JP2779528B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for forming an air bridge wiring formed on a semiconductor substrate.

<Conventional technology> Conventionally, various multilayer wiring technologies have been used to form multi-layered wiring in an integrated circuit and to form a high-density device by giving a degree of freedom in coupling between elements arranged in a substrate. Proposed. However, with the multilayer wiring, the parasitic capacitance generated between the upper wiring and the lower wiring limits the increase in the signal propagation speed of the integrated circuit. Therefore, an air bridge wiring has been developed to eliminate this drawback.

As a method of forming the air bridge wiring, there has been conventionally the following method.

In this method, after forming a resist pattern in which a region where the lower wiring and the upper wiring are in contact with each other is exposed, a thin metal layer is formed on the entire surface, and further, a resist pattern in which only a region to be an upper wiring is exposed is formed. I do. Thereafter, a desired upper layer wiring is formed by plating, and the resist is removed. By removing the resist under the upper wiring by the plating, a space is formed below the upper wiring.

The following method is also used. In this method, first, a pillar portion is erected on a lower layer wiring, then a release layer is applied so as to cover the lower layer wiring and the pillar portion, and only the upper surface of the pillar portion is exposed. After that, a metal layer to be an upper layer wiring is applied on the entire surface, and a resist pattern is formed only on the upper wiring region by photolithography thereon,
The metal layer in a region where there is no resist pattern is removed by etching. Finally, an air bridge wiring is formed by removing a lower layer wiring or a peeling layer between the substrate and the upper wiring.

<Problems to be Solved by the Invention> However, in such a conventional method of manufacturing a semiconductor device, in the case of plating, in order to form an upper layer wiring, a sputtering method and a completely different chemical method are used. It is necessary to use both plating methods. Further, the steps are complicated, for example, the lower and upper resist layers must be baked sufficiently to withstand plating.

In addition, in the latter formation method, after the pillars are erected, two release layers, ie, a release layer below the metal layer serving as the upper wiring and an upper resist layer must be applied. There was a problem of covering.

Therefore, a method of manufacturing a semiconductor device according to the present invention has an object to simplify the forming process.

<Means for Solving the Problems> According to the present invention, a lower wiring is formed on a semiconductor substrate, a pillar is erected on the lower wiring, and a photoresist for image reverse is coated so as to cover the lower wiring and the pillar. The photoresist for image reverse is selectively initial-exposed, the photoresist for image reverse is reversal baked, the entire surface of the photoresist for image reverse is flood-exposed, the photoresist for image reverse is developed, and grooves are formed on the photoresist for image reverse. By exposing the upper surface of the pillar portion, a metal layer thinner than the depth of the groove is deposited on the upper surface of the photoresist for image reverse, and the metal other than the metal layer deposited on the photoresist for image reverse and the bottom of the groove is formed. By removing the layer, a semiconductor device that forms a space below the remaining metal layer It is a manufacturing method.

<Operation> In the method of manufacturing a semiconductor device according to the present invention, the pillar portion is covered with an image reverse photoresist, and a groove having a predetermined width and a predetermined depth is formed in the photoresist by an image reverse lithography method. Then, an upper wiring is attached on the bottom surface of the groove. Step formation is performed when the upper wiring layer is formed. Thereafter, together with the photoresist, an unnecessary metal layer for the upper wiring is peeled off and removed. In this manner, the unnecessary metal layer is removed simultaneously with the removal of the photoresist when forming the upper wiring. As a result, the number of steps is reduced, and the steps can be simplified. Further, since the image reverse method is used, the taper of the groove can be formed clearly, and the wiring pattern can be formed accurately.

<Example> Hereinafter, an example of a method for manufacturing a semiconductor device according to the present invention will be described with reference to the drawings.

1 (a) to 1 (g) are cross-sectional views for explaining steps of a method for forming an air bridge wiring according to one embodiment of the present invention.

A lower wiring 12 or 13 made of a predetermined pattern of metal or the like is formed on a semiconductor substrate 11 (FIG. 1A).

