Carbon　nanotips　were　grown　on　a　silicon　substrate　by　negative　bias-enhanced　hot　filament　chemical　vapor　deposition　without　catalyst,　using　a　mixture　of　methane,　ammonia　and　hydrogen　as　the　reaction　gases.　It　was　evidenced　that　the　plasma　caused　by　the　bias　played　a　key　role　in　the　formation　of　the　carbon　nanotips.　Due　to　occurrence　of　plasma　during　growing　carbon　nanotips,　the　gases　were　ionized　into　various　ions.　Based　on　different　effects　of　the　ions,　a　growth　mechanism　of　the　carbon　nanotips　was　put　forward.