   the following operations: apply (1, 2) on   the substrate (11) a layer of photoresist   positive graph (13), which comprises an o-quinone diazide sensitizer, or an equivalent resist material sensitizer; subjecting the photoresist layer (13) to an imaging exposure (3) with actinic radiation,   to decompose the exposed o-quinone diazide and to   an indene-carboxylic acid or equivalent; we   exposes (4) the substrate to an amine vapor to decarbonize   xylate indene-carboxylic acid and to make the reserve material regions partially exposed   insoluble in aqueous alkaline solutions, and   are insensitive to subsequent exposure to.   actinic radiation; the photoresist layer is subjected to a general exposure (5) with actinic radiation, to expose all regions which initially were not exposed or entirely   exhibited during the image exhibition; and we develop   loppe (6) the image with a developer consisting of an alkali, to keep the regions exposed totally or partially in the image display, and to remove   regions of the photographic reserve material its at the general exhibition.   15. Process for improving a formed image   in a layer of photographic resist material posi-   tive (13) containing a sensitizer which forms a first   first reaction product under the effect of exposure to actinic radiation, characterized in that it comprises the following operations: subjecting the layer of material   photographic reserve (13) at an exhibition of   image (3), with actinic radiation, to form in this layer a concentration gradient of the first reaction product which corresponds to the continuous exposure gradient of the imaging exposure.   (3); the photoresist resist material layer is   (13) to an inversion treatment (4) by exposing said photoresist layer to a substance which reacts with the first reaction product   to form a second reaction product having a solubility   significantly different, this second product of reaction   tion with a concentration gradient throughout   layer; the photoresist layer is subjected to   graph at a general exhibition (5) with a   actinic acid, to expose substantially all remaining sensitizer unreacted or partially reacted; the image is developed (6) by dissolving and removing the first reaction product and retaining   the second reaction product, the final image being con-   by regions in the reservoir material layer.   photographs in which the concentration gradient   second reaction product is relatively   high; and improve the image by acting on the conditions   operations of imaging exposure operations   (3), reversal treatment (4) and general exposure   (5), to determine the concentration gradient of the second reaction product throughout the layer of material photographic reserve.