DYNAMIC DEVELOPMENT PROCESS WITH DE-IONIZED WATER PUDDLE

The invention relates to semiconductor processing. More particularly this invention relates to increasing the consistency of photo resist development in a photo-lithographic process.

The electronics industry continues to rely upon advances in semiconductor technology to realize higher-function devices in more compact areas. For many applications realizing higher-functioning devices requires integrating a large number of electronic devices into a single silicon wafer. As the number of electronic devices per given area of the silicon wafer increases, the manufacturing process becomes more difficult. Many varieties of semiconductor devices have been manufactured with various applications in numerous disciplines. Such silicon-based semiconductor devices often include metal-oxide- semiconductor field-effect transistors (MOSFET), such as p-channel MOS (PMOS), n-channel MOS (NMOS) and complementary MOS (CMOS) transistors, bipolar transistors, BiCMOS transistors. Such MOSFET devices include an insulating material between a conductive gate and silicon-like substrate; therefore, these devices are generally referred to as IGFETs (insulated-gate FET).

Each of these semiconductor devices generally includes a semiconductor substrate on which a number of active devices are formed. The particular structure of a given active device can vary between device types. For example, in MOS transistors, an active device generally includes source and drain regions and a gate electrode that modulates current between the source and drain regions.

Furthermore, such devices may be digital or analog devices produced in a number of wafer fabrication processes, for example, CMOS, BiCMOS, Bipolar, etc. The substrates may be silicon, gallium arsenide (GaAs) or other substrate suitable for building microelectronic circuits thereon.

One important aspect in manufacturing is the formation of devices, or portions thereof, using photolithography and etching processes. In photolithography, a wafer substrate is coated with a light-sensitive material called photo-resist. Next, the wafer is exposed to light; the light striking the wafer is passed through a mask plate. This mask plate defines the desired features to be printed on the substrate. After exposure, the resist- coated wafer substrate is developed. The desired features as defined on the mask are retained on the photo resist-coated substrate. Exposed areas of resist are washed away with

a developer. The wafer having the desired features defined is subjected to etching, or ion implantation. Depending upon the production process, the etching may either be a wet etch, in which liquid chemicals are used to remove wafer material or a dry etch, in which wafer material is subjected to a radio frequency (RF) induced plasma. Depending upon the features defined in the photo resist, ion implantation defines the local doping level.

More details regarding apparatus used to develop exposed photo resist may be found in U.S. Patent 5,885, 755 of Nakagawa et al. titled, "Developing Treatment Apparatus Used in the Process for Manufacturing a Semiconductor Device, and Method for the Developing Treatment," relates to a developing treatment apparatus used in the process for manufacturing a semiconductor device, and a method for the developing treatment, in particular to an apparatus and a method applied to treatment for developing a photo resist which is formed on a semiconductor wafer and has a circuit pattern exposed to light, in a photolithography process, and is incorporated by reference in its entirety.

As device geometry approaches the sub-micron realm, preparation of the wafer for . photolithography becomes increasingly important. Integral to successful wafer fabrication is the consistent and reliable application of photo resist. Improper application of photo resist on the wafer substrate may result in having to rework the wafer at the given process step. Rework results in higher production costs and oftentimes, lower product yield.

Photo resist if often applied to a substrate that is mounted on chuck in a machine that. spins-on the resist. The wafer is loaded on the chuck and held down with vacuum.

Through a nozzle, a measured amount of resist is deposited on the wafer. The chuck is rotated at high speed and the centrifugal force on the surface of the wafer spreads the resist across the wafer. A number of parameters determine the characteristics of the applied photo resist. Of particular importance is the development process a substrate undergoes after the application and exposure of the resist. Obviously the developer and the development process play a crucial role in the semiconductor manufacturing with the following requirements: 1) Resolution of the lithography process, contrast; 2) Process window regarding focus (depth of focus); 3) Process window regarding light intensity (exposure latitude); 4) Low variation of line width across wafer; and 5) Low variation of line width of neighboring lines; 6) low defect rate.

The consistent maintenance of critical dimensions (CDs) of features is important in analog and RF circuits in which components have to be matched in terms of gain, resistance, and other parameters.

