1. Multiple implants:

In number of situations we need multiple implants. Multiple implants are used when it is desired to obtain deep, flat doping profile.

Multiple $H^+$ implants, for the purpose of forming Si region in GaAs have been found to produce more temperature stable material than single implant.

Multiple implants have been used as means for preserving stoichiometry during implantation and annealing for GaAs.

2. Masking:

We can use wide variety of masking material in ion implantation since it is a low temperature process.

Thickness required for masking is a function of stopping parameters of masking material.

There are many practical considerations in use of masking material in ion implantation.

For instance, ion bombardment of photoresist releases hydrogen during early stages of implantation process.

This effect is significant and can affect accuracy as well as vacuum conditions.

3. Contacts to implanted layers:

We can form a deep diffused region of same impurity type, connected to implanted layer and making metal contact to this region.

This technique is always not possible.

An ohmic contact to shallow implanted region must be made by making a Schottky barrier contact to semiconductor.

4. Implantation through an oxide:

Implants may be made through oxide in number of ways.

Specific applications for this are junction and precise resistor fabrication.

One method for obtaining junction protection is drive in implant with a high temperature diffusion step. And another method is to use double photolithography.

Using implantation for resistor fabrication, it is possible to get any sheet resistance and it is settable within ±1% of its designed value.

5. Diffusion effects during annealing:

Gaussian ion profile, resulted after ion implantation into amorphous target, is modified by diffusion effects during annealing.