1. Field of the Invention
The invention relates to resistors on semiconductor devices and methods for the formation of such resistors. More particularly, the invention relates to methods for forming resistive areas on a semiconductor device and the resistive structures formed by those methods.
2. Technical Background
Resistors and resistive devices are commonly used with semiconductor devices. For example, semiconductor devices may employ resistors formed by the diffusion of one or more dopants in a silicon substrate of a semiconductor device. In other instances, resistors may be formed of thin-films deposited on a semiconductor wafer surface. In either instance, it is preferred that the semiconductor fabrication processes allow the formation of the desired resistors or resistive structures without the addition of excessive processing steps and while maintaining the integrity of the semiconductor device.
The amount of resistance in a resistor may depend upon the length of the resistive structure, the width of the resistive structure, the depth of the diffusion, and the resistive value of the material from which the resistor is formed. The resistance of a resistor in a semiconductor device may be calculated by multiplying the number of squares of the resistor by the sheet resistance of the resistor structure. The squares of the resistor are a ratio of the length of the resistor (L) to the width of the resistor (W) and the sheet resistance defines the resistance of the resistor in ohms per square. For example, a resistor having a sheet resistance of 50 ohms per square will have a total resistance based upon the number of squares in the resistor. If the resistor is five squares, the total resistance of the resistor is 250 ohms; if the resistor is ten squares, the total resistance of the resistor is 500 ohms. Methods for calculating the amount of resistance of a resistor using squares of resistance are well known and are commonly used to determine the size of the resistors required when forming semiconductor device structures.
During design and fabrication of a semiconductor device, the resistive structures are formed according to the desired resistance of the resistor. In some instances, large resistors are desired. To increase the amount of resistance of a resistor while minimizing the amount of space on a semiconductor substrate used by the resistor, the resistor may be configured in a serpentine manner. For example,
In many instances, glass is formed over a resistor in a semiconductor device. Glass formed over the resistive structures is often planarized by chemical mechanical planarization (CMP) techniques. However, the planarization of the glass often results in the dishing of the glass over the expanse of a resistor because of the amount of space between semiconductor features. Dishing occurs due to the large areas that are unsupported by features on a semiconductor device. For example, glass 16 disposed over the resistor illustrated in
Resistor configurations such as those illustrated in
Therefore, it is desirable to develop resistors and methods of forming resistors that will minimize or eliminate dishing effects. It is also desirable to develop resistors and methods of forming resistors that will minimize or eliminate resistive losses due to field edge effects.
The present invention relates to resistors and the formation of resistors in semiconductor devices. More particularly, the present invention relates to novel resistor structures having resistive diffused regions defined by patterned polysilicon layers and methods of forming such resistors.
According to some embodiments of the invention, a resistor incorporated into a semiconductor device may include diffused regions defining a resistive path in an isolated area of a semiconductor substrate. The isolated area may include, for example, an isolated trench in the semiconductor substrate formed by a process such as shallow trench isolation (STI) or an isolated oxide feature in a semiconductor substrate. The diffused regions may be defined by a patterned polysilicon layer. The polysilicon layer may be deposited on the isolated area and patterned to define the diffused regions, which may be doped with a conductive material such as a p-type or n-type dopant. The patterned polysilicon layer pinches the diffused region allowing the formation of smaller diffused regions and more diffused regions per given area on the semiconductor substrate. Thus, more resistors or larger resistors may be incorporated with a semiconductor substrate than with conventional resistors.
The resistors of embodiments of the invention may also be less prone to dishing effects when coated with glass or another semiconductor material. The presence of the patterned polysilicon layers may support a glass or other semiconductor material deposited over the resistor. When the glass or other semiconductor material is polished such as by chemical mechanical planarization processes, the patterned polysilicon layers may decrease or prevent dishing of the glass or other semiconductor material.
The resistors of embodiments of the invention may also demonstrate improved resistance, especially with respect to the desired design resistance. The diffused regions of the resistors of the invention are pinched between the patterned polysilicon layers, which may decrease or eliminate the effects of field effects between the diffused regions. In addition, the patterning of the polysilicon layers may be accomplished such that the resistors may be positioned away from the edges of the isolated area which may result in the diminishing or elimination of field edge effects and active area effects on the resistors.
According to other embodiments of the invention, methods for forming resistors on semiconductor devices are provided. A resistor may be formed on a semiconductor device by providing an isolated area, such as an isolated trench formed by shallow trench isolation (STI) processes or an isolated oxide area. A polysilicon layer may be deposited over at least a portion of the isolated area where a resistor is to be formed. The polysilicon layer may be patterned to define one or more resistive paths in the polysilicon layer. Diffusion or implantation of a dopant, such as a conductive material, p-type dopant, or n-type dopant, over the patterned polysilicon layer may form diffused regions within the patterns of the polysilicon layer; the diffused regions may provide a resistive path for the one or more resistors. A glass or other semiconductor material may be formed over the polysilicon layer and in the patterns of the polysilicon layer to cover the diffused regions. The glass or other semiconductor material may be planarized and one or more contacts may be formed through the glass or other semiconductor material to the diffused region to provide contacts of a resistor according to embodiments of the invention.
