JP2703276B2 - Aluminum nitride thin film circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an aluminum nitride (AlN) thin film circuit board.

(Prior Art) Conventionally, alumina is mainly used as a base material of a thin film circuit board used for a semiconductor module. However, the amount of heat generated from the active element during operation tends to increase with the improvement in the performance of the mounted active element, and there has been a problem that the thermal conductivity of alumina limits the number of mounted active elements.

For this reason, instead of alumina, thin-film circuit boards based on BeO, which has a high thermal conductivity, have been used.However, such BeO is highly toxic during manufacturing and polishing. Is limited. For this reason, AlN is widely used as an alternative material. This AlN is harmless and has the advantage that there is no restriction on production, parts and disposal, and in particular, the thermal conductivity is in a wide range of 70 to 280 W / m ・ k, that is, the heat dissipation is 3.5 times that of alumina, depending on the case. Can be prepared to a level superior to BeO, so not only can a higher mounting density be achieved than a thin film circuit board using an alumina base material, but also the desired thermal conductivity can be provided in accordance with the higher density of active elements Have the advantages that can be. The thin film conductor of the thin film circuit board using such an AlN base material is conventionally Au / Pt / Ti, Au / Pd / Ti,
Au / Pt / Cr and the like are generally used. However, in order to form these conductors on the AlN substrate, a method of selective etching using a highly corrosive etchant such as aqua regia or hydrofluoric acid is adopted, and therefore, the AlN substrate is also etched. There was a problem. That is, AlN material is alumina or Si
Corrosion resistance to strong acids and strong alkalis is lower than that, and it is easily decomposed, so that pits and trenches are formed on the surface of the AlN base material around the derivative when the conductor is formed by the etching,
It is difficult to form the conductor in a stable shape and with high reliability.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and suppresses the etching of the AlN base material surface during the etching at the time of patterning for forming the conductor, thereby achieving a stable operation. A highly reliable conductor can be realized with the shape, and the conductor
An object of the present invention is to provide an AlN thin film circuit board having improved adhesion to an AlN substrate.

[Constitution of the Invention] (Means for Solving the Problems) The present invention provides a three-layer structure in which a Ti layer, a Ni layer, and an Au layer are laminated in this order on an aluminum nitride substrate having an average line surface roughness of 150 nm or less. An aluminum nitride thin-film circuit board characterized by forming the above conductor.

The reason for limiting the average line surface roughness (Ra) of the AlN base material to 150 nm or less is that if the surface roughness exceeds 150 nm, the conductor breaks or the width becomes uneven in the patterning step for forming the conductor. This is because the adhesion of the conductor to the AlN substrate is further reduced, and the reliability of the thin film circuit board is reduced. Adjustment to such a surface roughness can be achieved by a sintering operation using a submillon AlN particle raw material or polishing of a sintered base material.

The AlN substrate preferably has a crystal grain size in the range of 0.5 to 20 μm. The reason for this is that if the crystal grain size is less than 0.5 μm, the thermal conductivity of the AlN substrate cannot be improved, and the undulation and warpage during sintering will increase, resulting in a decrease in mask exposure accuracy in the conductor formation process. On the other hand, if the crystal grain size exceeds 20 μm, when polishing the surface of the base material, it may be difficult to obtain a base material having a surface Ra of 150 nm or less due to dropout of crystal grains and the like. .

The lower Ti layer disposed on the AlN substrate side, which is a constituent material of the conductor, serves to enhance the adhesion to the substrate,
The Ni layer disposed in the middle acts as a barrier to prevent the lower Ti layer from diffusing into the upper Au layer, and the upper Au layer has a function of imparting low resistance, which is a characteristic of the conductor itself. Regarding the thickness of each metal layer constituting such a conductor,
Ti layer 10 ~ 200nm, Ni layer 100nm ~ 1μm, Au layer 50nm ~
Desirably, it is 4 μm.

Between the AlN substrate and the Ti layer of the conductor, oxygen is 0.02 to 30a.
tm% at least constituent materials of AlN (Al, N, etc.) and Ti
It is desirable to interpose a compound layer consisting of The reason for limiting the amount of oxygen in such a compound layer is that the amount is set to 0.02 at.
If it is less than m%, it becomes difficult to adhere the conductor to the AlN substrate with sufficient strength, but the amount of oxygen is 30at.
If the amount exceeds m%, the conductor is separated from the surface of the substrate due to a difference in thermal expansion coefficient between the conductors of the substrate and lattice distortion.

