Simply using math mode in latex to generate the SI micro- prefix isn’t correct since this will produce an italic symbol.
One way to properly write micrometer is by using the SIunits package, this may well be included as a package with the latex on your computer. An example latex document to achieve this is demonstrated here:
There are many options specified for the package SIunits in the example above, the first two can be used to control the use of white space, Grey and squaren can be specified to avoid conflicts with other packages you may be using.
There is at least one more package that solves this problem, the package “upgreek” allows us to write upmu, uptau, etc.