Patent Publication Number: US-11651963-B2

Title: Method of improving deposition induced CD imbalance using spatially selective ashing of carbon based film

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 15/974,172 dated May 8, 2018, which claims the benefit of priority of U.S. Provisional Application No. 62/591,949, filed Nov. 29, 2017, which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates to the formation of semiconductor devices. More specifically, the disclosure relates to the formation of semiconductor devices where pattern multiplication is used to double or quadruple a mask density or line frequency. Such pattern multiplication may form oxide spacers around carbon features and then remove the carbon features, leaving the oxide spacers to act as a mask. 
     SUMMARY 
     To achieve the foregoing and in accordance with the purpose of the present disclosure, a method for forming features over a wafer with a carbon based deposition is provided. The carbon based deposition is pretuned, wherein the pretuning causes a non-uniform removal of some of the carbon based deposition. An oxide deposition of a silicon oxide (SiO 2 ) based material is deposited through an atomic layer deposition process, wherein the depositing the oxide deposition causes a non-uniform removal of some of the carbon based deposition, which is complementary to the non-uniform removal of some of the carbon based deposition by the pretuning. 
     In another manifestation, a method for forming features over a wafer with a carbon based deposition is provided. The carbon based deposition is pretuned, wherein the pretuning causes a non-uniform removal of some of the carbon based deposition. An oxide deposition is deposited through an atomic layer deposition process, wherein the depositing the oxide deposition causes a non-uniform removal of some of the carbon based deposition. At least one additional process is provided, wherein the at least one additional process completes formation of features over the wafer, wherein the features are more uniform than features that would be formed without pretuning. 
     These and other features of the present disclosure will be described in more detail below in the detailed description of the disclosure and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG.  1    is a high level flow chart of an embodiment. 
         FIG.  2    is a schematic view of a process chamber that may be used in an embodiment. 
         FIG.  3    is a schematic view of a computer system that may be used in practicing an embodiment. 
         FIGS.  4 A-F  are schematic cross-sectional views of a stack processed according to an embodiment. 
         FIG.  5    is a more detailed flow chart of a pretuning process. 
         FIG.  6    is a more detailed flow chart of a lower energy oxide deposition. 
         FIG.  7    is a more detailed flow chart of a higher energy oxide deposition. 
         FIG.  8    is a graph of carbon removal according to an embodiment. 
         FIG.  9    is a flow chart another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art, that the present disclosure may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present disclosure. 
     In a common multi-patterning scheme, a carbon based film is deposited and patterned to define an initial structure. An oxide spacer film is then deposited over the carbon based film. The oxide spacer film may be etched to expose the carbon based film, leaving oxide spacers on sides of carbon based film features. The carbon based film is removed leaving oxide spacers with twice the frequency and half the spacing and CD between features. If the process is repeated N times, the CD of the final structure would be 2 −N  of the initial structure of the carbon film. The deposition of the oxide spacer film and subsequent etching removes some of the carbon film in a non-uniform way across a wafer. Such a non-uniform removal of carbon is called loss non-uniformity (NU) across the wafer. In an example, more of the carbon film is removed within 3 cm of the edge of the wafer compared to the remaining parts of a wafer. 
     Conventional technology relies on tuning the deposition plasma itself to attempt to minimize the loss NU across the wafer. An obvious issue with this approach is the coupling of the carbon core loss profile and the oxide film thickness profile. If the plasma is already optimized for minimizing the film thickness NU, then re-optimizing for minimizing the loss NU may significantly degrade the former. This is a classical case of one knob trying to optimize two parameters simultaneously. 
     Another conventional method may be to tune the carbon core etch profile across the wafer to compensate for the loss NU imparted by the deposition process. However, etch profile tuning is often non-trivial and there is general unwillingness to modify a complex etch process to compensate for shortcomings in the deposition process. 
     One of the issues with the above scheme is the carbon core loss that can occur during plasma-enhanced ALD oxide deposition. The loss is mainly caused by oxygen radicals that are necessary to grow the oxide film, but may also be caused by heavy ions such as argon (Ar) that may also be present in the plasma. The loss is an adverse consequence of the oxide deposition process and may vary across the wafer. This, in turn, can shift the CD of the final structure differentially across the wafer; e.g. CD| edge &lt;CD| center . Hence, it would be difficult to achieve the target CD everywhere on the wafer without making the deposition plasma very uniform. 