Next, a method for manufacturing an AlN thin film circuit board of the present invention will be briefly described.

First, an AlN base material having a desired thermal conductivity and having a surface Ra of 150 nm or less is prepared. Subsequently, Ti is formed on the substrate by a general film forming technique such as an evaporation method or a sputtering method.
A layer, a Ni layer, and an Au layer are sequentially formed. At this time, the substrate temperature, atmosphere, degree of vacuum, power density, and port current are adjusted as necessary, and if degassing is insufficient, the substrate is heated to a desired temperature to clean the substrate surface. State. Prior to the formation of the Ti layer, the surface of the base material is etched by plasma to enhance the activation of the surface. Further, oxygen is supplied into the vapor deposition atmosphere to form the above-described compound layer at the interface between the AlN base material and the Ti layer. Next, the three layers are patterned by a photo-etching technique using a resist to form a conductor having a three-layer structure on the AlN substrate to manufacture an AlN thin film circuit board. During this photoetching, the Au layer is KI + I ₂ + deionized water, the Ni layer is CuSO ₄ + HCl + ethyl alcohol + deionized water, HCl + FeCl ₂ + ethyl alcohol + deionized water, Cu
The etching is performed using an etchant such as SO ₄ + deionized water and Ti is used with HF + deionized water.

(Action) According to the present invention, by using an AlN substrate having an average line surface roughness of 150 nm or less, disconnection of a conductor formed on the substrate and inconsistency of a conductor width in a step of patterning the conductor are achieved. Uniformity can be prevented, and the adhesion of the conductor to the substrate can be improved.

In addition, by forming the conductor into a three-layer structure in which a Ti layer, a Ni layer, and an Au layer are laminated in this order, the conductor has the composition described above when patterning the conductor (particularly, the Ni layer), and Since an etchant with low corrosiveness can be used, a highly reliable conductor having a stable shape can be formed on the AlN substrate surface. That is, as described above, the surface of the AlN substrate is mirror-finished in order to improve the pattern accuracy of the conductor. However, this mirror surface is a macroscopic expression, and microscopically, the AlN base material 2 on which the conductor 1 is formed as shown in FIG. The surface 4 has irregularities due to impurities and the like, and a discontinuous surface (step) 5 is formed at the polishing position of each crystal particle 3. When a conductor thin layer is patterned using an etchant having a large effect on the AlN substrate as in the conventional case, the etchant promotes a difference in the etching rate of each crystal grain having a different etching property in the orientation plane, and the discontinuous plane described above is promoted. 4 is increased, and as a result, it is difficult to reliably form a conductor having a stable shape. On the other hand, the above-mentioned three-layered conductor composed of the Ti layer, the Ni layer and the Au layer enables patterning with an etchant having low corrosiveness, and allows etching of the AlN base material surface (particularly, the degree of step difference at a discontinuous surface). (Enlargement by etching) can be prevented, so that a highly reliable conductor having a stable shape can be formed on the surface of the AlN base material.

Further, oxygen is added between the AlN substrate and the Ti layer of the conductor by 0.20 to 30 atm.
%, By interposing a compound layer composed of at least a constituent material (Al, N, etc.) of AlN and Ti, the adhesion strength of the conductor to the base material can be significantly improved. That is, in the conventional alumina substrate, an oxide layer exists between the conductors, and the conductor can be satisfactorily adhered to the surface of the alumina substrate. However, AlN
In the base material, it is difficult to obtain a sufficient adhesion strength even when an oxide alone is interposed between the conductor and the conductor, and there is a problem that the conductor is easily peeled off due to a difference in thermal expansion coefficient between the members. On the other hand, by interposing a compound layer composed of Ti and at least a constituent material of AlN (Al, N, etc.) containing a specific amount of oxygen between the AlN substrate and the Ti layer of the conductor, the conductor adheres to the substrate. Strength can be remarkably improved, and peeling of the conductor due to a difference in thermal expansion coefficient between the base material and Ti can be prevented.

Therefore, according to the present invention, the conductor having a fine line width is made of AlN
Highly reliable, useful for semiconductor modules that are provided with high adhesion strength to the substrate and can be mounted at high density such as active elements
An AlN thin film circuit board can be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail.

