The present invention relates to a thin film resistor and a circuit board internally including a thin film resistor, and more specifically to a method for forming a thin film which constitutes a built-in thin film resistor.
Recently, a demand for miniaturization of a mounting board is increasing, so that interconnections are microminiaturized and a circuit density is elevated. On the other hand, reports of the miniaturization of the mounting board attained by internally having a built-in resistor in the mounting board are increasing. A structure of the mounting board having a built-in resistor is classified into a board internally including a chip resistor, a board internally including a thick film resistor, and a board internally including a thin film resistor. The a board internally including the chip resistor has a limitation in miniaturization, and on the other hand, in the board internally including the thick film resistor, precision of a resistance value cannot be elevated.
The board internally including the thin film resistor, called a xe2x80x9cthin film resistor built-in boardxe2x80x9d hereinafter, is the most suitable to miniaturization, and the precision of the resistance value can be elevated to a relatively high level. As a resistor material used in the thin film resistor built-in board, JP-04-174590-A, JP-06-085100-A and JP-07-034510-B propose a Nichrome alloy, a tantalum nitride, ITO (Indium Tin Oxide) and metal silicide. However, when these materials are used, if the resistor material is patterned by a wet etching, the mounting board is subjected to damage, since a strong acid is used for the wet etching. On the other hand, if the resistor material is patterned by a dry etching, a forming process becomes long. In addition, in certain kind of resistor material, it is difficult to selectively etch a resistor and a wiring conductor and an electrode, even by the wet etching.
JP-63-156341-A proposes to use a thin film of titanium nitride as a contact barrier in a semiconductor device. JP-03-276755-A discloses a method for fabricating a semiconductor device, which uses the titanium nitride as a barrier metal and also as a resistor in the semiconductor device.
In the case of using the titanium nitride as the resistor material, a thin film of polycrystalline titanium nitride is used. In addition, resistivity of the thin film of polycrystalline titanium nitride is on the order of 20 to 25 xcexcxcexa9xc2x7cm at a small value to )1300 xcexcxcexa9xc2x7cm at a large value, which are reported in J. Vac. Sci. Technol. A5, p1778 (1987) and Semiconductor Integrated Circuit Technology Symposium Transactions, 28, p97 (1985). In other words, it is difficult to form a high resistance thin film. In addition, a temperature coefficient of resistance was adversely large.
JP-61-148732-A shows an example of a temperature sensor resistor formed of amorphous metal nitride such as TiN and TaN formed by a high frequency magnetron sputtering. However, this resistor is not suitable for an ordinary circuit resistor such as a terminating resistor, because the resistance value greatly varies dependently upon a temperature change.
In Japanese Patent Application No. Heisei 10-165122 which was published as JP-11-354303-A, the co-inventors of this application propose a thin film resistor formed of crystalline titanium nitride and amorphous titanium nitride, which is excellent in characteristics as a resistor and which can assume a resistance value of a wide range, by controlling a forming condition. However, the resistance of this thin film resistor adversely increases when it is subjected to a thermal hysteresis. Therefore, this thin film resistor is not suitable as a resistor which is required to have a high precision as a resistor for a time constant circuit.
On the other hand, a compound composed of titanium, nitrogen and oxygen is proposed in JP-07-263359-A, JP-05-114581-A, JP-04-045536-A, JP-07-291668-A, JP-05-085776-A, JP-60-081048-A and JP-07-057905-B. JP-07-263359-A discloses a method for forming a barrier layer of TiOxNy by an ECR (electronic cyclotron resoniance) plasma CVD (chemical vapor deposition) process. JP-05-114581-A shows a method for forming a refractory metal oxynitride film (TiON) as a barrier layer on a refractory metal nitride film (TiN) by a CVD process.
JP-04-045536-A proposes a copper interconnection film composed of a copper thin film formed on an antioxidation film of a conducting material containing no oxygen, formed on a barrier metal formed of a titanium oxynitride (TiON) film. JP-07-291668-A shows a radio wave transparent type heat ray shielding glass composed of a first layer of tin oxide or tin oxynitride formed on a glass plate, a thin film of titanium oxynitride film coated on the first layer, and a second layer of tin oxide or tin oxynitride formed on the thin film of titanium oxynitride film. JP-05-085776-A discloses a radio wave low-reflection colored glass composed of a transparent colored glass, a first layer coated on the transparent color glass and formed of a TiNO film or a composite thin film including TiNO as a main component, and a second layer coated on the first layer and formed of a TiON film or a composite thin film including TiON as a main component. JP-60-081048-A shows a titanium nitride thin film coated glass composed of a titanium oxide (TiO2) layer, a buffer layer of titanium oxide and titanium nitride (TiN), a titanium nitride layer deposited on a surface of a glass plate in the named order. JP-07-057905-B discloses an ornament including a coating layer of Ti(NxOy)z (where 0.005xe2x89xa6yxe2x89xa60.060, x=1xe2x88x92y, 0.8xe2x89xa6zxe2x89xa61.0) between a substrate and an uppermost layer. None of the above referred patent publications uses the compound composed of titanium, nitrogen and oxygen, as a material for a thin film resistor,
Accordingly, it is an object of the present invention to provide a thin film resistor which has overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a thin film resistor which can be simply patterned by a wet etching.