     To facilitate understanding,  FIG.  1    is a high level flow chart of an embodiment. A carbon based deposition is deposited over a wafer (step  104 ). The carbon based deposition is pretuned where the pretuning causes a non-uniform removal of some of the carbon based deposition (step  108 ). A lower energy atomic layer deposition (ALD) process is used to deposit an oxide deposition (step  110 ), where the lower energy ALD process does not remove or minimally removes some of the carbon based deposition. A higher energy ALD process is used to deposit an oxide deposition (step  112 ), where the depositing the oxide deposition causes a non-uniform removal of some of the carbon based deposition that is complementary to the non-uniform removal of some of the carbon based deposition by the pretuning. The oxide deposition is a silicon oxide based material. The oxide deposition is etched back (step  116 ). The carbon based deposition is removed (step  120 ). An underlying layer is etched, where the oxide deposition is used as a mask (step  124 ). 
     Example 
       FIG.  2    is a schematic view of a process chamber which may be used in an embodiment. In one or more embodiments, a process chamber  200  comprises a gas distribution plate  206  providing a gas inlet and a wafer support  208 , within a chamber  249 , enclosed by a chamber wall  252 . Within the chamber  249 , a wafer  203  is positioned over the wafer support  208 . An edge ring  209  surrounds the wafer support  208 . A gas source  210  is connected to the chamber  249  through the gas distribution plate  206 . A support temperature controller  250  is connected the wafer support  208 . A radio frequency (RF) source  230  provides RF power to an upper electrode, which in this embodiment is the gas distribution plate  206 . In an exemplary embodiment, 400 kHz, 13.56 MHz, and optionally 2 MHz, 27 MHz power sources make up the RF source  230 . In this embodiment, the wafer support  208  is grounded. In this embodiment, one generator is provided for each frequency. In other embodiments, the generators may be in separate RF sources, or separate RF generators may be connected to different electrodes. For example, the upper electrode may have inner and outer electrodes connected to different RF sources. Other arrangements of RF sources and electrodes may be used in other embodiments. A controller  235  is controllably connected to the RF source  230 , an exhaust pump  220 , and the gas source  210 . An example of such a chamber is the Striker™ Oxide system manufactured by Lam Research Corporation of Fremont, Calif. 
       FIG.  3    is a high level block diagram showing a computer system  300 , which is suitable for implementing a controller  235  used in embodiments. The computer system may have many physical forms ranging from an integrated circuit, a printed circuit board, and a small handheld device up to a huge super computer. The computer system  300  includes one or more processors  302 , and further can include an electronic display device  304  (for displaying graphics, text, and other data), a main memory  306  (e.g., random access memory (RAM)), storage device  308  (e.g., hard disk drive), removable storage device  310  (e.g., optical disk drive), user interface devices  312  (e.g., keyboards, touch screens, keypads, mice or other pointing devices, etc.), and a communications interface  314  (e.g., wireless network interface). The communications interface  314  allows software and data to be transferred between the computer system  300  and external devices via a link. The system may also include a communications infrastructure  316  (e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices/modules are connected. 
     Information transferred via communications interface  314  may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface  314 , via a communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, a radio frequency link, and/or other communication channels. With such a communications interface, it is contemplated that the one or more processors  302  might receive information from a network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments may execute solely upon the processors or may execute over a network such as the Internet, in conjunction with remote processors that shares a portion of the processing. 
     The term “non-transient computer readable medium” is used generally to refer to media such as main memory, secondary memory, removable storage, and storage devices, such as hard disks, flash memory, disk drive memory, CD-ROM, and other forms of persistent memory and shall not be construed to cover transitory subject matter, such as carrier waves or signals. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor. 
     In an example of an implementation of the embodiment, a carbon based deposition is formed over a wafer (step  104 ).  FIG.  4 A  is a schematic cross sectional view of part of a stack  400  with a wafer  404  disposed below an intermediate layer  408 , disposed below a carbon based deposition  412 . In this example, the carbon based deposition  412  is an organic patterned mask, such as a photoresist mask, with a first mask feature  414  and a second mask feature  416 . One or more layers (not shown) may be disposed between the wafer  404  and the intermediate layer  408 . One or more layers (not shown), such as an antireflective coating, may also be disposed between the intermediate layer  408  and the carbon based deposition  412 . 
