Adsorption of TiCl4 and Ti growth on Si(001) were investigated over a range of temperatures by scanning tunneling microscopy. At 300 K, intact TiCl4, Ti and Cl, and mobile TiCl2, are identified on the Si surface. At higher temperatures, deposition initially produces two-dimensional Ti islands, and continued deposition produces three-dimensional clusters. Above 630 K, both Si and Ti islands and Si/Ti clusters are formed. However, cluster growth is limited by Cl passivation of Si and Ti surfaces below 950 K. Above 950 K, the tops of partially submerged titanium silicide crystals are observed.