NOVELTY - Atomic layer deposition (ALD) process (20) comprises deposition cycles comprising providing pulse of first vapor phase reactant (21) into reaction chamber to form single molecular layer of first reactant on substrate; removing excess first reactant (23) from reaction chamber; providing pulse of second vapor phase reactant (25) i.e. tellurium (Te) or selenium (Se) reactant to reaction chamber such that the second vapor phase reactant reacts with first reactant on substrate; and removing excess second reactant (27) and reaction by-products, if any, from reaction chamber.    USE - ALD Process for forming Te-, Se-, Sb- or Ge-containing thin film used in phase change memory or solar cell absorber (claimed) and optical storage media.    ADVANTAGE - The ALD process provides greater precision and control over the deposition, including better conformality and better control of composition of deposited film.    DETAILED DESCRIPTION - ALD Process (20) comprises deposition cycles, each comprising:    (A) providing pulse of first vapor phase reactant (21) into reaction chamber to form single molecular layer of first reactant on substrate;    (B) removing excess first reactant (23) from reaction chamber;    (C) providing pulse of second vapor phase reactant (25) i.e. Te or Se to reaction chamber such that the second vapor phase reactant reacts with first reactant on substrate to form Te- or Se-containing thin film; and    (D) removing excess second reactant (27) and reaction by-products, if any, from reaction chamber.    The Te or Se reactant is of formula Te(SiR1R2R3)2 or Se(SiR1R2R3)2. The method is also used to form antimony (Sb)-containing thin film on substrate in reaction chamber, where first vapor phase reactant used is Sb reactant of formula SbX'3.    R1-R3= greater than or equal to 1C alkyl;and    X'=halo.    INDEPENDENT CLAIMS are included for:    (1) germanium (Ge)-containing thin film on substrate in reaction chamber, comprising providing first vapor phase reactant pulse comprising Ge precursor of formula GeX"2 into reaction chamber to form single molecular layer of Ge precursor on substrate; removing excess first reactant from reaction chamber; providing second vapor phase reactant pulse to reaction chamber such that the second vapor phase reactant reacts with Ge precursor on substrate; removing excess second reactant and reaction by-products, if any, from reaction chamber; and repeating providing and removing steps until a film of desired thickness is formed; and    (2) preparation of Te or Se precursor, comprising forming first product by reacting Group IA metal with material comprising Te or Se; and subsequently adding second reactant comprising silicon atom bound to halogen atom to form compound comprising Te or Se bound to two silicon atoms.    X"=F, Cl, Br or I.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart of a process for formation of antimony-tellurium film.    ALD process (20)    First vapor phase reactant pulse providing step (21)    Excess first reactant removing step (23)    Second vapor phase reactant pulse providing step (25)    Excess second reactant removing step (27)