Still another object of the present invention is to provide a thin film resistor which has an excellent thermal stability and a high precision of resistance value.
A further object of the present invention is to provide a thin film resistor which has an excellent temperature characteristics of resistance.
A still further object of the present invention is to provide a substrate internally including a thin film resistor as mentioned above.
A further object of the present invention is to provide a thin film resistor material which can assume a resistance value of a wide range by controlling a forming condition, and a method for forming a thin film resistor.
The above and other objects of the present invention are achieved in accordance with the present invention by a thin film resistor formed of a thin film of titanium nitride containing oxygen in a solid solution condition.
According to another aspect of the present invention, there is provided a substrate internally including a resistor which is constituted of a thin film resistor formed of a thin film of titanium nitride containing oxygen in a solid solution condition
According to still another aspect of the present invention, there is provided a method for forming a thin film resistor formed of titanium nitride containing oxygen in a solid solution condition, wherein a thin film of titanium nitride containing oxygen in a solid solution condition is deposited by a reactive-sputtering using a titanium target and a process gas composed of a mixed gas including at least a nitrogen gas and a gas which contains an oxygen element.
According to a further aspect of the present invention, there is provided a method for forming a thin film resistor formed of titanium nitride containing oxygen in the solid solution condition, wherein a thin film of titanium nitride containing oxygen in a solid solution condition is deposited on a water-deposited substrate by a reactive-sputtering using a titanium target and a process gas including at least a nitrogen gas.
With the above mentioned arrangement, the thin film resistor in accordance with the present invention formed of the thin film of titanium nitride containing oxygen in the solid solution condition, can be patterned by a wet etching with a high degree of precision in dimension. Therefore, it is possible to shorten the fabricating process so as to lower a production cost, and also to elevate the precision of the resistance value. Because of the oxygen contained in the solid solution condition, a heat-resistance of the thin film is elevated, so that the change in resistance value caused by a thermal hysteresis can be minimized.
Furthermore, since an etchant used at the time of patterning the thin film resistor by the wet etching does not deteriorate a substrate, it is possible to fabricate a substrate internally including the thin film resistor in accordance with the present invention.
In addition, the thin film resistor is required to be able to assume a resistivity value of a wide range,. For example, in order to have a resistance value of 50xcexa9, it is sufficient if a material having the resistivity of 0.1 mxcexa9xc2x7cm is patterned to have a thickness of 20 nm and a width and a length which are equal to each other. On the other hand, if the resistor patterned to have the same dimensions as those mentioned above, is formed of a material having the resistivity of 100 mxcexa9xc2x7cm, the resistor can have the resistance value of 50 kxcexa9.
By changing the dimensions, it is possible to adjust the resistance value. However, it can be generally said that, if the thin film is too thin in thickness, a defect occurs in the thin film, or alternatively, the nature of the film changes under influence of a surface structure. On the other hand, if the thickness is increased, the time required for forming the film adversely becomes long, and in addition, the film becomes apt to peal off from a substrate because of an increased internal stress in the film. Furthermore, it is not preferred to change the ratio of the width and the length, from the viewpoint of miniaturization of the resistor. It was an ordinary practice to realize various resistance values in a required range by using different resistive materials. However, the thin film resistor in accordance with the present invention can assume a resistance value in a wide range by controlling the amount of oxygen in a solid solution condition while using one target.
Furthermore, it is also possible to control the temperature coefficient of resistance in the thin film resistor in accordance with the present invention, by controlling the amount of oxygen in a solid solution condition. The amount of oxygen in a solid solution condition can be controlled in a reactive sputtering for forming the thin film resistor, by controlling the flow rate of a gas which contains the oxygen, or alternatively the partial pressure of a gas which contains the oxygen, or the partial pressure of water vapor in a sputtering chamber.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.