     The carbon based deposition is pretuned, wherein the pretuning causes a non-uniform removal of some of the carbon based deposition.  FIG.  5    is a more detailed flow chart of the step of pretuning. A pretuning gas is provided is flowed into the process chamber (step  504 ). In this example, the pretuning gas is 1000 sccm O 2 , 1500 sccm Ar, and 25,000 sccm N 2 . The pretuning gas is transformed into a plasma (step  508 ). In this example, 750 watts of RF are provided at a frequency of 13.56 MHz. A bias of 15 volts is provided. After 3 seconds, the flow of the pretuning gas into the process chamber is stopped (step  512 ).  FIG.  4 B  is a cross sectional view of the stack  400  after the carbon based deposition  412  has been pretuned (step  108 ). Generally, the NU is across a wafer  404 , where the center of a wafer  404  may not be uniformly processed with respect to features at the edge of the wafer.  FIG.  4 B  schematically illustrates nonuniformity in features that are illustrated as being side by side, where such nonuniformity is actually in features that are spaced apart. In addition, certain aspects have been exaggerated in order to illustrate general aspects of the embodiment. In this example, some of the first mask feature  414  is removed by the pretuning and none of the second mask feature  416  is removed by the pretuning. 
     A lower energy oxide deposition is deposited on the carbon based deposition (step  110 ) through an ALD process.  FIG.  6    is a more detailed flow chart of the lower energy oxide deposition (step  110 ). A precursor gas flowed into the process chamber (step  604 ). In this example the precursor gas is 400 sccm aminosilane. After 0.4 second, the flow of the precursor gas into the process chamber is stopped (step  612 ). A silicon containing precursor layer is deposited over the carbon based deposition  412 . A first purge gas is flowed into the process chamber (step  616 ). In this example, the first purge gas is argon and oxygen (O 2 ). The flow of the first purge gas is stopped (step  620 ). An oxidation gas flowed into the process chamber (step  624 ). In this example the oxidation gas is 13,000 sccm Ar and 1500 sccm O 2 . The oxidation gas is transformed into a plasma (step  628 ). In this example, 100 to 500 watts of RF are provided at a frequency of 13.56 MHz. After 0.25 seconds, the flow of the oxidation gas into the process chamber is stopped (step  632 ). The plasma from the oxidation gas transforms the deposited silicon containing precursor layer into silicon oxide. A second purge gas is flowed into the process chamber (step  636 ). The flow of the second purge gas is stopped (step  640 ). The cycle then repeats from the step of flowing the precursor gas into the process chamber (step  604 ). In this example, the process is repeated for 2 to 10 cycles. The lower energy oxide deposition (step  110 ) is performed at a sufficiently low energy for depositing a silicon oxide layer, with minimal damage to the carbon based deposition  412 . 
     A higher energy oxide deposition is deposited on the carbon based deposition (step  112 ) through an ALD process.  FIG.  7    is a more detailed flow chart of the higher energy oxide deposition (step  112 ). A precursor gas flowed into the process chamber (step  704 ). In this example the precursor gas is 400 sccm aminosilane. After 0.25 seconds, the flow of the precursor gas into the process chamber is stopped (step  712 ). A silicon containing precursor layer is deposited over the carbon based deposition  412 . A first purge gas is flowed into the process chamber (step  716 ). In this example, the first purge gas is argon and oxygen. The flow of the first purge gas is stopped (step  720 ). An oxidation gas flowed into the process chamber (step  724 ). In this example the oxidation gas is 13,000 sccm Ar and 1500 sccm O 2 . The oxidation gas is transformed into a plasma (step  728 ). In this example, 800 to 1200 watts of RF are provided at a frequency of 13.56 MHz. In this example, the RF power provided during the higher energy oxide deposition is higher than the RF power provided during the lower energy oxide deposition. More preferably, the RF power provided during the higher energy oxide deposition is at least 300 watts higher than the RF power provided during the lower energy oxide deposition. In some embodiments, the RF power provided during the higher energy oxide deposition is at least twice the RF power provided during the lower energy oxide deposition. After 0.4 seconds, the flow of the oxidation gas into the process chamber is stopped (step  732 ). The plasma from the oxidation gas transforms the deposited silicon containing precursor layer into silicon oxide. A second purge gas is flowed into the process chamber (step  736 ). The flow of the second purge gas is stopped (step  740 ). The cycle then repeats from the step of flowing the precursor gas into the process chamber (step  704 ). In this example, the process is repeated for 126 to 134 cycles. The higher energy oxide deposition (step  112 ) imparts less damage to the carbon based deposition  412  due to the protective film formed during the preceding lower energy oxide deposition. 
