JP3367688B2 - Circuit board - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board using a ceramic substrate. [0002] In recent years, the speeding up of computer systems,
The trend toward miniaturization has further accelerated the high integration of semiconductor devices used in these devices. Recently, semiconductor devices having a power consumption of 30 W or more per chip have been put into practical use. Along with this, a circuit board on which such a semiconductor element is mounted is required to have higher wiring density and improved heat dissipation in order to reflect element characteristics to system characteristics. [0003] In view of the above, a circuit board formed by forming a thin film conductor pattern as a wiring on a ceramic base has been widely used. In consideration of heat dissipation, this circuit board can particularly suitably use a high thermal conductivity such as AlN or SiC as the ceramic substrate. Hereinafter, a manufacturing process of such a circuit board will be described. First, a conductive thin film is formed over the entire surface of the ceramic substrate. Subsequently, the thin film is patterned by wet etching or dry etching according to a conventional method, and a plating process is performed thereon until a predetermined thickness is obtained, thereby forming a wiring having a desired pattern. However, in the above process, the surface of the ceramic substrate is exposed to various environments. For example, washing with an acid before the plating step, immersion in a high-temperature acid or alkali solution after the plating step, contact with active radical species in an acid or alkali etchant used at the time of etching, and bonding of the ceramic substrate and the conductive thin film Exposure to a high temperature atmosphere for performing the above. For this reason, the surface of the ceramic substrate is deteriorated by various contaminants attached in these environments,
Defects such as generation of pinholes and peeling of the thin film conductor pattern formed on the surface occur. [0006] In the manufactured circuit board, the contaminants adhering to the surface of the ceramic base cannot be removed even by washing or the like and remain permanently. Furthermore, in the circuit board, the surface of the ceramic base exposed between the lines of the thin-film conductor pattern as a thin wire is again exposed to the surrounding environment and deteriorates, thereby causing a defect in the circuit. As a result, the long-term reliability of the circuit board is significantly impaired. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has improved the environmental resistance of the ceramic substrate surface during the manufacturing process and for a long time after the manufacturing. It is an object of the present invention to provide a highly reliable circuit board. A circuit board according to the present invention comprises a ceramic substrate and Ti, Cr, Ta, Nb, Zr, M, which cover the entire surface of the ceramic substrate.
A circuit board comprising a protective film of at least one of o, W, V and a compound of these metals having a thickness of 200 pm to 5 nm, and a thin film conductor pattern formed on the protective film. The circuit board of the present invention is characterized in that the above-mentioned protective film is interposed between the ceramic base and the thin film conductor pattern corresponding to the wiring. The protective film,
The coating covers the entire surface of the ceramic substrate, and protects the surface of the ceramic substrate from the environment during the manufacturing process of the circuit board such as formation of a thin film conductor pattern and permanently after manufacturing the circuit board. That is, at the time of forming the thin film conductor pattern, the deterioration, contamination, corrosion, and the like of the ceramic substrate surface due to acid, alkali solution, active radical species, and high temperature atmosphere.
This prevents the occurrence of defective products due to peeling of the thin film conductor pattern and the like. Further, after the formation of the thin film conductor pattern, deterioration of the surface of the ceramic base exposed particularly between the lines of the pattern is prevented, and the occurrence of circuit defects,
Peeling of the thin film conductor pattern is prevented. Thus, in the circuit board of the present invention, the environmental resistance of the surface of the ceramic substrate is improved during the manufacturing process and for a long time after the manufacturing, the peeling of the thin film conductor pattern is suppressed, and the long-term reliability of various performances is reduced. Can be realized. In the circuit board of the present invention, the material of the protective film includes Ti, Cr, Ta, Nb, Zr,
Mo, W, V, or a compound of these metals is used. Specific examples of the compound include nitrides, carbides, and borides of the above-mentioned metals, and intermetallic compounds of the above-mentioned metals with the metal elements constituting the lower ceramic substrate or other metal elements. At this time, nitrogen, carbon, boron, the above-described metal elements, and the like may be partially dissolved and diffused in the protective film, and a small amount of impurity elements such as Ar may be mixed. The reasons for limiting the material of the protective film in the present invention are as follows. Ti, Cr, Ta, Nb, Z
r, Mo, W, and V are all active metals and are provided between the ceramic substrate and the thin film conductor pattern to provide good adhesion strength. Also, depending on the surrounding environment, the ceramic substrate And constituent elements in the thin film conductor pattern and nitride, carbide, and intermetallic compound, etc.
