Method and apparatus for reducing isolation stress in integrated circuits

A method for forming an oxidation mask on a silicon substrate, comprising:

• forming a pad layer of oxide-nitride-oxide on a base layer
• forming a layer of silicon nitride on the pad layer;
• and
• varying the silicon content in the silicon nitride layer as it is formed, wherein the silicon content of the silicon nitride is graded substantially linearly.

A method for forming an oxidation mask on a silicon substrate, comprising:

• forming a pad layer of oxide-nitride-oxide on a base layer;
• forming a layer of silicon nitride on the pad layer;
• and
• varying substantially continuously the silicon content in the silicon nitride layer as it is formed, wherein the silicon content of the silicon nitride is graded substantially non-linearly.

A method for forming an oxidation mask on a silicon substrate, comprising:

• forming a pad layer of oxide-nitride-oxide on a base layer
• forming a layer of silicon nitride on the pad layer;
• and
• varying the silicon content in the silicon nitride layer as it is formed, wherein the silicon content of the silicon nitride is graded substantially linearly and the base layer is pad oxide.

A method for forming an oxidation mask on a silicon substrate, comprising:

• forming a pad layer of oxide-nitride-oxide on a base layer;
• forming a layer of silicon nitride on the pad layer;
• and
• varying the silicon content in the silicon nitride layer as it is formed, wherein the silicon content of the silicon nitride is graded substantially linearly, wherein forming a layer of silicon nitride further includes forming a first portion having a first varying silicon concentration and a second portion having a second varying silicon concentration such that one of the first or second varying silicon concentrations results in an index of refraction for that portion of the silicon nitride layer of between about 1.6 and 3.0.

A method for forming an oxidation mask on a silicon substrate, comprising:

• growing a pad layer on a base layer;
• forming a layer of silicon nitride on the pad layer wherein the pad layer comprises oxide-nitride-oxide;
• and
• increasing the silicon content in the silicon nitride layer as it is formed, wherein increasing the silicon content in the silicon nitride layer as it is formed comprises increasing the concentration of silicon as the silicon nitride layer is formed so that the concentration increases from a first concentration where the layer of silicon nitride meets the pad layer to a second concentration and the increase in silicon concentration from the first concentration to the second concentration is a linear function of the thickness of the silicon nitride layer.

A method for forming an oxidation mask on a silicon substrate, comprising:

• growing a pad layer on a base layer;
• forming a layer of silicon nitride on the pad layer wherein the pad layer comprises oxide-nitride-oxide;
• and
• increasing the silicon content in the silicon nitride layer as it is formed, wherein increasing the silicon content in the silicon nitride layer as it is formed comprises increasing the concentration of silicon as the silicon nitride layer is formed so that the concentration increases from a first concentration where the layer of silicon nitride meets the pad layer to a second concentration and the increase in silicon concentration from the first concentration to the second concentration is an exponential function of the thickness of the silicon nitride layer.

A method for forming an oxidation mask on a silicon substrate, comprising:

• forming a pad layer of oxide-nitride-oxide on a base layer
• forming a layer of silicon nitride on the pad layer;
• and
• varying the silicon content in the silicon nitride layer as it is formed, wherein the silicon content of the silicon nitride is graded substantially linearly, wherein varying the silicon content in the silicon nitride layer as it is formed comprises varying the concentration of silicon as the silicon nitride layer is formed so that the concentration increases from a first concentration where the layer of silicon nitride meets the pad layer to a second concentration and the increase in silicon concentration from the first concentration to the second concentration is a linear function of the thickness of the silicon nitride layer.

A method for forming an oxidation mask on a silicon substrate, comprising:

• forming a pad layer of oxide-nitride-oxide on a base layer
• forming a layer of silicon nitride on the pad layer;
• and
• varying the silicon content in the silicon nitride layer as it is formed, wherein the silicon content of the silicon nitride is graded substantially linearly, wherein the thickness of the silicon nitride layer is at least about 500 angstroms.