Roger Patrick

Global model for high pressure electronegative radio-frequency discharges

We develop a global model for high pressure (0.1–1 Torr) electronegative rf discharges and apply it to model a capacitively driven plasma etcher. The molecular gases considered consist of either pure chlorine species or a mixture of chlorine and helium species. The charged and neutral heavy particle densities together with the electron density and electron temperature are calculated by using the equations of particle balance and power balance for the input discharge parameters rf power or rf current, inlet pressure, gas flow rates, reactor diameter, and gap spacing. The power is deposited in the electrons via ohmic heating and in those ions accelerated across the dc sheath potential. The voltage across the sheath is calculated self-consistently with the densities and the electron temperature by using a collisional Child law sheath model. Analytic scaling laws for the dependence of charged and neutral particle densities, electron temperature, rf voltage and current, sheath width, and plasma impedance on pressure and absorbed rf power are presented and used to explain the numerical results obtained from the global model. The model results are compared to recent experimental measurements in a chlorine discharge over a range of absorbed power Pabs=20–180u2009W at an inlet pressure pin=0.4u2002Torr and a range of pressure 0.1–1.6 Torr with a fixed input power of 100 W. We obtain reasonable agreement for Pabs<200u2009W and for 0.2 Torr<pin<1u2009Torr.We develop a global model for high pressure (0.1–1 Torr) electronegative rf discharges and apply it to model a capacitively driven plasma etcher. The molecular gases considered consist of either pure chlorine species or a mixture of chlorine and helium species. The charged and neutral heavy particle densities together with the electron density and electron temperature are calculated by using the equations of particle balance and power balance for the input discharge parameters rf power or rf current, inlet pressure, gas flow rates, reactor diameter, and gap spacing. The power is deposited in the electrons via ohmic heating and in those ions accelerated across the dc sheath potential. The voltage across the sheath is calculated self-consistently with the densities and the electron temperature by using a collisional Child law sheath model. Analytic scaling laws for the dependence of charged and neutral particle densities, electron temperature, rf voltage and current, sheath width, and plasma impedance on pr...

Application of direct bias control in high-density inductively coupled plasma etching equipment

The use of a novel method of power delivery control at the wafer chuck in a high-density inductively coupled plasma reactor has been investigated. This method involves using a peak voltage sensor mounted immediately below the chuck in a feedback loop to the rf generator such that the rf peak voltage can be set as a recipe parameter. By controlling the power delivery in this manner, it is demonstrated that the effects of power losses in the rf circuit between the generator and the chuck, especially in the match network, can be compensated for. In addition, the effect of interactions among source power, bias power and other process parameters on sheath voltage can also be eliminated. In this manner a more complete decoupling of plasma density and ion energy can be achieved than more conventional methods of power delivery allow.

Characterization of plasma etch processes using measurements of discharge impedance

Actual power delivered to the discharge, rf voltage, rf current, phase angle, and dc bias have been measured using commercially available impedance and power meters placed directly on the powered electrode of a parallel‐plate diode etcher. The variation of these electrical quantities as discharge parameters such as power, pressure, electrode spacing, gas mixing ratio, and total flow are varied has been investigated for both electropositive and electronegative gases. It was found that the transfer efficiency of the matching network depends significantly on the process conditions and can be as low as 55% of the generator output. Polysilicon etch rate experiments were performed to determine the effect of varying the actual power delivered to the discharge and possible interaction with other process parameters such as pressure, as opposed to considering solely the rf generator output. End point was detected by measuring the change in the discharge impedance while etching through a polysilicon film. The sensit...

Effect of plasma density and uniformity, electron temperature, process gas, and chamber on electron shading damage

Electron shading is a major plasma process-induced device damage mechanism in high-density etching. Patrick et al (1997) showed that although gross plasma nonuniformity can cause damage, nonuniformities seen in modern commercial etchers contribute negligible damage. Vahedi et al. (1997) derived an analytic model that clarifies the contribution of plasma and device parameters to topography induced charging. Electron temperature and plasma density are the major damage parameters for plasma. Modeling and preliminary shading coefficient measurements show that plasma nonuniformity is indeed only a small contribution. Other major factors in plasma processing induced damage relate to the device, and are the gate oxide activation electric field, effective mass constant, and gate oxide thickness. Finally, topography dependent shading parameters need to be considered. These are a function of minimum line width, aspect ratio, and antenna ratio. Protection diodes and transient fuses (Krishnan et al., 1998) may help mitigate shading damage effects, but do not change the charging mechanism, namely electron shading. This work examines the role of plasma parameters on V/sub th/ shifts in transistors fabricated in a flash memory process where metal 1 and/or metal 2 were etched in either a Lam TCP/sup TM/ 9600SE or Lam TCP/sup TM/ 9600PTX chamber. The plasma parameters varied were plasma density, electron temperature, and plasma uniformity. The role of chamber gap height in the 9600SE was examined and the results compared to the those in the 9600PTX. The role of a lighter ion in decreasing damage as suggested by Tabara (1998) was also examined.

