Selective spacer layer deposition method for forming spacers with different widths

The present invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of forming spacers with different widths on a semiconductor substrate.

Fabricating integrated circuits with faster and/or an increasing number of semiconductor devices is a continuing trend in integrated circuit technology. A very influential factor in this trend is technology scaling, i.e., the reduction in transistor feature sizes. Technology scaling has enabled transistors to become smaller, thus allowing for more dense integrated circuits in terms of the number of transistors packed on a chip.

At virtually the same time that transistors are becoming smaller, chip sizes have been increasing in size. The chip size increase has, in turn, resulted in transistor driving capability decreases and interconnect parasitics increases. Accordingly, integrated circuits, such as, embedded memory circuits, mixed-mode/RF signal circuits, and System on a Chip (SOC) circuits, must be very carefully designed to meet future speed demands. Design issues which are very critical in the development of such circuits include, for example, transistor architecture. Specifically, careful gate design, transistor sizing, and other such feature parameters are extremely important in order to optimize transistor performance.

Spacers are commonly used in the fabrication of semiconductor devices and integrated circuits. The spacers may be used, for example, to control transistor gate size, source and drain regions placement or other features. Because variously sized transistors and other features are often required in a particular integrated circuit design, spacers of different widths must be utilized during the fabrication thereof.

Spacers of different widths are typically formed using conventional etching methods. These etching methods, unfortunately, may damage the thin, dielectric gate insulating layer and substrate. Accordingly, a new method is needed for forming spacers of varying width.

A method is disclosed herein for forming spacers with different widths on a semiconductor substrate. The method comprises the steps of disposing a first spacer layer over the substrate, defining the first spacer layer into a plurality of spacers of a first width, and disposing a second spacer layer selectively over the first spacer layer of a number of the spacers preselected for the second spacer layer, the predetermined number of the spacers with the second spacer layer each having a second width which is different from the first width.

FIGS. 1-7 are cross sectional views illustrating a method for forming spacers with different widths on a semiconductor device according to the present invention.

FIGS. 1-7 illustrate a method for forming two or more spacers with different widths on a semiconductor device according to the present invention.

Referring to FIG. 1 , there is illustrated a cross-section of a portion of a semiconductor device 10 . The semiconductor device 10 includes a substrate 20 that may be comprised of a semiconductor material, such as single crystal silicon or gallium arsenide. A plurality of features with different line widths are disposed over the substrate 20 and may include, for purposes of illustrating the method of the invention and not limitation, a first gate electrode 30 a of a first length, a second gate electrode 30 b of a second length, and a third gate electrode 30 c of a third length are disposed over the substrate 20 . The different gate lengths used in this embodiment of the invention may be provided, for example, to optimize the transistor performance of an embedded DRAM semiconductor device 10 . The gate electrodes 30 a - 30 c are electrically insulated from the substrate 20 by thin, dielectric gate insulating layers 32 a - 32 c.

The gate electrodes 30 a - 30 c may be formed from a polysilicon, such as undoped poly, amorphous poly, doped poly, and the like, using conventional forming methods, such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). The thin, dielectric gate insulating layers 32 a - 32 c, may be formed on the substrate 20 from an oxide layer using conventional forming methods, such as physical or chemical vapor deposition, prior to the formation of the gate electrodes 30 a - 30 c. In another embodiment, the thin, dielectric gate insulating layers may be formed from a nitride layer.

Referring to FIG. 2 , a first dielectric insulating spacer layer 40 is formed over the substrate 10 and gate electrodes 30 a - 30 c using conventional forming methods, such as PVD or CVD. The first spacer layer 40 may be formed from a nitride such as silicon nitride SiN, or an oxide such as silicon oxide SiO 2 . The first spacer layer 40 may be deposited to a thickness ranging from approximately 500 Å to 1000 Å.

Referring to FIG. 3 , a first patterned photoresist layer or mask layer (not shown) is provided over the first spacer layer 40 , and the semiconductor device 10 is anisotropically etched to define the first spacer layer 40 into three spacers 50 a - 50 c each having the same width W 1 , adjacent the side walls of the gate electrodes 30 a - 30 c. The anisotropic etch may be performed using a conventional plasma reactive-ion etching method. After etching, the first mask layer is removed.

Referring to FIG. 4 , spacers of other widths are formed in accordance with the present invention using selective deposition. For example, spacers having a width W 2 , which is greater than width W 1 , may be formed by providing a second mask layer 60 over the spacer 50 a of the first width and adjacent gate electrode 30 a, and then selectively depositing a second spacer layer 70 over the first spacer layer 40 of the two unmasked spacers 50 b and 50 c. The selective deposition may be accomplished by treating the substrate 20 with a plasma to generate dangling bonds on the surface of the first spacer layer 40 of the two unmasked spacers 50 b and 50 c. The dangling bonds alter the chemical properties of the surface, e.g. the bonding properties, solvent resistivity properties, and the like. The plasma treatment does not generate dangling bonds on the unmasked gate electrodes 30 b and 30 c and the substrate 20 because these features are made from different materials than the first spacer layer 40 . After the plasma treatment, the second spacer layer 70 may be formed over the substrate using PVD or CVD. The portions 70 a of the second spacer layer 70 overlying the first spacer layers 40 of the unmasked spacers 50 b and 50 c firmly bond thereto via the dangling bonds at the interface of the first spacer layer 40 and the directly overlying portions 70 a of the second spacer layer 70 . However, the portions 70 b of the second spacer layer 70 directly overlying the untreated features are easily removed using for example, a wet bench, due to the lack of dangling bonds at the interface thereof. After enlarging the spacers 50 b and 50 c , the second mask layer 60 may then be removed.

