EP1220262A1 - Method of manufacturing a cathode with aligned extraction- and focusing grid - Google Patents

Abstract

Method for fabricating a structure involves: forming on a substrate, first insulating layer, first level of metallization, second insulating layer and second level of metallization; opening first and second windows; forming third windows; engraving first level of metallization; engraving first insulating layer and simultaneously eliminating second insulating layer inside contour of second windows. A method for the fabrication of a structure consists of: (a) forming on a substrate (1) a pile of a first insulating layer (7), a first level of metallization (6), a second insulating layer (8) and a second level of metallization (9); (b) opening, in the second level of metallization and the second insulating layer, some first windows corresponding to the contour of the first openings and some second windows of which the external contour corresponds to the internal contour of the second openings; (c) forming in a masking layer (20) some third windows overlapping the first windows: (d) engraving the first level of metallization under the masking layer up to the internal periphery of the second windows; (e) engraving to a chosen distance the first insulating layer and simultaneously eliminating the second insulating layer inside the contour of the second windows; (f) and eliminating the masking layer.

Description

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

The operating principle and the details of the constitution of an example microtip screen are described in U.S. Patent 4,940,216 to the French Energy Commission Atomic to which we will refer for all general education on this type of screen. Usually a flat screen with microtips is formed from two glass plates. The plaque bottom has a microtip cathode structure, and one or more grid structures. The upper plate, arranged in operation opposite the bottom plate carries an anode structure. Elementary microdots are arranged in various ways, and can be addressed selectively by action on orthogonal cathode lines and extraction grid. Generally, a large number of microdots are addressed simultaneously for each pixel of a screen.

The present invention relates more particularly to the production of a screen of the type illustrated in FIG. 1. This screen includes a bottom plate or cathode plate 1 and a upper plate or anode plate 2. The upper plate includes a layer, lines or pixels of electroluminescent material or phosphor 3.

On the cathode plate 1, an upper layer corresponds to cathode conducting lines, possibly covered with resistive material. On these cathode lines microdots 5 are formed in openings of a grid 6. The extraction grid 6 is formed on a first insulating layer 7 formed on the upper surface of cathode 1. You will say that this upper surface corresponds to the top surface of the system substrate. Above the grid layer 6 is formed a second insulating layer 8 in which a second conductive layer 9 rests corresponding to a focus grid. In this grid of focusing, and in the second insulating layer 8, are formed of openings which must be precisely arranged relative to the openings formed in the extraction grid.

Various processes, described for example in the application French Patent 2,779,271 to the French Commissariat à l'Energie Atomic, are known to form self-aligned openings in the two metal levels 6 and 9 and in the insulating layers 7 and 8. However, it turns out in practice that these processes are either imprecise or difficult to implement in action. In addition, these methods do not always allow independently and precisely set the engraving withdrawal of the first insulating layer compared to the first layer conductive and removing the etching of the second layer conductive with respect to the first conductive layer.

Thus, an object of the present invention is to provide a process for manufacturing structures comprising two metallization levels and defined openings specifies 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 process applicable to the manufacture of screens with microdots.

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 insulating layer, first openings being formed in the first metallization level and in the first insulating layer and second openings larger than the first being defined in the second level of metallization and the second insulating layer. This process includes the steps of forming on the substrate a stacking of a first insulating layer, of a first level metallization, a second insulating layer and a second level of metallization, open in the second level metallization and the second insulating layer of the first windows corresponding to the outline of the first openings and second strip-shaped windows with a contour external corresponds to the internal contour of the second openings, form in a masking layer covering the structure of third windows protruding from the first windows, etching the first level of metallization in the first windows, eliminate the second level of metallization under the masking layer up to the inner periphery of the second windows, burn from a chosen distance the first insulating layer and simultaneously remove the second layer insulating inside the outline of the second windows, remove the masking layer.

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

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

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

According to an 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 firsts 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 objects, characteristics and advantages, as well as others of the present invention will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

Figure 1 shows a schematic sectional view of a structure which aims to achieve the present invention;

Figures 2 to 8 are schematic sectional views illustrating successive stages of manufacturing a structure according to the present invention; and

FIGS. 3A, 5A and 8A are top views corresponding respectively to the steps of FIGS. 3, 5 and 8.

As shown in Figure 2, to achieve a structure according to the present invention, we begin by making a stack of layers corresponding successively to substrate 1, at the first insulating layer 7, at the first level metallization 6, the second insulating layer 8, and the second metallization level 9. On this second level of metallization, a layer of photosensitive material is formed or photoresist 10. Then, by photolithography, we successively open windows in photoresist layer 10 and in the second metallization level 9. The etching in the second metallization level 9 is produced by any process isotropic or anisotropic etching.