Then, in order to connect the lower layer wirings 13 across the lower layer wirings 12, metal pillars 14, 14 are respectively erected on the lower wirings 13 by using, for example, a lift-off method (FIG. 2B). .

Next, a photoresist 15 (release layer) is spin-coated to a predetermined thickness (for example, about 2 to 4 μm) by a spinner so as to cover the lower wirings 12 and 13 and the pillars 14 and 14. The resist 15 is a positive resist to which a photosensitizing agent is added so as to reduce the dissolution rate in a developer under a constant exposure dose and reversal baking conditions.

Thereafter, a resist having a thickness smaller than the height of the column portion 14 remains at a predetermined bottom portion by image reverse photolithography, and a reverse tapered groove 17 whose cross section becomes narrower from the bottom portion toward the opening is formed in the resist 15. (FIGS. (D) and (e)).

That is, after spin coating of a resist, pre-baking is performed, and initial exposure is performed with weak light from a light source via a photomask 16 (FIG. 4D). As a result, the pattern of the photomask is transferred to the resist 15. Then, a reversal bake is performed to stabilize the initial exposed portion of the resist 15. Next, flood exposure is performed on the entire surface of the resist 15 to increase the dissolution rate of the unexposed portion of the resist in the alkali developing solution in the above process. That is, the initially exposed portion becomes less soluble in the developing solution, whereas the unexposed portion of the resist becomes more soluble.
Then, a groove 17 having a predetermined depth is formed in an inversely tapered shape by development with an alkali developing solution (FIG. 3E). At this time, by making the exposure amount of the flood exposure smaller than usual, a resist having a thickness enough to expose the tips of the pillars 14 and 14 is left on the bottom surface of the groove 17. The thickness of the remaining resist can be controlled by adjusting the exposure amount of the flood exposure.

Then, from this state, a metal is deposited to a predetermined thickness by, for example, a vacuum evaporation method or the like. The thickness of the metal film 18 is smaller than the depth of the groove 17. Therefore, the metal film 18 applied with a uniform thickness over the entire surface of the resist 15
(FIG. 1 (f)). The metal film 18 is directly deposited and deposited on the upper surface of the pillar portion 14 at the portion where the groove 17 of the metal film 18 is deposited on the bottom surface of the groove 17.

Thereafter, by removing the photoresist 15 by dissolving it with an organic solvent or the like, the metal films 18 other than the metal film 18 at the bottom of the groove 17 are simultaneously removed. As a result, as shown in FIG. 1 (g), a space is formed below the metal film 18 remaining as the upper layer wiring. That is, the upper wiring 18 supported by the pillars 14 and 14 above the lower wirings 12 and 13
Is formed, and the air bridge wiring is completed.

<Effect> As described above, according to the present invention, since the unnecessary metal layer is also removed simultaneously with the removal of the peeling layer at the time of forming the upper wiring, the number of steps such as an etching step is reduced, and the overall The process could be simplified.

[Brief description of the drawings]

1 (a) to 1 (g) are cross-sectional views showing steps for explaining a method of manufacturing a semiconductor device according to one embodiment of the present invention. 11 ... semiconductor substrate, 13 ... lower wiring, 14 ... pillar, 15 ... photoresist (peeling layer), 17 ... groove, 18 ... metal film.

Claims (1)

(57) [Claims] A lower wiring is formed on a semiconductor substrate, a pillar is erected on the lower wiring, a photoresist for image reverse is applied to cover the lower wiring and the pillar, and a photoresist for image reverse is formed. Selective initial exposure, reversal baking of the image reverse photoresist, flood exposure of the entire surface of the image reverse photoresist, developing the image reverse photoresist and forming grooves in the image reverse photoresist, By exposing the upper surface, a metal layer thinner than the depth of the groove is deposited on the upper surface of the image reverse photoresist, and the remaining metal layers other than the image reverse photoresist and the metal layer deposited on the groove bottom are removed. A method of manufacturing a semiconductor device, wherein a space is formed below a metal layer.