Utility of CHARM/sup /spl reg//-2 in diagnosing sources of plasma charging damage in high density etchers and in assisting hardware development

In the early years of plasma damage history, much of the focus was on plasma nonuniformity issues. With little understanding of electron shading, many etch related damage issues were diagnosed by placing a CHARM-2 in the etch chamber, running a process and seeing if there was a signal. With high density plasma etchers, typically CHARM-2 would show no signal, though it was suspected that some type of charging damage was taking place. As the understanding of the role of electron shading in plasma charging damage became clear (2), the role of CHARM-2 in detecting plasma damage issues in high density etchers diminished.

Trends in aluminum etch rate uniformity in a commercial inductively coupled plasma etch system

The effects of process conditions and chamber geometry on the uniformity of Al etched by Cl2 were measured in a Lam TCP™ 9600 SE etch reactor. A computer simulation accurately predicted etch uniformity and aided in the explanation of uniformity trends. Parameters used in the experimental matrix included pressures between 6 and 24 mT, flow between 25 and 100 sccm, power supplied to the plasma between 0 and 350 W, and chamber heights ranging from 6 to 12 cm. The distinctive features of this study include the large number of input parameters studied in a commercial reactor and the accurate predictions obtained from a self-consistent simulation without free parameters. Reducing residence time in the experiments by adjusting chamber height or flow rate produces a more center-fast etch, as expected. The flow simulations were useful in corroborating intuitive arguments and in explaining anomalous results such as the effect of pressure on etch uniformity. More specifically, comparison of simulations and measureme...

Techniques for studying charging in plasma processing

Introduction Two different techniques have been evaluated for their ability to measure the amount of charging, both voltage and current, that might be induced on a wafer surface during plasma processing in a transformer coupled plasmaTM (TCP.9 discharge. The first of these is a passive probe, (CHARge Monitor). This consists of EEPROM sensors on a device wafer which are configured to measure the peak positive and negative potentials seen at the wafer surface during a process. In addition, by connecting a resistance from the collector to the wafer substrate, the current drawn from the plasma may be inferred allowing the i-v characteristic of the plasma source to be determined. The second technique uses an active wafer probe, f i p e 1, which consists of capacitor pads sitting on a field oxide and a substrate connection allowing direct measurement of the charging voltage across the oxide using a digital voltmeter. In addition a ramp bias voltage can be applied to the pads allowing the maximum current which can be sustained by the discharge to be determined. This probe, referred to as a Plasma Charging Monitor (PCM) has a similar design to that described by McVittie3. Figure 1 Layout of Plasmin Charging Monitor (PCM)

Effect of pulsed plasma, pressure, and RF bias on electron shading damage

The electron shading damage mechanism as proposed by Hashimoto has been widely accepted as the major charge damage mechanism for the current device generation. Vahedi et al derived an analytic model that clarifies the contribution of plasma and device parameters in topography induced charging. The effects predicted by the analytic model have been verified by our previous work. This continuation of the work examines the role of plasma parameters on V/sub th/-shifts in transistors fabricated with a Flash memory process where metal 1 was etched in a Lam TCP/sup TM/ 9600 PTX chamber. The roles of low pressure, RF bias, and pulsed plasmas in reducing damage were investigated using these antenna device wafers. Initial results appeared to contradict analytic mode predictions, but investigation of the topography changes during etch eliminated the contradictions and is leading to work on a refined analytic model taking dynamic effects into consideration.

Study Of Pattern Dependent Charging In A High-density, Inductively Coupled Metal Etcher

It is becoming increasingly evident that pattern dependent charging or electron shading is a significant charging mechanism for high density plasma etch systems. This mechanism, described by Hashimoto , can occur in uniform plasmas and is caused by the difference in isotropy of electrons and ions crossing the plasma sheath to the wafer surface. As electrons and ions interact differently with closely spaced structures on the surface of the wafer this leads to a differential charging of the structure with the top charging more negatively than the bottom. In this paper the voltages and currents developed by electron shading at the wafer surface are measured directly using a modified CHARM wafer.

Plasma damage characterization of the Lam TCP/sup TM/ 9600PTX high-density, inductively coupled metal etcher and microwave asher

In the design of any new plasma processing equipment, it is of paramount importance to consider the potential for wafer charging and the device damage which might result from it. Plasma nonuniformity has been found to be an issue by a number of workers, although recent work has suggested that nonuniformities must be severe (>/spl plusmn/20%) before causing significant damage. For many metal etching applications, electron shading may be a more significant charging mechanism. In this case, the magnitude of the charging is determined primarily by the absolute plasma density, the electron temperature and the aspect ratio of the wafer structures. A new metal etching system, the TCP/sup TM/ 9600PTX, has recently been introduced by Lam Research Corporation. This paper describes the features of the chamber which were designed to minimize charging damage. Both CHARM wafers and full flow SPIDER testers have been run to characterize the final performance with regard to damage.