DD153950A1 - METHOD FOR THE STRUCTURED CHEMICAL REDUCTIVE DEPOSITION OF METAL LAYERS - Google Patents

Abstract

The process can be used in microelectronic hybrid technology, micro-conductor plate technology or for the production of components. According to the invention, existing problems are remedied by new technological steps in known processes. Thus, germ-displacement is prevented by removing the photosensitive substance in an emulsifier. Unnecessary nucleation with residual substances by the reducing agent is prevented by destruction of the nucleating agent with chemical reactions (deactivation process). Furthermore, a seed conversion by chemical reactions is applicable if the Badmetall should not deposit on the Primaerkeimen or is unfavorable for the connectivity. By the known exposure and development process, the number of germs, as well as the germ size can be technologically controlled. Thus, the desired bond strengths are controllable, as they depend directly on the number of adhesion points (germ count). Precise microstructures can be deposited directly. The resolution corresponds to the comparable photographic process.

Description

21 2 957

Title of the invention

Process for the structured chemical redulctive deposition of Lietall layers

Field of application of the invention

The method relates to an electroless (chemical-reductive) deposition of structured metal layers on electrically non-conductive surfaces

Characteristic of the known technical solutions

The metallization of surfaces is a frequently used process step in production technologies of different products.

In many cases, it is important not to continuously metallize a surface, for example of an insulator material, but to apply the metal layer in a particular structure. The requirements for such structuring in terms of their geometry can be quite different. In many cases, fairly coarse structuring in the mm range is sufficient in special cases (microelectronics, microacoustics and others), structurings in the, um area with exact adherence to the geometry are required.

For applying the metallic layer itself, the following methods are often used:

, steaming

, sputtering

• Electroless separation from baths (possibly with galvanic reinforcement)

, Coating with suspensions, pastes and the like and then baking the layer

Purely the structuring of the metal layers has become known methods, which can be roughly divided into the following variants:

Direct structuring of the metal layer by means of suitable metal masks or screen templates, which already contain the structure as a "breakthrough".

It is easy to see that only relatively simple structures can be applied and no increased demands are placed on the geometry of the structure. Furthermore, electroless deposition from metal salt baths is inapplicable for this process, since masks and templates are infiltrated.

- Structuring of a closed metal layer by means of photoresist. By an exposure of the paint and subsequent dissolution processes paint-free or lacquer-covered zones are created on the metal surface according to the desired structuring, which protect the metal in the following A'tzproseß or grant access to the etchant.

There are known positive and IT shares. In some cases, the photoresist is also applied first and then coated with metal. Furthermore, it is known that it is possible to work with light, electron beams or X-rays. The diverse process works have become known under the name Hagen photo-electron beam or X-ray lithography.

These methods have in common that the metal layer is always applied closed and

-3 - 21 2-957

then structured first. If the desired structuring is small compared to the total area, this is not rational when using precious metals.

After applying suitable layers to the surface, exposure to photomasks by chemical processes creates a "latent" image of the structure in the layer. With appropriate nucleation at the exposed points can be achieved that from baths only on the "germs" the desired metal is deposited and thus the structure is formed. The seeds may be reducing agents (for example Sn ⁺⁺ OS 2.256.9SO) or metals (for example Pd AS 2.224.471).

The method last described is suitable for electroless deposition from baths. It has the advantage of depositing the structure directly and the entire body is not metallized, as is the case with electroless deposition from baths.

However, practice has proven that these initially seemingly simple procedures (3rd group) 'carry large sources of error. The most important are:

, Upon exposure, some oxidation processes (for example, Sn ⁺ Sn) are not quantitative, so that reducing agents remain at the exposed sites as well.

, If a reduction process is used during the exposure (Ti ⁴⁺ to Ti ^ ⁺ or Pd ⁺⁺ Pd), the reducing agent in the unexposed cases during the Lletallabscheidung comes into action and produces unwanted germs. For this reason, Y / asch- and rinsing processes are switched on in these methods, which is a subsequent

To prevent reaction with the reducing agent. In the example mentioned, all Pd ions must therefore be removed. Practice has proven that they are very persistently adsorbed to the surface and can not be removed quantitatively, resulting in unwanted sites in the process of metal nucleation.

In some processes it is not possible to find selective additives for the reduction or oxidation product. Often also formed germs are abducted during the washing process.

• Another disadvantage of the methods of the 3rd group is that the seed size can not be controlled and thus the technological parameters can vary greatly (exposure time, deposition time and others) and the marginal sharpness is adversely affected.

• Furthermore, when using Pd ⁺⁺ solutions of insufficient concentration, too few nuclei can form, which results in a greatly reduced adhesive strength.

From the state of the art, the following conclusions can be drawn in summary:

- let the low investment costs, the ability to capture, primarily also base metals and other benefits is the electroless deposition of metal layers of baths particularly favorable.

- To avoid a total metallization of a body in many cases, the structure is deposited directly.

- This advantageous method, which can be done only by Group 3 methods, but has the shortcomings described. In practice, this leads to insta-

212 957

and failures in which a closed metal layer (or faulty structure) or no layer at all can deposit. Often the adhesive strength is insufficient.

