how to close the auto format html code

i use the ckeditor in the source mode ,when i paste some html codes ,then when i click the source button to the view mode ,then back to the source mode again , find the source is formatted ,

for examples my html codes <span style="background-color:red"><div>this is test for the bad tag</div>

then the codes become to <div><span style="background-color:red">this is test for the bad tag</span></div>

so the bad tag span has convert by the ckeditor

any one can help me to let the html code keep the same as we paste to the source mode

thanks