The present invention relates to a microfabrication technique which may be advantageously used, for example, for the manufacture of magnetic bubble memory devices, semiconductor devices, and the like. More particularly, the present invention relates to a method for forming a pattern of metal elements arranged with very small gaps therebetween on a substrate of a device.
In well-known field access types of magnetic bubble memory devices, a permalloy pattern for the propagation of magnetic bubbles (permalloy propagation pattern) is formed on the bubble-supporting magnetic layer of a substrate. The permalloy propagation pattern is constituted by a plurality of pattern elements made of thin films of permalloy. These permalloy pattern elements are chevron-shaped or half disc-shaped, for example, and are arranged with very small gaps therebetween. In a magnetic bubble memory device using 2 .mu.m diameter bubbles, the size of the gap is approximately 1 .mu.m.
The pattern of metal elements such as the permalloy propagation pattern described above is conventionally formed by using photolithographic techniques. That is, first, a pattern forming layer of metal is formed on a substrate of a device. Next, the pattern forming layer is coated with a layer of photosensitive resist material (photoresist). An optical exposure process is used to form a resist pattern corresponding to the pattern of metal elements to be formed from the layer of photoresist. Thereafter, an etching process is used to form the pattern of metal elements from the pattern forming layer.
However, the smallest size of the resist pattern which can be formed on the pattern forming layer by using the photolithographic technique is approximately 1 .mu.m. Therefore, according to the conventional method, it is impossible to form a pattern of metal elements with gaps of a size smaller than 1 .mu.m.
In recent years, there have been a number of proposals for realization of a high density magnetic bubble memory device using 1 .mu.m diameter bubbles. Such a device requires a permalloy propagation pattern with gaps of a size less than 0.5 .mu.m. In order to satisfy this requirement, the electron-beam lithographic technique or X-ray lithographic technique is used. However, electron-beam systems and X-ray systems are large in size and high priced, thereby increasing the overall cost of the equipment.