Object of the invention

The object of the invention is to provide a stable process for the structured deposition of metals from bath solutions, which does not reliably control the disadvantages for group 3, is technically reliable and also permits the separation of microstructures from baths directly, which have excellent adhesive strength and good connectivity (solderability, bondability).

Explanation of the essence of the invention

The deficiencies shown in Group 3 can only be avoided if

- no germs are kidnapped

- Residual chemicals that can form new germs with the reducing agent of the bath, made harmless

- The germ size and bacterial count can be controlled defined and thus the technological process parameters can be kept constant, also the number of detention sites can be controlled.

This is achieved according to the invention by applying the photosensitive layer (for example AgBr) in an emulsifier, and controlling the nuclei size by an exposure or development process. Great importance within the process has the destruction of the substances that can form new None with the reducing agent of the bath. This process should be called deactivation and is done by a suitable chemical reaction, such as

Ag "** + Cl"

Pd ⁺ " ¹ " +

AgGl PdS

The substances thus formed must no longer be able to react with the reducing agent and beispielswei

se Ag germs form.

Other steps may be included in the process, such as removing the emulsifier cycle by burnout, or converting seed to other seeds, if this facilitates deposition from the baths. The process of structuring can be taken from the following overview.

step

purpose

example

comment

Dissolve or disperse the yaw of the light during the sensitive sub-exposure process in an emul-emitting nucleus, so as to prevent carry-over

to prevent

Add AgBr in Gelantine

Apply the layer to the substrate

Exposure by photomask

Starting point of the structuring process

nucleation

Layer on ceramic substrate

Ag ⁺ + h · f

Control of the germ count

development

germ enlargement

developer

Step can be inserted but is not required in every case

- T -

21 2 95 7

step

fixation

purpose

Wash out the light-sensitive substance

example

comment

for AgBr

Removal of the Storage of burnout Other Ver emulsifier Germs directly drive, like. on the sub for example strat Evaporate in. Vacuum just if applicable bar Disabling Destruction of Ag ⁺ + Cl " He certainly Substances containing · AgCl conducive, with the reduc otherwise no the means of structuring

S t rct tion tion by deposition of the metal from bath solutions

Baths can form new germs

Deposition of Cu from baths desired metal layer

In the case of deposition of arid metals, for example Ni, a seed conversion can additionally take place

If a nucleus conversion occurs, it is necessary to reinsert a deactivation process.

Embodiment.

The structured lead titanate zirconate ceramic 1 to be structured is provided in thin disks polished on one side

-β- 212957

a roughness 0.1 to before. Due to the special pre-treatment, chemical activation of the surface can be dispensed with.

The ceramic discs are degreased in a neutral or weakly alkaline detergent, rinsed with water and then with isopropanol and dried. On the thus pretreated substrates 1, the photosensitive emulsion 2 is applied evenly under suitable lighting. After complete drying of the emulsion, the photosensitive layer 2 is exposed via the negative of the desired structure 3, 4 (FIGS. 1 to 3). In a developer bath ORWO E 102 (1: 3) is developed until complete blackening of the structure ..! After a short rinsing in a breaker bath with a 0.5% organic acid, the image is fixed in the fixer ORWO A 300 for 10 minutes and at least Watered for 30 minutes. The substrates are dried in a cold air stream and the volatile constituents of the emulsion are removed at a temperature between 473 K and 523 K. This step is followed by deactivation followed by an intensive rinse of 5 minutes under running water. In a bath containing 0.5 g / l palladium chloride, the nucleus conversion takes place in 10 seconds. This is followed by another rinse of 5 minutes under running water. After repaping the substrates are in an alkaline ITickelbad up to a layer thickness of 2 , via. chemically reductively nickel-plated.

The layers produced by this process show adhesion

-2

strengths of (Ο, Όδ - 0, I) ITm and a specific electrical conductivity of (0,15 - 1 _} 4). 10 centimeters) . The linear thermal expansion coefficient is 13 · .10 grd.

Claims (6)

Erfindung3anspruch Process for the structured chemical-reductive deposition of metal layers by means of a photographic process with the steps of exposing, fixing, characterized in that the photosensitive substance is first applied in an emulsifier, after removal of the emulsifier residual substances are deactivated and the used by the exposure process metal nuclei are used for the deposition of the structured layer of chemical baths. 2. The method according to 1, characterized in that the removal of the emulsifier by heating, burning out, extracting or distilling takes place. 3 «process according to 1.sgekennzeichnet characterized in that the deactivation of the Ag ⁺ nuclei by halides, sulfides or complexing agent takes place. 4 «method according to 1., characterized in that a seed conversion by means of a chemical reaction takes place, if this is required for a specific deposition of metal salt baths. 5. The method according to 1, and 4, characterized in that a Germination of the Me nuclei Me- using the stress series in nuclei LIe ₂ takes place. 6. Method according to 1, 4 and 5, characterized by being deactivated again after germination. , For this 1 string drawings