Example 1 First, an AlN substrate having a thermal conductivity of 280 W / m · k was lapped and polished so that the average line surface roughness became 150 nm. Then, the surface of the AlN substrate was
After oxygen gas was supplied to the AlN substrate surface by performing plasma etching of an Ar gas containing vol% of oxygen, a Ti layer, a Ni layer, and an Au layer were formed by RF sputtering under the conditions shown in Table 1 below. Next, the uppermost Au layer was formed to a thickness of 7 μm by photolithography.
After forming a resist pattern having a width, using the pattern as a mask, the Au layer is etched with KI + I ₂ + deionized water etchant, Ni
The layer was successively etched by an etchant of CuSO ₄ + HCl + ethyl alcohol + deionized water and an etchant of the Ti layer by an etchant of HF + deionized water to form a three-layer conductor, thereby producing an AlN thin film circuit board.

Example 2 In the same manner as in Example 1, a Ti layer, a Ni layer and an Au layer were formed on the surface of an AlN substrate subjected to lapping, polishing, and Ar gas plasma treatment containing oxygen by RF sputtering under the conditions shown in Table 1 below. Films were formed, and then these layers were patterned in the same manner as in Example 1 to manufacture an AlN thin film circuit board having a conductor having a three-layer structure.

Comparative Example 1 First, lapping and polishing were performed on an AlN substrate having a thermal conductivity of 20 W / m · k so that the average line surface roughness became 150 nm. Then, Ti layer, Pt layer and Au
The layers were formed under the conditions shown in Table 1 below. Next, a resist pattern having a width of 7 μm is formed on the uppermost Au layer by photolithography, and the Au layer is then KI + I _{2 using the} pattern as a mask.
An etchant of + deionized water, an etchant of Pt layer of HCl + HNO _{3 and} an etchant of Ti layer were sequentially etched with an etchant of HF + deionized water to form a three-layer conductor, thereby producing an AlN thin film circuit board.

Comparative Example 2 First, an AlN substrate having a thermal conductivity of 20 W / m · k was lapped and polished so that the average line surface roughness became 150 nm. Subsequently, the surface of the AlN base material
% Plasma etching of Ar gas containing oxygen
After supplying oxygen to the AlN substrate surface, T
An i layer, a Pt layer, and an Au layer were formed under the conditions shown in Table 1 below. Next, a resist pattern having a width of 7 μm was formed on the uppermost Au layer by photolithography, and the Au layer, the Pt layer, and the Ti layer were sequentially etched using the pattern as a mask in the same manner as in Comparative Example 1 to form three layers. An AlN thin film circuit board was manufactured by forming a conductor having the structure.

Thus, the bonding strength of the conductor (Ti layer) to the AlN substrate and the presence / absence of disconnection of the conductor were examined for the thin film circuit boards of Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1.

As is evident from Table 1, the thin film circuit boards of Examples 1 and 2 have conductors of AlN compared to the thin film circuit boards of Comparative Examples 1 and 2.
It can be seen that the adhesive strength to the substrate is extremely high, and the reliability without disconnection is extremely high.

[Effects of the Invention] As described in detail above, according to the present invention, a highly reliable conductor having a fine and stable shape is suppressed by suppressing the etching of the AlN substrate surface during etching for patterning for conductor formation. It is possible to provide a highly reliable AlN thin-film circuit board useful for a semiconductor module capable of improving the adhesion of the conductor to an AlN base material, and thus enabling high-density mounting of active elements and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a microscopic view of the surface of an AlN substrate on which a conductor is formed. 1 ... conductor, 2 ... AlN base material, 3 ... crystal particles, 4 ...
Heterophase interface, 5: discontinuous surface.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Reference number in the agency FI Technical display location H05K 1/03 630 H01L 23/12 Q

Claims (2)

(57) [Claims] An aluminum nitride thin film comprising a three-layer conductor formed by laminating a Ti layer, a Ni layer and an Au layer in this order on an aluminum nitride substrate having an average line surface roughness of 150 nm or less. Circuit board. 2. The method according to claim 1, wherein a compound layer containing at least a constituent material of aluminum nitride containing 0.02 to 30 atm% oxygen and Ti is interposed between the aluminum nitride base material and the Ti layer of the conductor. Aluminum nitride thin film circuit board.