The windows formed in layer 10 comprising, on the one hand, first windows 11 having the shape of the first openings that we want to form in the first metallization level 6, on the other hand, of the second windows 12 in the form of a strip having a desired closed contour whose edge external corresponds to the internal contour of the second openings that we want to train in the second level of metallization 9.

In the step illustrated in FIG. 3, the openings by etching the second layer insulator 8, by any vertical anisotropic etching process, by example by plasma attack.

Figure 3A shows an example of a top view of the structure shown in section in Figure 3. You can see the form of the first windows 11 and of a second window 12 in strip shape. Note that the shapes of the various windows shown in this top view and in the top views below are only one example of how the present invention. The first windows will usually have a circular shape substantially identical to that shown to receive spikes 5, as shown in the figure 1. On the other hand, the second windows can have any shape chosen. They may be concentric circular rings at the first windows, each second opening including a and only one first opening. It could be as it is represented by a band surrounding a plurality of firsts openings. These first openings can be arranged in line, as shown or grouped from any other desired way. In addition, the contours of the second openings can be chosen to obtain any focusing effect longed for.

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

In the step of figure 5, using the mask corresponding to the openings in the second level of metallization 9 and in the first insulating layer 8, we open the first metallization level 6 to thereby form first openings sought corresponding to the outline of first windows.

FIG. 5A shows an example of a top view of the structure shown in section in Figure 5. We can see a example of the shape of the third window 22.

In the step illustrated in Figure 6, we start with remove the second metallization level by wet etching 9 from its upper surface discovered by the third window and we prolong this wet etching until eliminating laterally the entire second metallization level up to internal contour 2 of the second annular windows. We will use a specific wet etching product allowing engrave 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 metallization level.

In the step illustrated in FIG. 7, assuming that the first and second insulating layers are made of the same material, or at least of materials that can be etched by the same etching product, wet etching is used to attack these insulating layers. The entire 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 with 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 quickly. The duration of the etching is chosen so that the shrinkage d of the first insulating layer 7 relative to the contour of the first opening is of a chosen value. Wet etching can be preceded by an anisotropic partial etching.

Finally, in the step illustrated in FIG. 8, we eliminated the second layer of photoresist 20 to obtain the structure sought. Thus, as shown in Figure 8 in view section and Figure 8A in top view, we made the first openings in the first metallization level 6, a etching in the underlying layer back from a distance d well determined with respect to this opening, and a second opening in the second metallization level 9 and the first insulating layer 8 whose distance is perfectly fine determined by the unique mask used in the figure step 2. The size of this second opening is determined especially independently of any engraving operation on the first insulating layer. Note that the third mask of Figure 4 has no critical character and that none of the dimensions of the final structure does not depend on its outline.

Various engraving materials and techniques may be used by those skilled in the art to realize the structure sought. For example, the first and second layers insulators may be made of silicon oxide, the first level metallization in niobium and the second level of chrome plating. However, other materials may be chosen and, as previously stated others shapes can be used for second openings in the second metallization level and the insulating layer Underlying.

Claims (6)

Method for manufacturing a structure comprising 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 being defined in the second metallization level and the second insulating layer, characterized in that that it includes the following stages: forming on the substrate a stack of a first insulating layer (7), a first metallization level (6), a second insulating layer (8) and a second metallization level (9), open in the second metallization level and the second insulating layer of the first windows (11) corresponding to the outline of the first openings and of the second windows (12) in the form of strips whose external outline corresponds to the internal outline of the second openings, forming in a masking layer (20) covering the structure of the third windows extending beyond the first windows, engrave the first level of metallization in the first windows, eliminating the second metallization level (9) under the masking layer up to the internal periphery of the second windows, engrave the first insulating layer (7) from a selected distance and simultaneously eliminate the second insulating layer (8) inside the contour of the second windows, remove the masking layer. Method according to claim 1, characterized in that the etchings of the second metallization level, of the second insulating layer and of the first metallization level along the contour of the first windows are vertical anisotropic etchings. Method according to claim 1, characterized in that the first and second metallization levels are made of separate materials which can be etched selectively. Method according to claim 3, characterized in that the material of the first metallization level is niobium and the material of the second metallization level is chromium. Method according to claim 1, characterized in that each second opening surrounds a first opening. Method according to claim 1, characterized in that each second opening surrounds a group of first openings.

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