Increase the adhesion strength. In particular, A as a ceramic substrate
When 1N is used, the adhesion strength of the thin film conductor pattern is significantly improved by interposing such a protective film. Furthermore, these metals and their compounds are acid resistant,
Since it is very excellent in alkali resistance and heat resistance, when the surface of the ceramic substrate is coated in the form of a film, the surface can be shielded from various surrounding environments. Therefore, the above metals and compounds of these metals are suitable materials for the protective film. On the other hand, in the circuit board of the present invention, the thickness of the protective film is in the range of 200 pm to 5 nm as described above. When the thickness of the protective film is in the above range, about 9 × 10 ⁹ It shows an appropriate resistance value of about 2 × 10 ¹³ Ω. Therefore, even though the protective film covers the surface of the ceramic substrate and is provided on the entire lower layer between the lines of the thin-film conductor pattern, the lines of the pattern, that is, the wiring are insulated, and the circuit is insulated. A semiconductor element or the like mounted on the substrate can operate without any abnormality. [0013] In this case, the thickness of the protective film is 200pm Not
If it is full , the surface of the ceramic substrate cannot be sufficiently shielded from the surrounding environment. Further, the thickness of the protective film is 5
If it exceeds nm , the resistance between the lines of the thin film conductor pattern, that is, between the wirings is reduced to 1 × 10 ⁹ Ω or less, so that the operation of the semiconductor element to be mounted becomes abnormal. More preferably,
The thickness of the protective film is in the range of 250 pm to 3 nm. In addition, the ceramic substrate and the conductor forming the thin film conductor pattern in the circuit board of the present invention are not particularly limited, but common materials can be used. As the ceramic substrate, for example, A
Low dielectric constant materials such as 1N, BN, SiO ₂ , SiC, borosilicate glass, and high thermal conductivity materials can be used.
By appropriately selecting the material of the ceramic base, a circuit board having a high signal propagation speed or excellent heat dissipation can be obtained. On the other hand, as a conductor, for example,
Metals such as Au, Cu, Ni, Ag, Pt may be used. The thin film conductor pattern is made of Ti, Cr, Ta, N
b, Zr, Mo, W, V, etc .;
A barrier metal layer made of t, Mo, Nb, W, V, Ti, or the like, and a conductive thin film made of the above metal may have a multilayer structure in which they are stacked in this order. Next, the manufacturing process of the circuit board of the present invention will be described. First, a ceramic substrate as described above is prepared, and one surface thereof is cleaned as necessary by a wet cleaning method, a reverse sputtering method, a dry etching method or the like. Subsequently, over the entire surface of the ceramic substrate, Ti, Cr,
A protective film is formed by forming at least one of Ta, Nb, Zr, Mo, W, V, and a compound of these metals to a thickness of 200 pm to 5 nm. As the film forming method, a general method such as a vacuum deposition method, a sputtering method, a cluster ion beam, an ion plating, an ion mixing, and a CVD is adopted. In each method, it is necessary to adjust conditions such as a substrate temperature, an atmosphere, a degree of vacuum, and a film forming speed according to the material of the protective film. Next, if necessary, a bonding layer having a thickness of about 1 to 100 nm and a thickness of 90 to 500 n are formed on the surface of the protective film.
