JP3207827B2 - How to microfabricate wafers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for microfabricating a wafer using a photoresist material.

[0002]

BACKGROUND OF THE INVENTION Photoresist materials are widely used in the semiconductor industry. The photoresist material is easily patterned and developed by the mask. This pattern is created on the base substrate by an etching process.

[0003] Microfabrication operations require photoresists that can withstand exposure to harsh dry etching environments. Since the selectivity between the wafer and the photoresist can be very small, the photoresist must be very thick, which is typically greater than 0.025 mm (0.001 inch) . Known photoresists used to perform micromachining operations are deposited on a wafer by a process called spin coating. By using the spin coating process several times, the photoresist thickness was reduced to 0.025 mm (0.025 mm).
01 inches). The spin-coating process fills the photoresist with low spots on the wafer.

In micromachining applications, wafers can have existing low spots, such as via holes, whose diameter is typically between 10 μm and 100 μm.
m. However, if the via holes described above have vertical walls, the photoresist may not be able to completely cover the edges of the via holes, or may be thinner, and thus may be used as an etch mask. May limit its usefulness.

[0005] There are several uses for micromachining that require etching holes of different sizes into the surface. Since the etch rate usually depends on the size of the openings, large openings are etched faster than small openings. Forming both large and small holes requires two masking steps. If the holes to be initially etched are very deep, it is not possible to cover said holes with a photoresist applied using a spin-coating method, ie a spin-coating process. To eliminate this problem, the above process is totally modified so that the photoresist does not need to cover deep holes.

In order to enhance functionality, a thicker photoresist is needed that forms a tent above the low spot, rather than filling the low spot on the surface of the wafer. This allows such photoresists to cover the low spots, thus allowing at least two different sized holes to be etched in the surface of the wafer.

[0007]

SUMMARY OF THE INVENTION Briefly, the present invention relates to a method for performing micro-machining dry etching operations using a photoresist material in the form of a dry film. The present invention, in an important aspect of the one, the wafer is provided a method for micro-machining, the method already low spots
And a step of laminating a photoresist material on the wafer. The photoresist material is a dry film photoresist. The laminated wafer is then exposed to an energy source that has the effect of patterning and crosslinking the photoresist material. The dry film-like photoresist material forms a tent above a low spot having a vertical portion of a wafer, and covers the tent without causing a thinning or a discontinuous coating. It is effective for The photoresist material is developed and the laminated wafer is dry etched to form holes in the wafer .

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects of the present invention will be readily understood by referring to the following description and drawings.

According to the present invention, a dry film-shaped photoresist is used when performing dry etching by micromachining. The method comprises starting from a wafer with existing holes that must be protected before etching larger holes. Dry film photoresist
It is stacked on a wafer and performs tenting (forming a tent) above the existing hole. The photoresist in the form of a dry film is patterned to form holes of larger dimensions than described above, and then dry etched.
Finally, the dry film-shaped photoresist is peeled from the wafer. As long as the larger holes do not exceed the tenting function of the dry film photoresist, the process can be repeated to etch larger holes while protecting smaller holes previously etched. The overall microfabrication process utilizing the dry film photoresist of the present invention is shown in FIG.

Referring to FIG. 1, the wafer is effectively cleaned and then subjected to a lamination process using conventional lamination techniques. An example of a dry film resist is ETERT
EC (registered trademark) 7200 series. However, other dry film photoresists known in the art can be substituted. In an important aspect, the pressure used during the lamination process is about 1.4 kg /
Square cm (20 PSI) to about 2.1 kg / square cm
(30 PSI). After the lamination process, the cross-linking action is performed, for example, by exposing the laminate or laminate to an energy source well known in the art and holding the resist for at least about 15 minutes after this exposure and prior to development. Let After the lamination process, the wafer is developed, subjected to an etching process, and the photoresist is stripped. In an important aspect, the process can be repeated as necessary to obtain the desired end product.

In an important aspect of the present invention, the use of a photoresist in the form of a dry film allows the wafer surface to be etched twice or more times before the next process step. Each etching process can have a different depth, or can have a significantly different etching area.

In another aspect of the invention, dry film photoresist can form waveguides of different dimensions and depths on a wafer. The waveguide can have a width of about 25 microns to about 250 microns, as well as a depth of about 50 microns to about 200 microns. By using a photoresist in the form of a dry film, at least two waveguides of different dimensions can be etched on the same wafer surface.

In another aspect, using the dry film photoresist of the present invention, a wide range of different size backside via holes are formed in an indium phosphide or gallium arsenide wafer by a micromachining process. can do. The size of the hole can vary in diameter from about 10 μm to about 100 μm, and the etching depth can be about 30 μm.
It can vary from m to about 100 μm.

