1. Field of the Invention
The present invention relates to a polymer having a cage structure. More specifically, the invention pertains to an insulating film forming composition to be used for electronic devices or the like and superior in film properties such as dielectric constant and mechanical strength and moreover, an electronic device having an insulating film available by using the composition.
2. Description of the Related Art
In recent years, power consumption and delay time have increased because the progress of high integration, multifunction and high performance in the field of electronic materials has led to an increase in circuit resistance and condenser capacity between interconnects. Particularly, an increase of delay time becomes a large factor for the reduction of signal speed of devices and generation of crosstalk so that reduction of parasitic resistance and parasitic capacitance is required in order to reduce this delay time and accelerate the speed of devices. As one concrete measure for reducing this parasitic capacitance, an attempt has been made to cover the periphery of interconnects with a low-dielectric-constant interlayer insulating film. In addition, the interlayer insulating film is expected to have heat resistance high enough to withstand the thin film formation step at the time of producing a mount board and post steps such as chip connection and pin insertion and also chemical resistance high enough to withstand a wet process. Moreover, Al interconnects have recently been replaced by low resistance Cu interconnects and it is therefore common practice to carry out planarization by CMP (chemical mechanical polishing). They are therefore required to have mechanical resistance high enough to withstand this process.
Although polybenzoxazole and polyimide are widely known as materials for insulating films having high heat resistance, insulating films obtained from them are not satisfactory from the viewpoints of low dielectric constant, low water absorption, durability and hydrolysis resistance because they contain a hetero atom having high polarity such as oxygen atom or nitrogen atom.
High heat-resistant resins having polyarylene ether as a principal chain are known, but further reduction in dielectric constant is desired in order to actualize a high speed device.
In order to obtain an insulating film having a reduced dielectric constant, use of a polymer skeleton composed of a saturated hydrocarbon having a small electronic polarizability is effective. An insulating film making use of a thermal polymer of an adamantane monomer containing a carbon double bond is disclosed in JP-A-2003-292878, but it has a dielectric constant of about 2.6 and a further reduction is required.