There exists a need to provide for a photo resist development process that ensures consistent line width among neighboring lines printed on a substrate. In an example embodiment, in a process apparatus, there is method for developing an exposed photo resist surface on a substrate. The method comprises placing the substrate on a platen and rotating the platen. From a dispense nozzle during platen rotation, a wetting agent is dispensed on the exposed photo resist surface. Developer is dispensed from the dispense nozzle on the exposed photo resist surface. The developer mixes with the wetting agent present on the photo resist surface and the wafer is rotated at a first low speed. The dispense nozzle moves from wafer center to wafer edge repeatedly, forming a puddle of developer/wetting agent covering the exposed photo resist surface. By a second low speed rotation, the puddle of developer/wetting agent covering the exposed photo resist surface on the substrate is . agitated. An additional feature of this embodiment further comprises rinsing off with pure water, the developer/wetting agent covering the exposed photo resist surface, as the substrate is rotated at a high speed and spin drying the wafer substrate. Furthermore, the wetting agent may be an aqueous solution containing at least one selected from the group including pure water, organic ammonium hydroxide, metal hydroxides, alcohols, amines, and surfactants. Also the developer may be an aqueous solution containing at least one ^{1 ;} selected from the group including terra-methyl ammonium hydroxide, and metal hydroxides.

In another example embodiment, there is method for developing an exposed photo resist surface on a semiconductor wafer. The method comprises depositing DI water the exposed photo resist surface as the semiconductor wafer is rotated. Developer is deposited on the exposed photo resist surface. The developer mixes with the DI water present on the photo resist surface and the wafer is rotated at a first low speed, the dispense nozzle moves from wafer center to wafer edge repeatedly forming a puddle of developer/ DI water covering the exposed photo resist surface. The puddle of developer/DI water covering the exposed photo resist surface on the substrate is agitated by a second low speed rotation. With DI water, the developer/DI water covering the exposed photo resist surface is rinsed off as the semiconductor wafer is rotated at a high speed. The semiconductor wafer is spin- dried.

In yet another example embodiment, there is a method for manufacturing a semiconductor device; the method comprises, applying a photo resist surface onto a semiconductor wafer. By exposing the photo resist surface to light, a circuit pattern is rendered. The semiconductor wafer is placed into a process apparatus. While depositing DI water onto the photo resist surface, the semiconductor wafer is rotated. From a dispense nozzle in the process apparatus, developer is deposited on the photo resist surface; the developer mixes with the DI water present on the photo resist surface, as the semiconductor wafer being rotated at a first low speed, the dispense nozzle is moved from wafer center to wafer edge repeatedly, forming a puddle of developer/DI water covering the photo resist surface. The puddle of developer/DI water covering the photo resist surface on the semiconductor wafer is agitated by a second low speed rotation, thereby developing the photo resist. The embodiment may further comprise, after developing the photo resist, the rinsing off with DI water the puddle of developer/DI water covering the photo resist surface, as the semiconductor wafer is rotated at a high speed and spin drying the wafer substrate.

In yet another example embodiment, there is a system for manufacturing a semiconductor device. The system comprises means for applying a photo resist surface onto a semiconductor wafer, means for exposing the photo resist surface to light so as to render a circuit pattern, means for rotating the semiconductor wafer while depositing DI water on the photo resist surface, means for depositing developer on the photo resist surface, the developer mixing with the DI water present on the photo resist surface, the wafer being rotated at a first low speed, the dispense nozzle moving from wafer center to wafer edge repeatedly, forming a puddle of developer/DI water covering the photo resist surface, and means for agitating the puddle of developer/DI water covering the exposed photo resist surface on the semiconductor wafer by a second low speed rotation, thereby developing the photo resist.

The above summaries of the present invention are not intended to represent each disclosed embodiment, or every aspect, of the present invention. Other aspects and example embodiments are provided in the figures and the detailed description that follows. The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 illustrates the significance of a non- linear resist response to exposure dose;

FIG. 2 depicts the impact of flowing resist developer on two neighboring lines in a conventional process;

FIG. 3 is a flowchart of an example process according to the present invention; and

FIG. 4 is a plot of an example develop recipe according to the present invention. The present invention has been found to be useful in minimizing line width variation of neighboring lines. The process assures that features printed from the photo mask on a photo resist coated substrate receive consistent development across the entire substrate. Consistent development is achieved by overcoming topographical effects on the wafer surface that would tend to cause a difference in mechanical impact of the developer for one feature compared to another, resulting in local differences of the development rate. The user, as he applies developer on the exposed substrate, agitates the developer as it is dispensed onto the substrate. The agitation evens out the distribution of the developer so that the exposed resist is evenly developed over a pre-determined time.