The following examples illustrate the invention and are illustrative of the scope of the invention as set forth in the claims, and should not be construed as limiting the scope of the invention. Example 1 Coating operation: Dry film performance is best when processed in a clean room (dust-free air-conditioned room). Cleaning, lamination, exposure and development processes before lamination of workpieces with fine lines (20 micrometers) must always be completed in a clean room. To maximize the adhesion of the dry film, the surface to be coated must be clean, dry and free of contaminants before the lamination process.

[0015] The dry film is bonded to the substrate using standard lamination techniques. The temperature, rate and pressure of the lamination process are selected based on the particular dry film used. Appropriate exposure is determined based on overall process requirements or judgment.

The hold time allows the completion of the polymerization process as well as the strengthening of the tent. Otherwise, the resist will "wrinkle" or collapse into holes during development. Development conditions are selected based on the particular dry film used. Tenting operation: Due to the unique combination of epoxy and urethane in the ETERTEC 7200 series of dry film photoresists, the film is very suitable for strengthening tenting and plating adhesion. .

1. Excessive pressure in the lamination process forces the dry film into the holes, thinning the resist at the periphery of the holes. ETERTEC 7200 series dry film photoresists do not require excessive pressure to follow normal surface defects due to their flowability and adhesion. It is recommended that a minimum (not maximum) pressure be used during the lamination process. A pressure of 1.4 to 2.1 kg / sq cm (20 to 30 PSI) is usually sufficient to perform the lamination process.

2. After lamination, all wafers are kept apart until cooled to room temperature. The stacked wafers have a calorific value, and when stacked, will remain hot for several hours. If the wafer is kept separated and not cooled, the retained heat will cause the film to flow further into the hole, thereby thinning the resist around the periphery of the hole and tenting. Ability to do If the stacking process is automatic and the panels are stacked by an automatic stacker, a cooling module in the line is used to advise that the proper wafer temperature is achieved before the stacking operation. Cooling modules, vertical stackers and accumulators are available from GDI.

3. Dry film, even at room temperature,
Flows under pressure. Once coated on a wafer having large holes or slots, pressure is created at the perimeter of the holes, which causes the film to flow slowly into the holes or slots. For this reason, the stacked wafers should be exposed as soon as practicable or during a single shift. The exposure process polymerizes the resist and stops the resist from flowing further into the holes. Such inflow will weaken the tent. For best results, all wafers must be developed during a single shift once exposed.

4. The cross-linking action of the resist starts at the time of performing the exposure treatment and continues for 15 to 30 minutes. After the exposure process and before the development process,
Holding for 5 to 30 minutes significantly increases the reliability of the tenting. If developed without employing the hold times suggested above, the resist will only partially polymerize, causing large tent wrinkles.

5. The heated developer plays a role in the tenting operation by softening the resist. Set the temperature of the developer to the lower limit of the allowable range (about 2
Holding at 6.7 ° C. (80 ° F.) maximizes resist performance and makes the tent more reliable.

6. In order to prevent all the nozzles from being partially clogged, regularly scheduled preventive maintenance is required in the developing process. The partial blockage of the nozzle described above causes the high pressure flow of developer to impinge on the tent. A typical developer consists of a sector nozzle provided in both the first and last rows directed inward toward the center of the machine, and a conical nozzle provided in all other locations. ing. It is a good practice to check the nozzles each time the developer is changed, and avoid obstacles.

[Brief description of the drawings]

FIG. 1 shows the overall process of the present invention for performing micromachining of a wafer.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/302 J (72) Inventor Harvey N. Rogers 90293, California, United States of America, Playa del Rey, Manitoba Street 8180 No. 157 (72) Inventor Vladimir Medvedev, Ridge Grade Court, Rancho Palos Verdes, California 90275, U.S.A. 6319 (56) References JP-A-11-61447 (JP, A) JP-A-10-163711 ( JP, A) JP-A-6-34715 (JP, A) JP-A-59-95487 (JP, A) JP-B-53-6859 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , (DB name) B81C 1/00 G03F 7/004 G03F 7/26 H01L 21/027 H01L 21/3065

Claims (4)

(57) [Claims] 1. A method of microfabricating a wafer already having one or a plurality of low spots, comprising: (a) applying a dry film-like photoresist material to the wafer; (B) patterning the photoresist material and exposing the laminated wafer to an energy source having the effect of crosslinking the photoresist material; and (c) A) developing the photoresist material; and (d) forming a hole in the wafer by dry-etching the laminated wafer. 2. The method according to claim 1, wherein the method has the effect of forming at least two different sized holes in the same wafer by dry etching. 3. The method of claim 2, wherein the method has a width dimension between about 25 microns and about 250 microns.
And having the effect of forming a waveguide having a depth dimension of about 50 microns to about 200 microns. 4. The method of claim 2, wherein the method includes forming a backside via hole having a diameter dimension of about 10 microns to about 100 microns and a depth dimension of about 30 microns to about 100 microns. Having a forming effect.