Patent Application
20080305646
1. Field of the Invention
The present invention relates to atomic layer deposition.
2. Description of the Related Art
Atomic layer deposition (ALD), for example, disclosed in U.S. Pat. No. 6,764,927, is a well known deposition technique in the semiconductor industry. ALD employs a precursor and a reactive gas to form an ALD layer on a substrate in a chamber.
The deposited ALD layer, however, typically suffers from issues such as pinholes, or low density, leading to leakage current when applied in PMOS or NMOS transistors.
Accordingly, a denser ALD layer capable of solving the described issues is desirable.
An embodiment showing an atomic layer deposition (ALD) is disclosed, comprising the steps of (a) performing a hydroxylation pre-treatment on a silicon substrate to create a predetermined number of hydroxyl groups thereon; (b) performing a precursor pulse on the pre-treated silicon substrate, wherein the precursor reacts with the hydroxyl groups, forming a layer; (c) purging the silicon substrate with an inert carrier gas; (d) sufficiently exposing the layer to a water pulse to create a predetermined number of hydroxyl groups thereon; (e) purging the layer with the inert carrier gas; and (f) repeat the steps (b)˜(e) until the atomic layer deposition is completed. Furthermore, each layer overlying the silicon substrate has a minimum of 70 percent surface hydroxyl groups
Another embodiment showing an atomic layer deposition is disclosed, comprising: (a) performing a hydroxylation pre-treatment on a silicon substrate to create hydroxyl groups having a surface coverage of 30% thereon; (b) performing a precursor pulse on the pre-treated silicon substrate, wherein the precursor reacts with the hydroxyl groups, forming a layer; (c) purging the silicon substrate with an inert carrier gas; (d) sufficiently exposing the layer to a water pulse so that the layer has a minimum of 70 percent surface hydroxyl groups;(e) purging the layer with the inert carrier gas; and (f) repeating steps (b)˜(e) until the atomic layer deposition is completed.
Another embodiment showing an atomic layer deposition for forming a gate dielectric layer is disclosed, comprising: providing a semiconductor substrate; treating the semiconductor substrate with a wetting material to provide a wettable semiconductor substrate having a minimum of 60 percent surface hydroxyl groups; forming upon the wettable semiconductor substrate a first reactant material layer; and treating the first reactant material layer with a second reactant material to form a gate dielectric layer having a minimum of 70 percent surface hydroxyl groups upon the wettable semiconductor substrate.
According to the described embodiments, a denser and thinner ALD layer applicable to PMOS or NMOS transistors can be formed, thus eliminating issues such as leakage current therein.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
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As described, the comparative example is characterized in that hydroxyl groups having a surface coverage of 60% are generated over the silicon substrate. This facilitates deposition i.e. atomic layer deposition of the precursor; however, the density of the layer is inadequate.
To obtain a denser ALD layer, some embodiments of the invention provide methods for depositing each layer overlying the silicon substrate with a surface coverage of greater than 70%. Furthermore, the deposited layer of these embodiments is denser and thinner (thinner film could be formed using fewer cycle numbers with better leakage) than that of the comparative example.
In this embodiment the water vapor utilized in each water pulse is increased to a predetermined temperature for obtaining a high surface coverage of each layer overlying the silicon substrate.
As shown in
In step S23, a precursor such as HfCl4 is introduced into the chamber, and reacts with the hydroxyl groups (—OH) over the pre-treated silicon substrate, thus forming a first HfO2 layer (containing chlorine atoms thereon). Subsequent to completion of the reaction, an inert carrier gas such as nitrogen is then used to purge the unreacted HfCl4. To complete the reaction, the duration for which a sufficient number of HfCl4 is provided is extended.
To achieve a high surface coverage of a second HfO2 layer over the first HfO2 layer (containing chlorine atoms thereon), in step S24, a water pulse in which the water vapor is increased to a predetermined temperature is performed on the first HfO2 layer. The higher the water temperature increase, the more the water vapor can be generated. More water vapor means that more chlorine atoms over the first HfO2 layer can be replaced with the hydroxyl groups (—OH) of the generated water vapor. The surface coverage of the hydroxyl groups (—OH) over the first HfO2 layer can be greater than 70% here. After hydroxylation of the first HfO2 layer, an inert carrier gas such as nitrogen is then used to purge the remaining water vapor and the side products.
In step S25, a second HfO2 layer can be obtained by introducing a precursor such as HfCl4 into the chamber again, and an inert carrier gas such as nitrogen is then used to purge the unreacted HfCl4. The subsequent HfO2 layer (e.g. third HfO2 layer, fourth HfO2 layer . . . etc.) can be formed in this way i.e. repetition of steps S24 and S25 over ten times. A resultant HfO2 layer capable of serving as a gate dielectric layer is therefore obtained.
This embodiment features that the water vapor utilized in each water pulse is increased to a predetermined temperature for obtaining a high surface coverage of each layer overlying the silicon substrate. This embodiment will be described with reference to
As shown in
In step S24, a water pulse is performed on the first HfO2 layer for an extended period to achieve a high surface coverage of a second HfO2 layer over the first HfO2 layer (containing chlorine atoms). Sufficiently extending the period of the water pulse can generate more water vapor. Utilizing more water vapor can replace more of chlorine atoms over the first HfO2 layer with the hydroxyl groups (—OH) generated from water vapor. The surface coverage of the hydroxyl groups (—OH) over the first HfO2 layer can be greater than 70% here. After hydroxylation of the first HfO2 layer, an inert carrier gas such as nitrogen, helium etc. is then used to purge the remaining water vapor and the side products.
In step S25, a second HfO2 layer can be obtained by again introducing a precursor such as HfCl4 into the chamber, and an inert carrier gas such as nitrogen is then used to purge the unreacted HfCl4. The subsequent HfO2 layers (e.g. third HfO2 layer, fourth HfO2 layer . . . etc.) can be formed by repeating steps S24 and S25 ten times. A resultant HfO2 layer capable of serving as a gate dielectric layer is therefore obtained.
According to the first and second embodiments, a denser ALD layer applicable for PMOS or NMOS transistors can be formed, thus eliminating issues such as leakage current therein.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