After forming about m barrier metal layers, a conductive thin film is formed by, for example, sputtering or vacuum evaporation. Subsequently, the conductor thin film and, if necessary, the barrier metal layer and the bonding layer are patterned by wet etching or dry etching, and further patterned until the total thickness of the conductor thin film is about 200 nm to 10 μm. Then, a thin film conductor pattern to be a wiring is formed by appropriately performing electrolytic or electroless plating. After this, a dielectric layer, an interlayer insulating film, an upper wiring, and the like may be formed on the thin film conductor pattern as necessary. It also has the function of blocking the surface of the ceramic base. Hereinafter, the present invention will be described in detail with reference to examples. These examples are described for the purpose of facilitating understanding of the present invention, and do not particularly limit the present invention. Example A protective film and a thin-film conductor pattern were formed on one surface of a ceramic base under the conditions shown in Table 1 below. Nos. 1 to 21 were produced. That is, first, on one surface of the ceramic base,
Was formed by sputtering, and then a barrier metal layer made of Mo and having a thickness of 300 nm and a conductive thin film made of Au and having a thickness of 500 nm were sequentially formed by sputtering. Thereafter, the conductor thin film and the barrier metal layer are patterned by photolithography,
90 ° C. using an alkaline Au electroless solution
, A plated film was grown until the total thickness with the thin film conductor became 4 μm, and a thin film conductor pattern having a width of 50 μm and a pitch of 70 μm was formed as a wiring. Next, these samples were subjected to reliability tests using chemicals or plasma. That is, the samples were placed in the chemical and plasma atmospheres and conditions shown in Table 1, respectively, and thereafter, the surface roughness between the wirings (between the lines of the thin film conductor pattern), the resistance between the wirings, and the resistance of the thin film conductor pattern The presence or absence of peeling was evaluated. The results are shown in the same table. From the results shown in Table 1, in the circuit board of the above embodiment, the surface roughness between wirings,
It was confirmed that there was no practical problem in the line resistance value and the adhesion strength of the thin film conductor pattern. COMPARATIVE EXAMPLE Under the conditions shown in Table 1 below, a protective film and a thin film conductor pattern were formed on one surface of a ceramic substrate in the same manner as in the example. 22-2
5 was produced. However, these sample Nos. In the circuit boards Nos. 22 to 23, the thickness of the protective film was out of the range of 200 pm to 5 nm, and In the circuit boards 24 to 25, the protective film is not formed on the ceramic base, and the surface of the ceramic base is exposed between the wirings. These samples were evaluated for reliability with respect to various characteristics in the same manner as in the above examples. The results are shown in the same table. From the results shown in Table 1, in the case of a circuit board (sample No. 22) in which the thickness of the protective film is out of the predetermined range, the surface of the ceramic substrate between the wirings must be sufficiently shielded from the surrounding environment. Therefore, the surface roughness between the wirings after the reliability test was increased, and the deterioration of the ceramic base surface between the wirings was advanced. In the case of a circuit board (sample No. 23) in which the thickness of the protective film is out of the predetermined range, the line resistance is small, and the semiconductor element is mounted on the circuit board for operation. In this case, there is a high possibility of malfunction. Further, in the circuit board on which no protective film is formed (Sample Nos. 24 and 25), the surface roughness between the wirings is remarkably large, and the thin film conductor pattern is peeled off after the reliability test. It was confirmed that the adhesion strength of the thin film conductor pattern was insufficient. [Table 1] As described in detail above, according to the present invention,
A highly reliable circuit board having improved environmental resistance on the surface of a ceramic substrate during a manufacturing process and for a long time after the manufacturing is provided.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kaoru Koiwa 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba Research Institute, Inc. (72) Inventor Nobuo Iwase 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Address Toshiba Research Institute, Inc. (56) References JP-A-2-205096 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 1/09 H05K 3/38 C04B 37 / 00

Claims (1)

(57) [Claims 1] Ti, Cr, Ta, Nb, Z coated on a ceramic substrate and an entire surface of the ceramic substrate
A circuit board comprising: a protective film of at least one of r, Mo, W, V, and a compound of these metals having a thickness of 200 pm to 5 nm; and a thin-film conductor pattern formed on the protective film.