By the methods of materials science, the effect of intermediate Cu layer with low surface energy ($\cong 1.83$ J/m$^{2}$) (top, intermediate, and underlayer) in [Fe$_{50}$Pt$_{50}$(15 nm)/intermediate Cu(7.5 nm) layer/Fe$_{50}$Pt$_{50}$ (15 nm)]$_{n}$ (where $n = 1, 2$), top Cu(7.5 nm) layer/Fe$_{50}$Pt$_{50}$(15 nm) and Fe$_{50}$Pt$_{50}$(15 nm)/underlayer Cu(7.5 nm) film compositions on SiO$_{2}$(100 nm)/Si(001) substrates on diffusion phase-formation processes and $L1_{0}$ phase formation, its structure, and magnetic properties at annealing in vacuum is studied. The film compositions are prepared by magnetron sputtering on thermally oxidized SiO$_{2}$ layer by thickness of 100 nm on monocrystalline Si(001) substrate. Subsequent heat treatment is carried out at high vacuum of $1.3 \cdot 10^{-3}$ Pa in the 300—900°C temperature range during 30 s at each temperature. As determined, the chemically disordered $A1$(FePt) phase is formed in all as-deposited films. The formation of chemically ordered $L1_{0}$(FePt) phase in [Fe$_{50}$Pt$_{50}$(15 nm)/Сu(7.5 nm) intermediate layer/Fe$_{50}$Pt$_{50}$(15 nm)]$_{n}$ films (where $n = 1, 2$) with intermediate layers takes place during annealing at 700°C and is accompanied by sharp coercivity increase, which also rises after subsequent high-temperature annealing. In the films with top copper layer, the temperature of $L1_{0}$(FePt) phase formation rises up to 900°C. In the films with copper underlayer, the formation of $L1_{0}$(FePt) phase is not detected by X-ray analysis, but small coercivity increasing after annealing within the temperature range of 800—900°C can testify that ordering processes proceed.