       FIG.  4 C  is a cross sectional view of the stack  400  after the higher energy oxide deposition is deposited on the carbon based deposition  412  (step  112 ). In this example, the oxide deposition  420  has unevenly removed the carbon based deposition  412 , by removing more of the second mask feature  416  than the first mask feature  414 . The non-uniform removal of the carbon based deposition by the depositing the oxide deposition  420  is complementary to the non-uniform removal of some of the carbon based deposition  412  by the pretuning in that the combination of the non-uniform removal of some of the carbon based deposition by the depositing the oxide deposition and the non-uniform removal of some of the carbon based deposition by the pretuning results in a more uniform removal of the carbon based deposition than the non-uniform removal of some of the carbon based deposition by the depositing the oxide deposition alone. In this example, the amount removed from the first mask feature  414  is approximately equal to the amount removed from the second mask feature  416 . 
     In this example, a separate step is used to etch back the oxide deposition  420  (step  116 ) to expose part of the carbon based deposition  412 . An example recipe for etching back the oxide deposition  420  is a reactive ion etct (RIE) with fluorine containing species.  FIG.  4 D  is a cross sectional view of the stack  400  after the oxide deposition  420  has been etched back. 
     The carbon based deposition is removed (step  120 ). An example of a recipe would be plasma ashing with oxygen containing species.  FIG.  4 E  is a cross sectional view of the stack  400  after the carbon based deposition has been removed. 
     An underlying layer is etched, where the oxide deposition is used as a mask (step  124 ). In this example, the underlying layer that is etched is the intermediate layer  408 , which in this example is polysilicon.  FIG.  4 F  is a cross sectional view of the stack  400  after the intermediate layer  408  is etched. 
       FIG.  8    demonstrates how the final carbon based deposition removal profile can be flattened by superposing the loss profiles of the pretuning and depositing the oxide deposition.  FIG.  8    shows a graph of the carbon removal caused by the pretuning versus the distance from the center of the wafer  804 . A graph of the carbon removal caused by the higher energy oxide deposition versus the distance from the center of the wafer  808  is also shown. The sum of the carbon removed by both the pretuning and the higher energy oxide deposition  812  is also graphed. The sum of the carbon removed by both the pretuning and the higher energy oxide deposition  812  is equivalent to executing the two processes in sequence. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Dep Process 
                 Sum 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Loss Avg. (A) 
                 51.07 
                 64.74 
               
               
                 Loss Range (A) 
                 12.47 
                 6.01 
               
               
                   
               
            
           
         
       
     
     Table 1 shows the average loss and the loss range in angstroms of the carbon based deposition caused by the higher energy oxide deposition alone and the sum of the pretuning and the higher energy oxide deposition in an example. In this example, the bowl shaped loss profile of the higher energy oxide deposition process is compensated by the dome shaped profile of the pretuning. The final profile is substantially flatter than that of the higher energy oxide deposition alone, and a corresponding improvement in loss range from 12.5 A for the higher energy oxide deposition alone to 6.0 A for the sum of the loss due to pretuning and the higher energy oxide deposition is observed. In this example, improved uniformity is indicated by the lower range. By properly tailoring the pretuning using available process knobs (tuning inputs), the removal of the carbon based deposition from pretuning may be minimized Preferably, less than 20 {acute over (Å)} total of the thickness of the carbon based deposition is removed by the pretuning. More preferably, less than 10 {acute over (Å)} total of the thickness of the carbon based deposition is removed by the pretuning. Preferably, the removal or loss range of the carbon deposition by the pretuning and the higher energy oxide deposition is less than 10 {acute over (Å)}. More preferably, the removal or loss range of the carbon deposition by the pretuning and the higher energy oxide deposition is less than 5 {acute over (Å)}. In various embodiments, a target removal depth is provided, since the target removal depth is used in determining a complex manufacturing process. Providing a process where the thickness of the carbon removed is significantly greater or less than the target removal depth changes the complex manufacturing process in a way that reduces yield. In some embodiments, providing the pretuning increases the thickness of the carbon removed. If only standard higher energy oxide deposition is used then the carbon removed would be greater than the target thickness. Providing lower energy oxide deposition reduces the thickness of the carbon that is removed. By providing a combination of lower energy oxide deposition and higher energy oxide deposition the target removal depth is achieved. 