In additional embodiments of the invention, secondary contacts to the polysilicon layers may be provided such that a voltage may be applied to the polysilicon layer. The applied voltage may improve the function of the resistor.
While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, this invention can be more readily understood and appreciated by one of ordinary skill in the art from the following description of the invention when read in conjunction with the accompanying drawings in which:
According to embodiments of the invention, a resistor may be fabricated on a semiconductor device such that polysilicon or metal walls define a diffused region which acts as the resistor. The polysilicon walls may pinch the diffused region allowing smaller widths for the resistive path to be formed on the semiconductor substrate. The polysilicon walls may also provide support to the resistor, reducing or eliminating the dishing of glass or other material formed over the resistors of the invention. The use of polysilicon patterns to define the resistive paths of the resistor may also aid in the placement of the resistor diffused regions away from any active area edges on a semiconductor substrate such that active area field effects do not alter or impact the performance of the resistor.
Resistors formed on semiconductor substrates according to embodiments of the invention include diffused regions defined by one or more polysilicon or metal patterns overlying an isolated area of a semiconductor substrate in which the diffused regions are formed. The patterns overlie at least a portion of an isolated area on a semiconductor substrate and may extend beyond the boundaries of the isolated area. Openings in the polysilicon or metal provide patterns by which the isolated area of a semiconductor substrate may be doped to form a resistive structure or resistor having a general shape of the pattern. The patterns prevent diffused regions from extending on or over the boundaries of the isolated area of the semiconductor substrate, thereby decreasing field edge effects on the resistors due to active area edge effects. In addition, the presence of the polysilicon or metal patterns provides support for glass or other semiconductor materials deposited over the resistors such that planarization of the glass or other semiconductor materials over the resistors does not result in problematic dishing of the glass or other semiconductor materials.
An example of a resistor according to embodiments of the invention is illustrated in
A cross-sectional view of the resistor 100, along the cross-sectional line 2B, is illustrated in
A second cross-sectional view of a resistor 100 is illustrated in
Other embodiments of resistors 100 according to the invention are illustrated in
Another resistor 100 according to embodiments of the invention is illustrated in
In still other embodiments of the invention, a resistor 100 may include a serpentine shape or other shape as desired. For example, the resistor 100 illustrated in
The isolated regions 160 of the resistors 100 according to embodiments of the invention may include regions formed by shallow trench isolation (STI) processes or may include isolated oxide regions in a semiconductor substrate 150. The resistors 100 according to embodiments of the present invention may be formed in any portion of a semiconductor substrate 150 where conventional resistors are formed on semiconductor substrates or semiconductor devices.
Patterned layers 120 deposited over isolated areas 160 according to embodiments of the invention may include polysilicon layers. Patterned layers 120 formed of polysilicon may be deposited using low-pressure chemical vapor deposition (LPCVD) processes, plasma-enhanced chemical vapor deposition (PECVD) processes, laser crystallization of amorphous silicon, solid-phase crystallization of amorphous silicon, or other processes used or developed to deposit patterned layers 120 on a substrate. According to some embodiments of the invention, the patterned layers 120 may have a thickness that is between about 10 nm and about 200 nm.
According to other embodiments of the invention, the patterned layers 120 may comprise metal or metal layers. The metal may be deposited over the isolated areas 160 to form the patterned layers 120 using conventional deposition processes and in any pattern desired. In some instances, the deposited metal may have a thickness that is between about 10 nm and about 200 nm. Exemplary metals that may be used with embodiments of the invention include, but are not limited to, titanium nitride (TiN), tungsten (W), tungsten nitride (WNx), tungsten nitride/titanium nitride combinations or alloys (WNx/TiN), nickel (Ni), nickel silicide (NiSi), or nickel silicon combinations or alloys.
Dopants that may be used to form diffusion regions 110 in the isolated areas 160 may include any dopants capable of enhancing the conductive abilities of the region into which the dopants are diffused or implanted. For example, any n-type or p-type dopant used in the manufacture of semiconductor devices may be used with embodiments of the present invention. Such dopants may include, but are not limited to, boron, phosphorous, arsenic, indium, germanium, and antimony. Dopants may be implanted in the isolated areas 160 to form diffusion regions by conventional methods such as by implantation, plasma immersion doping, or solid source diffusion methods.
The shapes of the resistors 100 illustrated in
Embodiments of the invention also include methods for forming resistors. According to some embodiments of the invention, a resistor may be formed over an isolated area on a semiconductor substrate by forming one or more layers of polysilicon or metal over the substrate, patterning the polysilicon or metal layer to define a desired resistive path, implanting a dopant into the patterned area to form a resistive path in the semiconductor substrate along the patterned area, and forming two or more contacts to the resistive path to complete the resistor. The polysilicon or metal patterned over the substrate may be left on the substrate and may help to prevent the dishing of glass or other semiconductor materials deposited over the resistive areas in the polysilicon or metal pattern.
