The present invention relates to a method of manu- facturing a matrix for making optical storage media. The invention also relates to a blank for a matrix as well as a raw matrix.

When making optical storage media, such as compact disks, use is made of what is referred to as matrixes as a form for the information-carrying structure of the storage medium. The matrix constitutes one half of a mould for moulding said storage media. A matrix con- sists of a circular, planar plate of metal, in which a central opening is formed. The opening is used in the making of storage media.

In the methods that are traditionally used for making optical storage media, matrixes of metal are manufactured one by one by the matrixes being built up on a substrate provided with a pattern. This is time-consuming and costly work which comprises a plurality of steps of manufacture and which places high demands on advanced equipment for manufacturing the matrixes.

Therefore an object of the present invention is to provide an improved method of manufacturing matrixes for making optical storage media.

A specific object is to provide a rational method of manufacturing matrixes.

A special object is to ensure a high quality in the manufacture of matrixes.

According to the invention, these and other objects that will be apparent from the following description are now achieved by a method according to appended claim 1.

The objects are also achieved by a blank for a matrix according to appended claim 6 and by a raw matrix accord- ing to appended claim 7. Preferred embodiments are de- fined in the dependent claims.

The invention is based on the idea of manufacturing in a first step a"raw matrix", which in a subsequent step is provided with an inscription by working the sur- face of the raw matrix.

According to a first aspect of the invention, a plate-shaped matrix body is formed, on which a resist coating, such as a photoresist coating, is applied on one side. This is achieved according to the invention by spinning a polymer over the body starting from a central portion of the body.

By spinning the polymer from the central portion, a uniform resist coating can easily be obtained over the entire plate-shaped body. Any irregularities are limited to the central portion.

After the forming of the resist coating, a central opening is formed in the body by removing the central portion, preferably by punching the central portion of the body. As a result, the entire resist coating will be uniform from the edge of the opening radially outwards.

Thus the matrix can be provided with a high-quality in- scription up to the edge of the opening.

By spinning, in accordance with the inventive con- cept, the resist coating from a central position and only then punching a central opening, a higher quality, a larger writing surface and lower manufacturing costs will be obtained than in the case where the resist coatings are spun after the opening has been punched.

The opening formed after removal of the central por- tion preferably constitutes the final opening which is used in the making of optical storage media. It is pre- ferred for the matrix body to cover the entire central portion when applying the-resist since the resist mate- rial can thus be spun from a single central position.

However, the invention is rot limited in this respect. It may in some cases be advantageous to form a smaller open- ing in the body and apply the resist starting from a cen- tral area round the smaller opening, whereupon the cen-

tral area is removed. Also this embodiment is included in the inventive concept as will be expressed in the ap- pended claims.

In a preferred embodiment there is formed in a sub- sequent step an information-carrying inscription in the resist coating by an irradiation (exposure) and devel- oping process in some prior art manner, whereupon a corresponding structure is formed in the matrix body by an etching or application process.

According to a second aspect of the invention, it comprises a blank for a matrix, which has a plate-shaped matrix body extending from a central portion to a circu- lar peripheral line, and a resist coating extending radially outwards from the central portion of the body.

The central portion is adapted to be removed in a subse- quent step. No final central opening has thus yet been formed in the matrix body. In a particularly preferred embodiment, the blank has no opening at all inside the peripheral line.

According to a third aspect of the invention, it comprises a raw matrix with a plate-shaped matrix body, which has a central opening and a resist coating extend- ing from the peripheral edge of the central opening and having a uniform thickness. The raw matrix, which in itself constitutes an intermediate product in the manu- facture of a completed matrix, has thus been manufactured by forming a central opening in the matrix blank de- scribed above. Then no further change or working of the inner diameter or outer diameter is made after exposure or forming of structure, for instance by an etching or application process.

A preferred embodiment of the invention will now be described for the purpose of exemplification.

A matrix body in the form of a circular disk of nickel is formed. A suitable volume of a suitable resist material is placed in the centre of the disk, whereupon the disk is rotated sc that the resist material is spun

to a uniform layer over the matrix body which then con- stitutes a blank for a matrix. Subsequently, the central portion of the disk is punched, thereby forming a raw matrix. The raw matrix undergoes lithographic processing, in which an information-carrying pattern is exposed to radiation and developed according to prior art methods, so that the matrix body is uncovered in selected surface portions in a pattern corresponding to the information with which the matrix is to be provided. Then a structure is etched into the matrix body in the uncovered surface portions. Finally the rest of the resist coating is removed, thereby forming a completed matrix with an information-carrying surface structure. Optionally the surface structure is given a protective treatment before the matrix is ready for use.