     By providing a pretuning that has a non-uniform complementary removal of carbon based deposition with respect to the non-uniform removal of carbon based deposition by the oxide deposition, the above embodiment provides a more uniform pattern. As device sizes shrink, such an improvement increases uniformity and decreases defects. 
     In various embodiments, the pretuning can be done in-situ immediately preceding depositing the oxide deposition. In various embodiments, the cumulative carbon based deposition removal after the pretuning and depositing the oxide deposition is substantially uniform or otherwise tailored to fulfill a given integration requirement. In an embodiment, the removal of the carbon based deposition by the pretuning is minimized by maximally biasing the etch profile to where the removal caused by the depositing the oxide deposition is minimum. In various embodiments, the pretuning may use a pretuning gas comprising at least one of oxygen, nitrogen, or argon. The pretuning, allows for the tuning of the etch profile, which can be modulated and tailored by varying the respective ratios of the gas components. In addition, pressure and RF power of the pretuning can also be utilized to further tune the etch profile. 
     In various embodiments, both feedforward and feedback schemes can be utilized as part of the process implementation. For the former, inspection results from after the preceding etch step can be used as inputs to controllers that determine the optimal settings for the pretuning. For the latter, the final CD measurements after oxide deposition and etch can be used as the inputs. 
     Various embodiments provide independent controllability of the carbon deposition removal. The plasma pretuning has no other function than to pre-tune the loss profile, which gives flexibility in terms of the profiles it can achieve (e.g. bowl, dome, and flat). In some embodiments, pretuning is performed in-situ in the same module as oxide deposition and requires no additional hardware or facilities. For typical desired profiles, the pretuning adds less than ten seconds to the total deposition time thereby minimizing any time impact. The relative flow ratios and rates of different gases such as Ar, N 2 , and O 2  for the pretuning gas are used as control parameters for tuning the non-uniform pretuning of the carbon based deposition. 
       FIG.  9    is a high level flow chart of another embodiment. A carbon based deposition is deposited over a wafer (step  904 ). The carbon based deposition is pretuned where the pretuning causes a non-uniform removal of some of the carbon based deposition (step  908 ). An oxide deposition is deposited through an ALD process (step  912 ), where the depositing the oxide deposition causes a non-uniform removal of some of the carbon based deposition. The oxide deposition is a silicon oxide based deposition. At least one additional process is provided (step  916 ), where the at least one additional process completes formation of features over the wafer, wherein the features are more uniform than features that would be formed without pretuning. For a different process chamber, the process chamber may provide a non-uniform process for the at least one additional process. In such a case, instead of a uniform flat profile after the depositing the silicon oxide, a tailored profile that complements the non-uniformity of the at least one additional process is desired after depositing the oxide deposition, since the process chamber would use the tailored profile to provide more uniform semiconductors across the wafer after the at least one additional process. The pretuning is designed to provide the tailored profile after depositing the oxide deposition, so that the resulting features are more uniform than features formed without the pretuning. 
     In various embodiments, the oxygen in the pretuning gas provides some ashing to cause some carbon based deposition removal during the pretuning. The argon and nitrogen in the pretuning gas may be used for uniformity control, where the ratio of oxygen to argon to nitrogen is used to tune the profile of the carbon based deposition. In some embodiments, for the pretuning gas the ratio of oxygen to argon is between 2:1 to 1:2. 
     In various embodiments the carbon based deposition  412  may be amorphous carbon, photoresist, spin on carbon, or chemical vapor deposition (CVD) carbon, or ashable hardmask. 
     While this disclosure has been described in terms of several preferred embodiments, there are alterations, modifications, permutations, and various substitute equivalents, which fall within the scope of this disclosure. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present disclosure. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and various substitute equivalents as fall within the true spirit and scope of the present disclosure.