In modifying a resist process, it is desirable to amplify light intensity differences by the development process. Refer to FIG. 1. In an example process 100, a mask pattern 105 exposes a substrate (not illustrated) with radiation energy having an intensity distribution 110 shown as peaks and valleys. Depending upon the resist response function 115a, 115b, the response may be linear 115a or non-linear (e.g., a "step function") 115b. A resist that displays a linear rate versus dose behavior will reproduce (from mask 125a) the sinusoidal behavior of the aerial image 120a, while a non-linear resist response can reproduce (from the mask 125b) the desired binary image from the mask 125b in the final resist profiles 120b.

In using a more non-linear resist to achieve a sharp profile that closely corresponds with the mask pattern, the effects of uneven development have to be minimized. Refer to FIG. 2A. In example process, a photo resist-coated wafer substrate 200 has two neighboring lines 210 that have been printed onto resist surface. Developer 205 from nozzle is applied to the wafer substrate 200. Refer to FIG. 2B. The developer flows from nozzle 205 towards the wafer edge. The developer 205 has a stronger impact on an inner exposed line 210a than an outer, shadowed line 210b. Consequently, there is a systematic line width difference between neighboring lines. Such systematic deviation in line width is especially deleterious to analog circuits with respect to transistor, resistor, and capacitance mismatch.

Refer to FIG. 3. In an example embodiment according to the present invention, a process 300 may be used to develop an exposed photo resist coated substrate. Within a process apparatus, to reduce the mechanical impact of the developer during apply, de- ionized water is deposited onto the rotating substrate 310. Developer is deposited and puddled onto the rotating substrate 320. To assure complete and homogeneous coverage at the slow wafer rotation, the developer dispense nozzle is moved from substrate center to the edge 330. By resolving the resist, the developer is modified. Therefore, local differences of resist features may result in local differences of development rate. These differences are minimized by agitation achieved by slow rotation during puddle 340. Furthermore, the DI water (de-ionized) may be substituted by other aqueous solutions. These aqueous solutions may include but are not limited to organic ammonium hydroxide, metal hydroxides, alcohols, amines, and surfactants. In a particular process tetra-methyl-ammonia hydroxide (TMAH) has been found suitable.

Refer to FIG. 4. In another example embodiment according to the present invention, an exposed photo resist-coated substrate may be developed. A process 400 is depicted in a multi-axis plot. Spin speed 410 in revolutions per minute (RPM) and dispense nozzle arm position 430 are plotted against time 420 in seconds (S). In the example process, a wafer having been printed with desired circuit features is placed within a develop apparatus. This apparatus has a vacuum platen that holds the wafer in place as it is spun. The wafer initially receives a DI water pre-wet dispense 440 and is spun at about 800 rpm for about 5 to 10 seconds. The spin speed is reduced to about 250 rpm and TMAH is dispensed 441 (at about 8 seconds) on the exposed photo resist surface on the wafer. The DI water puddles with the TMAH for about 2 seconds, after which TMAH is dispensed 442 for about another 10 to 12 seconds, at a speed of about 250 rpm. During this TMAH dispense 442 the dispense nozzle position 415oscillates from the center of the wafer to the outer edge of the wafer. After the TMAH dispense 442, the wafer is spun at about 10 rpm for about 60 seconds. The dynamic puddle 443 provides for even development of features, especially neighboring lines 210 as was depicted in FIGS. 2A and 2B. Having completed the dynamic puddle 443, the wafer is subjected to a DI water rinse for about 20 seconds with the speed ramped up from about 10 rpm to about 1200 rpm. The DI water for the rinse may be supplied from the same nozzle as that used for the developer or be from a separate source. After rinsing, the wafer is goes through a spin-dry cycle at a speed of about 1200 to about 2500 rpm. The developed

features having been rendered onto the photo resist, the wafer is ready to undergo subsequent processing.

While the present invention has been described with reference to several particular example embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention, which is set forth in the following claims.