FIG. 5 illustrates the device 10 after removal of the weakly bonded portions of the second spacer layer 70 . As illustrated, the selective deposition process enlarges the spacers 50 b and 50 c to a width W 2 .

If spacers having a width W 3 , which is greater than width W 2 , are desired, a third mask layer 80 may be provided over the spacer 50 a of width W 1 and its adjacent gate electrode 30 a and spacer 50 b of width W 2 and its adjacent gate electrode 30 b as illustrated in FIG. 6. A third spacer layer 90 is then selectively deposited over the second spacer layer portions 70 a of the unmasked spacer 50 c using the selective deposition process described above, i.e., treating the substrate with a plasma to generate dangling bonds on the surface of the second spacer layer portions 70 a of the unmasked spacer 50 c ; forming the third spacer layer 90 over the substrate using PVD or CVD; removing the weakly bonded portions 90 b of the third spacer layer 90 using a wet bench, and removing the third mask layer 80 , thereby leaving the spacer 50 c enlarged by the firmly bonded third spacer layer portions 90 a to a width of W 3 as illustrated in FIG. 7 .

The plasma treatment may be performed using conventional CVD processing equipment. The plasma used in this process may comprise an NH 3 or N 2 O plasma, depending upon the composition of the spacer layer to be treated. For example, in one embodiment of the invention where the first spacer layer is composed of SiO 2 , an NH 3 plasma may be used to generate Si—N dangling bonds over the surface of the SiO 2 first spacer layer. The second spacer layer will then be formed by depositing SiO 2 over the plasma treated first spacer layer. The SiO 2 deposition produces an oxygen-rich, silicon oxynitride (SiON) film over the first spacer layer due to the Si—N dangling bonds, the oxygen-rich SiON film forming the second spacer layer. The unwanted portions of the second spacer layer formed over the other features of the device, such as the gate electrodes (made of poly-silicon for example) and the substrate (made of silicon for example), will still be composed of SiO 2 because these features do not have dangling bonds. These unwanted SiO 2 portions of the second spacer layer are easily removed by solvent selectivity due to the different materials.

If a third spacer layer is desired, the oxygen-rich SiON film forming the second spacer layer may be treated with an N 2 O plasma to generate Si—O dangling bonds over the surface of the second spacer layer. Next, the third spacer layer will be formed by depositing SiN over the second spacer layer. The SiN deposition produces a nitrogen-rich, SiON film over the second spacer layer, the nitrogen-rich SiON film forming the third spacer layer. The unwanted portions of the third spacer layer formed over the other features of the device are still composed of SiN. These unwanted portions of the third spacer layer are easily removed by solvent selectivity due to the different materials.

In a second embodiment of the invention where the first spacer layer is composed of SiN, an N 2 O plasma may be used to generate Si—O dangling bonds over the surface of the SiN first spacer layer. The second spacer layer will then be formed by depositing SiN over the plasma treated first spacer layer. The SiN deposition produces an nitrogen-rich, silicon oxynitride (SiON) film over the first spacer layer due to the Si—O dangling bonds, the nitrogen-rich SiON film forming the second spacer layer. The unwanted portions of the second spacer layer formed over the other features of the device, such as the gate electrodes and the substrate, will still be composed of SiN because these features do not have dangling bonds. These unwanted SiN portions of the second spacer layer are easily removed by solvent selectivity due to the different materials.

If a third spacer layer is desired, the nitrogen-rich SiON film forming the second spacer layer is treated with an NH 3 plasma to generate Si—N dangling bonds over the surface of the second spacer layer. Next, the third spacer layer will be formed by depositing SiO 2 over the second spacer layer. The SiO 2 deposition produces an oxygen-rich, SiON film over the second spacer layer, the oxygen-rich SiON film forming the third spacer layer. The unwanted portions of the third spacer layer formed over the other features of the device are still composed of SiO 2 . These unwanted portions of the third spacer layer are easily removed by solvent selectivity due to the different materials.

Spacers of increasing widths may be formed by repeating the selective deposition process as many times as desired. The width of a spacer formed in accordance with the present invention is determined by the number of spacer layers used to form the spacer.

The present invention addresses and solves the problems associated with forming spacers of varying widths. Through selective deposition to form spacers of varying width, damage to the thin, dielectric gate insulating layer and substrate is avoided.

While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.