EP1220262B1 - Method of manufacturing a cathode with aligned extraction- and focusing grid - Google Patents

Description

The present invention generally relates to the realization of self-aligned structures in multilayer devices. It relates more particularly to the realization of a microtip cathode of a flat screen display.

The operating principle and the detail of the constitution of an example of a microtip screen are described in US Pat. No. 4,940,916 to the Atomic Energy Commission which will be referred to for any general teaching on this type of screen. Usually, a microtip flat screen is formed from two glass plates. The bottom plate has a micropoint cathode structure, and one or more gate structures. The upper plate, arranged in operation opposite the bottom plate, has an anode structure. The elementary microtips are arranged in various ways, and can be selectively addressed by action on orthogonal cathode and extraction grid lines. Generally, a large number of microtips are addressed simultaneously for each pixel of a screen.

The present description is aimed more particularly at producing a screen of the type illustrated in FIG. comprises a bottom plate or cathode plate 1 and an upper plate or anode plate 2. The top plate comprises a layer, lines or pixels of electroluminescent material or phosphor 3.

On the cathode plate 1, an upper layer corresponds to conductive cathode lines, optionally covered with a resistive material. On these cathode lines are formed microtips 5 in openings of an extraction grid 6. The extraction grid 6 is formed on a first insulating layer 7 formed on the upper surface of cathode 1. It will be said that this surface upper is the upper surface of the system substrate. Above the gate layer 6 is formed a second insulating layer 8 in which rests a second conductive layer 9 corresponding to a focusing grid. In this focusing grid, and in the second insulating layer 8, openings are formed which must be arranged precisely with respect to the openings formed in the extraction grid.

Various processes, described for example in the French Patent Application 2,779,271 of the Atomic Energy Commission, are known to form in a self-aligned manner the openings in the two metal levels 6 and 9 and in the insulating layers 7 and 8. Nevertheless, it turns out in practice that these methods are either imprecise or difficult to implement. In addition, these methods do not always make it possible to regulate independently and precisely the removal of the etching of the first insulating layer with respect to the first conductive layer and the removal of etching of the second conductive layer with respect to the first conductive layer.

Thus, an object of the present invention is to provide a method of manufacturing structures comprising two metallization levels and openings defined precisely with respect to each other in each of these two levels and in the underlying insulating layers.

A more particular object of the present invention is to provide such a method applicable to the manufacture of microtip screens.

To achieve these objects, the present invention provides a method of manufacturing a structure comprising on a substrate a first metallization level separated from the substrate by a first insulating layer and a second level of metallization separated from the first metallization level by a second layer insulating, first openings being formed in the first metallization level and in the first insulating layer and second openings larger than the first openings being defined in the second metallization level and the second insulating layer. This method comprises the steps of forming on the substrate a stack of a first insulating layer, a first metallization level, a second insulating layer and a second metallization level, open in the second metallization level. and the second insulating layer of the first windows corresponding to the contour of the first openings and the second strip-shaped windows whose outer contour corresponds to the internal contour of the second openings, forming in a masking layer covering the structure of the third windows projecting from the first windows, burn the first level of metallization in the first windows, eliminate the second level of metallization under the masking layer to the inner periphery of the second windows, burn a selected distance the first insulating layer and simultaneously eliminate the second insulating layer inside the cont For second windows, eliminate the masking layer.

According to one embodiment of the present invention, the etchings of the second metallization level, the second insulating layer and the first level of metallization according to the outline of the first windows are vertical anisotropic etchings.

According to an embodiment of the present invention, the first and second metallization levels are in separate materials selectively etchable.

According to one embodiment of the present invention, the material of the first metallization level is niobium and the material of the second level of metallization is chromium.

According to one embodiment of the present invention, each second opening surrounds a first opening.

According to an embodiment of the present invention, each second opening surrounds a group of first openings.

• la figure 1 représente une vue en coupe schématique d'une structure que vise à réaliser la présente invention ;
• les figures 2 à 8 sont des vues en coupe schématiques illustrant des étapes successives de fabrication d'une structure selon la présente invention ; et
• les figures 3A, 5A et 8A sont des vues de dessus correspondant respectivement aux étapes des figures 3, 5 et 8.

These and other objects, features, and advantages of the present invention will be set forth in detail in the following description of particular embodiments given as a non-limiting example in connection with the accompanying drawings in which:

• Figure 1 shows a schematic sectional view of a structure that is intended to achieve the present invention;
• Figures 2 to 8 are schematic sectional views illustrating successive steps of manufacturing a structure according to the present invention; and
• FIGS. 3A, 5A and 8A are top views respectively corresponding to the steps of FIGS. 3, 5 and 8.

As shown in FIG. 2, to produce a structure according to the present invention, a stack of layers corresponding successively to the substrate 1, to the first insulating layer 7, to the first metallization level 6, to the second insulating layer 8 is first made. and at the second level of metallization 9. On this second level of metallization, a layer of photosensitive material or photoresin 10 is formed. Then, by photolithography, windows are successively opened in the photoresist layer 10 and in the second level of metallization. 9. The etching in the second level of metallization 9 is carried out by any isotropic or anisotropic etching process.