A method for forming a resistor according to embodiments of the present invention is illustrated in
As illustrated in
Semiconductor substrates 150 having isolated regions 160 for use with embodiments of the invention may include isolated oxide regions on a semiconductor substrate 150 or an isolated trench formed by shallow trench isolation (STI) processes. For example, an isolated area 160 may be formed by first forming a trench or trenched area in a semiconductor substrate 150. The trench or trenched area may be filled with a glass using spin-on dielectric processes. The glass formed in the trench or trench area may then be planarized, finalizing the formation of an isolated area 160 in the semiconductor substrate 150.
According to other embodiments of the invention, a method for forming a resistor may include the steps illustrated in the flow diagram of
Although methods according to embodiments of the invention have been described with respect to particular fabrication steps, it is understood that additional fabrication steps may be incorporated with the steps of the inventive methods to form resistors according to embodiments of the invention. Furthermore, it is understood that additional fabrication steps may be included to provide a semiconductor substrate having an isolated region that may be used to form embodiments of the invention. For instance, a semiconductor substrate may first be exposed to a shallow trench isolation (STI) process whereby a shallow trench in a semiconductor is formed and isolated from other portions of the semiconductor substrate. STI processes are well known and may be incorporated with embodiments of the invention to provide semiconductor substrates having isolated areas upon which resistors of embodiments of the invention may be formed. In other instances, the isolated area may include an isolated oxide region in a semiconductor substrate.
According to embodiments of the invention, one or more resistors 100 may be formed in a patterned layer 120 according to embodiments of the invention. For instance, if multiple resistors are desired in a defined area on a semiconductor substrate 150, a single patterned layer 120 may be formed over the defined area. Multiple resistor shapes may then be patterned in the patterned layer 120 such that multiple resistors 100 may be formed from the patterning. The implantation or diffusion of dopants into the patterns of the patterned layer 120 may take place in a single step and the remaining fabrication steps may be completed to form multiple resistors 100 in the single patterned layer 120.
The patterned layers 120 formed according to embodiments of the invention may be positioned over an isolated area 160 on a semiconductor substrate 150 in any desired manner. The ability to position the patterned layers 120 in a desired location facilitates the placement of the resistor 100. In addition, the patterned layers 120 may be made large enough such that alteration of the placement of the patterned layers 120 due to errors in the fabrication process may not effect the placement of the resistor 100 on the semiconductor substrate 150. For example, a resistive path may be designed so that there are sufficient amounts of a patterned layer 120 around the outmost portions of the defined resistive path to compensate for errors in the fabrication placement of the patterned layer 120. If the patterned layer 120 positioning is off by a small distance, the placement of the patterns in the patterned layer 120 may still be made in the designed position relative to the semiconductor substrate because of the sufficient amount of patterned layer 120 used to coat the isolated area 160 of the semiconductor substrate 150. Thus, placement of the patterned layer 120 is not critical to the formation of the resistive paths in the patterned layer 120 as long as a sufficiently sized patterned layer 120 is used to compensate for fabrication or masking errors.
The width of resistors 100 formed according to embodiments of the invention is dependent upon the pinch region between the patterns of the patterned layer 120. The use of patterned layers 120 as pinch regions to form the diffused regions 110 and the resistor shapes may improve the number of squares that may be achieved for the given resistors 100. The improvement may be achieved because the patterned layers 120 act as gates preventing the diffusion of charge from the diffused regions to other portions of the semiconductor device or to other adjacent diffused regions 110. Thus, smaller widths for the diffused regions may be generated, resulting in resistors 100 having longer diffused regions 110 and larger squares of resistance.
In addition, charges applied to the patterned layers 120 of the resistors 100 may act to isolate the charges in the diffused regions 110, thereby preventing diffusion of current in a diffused region 110 to an adjacent diffused region 110. For example, in an MOS device formed according to embodiments of the invention, a charge applied to a patterned layer 120 creates an “off” state bias on the patterned layer 120 which prevents conduction between the isolated resistor lengths of the resistors 100.
The patterned layers 120 formed with the resistors 100 according to embodiments of the invention may also help to reduce or eliminate the dishing of glass or other semiconductor materials 125 deposited over the resistors 100 and in the openings 122 in the patterned layers 120.
Furthermore, the resistors 100 of the present invention may be formed on semiconductor substrates 150 without altering or adding to the number of fabrication steps used in a semiconductor fabrication process. Deposition of the patterned layers 120 may be performed with the deposition of other polysilicon features on the semiconductor substrate and the diffusion of the diffused regions 110 may be performed as other features of the semiconductor are being doped by diffusion or implantation. Thus, embodiments of the present invention may be incorporated with conventional semiconductor fabrication processes without adding to the costs or time required for such processes.
Having thus described certain currently preferred embodiments of the present invention, it is understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description, as many apparent variations thereof are contemplated without departing from the spirit or scope thereof as hereinafter claimed.