Nitrogen-rich barrier layer and structures formed

#The present invention generally relates to a method for forming a layer of nitrogen and silicon containing material on a substrate and more particularly, relates to a method for forming a layer of nitrogen and silicon containing material on a substrate by flowing a gas which has silicon and nitrogen atoms in the same molecule over a heated substrate at a pressure of less than 500 Torr wherein the molecules do not contain carbon.

#In the recent advancement in semiconductor fabrication technologies, semiconductor devices are continuously being made smaller such that a larger number of devices can be packaged on the same chip real estate. The continuing miniaturization of devices, such as very large scale integrated (VLSI) and ultra large scale integrated (ULSI) devices, demands that each component must be reduced in dimensions. For instance, as the lateral dimensions of a semiconductor device are reduced, the thickness of each of the component layers such as an insulating layer or a conducting layer must be reduced accordingly. As the characteristic dimensions of complementary metal oxide semiconductor (CMOS) technology decrease, more stringent demands are being placed on the silicon dioxide gate insulator layer in the field effect transistor. In addition to its normal function as a circuit element in the device, the gate insulator layer must also protect the silicon substrate from possible diffusion of chemical species originating from a polysilicon gate electrode through the gate insulator/silicon substrate interface. Such chemical species include dopant atoms such as boron which can diffuse from the gate electrode through the gate insulator into the silicon substrate and thus, result in a device that no longer performs within specification. Another chemical species, hydrogen, which is normally present in the gate electrode, is also highly mobile and can react at the silicon substrate/gate insulator interface during the operation of the device. Such reaction may result in a degradation of the gate insulating layer leading to a reduced lifetime of the device. Traditionally, as long as the gate insulating layer is sufficiently thick, the layer serves to protect the substrate from the diffusive chemical species. However, with the thickness of gate insulators in modern ULSI devices shrinking to dimensions of 3 nm or less, the protection of the substrate is no longer assured. Other remedies must be provided for such devices in order to guarantee the fabrication of a transistor that operatesment.

#Different ways to increase the chemical isolation provided by a thin gate insulator in a modern semiconductor device have been proposed by others. One of the methods for suppressing diffusive chemical species from the gate electrode is to introduce a very small amount of nitrogen into the silicon dioxide normally used as the gate insulator. Nitrogen acts as a barrier to a number of elemental species such as B, H, and alkali metals such as Li, Na, K, etc. Traditionally, small amounts of nitrogen can be incorporated into silicon dioxide in an uncontrolled manner, i.e., through high temperature annealing of the oxide in a nitrogen-containing gas such as NO, N2O or NH3. The high temperature required for the annealing process is normally greater than 800° C. A nitrided oxide is thus formed which has been shown to slightly suppress boron penetration and improve hot carrier reliability.

#These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which:

#FIG. 1 is an enlarged, cross-sectional view of a semiconductor structure utilizing the present invention novel nitrogen-rich diffusion barrier layer.

#FIG. 2A is an enlarged, cross-sectional view of the present invention semiconducting substrate.

#The present invention discloses a method for forming a layer of nitrogen and silicon containing material on a substrate by first heating the substrate to a temperature of at least 400° C. and then flowing a gas which has silicon and nitrogen atoms in the same molecule over the heated substrate at a pressure of not higher than 500 Torr, wherein the molecules do not contain carbon such that the layer of nitrogen and silicon containing material formed is a diffusion barrier layer on the surface of the substrate.

#The present invention novel structure that has a nitrogen-rich barrier layer can be advantageously used in a semiconductor structure such as that shown in FIG. 1. A preferred embodiment of the present invention structure 10 is shown in FIG. 1 in a CMOS transistor pair. The present invention novel structure 10 is built on a substrate 12 which can be P-type crystalline silicon into which trenches 14 are first formed. An insulating material such as silicon dioxide is then used to fill the trenches 14, in order to provide isolation between the two transistors, i.e., a p-FET (field effect transistor) 20 and an n-FET 30. The substrate 12 is then doped by an ion implantation method to create a deep implanted area of p-type silicon 18 and n-type silicon 22. An insulating layer 24 is then formed on the surface of the substrate 12. The insulating layer 24 is normally formed of silicon dioxide or any other suitable dielectric material. A nitrogen-rich layer 26 is then deposited followed by the deposition of a conducting gate electrode layer 28. The conducting gate electrode layer 28 is normally composed of polysilicon. The insulating layer 24, the nitrogen-rich layer 26 and the polysilicon layer 28 are then etched to form the stack shown in FIG. 1. After the formation of the stack, an ion implantation process is carried out to dope shallow regions of n-type silicon 32 and p-type silicon 34. The semiconductor device 10 is therefore completed for a CMOS transistor pair of an n-FET 30 and a p-FET 20.

#The fabrication details of the present invention nitrogen-rich layer 26 are illustrated below and in appended drawings of FIGS. 2A-2D. As shown in FIG. 2A, a substrate 40 is first provided. The substrate 40 should be formed of a semiconducting material since the present invention nitrogen-rich layer is essentially located in a metal-insulator-semiconductor capacitor structure. The substrate 40 can be advantageously made of doped crystalline silicon or polycrystalline silicon. The substrate 40 may also be formed by any other semiconducting material. In the next fabrication step, as shown in FIG. 2B, a capacitor is fabricated by the deposition or growth of an insulating layer 42 on top of the semiconducting substrate 40. The insulating layer 42 is typically pure silicon dioxide or silicon dioxide that contains a small amount, i.e., smaller than 2 atomic %, of nitrogen. It should be noted that this amount of nitrogen is not adequate to stop the diffusion of chemical species from the gate electrode 28 to the substrate 12. The insulating layer 42 therefore, cannot be utilized as a substitute for the present invention nitrogen-rich layer. It should be noted that the insulating layer 42 does not have to be a homogenous material. Instead, it can be suitably formed of an insulating stack of materials such as silicon dioxide and a metal oxide. It is also possible that the subsequently formed nitrogen-rich layer 44 shown in FIG. 2C, can be used to completely replace the insulating layer 42 as long as the nitrogen-rich layer is insulating.