The windows formed in the layer 10 having, on the one hand, first windows 11 having the shape of the first openings that it is desired to form in the first level of metallization 6, on the other hand, second windows 12 in the form of strip having a desired closed contour whose outer edge corresponds to the inner contour of the second openings which it is desired to form in the second level of metallization 9.

In the step illustrated in FIG. 3, the openings are extended by etching the second insulating layer 8 by any vertical anisotropic etching process, for example by plasma etching.

FIG. 3A represents an example of a top view of the structure shown in section in FIG. 3. It can be seen the shape of the first windows 11 and of a second window 12 in the form of a strip. It will be appreciated that the shapes of the various windows shown in this plan view and in the following plan views are only one exemplary embodiment of the present invention. The first windows will generally have a circular shape substantially identical to that shown to receive spikes 5, as shown in Figure 1. However, the second windows may have any shape chosen. It may be circular rings concentric to the first windows, each second opening including one and only one opening. It may be as shown by a band surrounding a plurality of first openings. These first openings may be arranged in line, as shown or grouped in any other desired manner. In addition, the contours of the second openings may be chosen to obtain any desired focusing effect.

At the step illustrated in FIG. 4, the photoresist layer 10 is removed and a second layer of photoresin 20 is deposited, which fills in particular the second windows. Then, we open a third window 22 in this second layer of The third window 22 surrounds each of the first windows or a set of first windows, but does not encroach on the second windows shown in FIGS. 3 and 3A.

In the step of FIG. 5, using the mask corresponding to the openings in the second level of metallization 9 and in the first insulating layer 8, the first level of metallization 6 is opened to thereby form the first desired openings corresponding to the outline first windows.

FIG. 5A represents an example of a top view of the structure shown in section in FIG. 5. An exemplary form of the third window 22 can be seen therein.

In the step illustrated in FIG. 6, the first level of metallization 9 is first removed by wet etching from its upper surface discovered by the third window and this wet etching is prolonged until laterally all the second level of metallization to the inner contour 2 of the second annular windows. A specific wet etching product will be used to etch the second level of metallization and not (or very little) the materials of the first and second insulating layers and the material of the first level of metallization.

At the step illustrated in FIG. 7, assuming that the first and second insulating layers are made of the same material, or at least the materials that can be etched by the same etching product, a wet etching is carried out to attack these insulating layers. All the part of the second insulating layer 8 located inside the internal contour of the second window is eliminated, both by lateral etching from the opening corresponding to the first window and by vertical etching by the etching product penetrating into the gap between the second metallization level and the photoresist layer 20. Thus, this second insulating layer 8 is eliminated very rapidly. The duration of the engraving is chosen so that the withdrawal d of the first insulating layer 7 relative to the contour of the first opening is of a chosen value. The wet etching may be preceded by anisotropic partial etching.

Finally, in the step illustrated in FIG. 8, the second photoresist layer 20 was removed to obtain the desired structure. Thus, as shown in FIG. 8 in sectional view and FIG. 8A in plan view, first openings in the first level of metallization 6 have been made, etching in the underlying layer set back by a distance of well determined with respect to this opening, and a second opening in the second level of metallization 9 and the first insulating layer 8 whose distance is perfectly well determined by the single mask used in the step of Figure 2. The size of this second opening is determined in particular regardless of any etching operation of the first insulating layer. It will be noted that the third mask of FIG. 4 is not critical and that none of the dimensions of the final structure depends on its outline.

Various materials and engraving techniques may be used by those skilled in the art to achieve the desired structure. For example, the first and second insulating layers may be silicon oxide, the first niobium metallization level and the second chromium metallization level. However, other materials may be selected and, as previously indicated, other shapes may be used for the second openings in the second level of metallization and the underlying insulating layer.

Claims (6)

1. A method for manufacturing a self-aligned structure including on a substrate (1) a first metallization level (6) separated from the substrate by a first insulating layer (7) and a second metallization level (9) separated from the first metallization level by a second insulating layer (8), first openings being formed in the first metallization level and in the first insulating layer, and second openings, larger than the first ones being defined in the second metallization level and the second insulating layer, characterized in that it includes the steps of:

   forming on the substrate a piling of a first insulating layer (7), a first metallization level (6), a second insulating layer (8), and a second metallization level (9),

   opening in the second metallization level and in the second insulating layer first windows (11) corresponding to the contour of the first openings and second strip-shaped windows (12), the external contour of which corresponds to the internal contour of the second openings,

   forming in a masking layer (20) covering the structure third windows larger than the first windows,

   etching the first metallization level in the first windows,

   removing the second metallization level (9) under the masking layer to as far as the internal periphery of the second windows,

   etching by a chosen distance the first insulating layer (7), and simultaneously removing the second insulating layer (8) within the contour of the second windows, and

   removing the masking layer.
2. The method of claim 1, characterized in that the etchings of the second metallization level, the second insulating layer, and the first metallization level according to the contour of the first windows are vertical anisotropic etchings.
3. The method of claim 1, characterized in that the first and second metallization levels are made of distinct selectively etchable materials.
4. The method of claim 3, characterized in that the first metallization level is made of niobium and the second metallization level is made of chromium.
5. The method of claim 1, characterized in that each second opening surrounds a first opening.
6. The method of claim 1, characterized in that each second opening surrounds a group of first openings.

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